WO2024075761A1 - Duplex stainless steel material - Google Patents

Duplex stainless steel material Download PDF

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Publication number
WO2024075761A1
WO2024075761A1 PCT/JP2023/036160 JP2023036160W WO2024075761A1 WO 2024075761 A1 WO2024075761 A1 WO 2024075761A1 JP 2023036160 W JP2023036160 W JP 2023036160W WO 2024075761 A1 WO2024075761 A1 WO 2024075761A1
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content
steel material
temperature
pressure
stainless steel
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PCT/JP2023/036160
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French (fr)
Japanese (ja)
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亜希子 富尾
悠索 富尾
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日本製鉄株式会社
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Priority to JP2024512953A priority Critical patent/JP7486013B1/en
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment

Definitions

  • This disclosure relates to duplex stainless steel materials.
  • Geothermal power generation is attracting attention as a form of low-carbon energy.
  • steam is generated using geothermal fluid extracted from geothermal wells where high-temperature, high-pressure hot water has accumulated.
  • Geothermal fluid refers to high-temperature, high-pressure hot water and steam. This steam is supplied to a steam turbine to generate electricity.
  • Patent Document 1 An alloy material that provides excellent corrosion resistance in a strongly acidic environment containing reducing acid is proposed in International Publication No. 2009/119630 (Patent Document 1).
  • the alloy material disclosed in this document is a Ni alloy material that contains, in mass percent, C: 0.03% or less, Si: 0.01-0.5%, Mn: 0.01-1.0%, P: 0.03% or less, S: 0.01% or less, Cr: 20% or more and less than 30%, Ni: more than 40% and less than 60%, Cu: more than 2.0% and less than 5.0%, Mo: 4.0-10%, Al: 0.005-0.5%, and N: more than 0.02% and less than 0.3%, and satisfies 0.5Cu+Mo ⁇ 6.5.
  • duplex stainless steel material that has excellent corrosion resistance in a corrosive environment of about 150°C containing hydrogen sulfide and chloride ions is proposed in International Publication No. 2013/035588 (Patent Document 2).
  • the duplex stainless steel material disclosed in this document contains, by mass%, C: 0.03% or less, Si: 0.2-1%, Mn: higher than 5.0% and lower than 10%, P: 0.040% or less, S: 0.010% or less, Ni: 4.5-8%, sol.
  • Patent Documents 1 and 2 do not consider the general corrosion resistance in the above-mentioned high-temperature, high-pressure, strongly acidic corrosive environment, or the pitting corrosion resistance in the high-temperature, high-pressure chloride corrosive environment.
  • the objective of this disclosure is to provide a duplex stainless steel material that exhibits excellent general corrosion resistance in high-temperature, high-pressure, strongly acidic corrosive environments, and excellent pitting corrosion resistance in high-temperature, high-pressure chloride corrosive environments.
  • the duplex stainless steel material of the present disclosure is The chemical composition, in mass%, is C: 0.050% or less, Si: 0.2 to 1.2%, Mn: 0.5 to 7.0%, P: 0.040% or less, S: 0.010% or less, Cr: 20.0 to 27.0%, Ni: 4.0 to 9.0%, Mo: 0.5 to 5.0%, As: 0.0005 to 0.0100%, One or more of Ca and Mg: 0.0005 to 0.0100% in total, sol.
  • duplex stainless steel material disclosed herein provides excellent general corrosion resistance in high-temperature, high-pressure, strongly acidic corrosive environments, and excellent pitting corrosion resistance in high-temperature, high-pressure chloride corrosive environments.
  • FIG. 1 is a graph showing the relationship between Fn1 and the corrosion rate (g ⁇ cm ⁇ 2 ⁇ h ⁇ 1 ) in a high-temperature, high-pressure, strongly acidic corrosive environment for a duplex stainless steel material.
  • FIG. 2 is a diagram showing the relationship between Fn2 and the corrosion rate (g ⁇ cm ⁇ 2 ⁇ h ⁇ 1 ) in a high-temperature, high-pressure chloride corrosive environment for a duplex stainless steel material.
  • the high-temperature, high-pressure strongly acidic corrosive environment and the high-temperature, high-pressure chloride corrosive environment are defined as follows.
  • High-temperature, high-pressure, strong acidic corrosive environment an environment with a high temperature of 180°C and a high pressure of 5 bar, containing hydrogen sulfide and sulfuric acid.
  • High-temperature, high-pressure chloride corrosive environment an environment with a high temperature of 180°C and a high pressure of 5 bar, containing hydrogen sulfide and chloride ions.
  • the present inventors have investigated, from the standpoint of chemical composition, duplex stainless steel materials that provide excellent general corrosion resistance in high-temperature, high-pressure, strong acidic corrosion environments and excellent pitting corrosion resistance in high-temperature, high-pressure chloride corrosion environments.
  • the present inventors have found that the composition is, by mass%, C: 0.050% or less, Si: 0.2-1.2%, Mn: 0.5-7.0%, P: 0.040% or less, S: 0.010% or less, Cr: 20.0-27.0%, Ni: 4.0-9.0%, Mo: 0.5-5.0%, one or more of Ca and Mg: 0.0005-0.0100% in total, sol.
  • Al 0.001 to 0.050%, N: 0.40% or less, O: 0.100% or less, Cu: 0 to 4.0%, V: 0 to 1.50%, Co: 0 to 2.00%, Ta: 0 to 2.00%, W: 0 to 4.00%, Nb: 0 to 2.00%, Ti: 0 to 2.00%, Zn: 0 to 0.0100%, Pb: 0 to 0.0100%, Sb: 0 to 0.0100%, Sn: 0 to 0.0100%, It was believed that a duplex stainless steel material with a chemical composition of Bi: 0-0.0100%, B: 0-0.0100%, rare earth elements: 0-0.050%, Zr: 0-2.00%, Hf: 0-2.00%, and the balance being Fe and impurities, could provide excellent general corrosion resistance in high-temperature, high-pressure, strong acidic corrosion environments, and excellent pitting corrosion resistance in high-temperature, high-pressure chloride corrosion environments.
  • the chemical composition, in mass%, is C: 0.050% or less, Si: 0.2 to 1.2%, Mn: 0.5 to 7.0%, P: 0.040% or less, S: 0.010% or less, Cr: 20.0 to 27.0%, Ni: 4.0 to 9.0%, Mo: 0.5 to 5.0%, As: 0.0005 to 0.0100%, one or more of Ca and Mg: 0.0005 to 0.0100% in total, sol.
  • Al 0.001-0.050%, N: 0.40% or less, O: 0.100% or less, Cu: 0-4.0%, V: 0-1.50%, Co: 0-2.00%, Ta: 0-2.00%, W: 0-4.00%, Nb: 0-2.00%, Ti: 0-2.00%, Zn: 0-0.0100%, Pb: 0-0.0100%, Sb: 0-0.0100%, Sn: 0-0.0100%, Bi: 0-0.0100%, B: 0-0.0100%, rare earth elements: 0-0.050%, Zr: 0-2.00%, and Hf: 0-2.00%, and the balance is Fe and impurities.
  • duplex stainless steel materials that satisfy characteristic 1 may still not provide excellent general corrosion resistance in high-temperature, high-pressure, strong acidic corrosion environments. Also, even duplex stainless steel materials that satisfy characteristic 1 may not provide excellent pitting corrosion resistance in high-temperature, high-pressure chloride corrosion environments.
  • the present inventors conducted further studies on means for improving the general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment and the pitting corrosion resistance in a high-temperature, high-pressure, chloride corrosive environment in a duplex stainless steel material satisfying characteristic 1.
  • a duplex stainless steel material satisfying characteristic 1 also satisfies characteristics 2 and 3
  • it can obtain excellent general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment and excellent pitting corrosion resistance in a high-temperature, high-pressure, chloride corrosive environment.
  • the chemical composition satisfies formula (1).
  • Fn1 10000 x As/Ni.
  • Fn1 is an index of general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment.
  • Ni, and Cu all increase general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment.
  • by adjusting the ratio of the As content to the total Ni and Cu content general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment is significantly increased.
  • Fig. 1 is a diagram showing the relationship between Fn1 and general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosive environment for a duplex stainless steel material satisfying Features 1 and 3.
  • Fig. 1 is created based on the results obtained from a general corrosion resistance evaluation test in a high-temperature, high-pressure, strong acidic corrosive environment in the examples described later. Referring to FIG. 1, when Fn1 is 0.70 or less, the corrosion rate in a high-temperature, high-pressure, strong acidic corrosion environment is significantly increased, and excellent general corrosion resistance is not obtained.
  • Fn1 when Fn1 is higher than 0.70, the corrosion rate in a high-temperature, high-pressure, strong acidic corrosion environment is significantly decreased, and general corrosion resistance is significantly improved. Therefore, if Fn1 satisfies formula (1), excellent general corrosion resistance can be obtained in a high-temperature, high-pressure, strong acidic corrosion environment, provided that the duplex stainless steel material satisfies features 1 and 3. If Fn1 is too high, the hot workability of the duplex stainless steel material is reduced. Therefore, the upper limit of Fn1 is set to be less than 16.00.
  • Figure 2 shows the relationship between Fn2 and pitting corrosion resistance in a high-temperature, high-pressure chloride corrosion environment for duplex stainless steel materials that satisfy features 1 and 2.
  • Figure 2 was created based on the results obtained from a pitting corrosion resistance evaluation test in a high-temperature, high-pressure chloride corrosion environment in the examples described later.
  • Fn2 is 1.50 or more, even if the duplex stainless steel material satisfies Features 1 and 2, the corrosion rate is high and the pitting corrosion resistance in a high-temperature, high-pressure chloride corrosion environment is low. On the other hand, if Fn2 is less than 1.50, the corrosion rate is significantly slower and excellent pitting corrosion resistance is obtained in a high-temperature, high-pressure chloride corrosion environment, provided that the duplex stainless steel material satisfies Features 1 and 2.
  • duplex stainless steel material of this embodiment was completed based on the above technical concept and has the following configuration.
  • the duplex stainless steel material of the first configuration is The chemical composition, in mass%, is C: 0.050% or less, Si: 0.2 to 1.2%, Mn: 0.5 to 7.0%, P: 0.040% or less, S: 0.010% or less, Cr: 20.0 to 27.0%, Ni: 4.0 to 9.0%, Mo: 0.5 to 5.0%, As: 0.0005 to 0.0100%, One or more of Ca and Mg: 0.0005 to 0.0100% in total, sol.
  • the duplex stainless steel material of the second configuration is 1.
  • a duplex stainless steel material of a first configuration comprising: Fine Ca oxysulfides are defined as particles having an equivalent circle diameter of 1.0 to 2.0 ⁇ m, a total of Ca content and S content of more than 5.0%, an O content of 1.0% or more, and a Ca content higher than a S content, in terms of mass%, Fine Mg oxide particles are defined as particles having an equivalent circle diameter of 1.0 to 2.0 ⁇ m, and, in mass%, an Mg content of 5.0% or more, an O content of 1.0% or more, and an S content of 15.0% or less.
  • Particles having an equivalent circle diameter of 1.0 to 2.0 ⁇ m, an Al content of 20.0% or more, and an N content of 20.0% or more, in mass%, are defined as fine Al nitrides;
  • a Ti content of 30.0% or more, and a N content of 20.0% or more are defined as fine Ti nitrides.
  • the total density of the fine Ca oxysulfides, the fine Mg oxides, the fine Al nitrides, and the fine Ti nitrides is 2.00 pieces/ mm2 or more.
  • the duplex stainless steel material of the third configuration is A duplex stainless steel material of the first or second configuration,
  • the chemical composition is Cu: 0.1 to 4.0%, V: 0.01 to 1.50%, Co: 0.01 to 2.00%, Ta: 0.01 to 2.00%, W: 0.01 to 4.00%, Nb: 0.01 to 2.00%, Ti: 0.01 to 2.00%, Zn: 0.0001 to 0.0100%, Pb: 0.0001 to 0.0100%, Sb: 0.0001 to 0.0100%, Sn: 0.0001 to 0.0100%, Bi: 0.0001 to 0.0100%, B: 0.0001 to 0.0100%, Rare earth elements: 0.001 to 0.050%, Zr: 0.01 to 2.00%, and Hf: 0.01 to 2.00%.
  • duplex stainless steel material of this embodiment will be described below. Note that "%" for elements means mass % unless otherwise specified. In the following description, the duplex stainless steel material will also be simply referred to as "steel material.”
  • the duplex stainless steel material of this embodiment satisfies the following features 1 to 3.
  • the chemical composition, in mass%, is C: 0.050% or less, Si: 0.2 to 1.2%, Mn: 0.5 to 7.0%, P: 0.040% or less, S: 0.010% or less, Cr: 20.0 to 27.0%, Ni: 4.0 to 9.0%, Mo: 0.5 to 5.0%, As: 0.0005 to 0.0100%, one or more of Ca and Mg: 0.0005 to 0.0100% in total, sol.
  • C 0.050% or less Carbon (C) is unavoidably contained.
  • the C content is more than 0%.
  • C forms Cr carbides at the grain boundaries and increases the corrosion susceptibility at the grain boundaries, so if the C content exceeds 0.050%, excellent general corrosion resistance cannot be obtained in a high-temperature, high-pressure, strong acidic corrosive environment even if the contents of other elements are within the ranges of this embodiment. Therefore, the C content is 0.050% or less.
  • the C content is preferably as low as possible. However, if the C content is excessively reduced, the manufacturing cost increases significantly. Therefore, in consideration of industrial production, the preferred lower limit of the C content is 0.001%, more preferably 0.002%, and even more preferably 0.003%.
  • the upper limit of the C content is preferably 0.048%, more preferably 0.046%, further preferably 0.044%, and further preferably 0.042%.
  • Si 0.2 to 1.2% Silicon (Si) deoxidizes steel during the steel manufacturing process. If the Si content is less than 0.2%, the above effect cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Si content exceeds 1.2%, the toughness and hot workability of the steel material decrease even if the contents of other elements are within the ranges of this embodiment. Therefore, the Si content is 0.2 to 1.2%.
  • the lower limit of the Si content is preferably 0.3%, more preferably 0.4%, and further preferably 0.5%.
  • the upper limit of the Si content is preferably 1.1%, more preferably 1.0%, and further preferably 0.9%.
  • Mn 0.5 to 7.0%
  • Mn Manganese
  • Mn improves the hardenability of steel material and increases its strength. If the Mn content is less than 0.5%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment.
  • Mn content exceeds 7.0% Mn forms a large number of coarse Mn sulfides. In a high-temperature, high-pressure chloride corrosive environment, the coarse Mn sulfides present near the surface of the steel material dissolve. In the portion where the coarse Mn sulfides dissolve, a depression is formed. This depression becomes the starting point of pitting corrosion.
  • the Mn content is 0.5 to 7.0%.
  • the lower limit of the Mn content is preferably 0.6%, more preferably 0.7%, and further preferably 0.8%.
  • the upper limit of the Mn content is preferably 6.8%, more preferably 6.0%, more preferably 5.5%, more preferably 4.5%, more preferably 3.5%, more preferably 2.5%, and more preferably 2.0%.
  • Phosphorus (P) is an unavoidable impurity. That is, the P content is more than 0%. If the P content exceeds 0.040%, P will segregate excessively at grain boundaries, and therefore the toughness of the steel material will decrease even if the contents of other elements are within the ranges of this embodiment. Therefore, the P content is 0.040% or less.
  • the P content is preferably as low as possible. However, if the P content is excessively reduced, the manufacturing cost increases significantly. Therefore, in consideration of industrial production, the lower limit of the P content is preferably 0.001%, more preferably 0.002%, more preferably 0.003%, and even more preferably 0.005%.
  • the upper limit of the P content is preferably 0.035%, more preferably 0.030%, further preferably 0.026%, and further preferably 0.022%.
  • S 0.010% or less Sulfur (S) is an unavoidable impurity. That is, the S content is more than 0%. If the S content exceeds 0.010%, S will segregate excessively at grain boundaries, and therefore the toughness and hot workability of the steel material will decrease even if the contents of other elements are within the ranges of this embodiment. Therefore, the S content is 0.010% or less.
  • the S content is preferably as low as possible. However, if the S content is reduced too much, the manufacturing cost increases significantly. Therefore, in consideration of industrial production, the lower limit of the S content is preferably 0.001%, and more preferably 0.002%.
  • the upper limit of the S content is preferably 0.009%, more preferably 0.008%, and further preferably 0.007%.
  • Chromium (Cr) forms a passive film, which is an oxide, on the surface of the steel material.
  • Cr Chromium
  • the general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosive environment is improved.
  • the pitting corrosion resistance in a high-temperature, high-pressure chloride corrosive environment is improved.
  • the Cr content is less than 20.0%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment.
  • the Cr content exceeds 27.0%, intermetallic compounds such as sigma phases are likely to be formed, and therefore the toughness of the steel material decreases even if the contents of other elements are within the ranges of this embodiment.
  • the Cr content is 20.0 to 27.0%.
  • the lower limit of the Cr content is preferably 20.2%, more preferably 20.5%, further preferably 21.0%, and further preferably 21.5%.
  • the upper limit of the Cr content is preferably 26.8%, more preferably 26.6%, further preferably 26.4%, and further preferably 26.2%.
  • Ni 4.0 to 9.0%
  • Nickel (Ni) enhances the general corrosion resistance of steel materials in high-temperature, high-pressure, strong acidic corrosive environments. If the Ni content is less than 4.0%, the above effect cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Ni content exceeds 9.0%, the volume fraction of austenite becomes too high, and in this case, the strength of the steel material decreases even if the contents of other elements are within the ranges of this embodiment. Therefore, the Ni content is 4.0 to 9.0%.
  • the lower limit of the Ni content is preferably 4.2%, more preferably 4.4%, further preferably 4.6%, and further preferably 4.8%.
  • the upper limit of the Ni content is preferably 8.8%, more preferably 8.6%, more preferably 8.2%, more preferably 7.9%, more preferably 7.8%, more preferably 7.7%, and more preferably 7.6%.
  • Mo 0.5 to 5.0% Molybdenum (Mo) enhances the pitting corrosion resistance of steel materials in high-temperature and high-pressure chloride corrosion environments. If the Mo content is less than 0.5%, the above effect cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Mo content exceeds 5.0%, the hot workability of the steel material decreases even if the contents of other elements are within the ranges of this embodiment. Therefore, the Mo content is 0.5 to 5.0%.
  • the lower limit of the Mo content is preferably 0.7%, more preferably 1.0%, more preferably 1.5%, more preferably 2.0%, more preferably 2.4%, more preferably 2.6%, and more preferably 2.8%.
  • the upper limit of the Mo content is preferably 4.8%, more preferably 4.6%, further preferably 4.4%, and further preferably 4.2%.
  • Arsenic enhances the general corrosion resistance of steel materials in high-temperature, high-pressure, strongly acidic corrosive environments. If the As content is less than 0.0005%, the above effect cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the As content exceeds 0.0100%, the hot workability of the steel material decreases even if the contents of other elements are within the ranges of this embodiment. Therefore, the As content is 0.0005 to 0.0100%.
  • the lower limit of the As content is preferably 0.0010%, more preferably 0.0015%, further preferably 0.0020%, and further preferably 0.0025%.
  • the upper limit of the As content is preferably 0.0090%, more preferably 0.0080%, further preferably 0.0070%, and further preferably 0.0060%.
  • One or more of Ca and Mg 0.0005 to 0.0100% in total Calcium (Ca) and magnesium (Mg) form fine Ca oxysulfides or fine Mg oxides.
  • the fine Ca oxysulfides and fine Mg oxides function as segregation sites for As at the interface with the parent phase.
  • the As segregated on the surfaces of these fine particles is also dispersed in the steel material.
  • the general corrosion resistance of the steel material in a high-temperature, high-pressure, strong acidic corrosion environment is improved. If the total content of Ca and Mg is less than 0.0005%, the above effect cannot be sufficiently obtained.
  • the total content of Ca and Mg exceeds 0.0100%, coarse Ca oxysulfides or coarse Mg oxides are generated.
  • the coarse Ca oxysulfides and coarse Mg oxides generated in the steel surface layer are easily dissolved. Therefore, even if the contents of other elements are within the ranges of this embodiment, the pitting corrosion resistance of the steel in a high-temperature, high-pressure chloride corrosive environment is reduced. Therefore, the total content of Ca and Mg is 0.0005 to 0.0100%.
  • the lower limit of the total content of Ca and Mg is preferably 0.0010%, more preferably 0.0015%, further preferably 0.0020%, further preferably 0.0025%, and further preferably 0.0030%.
  • the upper limit of the combined Ca and Mg content is preferably 0.0095%, more preferably 0.0090%, still more preferably 0.0085%, still more preferably 0.0080%, and still more preferably 0.0075%.
  • sol. Al 0.001 to 0.050%
  • Aluminum (Al) deoxidizes steel during the manufacturing process of steel. Furthermore, Al combines with N to form fine Al nitrides. The fine Al nitrides function as segregation sites for As. Therefore, if a large amount of fine Al nitrides are generated and dispersed in the steel material, As will be more likely to disperse in the steel material, which will result in improved general corrosion resistance of the steel material in a high-temperature, high-pressure, strong acidic corrosive environment. If the sol. Al content is less than 0.001%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the sol.
  • the sol. Al content exceeds 0.050%, coarse oxides are generated in excess, and therefore the toughness of the steel material is reduced even if the contents of other elements are within the ranges of this embodiment. do. Therefore, the sol. Al content is 0.001 to 0.050%.
  • the lower limit of the sol. Al content is preferably 0.002%, more preferably 0.005%, and further preferably 0.010%.
  • the upper limit of the sol. Al content is preferably 0.045%, more preferably 0.040%, still more preferably 0.035%, and still more preferably 0.030%.
  • the sol. Al content in the specification means the content of acid-soluble Al.
  • N 0.40% or less Nitrogen (N) is unavoidably contained. In other words, the N content is more than 0%. N stabilizes austenite in steel. N also enhances the general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosion environment and the pitting corrosion resistance of steel in a high-temperature, high-pressure chloride corrosion environment. N also combines with Al and Ti to generate fine Al nitrides and fine Ti nitrides. The fine Al nitrides and fine Ti nitrides function as segregation sites for As. Therefore, if a large amount of fine Al nitrides and fine Ti nitrides are generated and dispersed in the steel, As becomes more likely to disperse in the steel.
  • the general corrosion resistance of the steel in a high-temperature, high-pressure, strong acidic corrosion environment is improved. If even a small amount of N is contained, the above effect can be obtained to a certain extent. However, if the N content exceeds 0.40%, the toughness and hot workability of the steel material decrease even if the contents of other elements are within the ranges of this embodiment. Therefore, the N content is 0.40% or less.
  • the lower limit of the N content is preferably 0.01%, more preferably 0.02%, still more preferably 0.05%, still more preferably 0.10%, and still more preferably 0.15%.
  • the upper limit of the N content is preferably 0.38%, more preferably 0.36%, still more preferably 0.34%, still more preferably 0.32%, and still more preferably 0.30%.
  • Oxygen (O) is an unavoidable impurity.
  • the O content is more than 0%. If the O content exceeds 0.100%, coarse Ca oxysulfides and coarse Mg oxides are excessively generated, and therefore, even if the contents of other elements are within the ranges of this embodiment, excellent pitting corrosion resistance cannot be obtained in a high-temperature and high-pressure chloride corrosive environment. Therefore, the O content is 0.100% or less.
  • the O content is preferably as low as possible. However, if the O content is excessively reduced, the manufacturing cost increases. Therefore, in consideration of industrial production, the lower limit of the O content is preferably 0.001%, more preferably 0.005%, and even more preferably 0.010%.
  • the upper limit of the O content is preferably 0.090%, more preferably 0.085%, further preferably 0.080%, and further preferably 0.075%.
  • the remainder of the chemical composition of the duplex stainless steel material according to this embodiment is composed of Fe and impurities.
  • impurities in the chemical composition refers to substances that are mixed in from the raw materials, such as ore, scrap, or the manufacturing environment, during the industrial production of duplex stainless steel material, and are not intentionally included, but are acceptable within a range that does not adversely affect the effects of the duplex stainless steel material according to this embodiment.
  • the chemical composition of the duplex stainless steel material of this embodiment further includes, instead of a part of Fe, Cu: 0 to 4.0%, V: 0 to 1.50%, Co: 0 to 2.00%, Ta: 0 to 2.00%, W: 0 to 4.00%, Nb: 0 to 2.00%, Ti: 0 to 2.00%, Zn: 0 to 0.0100%, Pb: 0 to 0.0100%, Sb: 0 to 0.0100%, Sn: 0 to 0.0100%, Bi: 0 to 0.0100%, B: 0 to 0.0100%, Rare earth elements: 0 to 0.050%, Zr: 0 to 2.00%, and Hf: 0 to 2.00%.
  • Each optional element will be described below.
  • the chemical composition of the duplex stainless steel material of this embodiment may contain at least one element selected from the group consisting of Cu, V, Co, Ta, W, Nb, Ti, Zn, Pb, Sb, Sn, and Bi, instead of a portion of Fe. All of these elements are optional elements, and enhance the general corrosion resistance of the steel material in a high-temperature, high-pressure, strongly acidic corrosive environment. Each element will be described below.
  • Cu 0 to 4.0% Copper (Cu) is an optional element and may not be contained, that is, the Cu content may be 0%.
  • Cu When Cu is contained, that is, when the Cu content is more than 0%, Cu generates sulfides on the passive film in a high-temperature, high-pressure, strongly acidic corrosive environment. These sulfides suppress active dissolution of the steel material. Therefore, the general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment is improved. Even if even a small amount of Cu is contained, the above effect can be obtained to a certain extent. However, if the Cu content exceeds 4.0%, the hot workability of the steel material decreases even if the contents of other elements are within the ranges of this embodiment.
  • the Cu content is 0 to 4.0%, and if contained, it is 4.0% or less.
  • the lower limit of the Cu content is preferably 0.1%, more preferably 0.2%, further preferably 0.5%, and further preferably 1.0%.
  • the upper limit of the Cu content is preferably 3.8%, more preferably 3.5%, further preferably 2.5%, and further preferably 2.0%.
  • V Vanadium (V) is an optional element and may not be contained, that is, the V content may be 0%.
  • V is contained, that is, when the V content exceeds 0%, V suppresses active dissolution of the steel material in a high-temperature, high-pressure, strongly acidic corrosive environment, and enhances general corrosion resistance. Even if even a small amount of V is contained, the above effect can be obtained to a certain degree. However, if the V content exceeds 1.50%, the strength of the steel material becomes excessively high, and in this case, even if the contents of other elements are within the ranges of this embodiment, the hot workability of the steel material decreases.
  • the V content is 0 to 1.50%, and if contained, it is 1.50% or less.
  • the lower limit of the V content is preferably 0.01%, more preferably 0.05%, further preferably 0.10%, and further preferably 0.20%.
  • the upper limit of the V content is preferably 1.40%, more preferably 1.30%, further preferably 1.20%, and further preferably 1.00%.
  • Co is an optional element and may not be contained, that is, the Co content may be 0%.
  • the Co content When contained, that is, when the Co content is more than 0%, Co enhances the general corrosion resistance of the steel material in a high-temperature, high-pressure, strongly acidic corrosive environment. Even if even a small amount of Co is contained, the above effect can be obtained to a certain degree. However, if the Co content exceeds 2.00%, the hot workability of the steel material decreases even if the contents of other elements are within the ranges of this embodiment. Therefore, the Co content is 0 to 2.00%, and if Co is contained, it is 2.00% or less.
  • the lower limit of the Co content is preferably 0.01%, more preferably 0.05%, further preferably 0.10%, further preferably 0.20%, and further preferably 0.30%.
  • the upper limit of the Co content is preferably 1.90%, more preferably 1.80%, more preferably 1.70%, more preferably 1.60%, more preferably 1.50%, and even more preferably 1.00%.
  • Tantalum (Ta) is an optional element and may not be contained, that is, the Ta content may be 0%.
  • Ta enhances the general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment. Even if even a small amount of Ta is contained, the above effect can be obtained to some extent.
  • the Ta content exceeds 2.00%, the strength of the steel material becomes excessively high, and in this case, even if the contents of other elements are within the ranges of this embodiment, the hot workability of the steel material decreases. Therefore, the Ta content is 0 to 2.00%, and if contained, it is 2.00% or less.
  • the lower limit of the Ta content is preferably 0.01%, more preferably 0.05%, and further preferably 0.08%.
  • the upper limit of the Ta content is preferably 1.50%, more preferably 1.00%, further preferably 0.70%, and further preferably 0.50%.
  • Tungsten (W) is an optional element and may not be contained, that is, the W content may be 0%.
  • W When W is contained, that is, when the W content exceeds 0%, W suppresses active dissolution of the steel material in a high-temperature, high-pressure, strongly acidic corrosive environment, and enhances general corrosion resistance. Even if even a small amount of W is contained, the above effect can be obtained to a certain degree. However, if the W content exceeds 4.00%, the strength of the steel material becomes excessively high, and in this case, even if the contents of other elements are within the ranges of this embodiment, the hot workability of the steel material decreases.
  • the W content is 0 to 4.00%, and if W is contained, it is 4.00% or less.
  • the lower limit of the W content is preferably 0.01%, more preferably 0.05%, more preferably 0.10%, more preferably 0.20%, more preferably 0.30%, and more preferably 0.50%.
  • the upper limit of the W content is preferably 3.90%, more preferably 3.80%, more preferably 3.70%, more preferably 3.50%, more preferably 3.00%, more preferably 2.50%, more preferably 2.00%, and more preferably 1.80%.
  • Niobium (Nb) is an optional element and may not be contained, that is, the Nb content may be 0%.
  • Nb is contained, that is, when the Nb content is more than 0%, Nb forms carbides or nitrides to suppress the formation of Cr carbides. Therefore, the generation of Cr-depleted regions at grain boundaries is suppressed. As a result, the general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosion environment is improved. Even if even a small amount of Nb is contained, the above effect can be obtained to a certain extent.
  • the Nb content is 0 to 2.00%, and if Nb is contained, it is 2.00% or less.
  • the lower limit of the Nb content is preferably 0.01%, more preferably 0.05%, more preferably 0.10%, more preferably 0.20%, more preferably 0.30%, and even more preferably 0.40%.
  • the upper limit of the Nb content is preferably 1.50%, more preferably 1.00%, further preferably 0.70%, and further preferably 0.50%.
  • Titanium (Ti) is an optional element and may not be contained, that is, the Ti content may be 0%.
  • Ti When Ti is contained, that is, when the Ti content is more than 0%, Ti forms carbides or nitrides to suppress the formation of Cr carbides. Therefore, the generation of Cr-depleted regions at grain boundaries is suppressed. As a result, the general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosion environment is improved.
  • Ti forms a large number of fine Ti nitrides, the fine Ti nitrides dispersed in the steel material further function as segregation sites for As. Therefore, As is more easily dispersed in the steel material.
  • the general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosion environment is further improved. If even a small amount of Ti is contained, the above effect can be obtained to a certain extent. However, if the Ti content exceeds 2.00%, the strength of the steel material becomes excessively high, and in this case, even if the contents of other elements are within the ranges of this embodiment, the hot workability of the steel material decreases. Therefore, the Ti content is 0 to 2.00%, and if contained, it is 2.00% or less.
  • the lower limit of the Ti content is preferably 0.01%, and more preferably 0.05%.
  • the upper limit of the Ti content is preferably 1.50%, more preferably 1.00%, further preferably 0.70%, and further preferably 0.50%.
  • Zinc (Zn) is an optional element and may not be contained, that is, the Zn content may be 0%.
  • Zn content When contained, that is, when the Zn content is more than 0%, Zn forms stable sulfides to enhance the general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment. Even if even a small amount of Zn is contained, the above effect can be obtained to some extent. However, if the Zn content exceeds 0.0100%, the mechanical properties of the steel material will deteriorate even if the contents of other elements are within the ranges of this embodiment. Therefore, the Zn content is 0 to 0.0100%, and if contained, it is 0.0100% or less.
  • the lower limit of the Zn content is preferably 0.0001%, more preferably 0.0005%, and further preferably 0.0010%.
  • the upper limit of the Zn content is preferably 0.0050%, more preferably 0.0030%, and further preferably 0.0025%.
  • Pb 0 to 0.0100%
  • Lead (Pb) is an optional element and may not be contained, that is, the Pb content may be 0%.
  • Pb When Pb is contained, that is, when the Pb content is more than 0%, Pb forms stable sulfides to improve the general corrosion resistance in a high-temperature, high-pressure, highly acidic corrosive environment. Even if even a small amount of Pb is contained, the above effect can be obtained to some extent. However, if the Pb content exceeds 0.0100%, the mechanical properties of the steel material will deteriorate even if the contents of other elements are within the ranges of this embodiment. Therefore, the Pb content is 0 to 0.0100%, and if contained, it is 0.0100% or less.
  • the lower limit of the Pb content is preferably 0.0001%, more preferably 0.0003%, still more preferably 0.0005%, still more preferably 0.0008%, and still more preferably 0.0010%.
  • the upper limit of the Pb content is preferably 0.0070%, more preferably 0.0050%, further preferably 0.0030%, and further preferably 0.0020%.
