WO2020166668A1 - サワー環境での使用に適した鋼材 - Google Patents

サワー環境での使用に適した鋼材 Download PDF

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WO2020166668A1
WO2020166668A1 PCT/JP2020/005617 JP2020005617W WO2020166668A1 WO 2020166668 A1 WO2020166668 A1 WO 2020166668A1 JP 2020005617 W JP2020005617 W JP 2020005617W WO 2020166668 A1 WO2020166668 A1 WO 2020166668A1
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steel material
content
tempering
steel
test
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PCT/JP2020/005617
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English (en)
French (fr)
Japanese (ja)
Inventor
裕紀 神谷
陽平 乙▲め▼
貴志 相馬
大江　太郎
伸明 小松原
晋士 吉田
勇次 荒井
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日本製鉄株式会社
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Priority to EP20755579.8A priority Critical patent/EP3926059A4/de
Priority to US17/422,870 priority patent/US20220098712A1/en
Priority to BR112021013441-7A priority patent/BR112021013441A2/pt
Priority to JP2020572313A priority patent/JP7036237B2/ja
Priority to MX2021009588A priority patent/MX2021009588A/es
Publication of WO2020166668A1 publication Critical patent/WO2020166668A1/ja

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Definitions

  • the present disclosure relates to steel materials, and more particularly to steel materials suitable for use in sour environments.
  • oil wells and gas wells are collectively referred to simply as "oil wells").
  • steel pipes for oil wells of 80 ksi class yield strength of 80 to less than 95 ksi, that is, 552 to 655 MPa
  • 95 ksi class yield strength of 95 to less than 110 ksi, that is, 655 to 758 MPa
  • 110 ksi class yield strength of 110 to 125 ksi, that is, 758 to 862 MPa
  • the sour environment means an environment that contains hydrogen sulfide and is acidified. Note that carbon dioxide may be included in the sour environment. Oil well steel pipes used in such a sour environment are required to have not only high strength but also sulfide stress cracking resistance (Sulfide Stress Cracking resistance: hereinafter referred to as SSC resistance).
  • SSC resistance sulfide Stress Cracking resistance
  • Patent Document 1 JP-A-62-253720
  • Patent Document 2 JP-A-59-232220
  • Patent Document 3 Japanese Unexamined Patent Publication (Kokai) No. 8-311551
  • Patent Document 4 Japanese Unexamined Patent Application Publication No. 2000-256783
  • Patent Document 6 Japanese Unexamined Patent Application Publication 2000-297344
  • Patent Document 7 Japanese Patent Laid-Open No. 2012-510238
  • Patent Document 9 Japanese Patent Laid-Open No. 2012-26030
  • Patent Document 1 proposes a method of reducing impurities such as Mn and P to enhance SSC resistance of oil well steel.
  • Patent Document 2 proposes a method in which quenching is performed twice to make crystal grains finer and enhance the SSC resistance of steel.
  • Patent Document 3 proposes a method of refining the steel structure by induction heating heat treatment to enhance the SSC resistance of 125 ksi class steel materials.
  • Patent Document 4 proposes a method of improving the SSC resistance of a 110 to 140 ksi class steel pipe by increasing the hardenability of steel by using a direct quenching method and further increasing the tempering temperature.
  • Patent Documents 5 and 6 propose a method of controlling the morphology of carbides to enhance the SSC resistance of 110-140 ksi grade low alloy oil country tubular goods steels.
  • Patent Document 7 proposes a method of controlling the dislocation density and the hydrogen diffusion coefficient to desired values to enhance the SSC resistance of steel materials of 125 ksi class or higher.
  • Patent Document 8 proposes a method of increasing the SSC resistance of 125 ksi class steel by performing quenching a plurality of times on a low alloy steel containing 0.3 to 0.5% C.
  • Patent Document 9 proposes a method of controlling the form and number of carbides by adopting a tempering process of a two-stage heat treatment. More specifically, in Patent Document 9, the number density of large M 3 C or M 2 C is suppressed and the SSC resistance of 125 ksi grade steel is increased.
  • a steel material for example, oil well steel pipe
  • a yield strength of 110 ksi class (758 to 862 MPa) and excellent SSC resistance can be obtained by a technique other than the techniques disclosed in Patent Documents 1 to 9 above. Good.
  • An object of the present disclosure is to provide a steel material having a yield strength of 758 to 862 MPa (110 ksi class) and excellent SSC resistance in a sour environment.