  • Sb 0 to 0.0100%
  • Antimony (Sb) is an optional element and may not be contained, that is, the Sb content may be 0%.
  • Sb enhances the general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment. Even if even a small amount of Sb is contained, the above effect can be obtained to some extent.
  • the Sb content exceeds 0.0100%, the hot workability of the steel material decreases even if the contents of other elements are within the ranges of this embodiment. Therefore, the Sb content is 0 to 0.0100%, and if contained, it is 0.0100% or less.
  • the lower limit of the Sb content is preferably 0.0001%, more preferably 0.0002%, and further preferably 0.0005%.
  • the upper limit of the Sb content is preferably 0.0070%, more preferably 0.0050%, further preferably 0.0030%, further preferably 0.0020%, and further preferably 0.0015%.
  • Tin (Sn) is an optional element and may not be contained, that is, the Sn content may be 0%.
  • Sn enhances the general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment. Even if even a small amount of Sn is contained, the above effect can be obtained to some extent.
  • the Sn content exceeds 0.0100%, the hot workability of the steel material decreases even if the contents of other elements are within the ranges of this embodiment. Therefore, the Sn content is 0 to 0.0100%, and if contained, it is 0.0100% or less.
  • the lower limit of the Sn content is preferably 0.0001%, more preferably 0.0002%, and further preferably 0.0005%.
  • the upper limit of the Sn content is preferably 0.0070%, more preferably 0.0050%, still more preferably 0.0030%, still more preferably 0.0020%, and still more preferably 0.0015%.
  • Bi 0 to 0.0100%
  • Bismuth (Bi) is an optional element and may not be contained, that is, the Bi content may be 0%.
  • Bi enhances the general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment. Even if even a small amount of Bi is contained, the above effect can be obtained to a certain degree.
  • the Bi content exceeds 0.0100%, the hot workability of the steel material decreases even if the contents of other elements are within the ranges of this embodiment. Therefore, the Bi content is 0 to 0.0100%, and if contained, it is 0.0100% or less.
  • the lower limit of the Bi content is preferably 0.0001%, more preferably 0.0002%, and further preferably 0.0005%.
  • the upper limit of the Bi content is preferably 0.0070%, more preferably 0.0050%, further preferably 0.0030%, further preferably 0.0020%, and further preferably 0.0015%.
  • the chemical composition of the duplex stainless steel material of this embodiment may contain one or more elements selected from the group consisting of B, rare earth elements (REM), Zr, and Hf, instead of a part of Fe. All of these elements are optional elements, and improve the hot workability of the steel material. Each element will be described below.
  • B 0 to 0.0100% Boron (B) is an optional element and may not be contained.
  • the B content may be 0%.
  • B When B is contained, that is, when the B content exceeds 0%, B suppresses the segregation of P and S to grain boundaries in the steel material, and improves the hot workability of the steel material. Even if even a small amount of B is contained, the above effects can be obtained to a certain extent.
  • the B content exceeds 0.0100%, B nitrides are formed in excess, and therefore the toughness of the steel material decreases even if the contents of other elements are within the ranges of this embodiment. Therefore, the B content is 0 to 0.0100%, and if contained, it is 0.0100% or less.
  • the lower limit of the B content is preferably 0.0001%, more preferably 0.0005%, further preferably 0.0010%, and further preferably 0.0020%.
  • the upper limit of the B content is preferably 0.0090%, more preferably 0.0080%, further preferably 0.0070%, and further preferably 0.0050%.
  • the rare earth elements are optional elements and may not be contained, i.e., the REM content may be 0%.
  • the REM content When contained, that is, when the REM content is more than 0%, REM controls the morphology of inclusions and improves the hot workability of the steel material. Even if even a small amount of REM is contained, the above effect can be obtained to some extent. However, if the REM content exceeds 0.050%, the oxides in the steel material become coarse, and therefore the toughness of the steel material decreases even if the contents of other elements are within the ranges of this embodiment. Therefore, the REM content is 0 to 0.050%, and if contained, it is 0.050% or less.
  • the lower limit of the REM content is preferably 0.001%, more preferably 0.003%, still more preferably 0.005%, still more preferably 0.008%, and still more preferably 0.010%.
  • the upper limit of the REM content is preferably 0.045%, more preferably 0.040%, further preferably 0.035%, and further preferably 0.030%.
  • REM refers to one or more elements selected from the group consisting of scandium (Sc), atomic number 21; yttrium (Y), atomic number 39; and the lanthanides lanthanum (La), atomic number 57, to lutetium (Lu), atomic number 71.
  • the REM content refers to the total content of these elements.
  • Zr 0 to 2.00%
  • Zirconium (Zr) is an optional element and may not be contained, that is, the Zr content may be 0%.
  • Zr forms carbonitrides to improve the strength and hot workability of the steel material. Even if even a small amount of Zr is contained, the above effects can be obtained to some extent.
  • the Zr content exceeds 2.00%, the strength of the steel material becomes excessively high, and therefore the toughness of the steel material decreases even if the contents of other elements are within the ranges of this embodiment. Therefore, the Zr content is 0 to 2.00%, and if contained, it is 2.00% or less.
  • the lower limit of the Zr content is preferably 0.01%, more preferably 0.02%, and further preferably 0.05%.
  • the upper limit of the Zr content is preferably 1.50%, more preferably 1.00%, further preferably 0.50%, and further preferably 0.30%.
  • Hf 0 to 2.00%
  • Hafnium (Hf) is an optional element and may not be contained, that is, the Hf content may be 0%.
  • Hf forms carbonitrides to improve the strength and hot workability of the steel material. Even if even a small amount of Hf is contained, the above effects can be obtained to some extent.
  • the Hf content exceeds 2.00%, the strength of the steel material becomes excessively high, and therefore the toughness of the steel material decreases even if the contents of other elements are within the ranges of this embodiment. Therefore, the Hf content is 0 to 2.00%, and if contained, it is 2.00% or less.
  • the lower limit of the Hf content is preferably 0.01%, more preferably 0.10%, further preferably 0.15%, and further preferably 0.20%.
  • the upper limit of the Hf content is preferably 1.50%, more preferably 1.00%, further preferably 0.80%, and further preferably 0.75%.
  • general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosive environment is significantly improved.
  • Fn1 is higher than 0.70, the corrosion rate in a high-temperature, high-pressure, strong acidic corrosive environment is significantly slowed, assuming that the duplex stainless steel material satisfies Features 1 and 3. Therefore, excellent general corrosion resistance is obtained in a high-temperature, high-pressure, strong acidic corrosive environment.
  • Fn1 should be greater than 0.70 and less than 16.00.
  • the preferred lower limit of Fn1 is 0.71, more preferably 1.00, more preferably 2.00, more preferably 3.00, and more preferably 4.00.
  • Fn1 is 5.50 or more
  • the corrosion rate in a high-temperature, high-pressure, strongly acidic corrosive environment is significantly reduced compared to when Fn1 is higher than 0.70 and less than 5.50. Therefore, the more preferred lower limit of Fn1 is 5.50, and more preferably 6.00.
  • the upper limit of Fn1 is preferably 15.50, more preferably 15.00, and even more preferably 14.50.
  • Fn1 is the value obtained by rounding off the obtained value to one decimal place.
  • Fn2 (Ca + Mg)/O) is an index of pitting corrosion resistance in high-temperature, high-pressure chloride corrosive environments.
  • Ca and Mg combine with S to form sulfides. This suppresses the formation of coarse Mn sulfides. As a result, pitting corrosion resistance in high-temperature, high-pressure chloride corrosive environments is improved.
  • the upper limit of Fn2 is preferably 1.45, more preferably 1.43, more preferably 1.40, more preferably 1.35, and even more preferably 1.30.
  • the lower limit of Fn2 is not particularly limited.
  • the lower limit of Fn2 is preferably 0.01, and more preferably 0.02.
  • Fn2 is the value obtained by rounding off the obtained value to one decimal place.
  • the duplex stainless steel material of this embodiment satisfies Features 1 to 3. Therefore, the duplex stainless steel material of this embodiment can obtain excellent general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment, and can also obtain excellent pitting corrosion resistance in a high-temperature, high-pressure chloride corrosive environment.
  • the excellent general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment and the excellent pitting corrosion resistance in a high-temperature, high-pressure, chloride corrosive environment are defined as follows based on a general corrosion resistance evaluation test in a high-temperature, high-pressure, strongly acidic corrosive environment and a pitting corrosion resistance evaluation test in a high-temperature, high-pressure, chloride corrosive environment, which are shown below.
  • the general corrosion resistance evaluation test in a high-temperature, high-pressure, strong acidic corrosive environment is carried out in the following manner.
  • a test piece is taken from the duplex stainless steel material.
  • the duplex stainless steel material is a steel pipe
  • the test piece is taken from the center position of the wall thickness.
  • the longitudinal direction of the test piece is parallel to the axial direction of the steel pipe.
  • the duplex stainless steel material is a round bar
  • the test piece is taken from the R/2 position.
  • the R/2 position means the center position of the radius R in a cross section perpendicular to the axial direction of the round bar.
  • the longitudinal direction of the test piece is parallel to the axial direction of the round bar.
  • the duplex stainless steel material is a steel plate
  • the test piece is taken from the center position of the plate thickness.
  • the longitudinal direction of the test piece is parallel to the rolling direction of the steel plate.
  • the size of the test piece is, for example, length: 40 mm, width: 10 mm, and thickness: 3 mm. The mass of the test piece is measured before the start of the test.
  • a 0.01 mol/L aqueous solution of sulfuric acid ( H2SO4 ) is prepared as the test liquid.
  • the test liquid is stored in an autoclave.
  • the test piece is immersed in the test liquid, and a mixture of 0.05 bar of H2S gas and 5.00 bar of CO2 gas is pressurized and sealed in the autoclave to start the corrosion test.
  • the test time is 336 hours.
  • the temperature inside the autoclave during the test is maintained at 180°C.
  • the corrosion products are removed from the test piece.
  • the removal of the corrosion products from the test piece is performed, for example, based on the method specified in ASTM G31-21.
  • the mass of the test piece from which the corrosion products have been removed is measured.
  • the corrosion rate (g ⁇ cm ⁇ 2 ⁇ h ⁇ 1 ) is obtained by dividing the difference between the mass of the test piece before the start of the test and the mass of the test piece from which the corrosion products have been removed after the test time has elapsed by the surface area of the test piece and the test time. If the corrosion rate is 0.100 g ⁇ cm ⁇ 2 ⁇ h ⁇ 1 or less, it is determined that the test piece has excellent general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosion environment.
  • the pitting corrosion resistance evaluation test in a high-temperature and high-pressure chloride corrosion environment is carried out in the following manner.
  • a test piece is taken from the duplex stainless steel material.
  • the duplex stainless steel material is a steel pipe
  • the test piece is taken from the center position of the wall thickness.
  • the longitudinal direction of the test piece is parallel to the axial direction of the steel pipe.
  • the duplex stainless steel material is a round bar
  • the test piece is taken from the R/2 position.
  • the longitudinal direction of the test piece is parallel to the axial direction of the round bar.
  • the duplex stainless steel material is a steel plate
  • the test piece is taken from the center position of the plate thickness.
  • the longitudinal direction of the test piece is parallel to the rolling direction of the steel plate.
  • the size of the test piece is, for example, length: 40 mm, width: 10 mm, and thickness: 3 mm. The mass of the test piece is measured before the start of the test.
  • a 25% by mass aqueous solution of sodium chloride (NaCl) is prepared as the test liquid.
  • the test liquid is stored in an autoclave.
  • the test piece is immersed in the test liquid, and a mixture of 0.05 bar of H2S gas and 5.00 bar of CO2 gas is pressurized and sealed in the autoclave to start the corrosion test.
  • the test time is 336 hours.
  • the temperature inside the autoclave during the test is maintained at 180°C.
  • the corrosion products are removed from the test specimen.
  • the removal of the corrosion products from the test specimen is performed, for example, based on the method specified in ASTM G31-21.
  • the mass of the test specimen from which the corrosion products have been removed is measured.
  • the corrosion rate (g cm -2 h -1 ) is calculated by dividing the difference between the mass of the test specimen before the start of the test and the mass of the test specimen from which the corrosion products have been removed after the test time has elapsed by the surface area of the test specimen and the test time.
  • the surface of the test piece is observed with a loupe at 10x magnification to confirm the presence or absence of pitting corrosion. If pitting corrosion is suspected in the loupe observation, the cross section of the suspected area is observed with an optical microscope at 100x magnification to confirm the presence or absence of pitting corrosion.
  • the corrosion rate is 0.005 g ⁇ cm ⁇ 2 ⁇ h ⁇ 1 or less and no pitting corrosion is observed on the entire surface of the test piece, it is determined that the test piece has excellent pitting corrosion resistance in a high-temperature, high-pressure chloride corrosive environment.
  • the duplex stainless steel material of this embodiment satisfies Features 1 to 3. Therefore, it has excellent general corrosion resistance in high-temperature, high-pressure, strongly acidic corrosive environments, and excellent pitting corrosion resistance in high-temperature, high-pressure chloride corrosive environments.
  • the microstructure of the duplex stainless steel material of this embodiment is composed of ferrite and austenite.
  • “composed of ferrite and austenite” means that the microstructure contains, for example, 30 to 80% by volume of ferrite, with the remainder being composed of austenite.
  • structures other than ferrite and austenite are negligibly small.
  • the volume fraction of precipitates and inclusions is negligibly small compared to the volume fraction of ferrite and austenite. That is, the microstructure of the duplex stainless steel material of this embodiment may contain precipitates and/or inclusions, etc., in addition to ferrite and austenite.
  • the volume fraction of ferrite in the duplex stainless steel material can be determined by a method conforming to JIS G 0555 (2020). Specifically, a test piece for microstructure observation is prepared from the duplex stainless steel material. When the steel material is a steel pipe, a test piece having an observation surface, for example, 5 mm in the pipe axial direction and 5 mm in the pipe radial direction from the center position of the wall thickness is prepared. When the steel material is a round steel, a test piece having an observation surface, for example, 5 mm in the axial direction and 5 mm in the radial direction from the R/2 position is prepared.
  • test piece having an observation surface for example, 5 mm in the rolling direction and 5 mm in the plate thickness direction from the center position of the plate thickness is prepared. Note that the size of the test piece is not particularly limited as long as the above observation surface can be obtained.
  • the observation surface of the prepared test piece is mirror-polished.
  • the mirror-polished observation surface is electrolytically etched in a 7% potassium hydroxide etchant to reveal the structure.
  • the observation surface with the revealed structure is observed in 10 fields of view using an optical microscope.
  • the field area is not particularly limited, but is, for example, 1.00 mm 2 (100x magnification).
  • ferrite and austenite are identified from the contrast.
  • the area ratio of the identified ferrite is measured by a point counting method in accordance with JIS G 0555 (2020).
  • the arithmetic average value of the area ratio of the obtained ferrite in 10 fields of view is defined as the volume ratio of ferrite (%).
  • the volume ratio of ferrite (%) is the value obtained by rounding off the first decimal place of the obtained value.
  • the value obtained by subtracting the volume ratio of ferrite from 100% is defined as the volume ratio of austenite (%).
  • the shape of the duplex stainless steel material of this embodiment is not particularly limited.
  • the duplex stainless steel material of this embodiment may be a steel pipe, a round bar (solid material), or a steel plate.
  • the steel pipe may be a seamless steel pipe or a welded steel pipe.
  • duplex stainless steel material of this embodiment is widely applicable to applications in high-temperature, high-pressure, highly acidic corrosive environments or high-temperature, high-pressure, chloride corrosive environments.
  • the duplex stainless steel material of this embodiment may be used in geothermal well applications or oil well applications.
  • the duplex stainless steel material of the present embodiment satisfies the above-mentioned characteristics 1 to 3, and further satisfies the following characteristic 4.
  • Fine Ca oxysulfides are defined as particles having an equivalent circle diameter of 1.0 to 2.0 ⁇ m, a total of Ca content and S content of more than 5.0%, an O content of 1.0% or more, and a Ca content higher than a S content, in terms of mass%
  • Fine Mg oxide particles are defined as particles having an equivalent circle diameter of 1.0 to 2.0 ⁇ m, and, in mass%, an Mg content of 5.0% or more, an O content of 1.0% or more, and an S content of 15.0% or less.
  • Particles having an equivalent circle diameter of 1.0 to 2.0 ⁇ m, an Al content of 20.0% or more, and an N content of 20.0% or more, in mass%, are defined as fine Al nitrides;
  • a Ti content of 30.0% or more, and a N content of 20.0% or more are defined as fine Ti nitrides,
  • the total number density ND of the fine Ca oxysulfides, the fine Mg oxides, the fine Al nitrides, and the fine Ti nitrides is 2.00 pieces/ mm2 or more.
  • duplex stainless steel material of this embodiment satisfies features 1 to 3 and also satisfies feature 4, it will have even better general corrosion resistance in a high-temperature, high-pressure, highly acidic corrosive environment.
  • Feature 4 will be explained below.
  • fine Ca oxysulfides, fine Mg oxides, fine Al nitrides, and fine Ti nitrides account for a high percentage of the number of all fine particles in the duplex stainless steel material. Therefore, if the total number density ND of fine Ca oxysulfides, fine Mg oxides, fine Al nitrides, and fine Ti nitrides can be increased, it is possible to sufficiently disperse As segregation sites in the steel material. As a result, it is possible to further improve general corrosion resistance in high-temperature, high-pressure, strongly acidic corrosion environments.
  • the total number density ND (pieces/ mm2 ) is the total number density of the main fine particles (fine Ca oxysulfides, fine Mg oxides, fine Al nitrides, and fine Ti nitrides) that become As segregation sites. If the total number density ND is 2.00 pieces/ mm2 or more, a sufficient amount of As segregation sites are dispersed and present in the steel material. Therefore, As is easily dispersed in the steel material. As a result, the general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosion environment is further improved.
  • the corrosion rate obtained in the above-mentioned is 0.080 g cm -2 h -1 or less, and further excellent general corrosion resistance is obtained.
  • the preferred lower limit of the total number density ND is 2.01 pieces/mm 2 , more preferably 2.05 pieces/mm 2 , even more preferably 2.07 pieces/mm 2 , and even more preferably 2.10 pieces/mm 2 .
  • the higher the total number density ND the more As segregation sites there are, and therefore the general corrosion resistance is likely to be improved. Therefore, the upper limit of the total number density ND is not particularly limited.
  • the upper limit of the total number density ND is, for example, 30.00 pieces/mm 2 , preferably 28.50 pieces/mm 2 , more preferably 25.00 pieces/mm 2 , more preferably 20.00 pieces/mm 2 , more preferably 17.00 pieces/mm 2 , more preferably 15.00 pieces/mm 2 , more preferably 10.00 pieces/mm 2 , more preferably 5.00 pieces/mm 2 , and more preferably 3.00 pieces/mm 2 .
  • the total number density ND (pieces/mm 2 ) of the fine Ca oxysulfides, fine Mg oxides, fine Al nitrides and fine Ti nitrides can be determined by the following method.
  • test pieces are prepared from duplex stainless steel material. If the steel material is a steel pipe, a test piece is prepared from the center of the wall thickness, with an observation surface including the pipe axial direction and the pipe radial direction (wall thickness direction). If the steel material is a steel plate, a test piece is prepared from the center of the plate thickness, with an observation surface including the rolling direction and plate thickness direction. If the steel material is a round bar, one test piece is prepared from the R/2 position on a cross section perpendicular to the axial direction of the round bar, with an observation surface including the axial and radial directions.
  • the observation surface of the prepared test piece is mirror-polished using a diamond paste abrasive.
  • the observation field at the thickness center position of the mirror-polished observation surface is observed at 500 times magnification using a scanning electron microscope (SEM).
  • SEM scanning electron microscope
  • the thickness center position of the observation surface means the center position in the thickness direction of the steel pipe on the observation surface.
  • the thickness center position of the observation surface means the center position in the thickness direction of the steel plate on the observation surface.
  • the thickness center position of the observation surface means the center position in the radial direction of the round steel on the observation surface.
  • the number of observation fields is not particularly limited.
  • the observation fields are selected so that the observation fields are arranged in a row on the observation surface and one side of adjacent observation fields is in contact with each other.
  • the size of each observation field is a rectangle measuring 15 mm x 15 mm
  • circle equivalent diameter means the diameter ( ⁇ m) of a circle having the same area as the particle.
  • element concentration analysis is performed on each identified particle. Element concentration analysis can be performed using a scanning electron microscope equipped with element concentration analysis function (SEM-EDS device). In element concentration analysis, the accelerating voltage is set to 20 kV, and the target elements are quantified as N, O, Mg, Al, Si, P, S, Ca, Ti, Cr, Mn, Fe, Cu, Zr, and Nb.
  • Particles having an equivalent circle diameter of 1.0 to 2.0 ⁇ m, a total Ca content and S content of more than 5.0%, an O content of 1.0% or more, and a Ca content higher than the S content are specified as "fine Ca oxysulfides”.
  • Particles having an equivalent circle diameter of 1.0 to 2.0 ⁇ m and, in mass%, an Mg content of 5.0% or more, an O content of 1.0% or more, and an S content of 15.0% or less are specified as "fine Mg oxides”.
  • Particles having an equivalent circle diameter of 1.0 to 2.0 ⁇ m, an Al content of 20.0% or more, and an N content of 20.0% or more, in mass % are specified as "fine Al nitrides”.
  • Particles having an equivalent circle diameter of 1.0 to 2.0 ⁇ m, a Ti content of 30.0% or more, and a N content of 20.0% or more, in mass % are specified as "fine Ti nitrides”.
  • the total number density ND (pieces/ mm2 ) of fine Ca oxysulfides, fine Mg oxides, fine Al nitrides and fine Ti nitrides is calculated.
  • the total number density ND is the value obtained by rounding off the obtained value to one decimal place.
  • the example of the method for producing the duplex stainless steel material of this embodiment includes a material production process, a hot working process, and a solution treatment process. Each process will be described in detail.
  • molten steel satisfying Features 1 to 3 is produced.
  • the method for producing the molten steel is not particularly limited.
  • the molten steel may be produced using a converter, an electric furnace, or another method.
  • the produced molten steel is used to manufacture materials.
  • the materials are, for example, slabs or ingots.
  • the molten steel is used to manufacture slabs by continuous casting.
  • the slabs may be slabs, blooms, or billets.
  • the molten steel may be used to make ingots by ingot casting.
  • the slabs or ingots may be further subjected to hot forging or blooming to manufacture billets.
  • the materials are manufactured by the above process.
  • the manufactured material is subjected to well-known hot working to produce an intermediate steel material.
  • the intermediate steel material is a blank pipe.
  • the intermediate steel material is a bar-shaped steel material.
  • the intermediate steel material is a plate-shaped steel material.
  • the hot working may be hot forging, hot extrusion, or hot rolling.
  • the method of hot working is not particularly limited and may be a well-known method.
  • An example of a hot working process when the final product is a seamless steel pipe is as follows. First, the billet, which is the raw material, is heated in a heating furnace.
  • the heating temperature is not particularly limited, but is, for example, 1000 to 1300°C.
  • the billet extracted from the heating furnace is subjected to hot working to produce a blank pipe (seamless steel pipe), which is an intermediate steel material.
  • the method of hot working is not particularly limited, and may be a well-known method.
  • the blank pipe may be produced by performing Mannesmann piercing rolling as hot working. In this case, the round billet is pierced and rolled using a piercing machine.
  • the piercing ratio is not particularly limited, but is, for example, 1.0 to 4.0.
  • the pierced and rolled round billet is further hot rolled using a mandrel mill, reducer, sizing mill, etc. to produce a blank pipe.
  • the cumulative reduction in area in the hot working process is, for example, 20 to 70%.
  • Other hot working methods may be performed to produce a blank pipe from the billet.
  • the steel material is a short, thick-walled steel pipe such as a coupling
  • the blank pipe may be manufactured by forging using the Erhardt method or similar.
  • the blank pipe is manufactured through the above process.
  • An example of a hot processing process when the final product is round steel is as follows. First, the material is heated in a heating furnace.
  • the heating temperature is not particularly limited, but is, for example, 1000 to 1300°C.
  • the material extracted from the heating furnace is subjected to hot processing to produce intermediate steel material with a circular cross section perpendicular to the axial direction.
  • the hot processing is, for example, blooming using a blooming mill, or hot rolling using a continuous rolling mill.
  • a continuous rolling mill has an alternating arrangement of horizontal stands having a pair of grooved rolls arranged side by side in the vertical direction, and vertical stands having a pair of grooved rolls arranged side by side in the horizontal direction.
  • An example of a hot processing process when the final product is a steel plate is as follows. First, the material is heated in a heating furnace.
  • the heating temperature is not particularly limited, but is, for example, 1000 to 1300°C.
  • the material extracted from the heating furnace is hot rolled using a reverse mill and a tandem mill to produce a plate-shaped intermediate steel material. It is also possible to perform hot forging, and then reheat the hot-forged material to 1000 to 1300°C, and further hot roll the reheated material to produce a plate-shaped intermediate steel material.
  • the solution treatment process a known solution treatment is performed on the intermediate steel material produced in the hot working process.
  • the intermediate steel material may be charged into a heat treatment furnace, held at a desired temperature, and then quenched.
  • the solution temperature means the temperature (°C) of the heat treatment furnace for performing the solution treatment.
  • the solution time means the time during which the intermediate steel material is held at the solution temperature.
  • the solution temperature is, for example, 900 to 1100°C.
  • the solution time is, for example, 5 to 180 minutes.
  • the quenching method in the solution treatment is, for example, water cooling.
  • the duplex stainless steel material of this embodiment is produced by the above manufacturing method.
  • the method for producing the duplex stainless steel material of the present embodiment preferably satisfies the following conditions 1 and 2.
  • the average cooling rate CR1 during the process in which the surface temperature of the material when casting molten steel is from 1350° C. to 1100° C. is set to 8 to 25° C./min.
  • the average cooling rate CR2 for the surface temperature of the intermediate material to decrease from the solution temperature to 850°C is set to 200°C/min or less
  • the average cooling rate CR3 for the surface temperature of the intermediate material to decrease from 850°C to 300°C is set to 1000°C/min or more. If condition 1 and condition 2 are satisfied, the produced duplex stainless steel material satisfies features 1 to 3 and further satisfies feature 4. Condition 1 and condition 2 will be explained below.
  • the method for controlling the average cooling rate CR1 is not particularly limited, and any known method may be used.
  • the cooling rate can be controlled by adjusting the amount of cooling water (specific water amount) used to cool the slab.
  • the cooling rate can be controlled by the material of the mold or the water cooling of the mold.
  • the surface temperature of the material can be measured using a non-contact infrared thermometer.
  • the average cooling rate CR1 (°C/min) can be calculated by measuring the time it takes for the surface temperature of the material to drop from 1350°C to 1100°C.
  • the temperature region T2 from when the intermediate steel is extracted from the heat treatment furnace until the surface temperature of the intermediate steel reaches 850°C is the temperature region in which fine Al nitrides and fine Ti nitrides are generated. If the average cooling rate CR2 in the temperature region T2 exceeds 200°C/min, the amount of fine Al nitrides and fine Ti nitrides generated in the temperature region T2 is insufficient. If the average cooling rate CR2 is 200°C/min or less, a sufficient amount of fine Al nitrides and fine Ti nitrides are generated. As a result, the total number density ND is 2.00 pieces/ mm2 or more.
  • the average cooling rate CR3 for the surface temperature of the intermediate steel material to decrease from 850° C. to 300° C. is set to 1000° C./min or more. If the intermediate steel material is water-cooled, the average cooling rate CR3 becomes 1000° C./min or more.
  • the surface temperature of the intermediate steel can be measured with a non-contact infrared thermometer.
  • the average cooling rate CR2 (°C/min) can be determined by measuring the time it takes for the surface temperature of the intermediate steel to reach 850°C from the solution treatment temperature.
  • the average cooling rate CR3 (°C/min) can be determined by measuring the time it takes for the surface temperature of the intermediate steel to reach 300°C from 850°C. As mentioned above, if water cooling is performed on the intermediate steel, the average cooling rate CR3 will be 1000°C/min or more.
  • the method for producing a duplex stainless steel material according to the present embodiment may include other steps in addition to the steps described above.
  • a cold working step may be performed on the intermediate steel material after the solution treatment step.
  • the cold working step is an optional step.
  • the intermediate steel material is subjected to well-known cold working.
  • the cold working may be, for example, cold drawing or cold rolling.
  • the manufacturing method of the duplex stainless steel material of this embodiment is not limited to the above example.
  • duplex stainless steel material of this embodiment will be explained more specifically using examples.
  • the conditions in the following examples are one example of conditions adopted to confirm the feasibility and effects of the duplex stainless steel material of this embodiment. Therefore, the duplex stainless steel material of this embodiment is not limited to this one example of conditions.
  • Duplex stainless steel materials were manufactured with the chemical compositions shown in Tables 1-1 and 1-2.
  • the "-" in Tables 1-1 and 1-2 means that the content of the corresponding element was at the impurity level.
  • the ingots of each test number were heated at 1200°C for 3 hours. After heating, the ingots were hot forged to produce intermediate steel materials with a cross section perpendicular to the longitudinal direction of 70 mm x 100 mm. The intermediate steel materials were heated at 1250°C for 1 hour. After heating, the intermediate steel materials were hot rolled to produce intermediate steel materials in the form of steel plates with a thickness of 17 mm.
  • the intermediate steel material after hot rolling was subjected to a solution treatment.
  • the solution temperature was 950°C, and the holding time at the solution temperature was 15 minutes.
  • the intermediate steel material was cooled after the holding time had elapsed.
  • the average cooling rate CR2 at which the surface temperature of the intermediate material was reduced from the solution temperature (950°C) to 850°C was as shown in the "CR2 (°C/min)" column in Table 2.
  • the subsequent cooling was performed by water cooling. Therefore, the average cooling rate CR3 at which the surface temperature of the intermediate material was reduced from 850°C to 300°C was 1000°C/min or more.
  • the microstructure of the duplex stainless steel material of each test number was observed using the method described in the "Microstructure Observation Method" above.
  • test pieces were prepared with an observation surface 5 mm in the rolling direction and 5 mm in the thickness direction from the center of the steel plate thickness.
  • the microstructure of the duplex stainless steel material of each test number was composed of ferrite and austenite, with the volume fraction of ferrite being 30-80%.
  • Test 1 The following evaluation tests were carried out on the duplex stainless steel materials with each test number.
  • Test 2 Measurement test of total number density ND
  • Test 3 Evaluation test of general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosive environment
  • Tests 1 to 3 will be described below.
  • the duplex stainless steel materials of test numbers 1 to 39 satisfied features 1 to 3. Therefore, the corrosion rate in a high-temperature, high-pressure, strongly acidic corrosion environment was 0.100 g cm -2 h -1 or less. Furthermore, the corrosion rate in a high-temperature, high-pressure chloride corrosion environment was 0.005 g cm -2 h -1 or less, and no pitting corrosion was observed. Therefore, the duplex stainless steel materials of these test numbers obtained excellent general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosion environment, and excellent pitting corrosion resistance in a high-temperature, high-pressure chloride corrosion environment.
  • test numbers 1 to 39 test numbers 1 to 10, 12 to 22, 24 to 36, 38 and 39 met the above-mentioned conditions 1 and 2 in the manufacturing process. Therefore, the duplex stainless steel materials of these test numbers met characteristics 1 to 3, and also characteristic 4. As a result, the duplex stainless steel materials of these test numbers had even better corrosion rates in high-temperature, high-pressure, strongly acidic corrosive environments.
  • duplex stainless steel materials that satisfied characteristics 1 to 4 exhibited superior general corrosion resistance compared to duplex stainless steel materials that satisfied characteristics 1 to 3 but did not satisfy characteristic 4.
  • the duplex stainless steel material of test number 11 met characteristics 1 to 3 but did not meet characteristic 4, whereas the duplex stainless steel material of test number 14 met characteristics 1 to 4.
  • the corrosion rate of test number 14 in a high-temperature, high-pressure, strongly acidic corrosion environment was slower than that of test number 11, and even better general corrosion resistance was obtained in a high-temperature, high-pressure, strongly acidic corrosion environment.
  • the duplex stainless steel material for test number 18 met characteristics 1 to 4, while the duplex stainless steel material for test number 23 met characteristics 1 to 3 but did not meet characteristic 4.
  • the corrosion rate of test number 18 in a high-temperature, high-pressure, strongly acidic corrosion environment was slower than that of test number 23, and even better general corrosion resistance was obtained in a high-temperature, high-pressure, strongly acidic corrosion environment.
  • the duplex stainless steel material for test number 9 met characteristics 1 to 4, while the duplex stainless steel material for test number 37 met characteristics 1 to 3 but did not meet characteristic 4.
  • the corrosion rate of test number 9 in a high-temperature, high-pressure, strongly acidic corrosion environment was slower than that of test number 37, and even better general corrosion resistance was obtained in a high-temperature, high-pressure, strongly acidic corrosion environment.
  • Fn1 was 5.50 or more in test numbers 2, 3, 7, 8, 10, 18 to 21, 23, 27 to 30, 33, and 34. Therefore, in the duplex stainless steel materials of these test numbers, regardless of whether or not they satisfied feature 4, the corrosion rate in a high-temperature, high-pressure, strongly acidic corrosive environment was 0.040 g cm -2 h -1 or less, and further excellent general corrosion resistance was obtained in a high-temperature, high-pressure, strongly acidic corrosive environment.
  • test number 40 the Cr content was too low. Therefore, the corrosion rate in a high-temperature, high-pressure, strong acidic corrosion environment exceeded 0.100 g cm -2 h -1 , and excellent general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosion environment was not obtained. Furthermore, the corrosion rate in a high-temperature, high-pressure chloride corrosion environment exceeded 0.005 g cm -2 h -1 , and pitting corrosion was also confirmed, and excellent pitting corrosion resistance in a high-temperature, high-pressure chloride corrosion environment was not obtained.
  • test numbers 41 and 42 the As content was too low.
  • the corrosion rate in a high-temperature, high-pressure, strongly acidic corrosive environment exceeded 0.100 g cm -2 h -1 , and excellent general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment was not obtained.
  • test number 43 the total content of Ca and Mg was too low, so that the corrosion rate in a high-temperature, high-pressure, strong acidic corrosive environment exceeded 0.100 g cm -2 h -1 , and excellent general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosive environment was not obtained.
  • Test numbers 44 to 46 met characteristic 1, but Fn1 was too high. As a result, cracks occurred during the hot forging process of the ingots in the manufacturing process. Therefore, for these test numbers, manufacturing processes and tests after hot forging were not carried out.
  • test numbers 50 to 52 although characteristic 1 was satisfied, Fn2 was too high.
  • the corrosion rate in a high-temperature, high-pressure chloride corrosive environment exceeded 0.005 g cm -2 h -1 , and pitting corrosion was also confirmed, so that excellent pitting corrosion resistance in a high-temperature, high-pressure chloride corrosive environment was not obtained.

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Abstract

Provided is a duplex stainless steel material having excellent whole surface corrosion resistance in a high-temperature, high-pressure, strong acidic corrosive environment, and excellent pitting corrosion resistance in a high-temperature, high-pressure, chloride corrosive environment. The duplex stainless steel material according to the present disclosure has a chemical composition containing, in mass%, 0.050% or less of C, 0.2-1.2% of Si, 0.5-7.0% of Mn, 0.040% or less of P, 0.010% or less of S, 20.0-27.0% of Cr, 4.0-9.0% of Ni, 0.5-5.0% of Mo, 0.0005-0.0100% of As, a total of 0.0005-0.0100% of one or more of Ca and Mg, 0.001-0.050% of sol.Al, 0.40% or less of N, and 0.100% or less of O, with the remainder comprising Fe and impurities, and satisfies relationships (1) and (2).　(1) 0.70 < 10000 × As/(Ni + Cu) < 16.00; (2) (Ca + Mg)/O < 1.50

Description

二相ステンレス鋼材Duplex Stainless Steel Material
　本開示は、二相ステンレス鋼材に関する。 This disclosure relates to duplex stainless steel materials.
　低炭素エネルギーの１つとして、地熱発電が注目されている。地熱発電では、高温及び高圧の熱水が蓄積された地熱井から採取される地熱流体を用いて蒸気を発生させる。地熱流体とは、高温及び高圧の熱水及び蒸気を意味する。この蒸気を蒸気タービンに供給し、発電する。 Geothermal power generation is attracting attention as a form of low-carbon energy. In geothermal power generation, steam is generated using geothermal fluid extracted from geothermal wells where high-temperature, high-pressure hot water has accumulated. Geothermal fluid refers to high-temperature, high-pressure hot water and steam. This steam is supplied to a steam turbine to generate electricity.
　最近では、従来よりも深層での大深度地熱井の開発が進められている。このような大深度地熱井から得られる蒸気は、硫化水素（Ｈ２Ｓ）及び二酸化炭素（ＣＯ２）を含有し、さらに、硫酸（Ｈ２ＳＯ４）及び／又は塩酸（ＨＣｌ）等の還元性の酸を含有する。このような蒸気を採取する配管、又は、このような蒸気を搬送する配管は、１８０℃の高温及び５ｂａｒの高圧の環境となる場合がある。そのため、配管内の高温高圧環境下で硫酸及び／又は塩化物イオンを含有する強酸性水溶液が生成する。配管内の蒸気は上述のとおり、腐食性の高い硫化水素（Ｈ２Ｓ）を含有している。そのため、地熱発電用途の配管内は、極めて厳しい腐食環境となる。 Recently, development of deep geothermal wells at deeper layers than before has been promoted. Steam obtained from such deep geothermal wells contains hydrogen sulfide (H 2 S) and carbon dioxide (CO 2 ), and further contains reducing acids such as sulfuric acid (H 2 SO 4 ) and/or hydrochloric acid (HCl). The piping for collecting such steam or the piping for transporting such steam may be in an environment of high temperature of 180° C. and high pressure of 5 bar. Therefore, a strongly acidic aqueous solution containing sulfuric acid and/or chloride ions is generated in the high temperature and high pressure environment in the piping. As described above, the steam in the piping contains highly corrosive hydrogen sulfide (H 2 S). Therefore, the inside of the piping for geothermal power generation is an extremely severe corrosive environment.
　硫化水素と還元性の酸とを含有する環境では、全面腐食が主たる腐食要因となる。また、硫化水素と塩化物イオンとを含有する環境では、孔食が主たる腐食要因となる。したがって、上述の高温高圧の腐食環境で優れた耐食性を有するためには、１８０℃の高温及び５ｂａｒの高圧の環境であって、硫化水素及び硫酸を含有する高温高圧強酸性腐食環境において、優れた耐全面腐食性を有し、１８０℃の高温及び５ｂａｒの高圧の環境であって、硫化水素及び塩化物イオンを含有する高温高圧塩化物腐食環境において、優れた耐孔食性を有することが求められる。 In an environment containing hydrogen sulfide and reducing acid, general corrosion is the main corrosion factor. In an environment containing hydrogen sulfide and chloride ions, pitting corrosion is the main corrosion factor. Therefore, in order to have excellent corrosion resistance in the above-mentioned high-temperature and high-pressure corrosive environment, it is necessary to have excellent general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment containing hydrogen sulfide and sulfuric acid at a high temperature of 180°C and a high pressure of 5 bar, and to have excellent pitting corrosion resistance in a high-temperature, high-pressure chloride corrosive environment containing hydrogen sulfide and chloride ions at a high temperature of 180°C and a high pressure of 5 bar.
　還元性の酸を含有する強酸性環境での優れた耐食性が得られる合金材が、国際公開第２００９／１１９６３０号（特許文献１）に提案されている。この文献に開示された合金材はＮｉ合金材であって、質量％で、Ｃ：０．０３％以下、Ｓｉ：０．０１～０．５％、Ｍｎ：０．０１～１．０％、Ｐ：０．０３％以下、Ｓ：０．０１％以下、Ｃｒ：２０％以上３０％未満、Ｎｉ：４０％を超えて６０％以下、Ｃｕ：２．０％を超えて５．０％以下、Ｍｏ：４．０～１０％、Ａｌ：０．００５～０．５％、及び、Ｎ：０．０２％を超えて０．３％以下を含有し、０．５Ｃｕ＋Ｍｏ≧６．５を満たす。 An alloy material that provides excellent corrosion resistance in a strongly acidic environment containing reducing acid is proposed in International Publication No. 2009/119630 (Patent Document 1). The alloy material disclosed in this document is a Ni alloy material that contains, in mass percent, C: 0.03% or less, Si: 0.01-0.5%, Mn: 0.01-1.0%, P: 0.03% or less, S: 0.01% or less, Cr: 20% or more and less than 30%, Ni: more than 40% and less than 60%, Cu: more than 2.0% and less than 5.0%, Mo: 4.0-10%, Al: 0.005-0.5%, and N: more than 0.02% and less than 0.3%, and satisfies 0.5Cu+Mo≧6.5.
　また、硫化水素と塩化物イオンとを含有する１５０℃程度の腐食環境での優れた耐食性が得られる二相ステンレス鋼材が、国際公開第２０１３／０３５５８８号（特許文献２）に提案されている。この文献に開示された二相ステンレス鋼材は、質量％で、Ｃ：０．０３％以下、Ｓｉ：０．２～１％、Ｍｎ：５．０％よりも高く１０％以下、Ｐ：０．０４０％以下、Ｓ：０．０１０％以下、Ｎｉ：４．５～８％、ｓｏｌ．Ａｌ：０．０４０％以下、Ｎ：０．２％よりも高く０．４％以下、Ｃｒ：２４～２９％、Ｍｏ：０．５～１．５％未満、Ｃｕ：１．５～３．５％、及び、Ｗ：０．０５～０．２％を含有し、残部はＦｅ及び不純物からなり、Ｃｒ＋８Ｎｉ＋Ｃｕ＋Ｍｏ＋Ｗ／２≧６５を満たす。 　Also, a duplex stainless steel material that has excellent corrosion resistance in a corrosive environment of about 150°C containing hydrogen sulfide and chloride ions is proposed in International Publication No. 2013/035588 (Patent Document 2). The duplex stainless steel material disclosed in this document contains, by mass%, C: 0.03% or less, Si: 0.2-1%, Mn: higher than 5.0% and lower than 10%, P: 0.040% or less, S: 0.010% or less, Ni: 4.5-8%, sol. Al: 0.040% or less, N: higher than 0.2% and lower than 0.4%, Cr: 24-29%, Mo: 0.5-less than 1.5%, Cu: 1.5-3.5%, and W: 0.05-0.2%, with the remainder being Fe and impurities, and satisfies Cr+8Ni+Cu+Mo+W/2≧65.
国際公開第２００９／１１９６３０号International Publication No. WO 2009/119630 国際公開第２０１３／０３５５８８号International Publication No. 2013/035588
　しかしながら、特許文献１及び特許文献２では、上述の高温高圧強酸性腐食環境での耐全面腐食性、及び、高温高圧塩化物腐食環境での耐孔食性については検討されていない。 However, Patent Documents 1 and 2 do not consider the general corrosion resistance in the above-mentioned high-temperature, high-pressure, strongly acidic corrosive environment, or the pitting corrosion resistance in the high-temperature, high-pressure chloride corrosive environment.
　本開示の目的は、高温高圧強酸性腐食環境において優れた耐全面腐食性が得られ、高温高圧塩化物腐食環境において優れた耐孔食性が得られる二相ステンレス鋼材を提供することである。 The objective of this disclosure is to provide a duplex stainless steel material that exhibits excellent general corrosion resistance in high-temperature, high-pressure, strongly acidic corrosive environments, and excellent pitting corrosion resistance in high-temperature, high-pressure chloride corrosive environments.
　本開示の二相ステンレス鋼材は、
　化学組成が、質量％で、
　Ｃ：０．０５０％以下、
　Ｓｉ：０．２～１．２％、
　Ｍｎ：０．５～７．０％、
　Ｐ：０．０４０％以下、
　Ｓ：０．０１０％以下、
　Ｃｒ：２０．０～２７．０％、
　Ｎｉ：４．０～９．０％、
　Ｍｏ：０．５～５．０％、
　Ａｓ：０．０００５～０．０１００％、
　Ｃａ及びＭｇの１種以上：合計で０．０００５～０．０１００％、
　ｓｏｌ．Ａｌ：０．００１～０．０５０％、
　Ｎ：０．４０％以下、
　Ｏ：０．１００％以下、
　Ｃｕ：０～４．０％、
　Ｖ：０～１．５０％、
　Ｃｏ：０～２．００％、
　Ｔａ：０～２．００％、
　Ｗ：０～４．００％、
　Ｎｂ：０～２．００％、
　Ｔｉ：０～２．００％、
　Ｚｎ：０～０．０１００％、
　Ｐｂ：０～０．０１００％、
　Ｓｂ：０～０．０１００％、
　Ｓｎ：０～０．０１００％、
　Ｂｉ：０～０．０１００％、
　Ｂ：０～０．０１００％、
　希土類元素：０～０．０５０％、
　Ｚｒ：０～２．００％、
　Ｈｆ：０～２．００％、及び、
　残部がＦｅ及び不純物からなり、
　式（１）及び（２）を満たす。
　０．７０＜１００００×Ａｓ／（Ｎｉ＋Ｃｕ）＜１６．００　（１）
　（Ｃａ＋Ｍｇ）／Ｏ＜１．５０　（２）
　ここで、式中の各元素記号には、対応する元素の質量％での含有量が代入される。元素が含有されていない場合、対応する元素記号には「０」が代入される。 The duplex stainless steel material of the present disclosure is
The chemical composition, in mass%, is
C: 0.050% or less,
Si: 0.2 to 1.2%,
Mn: 0.5 to 7.0%,
P: 0.040% or less,
S: 0.010% or less,
Cr: 20.0 to 27.0%,
Ni: 4.0 to 9.0%,
Mo: 0.5 to 5.0%,
As: 0.0005 to 0.0100%,
One or more of Ca and Mg: 0.0005 to 0.0100% in total,
sol. Al: 0.001 to 0.050%,
N: 0.40% or less,
O: 0.100% or less,
Cu: 0 to 4.0%,
V: 0 to 1.50%,
Co: 0 to 2.00%,
Ta: 0 to 2.00%,
W: 0 to 4.00%,
Nb: 0 to 2.00%,
Ti: 0 to 2.00%,
Zn: 0 to 0.0100%,
Pb: 0 to 0.0100%,
Sb: 0 to 0.0100%,
Sn: 0 to 0.0100%,
Bi: 0 to 0.0100%,
B: 0 to 0.0100%,
Rare earth elements: 0 to 0.050%,
Zr: 0 to 2.00%,
Hf: 0 to 2.00%, and
The balance is Fe and impurities,
Formulas (1) and (2) are satisfied.
0.70<10000×As/(Ni+Cu)<16.00 (1)
(Ca+Mg)/O<1.50 (2)
Here, the content of the corresponding element in mass % is substituted for each element symbol in the formula. When an element is not contained, "0" is substituted for the corresponding element symbol.
　本開示の二相ステンレス鋼材では、高温高圧強酸性腐食環境において優れた耐全面腐食性が得られ、高温高圧塩化物腐食環境において優れた耐孔食性が得られる。 The duplex stainless steel material disclosed herein provides excellent general corrosion resistance in high-temperature, high-pressure, strongly acidic corrosive environments, and excellent pitting corrosion resistance in high-temperature, high-pressure chloride corrosive environments.
図１は、二相ステンレス鋼材での、Ｆｎ１と高温高圧強酸性腐食環境での腐食速度（ｇ・ｃｍ－２・ｈ－１）との関係を示す図である。FIG. 1 is a graph showing the relationship between Fn1 and the corrosion rate (g·cm −2 ·h −1 ) in a high-temperature, high-pressure, strongly acidic corrosive environment for a duplex stainless steel material. 図２は、二相ステンレス鋼材での、Ｆｎ２と高温高圧塩化物腐食環境での腐食速度（ｇ・ｃｍ－２・ｈ－１）との関係を示す図である。FIG. 2 is a diagram showing the relationship between Fn2 and the corrosion rate (g·cm −2 ·h −1 ) in a high-temperature, high-pressure chloride corrosive environment for a duplex stainless steel material.
　本明細書において、高温高圧強酸性腐食環境、及び、高温高圧塩化物腐食環境を次のとおり定義する。
　高温高圧強酸性腐食環境：１８０℃の高温及び５ｂａｒの高圧の環境であって、硫化水素及び硫酸を含有する環境
　高温高圧塩化物腐食環境：１８０℃の高温及び５ｂａｒの高圧の環境であって、硫化水素及び塩化物イオンを含有する環境 In this specification, the high-temperature, high-pressure strongly acidic corrosive environment and the high-temperature, high-pressure chloride corrosive environment are defined as follows.
High-temperature, high-pressure, strong acidic corrosive environment: an environment with a high temperature of 180°C and a high pressure of 5 bar, containing hydrogen sulfide and sulfuric acid. High-temperature, high-pressure chloride corrosive environment: an environment with a high temperature of 180°C and a high pressure of 5 bar, containing hydrogen sulfide and chloride ions.
　本発明者らは、高温高圧強酸性腐食環境で優れた耐全面腐食性が得られ、高温高圧塩化物腐食環境で優れた耐孔食性が得られる二相ステンレス鋼材について、化学組成の観点から検討を行った。その結果、本発明者らは、質量％で、Ｃ：０．０５０％以下、Ｓｉ：０．２～１．２％、Ｍｎ：０．５～７．０％、Ｐ：０．０４０％以下、Ｓ：０．０１０％以下、Ｃｒ：２０．０～２７．０％、Ｎｉ：４．０～９．０％、Ｍｏ：０．５～５．０％、Ｃａ及びＭｇの１種以上：合計で０．０００５～０．０１００％、ｓｏｌ．Ａｌ：０．００１～０．０５０％、Ｎ：０．４０％以下、Ｏ：０．１００％以下、Ｃｕ：０～４．０％、Ｖ：０～１．５０％、Ｃｏ：０～２．００％、Ｔａ：０～２．００％、Ｗ：０～４．００％、Ｎｂ：０～２．００％、Ｔｉ：０～２．００％、Ｚｎ：０～０．０１００％、Ｐｂ：０～０．０１００％、Ｓｂ：０～０．０１００％、Ｓｎ：０～０．０１００％、Ｂｉ：０～０．０１００％、Ｂ：０～０．０１００％、希土類元素：０～０．０５０％、Ｚｒ：０～２．００％、Ｈｆ：０～２．００％、及び、残部がＦｅ及び不純物からなる化学組成を有する二相ステンレス鋼材であれば、高温高圧強酸性腐食環境で優れた耐全面腐食性が得られ、高温高圧塩化物腐食環境で優れた耐孔食性が得られる可能性があると考えた。 The present inventors have investigated, from the standpoint of chemical composition, duplex stainless steel materials that provide excellent general corrosion resistance in high-temperature, high-pressure, strong acidic corrosion environments and excellent pitting corrosion resistance in high-temperature, high-pressure chloride corrosion environments. As a result, the present inventors have found that the composition is, by mass%, C: 0.050% or less, Si: 0.2-1.2%, Mn: 0.5-7.0%, P: 0.040% or less, S: 0.010% or less, Cr: 20.0-27.0%, Ni: 4.0-9.0%, Mo: 0.5-5.0%, one or more of Ca and Mg: 0.0005-0.0100% in total, sol. Al: 0.001 to 0.050%, N: 0.40% or less, O: 0.100% or less, Cu: 0 to 4.0%, V: 0 to 1.50%, Co: 0 to 2.00%, Ta: 0 to 2.00%, W: 0 to 4.00%, Nb: 0 to 2.00%, Ti: 0 to 2.00%, Zn: 0 to 0.0100%, Pb: 0 to 0.0100%, Sb: 0 to 0.0100%, Sn: 0 to 0.0100%, It was believed that a duplex stainless steel material with a chemical composition of Bi: 0-0.0100%, B: 0-0.0100%, rare earth elements: 0-0.050%, Zr: 0-2.00%, Hf: 0-2.00%, and the balance being Fe and impurities, could provide excellent general corrosion resistance in high-temperature, high-pressure, strong acidic corrosion environments, and excellent pitting corrosion resistance in high-temperature, high-pressure chloride corrosion environments.
　しかしながら、上述の化学組成を有する二相ステンレス鋼材を高温高圧強酸性腐食環境に適用した場合、優れた耐全面腐食性が得られない場合があった。そこで、本発明者らはさらに検討を行った。その結果、高温高圧強酸性腐食環境では、砒素（Ａｓ）が耐全面腐食性を高めることを本発明者らは見出した。そこで、さらに検討を行った結果、二相ステンレス鋼材が、上述の化学組成のＦｅの一部に代えて、Ａｓを０．０００５～０．０１００％含有する特徴１を満たせば、高温高圧強酸性腐食環境において、優れた耐全面腐食性が得られる可能性があると考えた。
　（特徴１）
　化学組成が、質量％で、Ｃ：０．０５０％以下、Ｓｉ：０．２～１．２％、Ｍｎ：０．５～７．０％、Ｐ：０．０４０％以下、Ｓ：０．０１０％以下、Ｃｒ：２０．０～２７．０％、Ｎｉ：４．０～９．０％、Ｍｏ：０．５～５．０％、Ａｓ：０．０００５～０．０１００％、Ｃａ及びＭｇの１種以上：合計で０．０００５～０．０１００％、ｓｏｌ．Ａｌ：０．００１～０．０５０％、Ｎ：０．４０％以下、Ｏ：０．１００％以下、Ｃｕ：０～４．０％、Ｖ：０～１．５０％、Ｃｏ：０～２．００％、Ｔａ：０～２．００％、Ｗ：０～４．００％、Ｎｂ：０～２．００％、Ｔｉ：０～２．００％、Ｚｎ：０～０．０１００％、Ｐｂ：０～０．０１００％、Ｓｂ：０～０．０１００％、Ｓｎ：０～０．０１００％、Ｂｉ：０～０．０１００％、Ｂ：０～０．０１００％、希土類元素：０～０．０５０％、Ｚｒ：０～２．００％、及び、Ｈｆ：０～２．００％、及び、残部はＦｅ及び不純物からなる。 However, when a duplex stainless steel material having the above-mentioned chemical composition is applied to a high-temperature, high-pressure, strong acidic corrosive environment, there are cases where excellent general corrosion resistance is not obtained. Therefore, the present inventors conducted further studies. As a result, the present inventors found that arsenic (As) enhances general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosive environment. Therefore, as a result of further studies, it was thought that if a duplex stainless steel material satisfies Feature 1 in which 0.0005 to 0.0100% As is contained instead of a part of the Fe in the above-mentioned chemical composition, excellent general corrosion resistance may be obtained in a high-temperature, high-pressure, strong acidic corrosive environment.
(Feature 1)
The chemical composition, in mass%, is C: 0.050% or less, Si: 0.2 to 1.2%, Mn: 0.5 to 7.0%, P: 0.040% or less, S: 0.010% or less, Cr: 20.0 to 27.0%, Ni: 4.0 to 9.0%, Mo: 0.5 to 5.0%, As: 0.0005 to 0.0100%, one or more of Ca and Mg: 0.0005 to 0.0100% in total, sol. Al: 0.001-0.050%, N: 0.40% or less, O: 0.100% or less, Cu: 0-4.0%, V: 0-1.50%, Co: 0-2.00%, Ta: 0-2.00%, W: 0-4.00%, Nb: 0-2.00%, Ti: 0-2.00%, Zn: 0-0.0100%, Pb: 0-0.0100%, Sb: 0-0.0100%, Sn: 0-0.0100%, Bi: 0-0.0100%, B: 0-0.0100%, rare earth elements: 0-0.050%, Zr: 0-2.00%, and Hf: 0-2.00%, and the balance is Fe and impurities.
　しかしながら、特徴１を満たす二相ステンレス鋼材であっても、依然として、高温高圧強酸性腐食環境において、優れた耐全面腐食性が得られない場合があった。また、特徴１を満たす二相ステンレス鋼材であっても、高温高圧塩化物腐食環境において、優れた耐孔食性が得られない場合があった。 However, even duplex stainless steel materials that satisfy characteristic 1 may still not provide excellent general corrosion resistance in high-temperature, high-pressure, strong acidic corrosion environments. Also, even duplex stainless steel materials that satisfy characteristic 1 may not provide excellent pitting corrosion resistance in high-temperature, high-pressure chloride corrosion environments.
　そこで、本発明者らは、特徴１を満たす二相ステンレス鋼材において、高温高圧強酸性腐食環境での耐全面腐食性と、高温高圧塩化物腐食環境での耐孔食性とを高める手段において、さらに検討を行った。その結果、特徴１を満たす二相ステンレス鋼材がさらに、特徴２及び特徴３を満たせば、高温高圧強酸性腐食環境において優れた耐全面腐食性が得られ、かつ、高温高圧塩化物腐食環境において優れた耐孔食性が得られることを見出した。
　（特徴２）
　化学組成が式（１）を満たす。
　０．７０＜１００００×Ａｓ／（Ｎｉ＋Ｃｕ）＜１６．００　（１）
　ここで、式中の各元素記号には、対応する元素の質量％での含有量が代入される。元素が含有されていない場合、対応する元素記号には「０」が代入される。
　（特徴３）
　化学組成が式（２）を満たす。
　（Ｃａ＋Ｍｇ）／Ｏ＜１．５０　（２）
　ここで、式中の各元素記号には、対応する元素の質量％での含有量が代入される。元素が含有されていない場合、対応する元素記号には「０」が代入される。 Therefore, the present inventors conducted further studies on means for improving the general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment and the pitting corrosion resistance in a high-temperature, high-pressure, chloride corrosive environment in a duplex stainless steel material satisfying characteristic 1. As a result, they found that if a duplex stainless steel material satisfying characteristic 1 also satisfies characteristics 2 and 3, it can obtain excellent general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment and excellent pitting corrosion resistance in a high-temperature, high-pressure, chloride corrosive environment.
(Feature 2)
The chemical composition satisfies formula (1).
0.70<10000×As/(Ni+Cu)<16.00 (1)
Here, the content of the corresponding element in mass % is substituted for each element symbol in the formula. When an element is not contained, "0" is substituted for the corresponding element symbol.
(Feature 3)
The chemical composition satisfies formula (2).
(Ca+Mg)/O<1.50 (2)
Here, the content of the corresponding element in mass % is substituted for each element symbol in the formula. When an element is not contained, "0" is substituted for the corresponding element symbol.
　［特徴２について］
　特徴２について、Ｆｎ１を以下のとおり定義する。
　Ｆｎ１＝１００００×Ａｓ／（Ｎｉ＋Ｃｕ）
　ここで、本実施形態の二相ステンレス鋼材の化学組成が必須元素からなる場合、Ｆｎ１中のＣｕには「０」が代入されるため、Ｆｎ１＝１００００×Ａｓ／Ｎｉとなる。 [Regarding feature 2]
For feature 2, Fn1 is defined as follows:
Fn1 = 10000 x As / (Ni + Cu)
Here, when the chemical composition of the duplex stainless steel material of this embodiment is made up of essential elements, "0" is substituted for Cu in Fn1, so that Fn1 = 10000 x As/Ni.
　Ｆｎ１は高温高圧強酸性腐食環境での耐全面腐食性に関する指標である。Ａｓ、Ｎｉ及びＣｕはいずれも高温高圧強酸性腐食環境での耐全面腐食性を高める。さらに、Ｎｉ及びＣｕの総含有量に対するＡｓ含有量の比を調整することにより、高温高圧強酸性腐食環境での耐全面腐食性が顕著に高まる。 Fn1 is an index of general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment. As, Ni, and Cu all increase general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment. Furthermore, by adjusting the ratio of the As content to the total Ni and Cu content, general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment is significantly increased.
　図１は、特徴１及び特徴３を満たす二相ステンレス鋼材での、Ｆｎ１と高温高圧強酸性腐食環境での耐全面腐食性との関係を示す図である。図１は後述の実施例中の高温高圧強酸性腐食環境での耐全面腐食性評価試験により得られた結果に基づいて作成している。
　図１を参照して、Ｆｎ１が０．７０以下である場合、高温高圧強酸性腐食環境での腐食速度は顕著に速くなり、優れた耐全面腐食性が得られない。一方、Ｆｎ１が０．７０よりも高い場合、高温高圧強酸性腐食環境での腐食速度が顕著に遅くなり、耐全面腐食性が顕著に高まる。したがって、Ｆｎ１が式（１）を満たせば、二相ステンレス鋼材が特徴１及び特徴３を満たすことを前提として、高温高圧強酸性腐食環境において、優れた耐全面腐食性が得られる。なお、Ｆｎ１が高すぎれば、二相ステンレス鋼材の熱間加工性が低下する。そのため、Ｆｎ１の上限を１６．００未満とする。 Fig. 1 is a diagram showing the relationship between Fn1 and general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosive environment for a duplex stainless steel material satisfying Features 1 and 3. Fig. 1 is created based on the results obtained from a general corrosion resistance evaluation test in a high-temperature, high-pressure, strong acidic corrosive environment in the examples described later.
Referring to FIG. 1, when Fn1 is 0.70 or less, the corrosion rate in a high-temperature, high-pressure, strong acidic corrosion environment is significantly increased, and excellent general corrosion resistance is not obtained. On the other hand, when Fn1 is higher than 0.70, the corrosion rate in a high-temperature, high-pressure, strong acidic corrosion environment is significantly decreased, and general corrosion resistance is significantly improved. Therefore, if Fn1 satisfies formula (1), excellent general corrosion resistance can be obtained in a high-temperature, high-pressure, strong acidic corrosion environment, provided that the duplex stainless steel material satisfies features 1 and 3. If Fn1 is too high, the hot workability of the duplex stainless steel material is reduced. Therefore, the upper limit of Fn1 is set to be less than 16.00.
　［特徴３について］
　特徴３について、Ｆｎ２を以下のとおり定義する。
　Ｆｎ２＝（Ｃａ＋Ｍｇ）／Ｏ
　Ｆｎ２は、高温高圧塩化物腐食環境での耐孔食性に関する指標である。Ｃａ及びＭｇは、Ｓと結合して硫化物を形成することにより、粗大なＭｎ硫化物が生成するのを抑制する。粗大なＭｎ硫化物が鋼材表層に存在している場合、高温高圧塩化物腐食環境では表層の粗大なＭｎ硫化物が溶解して孔食が発生しやすくなる。そのため、Ｃａ及びＭｇは高温高圧塩化物腐食環境での耐孔食性を高める。 [Regarding feature 3]
For feature 3, Fn2 is defined as follows:
Fn2 = (Ca + Mg) / O
Fn2 is an index of pitting corrosion resistance in a high-temperature, high-pressure chloride corrosive environment. Ca and Mg combine with S to form sulfides, thereby suppressing the generation of coarse Mn sulfides. If coarse Mn sulfides are present on the surface layer of a steel material, the coarse Mn sulfides on the surface layer will dissolve in a high-temperature, high-pressure chloride corrosive environment, making pitting corrosion more likely to occur. Therefore, Ca and Mg improve pitting corrosion resistance in a high-temperature, high-pressure chloride corrosive environment.
　しかしながら、鋼材中のＳ含有量が特徴１に記載の範囲内（０．０１０％以下）である場合、Ｏ含有量に対してＣａ及びＭｇの総含有量が高すぎれば、Ｃａ及びＭｇがＳだけでなくＯと結合して、粗大なＣａ酸硫化物及びＭｇ酸化物を過剰に形成する。粗大なＣａ酸硫化物及び粗大なＭｇ酸化物は粗大なＭｎ硫化物と同様に、高温高圧塩化物腐食環境で溶解しやすく、孔食の起点となりやすい。 However, when the S content in the steel is within the range described in Feature 1 (0.010% or less), if the total Ca and Mg content is too high relative to the O content, Ca and Mg will combine with not only S but also O to form excessive coarse Ca oxysulfides and Mg oxides. Like coarse Mn sulfides, coarse Ca oxysulfides and coarse Mg oxides are easily dissolved in a high-temperature, high-pressure chloride corrosion environment and are likely to become the starting point of pitting corrosion.
　図２は、特徴１及び特徴２を満たす二相ステンレス鋼材での、Ｆｎ２と高温高圧塩化物腐食環境での耐孔食性との関係を示す図である。図２は後述の実施例中の高温高圧塩化物腐食環境での耐孔食性評価試験により得られた結果に基づいて作成している。 Figure 2 shows the relationship between Fn2 and pitting corrosion resistance in a high-temperature, high-pressure chloride corrosion environment for duplex stainless steel materials that satisfy features 1 and 2. Figure 2 was created based on the results obtained from a pitting corrosion resistance evaluation test in a high-temperature, high-pressure chloride corrosion environment in the examples described later.
　図２を参照して、Ｆｎ２が１．５０以上であれば、二相ステンレス鋼材が特徴１及び特徴２を満たしていても、腐食速度が高く、高温高圧塩化物腐食環境での耐孔食性が低い。一方、Ｆｎ２が１．５０未満であれば、二相ステンレス鋼材が特徴１及び特徴２を満たすことを前提として、高温高圧塩化物腐食環境において、腐食速度が顕著に遅くなり、優れた耐孔食性が得られる。 Referring to Figure 2, if Fn2 is 1.50 or more, even if the duplex stainless steel material satisfies Features 1 and 2, the corrosion rate is high and the pitting corrosion resistance in a high-temperature, high-pressure chloride corrosion environment is low. On the other hand, if Fn2 is less than 1.50, the corrosion rate is significantly slower and excellent pitting corrosion resistance is obtained in a high-temperature, high-pressure chloride corrosion environment, provided that the duplex stainless steel material satisfies Features 1 and 2.
　本実施形態の二相ステンレス鋼材は、以上の技術思想により完成したものであって、次の構成を有する。 The duplex stainless steel material of this embodiment was completed based on the above technical concept and has the following configuration.