  • the steel material according to the present disclosure has a mass% of C: 0.20 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.01 to 1.00%, and P: 0.030% or less. , S: 0.0050% or less, Al: 0.005 to 0.100%, Cr: 0.60 to 1.50%, Mo: over 1.00 to 2.00%, Ti: 0.002 to 0 0.020%, V: 0.05 to 0.30%, Nb: 0.005 to 0.100%, B: 0.0005 to 0.0040%, N: 0.0100% or less, O: 0.0020 %, Ca: 0 to 0.0100%, Mg: 0 to 0.0100%, Zr: 0 to 0.0100%, rare earth element: 0 to 0.0100%, Cu: 0 to 0.50%, Ni : 0 to 0.50%, Co: 0 to 0.50%, and W: 0 to 0.50%, the balance being Fe and impurities, and having a chemical composition satisfying the formula (1).
  • the steel material according to the present disclosure has a yield strength of 758 to 862 MPa (110 ksi class) and excellent SSC resistance in a sour environment.
  • FIG. 1 is a diagram showing the relationship between the Mo content and the old ⁇ particle size.
  • the present inventors have investigated and investigated a method for obtaining excellent SSC resistance while maintaining a yield strength of 758 to 862 MPa (110 ksi class) in a steel material that is supposed to be used in a sour environment, and made the following findings. Obtained.
  • the yield strength YS Yield Strength
  • dislocations in the steel material may occlude hydrogen. Therefore, if the dislocation density of the steel material increases, the amount of hydrogen stored in the steel material may increase. If the hydrogen concentration in the steel material increases as a result of increasing the dislocation density, the SSC resistance of the steel material deteriorates even if high strength is obtained. Therefore, in order to achieve both 110 ksi class yield strength and excellent SSC resistance, it is not preferable to increase the strength using the dislocation density.
  • the inventors of the present invention may obtain excellent SSC resistance even if the yield strength of the steel material is increased to 110 ksi class. I thought it might be.
  • the present inventors have a chemical composition, in mass%, of C: 0.20 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.01 to 1.00%, P: 0.030% or less, S: 0.0050% or less, Al: 0.005 to 0.100%, Cr: 0.60 to 1.50%, Ti: 0.002 to 0.020%, V : 0.05-0.30%, Nb: 0.005-0.100%, B: 0.0005-0.0040%, N: 0.0100% or less, O: less than 0.0020%, Ca: 0 to 0.0100%, Mg: 0 to 0.0100%, Zr: 0 to 0.0100%, rare earth element: 0 to 0.0100%, Cu: 0 to 0.50%, Ni: 0 to 0. A steel material containing 50%, Co: 0 to 0.50%, and W: 0 to 0.50% is considered to be able to achieve both 110 ksi class yield strength and SSC resistance. It was
  • the inventors further thought that, in addition to the above-mentioned chemical composition, if Mo is contained, alloy carbide is formed, so that the yield strength can be increased without increasing the dislocation density too much. Therefore, the present inventors manufactured various steel materials in which Mo was added to the above-mentioned chemical composition, and investigated the characteristics thereof. As a result, the present inventors have found that in steel materials having the above chemical composition, there is a new dependence on the Mo content and the particle size of old austenite grains (hereinafter, also referred to as “old ⁇ grains”). I found out.
  • FIG. 1 is a diagram showing the relationship between the Mo content and the old ⁇ particle size.
  • FIG. 1 shows the Mo content (mass %) of a steel material manufactured by a preferred manufacturing method described later, in which the chemical composition other than the Mo content satisfies the above-mentioned chemical composition range in Examples described later.
  • the "old ⁇ grain size” means the crystal grain size of the old ⁇ grain obtained by the method based on the comparison method defined in ASTM E112-10.
  • the present inventors consider the reason for this as follows.
  • Mo is contained in the range of more than 1.00 to 2.00%
  • Mo dissolved in the steel material may be segregated to the austenite grain boundaries during heating during quenching. Therefore, the solid solution Mo segregated at the austenite grain boundaries suppresses the movement of the crystal grain boundaries. As a result, the austenite grains are less likely to coarsen during heating during quenching, and it is considered that the old ⁇ grains after tempering become fine.
  • the hardenability of the steel material is high.