　第１の構成の二相ステンレス鋼材は、
　化学組成が、質量％で、
　Ｃ：０．０５０％以下、
　Ｓｉ：０．２～１．２％、
　Ｍｎ：０．５～７．０％、
　Ｐ：０．０４０％以下、
　Ｓ：０．０１０％以下、
　Ｃｒ：２０．０～２７．０％、
　Ｎｉ：４．０～９．０％、
　Ｍｏ：０．５～５．０％、
　Ａｓ：０．０００５～０．０１００％、
　Ｃａ及びＭｇの１種以上：合計で０．０００５～０．０１００％、
　ｓｏｌ．Ａｌ：０．００１～０．０５０％、
　Ｎ：０．４０％以下、
　Ｏ：０．１００％以下、
　Ｃｕ：０～４．０％、
　Ｖ：０～１．５０％、
　Ｃｏ：０～２．００％、
　Ｔａ：０～２．００％、
　Ｗ：０～４．００％、
　Ｎｂ：０～２．００％、
　Ｔｉ：０～２．００％、
　Ｚｎ：０～０．０１００％、
　Ｐｂ：０～０．０１００％、
　Ｓｂ：０～０．０１００％、
　Ｓｎ：０～０．０１００％、
　Ｂｉ：０～０．０１００％、
　Ｂ：０～０．０１００％、
　希土類元素：０～０．０５０％、
　Ｚｒ：０～２．００％、
　Ｈｆ：０～２．００％、及び、
　残部がＦｅ及び不純物からなり、
　式（１）及び（２）を満たす。
　０．７０＜１００００×Ａｓ／（Ｎｉ＋Ｃｕ）＜１６．００　（１）
　（Ｃａ＋Ｍｇ）／Ｏ＜１．５０　（２）
　ここで、式中の各元素記号には、対応する元素の質量％での含有量が代入される。元素が含有されていない場合、対応する元素記号には「０」が代入される。 The duplex stainless steel material of the first configuration is
The chemical composition, in mass%, is
C: 0.050% or less,
Si: 0.2 to 1.2%,
Mn: 0.5 to 7.0%,
P: 0.040% or less,
S: 0.010% or less,
Cr: 20.0 to 27.0%,
Ni: 4.0 to 9.0%,
Mo: 0.5 to 5.0%,
As: 0.0005 to 0.0100%,
One or more of Ca and Mg: 0.0005 to 0.0100% in total,
sol. Al: 0.001 to 0.050%,
N: 0.40% or less,
O: 0.100% or less,
Cu: 0 to 4.0%,
V: 0 to 1.50%,
Co: 0 to 2.00%,
Ta: 0 to 2.00%,
W: 0 to 4.00%,
Nb: 0 to 2.00%,
Ti: 0 to 2.00%,
Zn: 0 to 0.0100%,
Pb: 0 to 0.0100%,
Sb: 0 to 0.0100%,
Sn: 0 to 0.0100%,
Bi: 0 to 0.0100%,
B: 0 to 0.0100%,
Rare earth elements: 0 to 0.050%,
Zr: 0 to 2.00%,
Hf: 0 to 2.00%, and
The balance is Fe and impurities,
Formulas (1) and (2) are satisfied.
0.70<10000×As/(Ni+Cu)<16.00 (1)
(Ca+Mg)/O<1.50 (2)
Here, the content of the corresponding element in mass % is substituted for each element symbol in the formula. When an element is not contained, "0" is substituted for the corresponding element symbol.
　第２の構成の二相ステンレス鋼材は、
　第１の構成の二相ステンレス鋼材であって、
　円相当径が１．０～２．０μｍであり、質量％で、Ｃａ含有量及びＳ含有量の合計が５．０％よりも高く、Ｏ含有量が１．０％以上であり、Ｃａ含有量がＳ含有量よりも高い粒子を微細Ｃａ酸硫化物と定義し、
　円相当径が１．０～２．０μｍであり、質量％で、Ｍｇ含有量が５．０％以上であり、Ｏ含有量が１．０％以上であり、Ｓ含有量が１５．０％以下である粒子を微細Ｍｇ酸化物と定義し、
　円相当径が１．０～２．０μｍであり、質量％で、Ａｌ含有量が２０．０％以上であり、Ｎ含有量が２０．０％以上である粒子を微細Ａｌ窒化物と定義し、
　円相当径が１．０～２．０μｍであり、質量％でＴｉ含有量が３０．０％以上であり、Ｎ含有量が２０．０％以上である粒子を微細Ｔｉ窒化物と定義したとき、
　微細Ｃａ酸硫化物、微細Ｍｇ酸化物、微細Ａｌ窒化物、及び、微細Ｔｉ窒化物の総個数密度は２．００個／ｍｍ２以上である。 The duplex stainless steel material of the second configuration is
1. A duplex stainless steel material of a first configuration, comprising:
Fine Ca oxysulfides are defined as particles having an equivalent circle diameter of 1.0 to 2.0 μm, a total of Ca content and S content of more than 5.0%, an O content of 1.0% or more, and a Ca content higher than a S content, in terms of mass%,
Fine Mg oxide particles are defined as particles having an equivalent circle diameter of 1.0 to 2.0 μm, and, in mass%, an Mg content of 5.0% or more, an O content of 1.0% or more, and an S content of 15.0% or less.
Particles having an equivalent circle diameter of 1.0 to 2.0 μm, an Al content of 20.0% or more, and an N content of 20.0% or more, in mass%, are defined as fine Al nitrides;
When particles having a circle equivalent diameter of 1.0 to 2.0 μm, a Ti content of 30.0% or more, and a N content of 20.0% or more are defined as fine Ti nitrides,
The total density of the fine Ca oxysulfides, the fine Mg oxides, the fine Al nitrides, and the fine Ti nitrides is 2.00 pieces/ mm2 or more.
　第３の構成の二相ステンレス鋼材は、
　第１又は第２の構成の二相ステンレス鋼材であって、
　化学組成は、
　Ｃｕ：０．１～４．０％、
　Ｖ：０．０１～１．５０％、
　Ｃｏ：０．０１～２．００％、
　Ｔａ：０．０１～２．００％、
　Ｗ：０．０１～４．００％、
　Ｎｂ：０．０１～２．００％、
　Ｔｉ：０．０１～２．００％、
　Ｚｎ：０．０００１～０．０１００％、
　Ｐｂ：０．０００１～０．０１００％、
　Ｓｂ：０．０００１～０．０１００％、
　Ｓｎ：０．０００１～０．０１００％、
　Ｂｉ：０．０００１～０．０１００％、
　Ｂ：０．０００１～０．０１００％、
　希土類元素：０．００１～０．０５０％、
　Ｚｒ：０．０１～２．００％、及び、
　Ｈｆ：０．０１～２．００％、からなる群から選択される１種以上を含有する。 The duplex stainless steel material of the third configuration is
A duplex stainless steel material of the first or second configuration,
The chemical composition is
Cu: 0.1 to 4.0%,
V: 0.01 to 1.50%,
Co: 0.01 to 2.00%,
Ta: 0.01 to 2.00%,
W: 0.01 to 4.00%,
Nb: 0.01 to 2.00%,
Ti: 0.01 to 2.00%,
Zn: 0.0001 to 0.0100%,
Pb: 0.0001 to 0.0100%,
Sb: 0.0001 to 0.0100%,
Sn: 0.0001 to 0.0100%,
Bi: 0.0001 to 0.0100%,
B: 0.0001 to 0.0100%,
Rare earth elements: 0.001 to 0.050%,
Zr: 0.01 to 2.00%, and
Hf: 0.01 to 2.00%.
　以下、本実施形態の二相ステンレス鋼材について説明する。なお、元素に関する「％」は、特に断りがない限り、質量％を意味する。また、以下の説明では、二相ステンレス鋼材を、単に「鋼材」ともいう。 The duplex stainless steel material of this embodiment will be described below. Note that "%" for elements means mass % unless otherwise specified. In the following description, the duplex stainless steel material will also be simply referred to as "steel material."
　［本実施形態の二相ステンレス鋼材の特徴］
　本実施形態の二相ステンレス鋼材は次の特徴１～特徴３を満たす。
　（特徴１）
　化学組成が、質量％で、Ｃ：０．０５０％以下、Ｓｉ：０．２～１．２％、Ｍｎ：０．５～７．０％、Ｐ：０．０４０％以下、Ｓ：０．０１０％以下、Ｃｒ：２０．０～２７．０％、Ｎｉ：４．０～９．０％、Ｍｏ：０．５～５．０％、Ａｓ：０．０００５～０．０１００％、Ｃａ及びＭｇの１種以上：合計で０．０００５～０．０１００％、ｓｏｌ．Ａｌ：０．００１～０．０５０％、Ｎ：０．４０％以下、Ｏ：０．１００％以下、Ｃｕ：０～４．０％、Ｖ：０～１．５０％、Ｃｏ：０～２．００％、Ｔａ：０～２．００％、Ｗ：０～４．００％、Ｎｂ：０～２．００％、Ｔｉ：０～２．００％、Ｚｎ：０～０．０１００％、Ｐｂ：０～０．０１００％、Ｓｂ：０～０．０１００％、Ｓｎ：０～０．０１００％、Ｂｉ：０～０．０１００％、Ｂ：０～０．０１００％、希土類元素：０～０．０５０％、Ｚｒ：０～２．００％、及び、Ｈｆ：０～２．００％、からなり、残部はＦｅ及び不純物からなる。
　（特徴２）
　化学組成が式（１）を満たす。
　０．７０＜１００００×Ａｓ／（Ｎｉ＋Ｃｕ）＜１６．００　（１）
　ここで、式中の各元素記号には、対応する元素の質量％での含有量が代入される。元素が含有されていない場合、対応する元素記号には「０」が代入される。
　（特徴３）
　化学組成が式（２）を満たす。
　（Ｃａ＋Ｍｇ）／Ｏ＜１．５０　（２）
　ここで、式中の各元素記号には、対応する元素の質量％での含有量が代入される。元素が含有されていない場合、対応する元素記号には「０」が代入される。
　以下、特徴１～特徴３について説明する。 [Features of the duplex stainless steel material according to this embodiment]
The duplex stainless steel material of this embodiment satisfies the following features 1 to 3.
(Feature 1)
The chemical composition, in mass%, is C: 0.050% or less, Si: 0.2 to 1.2%, Mn: 0.5 to 7.0%, P: 0.040% or less, S: 0.010% or less, Cr: 20.0 to 27.0%, Ni: 4.0 to 9.0%, Mo: 0.5 to 5.0%, As: 0.0005 to 0.0100%, one or more of Ca and Mg: 0.0005 to 0.0100% in total, sol. Al: 0.001-0.050%, N: 0.40% or less, O: 0.100% or less, Cu: 0-4.0%, V: 0-1.50%, Co: 0-2.00%, Ta: 0-2.00%, W: 0-4.00%, Nb: 0-2.00%, Ti: 0-2.00%, Zn: 0-0.0100%, Pb: 0-0.0100%, Sb: 0-0.0100%, Sn: 0-0.0100%, Bi: 0-0.0100%, B: 0-0.0100%, rare earth elements: 0-0.050%, Zr: 0-2.00%, and Hf: 0-2.00%, with the balance being Fe and impurities.
(Feature 2)
The chemical composition satisfies formula (1).
0.70<10000×As/(Ni+Cu)<16.00 (1)
Here, the content of the corresponding element in mass % is substituted for each element symbol in the formula. When an element is not contained, "0" is substituted for the corresponding element symbol.
(Feature 3)
The chemical composition satisfies formula (2).
(Ca+Mg)/O<1.50 (2)
Here, the content of the corresponding element in mass % is substituted for each element symbol in the formula. When an element is not contained, "0" is substituted for the corresponding element symbol.
Features 1 to 3 will be explained below.
　［（特徴１）化学組成について］
　本実施形態の二相ステンレス鋼材の化学組成は、次の元素を含有する。 [Feature 1: Chemical composition]
The chemical composition of the duplex stainless steel material of this embodiment contains the following elements.
　Ｃ：０．０５０％以下
　炭素（Ｃ）は不可避に含有される。つまり、Ｃ含有量は０％超である。
　Ｃは結晶粒界にＣｒ炭化物を形成し、粒界での腐食感受性を高める。そのため、Ｃ含有量が０．０５０％を超えれば、他の元素含有量が本実施形態の範囲内であっても、高温高圧強酸性腐食環境において、優れた耐全面腐食性が得られない。
　したがって、Ｃ含有量は０．０５０％以下である。
　Ｃ含有量はなるべく低い方が好ましい。しかしながら、Ｃ含有量を過度に低減すれば、製造コストが大幅に高まる。したがって、工業生産を考慮した場合、Ｃ含有量の好ましい下限は０．００１％であり、さらに好ましくは０．００２％であり、さらに好ましくは０．００３％である。
　Ｃ含有量の好ましい上限は０．０４８％であり、さらに好ましくは０．０４６％であり、さらに好ましくは０．０４４％であり、さらに好ましくは０．０４２％である。 C: 0.050% or less Carbon (C) is unavoidably contained. In other words, the C content is more than 0%.
C forms Cr carbides at the grain boundaries and increases the corrosion susceptibility at the grain boundaries, so if the C content exceeds 0.050%, excellent general corrosion resistance cannot be obtained in a high-temperature, high-pressure, strong acidic corrosive environment even if the contents of other elements are within the ranges of this embodiment.
Therefore, the C content is 0.050% or less.
The C content is preferably as low as possible. However, if the C content is excessively reduced, the manufacturing cost increases significantly. Therefore, in consideration of industrial production, the preferred lower limit of the C content is 0.001%, more preferably 0.002%, and even more preferably 0.003%.
The upper limit of the C content is preferably 0.048%, more preferably 0.046%, further preferably 0.044%, and further preferably 0.042%.
　Ｓｉ：０．２～１．２％
　シリコン（Ｓｉ）は、鋼材の製造工程において、鋼を脱酸する。Ｓｉ含有量が０．２％未満であれば、他の元素含有量が本実施形態の範囲内であっても、上記効果が十分に得られない。
　一方、Ｓｉ含有量が１．２％を超えれば、他の元素含有量が本実施形態の範囲内であっても、鋼材の靭性及び熱間加工性が低下する。
　したがって、Ｓｉ含有量は０．２～１．２％である。
　Ｓｉ含有量の好ましい下限は０．３％であり、さらに好ましくは０．４％であり、さらに好ましくは０．５％である。
　Ｓｉ含有量の好ましい上限は１．１％であり、さらに好ましくは１．０％であり、さらに好ましくは０．９％である。 Si: 0.2 to 1.2%
Silicon (Si) deoxidizes steel during the steel manufacturing process. If the Si content is less than 0.2%, the above effect cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment.
On the other hand, if the Si content exceeds 1.2%, the toughness and hot workability of the steel material decrease even if the contents of other elements are within the ranges of this embodiment.
Therefore, the Si content is 0.2 to 1.2%.
The lower limit of the Si content is preferably 0.3%, more preferably 0.4%, and further preferably 0.5%.
The upper limit of the Si content is preferably 1.1%, more preferably 1.0%, and further preferably 0.9%.
　Ｍｎ：０．５～７．０％
　マンガン（Ｍｎ）は鋼材の焼入れ性を高めて鋼材の強度を高める。Ｍｎ含有量が０．５％未満であれば、他の元素含有量が本実施形態の範囲内であっても、上記効果が十分に得られない。
　一方、Ｍｎ含有量が７．０％を超えれば、Ｍｎは、粗大なＭｎ硫化物を多数形成する。高温高圧塩化物腐食環境において、鋼材の表面近傍に存在する粗大なＭｎ硫化物は溶解する。粗大なＭｎ硫化物が溶解した部分では、凹みが形成される。この凹みが孔食の起点となる。そのため、他の元素含有量が本実施形態の範囲内であっても、高温高圧塩化物腐食環境において、優れた耐孔食性が得られない。
　したがって、Ｍｎ含有量は０．５～７．０％である。
　Ｍｎ含有量の好ましい下限は０．６％であり、さらに好ましくは０．７％であり、さらに好ましくは０．８％である。
　Ｍｎ含有量の好ましい上限は６．８％であり、さらに好ましくは６．０％であり、さらに好ましくは５．５％であり、さらに好ましくは４．５％であり、さらに好ましくは３．５％であり、さらに好ましくは２．５％であり、さらに好ましくは２．０％である。 Mn: 0.5 to 7.0%
Manganese (Mn) improves the hardenability of steel material and increases its strength. If the Mn content is less than 0.5%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment.
On the other hand, if the Mn content exceeds 7.0%, Mn forms a large number of coarse Mn sulfides. In a high-temperature, high-pressure chloride corrosive environment, the coarse Mn sulfides present near the surface of the steel material dissolve. In the portion where the coarse Mn sulfides dissolve, a depression is formed. This depression becomes the starting point of pitting corrosion. Therefore, even if the contents of other elements are within the ranges of this embodiment, excellent pitting corrosion resistance cannot be obtained in a high-temperature, high-pressure chloride corrosive environment.
Therefore, the Mn content is 0.5 to 7.0%.
The lower limit of the Mn content is preferably 0.6%, more preferably 0.7%, and further preferably 0.8%.
The upper limit of the Mn content is preferably 6.8%, more preferably 6.0%, more preferably 5.5%, more preferably 4.5%, more preferably 3.5%, more preferably 2.5%, and more preferably 2.0%.
　Ｐ：０．０４０％以下
　りん（Ｐ）は不可避に含有される不純物である。すなわち、Ｐ含有量は０％超である。
　Ｐ含有量が０．０４０％を超えれば、Ｐは粒界に過剰に偏析する。そのため、他の元素含有量が本実施形態の範囲内であっても、鋼材の靭性が低下する。
　したがって、Ｐ含有量は０．０４０％以下である。
　Ｐ含有量はなるべく低い方が好ましい。しかしながら、Ｐ含有量を過度に低減すれば、製造コストが大幅に高まる。したがって、工業生産を考慮した場合、Ｐ含有量の好ましい下限は０．００１％であり、さらに好ましくは０．００２％であり、さらに好ましくは０．００３％であり、さらに好ましくは０．００５％である。
　Ｐ含有量の好ましい上限は０．０３５％であり、さらに好ましくは０．０３０％であり、さらに好ましくは０．０２６％であり、さらに好ましくは０．０２２％である。 P: 0.040% or less Phosphorus (P) is an unavoidable impurity. That is, the P content is more than 0%.
If the P content exceeds 0.040%, P will segregate excessively at grain boundaries, and therefore the toughness of the steel material will decrease even if the contents of other elements are within the ranges of this embodiment.
Therefore, the P content is 0.040% or less.
The P content is preferably as low as possible. However, if the P content is excessively reduced, the manufacturing cost increases significantly. Therefore, in consideration of industrial production, the lower limit of the P content is preferably 0.001%, more preferably 0.002%, more preferably 0.003%, and even more preferably 0.005%.
The upper limit of the P content is preferably 0.035%, more preferably 0.030%, further preferably 0.026%, and further preferably 0.022%.
　Ｓ：０．０１０％以下
　硫黄（Ｓ）は不可避に含有される不純物である。すなわち、Ｓ含有量は０％超である。
　Ｓ含有量が０．０１０％を超えれば、Ｓは粒界に過剰に偏析する。そのため、他の元素含有量が本実施形態の範囲内であっても、鋼材の靭性及び熱間加工性が低下する。
　したがって、Ｓ含有量は０．０１０％以下である。
　Ｓ含有量はなるべく低い方が好ましい。しかしながら、Ｓ含有量を過度に低減すれば、製造コストが大幅に高まる。したがって、工業生産を考慮した場合、Ｓ含有量の好ましい下限は０．００１％であり、さらに好ましくは０．００２％である。
　Ｓ含有量の好ましい上限は０．００９％であり、さらに好ましくは０．００８％であり、さらに好ましくは０．００７％である。 S: 0.010% or less Sulfur (S) is an unavoidable impurity. That is, the S content is more than 0%.
If the S content exceeds 0.010%, S will segregate excessively at grain boundaries, and therefore the toughness and hot workability of the steel material will decrease even if the contents of other elements are within the ranges of this embodiment.
Therefore, the S content is 0.010% or less.
The S content is preferably as low as possible. However, if the S content is reduced too much, the manufacturing cost increases significantly. Therefore, in consideration of industrial production, the lower limit of the S content is preferably 0.001%, and more preferably 0.002%.
The upper limit of the S content is preferably 0.009%, more preferably 0.008%, and further preferably 0.007%.
　Ｃｒ：２０．０～２７．０％
　クロム（Ｃｒ）は、鋼材の表面に、酸化物である不動態被膜を形成する。その結果、高温高圧強酸性腐食環境での耐全面腐食性が高まる。さらに、高温高圧塩化物腐食環境での耐孔食性が高まる。Ｃｒ含有量が２０．０％未満であれば、他の元素含有量が本実施形態の範囲内であっても、上記効果が十分に得られない。
　一方、Ｃｒ含有量が２７．０％を超えれば、シグマ相（σ相）に代表される金属間化合物が生成しやすくなる。そのため、他の元素含有量が本実施形態の範囲内であっても、鋼材の靱性が低下する。
　したがって、Ｃｒ含有量は２０．０～２７．０％である。
　Ｃｒ含有量の好ましい下限は２０．２％であり、さらに好ましくは２０．５％であり、さらに好ましくは２１．０％であり、さらに好ましくは２１．５％である。
　Ｃｒ含有量の好ましい上限は２６．８％であり、さらに好ましくは２６．６％であり、さらに好ましくは２６．４％であり、さらに好ましくは２６．２％である。 Cr: 20.0 to 27.0%
Chromium (Cr) forms a passive film, which is an oxide, on the surface of the steel material. As a result, the general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosive environment is improved. Furthermore, the pitting corrosion resistance in a high-temperature, high-pressure chloride corrosive environment is improved. If the Cr content is less than 20.0%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment.
On the other hand, if the Cr content exceeds 27.0%, intermetallic compounds such as sigma phases are likely to be formed, and therefore the toughness of the steel material decreases even if the contents of other elements are within the ranges of this embodiment.
Therefore, the Cr content is 20.0 to 27.0%.
The lower limit of the Cr content is preferably 20.2%, more preferably 20.5%, further preferably 21.0%, and further preferably 21.5%.
The upper limit of the Cr content is preferably 26.8%, more preferably 26.6%, further preferably 26.4%, and further preferably 26.2%.
　Ｎｉ：４．０～９．０％
　ニッケル（Ｎｉ）は、高温高圧強酸性腐食環境での鋼材の耐全面腐食性を高める。Ｎｉ含有量が４．０％未満であれば、他の元素含有量が本実施形態の範囲内であっても、上記効果が十分に得られない。
　一方、Ｎｉ含有量が９．０％を超えれば、オーステナイトの体積率が高くなりすぎる。この場合、他の元素含有量が本実施形態の範囲内であっても、鋼材の強度が低下する。
　したがって、Ｎｉ含有量は４．０～９．０％である。
　Ｎｉ含有量の好ましい下限は４．２％であり、さらに好ましくは４．４％であり、さらに好ましくは４．６％であり、さらに好ましくは４．８％である。
　Ｎｉ含有量の好ましい上限は８．８％であり、さらに好ましくは８．６％であり、さらに好ましくは８．２％であり、さらに好ましくは７．９％であり、さらに好ましくは７．８％であり、さらに好ましくは７．７％であり、さらに好ましくは７．６％である。 Ni: 4.0 to 9.0%
Nickel (Ni) enhances the general corrosion resistance of steel materials in high-temperature, high-pressure, strong acidic corrosive environments. If the Ni content is less than 4.0%, the above effect cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment.
On the other hand, if the Ni content exceeds 9.0%, the volume fraction of austenite becomes too high, and in this case, the strength of the steel material decreases even if the contents of other elements are within the ranges of this embodiment.
Therefore, the Ni content is 4.0 to 9.0%.
The lower limit of the Ni content is preferably 4.2%, more preferably 4.4%, further preferably 4.6%, and further preferably 4.8%.
The upper limit of the Ni content is preferably 8.8%, more preferably 8.6%, more preferably 8.2%, more preferably 7.9%, more preferably 7.8%, more preferably 7.7%, and more preferably 7.6%.
　Ｍｏ：０．５～５．０％
　モリブデン（Ｍｏ）は高温高圧塩化物腐食環境での鋼材の耐孔食性を高める。Ｍｏ含有量が０．５％未満であれば、他の元素含有量が本実施形態の範囲内であっても、上記効果が十分に得られない。
　一方、Ｍｏ含有量が５．０％を超えれば、他の元素含有量が本実施形態の範囲内であっても、鋼材の熱間加工性が低下する。
　したがって、Ｍｏ含有量は０．５～５．０％である。
　Ｍｏ含有量の好ましい下限は０．７％であり、さらに好ましくは１．０％であり、さらに好ましくは１．５％であり、さらに好ましくは２．０％であり、さらに好ましくは２．４％であり、さらに好ましくは２．６％であり、さらに好ましくは２．８％である。
　Ｍｏ含有量の好ましい上限は４．８％であり、さらに好ましくは４．６％であり、さらに好ましくは４．４％であり、さらに好ましくは４．２％である。 Mo: 0.5 to 5.0%
Molybdenum (Mo) enhances the pitting corrosion resistance of steel materials in high-temperature and high-pressure chloride corrosion environments. If the Mo content is less than 0.5%, the above effect cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment.
On the other hand, if the Mo content exceeds 5.0%, the hot workability of the steel material decreases even if the contents of other elements are within the ranges of this embodiment.
Therefore, the Mo content is 0.5 to 5.0%.
The lower limit of the Mo content is preferably 0.7%, more preferably 1.0%, more preferably 1.5%, more preferably 2.0%, more preferably 2.4%, more preferably 2.6%, and more preferably 2.8%.
The upper limit of the Mo content is preferably 4.8%, more preferably 4.6%, further preferably 4.4%, and further preferably 4.2%.
　Ａｓ：０．０００５～０．０１００％
　砒素（Ａｓ）は、高温高圧強酸性腐食環境での鋼材の耐全面腐食性を高める。Ａｓ含有量が０．０００５％未満であれば、他の元素含有量が本実施形態の範囲内であっても、上記効果が十分に得られない。
　一方、Ａｓ含有量が０．０１００％を超えれば、他の元素含有量が本実施形態の範囲内であっても、鋼材の熱間加工性が低下する。
　したがって、Ａｓ含有量は０．０００５～０．０１００％である。
　Ａｓ含有量の好ましい下限は０．００１０％であり、さらに好ましくは０．００１５％であり、さらに好ましくは０．００２０％であり、さらに好ましくは０．００２５％である。
　Ａｓ含有量の好ましい上限は０．００９０％であり、さらに好ましくは０．００８０％であり、さらに好ましくは０．００７０％であり、さらに好ましくは０．００６０％である。 As: 0.0005 to 0.0100%
Arsenic (As) enhances the general corrosion resistance of steel materials in high-temperature, high-pressure, strongly acidic corrosive environments. If the As content is less than 0.0005%, the above effect cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment.
On the other hand, if the As content exceeds 0.0100%, the hot workability of the steel material decreases even if the contents of other elements are within the ranges of this embodiment.
Therefore, the As content is 0.0005 to 0.0100%.
The lower limit of the As content is preferably 0.0010%, more preferably 0.0015%, further preferably 0.0020%, and further preferably 0.0025%.
The upper limit of the As content is preferably 0.0090%, more preferably 0.0080%, further preferably 0.0070%, and further preferably 0.0060%.
　Ｃａ及びＭｇの１種以上：合計で０．０００５～０．０１００％
　カルシウム（Ｃａ）及びマグネシウム（Ｍｇ）は、微細なＣａ酸硫化物又は微細なＭｇ酸化物を形成する。微細なＣａ酸硫化物及び微細なＭｇ酸化物は、母相との界面でＡｓの偏析サイトとして機能する。微細なＣａ酸硫化物及び微細なＭｇ酸化物が鋼材中に分散することにより、これらの微細粒子の表面に偏析するＡｓも鋼材中に分散する。その結果、高温高圧強酸性腐食環境での鋼材の耐全面腐食性が高まる。Ｃａ及びＭｇの合計含有量が０．０００５％未満であれば、上記効果が十分に得られない。
　一方、Ｃａ及びＭｇの合計含有量が０．０１００％を超えれば、粗大なＣａ酸硫化物又は粗大なＭｇ酸化物が生成する。高温高圧塩化物腐食環境において、鋼材表層中に生成した粗大なＣａ酸硫化物及び粗大なＭｇ酸化物は溶解しやすい。そのため、他の元素含有量が本実施形態の範囲内であっても、高温高圧塩化物腐食環境での鋼材の耐孔食性が低下する。
　したがって、Ｃａ及びＭｇの合計含有量は、０．０００５～０．０１００％である。
　Ｃａ及びＭｇの合計含有量の好ましい下限は０．００１０％であり、さらに好ましくは０．００１５％であり、さらに好ましくは０．００２０％であり、さらに好ましくは０．００２５％であり、さらに好ましくは０．００３０％である。
　Ｃａ及びＭｇの合計含有量の好ましい上限は０．００９５％であり、さらに好ましくは０．００９０％であり、さらに好ましくは０．００８５％であり、さらに好ましくは０．００８０％であり、さらに好ましくは０．００７５％である。 One or more of Ca and Mg: 0.0005 to 0.0100% in total
Calcium (Ca) and magnesium (Mg) form fine Ca oxysulfides or fine Mg oxides. The fine Ca oxysulfides and fine Mg oxides function as segregation sites for As at the interface with the parent phase. By dispersing the fine Ca oxysulfides and fine Mg oxides in the steel material, the As segregated on the surfaces of these fine particles is also dispersed in the steel material. As a result, the general corrosion resistance of the steel material in a high-temperature, high-pressure, strong acidic corrosion environment is improved. If the total content of Ca and Mg is less than 0.0005%, the above effect cannot be sufficiently obtained.
On the other hand, if the total content of Ca and Mg exceeds 0.0100%, coarse Ca oxysulfides or coarse Mg oxides are generated. In a high-temperature, high-pressure chloride corrosive environment, the coarse Ca oxysulfides and coarse Mg oxides generated in the steel surface layer are easily dissolved. Therefore, even if the contents of other elements are within the ranges of this embodiment, the pitting corrosion resistance of the steel in a high-temperature, high-pressure chloride corrosive environment is reduced.
Therefore, the total content of Ca and Mg is 0.0005 to 0.0100%.
The lower limit of the total content of Ca and Mg is preferably 0.0010%, more preferably 0.0015%, further preferably 0.0020%, further preferably 0.0025%, and further preferably 0.0030%.
The upper limit of the combined Ca and Mg content is preferably 0.0095%, more preferably 0.0090%, still more preferably 0.0085%, still more preferably 0.0080%, and still more preferably 0.0075%.
　ｓｏｌ．Ａｌ：０．００１～０．０５０％
　アルミニウム（Ａｌ）は鋼材の製造工程において、鋼を脱酸する。Ａｌはさらに、Ｎと結合して微細なＡｌ窒化物を生成する。微細なＡｌ窒化物は、Ａｓの偏析サイトとして機能する。そのため、微細なＡｌ窒化物が多く生成して鋼材中に分散すれば、Ａｓが鋼材中にさらに分散しやすくなる。その結果、高温高圧強酸性腐食環境での鋼材の耐全面腐食性が高まる。ｓｏｌ．Ａｌ含有量が０．００１％未満であれば、他の元素含有量が本実施形態の範囲内であっても、上記効果が十分に得られない。
　一方、ｓｏｌ．Ａｌ含有量が０．０５０％を超えれば、粗大な酸化物が過剰に生成する。そのため、他の元素含有量が本実施形態の範囲内であっても、鋼材の靭性が低下する。
　したがって、ｓｏｌ．Ａｌ含有量は０．００１～０．０５０％である。
　ｓｏｌ．Ａｌ含有量の好ましい下限は０．００２％であり、さらに好ましくは０．００５％であり、さらに好ましくは０．０１０％である。
　ｓｏｌ．Ａｌ含有量の好ましい上限は０．０４５％であり、さらに好ましくは０．０４０％であり、さらに好ましくは０．０３５％であり、さらに好ましくは０．０３０％である。なお、本明細書にいうｓｏｌ．Ａｌ含有量とは、酸可溶Ａｌの含有量を意味する。 sol. Al: 0.001 to 0.050%
Aluminum (Al) deoxidizes steel during the manufacturing process of steel. Furthermore, Al combines with N to form fine Al nitrides. The fine Al nitrides function as segregation sites for As. Therefore, if a large amount of fine Al nitrides are generated and dispersed in the steel material, As will be more likely to disperse in the steel material, which will result in improved general corrosion resistance of the steel material in a high-temperature, high-pressure, strong acidic corrosive environment. If the sol. Al content is less than 0.001%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment.
On the other hand, if the sol. Al content exceeds 0.050%, coarse oxides are generated in excess, and therefore the toughness of the steel material is reduced even if the contents of other elements are within the ranges of this embodiment. do.
Therefore, the sol. Al content is 0.001 to 0.050%.
The lower limit of the sol. Al content is preferably 0.002%, more preferably 0.005%, and further preferably 0.010%.
The upper limit of the sol. Al content is preferably 0.045%, more preferably 0.040%, still more preferably 0.035%, and still more preferably 0.030%. The sol. Al content in the specification means the content of acid-soluble Al.
　Ｎ：０．４０％以下
　窒素（Ｎ）は不可避に含有される。つまり、Ｎ含有量は０％超である。
　Ｎは鋼材中のオーステナイトを安定化させる。Ｎはさらに、高温高圧強酸性腐食環境での耐全面腐食性及び高温高圧塩化物腐食環境での鋼材の耐孔食性を高める。Ｎはさらに、Ａｌ及びＴｉと結合して微細なＡｌ窒化物及び微細なＴｉ窒化物を生成する。微細なＡｌ窒化物及び微細なＴｉ窒化物は、Ａｓの偏析サイトとして機能する。そのため、微細なＡｌ窒化物及び微細なＴｉ窒化物が多く生成して鋼材中に分散すれば、Ａｓが鋼材中にさらに分散しやすくなる。その結果、高温高圧強酸性腐食環境での鋼材の耐全面腐食性が高まる。Ｎが少しでも含有されれば、上記効果がある程度得られる。
　しかしながら、Ｎ含有量が０．４０％を超えれば、他の元素含有量が本実施形態の範囲内であっても、鋼材の靭性及び熱間加工性が低下する。
　したがって、Ｎ含有量は０．４０％以下である。
　Ｎ含有量の好ましい下限は０．０１％であり、さらに好ましくは０．０２％であり、さらに好ましくは０．０５％であり、さらに好ましくは０．１０％であり、さらに好ましくは０．１５％である。
　Ｎ含有量の好ましい上限は０．３８％であり、さらに好ましくは０．３６％であり、さらに好ましくは０．３４％であり、さらに好ましくは０．３２％であり、さらに好ましくは０．３０％である。 N: 0.40% or less Nitrogen (N) is unavoidably contained. In other words, the N content is more than 0%.
N stabilizes austenite in steel. N also enhances the general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosion environment and the pitting corrosion resistance of steel in a high-temperature, high-pressure chloride corrosion environment. N also combines with Al and Ti to generate fine Al nitrides and fine Ti nitrides. The fine Al nitrides and fine Ti nitrides function as segregation sites for As. Therefore, if a large amount of fine Al nitrides and fine Ti nitrides are generated and dispersed in the steel, As becomes more likely to disperse in the steel. As a result, the general corrosion resistance of the steel in a high-temperature, high-pressure, strong acidic corrosion environment is improved. If even a small amount of N is contained, the above effect can be obtained to a certain extent.
However, if the N content exceeds 0.40%, the toughness and hot workability of the steel material decrease even if the contents of other elements are within the ranges of this embodiment.
Therefore, the N content is 0.40% or less.
The lower limit of the N content is preferably 0.01%, more preferably 0.02%, still more preferably 0.05%, still more preferably 0.10%, and still more preferably 0.15%.
The upper limit of the N content is preferably 0.38%, more preferably 0.36%, still more preferably 0.34%, still more preferably 0.32%, and still more preferably 0.30%.
　Ｏ：０．１００％以下
　酸素（Ｏ）は不可避に含有される不純物である。つまり、Ｏ含有量は０％超である。
　Ｏ含有量が０．１００％を超えれば、粗大なＣａ酸硫化物及び粗大なＭｇ酸化物が過剰に生成する。そのため、他の元素含有量が本実施形態の範囲内であっても、高温高圧塩化物腐食環境において優れた耐孔食性が得られない。
　したがって、Ｏ含有量は０．１００％以下である。
　Ｏ含有量はなるべく低い方が好ましい。しかしながら、Ｏ含有量を過度に低減すれば、製造コストが高くなる。したがって、工業生産を考慮すれば、Ｏ含有量の好ましい下限は０．００１％であり、さらに好ましくは０．００５％であり、さらに好ましくは０．０１０％である。
　Ｏ含有量の好ましい上限は０．０９０％であり、さらに好ましくは０．０８５％であり、さらに好ましくは０．０８０％であり、さらに好ましくは０．０７５％である。 O: 0.100% or less Oxygen (O) is an unavoidable impurity. In other words, the O content is more than 0%.
If the O content exceeds 0.100%, coarse Ca oxysulfides and coarse Mg oxides are excessively generated, and therefore, even if the contents of other elements are within the ranges of this embodiment, excellent pitting corrosion resistance cannot be obtained in a high-temperature and high-pressure chloride corrosive environment.
Therefore, the O content is 0.100% or less.
The O content is preferably as low as possible. However, if the O content is excessively reduced, the manufacturing cost increases. Therefore, in consideration of industrial production, the lower limit of the O content is preferably 0.001%, more preferably 0.005%, and even more preferably 0.010%.
The upper limit of the O content is preferably 0.090%, more preferably 0.085%, further preferably 0.080%, and further preferably 0.075%.
　本実施形態による二相ステンレス鋼材の化学組成の残部は、Ｆｅ及び不純物からなる。ここで、化学組成における不純物とは、二相ステンレス鋼材を工業的に製造する際に、原料としての鉱石、スクラップ、又は製造環境などから混入されるものであって、意図的に含有されるものではなく、本実施形態による二相ステンレス鋼材の効果に悪影響を与えない範囲で許容されるものを意味する。 The remainder of the chemical composition of the duplex stainless steel material according to this embodiment is composed of Fe and impurities. Here, the term "impurities" in the chemical composition refers to substances that are mixed in from the raw materials, such as ore, scrap, or the manufacturing environment, during the industrial production of duplex stainless steel material, and are not intentionally included, but are acceptable within a range that does not adversely affect the effects of the duplex stainless steel material according to this embodiment.
　［任意元素（Ｏｐｔｉｏｎａｌ　Ｅｌｅｍｅｎｔｓ）について］
　本実施形態の二相ステンレス鋼材の化学組成はさらに、Ｆｅの一部に代えて、
　Ｃｕ：０～４．０％、
　Ｖ：０～１．５０％、
　Ｃｏ：０～２．００％、
　Ｔａ：０～２．００％、
　Ｗ：０～４．００％、
　Ｎｂ：０～２．００％、
　Ｔｉ：０～２．００％、
　Ｚｎ：０～０．０１００％、
　Ｐｂ：０～０．０１００％、
　Ｓｂ：０～０．０１００％、
　Ｓｎ：０～０．０１００％、
　Ｂｉ：０～０．０１００％、
　Ｂ：０～０．０１００％、
　希土類元素：０～０．０５０％、
　Ｚｒ：０～２．００％、及び、
　Ｈｆ：０～２．００％、からなる群から選択される１種以上を含有してもよい。
　以下、各任意元素について説明する。 [Regarding optional elements]
The chemical composition of the duplex stainless steel material of this embodiment further includes, instead of a part of Fe,
Cu: 0 to 4.0%,
V: 0 to 1.50%,
Co: 0 to 2.00%,
Ta: 0 to 2.00%,
W: 0 to 4.00%,
Nb: 0 to 2.00%,
Ti: 0 to 2.00%,
Zn: 0 to 0.0100%,
Pb: 0 to 0.0100%,
Sb: 0 to 0.0100%,
Sn: 0 to 0.0100%,
Bi: 0 to 0.0100%,
B: 0 to 0.0100%,
Rare earth elements: 0 to 0.050%,
Zr: 0 to 2.00%, and
Hf: 0 to 2.00%.
Each optional element will be described below.
　［第１群：Ｃｕ、Ｖ、Ｃｏ、Ｔａ、Ｗ、Ｎｂ、Ｔｉ、Ｚｎ、Ｐｂ、Ｓｂ、Ｓｎ、及び、Ｂｉ］
　本実施形態の二相ステンレス鋼材の化学組成は、Ｆｅの一部に代えて、Ｃｕ、Ｖ、Ｃｏ、Ｔａ、Ｗ、Ｎｂ、Ｔｉ、Ｚｎ、Ｐｂ、Ｓｂ、Ｓｎ、及び、Ｂｉ、からなる群から選択される１種以上を含有してもよい。これらの元素はいずれも任意元素であり、高温高圧強酸性腐食環境での鋼材の耐全面腐食性を高める。以下、各元素について説明する。 [First group: Cu, V, Co, Ta, W, Nb, Ti, Zn, Pb, Sb, Sn, and Bi]
The chemical composition of the duplex stainless steel material of this embodiment may contain at least one element selected from the group consisting of Cu, V, Co, Ta, W, Nb, Ti, Zn, Pb, Sb, Sn, and Bi, instead of a portion of Fe. All of these elements are optional elements, and enhance the general corrosion resistance of the steel material in a high-temperature, high-pressure, strongly acidic corrosive environment. Each element will be described below.
　Ｃｕ：０～４．０％
　銅（Ｃｕ）は任意元素であり、含有されなくてもよい。つまり、Ｃｕ含有量は０％であってもよい。
　含有される場合、つまり、Ｃｕ含有量が０％超である場合、Ｃｕは、高温高圧強酸性腐食環境において、不働態皮膜上に硫化物を生成する。この硫化物により、鋼材の活性溶解が抑制される。そのため、高温高圧強酸性腐食環境での耐全面腐食性が高まる。Ｃｕが少しでも含有されれば、上記効果がある程度得られる。
　しかしながら、Ｃｕ含有量が４．０％を超えれば、他の元素含有量が本実施形態の範囲内であっても、鋼材の熱間加工性が低下する。
　したがって、Ｃｕ含有量は０～４．０％であり、含有される場合、４．０％以下である。
　Ｃｕ含有量の好ましい下限は０．１％であり、さらに好ましくは０．２％であり、さらに好ましくは０．５％であり、さらに好ましくは１．０％である。
　Ｃｕ含有量の好ましい上限は３．８％であり、さらに好ましくは３．５％であり、さらに好ましくは２．５％であり、さらに好ましくは２．０％である。 Cu: 0 to 4.0%
Copper (Cu) is an optional element and may not be contained, that is, the Cu content may be 0%.
When Cu is contained, that is, when the Cu content is more than 0%, Cu generates sulfides on the passive film in a high-temperature, high-pressure, strongly acidic corrosive environment. These sulfides suppress active dissolution of the steel material. Therefore, the general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment is improved. Even if even a small amount of Cu is contained, the above effect can be obtained to a certain extent.
However, if the Cu content exceeds 4.0%, the hot workability of the steel material decreases even if the contents of other elements are within the ranges of this embodiment.
Therefore, the Cu content is 0 to 4.0%, and if contained, it is 4.0% or less.
The lower limit of the Cu content is preferably 0.1%, more preferably 0.2%, further preferably 0.5%, and further preferably 1.0%.
The upper limit of the Cu content is preferably 3.8%, more preferably 3.5%, further preferably 2.5%, and further preferably 2.0%.
　Ｖ：０～１．５０％
　バナジウム（Ｖ）は任意元素であり、含有されなくてもよい。つまり、Ｖ含有量は０％であってもよい。
　含有される場合、つまり、Ｖ含有量が０％超である場合、Ｖは、高温高圧強酸性腐食環境での鋼材の活性溶解を抑制し、耐全面腐食性を高める。Ｖが少しでも含有されれば、上記効果がある程度得られる。
　しかしながら、Ｖ含有量が１．５０％を超えれば、鋼材の強度が過度に高くなる。この場合、他の元素含有量が本実施形態の範囲内であっても、鋼材の熱間加工性が低下する。
　したがって、Ｖ含有量は０～１．５０％であり、含有される場合、１．５０％以下である。
　Ｖ含有量の好ましい下限は０．０１％であり、さらに好ましくは０．０５％であり、さらに好ましくは０．１０％であり、さらに好ましくは０．２０％である。
　Ｖ含有量の好ましい上限は１．４０％であり、さらに好ましくは１．３０％であり、さらに好ましくは１．２０％であり、さらに好ましくは１．００％である。 V: 0 to 1.50%
Vanadium (V) is an optional element and may not be contained, that is, the V content may be 0%.
When V is contained, that is, when the V content exceeds 0%, V suppresses active dissolution of the steel material in a high-temperature, high-pressure, strongly acidic corrosive environment, and enhances general corrosion resistance. Even if even a small amount of V is contained, the above effect can be obtained to a certain degree.
However, if the V content exceeds 1.50%, the strength of the steel material becomes excessively high, and in this case, even if the contents of other elements are within the ranges of this embodiment, the hot workability of the steel material decreases.
Therefore, the V content is 0 to 1.50%, and if contained, it is 1.50% or less.
The lower limit of the V content is preferably 0.01%, more preferably 0.05%, further preferably 0.10%, and further preferably 0.20%.
The upper limit of the V content is preferably 1.40%, more preferably 1.30%, further preferably 1.20%, and further preferably 1.00%.
　Ｃｏ：０～２．００％
　コバルト（Ｃｏ）は任意元素であり、含有されなくてもよい。つまり、Ｃｏ含有量は０％であってもよい。
　含有される場合、つまり、Ｃｏ含有量が０％超である場合、Ｃｏは、高温高圧強酸性腐食環境での鋼材の耐全面腐食性を高める。Ｃｏが少しでも含有されれば、上記効果がある程度得られる。
　しかしながら、Ｃｏ含有量が２．００％を超えれば、他の元素含有量が本実施形態の範囲内であっても、鋼材の熱間加工性が低下する。
　したがって、Ｃｏ含有量は０～２．００％であり、含有される場合、２．００％以下である。
　Ｃｏ含有量の好ましい下限は０．０１％であり、さらに好ましくは０．０５％であり、さらに好ましくは０．１０％であり、さらに好ましくは０．２０％であり、さらに好ましくは０．３０％である。
　Ｃｏ含有量の好ましい上限は１．９０％であり、さらに好ましくは１．８０％であり、さらに好ましくは１．７０％であり、さらに好ましくは１．６０％であり、さらに好ましくは１．５０％であり、さらに好ましくは１．００％である。 Co: 0 to 2.00%
Cobalt (Co) is an optional element and may not be contained, that is, the Co content may be 0%.
When contained, that is, when the Co content is more than 0%, Co enhances the general corrosion resistance of the steel material in a high-temperature, high-pressure, strongly acidic corrosive environment. Even if even a small amount of Co is contained, the above effect can be obtained to a certain degree.
However, if the Co content exceeds 2.00%, the hot workability of the steel material decreases even if the contents of other elements are within the ranges of this embodiment.
Therefore, the Co content is 0 to 2.00%, and if Co is contained, it is 2.00% or less.
The lower limit of the Co content is preferably 0.01%, more preferably 0.05%, further preferably 0.10%, further preferably 0.20%, and further preferably 0.30%.
The upper limit of the Co content is preferably 1.90%, more preferably 1.80%, more preferably 1.70%, more preferably 1.60%, more preferably 1.50%, and even more preferably 1.00%.
　Ｔａ：０～２．００％
　タンタル（Ｔａ）は任意元素であり、含有されなくてもよい。つまり、Ｔａ含有量は０％であってもよい。
　含有される場合、つまり、Ｔａ含有量が０％超である場合、Ｔａは、高温高圧強酸性腐食環境での耐全面腐食性を高める。Ｔａが少しでも含有されれば、上記効果がある程度得られる。
　しかしながら、Ｔａ含有量が２．００％を超えれば、鋼材の強度が過度に高くなる。この場合、他の元素含有量が本実施形態の範囲内であっても、鋼材の熱間加工性が低下する。
　したがって、Ｔａ含有量は０～２．００％であり、含有される場合、２．００％以下である。
　Ｔａ含有量の好ましい下限は０．０１％であり、さらに好ましくは０．０５％であり、さらに好ましくは０．０８％である。
　Ｔａ含有量の好ましい上限は１．５０％であり、さらに好ましくは１．００％であり、さらに好ましくは０．７０％であり、さらに好ましくは０．５０％である。 Ta: 0 to 2.00%
Tantalum (Ta) is an optional element and may not be contained, that is, the Ta content may be 0%.
When contained, that is, when the Ta content exceeds 0%, Ta enhances the general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment. Even if even a small amount of Ta is contained, the above effect can be obtained to some extent.
However, if the Ta content exceeds 2.00%, the strength of the steel material becomes excessively high, and in this case, even if the contents of other elements are within the ranges of this embodiment, the hot workability of the steel material decreases.
Therefore, the Ta content is 0 to 2.00%, and if contained, it is 2.00% or less.
The lower limit of the Ta content is preferably 0.01%, more preferably 0.05%, and further preferably 0.08%.
The upper limit of the Ta content is preferably 1.50%, more preferably 1.00%, further preferably 0.70%, and further preferably 0.50%.
　Ｗ：０～４．００％
　タングステン（Ｗ）は任意元素であり、含有されなくてもよい。つまり、Ｗ含有量は０％であってもよい。
　含有される場合、つまり、Ｗ含有量が０％超である場合、Ｗは、高温高圧強酸性腐食環境での鋼材の活性溶解を抑制し、耐全面腐食性を高める。Ｗが少しでも含有されれば、上記効果がある程度得られる。
　しかしながら、Ｗ含有量が４．００％を超えれば、鋼材の強度が過度に高くなる。この場合、他の元素含有量が本実施形態の範囲内であっても、鋼材の熱間加工性が低下する。
　したがって、Ｗ含有量は０～４．００％であり、含有される場合、４．００％以下である。
　Ｗ含有量の好ましい下限は０．０１％であり、さらに好ましくは０．０５％であり、さらに好ましくは０．１０％であり、さらに好ましくは０．２０％であり、さらに好ましくは０．３０％であり、さらに好ましくは０．５０％である。
　Ｗ含有量の好ましい上限は３．９０％であり、さらに好ましくは３．８０％であり、さらに好ましくは３．７０％であり、さらに好ましくは３．５０％であり、さらに好ましくは３．００％であり、さらに好ましくは２．５０％であり、さらに好ましくは２．００％であり、さらに好ましくは１．８０％である。 W: 0 to 4.00%
Tungsten (W) is an optional element and may not be contained, that is, the W content may be 0%.
When W is contained, that is, when the W content exceeds 0%, W suppresses active dissolution of the steel material in a high-temperature, high-pressure, strongly acidic corrosive environment, and enhances general corrosion resistance. Even if even a small amount of W is contained, the above effect can be obtained to a certain degree.
However, if the W content exceeds 4.00%, the strength of the steel material becomes excessively high, and in this case, even if the contents of other elements are within the ranges of this embodiment, the hot workability of the steel material decreases.
Therefore, the W content is 0 to 4.00%, and if W is contained, it is 4.00% or less.
The lower limit of the W content is preferably 0.01%, more preferably 0.05%, more preferably 0.10%, more preferably 0.20%, more preferably 0.30%, and more preferably 0.50%.
The upper limit of the W content is preferably 3.90%, more preferably 3.80%, more preferably 3.70%, more preferably 3.50%, more preferably 3.00%, more preferably 2.50%, more preferably 2.00%, and more preferably 1.80%.
　Ｎｂ：０～２．００％
　ニオブ（Ｎｂ）は任意元素であり、含有されなくてもよい。つまり、Ｎｂ含有量は０％であってもよい。
　含有される場合、つまり、Ｎｂ含有量が０％超である場合、Ｎｂは、炭化物又は窒化物を形成してＣｒ炭化物の形成を抑制する。そのため、粒界でのＣｒ欠乏領域の生成が抑制される。その結果、高温高圧強酸性腐食環境での耐全面腐食性が高まる。Ｎｂが少しでも含有されれば、上記効果がある程度得られる。
　しかしながら、Ｎｂ含有量が２．００％を超えれば、鋼材の強度が過度に高くなる。この場合、他の元素含有量が本実施形態の範囲内であっても、鋼材の熱間加工性が低下する。
　したがって、Ｎｂ含有量は０～２．００％であり、含有される場合、２．００％以下である。
　Ｎｂ含有量の好ましい下限は０．０１％であり、さらに好ましくは０．０５％であり、さらに好ましくは０．１０％であり、さらに好ましくは０．２０％であり、さらに好ましくは０．３０％であり、さらに好ましくは０．４０％である。
　Ｎｂ含有量の好ましい上限は１．５０％であり、さらに好ましくは１．００％であり、さらに好ましくは０．７０％であり、さらに好ましくは０．５０％である。 Nb: 0 to 2.00%
Niobium (Nb) is an optional element and may not be contained, that is, the Nb content may be 0%.
When Nb is contained, that is, when the Nb content is more than 0%, Nb forms carbides or nitrides to suppress the formation of Cr carbides. Therefore, the generation of Cr-depleted regions at grain boundaries is suppressed. As a result, the general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosion environment is improved. Even if even a small amount of Nb is contained, the above effect can be obtained to a certain extent.
However, if the Nb content exceeds 2.00%, the strength of the steel material becomes excessively high, and in this case, even if the contents of other elements are within the ranges of this embodiment, the hot workability of the steel material decreases.
Therefore, the Nb content is 0 to 2.00%, and if Nb is contained, it is 2.00% or less.
The lower limit of the Nb content is preferably 0.01%, more preferably 0.05%, more preferably 0.10%, more preferably 0.20%, more preferably 0.30%, and even more preferably 0.40%.
The upper limit of the Nb content is preferably 1.50%, more preferably 1.00%, further preferably 0.70%, and further preferably 0.50%.
　Ｔｉ：０～２．００％
　チタン（Ｔｉ）は任意元素であり、含有されなくてもよい。つまり、Ｔｉ含有量は０％であってもよい。
　含有される場合、つまり、Ｔｉ含有量が０％超である場合、Ｔｉは、炭化物又は窒化物を形成してＣｒ炭化物の形成を抑制する。そのため、粒界でのＣｒ欠乏領域の生成が抑制される。その結果、高温高圧強酸性腐食環境での耐全面腐食性が高まる。Ｔｉが微細なＴｉ窒化物を多数形成する場合はさらに、鋼材中に分散した微細なＴｉ窒化物がＡｓの偏析サイトとして機能する。そのため、Ａｓが鋼材中にさらに分散しやすくなる。その結果、高温高圧強酸性腐食環境での耐全面腐食性がさらに高まる。Ｔｉが少しでも含有されれば、上記効果がある程度得られる。
　しかしながら、Ｔｉ含有量が２．００％を超えれば、鋼材の強度が過度に高くなる。この場合、他の元素含有量が本実施形態の範囲内であっても、鋼材の熱間加工性が低下する。
　したがって、Ｔｉ含有量は０～２．００％であり、含有される場合、２．００％以下である。
　Ｔｉ含有量の好ましい下限は０．０１％であり、さらに好ましくは０．０５％である。
　Ｔｉ含有量の好ましい上限は１．５０％であり、さらに好ましくは１．００％であり、さらに好ましくは０．７０％であり、さらに好ましくは０．５０％である。 Ti: 0 to 2.00%
Titanium (Ti) is an optional element and may not be contained, that is, the Ti content may be 0%.
When Ti is contained, that is, when the Ti content is more than 0%, Ti forms carbides or nitrides to suppress the formation of Cr carbides. Therefore, the generation of Cr-depleted regions at grain boundaries is suppressed. As a result, the general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosion environment is improved. When Ti forms a large number of fine Ti nitrides, the fine Ti nitrides dispersed in the steel material further function as segregation sites for As. Therefore, As is more easily dispersed in the steel material. As a result, the general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosion environment is further improved. If even a small amount of Ti is contained, the above effect can be obtained to a certain extent.
However, if the Ti content exceeds 2.00%, the strength of the steel material becomes excessively high, and in this case, even if the contents of other elements are within the ranges of this embodiment, the hot workability of the steel material decreases.
Therefore, the Ti content is 0 to 2.00%, and if contained, it is 2.00% or less.
The lower limit of the Ti content is preferably 0.01%, and more preferably 0.05%.
The upper limit of the Ti content is preferably 1.50%, more preferably 1.00%, further preferably 0.70%, and further preferably 0.50%.
　Ｚｎ：０～０．０１００％
　亜鉛（Ｚｎ）は任意元素であり、含有されなくてもよい。つまり、Ｚｎ含有量は０％であってもよい。
　含有される場合、つまり、Ｚｎ含有量が０％超である場合、Ｚｎは、安定な硫化物を形成して、高温高圧強酸性腐食環境での耐全面腐食性を高める。Ｚｎが少しでも含有されれば、上記効果がある程度得られる。
　しかしながら、Ｚｎ含有量が０．０１００％を超えれば、他の元素含有量が本実施形態の範囲内であっても、鋼材の機械的特性が低下する。
　したがって、Ｚｎ含有量は０～０．０１００％であり、含有される場合、０．０１００％以下である。
　Ｚｎ含有量の好ましい下限は０．０００１％であり、さらに好ましくは０．０００５％であり、さらに好ましくは０．００１０％である。
　Ｚｎ含有量の好ましい上限は０．００５０％であり、さらに好ましくは０．００３０％であり、さらに好ましくは０．００２５％である。 Zn: 0 to 0.0100%
Zinc (Zn) is an optional element and may not be contained, that is, the Zn content may be 0%.
When contained, that is, when the Zn content is more than 0%, Zn forms stable sulfides to enhance the general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment. Even if even a small amount of Zn is contained, the above effect can be obtained to some extent.
However, if the Zn content exceeds 0.0100%, the mechanical properties of the steel material will deteriorate even if the contents of other elements are within the ranges of this embodiment.
Therefore, the Zn content is 0 to 0.0100%, and if contained, it is 0.0100% or less.
The lower limit of the Zn content is preferably 0.0001%, more preferably 0.0005%, and further preferably 0.0010%.
The upper limit of the Zn content is preferably 0.0050%, more preferably 0.0030%, and further preferably 0.0025%.
　Ｐｂ：０～０．０１００％
　鉛（Ｐｂ）は任意元素であり、含有されなくてもよい。つまり、Ｐｂ含有量は０％であってもよい。
　含有される場合、つまり、Ｐｂ含有量が０％超である場合、Ｐｂは、安定な硫化物を形成して、高温高圧強酸性腐食環境での耐全面腐食性を高める。Ｐｂが少しでも含有されれば、上記効果がある程度得られる。
　しかしながら、Ｐｂ含有量が０．０１００％を超えれば、他の元素含有量が本実施形態の範囲内であっても、鋼材の機械的特性が低下する。
　したがって、Ｐｂ含有量は０～０．０１００％であり、含有される場合、０．０１００％以下である。
　Ｐｂ含有量の好ましい下限は０．０００１％であり、さらに好ましくは０．０００３％であり、さらに好ましくは０．０００５％であり、さらに好ましくは０．０００８％であり、さらに好ましくは０．００１０％である。
　Ｐｂ含有量の好ましい上限は０．００７０％であり、さらに好ましくは０．００５０％であり、さらに好ましくは０．００３０％であり、さらに好ましくは０．００２０％である。 Pb: 0 to 0.0100%
Lead (Pb) is an optional element and may not be contained, that is, the Pb content may be 0%.
When Pb is contained, that is, when the Pb content is more than 0%, Pb forms stable sulfides to improve the general corrosion resistance in a high-temperature, high-pressure, highly acidic corrosive environment. Even if even a small amount of Pb is contained, the above effect can be obtained to some extent.
However, if the Pb content exceeds 0.0100%, the mechanical properties of the steel material will deteriorate even if the contents of other elements are within the ranges of this embodiment.
Therefore, the Pb content is 0 to 0.0100%, and if contained, it is 0.0100% or less.
The lower limit of the Pb content is preferably 0.0001%, more preferably 0.0003%, still more preferably 0.0005%, still more preferably 0.0008%, and still more preferably 0.0010%.
The upper limit of the Pb content is preferably 0.0070%, more preferably 0.0050%, further preferably 0.0030%, and further preferably 0.0020%.
　Ｓｂ：０～０．０１００％
　アンチモン（Ｓｂ）は任意元素であり、含有されなくてもよい。つまり、Ｓｂ含有量は０％であってもよい。
　含有される場合、つまり、Ｓｂ含有量が０％超である場合、Ｓｂは、高温高圧強酸性腐食環境での耐全面腐食性を高める。Ｓｂが少しでも含有されれば、上記効果がある程度得られる。
　しかしながら、Ｓｂ含有量が０．０１００％を超えれば、他の元素含有量が本実施形態の範囲内であっても、鋼材の熱間加工性が低下する。
　したがって、Ｓｂ含有量は０～０．０１００％であり、含有される場合、０．０１００％以下である。
　Ｓｂ含有量の好ましい下限は０．０００１％であり、さらに好ましくは０．０００２％であり、さらに好ましくは０．０００５％である。
　Ｓｂ含有量の好ましい上限は０．００７０％であり、さらに好ましくは０．００５０％であり、さらに好ましくは０．００３０％であり、さらに好ましくは０．００２０％であり、さらに好ましくは０．００１５％である。 Sb: 0 to 0.0100%
Antimony (Sb) is an optional element and may not be contained, that is, the Sb content may be 0%.
When contained, that is, when the Sb content is more than 0%, Sb enhances the general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment. Even if even a small amount of Sb is contained, the above effect can be obtained to some extent.
However, if the Sb content exceeds 0.0100%, the hot workability of the steel material decreases even if the contents of other elements are within the ranges of this embodiment.
Therefore, the Sb content is 0 to 0.0100%, and if contained, it is 0.0100% or less.
The lower limit of the Sb content is preferably 0.0001%, more preferably 0.0002%, and further preferably 0.0005%.
The upper limit of the Sb content is preferably 0.0070%, more preferably 0.0050%, further preferably 0.0030%, further preferably 0.0020%, and further preferably 0.0015%.
　Ｓｎ：０～０．０１００％
　すず（Ｓｎ）は任意元素であり、含有されなくてもよい。つまり、Ｓｎ含有量は０％であってもよい。
　含有される場合、つまり、Ｓｎ含有量が０％超である場合、Ｓｎは、高温高圧強酸性腐食環境での耐全面腐食性を高める。Ｓｎが少しでも含有されれば、上記効果がある程度得られる。
　しかしながら、Ｓｎ含有量が０．０１００％を超えれば、他の元素含有量が本実施形態の範囲内であっても、鋼材の熱間加工性が低下する。
　したがって、Ｓｎ含有量は０～０．０１００％であり、含有される場合、０．０１００％以下である。
　Ｓｎ含有量の好ましい下限は０．０００１％であり、さらに好ましくは０．０００２％であり、さらに好ましくは０．０００５％である。
　Ｓｎ含有量の好ましい上限は０．００７０％であり、さらに好ましくは０．００５０％であり、さらに好ましくは０．００３０％であり、さらに好ましくは０．００２０％であり、さらに好ましくは０．００１５％である。 Sn: 0 to 0.0100%
Tin (Sn) is an optional element and may not be contained, that is, the Sn content may be 0%.
When contained, that is, when the Sn content is more than 0%, Sn enhances the general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment. Even if even a small amount of Sn is contained, the above effect can be obtained to some extent.
However, if the Sn content exceeds 0.0100%, the hot workability of the steel material decreases even if the contents of other elements are within the ranges of this embodiment.
Therefore, the Sn content is 0 to 0.0100%, and if contained, it is 0.0100% or less.
The lower limit of the Sn content is preferably 0.0001%, more preferably 0.0002%, and further preferably 0.0005%.
The upper limit of the Sn content is preferably 0.0070%, more preferably 0.0050%, still more preferably 0.0030%, still more preferably 0.0020%, and still more preferably 0.0015%.
　Ｂｉ：０～０．０１００％
　ビスマス（Ｂｉ）は任意元素であり、含有されなくてもよい。つまり、Ｂｉ含有量は０％であってもよい。
　含有される場合、つまり、Ｂｉ含有量が０％超である場合、Ｂｉは、高温高圧強酸性腐食環境での耐全面腐食性を高める。Ｂｉが少しでも含有されれば、上記効果がある程度得られる。
　しかしながら、Ｂｉ含有量が０．０１００％を超えれば、他の元素含有量が本実施形態の範囲内であっても、鋼材の熱間加工性が低下する。
　したがって、Ｂｉ含有量は０～０．０１００％であり、含有される場合、０．０１００％以下である。
　Ｂｉ含有量の好ましい下限は０．０００１％であり、さらに好ましくは０．０００２％であり、さらに好ましくは０．０００５％である。
　Ｂｉ含有量の好ましい上限は０．００７０％であり、さらに好ましくは０．００５０％であり、さらに好ましくは０．００３０％であり、さらに好ましくは０．００２０％であり、さらに好ましくは０．００１５％である。 Bi: 0 to 0.0100%
Bismuth (Bi) is an optional element and may not be contained, that is, the Bi content may be 0%.
When contained, that is, when the Bi content exceeds 0%, Bi enhances the general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment. Even if even a small amount of Bi is contained, the above effect can be obtained to a certain degree.
However, if the Bi content exceeds 0.0100%, the hot workability of the steel material decreases even if the contents of other elements are within the ranges of this embodiment.
Therefore, the Bi content is 0 to 0.0100%, and if contained, it is 0.0100% or less.
The lower limit of the Bi content is preferably 0.0001%, more preferably 0.0002%, and further preferably 0.0005%.
The upper limit of the Bi content is preferably 0.0070%, more preferably 0.0050%, further preferably 0.0030%, further preferably 0.0020%, and further preferably 0.0015%.
　［第２群：Ｂ、希土類元素、Ｚｒ及びＨｆ］
　本実施形態の二相ステンレス鋼材の化学組成は、Ｆｅの一部に代えて、Ｂ、希土類元素（ＲＥＭ）、Ｚｒ、及び、Ｈｆ、からなる群から選択される１種以上を含有してもよい。これらの元素はいずれも任意元素であり、鋼材の熱間加工性を高める。以下、各元素について説明する。 [Group 2: B, rare earth elements, Zr and Hf]
The chemical composition of the duplex stainless steel material of this embodiment may contain one or more elements selected from the group consisting of B, rare earth elements (REM), Zr, and Hf, instead of a part of Fe. All of these elements are optional elements, and improve the hot workability of the steel material. Each element will be described below.
　Ｂ：０～０．０１００％
　ホウ素（Ｂ）は任意元素であり、含有されなくてもよい。つまり、Ｂ含有量は０％であってもよい。
　含有される場合、つまり、Ｂ含有量が０％超である場合、Ｂは、鋼材中のＰ及びＳの粒界への偏析を抑制し、鋼材の熱間加工性を高める。Ｂが少しでも含有されれば、上記効果がある程度得られる。
　しかしながら、Ｂ含有量が０．０１００％を超えれば、Ｂ窒化物が過剰に生成する。そのため、他の元素含有量が本実施形態の範囲内であっても、鋼材の靱性が低下する。
　したがって、Ｂ含有量は０～０．０１００％であり、含有される場合、０．０１００％以下である。
　Ｂ含有量の好ましい下限は０．０００１％であり、さらに好ましくは０．０００５％であり、さらに好ましくは０．００１０％であり、さらに好ましくは０．００２０％である。
　Ｂ含有量の好ましい上限は０．００９０％であり、さらに好ましくは０．００８０％であり、さらに好ましくは０．００７０％であり、さらに好ましくは０．００５０％である。 B: 0 to 0.0100%
Boron (B) is an optional element and may not be contained. In other words, the B content may be 0%.
When B is contained, that is, when the B content exceeds 0%, B suppresses the segregation of P and S to grain boundaries in the steel material, and improves the hot workability of the steel material. Even if even a small amount of B is contained, the above effects can be obtained to a certain extent.
However, if the B content exceeds 0.0100%, B nitrides are formed in excess, and therefore the toughness of the steel material decreases even if the contents of other elements are within the ranges of this embodiment.
Therefore, the B content is 0 to 0.0100%, and if contained, it is 0.0100% or less.
The lower limit of the B content is preferably 0.0001%, more preferably 0.0005%, further preferably 0.0010%, and further preferably 0.0020%.
The upper limit of the B content is preferably 0.0090%, more preferably 0.0080%, further preferably 0.0070%, and further preferably 0.0050%.
　希土類元素：０～０．０５０％
　希土類元素（ＲＥＭ）は任意元素であり、含有されなくてもよい。つまり、ＲＥＭ含有量は０％であってもよい。
　含有される場合、つまり、ＲＥＭ含有量が０％超である場合、ＲＥＭは、介在物の形態を制御して、鋼材の熱間加工性を高める。ＲＥＭが少しでも含有されれば、上記効果がある程度得られる。
　しかしながら、ＲＥＭ含有量が０．０５０％を超えれば、鋼材中の酸化物が粗大化する。そのため、他の元素含有量が本実施形態の範囲内であっても、鋼材の靭性が低下する。
　したがって、ＲＥＭ含有量は０～０．０５０％であり、含有される場合、０．０５０％以下である。
　ＲＥＭ含有量の好ましい下限は０．００１％であり、さらに好ましくは０．００３％であり、さらに好ましくは０．００５％であり、さらに好ましくは０．００８％であり、さらに好ましくは０．０１０％である。
　ＲＥＭ含有量の好ましい上限は０．０４５％であり、さらに好ましくは０．０４０％であり、さらに好ましくは０．０３５％であり、さらに好ましくは０．０３０％である。 Rare earth elements: 0 to 0.050%
The rare earth elements (REM) are optional elements and may not be contained, i.e., the REM content may be 0%.
When contained, that is, when the REM content is more than 0%, REM controls the morphology of inclusions and improves the hot workability of the steel material. Even if even a small amount of REM is contained, the above effect can be obtained to some extent.
However, if the REM content exceeds 0.050%, the oxides in the steel material become coarse, and therefore the toughness of the steel material decreases even if the contents of other elements are within the ranges of this embodiment.
Therefore, the REM content is 0 to 0.050%, and if contained, it is 0.050% or less.
The lower limit of the REM content is preferably 0.001%, more preferably 0.003%, still more preferably 0.005%, still more preferably 0.008%, and still more preferably 0.010%.
The upper limit of the REM content is preferably 0.045%, more preferably 0.040%, further preferably 0.035%, and further preferably 0.030%.
　本明細書におけるＲＥＭとは、原子番号２１番のスカンジウム（Ｓｃ）、原子番号３９番のイットリウム（Ｙ）、及び、ランタノイドである原子番号５７番のランタン（Ｌａ）～原子番号７１番のルテチウム（Ｌｕ）からなる群から選択される１種以上の元素を意味する。本明細書におけるＲＥＭ含有量とは、これらの元素の合計含有量である。 In this specification, REM refers to one or more elements selected from the group consisting of scandium (Sc), atomic number 21; yttrium (Y), atomic number 39; and the lanthanides lanthanum (La), atomic number 57, to lutetium (Lu), atomic number 71. In this specification, the REM content refers to the total content of these elements.
　Ｚｒ：０～２．００％
　ジルコニウム（Ｚｒ）は任意元素であり、含有されなくてもよい。つまり、Ｚｒ含有量は０％であってもよい。
　含有される場合、つまり、Ｚｒ含有量が０％超である場合、Ｚｒは、炭窒化物を形成して、鋼材の強度及び熱間加工性を高める。Ｚｒが少しでも含有されれば、上記効果がある程度得られる。
　しかしながら、Ｚｒ含有量が２．００％を超えれば、鋼材の強度が過度に高くなる。そのため、他の元素含有量が本実施形態の範囲内であっても、鋼材の靱性が低下する。
　したがって、Ｚｒ含有量は０～２．００％であり、含有される場合、２．００％以下である。
　Ｚｒ含有量の好ましい下限は０．０１％であり、さらに好ましくは０．０２％であり、さらに好ましくは０．０５％である。
　Ｚｒ含有量の好ましい上限は１．５０％であり、さらに好ましくは１．００％であり、さらに好ましくは０．５０％であり、さらに好ましくは０．３０％である。 Zr: 0 to 2.00%
Zirconium (Zr) is an optional element and may not be contained, that is, the Zr content may be 0%.
When contained, that is, when the Zr content is more than 0%, Zr forms carbonitrides to improve the strength and hot workability of the steel material. Even if even a small amount of Zr is contained, the above effects can be obtained to some extent.
However, if the Zr content exceeds 2.00%, the strength of the steel material becomes excessively high, and therefore the toughness of the steel material decreases even if the contents of other elements are within the ranges of this embodiment.
Therefore, the Zr content is 0 to 2.00%, and if contained, it is 2.00% or less.
The lower limit of the Zr content is preferably 0.01%, more preferably 0.02%, and further preferably 0.05%.
The upper limit of the Zr content is preferably 1.50%, more preferably 1.00%, further preferably 0.50%, and further preferably 0.30%.
　Ｈｆ：０～２．００％
　ハフニウム（Ｈｆ）は任意元素であり、含有されなくてもよい。つまり、Ｈｆ含有量は０％であってもよい。
　含有される場合、つまり、Ｈｆ含有量が０％超である場合、Ｈｆは、炭窒化物を形成して、鋼材の強度及び熱間加工性を高める。Ｈｆが少しでも含有されれば、上記効果がある程度得られる。
　しかしながら、Ｈｆ含有量が２．００％を超えれば、鋼材の強度が過度に高くなる。そのため、他の元素含有量が本実施形態の範囲内であっても、鋼材の靱性を低下する。
　したがって、Ｈｆ含有量は０～２．００％であり、含有される場合、２．００％以下である。
　Ｈｆ含有量の好ましい下限は０．０１％であり、さらに好ましくは０．１０％であり、さらに好ましくは０．１５％であり、さらに好ましくは０．２０％である。
　Ｈｆ含有量の好ましい上限は１．５０％であり、さらに好ましくは１．００％であり、さらに好ましくは０．８０％であり、さらに好ましくは０．７５％である。 Hf: 0 to 2.00%
Hafnium (Hf) is an optional element and may not be contained, that is, the Hf content may be 0%.
When contained, that is, when the Hf content is more than 0%, Hf forms carbonitrides to improve the strength and hot workability of the steel material. Even if even a small amount of Hf is contained, the above effects can be obtained to some extent.
However, if the Hf content exceeds 2.00%, the strength of the steel material becomes excessively high, and therefore the toughness of the steel material decreases even if the contents of other elements are within the ranges of this embodiment.
Therefore, the Hf content is 0 to 2.00%, and if contained, it is 2.00% or less.
The lower limit of the Hf content is preferably 0.01%, more preferably 0.10%, further preferably 0.15%, and further preferably 0.20%.
The upper limit of the Hf content is preferably 1.50%, more preferably 1.00%, further preferably 0.80%, and further preferably 0.75%.
　［（特徴２）式（１）について］
　本実施形態の二相ステンレス鋼材の化学組成はさらに、式（１）を満たす。
　０．７０＜１００００×Ａｓ／（Ｎｉ＋Ｃｕ）＜１６．００　（１）
　ここで、式中の各元素記号には、対応する元素の質量％での含有量が代入される。元素が含有されていない場合、対応する元素記号には「０」が代入される。 [(Feature 2) Regarding Formula (1)]
The chemical composition of the duplex stainless steel material of this embodiment further satisfies formula (1).
0.70<10000×As/(Ni+Cu)<16.00 (1)
Here, each element symbol in the formula is substituted with the content of the corresponding element in mass %. When an element is not contained, the corresponding element symbol is substituted with "0".
　Ｆｎ１（＝１００００×Ａｓ／（Ｎｉ＋Ｃｕ））は、高温高圧強酸性腐食環境での耐全面腐食性に関する指標である。Ｎｉ及びＣｕの総含有量に対するＡｓ含有量の比を調整することにより、高温高圧強酸性腐食環境での耐全面腐食性が顕著に高まる。具体的には、図１に示すとおり、Ｆｎ１が０．７０よりも高くなれば、二相ステンレス鋼材が特徴１及び特徴３を満たすことを前提として、高温高圧強酸性腐食環境での腐食速度が顕著に遅くなる。そのため、高温高圧強酸性腐食環境において、優れた耐全面腐食性が得られる。 Fn1 (=10,000 x As/(Ni+Cu)) is an index of general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosive environment. By adjusting the ratio of the As content to the total content of Ni and Cu, general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosive environment is significantly improved. Specifically, as shown in Figure 1, if Fn1 is higher than 0.70, the corrosion rate in a high-temperature, high-pressure, strong acidic corrosive environment is significantly slowed, assuming that the duplex stainless steel material satisfies Features 1 and 3. Therefore, excellent general corrosion resistance is obtained in a high-temperature, high-pressure, strong acidic corrosive environment.
　一方、Ｆｎ１が高すぎれば、高温高圧強酸性腐食環境での耐全面腐食性は高まるものの、鋼材の熱間加工性が低下する。Ｆｎ１が１６．００未満であれば、鋼材において十分な熱間加工性が得られる。したがって、Ｆｎ１は０．７０よりも高く１６．００未満とする。 On the other hand, if Fn1 is too high, the steel will have increased general corrosion resistance in a high-temperature, high-pressure, highly acidic corrosive environment, but the hot workability of the steel will decrease. If Fn1 is less than 16.00, the steel will have sufficient hot workability. Therefore, Fn1 should be greater than 0.70 and less than 16.00.
　Ｆｎ１の好ましい下限は０．７１であり、さらに好ましくは１．００であり、さらに好ましくは２．００であり、さらに好ましくは３．００であり、さらに好ましくは４．００である。なお、図１を参照して、Ｆｎ１が５．５０以上の場合、Ｆｎ１が０．７０よりも高く５．５０未満の場合と比較して、高温高圧強酸性腐食環境での腐食速度が顕著に低下する。そのため、Ｆｎ１のさらに好ましい下限は５．５０であり、さらに好ましくは６．００である。
　Ｆｎ１の好ましい上限は１５．５０であり、さらに好ましくは１５．００であり、さらに好ましくは１４．５０である。
　なお、本実施形態においてＦｎ１は、得られた数値の小数第三位を四捨五入して得られた小数第二位の数値とする。 The preferred lower limit of Fn1 is 0.71, more preferably 1.00, more preferably 2.00, more preferably 3.00, and more preferably 4.00. With reference to FIG. 1, when Fn1 is 5.50 or more, the corrosion rate in a high-temperature, high-pressure, strongly acidic corrosive environment is significantly reduced compared to when Fn1 is higher than 0.70 and less than 5.50. Therefore, the more preferred lower limit of Fn1 is 5.50, and more preferably 6.00.
The upper limit of Fn1 is preferably 15.50, more preferably 15.00, and even more preferably 14.50.
In this embodiment, Fn1 is the value obtained by rounding off the obtained value to one decimal place.
　［（特徴３）式（２）について］
　本実施形態の二相ステンレス鋼材の化学組成はさらに、式（２）を満たす。
　（Ｃａ＋Ｍｇ）／Ｏ＜１．５０　（２）
　ここで、式中の各元素記号には、対応する元素の質量％での含有量が代入される。元素が含有されていない場合、対応する元素記号には「０」が代入される。 [(Feature 3) Regarding formula (2)]
The chemical composition of the duplex stainless steel material of this embodiment further satisfies formula (2).
(Ca+Mg)/O<1.50 (2)
Here, each element symbol in the formula is substituted with the content of the corresponding element in mass %. When an element is not contained, the corresponding element symbol is substituted with "0".
　Ｆｎ２（＝（Ｃａ＋Ｍｇ）／Ｏ）は、高温高圧塩化物腐食環境での耐孔食性に関する指標である。上述のとおり、Ｃａ及びＭｇは、Ｓと結合して硫化物を形成する。これにより、粗大なＭｎ硫化物の生成が抑制される。その結果、高温高圧塩化物腐食環境での耐孔食性が高まる。 Fn2 (= (Ca + Mg)/O) is an index of pitting corrosion resistance in high-temperature, high-pressure chloride corrosive environments. As mentioned above, Ca and Mg combine with S to form sulfides. This suppresses the formation of coarse Mn sulfides. As a result, pitting corrosion resistance in high-temperature, high-pressure chloride corrosive environments is improved.
　しかしながら、鋼材中のＳ含有量が上述の範囲内（０．０１０％以下）である場合において、Ｏ含有量に対してＣａ及びＭｇの総含有量が高すぎれば、Ｃａ及びＭｇがＳだけでなくＯと結合して、粗大なＣａ酸硫化物及びＭｇ酸化物を形成する。粗大なＣａ酸硫化物及び粗大なＭｇ酸化物は粗大なＭｎ硫化物と同様に、高温高圧塩化物腐食環境で溶解しやすく、孔食の起点となりやすい。そのため、Ｏ含有量に対してＣａ及びＭｇの総含有量が高すぎれば、高温高圧塩化物腐食環境での耐孔食性が低下する。 However, when the S content in the steel is within the above-mentioned range (0.010% or less), if the total content of Ca and Mg is too high relative to the O content, Ca and Mg will combine with not only S but also O to form coarse Ca oxysulfides and Mg oxides. Like coarse Mn sulfides, coarse Ca oxysulfides and coarse Mg oxides are prone to dissolution in high-temperature, high-pressure chloride corrosive environments and are likely to become the starting point of pitting corrosion. Therefore, if the total content of Ca and Mg is too high relative to the O content, pitting corrosion resistance in high-temperature, high-pressure chloride corrosive environments will decrease.
　図２に示すとおり、Ｆｎ２が１．５０未満であれば、二相ステンレス鋼材が特徴１及び特徴２を満たすことを前提として、高温高圧塩化物腐食環境での腐食速度が顕著に遅くなる。その結果、高温高圧塩化物腐食環境において、優れた耐孔食性が得られる。 As shown in Figure 2, if Fn2 is less than 1.50, the corrosion rate in a high-temperature, high-pressure chloride corrosion environment is significantly slowed, assuming that the duplex stainless steel material satisfies Features 1 and 2. As a result, excellent pitting corrosion resistance is obtained in a high-temperature, high-pressure chloride corrosion environment.
　Ｆｎ２の好ましい上限は１．４５であり、さらに好ましくは１．４３であり、さらに好ましくは１．４０であり、さらに好ましくは１．３５であり、さらに好ましくは１．３０である。
　Ｆｎ２の下限は特に限定されない。Ｆｎ２の好ましい下限は０．０１であり、さらに好ましくは０．０２である。
　なお、本実施形態においてＦｎ２は、得られた数値の小数第三位を四捨五入して得られた小数第二位の数値とする。 The upper limit of Fn2 is preferably 1.45, more preferably 1.43, more preferably 1.40, more preferably 1.35, and even more preferably 1.30.
The lower limit of Fn2 is not particularly limited. The lower limit of Fn2 is preferably 0.01, and more preferably 0.02.
In this embodiment, Fn2 is the value obtained by rounding off the obtained value to one decimal place.
　［本実施形態の二相ステンレス鋼材の効果］
　本実施形態の二相ステンレス鋼材は、特徴１～特徴３を満たす。そのため、本実施形態の二相ステンレス鋼材では、高温高圧強酸性腐食環境において優れた耐全面腐食性が得られ、さらに、高温高圧塩化物腐食環境において優れた耐孔食性が得られる。
　ここで、高温高圧強酸性腐食環境での優れた耐全面腐食性、及び、高温高圧塩化物腐食環境での優れた耐孔食性は、以下に示す高温高圧強酸性腐食環境での耐全面腐食性評価試験、及び、高温高圧塩化物腐食環境での耐孔食性評価試験により、次の通り定義される。 [Effects of the duplex stainless steel material according to this embodiment]
The duplex stainless steel material of this embodiment satisfies Features 1 to 3. Therefore, the duplex stainless steel material of this embodiment can obtain excellent general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment, and can also obtain excellent pitting corrosion resistance in a high-temperature, high-pressure chloride corrosive environment.
Here, the excellent general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment and the excellent pitting corrosion resistance in a high-temperature, high-pressure, chloride corrosive environment are defined as follows based on a general corrosion resistance evaluation test in a high-temperature, high-pressure, strongly acidic corrosive environment and a pitting corrosion resistance evaluation test in a high-temperature, high-pressure, chloride corrosive environment, which are shown below.
　［高温高圧強酸性腐食環境での耐全面腐食性評価試験］
　高温高圧強酸性腐食環境での耐全面腐食性評価試験は、次の方法で実施する。
　二相ステンレス鋼材から、試験片を採取する。二相ステンレス鋼材が鋼管である場合、肉厚中央位置から試験片を採取する。この場合、試験片の長手方向は、鋼管の管軸方向と平行とする。二相ステンレス鋼材が丸鋼である場合、Ｒ／２位置から試験片を採取する。ここで、Ｒ／２位置とは、丸鋼の軸方向に垂直な断面において、半径Ｒの中央位置を意味する。この場合、試験片の長手方向は、丸鋼の軸方向と平行とする。二相ステンレス鋼材が鋼板である場合、板厚中央位置から試験片を採取する。この場合、試験片の長手方向は、鋼板の圧延方向と平行とする。試験片のサイズは例えば、長さ：４０ｍｍ、幅：１０ｍｍ、厚さ：３ｍｍとする。試験開始前に試験片の質量を測定する。 [General corrosion resistance evaluation test in high-temperature, high-pressure, highly acidic corrosive environment]
The general corrosion resistance evaluation test in a high-temperature, high-pressure, strong acidic corrosive environment is carried out in the following manner.
A test piece is taken from the duplex stainless steel material. When the duplex stainless steel material is a steel pipe, the test piece is taken from the center position of the wall thickness. In this case, the longitudinal direction of the test piece is parallel to the axial direction of the steel pipe. When the duplex stainless steel material is a round bar, the test piece is taken from the R/2 position. Here, the R/2 position means the center position of the radius R in a cross section perpendicular to the axial direction of the round bar. In this case, the longitudinal direction of the test piece is parallel to the axial direction of the round bar. When the duplex stainless steel material is a steel plate, the test piece is taken from the center position of the plate thickness. In this case, the longitudinal direction of the test piece is parallel to the rolling direction of the steel plate. The size of the test piece is, for example, length: 40 mm, width: 10 mm, and thickness: 3 mm. The mass of the test piece is measured before the start of the test.
　０．０１ｍｏｌ／Ｌの硫酸（Ｈ２ＳＯ４）水溶液を試験液として準備する。オートクレーブ内に試験液を収納する。試験液中に試験片を浸漬し、オートクレーブ内に、０．０５ｂａｒのＨ２Ｓガスと５．００ｂａｒのＣＯ２ガスとの混合ガスを加圧封入して、腐食試験を開始する。試験時間は３３６時間とする。試験中のオートクレーブ内の温度を１８０℃に保持する。 A 0.01 mol/L aqueous solution of sulfuric acid ( H2SO4 ) is prepared as the test liquid. The test liquid is stored in an autoclave. The test piece is immersed in the test liquid, and a mixture of 0.05 bar of H2S gas and 5.00 bar of CO2 gas is pressurized and sealed in the autoclave to start the corrosion test. The test time is 336 hours. The temperature inside the autoclave during the test is maintained at 180°C.
　試験時間経過後、試験片から腐食生成物を除去する。腐食生成物の試験片からの除去は例えば、ＡＳＴＭ　Ｇ３１－２１に規定の方法に基づいて行う。腐食生成物が除去された試験片の質量を測定する。腐食速度（ｇ・ｃｍ－２・ｈ－１）は、試験開始前の試験片の質量と、試験時間経過後であって腐食生成物が除去された試験片の質量との差を、試験片の表面積と試験時間とで除することにより求める。腐食速度が０．１００ｇ・ｃｍ－２・ｈ－１以下である場合、高温高圧強酸性腐食環境において耐全面腐食性に優れると判定する。 After the test time has elapsed, the corrosion products are removed from the test piece. The removal of the corrosion products from the test piece is performed, for example, based on the method specified in ASTM G31-21. The mass of the test piece from which the corrosion products have been removed is measured. The corrosion rate (g·cm −2 ·h −1 ) is obtained by dividing the difference between the mass of the test piece before the start of the test and the mass of the test piece from which the corrosion products have been removed after the test time has elapsed by the surface area of the test piece and the test time. If the corrosion rate is 0.100 g·cm −2 ·h −1 or less, it is determined that the test piece has excellent general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosion environment.
　［高温高圧塩化物腐食環境での耐孔食性評価試験］
　高温高圧塩化物腐食環境での耐孔食性評価試験は、次の方法で実施する。
　二相ステンレス鋼材から、試験片を採取する。二相ステンレス鋼材が鋼管である場合、肉厚中央位置から試験片を採取する。この場合、試験片の長手方向は、鋼管の管軸方向と平行とする。二相ステンレス鋼材が丸鋼である場合、Ｒ／２位置から試験片を採取する。この場合、試験片の長手方向は、丸鋼の軸方向と平行とする。二相ステンレス鋼材が鋼板である場合、板厚中央位置から試験片を採取する。この場合、試験片の長手方向は、鋼板の圧延方向と平行とする。試験片のサイズは例えば、長さ：４０ｍｍ、幅：１０ｍｍ、厚さ：３ｍｍとする。試験開始前に試験片の質量を測定する。 [Pitting corrosion resistance evaluation test in high-temperature and high-pressure chloride corrosion environment]
The pitting corrosion resistance evaluation test in a high-temperature and high-pressure chloride corrosion environment is carried out in the following manner.
A test piece is taken from the duplex stainless steel material. When the duplex stainless steel material is a steel pipe, the test piece is taken from the center position of the wall thickness. In this case, the longitudinal direction of the test piece is parallel to the axial direction of the steel pipe. When the duplex stainless steel material is a round bar, the test piece is taken from the R/2 position. In this case, the longitudinal direction of the test piece is parallel to the axial direction of the round bar. When the duplex stainless steel material is a steel plate, the test piece is taken from the center position of the plate thickness. In this case, the longitudinal direction of the test piece is parallel to the rolling direction of the steel plate. The size of the test piece is, for example, length: 40 mm, width: 10 mm, and thickness: 3 mm. The mass of the test piece is measured before the start of the test.
　２５質量％の塩化ナトリウム（ＮａＣｌ）水溶液を試験液として準備する。オートクレーブ内に試験液を収納する。試験液中に試験片を浸漬し、オートクレーブ内に、０．０５ｂａｒのＨ２Ｓガスと５．００ｂａｒのＣＯ２ガスとの混合ガスを加圧封入して、腐食試験を開始する。試験時間は３３６時間とする。試験中のオートクレーブ内の温度を１８０℃に保持する。 A 25% by mass aqueous solution of sodium chloride (NaCl) is prepared as the test liquid. The test liquid is stored in an autoclave. The test piece is immersed in the test liquid, and a mixture of 0.05 bar of H2S gas and 5.00 bar of CO2 gas is pressurized and sealed in the autoclave to start the corrosion test. The test time is 336 hours. The temperature inside the autoclave during the test is maintained at 180°C.
　試験時間経過後、試験片から腐食生成物を除去する。腐食生成物の試験片からの除去は例えば、ＡＳＴＭ　Ｇ３１－２１に規定の方法に基づいて行う。腐食生成物が除去された試験片の質量を測定する。腐食速度（ｇ・ｃｍ－２・ｈ－１）は、試験開始前の試験片の質量と、試験時間経過後であって腐食生成物が除去された試験片の質量との差を、試験片の表面積と試験時間とで除することにより求める。 After the test time has elapsed, the corrosion products are removed from the test specimen. The removal of the corrosion products from the test specimen is performed, for example, based on the method specified in ASTM G31-21. The mass of the test specimen from which the corrosion products have been removed is measured. The corrosion rate (g cm -2 h -1 ) is calculated by dividing the difference between the mass of the test specimen before the start of the test and the mass of the test specimen from which the corrosion products have been removed after the test time has elapsed by the surface area of the test specimen and the test time.
　さらに、試験終了後の試験片の表面を、拡大率が１０倍のルーペで観察して、孔食の有無を確認する。ルーペ観察で孔食が疑われる箇所がある場合、孔食が疑われる箇所の断面を１００倍の光学顕微鏡で観察して、孔食の有無を確認する。 Furthermore, after the test is completed, the surface of the test piece is observed with a loupe at 10x magnification to confirm the presence or absence of pitting corrosion. If pitting corrosion is suspected in the loupe observation, the cross section of the suspected area is observed with an optical microscope at 100x magnification to confirm the presence or absence of pitting corrosion.
　腐食速度が０．００５ｇ・ｃｍ－２・ｈ－１以下であって、かつ、試験片の全表面において孔食が確認されない場合、高温高圧塩化物腐食環境において耐孔食性に優れると判定する。 If the corrosion rate is 0.005 g·cm −2 ·h −1 or less and no pitting corrosion is observed on the entire surface of the test piece, it is determined that the test piece has excellent pitting corrosion resistance in a high-temperature, high-pressure chloride corrosive environment.
　上述のとおり、本実施形態の二相ステンレス鋼材は、特徴１～特徴３を満たす。そのため、高温高圧強酸性腐食環境での優れた耐全面腐食性と、高温高圧塩化物腐食環境での優れた耐孔食性とが得られる。 As described above, the duplex stainless steel material of this embodiment satisfies Features 1 to 3. Therefore, it has excellent general corrosion resistance in high-temperature, high-pressure, strongly acidic corrosive environments, and excellent pitting corrosion resistance in high-temperature, high-pressure chloride corrosive environments.
　［ミクロ組織］
　なお、本実施形態の二相ステンレス鋼材のミクロ組織は、フェライト及びオーステナイトからなる。ここで、「フェライト及びオーステナイトからなる」とは、ミクロ組織が、例えば、体積率で３０～８０％のフェライトを含有し、残部がオーステナイトからなることを意味する。なお、フェライト及びオーステナイト以外の組織は無視できるほど少ない。例えば、本実施形態の二相ステンレス鋼材では、析出物及び介在物の体積率は、フェライト及びオーステナイトの体積率と比較して、無視できるほど小さい。すなわち、本実施形態の二相ステンレス鋼材のミクロ組織は、フェライト及びオーステナイト以外に、析出物及び／又は介在物等を含んでもよい。 [Microstructure]
The microstructure of the duplex stainless steel material of this embodiment is composed of ferrite and austenite. Here, "composed of ferrite and austenite" means that the microstructure contains, for example, 30 to 80% by volume of ferrite, with the remainder being composed of austenite. Note that structures other than ferrite and austenite are negligibly small. For example, in the duplex stainless steel material of this embodiment, the volume fraction of precipitates and inclusions is negligibly small compared to the volume fraction of ferrite and austenite. That is, the microstructure of the duplex stainless steel material of this embodiment may contain precipitates and/or inclusions, etc., in addition to ferrite and austenite.
　［ミクロ組織観察方法］
　二相ステンレス鋼材のフェライトの体積率は、ＪＩＳ　Ｇ　０５５５（２０２０）に準拠した方法で求めることができる。具体的には、二相ステンレス鋼材から、ミクロ組織観察用の試験片を作製する。鋼材が鋼管の場合、肉厚中央位置から、例えば、管軸方向５ｍｍ、管径方向５ｍｍの観察面を有する試験片を作製する。鋼材が丸鋼の場合、Ｒ／２位置から、例えば、軸方向５ｍｍ、径方向５ｍｍの観察面を有する試験片を作製する。鋼材が鋼板の場合、板厚中央位置から、例えば、圧延方向５ｍｍ、板厚方向５ｍｍの観察面を有する試験片を作製する。なお、上記観察面が得られれば、試験片の大きさは特に限定されない。 [Microstructure Observation Method]
The volume fraction of ferrite in the duplex stainless steel material can be determined by a method conforming to JIS G 0555 (2020). Specifically, a test piece for microstructure observation is prepared from the duplex stainless steel material. When the steel material is a steel pipe, a test piece having an observation surface, for example, 5 mm in the pipe axial direction and 5 mm in the pipe radial direction from the center position of the wall thickness is prepared. When the steel material is a round steel, a test piece having an observation surface, for example, 5 mm in the axial direction and 5 mm in the radial direction from the R/2 position is prepared. When the steel material is a steel plate, a test piece having an observation surface, for example, 5 mm in the rolling direction and 5 mm in the plate thickness direction from the center position of the plate thickness is prepared. Note that the size of the test piece is not particularly limited as long as the above observation surface can be obtained.
　作製した試験片の観察面を鏡面研磨する。鏡面研磨された観察面を７％水酸化カリウム腐食液中で電解腐食して、組織現出を行う。組織が現出された観察面を、光学顕微鏡を用いて１０視野観察する。視野面積は特に限定されないが、例えば、１．００ｍｍ２（倍率１００倍）である。各視野において、コントラストからフェライト及びオーステナイトを特定する。特定したフェライトの面積率をＪＩＳ　Ｇ　０５５５（２０２０）に準拠した点算法で測定する。得られたフェライトの面積率の１０視野における算術平均値を、フェライトの体積率（％）と定義する。なお、フェライトの体積率（％）は、得られた値の小数第一位を四捨五入した値とする。得られたフェライトの体積率を１００％から差し引いた値を、オーステナイトの体積率（％）と定義する。 The observation surface of the prepared test piece is mirror-polished. The mirror-polished observation surface is electrolytically etched in a 7% potassium hydroxide etchant to reveal the structure. The observation surface with the revealed structure is observed in 10 fields of view using an optical microscope. The field area is not particularly limited, but is, for example, 1.00 mm 2 (100x magnification). In each field of view, ferrite and austenite are identified from the contrast. The area ratio of the identified ferrite is measured by a point counting method in accordance with JIS G 0555 (2020). The arithmetic average value of the area ratio of the obtained ferrite in 10 fields of view is defined as the volume ratio of ferrite (%). The volume ratio of ferrite (%) is the value obtained by rounding off the first decimal place of the obtained value. The value obtained by subtracting the volume ratio of ferrite from 100% is defined as the volume ratio of austenite (%).
　［二相ステンレス鋼材の形状及び用途］
　本実施形態の二相ステンレス鋼材の形状は特に限定されない。本実施形態の二相ステンレス鋼材は、鋼管であってもよく、丸鋼（中実材）であってもよく、鋼板であってもよい。また、鋼管は継目無鋼管であってもよく、溶接鋼管であってもよい。 [Shapes and applications of duplex stainless steel materials]
The shape of the duplex stainless steel material of this embodiment is not particularly limited. The duplex stainless steel material of this embodiment may be a steel pipe, a round bar (solid material), or a steel plate. The steel pipe may be a seamless steel pipe or a welded steel pipe.
　本実施形態の二相ステンレス鋼材は、高温高圧強酸性腐食環境用途又は高温高圧塩化物腐食環境用途に広く適用可能である。本実施形態の二相ステンレス鋼材は例えば、地熱井用途に適用されてもよいし、油井用途に用いられてもよい。 The duplex stainless steel material of this embodiment is widely applicable to applications in high-temperature, high-pressure, highly acidic corrosive environments or high-temperature, high-pressure, chloride corrosive environments. For example, the duplex stainless steel material of this embodiment may be used in geothermal well applications or oil well applications.
　［本実施形態の二相ステンレス鋼材の好ましい実施形態］
　好ましくは、本実施形態の二相ステンレス鋼材は、上述の特徴１～特徴３を満たし、さらに、次の特徴４を満たす。
　（特徴４）
　円相当径が１．０～２．０μｍであり、質量％で、Ｃａ含有量及びＳ含有量の合計が５．０％よりも高く、Ｏ含有量が１．０％以上であり、Ｃａ含有量がＳ含有量よりも高い粒子を微細Ｃａ酸硫化物と定義し、
　円相当径が１．０～２．０μｍであり、質量％で、Ｍｇ含有量が５．０％以上であり、Ｏ含有量が１．０％以上であり、Ｓ含有量が１５．０％以下である粒子を微細Ｍｇ酸化物と定義し、
　円相当径が１．０～２．０μｍであり、質量％で、Ａｌ含有量が２０．０％以上であり、Ｎ含有量が２０．０％以上である粒子を微細Ａｌ窒化物と定義し、
　円相当径が１．０～２．０μｍであり、質量％でＴｉ含有量が３０．０％以上であり、Ｎ含有量が２０．０％以上である粒子を微細Ｔｉ窒化物と定義したとき、
　微細Ｃａ酸硫化物、微細Ｍｇ酸化物、微細Ａｌ窒化物、及び、微細Ｔｉ窒化物の総個数密度ＮＤは２．００個／ｍｍ２以上である。 [Preferred embodiment of the duplex stainless steel material of the present embodiment]
Preferably, the duplex stainless steel material of the present embodiment satisfies the above-mentioned characteristics 1 to 3, and further satisfies the following characteristic 4.
(Feature 4)
Fine Ca oxysulfides are defined as particles having an equivalent circle diameter of 1.0 to 2.0 μm, a total of Ca content and S content of more than 5.0%, an O content of 1.0% or more, and a Ca content higher than a S content, in terms of mass%,
Fine Mg oxide particles are defined as particles having an equivalent circle diameter of 1.0 to 2.0 μm, and, in mass%, an Mg content of 5.0% or more, an O content of 1.0% or more, and an S content of 15.0% or less.
Particles having an equivalent circle diameter of 1.0 to 2.0 μm, an Al content of 20.0% or more, and an N content of 20.0% or more, in mass%, are defined as fine Al nitrides;
When particles having a circle equivalent diameter of 1.0 to 2.0 μm, a Ti content of 30.0% or more, and a N content of 20.0% or more are defined as fine Ti nitrides,
The total number density ND of the fine Ca oxysulfides, the fine Mg oxides, the fine Al nitrides, and the fine Ti nitrides is 2.00 pieces/ mm2 or more.
　本実施形態の二相ステンレス鋼材が特徴１～特徴３を満たし、さらに、特徴４を満たす場合、高温高圧強酸性腐食環境において、さらに優れた耐全面腐食性が得られる。以下、特徴４について説明する。 If the duplex stainless steel material of this embodiment satisfies features 1 to 3 and also satisfies feature 4, it will have even better general corrosion resistance in a high-temperature, high-pressure, highly acidic corrosive environment. Feature 4 will be explained below.
　［（特徴４）総個数密度ＮＤについて］
　上述のとおり、Ａｓは高温高圧強酸性腐食環境での耐全面腐食性を高める。Ａｓが鋼材に分散して存在していれば、高温高圧強酸性腐食環境での耐全面腐食性がさらに高まる。ここで、鋼材中の介在物及び析出物である粒子のうち、円相当径が１．０～２．０μｍの微細粒子は、母相との界面にＡｓを偏析させやすい。つまり、このような微細粒子の表面は、Ａｓの偏析サイトとして機能する。鋼材中に偏析サイトが分散していれば、Ａｓも鋼材中に分散しやすい。そのため、Ａｓ含有量が少ない場合であっても、鋼材中にＡｓを分散させることができる。その結果、高温高圧強酸性腐食環境での耐全面腐食性が顕著に高まる。 [(Feature 4) Total Number Density ND]
As described above, As enhances the general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosion environment. If As is dispersed in the steel material, the general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosion environment is further improved. Here, among the particles that are inclusions and precipitates in the steel material, fine particles with a circle equivalent diameter of 1.0 to 2.0 μm tend to segregate As at the interface with the parent phase. In other words, the surface of such fine particles functions as a segregation site for As. If the segregation sites are dispersed in the steel material, As also tends to disperse in the steel material. Therefore, even if the As content is low, As can be dispersed in the steel material. As a result, the general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosion environment is significantly improved.
　特徴１～特徴３を満たす二相ステンレス鋼材において、微細Ｃａ酸硫化物、微細Ｍｇ酸化物、微細Ａｌ窒化物及び微細Ｔｉ窒化物は、二相ステンレス鋼材中での全ての微細粒子中に占める個数割合が高い。そのため、微細Ｃａ酸硫化物、微細Ｍｇ酸化物、微細Ａｌ窒化物及び微細Ｔｉ窒化物の総個数密度ＮＤを高めることができれば、鋼材中にＡｓの偏析サイトを十分に分散させることができる。その結果、高温高圧強酸性腐食環境での耐全面腐食性をさらに高めることができる。 In duplex stainless steel materials that satisfy features 1 to 3, fine Ca oxysulfides, fine Mg oxides, fine Al nitrides, and fine Ti nitrides account for a high percentage of the number of all fine particles in the duplex stainless steel material. Therefore, if the total number density ND of fine Ca oxysulfides, fine Mg oxides, fine Al nitrides, and fine Ti nitrides can be increased, it is possible to sufficiently disperse As segregation sites in the steel material. As a result, it is possible to further improve general corrosion resistance in high-temperature, high-pressure, strongly acidic corrosion environments.
　総個数密度ＮＤ（個／ｍｍ２）は、Ａｓの偏析サイトとなる主要な微細粒子（微細Ｃａ酸硫化物、微細Ｍｇ酸化物、微細Ａｌ窒化物及び微細Ｔｉ窒化物）の総個数密度である。総個数密度ＮＤが２．００個／ｍｍ２以上であれば、十分な量のＡｓ偏析サイトが鋼材中に分散して存在している。そのため、鋼材中においてＡｓが十分に分散しやすい。その結果、高温高圧強酸性腐食環境での耐全面腐食性がさらに高まる。 The total number density ND (pieces/ mm2 ) is the total number density of the main fine particles (fine Ca oxysulfides, fine Mg oxides, fine Al nitrides, and fine Ti nitrides) that become As segregation sites. If the total number density ND is 2.00 pieces/ mm2 or more, a sufficient amount of As segregation sites are dispersed and present in the steel material. Therefore, As is easily dispersed in the steel material. As a result, the general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosion environment is further improved.
　特に、二相ステンレス鋼材が特徴１～特徴３だけでなく、特徴４も満たす場合、Ｆｎ１が０．７０より高く５．５０未満である場合であっても、上述の［高温高圧強酸性腐食環境での耐全面腐食性評価試験］で得られる腐食速度が０．０８０ｇ・ｃｍ－２・ｈ－１以下になり、さらに優れた耐全面腐食性が得られる。 In particular, when a duplex stainless steel material satisfies not only characteristics 1 to 3 but also characteristic 4, even when Fn1 is higher than 0.70 and less than 5.50, the corrosion rate obtained in the above-mentioned [General corrosion resistance evaluation test in a high-temperature, high-pressure, strongly acidic corrosive environment] is 0.080 g cm -2 h -1 or less, and further excellent general corrosion resistance is obtained.
　総個数密度ＮＤの好ましい下限は２．０１個／ｍｍ２であり、さらに好ましくは２．０５個／ｍｍ２であり、さらに好ましくは２．０７個／ｍｍ２であり、さらに好ましくは２．１０個／ｍｍ２である。
　なお、総個数密度ＮＤが多いほどＡｓの偏析サイトが増加するため、耐全面腐食性が高まりやすい。そのため、総個数密度ＮＤの上限は特に限定されない。特徴１を満たす二相ステンレス鋼材であれば、総個数密度ＮＤの上限は例えば、３０．００個／ｍｍ２であり、好ましくは２８．５０個／ｍｍ２であり、さらに好ましくは２５．００個／ｍｍ２であり、さらに好ましくは２０．００個／ｍｍ２であり、さらに好ましくは１７．００個／ｍｍ２であり、さらに好ましくは１５．００個／ｍｍ２であり、さらに好ましくは１０．００個／ｍｍ２であり、さらに好ましくは５．００個／ｍｍ２であり、さらに好ましくは３．００個／ｍｍ２である。 The preferred lower limit of the total number density ND is 2.01 pieces/mm 2 , more preferably 2.05 pieces/mm 2 , even more preferably 2.07 pieces/mm 2 , and even more preferably 2.10 pieces/mm 2 .
In addition, the higher the total number density ND, the more As segregation sites there are, and therefore the general corrosion resistance is likely to be improved. Therefore, the upper limit of the total number density ND is not particularly limited. In the case of a duplex stainless steel material that satisfies the feature 1, the upper limit of the total number density ND is, for example, 30.00 pieces/mm 2 , preferably 28.50 pieces/mm 2 , more preferably 25.00 pieces/mm 2 , more preferably 20.00 pieces/mm 2 , more preferably 17.00 pieces/mm 2 , more preferably 15.00 pieces/mm 2 , more preferably 10.00 pieces/mm 2 , more preferably 5.00 pieces/mm 2 , and more preferably 3.00 pieces/mm 2 .
　［総個数密度ＮＤの測定方法］
　微細Ｃａ酸硫化物、微細Ｍｇ酸化物、微細Ａｌ窒化物及び微細Ｔｉ窒化物の総個数密度ＮＤ（個／ｍｍ２）は、次の方法により求めることができる。 [Method for measuring total number density ND]
The total number density ND (pieces/mm 2 ) of the fine Ca oxysulfides, fine Mg oxides, fine Al nitrides and fine Ti nitrides can be determined by the following method.
　具体的には、二相ステンレス鋼材から、試験片を作製する。鋼材が鋼管である場合、肉厚中央位置から、管軸方向及び管径方向（肉厚方向）を含む観察面を有する試験片を作製する。鋼材が鋼板の場合、板厚中央位置から、圧延方向及び板厚方向を含む観察面を有する試験片を作製する。鋼材が丸鋼である場合、軸方向及び径方向を含む観察面を有する試験片を、丸鋼の軸方向に垂直な断面におけるＲ／２位置から１つ作製する。 Specifically, test pieces are prepared from duplex stainless steel material. If the steel material is a steel pipe, a test piece is prepared from the center of the wall thickness, with an observation surface including the pipe axial direction and the pipe radial direction (wall thickness direction). If the steel material is a steel plate, a test piece is prepared from the center of the plate thickness, with an observation surface including the rolling direction and plate thickness direction. If the steel material is a round bar, one test piece is prepared from the R/2 position on a cross section perpendicular to the axial direction of the round bar, with an observation surface including the axial and radial directions.
　ダイヤモンドペースト研磨剤を用いて、作製した試験片の観察面を鏡面研磨する。鏡面研磨された観察面の厚さ中央位置の観察視野を、走査電子顕微鏡（ＳＥＭ）により５００倍で観察する。鋼材が鋼管である場合、観察面の厚さ中央位置とは、観察面において、鋼管の肉厚方向の中央位置を意味する。鋼材が鋼板である場合、観察面の厚さ中央位置とは、観察面において、鋼板の板厚方向の中央位置を意味する。鋼材が丸鋼である場合、観察面の厚さ中央位置とは、観察面において、丸鋼の径方向の中央位置を意味する。観察視野の総面積が１１２５ｍｍ２であれば、観察視野の個数は特に限定されない。観察視野の総面積が１１２５ｍｍ２となるように複数個の矩形の観察視野を選択する場合、観察面において複数の観察視野が一列に配列し、かつ、隣り合う観察視野の一辺が互いに接するように、複数の観察視野を選択する。
　例えば、各観察視野のサイズが１５ｍｍ×１５ｍｍの矩形である場合、観察視野の個数は５個とする（１５ｍｍ×１５ｍｍ×５個＝１１２５ｍｍ２）。また、観察面において５箇所の観察視野が一列に配列し、かつ、隣り合う観察視野の一辺（１５ｍｍ）が互いに接するように、５箇所の観察視野を選択する。 The observation surface of the prepared test piece is mirror-polished using a diamond paste abrasive. The observation field at the thickness center position of the mirror-polished observation surface is observed at 500 times magnification using a scanning electron microscope (SEM). When the steel material is a steel pipe, the thickness center position of the observation surface means the center position in the thickness direction of the steel pipe on the observation surface. When the steel material is a steel plate, the thickness center position of the observation surface means the center position in the thickness direction of the steel plate on the observation surface. When the steel material is a round steel, the thickness center position of the observation surface means the center position in the radial direction of the round steel on the observation surface. As long as the total area of the observation field is 1125 mm2 , the number of observation fields is not particularly limited. When selecting a plurality of rectangular observation fields so that the total area of the observation fields is 1125 mm2 , the observation fields are selected so that the observation fields are arranged in a row on the observation surface and one side of adjacent observation fields is in contact with each other.
For example, if the size of each observation field is a rectangle measuring 15 mm x 15 mm, the number of observation fields is five (15 mm x 15 mm x 5 = 1125 mm2 ). The five observation fields are selected so that they are arranged in a row on the observation surface and one side (15 mm) of adjacent observation fields touch each other.
　観察視野中の粒子をコントラストから特定する。特定された各粒子の円相当径（μｍ）を求める。ここで、円相当径とは、粒子の面積と同じ面積を有する円の直径（μｍ）を意味する。さらに、特定された各粒子について、元素濃度分析（ＥＤＳ分析）を実施する。元素濃度分析は、走査電子顕微鏡に元素濃度分析機能を備えた装置（ＳＥＭ－ＥＤＳ装置）を用いて実施することができる。元素濃度分析では、加速電圧を２０ｋＶとし、対象元素をＮ、Ｏ、Ｍｇ、Ａｌ、Ｓｉ、Ｐ、Ｓ、Ｃａ、Ｔｉ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｕ、Ｚｒ、及び、Ｎｂとして定量する。各粒子のＥＤＳ分析結果に基づいて、Ｎ、Ｏ、Ｍｇ、Ａｌ、Ｓｉ、Ｐ、Ｓ、Ｃａ、Ｔｉ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｕ、Ｚｒ、及び、Ｎｂの合計含有量を質量％で１００％とした場合に、微細Ｃａ酸硫化物と、微細Ｍｇ酸化物と、微細Ａｌ窒化物と、微細Ｔｉ窒化物とを以下のとおり特定する。 Particles in the observation field are identified from the contrast. The circle equivalent diameter (μm) of each identified particle is determined. Here, circle equivalent diameter means the diameter (μm) of a circle having the same area as the particle. Furthermore, element concentration analysis (EDS analysis) is performed on each identified particle. Element concentration analysis can be performed using a scanning electron microscope equipped with element concentration analysis function (SEM-EDS device). In element concentration analysis, the accelerating voltage is set to 20 kV, and the target elements are quantified as N, O, Mg, Al, Si, P, S, Ca, Ti, Cr, Mn, Fe, Cu, Zr, and Nb. Based on the EDS analysis results of each particle, when the total content of N, O, Mg, Al, Si, P, S, Ca, Ti, Cr, Mn, Fe, Cu, Zr, and Nb is taken as 100% by mass, the fine Ca oxysulfides, fine Mg oxides, fine Al nitrides, and fine Ti nitrides are identified as follows:
　円相当径が１．０～２．０μｍであり、質量％で、Ｃａ含有量及びＳ含有量の合計が５．０％よりも高く、Ｏ含有量が１．０％以上であり、Ｃａ含有量がＳ含有量よりも高い粒子を、「微細Ｃａ酸硫化物」と特定する。
　円相当径が１．０～２．０μｍであり、質量％で、Ｍｇ含有量が５．０％以上であり、Ｏ含有量が１．０％以上であり、Ｓ含有量が１５．０％以下である粒子を、「微細Ｍｇ酸化物」と特定する。
　円相当径が１．０～２．０μｍであり、質量％で、Ａｌ含有量が２０．０％以上であり、Ｎ含有量が２０．０％以上である粒子を、「微細Ａｌ窒化物」と特定する。
　円相当径が１．０～２．０μｍであり、質量％でＴｉ含有量が３０．０％以上であり、Ｎ含有量が２０．０％以上である粒子を、「微細Ｔｉ窒化物」と特定する。 Particles having an equivalent circle diameter of 1.0 to 2.0 μm, a total Ca content and S content of more than 5.0%, an O content of 1.0% or more, and a Ca content higher than the S content, are specified as "fine Ca oxysulfides".
Particles having an equivalent circle diameter of 1.0 to 2.0 μm and, in mass%, an Mg content of 5.0% or more, an O content of 1.0% or more, and an S content of 15.0% or less are specified as "fine Mg oxides".
Particles having an equivalent circle diameter of 1.0 to 2.0 μm, an Al content of 20.0% or more, and an N content of 20.0% or more, in mass %, are specified as "fine Al nitrides".
Particles having an equivalent circle diameter of 1.0 to 2.0 μm, a Ti content of 30.0% or more, and a N content of 20.0% or more, in mass %, are specified as "fine Ti nitrides".
　観察視野において、上述の方法で特定された微細Ｃａ酸硫化物、微細Ｍｇ酸化物、微細Ａｌ窒化物及び微細Ｔｉ窒化物を計数する。 In the observation field, count the number of fine Ca oxysulfides, fine Mg oxides, fine Al nitrides, and fine Ti nitrides identified using the method described above.
　全ての観察視野での微細Ｃａ酸硫化物、微細Ｍｇ酸化物、微細Ａｌ窒化物及び微細Ｔｉ窒化物の総個数と、観察視野の総面積とに基づいて、微細Ｃａ酸硫化物、微細Ｍｇ酸化物、微細Ａｌ窒化物、及び、微細Ｔｉ窒化物の総個数密度ＮＤ（個／ｍｍ２）を求める。総個数密度ＮＤは、得られた数値の小数第三位を四捨五入した小数第二位の数値とする。 Based on the total number of fine Ca oxysulfides, fine Mg oxides, fine Al nitrides and fine Ti nitrides in all observation fields and the total area of the observation fields, the total number density ND (pieces/ mm2 ) of fine Ca oxysulfides, fine Mg oxides, fine Al nitrides and fine Ti nitrides is calculated. The total number density ND is the value obtained by rounding off the obtained value to one decimal place.
　［製造方法］
　本実施形態の二相ステンレス鋼材の製造方法の一例を説明する。本実施形態の二相ステンレス鋼材の製造方法の一例は、素材製造工程と、熱間加工工程と、溶体化処理工程と、を含む。各工程について詳述する。 [Production method]
An example of a method for producing the duplex stainless steel material of this embodiment will be described. The example of the method for producing the duplex stainless steel material of this embodiment includes a material production process, a hot working process, and a solution treatment process. Each process will be described in detail.
　［素材製造工程］
　素材製造工程では、特徴１～特徴３を満たす素材を準備する。具体的には、特徴１～特徴３を満たす溶鋼を製造する。溶鋼の製造方法は特に限定されない。溶鋼は、転炉を用いて製造されてもよく、電炉を用いて製造されてもよく、その他の方法により製造されてもよい。 [Material manufacturing process]
In the material production process, a material satisfying Features 1 to 3 is prepared. Specifically, molten steel satisfying Features 1 to 3 is produced. The method for producing the molten steel is not particularly limited. The molten steel may be produced using a converter, an electric furnace, or another method.
　製造された溶鋼を用いて、素材を製造する。素材は例えば、鋳片又はインゴットである。具体的には、溶鋼を用いて連続鋳造法により鋳片を製造する。鋳片はスラブでもよいし、ブルームでもよいし、ビレットでもよい。又は、溶鋼を用いて造塊法によりインゴットとしてもよい。鋳片又はインゴットに対してさらに、熱間鍛造又は分塊圧延等を実施して、ビレットを製造してもよい。以上の工程により素材を製造する。 The produced molten steel is used to manufacture materials. The materials are, for example, slabs or ingots. Specifically, the molten steel is used to manufacture slabs by continuous casting. The slabs may be slabs, blooms, or billets. Alternatively, the molten steel may be used to make ingots by ingot casting. The slabs or ingots may be further subjected to hot forging or blooming to manufacture billets. The materials are manufactured by the above process.
　［熱間加工工程］
　熱間加工工程では、製造された素材に対して周知の熱間加工を実施して、中間鋼材を製造する。最終製品が鋼管の場合の中間鋼材は素管である。最終製品が丸鋼の場合の中間鋼材は棒状の鋼材である。最終製品が鋼板の場合の中間鋼材は板状の鋼材である。熱間加工は、熱間鍛造であってもよく、熱間押出であってもよく、熱間圧延であってもよい。熱間加工の方法は、特に限定されず、周知の方法でよい。 [Hot processing process]
In the hot working process, the manufactured material is subjected to well-known hot working to produce an intermediate steel material. When the final product is a steel pipe, the intermediate steel material is a blank pipe. When the final product is a round bar, the intermediate steel material is a bar-shaped steel material. When the final product is a steel plate, the intermediate steel material is a plate-shaped steel material. The hot working may be hot forging, hot extrusion, or hot rolling. The method of hot working is not particularly limited and may be a well-known method.
　最終製品が継目無鋼管の場合の熱間加工工程の一例は次のとおりである。初めに、素材であるビレットを加熱炉で加熱する。加熱温度は特に限定されないが、例えば、１０００～１３００℃である。加熱炉から抽出されたビレットに対して熱間加工を実施して、中間鋼材である素管（継目無鋼管）を製造する。熱間加工の方法は、特に限定されず、周知の方法でよい。例えば、熱間加工としてマンネスマン方式の穿孔圧延を実施して、素管を製造してもよい。この場合、穿孔機により丸ビレットを穿孔圧延する。穿孔圧延する場合、穿孔比は特に限定されないが、例えば、１．０～４．０である。穿孔圧延された丸ビレットをさらに、マンドレルミル、レデューサー、サイジングミル等により熱間圧延して素管にする。熱間加工工程での累積の減面率は例えば、２０～７０％である。他の熱間加工方法を実施して、ビレットから素管を製造してもよい。例えば、鋼材がカップリングのように短尺の厚肉鋼管の場合、エルハルト法等の鍛造により素管を製造してもよい。以上の工程により素管が製造される。 An example of a hot working process when the final product is a seamless steel pipe is as follows. First, the billet, which is the raw material, is heated in a heating furnace. The heating temperature is not particularly limited, but is, for example, 1000 to 1300°C. The billet extracted from the heating furnace is subjected to hot working to produce a blank pipe (seamless steel pipe), which is an intermediate steel material. The method of hot working is not particularly limited, and may be a well-known method. For example, the blank pipe may be produced by performing Mannesmann piercing rolling as hot working. In this case, the round billet is pierced and rolled using a piercing machine. When piercing and rolling is performed, the piercing ratio is not particularly limited, but is, for example, 1.0 to 4.0. The pierced and rolled round billet is further hot rolled using a mandrel mill, reducer, sizing mill, etc. to produce a blank pipe. The cumulative reduction in area in the hot working process is, for example, 20 to 70%. Other hot working methods may be performed to produce a blank pipe from the billet. For example, if the steel material is a short, thick-walled steel pipe such as a coupling, the blank pipe may be manufactured by forging using the Erhardt method or similar. The blank pipe is manufactured through the above process.
　最終製品が丸鋼の場合の熱間加工工程の一例は次のとおりである。初めに、素材を加熱炉で加熱する。加熱温度は特に限定されないが、例えば、１０００～１３００℃である。加熱炉から抽出された素材に対して熱間加工を実施して、軸方向に垂直な断面が円形の中間鋼材を製造する。熱間加工は例えば、分塊圧延機による分塊圧延、又は、連続圧延機による熱間圧延である。連続圧延機は、上下方向に並んで配置された一対の孔型ロールを有する水平スタンドと、水平方向に並んで配置された一対の孔型ロールを有する垂直スタンドとが交互に配列されている。 An example of a hot processing process when the final product is round steel is as follows. First, the material is heated in a heating furnace. The heating temperature is not particularly limited, but is, for example, 1000 to 1300°C. The material extracted from the heating furnace is subjected to hot processing to produce intermediate steel material with a circular cross section perpendicular to the axial direction. The hot processing is, for example, blooming using a blooming mill, or hot rolling using a continuous rolling mill. A continuous rolling mill has an alternating arrangement of horizontal stands having a pair of grooved rolls arranged side by side in the vertical direction, and vertical stands having a pair of grooved rolls arranged side by side in the horizontal direction.
　最終製品が鋼板の場合の熱間加工工程の一例は次のとおりである。初めに、素材を加熱炉で加熱する。加熱温度は特に限定されないが、例えば、１０００～１３００℃である。加熱炉から抽出された素材に対して、リバースミル、及び、タンデムミルを用いて熱間圧延を実施して、板状の中間鋼材を製造する。なお、熱間鍛造を実施して、その後、熱間鍛造後の素材を１０００～１３００℃に再加熱し、再加熱後の素材に対してさらに熱間圧延を実施して、板状の中間鋼材を製造してもよい。 An example of a hot processing process when the final product is a steel plate is as follows. First, the material is heated in a heating furnace. The heating temperature is not particularly limited, but is, for example, 1000 to 1300°C. The material extracted from the heating furnace is hot rolled using a reverse mill and a tandem mill to produce a plate-shaped intermediate steel material. It is also possible to perform hot forging, and then reheat the hot-forged material to 1000 to 1300°C, and further hot roll the reheated material to produce a plate-shaped intermediate steel material.
　［溶体化処理工程］
　溶体化処理工程では、熱間加工工程で製造された中間鋼材に対して、周知の溶体化処理を実施する。例えば、中間鋼材を熱処理炉に装入し、所望の温度で保持した後、急冷してもよい。なお、中間鋼材を熱処理炉に装入し、所望の温度で保持した後、急冷して溶体化処理を実施する場合、溶体化温度とは、溶体化処理を実施するための熱処理炉の温度（℃）を意味する。溶体化時間とは、中間鋼材が溶体化温度で保持される時間を意味する。溶体化温度は例えば、９００～１１００℃である。溶体化時間は例えば、５～１８０分である。溶体化処理での急冷方法は例えば、水冷である。 [Solution treatment process]
In the solution treatment process, a known solution treatment is performed on the intermediate steel material produced in the hot working process. For example, the intermediate steel material may be charged into a heat treatment furnace, held at a desired temperature, and then quenched. When the intermediate steel material is charged into a heat treatment furnace, held at a desired temperature, and then quenched to perform the solution treatment, the solution temperature means the temperature (°C) of the heat treatment furnace for performing the solution treatment. The solution time means the time during which the intermediate steel material is held at the solution temperature. The solution temperature is, for example, 900 to 1100°C. The solution time is, for example, 5 to 180 minutes. The quenching method in the solution treatment is, for example, water cooling.
　以上の製造方法により、本実施形態の二相ステンレス鋼材が製造される。 The duplex stainless steel material of this embodiment is produced by the above manufacturing method.
　［好ましい製造条件］
　本実施形態の二相ステンレス鋼材の製造方法は、好ましくは、次の条件１及び条件２を満たす。
　（条件１）
　素材製造工程において、溶鋼を鋳造するときの素材の表面温度が１３５０℃から１１００℃に至るまでの平均冷却速度ＣＲ１を８～２５℃／分とする。
　（条件２）
　溶体化処理工程において、溶体化温度で溶体化時間保持した後、中間素材の表面温度が溶体化温度から８５０℃に至るまでの平均冷却速度ＣＲ２を２００℃／分以下とし、中間素材の表面温度が８５０℃から３００℃に至るまでの平均冷却速度ＣＲ３を１０００℃／分以上とする。
　条件１及び条件２を満たせば、製造される二相ステンレス鋼材が特徴１～特徴３を満たし、さらに、特徴４を満たす。以下、条件１及び条件２について説明する。 [Preferable manufacturing conditions]
The method for producing the duplex stainless steel material of the present embodiment preferably satisfies the following conditions 1 and 2.
(Condition 1)
In the material manufacturing process, the average cooling rate CR1 during the process in which the surface temperature of the material when casting molten steel is from 1350° C. to 1100° C. is set to 8 to 25° C./min.
(Condition 2)
In the solution treatment step, after holding at the solution temperature for the solution time, the average cooling rate CR2 for the surface temperature of the intermediate material to decrease from the solution temperature to 850°C is set to 200°C/min or less, and the average cooling rate CR3 for the surface temperature of the intermediate material to decrease from 850°C to 300°C is set to 1000°C/min or more.
If condition 1 and condition 2 are satisfied, the produced duplex stainless steel material satisfies features 1 to 3 and further satisfies feature 4. Condition 1 and condition 2 will be explained below.
　［（条件１について）］
　特徴１～特徴３を満たす二相ステンレス鋼材では、溶鋼の鋳造時において、素材の表面温度が１３５０℃から１１００℃の温度域で、Ｃａ酸硫化物及びＭｇ酸化物が生成する。平均冷却速度ＣＲ１が遅すぎれば、Ｃａ酸硫化物及びＭｇ酸化物が粗大化する。この場合、微細Ｃａ酸硫化物及び微細Ｍｇ酸化物の個数密度が低くなる。その結果、総個数密度ＮＤが低くなる。一方、平均冷却速度ＣＲ１が速すぎれば、微細Ｃａ酸硫化物及び微細Ｍｇ酸化物の生成量が不足する。
　平均冷却速度ＣＲ１が８～２５℃／分であれば、条件２を満たすことを前提として、総個数密度ＮＤが２．００個／ｍｍ２以上となる。 [(Regarding condition 1)]
In a duplex stainless steel material satisfying Features 1 to 3, Ca oxysulfides and Mg oxides are generated when the surface temperature of the material is in the range of 1350°C to 1100°C during casting of molten steel. If the average cooling rate CR1 is too slow, the Ca oxysulfides and Mg oxides coarsen. In this case, the number density of the fine Ca oxysulfides and fine Mg oxides decreases. As a result, the total number density ND decreases. On the other hand, if the average cooling rate CR1 is too fast, the amount of fine Ca oxysulfides and fine Mg oxides generated becomes insufficient.
If the average cooling rate CR1 is 8 to 25° C./min, the total number density ND will be 2.00 pieces/mm 2 or more, assuming that condition 2 is satisfied.
　なお、平均冷却速度ＣＲ１を制御する方法は特に限定されず、周知の方法でよい。例えば、連続鋳造で素材を製造する場合、鋳片を冷却する冷却水の水量（比水量）を調整して、冷却速度を制御することができる。例えばさらに、造塊法で素材を製造する場合、鋳型の材質や鋳型の水冷によって、冷却速度を制御することができる。 The method for controlling the average cooling rate CR1 is not particularly limited, and any known method may be used. For example, when manufacturing a material by continuous casting, the cooling rate can be controlled by adjusting the amount of cooling water (specific water amount) used to cool the slab. Furthermore, when manufacturing a material by ingot casting, the cooling rate can be controlled by the material of the mold or the water cooling of the mold.
　なお、素材の表面温度は、非接触型の赤外線放射温度計により、測定することができる。素材の表面温度が１３５０℃から１１００℃に至るまでの時間を測定することにより、平均冷却速度ＣＲ１（℃／分）を求めることができる。 The surface temperature of the material can be measured using a non-contact infrared thermometer. The average cooling rate CR1 (°C/min) can be calculated by measuring the time it takes for the surface temperature of the material to drop from 1350°C to 1100°C.
　［（条件２について）］
　溶体化処理工程において、中間鋼材を熱処理炉から抽出してから中間鋼材の表面温度が８５０℃に至るまでの温度域Ｔ２は、微細Ａｌ窒化物及び微細Ｔｉ窒化物が生成する温度域である。温度域Ｔ２での平均冷却速度ＣＲ２が２００℃／分を超えれば、温度域Ｔ２で微細Ａｌ窒化物及び微細Ｔｉ窒化物の生成量が不足する。平均冷却速度ＣＲ２が２００℃／分以下であれば、十分な量の微細Ａｌ窒化物及び微細Ｔｉ窒化物が生成する。その結果、総個数密度ＮＤが２．００個／ｍｍ２以上となる。
　なお、中間鋼材の表面温度が８５０℃から３００℃に至るまでの平均冷却速度ＣＲ３は１０００℃／分以上とする。中間鋼材を水冷すれば、平均冷却速度ＣＲ３は１０００℃／分以上となる。 [(Regarding condition 2)]
In the solution treatment process, the temperature region T2 from when the intermediate steel is extracted from the heat treatment furnace until the surface temperature of the intermediate steel reaches 850°C is the temperature region in which fine Al nitrides and fine Ti nitrides are generated. If the average cooling rate CR2 in the temperature region T2 exceeds 200°C/min, the amount of fine Al nitrides and fine Ti nitrides generated in the temperature region T2 is insufficient. If the average cooling rate CR2 is 200°C/min or less, a sufficient amount of fine Al nitrides and fine Ti nitrides are generated. As a result, the total number density ND is 2.00 pieces/ mm2 or more.
The average cooling rate CR3 for the surface temperature of the intermediate steel material to decrease from 850° C. to 300° C. is set to 1000° C./min or more. If the intermediate steel material is water-cooled, the average cooling rate CR3 becomes 1000° C./min or more.
　中間鋼材の表面温度は、非接触型の赤外線放射温度計により、測定することができる。中間鋼材の表面温度が溶体化処理温度から８５０℃に至るまでの時間を測定することにより、平均冷却速度ＣＲ２（℃／分）を求めることができる。同様に、中間鋼材の表面温度が８５０℃から３００℃に至るまでの時間を測定することにより、平均冷却速度ＣＲ３（℃／分）を求めることができる。なお、上述のとおり、中間鋼材に対して水冷を実施すれば、平均冷却速度ＣＲ３は１０００℃／分以上となる。 The surface temperature of the intermediate steel can be measured with a non-contact infrared thermometer. The average cooling rate CR2 (°C/min) can be determined by measuring the time it takes for the surface temperature of the intermediate steel to reach 850°C from the solution treatment temperature. Similarly, the average cooling rate CR3 (°C/min) can be determined by measuring the time it takes for the surface temperature of the intermediate steel to reach 300°C from 850°C. As mentioned above, if water cooling is performed on the intermediate steel, the average cooling rate CR3 will be 1000°C/min or more.
　［その他の工程について］
　本実施形態による二相ステンレス鋼材の製造方法は、以上の工程以外の他の工程を実施してもよい。例えば、溶体化処理工程後の中間鋼材に対して、冷間加工工程を実施してもよい。つまり、冷間加工工程は任意の工程である。 [Other processes]
The method for producing a duplex stainless steel material according to the present embodiment may include other steps in addition to the steps described above. For example, a cold working step may be performed on the intermediate steel material after the solution treatment step. In other words, the cold working step is an optional step.
　冷間加工工程では、中間鋼材に対して周知の冷間加工を実施する。冷間加工は例えば、冷間引抜であってもよく、冷間圧延であってもよい。溶体化処理後の中間鋼材に対して冷間加工を実施することにより、二相ステンレス鋼材の強度を高めることができる。 In the cold working process, the intermediate steel material is subjected to well-known cold working. The cold working may be, for example, cold drawing or cold rolling. By performing cold working on the intermediate steel material after the solution treatment, the strength of the duplex stainless steel material can be increased.
　なお、上述の製造方法一例である。したがって、本実施形態の二相ステンレス鋼材の製造方法は、上述の一例に限定されない。 Note that the above is just one example of the manufacturing method. Therefore, the manufacturing method of the duplex stainless steel material of this embodiment is not limited to the above example.
　実施例により本実施形態の二相ステンレス鋼材の効果をさらに具体的に説明する。以下の実施例での条件は、本実施形態の二相ステンレス鋼材の実施可能性及び効果を確認するために採用した一条件例である。したがって、本実施形態の二相ステンレス鋼材はこの一条件例に限定されない。 The effects of the duplex stainless steel material of this embodiment will be explained more specifically using examples. The conditions in the following examples are one example of conditions adopted to confirm the feasibility and effects of the duplex stainless steel material of this embodiment. Therefore, the duplex stainless steel material of this embodiment is not limited to this one example of conditions.
　表１－１及び表１－２に示す化学組成を有する二相ステンレス鋼材を製造した。 Duplex stainless steel materials were manufactured with the chemical compositions shown in Tables 1-1 and 1-2.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　表１－１及び表１－２中の「－」は、該当する元素の含有量が不純物レベルであったことを意味する。例えば、試験番号１のＶ含有量は、小数第三位を四捨五入して、０％であったことを意味する。試験番号２のＣａ含有量は、小数第五位を四捨五入して、０％であったことを意味する。 The "-" in Tables 1-1 and 1-2 means that the content of the corresponding element was at the impurity level. For example, the V content of test number 1, rounded off to the third decimal place, was 0%. The Ca content of test number 2, rounded off to the fifth decimal place, was 0%.
　各試験番号の３０ｋｇの溶鋼を、高周波真空溶解炉を用いて溶製した。溶鋼を用いて、造塊法によりインゴットを製造した。鋳造時において、インゴットの表面温度が１３５０℃から１１００℃に至るまでの平均冷却速度ＣＲ１（℃／分）は、表２中の「ＣＲ１（℃／分）」欄に示すとおりであった。 30 kg of molten steel for each test number was melted using a high-frequency vacuum melting furnace. The molten steel was used to manufacture ingots by the ingot casting method. During casting, the average cooling rate CR1 (°C/min) at which the surface temperature of the ingot decreased from 1350°C to 1100°C was as shown in the "CR1 (°C/min)" column in Table 2.
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　各試験番号のインゴットを１２００℃で３時間加熱した。加熱後のインゴットに対して熱間鍛造を実施して、長手方向に垂直な断面が７０ｍｍ×１００ｍｍの中間鋼材を製造した。中間鋼材を１２５０℃で１時間加熱した。加熱後の中間鋼材に対して熱間圧延を実施して、板厚１７ｍｍの鋼板状の中間鋼材とした。 The ingots of each test number were heated at 1200°C for 3 hours. After heating, the ingots were hot forged to produce intermediate steel materials with a cross section perpendicular to the longitudinal direction of 70 mm x 100 mm. The intermediate steel materials were heated at 1250°C for 1 hour. After heating, the intermediate steel materials were hot rolled to produce intermediate steel materials in the form of steel plates with a thickness of 17 mm.
　熱間圧延後の中間鋼材に対して、溶体化処理を実施した。溶体化温度は９５０℃とし、溶体化温度での保持時間は１５分とした。保持時間経過後の中間鋼材を冷却した。具体的には、中間素材の表面温度が溶体化温度（９５０℃）から８５０℃に至るまでの平均冷却速度ＣＲ２は表２中の「ＣＲ２（℃／分）」欄に示すとおりであった。また、いずれの試験番号においても、その後の冷却は水冷を実施した。そのため、中間素材の表面温度が８５０℃から３００℃に至るまでの平均冷却速度ＣＲ３は１０００℃／分以上であった。
　以上の製造工程により、各試験番号の二相ステンレス鋼材（鋼板）を製造した。 The intermediate steel material after hot rolling was subjected to a solution treatment. The solution temperature was 950°C, and the holding time at the solution temperature was 15 minutes. The intermediate steel material was cooled after the holding time had elapsed. Specifically, the average cooling rate CR2 at which the surface temperature of the intermediate material was reduced from the solution temperature (950°C) to 850°C was as shown in the "CR2 (°C/min)" column in Table 2. In addition, in all test numbers, the subsequent cooling was performed by water cooling. Therefore, the average cooling rate CR3 at which the surface temperature of the intermediate material was reduced from 850°C to 300°C was 1000°C/min or more.
Through the above manufacturing process, duplex stainless steel materials (steel plates) of each test number were manufactured.
　なお、各試験番号の二相ステンレス鋼材のミクロ組織を上述の「ミクロ組織観察方法」に記載の方法で観察した。なお、ミクロ組織観察では、鋼板の板厚中央位置から、圧延方向に５ｍｍ、板厚方向に５ｍｍの観察面を有する試験片を作製した。その結果、いずれの試験番号においても、二相ステンレス鋼材のミクロ組織はフェライト及びオーステナイトからなり、フェライトの体積率は３０～８０％であった。 The microstructure of the duplex stainless steel material of each test number was observed using the method described in the "Microstructure Observation Method" above. For the microstructure observation, test pieces were prepared with an observation surface 5 mm in the rolling direction and 5 mm in the thickness direction from the center of the steel plate thickness. As a result, the microstructure of the duplex stainless steel material of each test number was composed of ferrite and austenite, with the volume fraction of ferrite being 30-80%.
　［評価試験］
　各試験番号の二相ステンレス鋼材に対して、次の評価試験を実施した。
　（試験１）総個数密度ＮＤの測定試験
　（試験２）高温高圧強酸性腐食環境での耐全面腐食性評価試験
　（試験３）高温高圧塩化物腐食環境での耐孔食性評価試験
　以下、試験１～試験３について説明する。 [Evaluation test]
The following evaluation tests were carried out on the duplex stainless steel materials with each test number.
(Test 1) Measurement test of total number density ND (Test 2) Evaluation test of general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosive environment (Test 3) Evaluation test of pitting corrosion resistance in a high-temperature, high-pressure chloride corrosive environment Tests 1 to 3 will be described below.
　［（試験１）総個数密度ＮＤの測定試験］
　上述の［総個数密度ＮＤの測定方法］に記載の方法で、各試験番号の二相ステンレス鋼材での微細Ｃａ酸硫化物、微細Ｍｇ酸化物、微細Ａｌ窒化物及び微細Ｔｉ窒化物の総個数密度ＮＤ（個／ｍｍ２）を求めた。なお、試験片の観察面において、観察視野のサイズは１５ｍｍ×１５ｍｍの矩形とし、観察視野の個数は５個とした。ＳＥＭにより５００倍で観察した。得られた総個数密度ＮＤを表２中の「ＮＤ（個／ｍｍ２）」欄に示す。 [(Test 1) Measurement test of total number density ND]
The total number density ND (pieces/mm2) of fine Ca oxysulfides, fine Mg oxides, fine Al nitrides and fine Ti nitrides in the duplex stainless steel material of each test number was determined using the method described in [Method for measuring total number density ND] above. The size of the observation field on the observation surface of the test piece was a rectangle of 15 mm x 15 mm, and the number of observation fields was 5. Observation was performed at 500 times magnification using an SEM. The obtained total number density ND is shown in the "ND (pieces/ mm2 )" column in Table 2.
　［（試験２）高温高圧強酸性腐食環境での耐全面腐食性評価試験］
　上述の［高温高圧強酸性腐食環境での耐全面腐食性評価試験］に記載の方法で、各試験番号の二相ステンレス鋼材の高温高圧強酸性腐食環境での腐食速度（ｇ・ｃｍ－２・ｈ－１）を求めた。腐食生成物の試験片からの除去は、ＡＳＴＭ　Ｇ３１－２１に規定の方法に基づいて行った。試験片のサイズは、長さ：４０ｍｍ、幅：１０ｍｍ、厚さ：３ｍｍとした。得られた腐食速度を、表２中の「高温高圧強酸性腐食環境」欄の「腐食速度（ｇ・ｃｍ－２・ｈ－１）」欄に示す。 [(Test 2) General corrosion resistance evaluation test in a high-temperature, high-pressure, strong acidic corrosive environment]
The corrosion rate (g cm -2 h -1 ) of the duplex stainless steel material of each test number in a high-temperature, high-pressure, strong acidic corrosive environment was determined by the method described in the above-mentioned [Evaluation test of general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosive environment]. The corrosion products were removed from the test pieces based on the method specified in ASTM G31-21. The size of the test pieces was 40 mm in length, 10 mm in width, and 3 mm in thickness. The obtained corrosion rates are shown in the "Corrosion rate (g cm -2 h -1 )" column in the "High-temperature, high-pressure, strong acidic corrosive environment" column in Table 2.
　［（試験３）高温高圧塩化物腐食環境での耐孔食性評価試験］
　上述の［高温高圧塩化物腐食環境での耐孔食性評価試験］に記載の方法で、各試験番号の二相ステンレス鋼材の高温高圧塩化物腐食環境での腐食速度（ｇ・ｃｍ－２・ｈ－１）を求め、かつ、孔食の有無を確認した。腐食生成物の試験片からの除去は、ＡＳＴＭ　Ｇ３１－２１に規定の方法に基づいて行った。試験片のサイズは、長さ：４０ｍｍ、幅：１０ｍｍ、厚さ：３ｍｍとした。得られた腐食速度を、表２中の「高温高圧塩化物腐食環境」欄の「腐食速度（ｇ・ｃｍ－２・ｈ－１）」欄に示し、孔食の有無を「孔食」欄に示す。 [(Test 3) Pitting corrosion resistance evaluation test in a high-temperature, high-pressure chloride corrosion environment]
The corrosion rate (g cm -2 h -1 ) of the duplex stainless steel material of each test number in a high-temperature, high-pressure chloride corrosion environment was determined and the presence or absence of pitting corrosion was confirmed by the method described in the above-mentioned [Evaluation test of pitting corrosion resistance in a high-temperature, high-pressure chloride corrosion environment]. The corrosion products were removed from the test pieces based on the method specified in ASTM G31-21. The size of the test pieces was length: 40 mm, width: 10 mm, and thickness: 3 mm. The obtained corrosion rates are shown in the "Corrosion rate (g cm -2 h -1 )" column of the "High-temperature, high-pressure chloride corrosion environment" column in Table 2, and the presence or absence of pitting corrosion is shown in the "Pitting corrosion" column.
　［評価結果］
　評価結果を表２に示す。なお、表２中の「Ｆｎ１」欄には、各試験番号のＦｎ１を示し、「Ｆｎ２」欄には、各試験番号のＦｎ２を示す。 [Evaluation results]
The evaluation results are shown in Table 2. In Table 2, the "Fn1" column shows Fn1 for each test number, and the "Fn2" column shows Fn2 for each test number.
　表１－１、表１－２及び表２を参照して、試験番号１～３９の二相ステンレス鋼材は特徴１～特徴３を満たした。そのため、高温高圧強酸性腐食環境での腐食速度が０．１００ｇ・ｃｍ－２・ｈ－１以下となった。さらに、高温高圧塩化物腐食環境での腐食速度が０．００５ｇ・ｃｍ－２・ｈ－１以下となり、孔食も確認されなかった。したがって、これらの試験番号の二相ステンレス鋼材では、高温高圧強酸性腐食環境での優れた耐全面腐食性が得られ、高温高圧塩化物腐食環境での優れた耐孔食性が得られた。 With reference to Tables 1-1, 1-2, and 2, the duplex stainless steel materials of test numbers 1 to 39 satisfied features 1 to 3. Therefore, the corrosion rate in a high-temperature, high-pressure, strongly acidic corrosion environment was 0.100 g cm -2 h -1 or less. Furthermore, the corrosion rate in a high-temperature, high-pressure chloride corrosion environment was 0.005 g cm -2 h -1 or less, and no pitting corrosion was observed. Therefore, the duplex stainless steel materials of these test numbers obtained excellent general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosion environment, and excellent pitting corrosion resistance in a high-temperature, high-pressure chloride corrosion environment.
　さらに、試験番号１～３９のうち、試験番号１～１０、１２～２２、２４～３６、３８及び３９では、製造工程において、上述の条件１及び条件２を満たした。そのため、これらの試験番号の二相ステンレス鋼材では、特徴１～特徴３を満たし、さらに、特徴４を満たした。その結果、これらの試験番号の二相ステンレス鋼材では、高温高圧強酸性腐食環境での腐食速度がさらに優れた。 Furthermore, among test numbers 1 to 39, test numbers 1 to 10, 12 to 22, 24 to 36, 38 and 39 met the above-mentioned conditions 1 and 2 in the manufacturing process. Therefore, the duplex stainless steel materials of these test numbers met characteristics 1 to 3, and also characteristic 4. As a result, the duplex stainless steel materials of these test numbers had even better corrosion rates in high-temperature, high-pressure, strongly acidic corrosive environments.
　具体的には、試験番号１～３９では、同程度のＦｎ１値である場合、特徴１～特徴４を満たす二相ステンレス鋼材の方が、特徴１～特徴３を満たし特徴４を満たさなかった二相ステンレス鋼材よりも、さらに優れた耐全面腐食性が得られた。 Specifically, in test numbers 1 to 39, when the Fn1 values were similar, duplex stainless steel materials that satisfied characteristics 1 to 4 exhibited superior general corrosion resistance compared to duplex stainless steel materials that satisfied characteristics 1 to 3 but did not satisfy characteristic 4.
　例えば、試験番号１１及び試験番号１４に注目すると、試験番号１１のＦｎ１は０．８９であり、試験番号１４のＦｎ１（＝０．８７）と近い値であった。しかしながら、試験番号１１の二相ステンレス鋼材は特徴１～特徴３を満たすものの特徴４を満たさず、試験番号１４の二相ステンレス鋼材は特徴１～特徴４を満たした。その結果、試験番号１４の高温高圧強酸性腐食環境での腐食速度は試験番号１１よりも遅く、高温高圧強酸性腐食環境において、さらに優れた耐全面腐食性が得られた。 For example, looking at test numbers 11 and 14, Fn1 for test number 11 was 0.89, a value close to Fn1 for test number 14 (=0.87). However, the duplex stainless steel material of test number 11 met characteristics 1 to 3 but did not meet characteristic 4, whereas the duplex stainless steel material of test number 14 met characteristics 1 to 4. As a result, the corrosion rate of test number 14 in a high-temperature, high-pressure, strongly acidic corrosion environment was slower than that of test number 11, and even better general corrosion resistance was obtained in a high-temperature, high-pressure, strongly acidic corrosion environment.
　同様に、試験番号１８及び試験番号２３に注目すると、試験番号１８のＦｎ１は８．７８であり、試験番号２３のＦｎ１（＝８．３３）と近い値であった。しかしながら、試験番号１８の二相ステンレス鋼材は特徴１～特徴４を満たし、試験番号２３の二相ステンレス鋼材は特徴１～特徴３を満たすものの特徴４を満たさなかった。その結果、試験番号１８の高温高圧強酸性腐食環境での腐食速度は試験番号２３よりも遅く、高温高圧強酸性腐食環境において、さらに優れた耐全面腐食性が得られた。 Similarly, looking at test numbers 18 and 23, Fn1 for test number 18 was 8.78, a value close to Fn1 for test number 23 (= 8.33). However, the duplex stainless steel material for test number 18 met characteristics 1 to 4, while the duplex stainless steel material for test number 23 met characteristics 1 to 3 but did not meet characteristic 4. As a result, the corrosion rate of test number 18 in a high-temperature, high-pressure, strongly acidic corrosion environment was slower than that of test number 23, and even better general corrosion resistance was obtained in a high-temperature, high-pressure, strongly acidic corrosion environment.
　試験番号９と試験番号３７とに注目すると、試験番号９のＦｎ１は１．４１であり、試験番号３７のＦｎ１（＝１．４５）と近い値であった。しかしながら、試験番号９の二相ステンレス鋼材は特徴１～特徴４を満たし、試験番号３７の二相ステンレス鋼材は特徴１～特徴３を満たすものの特徴４を満たさなかった。その結果、試験番号９の高温高圧強酸性腐食環境での腐食速度は試験番号３７よりも遅く、高温高圧強酸性腐食環境において、さらに優れた耐全面腐食性が得られた。 Looking at test numbers 9 and 37, Fn1 for test number 9 was 1.41, a value close to Fn1 for test number 37 (= 1.45). However, the duplex stainless steel material for test number 9 met characteristics 1 to 4, while the duplex stainless steel material for test number 37 met characteristics 1 to 3 but did not meet characteristic 4. As a result, the corrosion rate of test number 9 in a high-temperature, high-pressure, strongly acidic corrosion environment was slower than that of test number 37, and even better general corrosion resistance was obtained in a high-temperature, high-pressure, strongly acidic corrosion environment.
　特に、Ｆｎ１が０．７０超～５．５０未満の場合に、特徴１～特徴４を満たす二相ステンレス鋼材（試験番号１、４～６、９、１２～１７、２２、２４～２６、３１、３２、３５、３６、３８及び３９）では、高温高圧強酸性腐食環境での腐食速度がいずれも０．０８０ｇ・ｃｍ－２・ｈ－１以下であった。一方、Ｆｎ１が０．７０超～５．５０未満の場合に、特徴１～特徴３を満たし、特徴４を満たさなかった二相ステンレス鋼材（試験番号１１及び３７）では、高温高圧強酸性腐食環境での腐食速度が０．１００ｇ・ｃｍ－２・ｈ－１以下であったものの、０．０８０ｇ・ｃｍ－２・ｈ－１を超えた。 In particular, when Fn1 was greater than 0.70 and less than 5.50, the corrosion rates in a high-temperature, high-pressure, strongly acidic corrosive environment were all 0.080 g cm -2 h -1 or less for the duplex stainless steel materials (Test Nos. 1, 4 to 6, 9, 12 to 17, 22, 24 to 26, 31, 32, 35, 36, 38, and 39) that satisfied Features 1 to 4. On the other hand, when Fn1 was greater than 0.70 and less than 5.50, the corrosion rates in a high-temperature, high-pressure, strongly acidic corrosive environment for the duplex stainless steel materials (Test Nos. 11 and 37) that satisfied Features 1 to 3 but did not satisfy Features 4 were 0.100 g cm-2 h -1 or less, but exceeded 0.080 g cm -2 h -1 .
　なお、試験番号２、３、７、８、１０、１８～２１、２３、２７～３０、３３及び３４では、Ｆｎ１が５．５０以上であった。そのため、これらの試験番号の二相ステンレス鋼材では、特徴４を満たすか否かに関わらず、高温高圧強酸性腐食環境での腐食速度が０．０４０ｇ・ｃｍ－２・ｈ－１以下となり、高温高圧強酸性腐食環境においてさらに優れた耐全面腐食性が得られた。 In addition, Fn1 was 5.50 or more in test numbers 2, 3, 7, 8, 10, 18 to 21, 23, 27 to 30, 33, and 34. Therefore, in the duplex stainless steel materials of these test numbers, regardless of whether or not they satisfied feature 4, the corrosion rate in a high-temperature, high-pressure, strongly acidic corrosive environment was 0.040 g cm -2 h -1 or less, and further excellent general corrosion resistance was obtained in a high-temperature, high-pressure, strongly acidic corrosive environment.
　一方、試験番号４０では、Ｃｒ含有量が低すぎた。そのため、高温高圧強酸性腐食環境での腐食速度が０．１００ｇ・ｃｍ－２・ｈ－１を超え、高温高圧強酸性腐食環境での優れた耐全面腐食性が得られなかった。さらに、高温高圧塩化物腐食環境での腐食速度が０．００５ｇ・ｃｍ－２・ｈ－１を超え、孔食も確認され、高温高圧塩化物腐食環境での優れた耐孔食性が得られなかった。 On the other hand, in test number 40, the Cr content was too low. Therefore, the corrosion rate in a high-temperature, high-pressure, strong acidic corrosion environment exceeded 0.100 g cm -2 h -1 , and excellent general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosion environment was not obtained. Furthermore, the corrosion rate in a high-temperature, high-pressure chloride corrosion environment exceeded 0.005 g cm -2 h -1 , and pitting corrosion was also confirmed, and excellent pitting corrosion resistance in a high-temperature, high-pressure chloride corrosion environment was not obtained.
　試験番号４１及び４２では、Ａｓ含有量が低すぎた。そのため、高温高圧強酸性腐食環境での腐食速度が０．１００ｇ・ｃｍ－２・ｈ－１を超え、高温高圧強酸性腐食環境での優れた耐全面腐食性が得られなかった。 In test numbers 41 and 42, the As content was too low. As a result, the corrosion rate in a high-temperature, high-pressure, strongly acidic corrosive environment exceeded 0.100 g cm -2 h -1 , and excellent general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment was not obtained.
　試験番４３では、Ｃａ及びＭｇの合計含有量が低すぎた。そのため、高温高圧強酸性腐食環境での腐食速度が０．１００ｇ・ｃｍ－２・ｈ－１を超え、高温高圧強酸性腐食環境での優れた耐全面腐食性が得られなかった。 In test number 43, the total content of Ca and Mg was too low, so that the corrosion rate in a high-temperature, high-pressure, strong acidic corrosive environment exceeded 0.100 g cm -2 h -1 , and excellent general corrosion resistance in a high-temperature, high-pressure, strong acidic corrosive environment was not obtained.
　試験番号４４～４６では、特徴１を満たすものの、Ｆｎ１が高すぎた。そのため、製造工程中でインゴットを熱間鍛造する工程において、割れが発生した。そのため、これらの試験番号については、熱間鍛造以降の製造工程及び試験を実施しなかった。 　Test numbers 44 to 46 met characteristic 1, but Fn1 was too high. As a result, cracks occurred during the hot forging process of the ingots in the manufacturing process. Therefore, for these test numbers, manufacturing processes and tests after hot forging were not carried out.
　試験番号４７～４９では、特徴１を満たすものの、Ｆｎ１が低すぎた。そのため、高温高圧強酸性腐食環境での腐食速度が０．１００ｇ・ｃｍ－２・ｈ－１を超え、高温高圧強酸性腐食環境での優れた耐全面腐食性が得られなかった。 In test numbers 47 to 49, although characteristic 1 was satisfied, Fn1 was too low. Therefore, the corrosion rate in a high-temperature, high-pressure, strongly acidic corrosive environment exceeded 0.100 g cm -2 h -1 , and excellent general corrosion resistance in a high-temperature, high-pressure, strongly acidic corrosive environment was not obtained.
　試験番号５０～５２では、特徴１を満たすものの、Ｆｎ２が高すぎた。高温高圧塩化物腐食環境での腐食速度が０．００５ｇ・ｃｍ－２・ｈ－１を超え、孔食も確認され、高温高圧塩化物腐食環境での優れた耐孔食性が得られなかった。 In test numbers 50 to 52, although characteristic 1 was satisfied, Fn2 was too high. The corrosion rate in a high-temperature, high-pressure chloride corrosive environment exceeded 0.005 g cm -2 h -1 , and pitting corrosion was also confirmed, so that excellent pitting corrosion resistance in a high-temperature, high-pressure chloride corrosive environment was not obtained.
　以上、本開示の実施の形態を説明した。しかしながら、上述した実施の形態は本開示を実施するための例示に過ぎない。したがって、本開示は上述した実施の形態に限定されることなく、その趣旨を逸脱しない範囲内で上述した実施の形態を適宜変更して実施することができる。 The above describes the embodiments of the present disclosure. However, the above-described embodiments are merely examples for implementing the present disclosure. Therefore, the present disclosure is not limited to the above-described embodiments, and can be implemented by modifying the above-described embodiments as appropriate within the scope of the spirit of the present disclosure.

Claims (3)

  1. 　化学組成が、質量％で、
    　Ｃ：０．０５０％以下、
    　Ｓｉ：０．２～１．２％、
    　Ｍｎ：０．５～７．０％、
    　Ｐ：０．０４０％以下、
    　Ｓ：０．０１０％以下、
    　Ｃｒ：２０．０～２７．０％、
    　Ｎｉ：４．０～９．０％、
    　Ｍｏ：０．５～５．０％、
    　Ａｓ：０．０００５～０．０１００％、
    　Ｃａ及びＭｇの１種以上：合計で０．０００５～０．０１００％、
    　ｓｏｌ．Ａｌ：０．００１～０．０５０％、
    　Ｎ：０．４０％以下、
    　Ｏ：０．１００％以下、
    　Ｃｕ：０～４．０％、
    　Ｖ：０～１．５０％、
    　Ｃｏ：０～２．００％、
    　Ｔａ：０～２．００％、
    　Ｗ：０～４．００％、
    　Ｎｂ：０～２．００％、
    　Ｔｉ：０～２．００％、
    　Ｚｎ：０～０．０１００％、
    　Ｐｂ：０～０．０１００％、
    　Ｓｂ：０～０．０１００％、
    　Ｓｎ：０～０．０１００％、
    　Ｂｉ：０～０．０１００％、
    　Ｂ：０～０．０１００％、
    　希土類元素：０～０．０５０％、
    　Ｚｒ：０～２．００％、
    　Ｈｆ：０～２．００％、及び、
    　残部がＦｅ及び不純物からなり、
    　式（１）及び（２）を満たす、
    　二相ステンレス鋼材。
    　０．７０＜１００００×Ａｓ／（Ｎｉ＋Ｃｕ）＜１６．００　（１）
    　（Ｃａ＋Ｍｇ）／Ｏ＜１．５０　（２）
    　ここで、式中の各元素記号には、対応する元素の質量％での含有量が代入される。元素が含有されていない場合、対応する元素記号には「０」が代入される。     The chemical composition, in mass%, is
    C: 0.050% or less,
    Si: 0.2 to 1.2%,
    Mn: 0.5 to 7.0%,
    P: 0.040% or less,
    S: 0.010% or less,
    Cr: 20.0 to 27.0%,
    Ni: 4.0 to 9.0%,
    Mo: 0.5 to 5.0%,
    As: 0.0005 to 0.0100%,
    One or more of Ca and Mg: 0.0005 to 0.0100% in total,
    sol. Al: 0.001 to 0.050%,
    N: 0.40% or less,
    O: 0.100% or less,
    Cu: 0 to 4.0%,
    V: 0 to 1.50%,
    Co: 0 to 2.00%,
    Ta: 0 to 2.00%,
    W: 0 to 4.00%,
    Nb: 0 to 2.00%,
    Ti: 0 to 2.00%,
    Zn: 0 to 0.0100%,
    Pb: 0 to 0.0100%,
    Sb: 0 to 0.0100%,
    Sn: 0 to 0.0100%,
    Bi: 0 to 0.0100%,
    B: 0 to 0.0100%,
    Rare earth elements: 0 to 0.050%,
    Zr: 0 to 2.00%,
    Hf: 0 to 2.00%, and
    The balance is Fe and impurities,
    Satisfying formulas (1) and (2),
    Duplex stainless steel material.
    0.70<10000×As/(Ni+Cu)<16.00 (1)
    (Ca+Mg)/O<1.50 (2)
    Here, each element symbol in the formula is substituted with the content of the corresponding element in mass %. When an element is not contained, the corresponding element symbol is substituted with "0".
  2. 　請求項１に記載の二相ステンレス鋼材であって、
    　円相当径が１．０～２．０μｍであり、質量％で、Ｃａ含有量及びＳ含有量の合計が５．０％よりも高く、Ｏ含有量が１．０％以上であり、Ｃａ含有量がＳ含有量よりも高い粒子を微細Ｃａ酸硫化物と定義し、
    　円相当径が１．０～２．０μｍであり、質量％で、Ｍｇ含有量が５．０％以上であり、Ｏ含有量が１．０％以上であり、Ｓ含有量が１５．０％以下である粒子を微細Ｍｇ酸化物と定義し、
    　円相当径が１．０～２．０μｍであり、質量％で、Ａｌ含有量が２０．０％以上であり、Ｎ含有量が２０．０％以上である粒子を微細Ａｌ窒化物と定義し、
    　円相当径が１．０～２．０μｍであり、質量％でＴｉ含有量が３０．０％以上であり、Ｎ含有量が２０．０％以上である粒子を微細Ｔｉ窒化物と定義したとき、
    　前記微細Ｃａ酸硫化物、前記微細Ｍｇ酸化物、前記微細Ａｌ窒化物、及び、前記微細Ｔｉ窒化物の総個数密度は２．００個／ｍｍ２以上である、
    　二相ステンレス鋼材。     2. The duplex stainless steel material according to claim 1,
    Fine Ca oxysulfides are defined as particles having an equivalent circle diameter of 1.0 to 2.0 μm, a total of Ca content and S content of more than 5.0%, an O content of 1.0% or more, and a Ca content higher than a S content, in terms of mass%,
    Fine Mg oxide particles are defined as particles having an equivalent circle diameter of 1.0 to 2.0 μm, and, in mass%, an Mg content of 5.0% or more, an O content of 1.0% or more, and an S content of 15.0% or less.
    Particles having an equivalent circle diameter of 1.0 to 2.0 μm, an Al content of 20.0% or more, and an N content of 20.0% or more, in mass%, are defined as fine Al nitrides;
    When particles having a circle equivalent diameter of 1.0 to 2.0 μm, a Ti content of 30.0% or more, and a N content of 20.0% or more are defined as fine Ti nitrides,
    The total number density of the fine Ca oxysulfides, the fine Mg oxides, the fine Al nitrides, and the fine Ti nitrides is 2.00 pieces/ mm2 or more;
    Duplex stainless steel material.
  3. 　請求項１又は請求項２に記載の二相ステンレス鋼材であって、
    　前記化学組成は、
    　Ｃｕ：０．１～４．０％、
    　Ｖ：０．０１～１．５０％、
    　Ｃｏ：０．０１～２．００％、
    　Ｔａ：０．０１～２．００％、
    　Ｗ：０．０１～４．００％、
    　Ｎｂ：０．０１～２．００％、
    　Ｔｉ：０．０１～２．００％、
    　Ｚｎ：０．０００１～０．０１００％、
    　Ｐｂ：０．０００１～０．０１００％、
    　Ｓｂ：０．０００１～０．０１００％、
    　Ｓｎ：０．０００１～０．０１００％、
    　Ｂｉ：０．０００１～０．０１００％、
    　Ｂ：０．０００１～０．０１００％、
    　希土類元素：０．００１～０．０５０％、
    　Ｚｒ：０．０１～２．００％、及び、
    　Ｈｆ：０．０１～２．００％、からなる群から選択される１種以上を含有する、
    　二相ステンレス鋼材。     The duplex stainless steel material according to claim 1 or 2,
    The chemical composition is
    Cu: 0.1 to 4.0%,
    V: 0.01 to 1.50%,
    Co: 0.01 to 2.00%,
    Ta: 0.01 to 2.00%,
    W: 0.01 to 4.00%,
    Nb: 0.01 to 2.00%,
    Ti: 0.01 to 2.00%,
    Zn: 0.0001 to 0.0100%,
    Pb: 0.0001 to 0.0100%,
    Sb: 0.0001 to 0.0100%,
    Sn: 0.0001 to 0.0100%,
    Bi: 0.0001 to 0.0100%,
    B: 0.0001 to 0.0100%,
    Rare earth elements: 0.001 to 0.050%,
    Zr: 0.01 to 2.00%, and
    Hf: 0.01 to 2.00%,
    Duplex stainless steel material.
PCT/JP2023/036160 2022-10-06 2023-10-04 Duplex stainless steel material WO2024075761A1 (en)

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2017002352A (en) * 2015-06-09 2017-01-05 株式会社神戸製鋼所 Duplex stainless steel material and duplex stainless steel pipe
WO2022145061A1 (en) * 2020-12-28 2022-07-07 日本製鉄株式会社 Steel material

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2017002352A (en) * 2015-06-09 2017-01-05 株式会社神戸製鋼所 Duplex stainless steel material and duplex stainless steel pipe
WO2022145061A1 (en) * 2020-12-28 2022-07-07 日本製鉄株式会社 Steel material

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