  • F1 is an index of the hardenability of the steel material. If F1 is too low, the hardenability of the steel material may not be sufficiently obtained and 110 ksi class yield strength may not be obtained. Therefore, the steel material according to the present embodiment has the above-described chemical composition and further has F1 of 3.90 or more.
  • the chemical composition of the steel material according to the present embodiment is, in mass %, C: 0.20 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.01 to 1.00%, P: 0.030% or less, S: 0.0050% or less, Al: 0.005 to 0.100%, Cr: 0.60 to 1.50%, Mo: more than 1.00 to 2.00%, Ti: 0.002 to 0.020%, V: 0.05 to 0.30%, Nb: 0.005 to 0.100%, B: 0.0005 to 0.0040%, N: 0.0100% Below, O: less than 0.0020%, Ca: 0 to 0.0100%, Mg: 0 to 0.0100%, Zr: 0 to 0.0100%, rare earth element: 0 to 0.0100%, Cu: 0 .About.0.50%, Ni:0.about.0.50%, Co:0.about.0.50%, and W:0.about.0.50%, the balance consisting of Fe and impurities.
  • F1 is 3.90 or more.
  • the present inventors examined in more detail the carbides that reduce the SSC resistance in the steel materials having the above-described chemical composition. As a result, the following findings were obtained. Coarse carbides tend to be a source of stress concentration and promote the propagation of cracks caused by SSC. Therefore, it has been considered that if the coarse carbides are reduced, the SSC resistance of the steel material is enhanced.
  • the coarse carbides precipitated in the old ⁇ grain boundaries may reduce the SSC resistance of the steel material.
  • the present inventors have found that the SSC resistance of the steel material can be enhanced by not simply reducing the coarse carbides but by reducing the coarse carbides precipitated at the old ⁇ grain boundaries.
  • the steel material according to the present embodiment has the above-described chemical composition, the old ⁇ grain size is 11.0 ⁇ m or less, and further reduces the coarse carbides precipitated at the old ⁇ grain boundaries.
  • the steel material according to the present embodiment has the above-described chemical composition, the old ⁇ grain size is 11.0 ⁇ m or less, and the average area of the precipitates of the old ⁇ grain boundary is 10.0 ⁇ 10 ⁇ . It is 3 ⁇ m 2 or less.
  • the steel material according to the present embodiment can achieve both a yield strength of 758 to 862 MPa (110 ksi class) and excellent SSC resistance in a sour environment.
  • the steel material according to the present embodiment completed on the basis of the above findings is, in mass%, C: 0.20 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.01 to 1.00. %, P: 0.030% or less, S: 0.0050% or less, Al: 0.005 to 0.100%, Cr: 0.60 to 1.50%, Mo: over 1.00 to 2.00 %, Ti: 0.002 to 0.020%, V: 0.05 to 0.30%, Nb: 0.005 to 0.100%, B: 0.0005 to 0.0040%, N: 0.
  • the crystal grain size of the former austenite grains is 11.0 ⁇ m or less.
  • the average area of the precipitates precipitated at the former austenite grain boundaries is 10.0 ⁇ 10 ⁇ 3 ⁇ m 2 or less.
  • the yield strength of steel is 758 to 862 MPa. 2.7 ⁇ C+0.4 ⁇ Si+Mn+0.45 ⁇ Ni+0.45 ⁇ Cu+0.8 ⁇ Cr+2 ⁇ Mo ⁇ 3.90 (1)
  • the content (mass %) of the corresponding element is substituted for the element symbol in the formula (1).
  • "0" is substituted for the element symbol.
  • the steel material is not particularly limited, but is, for example, a steel pipe or a steel plate.
  • the above chemical composition may contain at least one selected from the group consisting of Cu: 0.02 to 0.50% and Ni: 0.02 to 0.50%.
  • the above steel material may be a steel pipe for oil wells.
  • the oil well steel pipe may be a line pipe steel pipe or an oil well pipe.
  • the shape of the oil well steel pipe is not limited, and may be, for example, a seamless steel pipe or a welded steel pipe.
  • the oil country tubular goods are, for example, steel tubes used for casings and tubing applications.
  • the above steel material may be a seamless steel pipe. If the steel material according to the present embodiment is a seamless steel tube, it has a yield strength of 758 to 862 MPa (110 ksi class) even if the wall thickness is 15 mm or more, and has more stable SSC resistance in a sour environment. ..
  • the excellent SSC resistance can be evaluated specifically by a method based on NACE TM0177-2005 Method A and a 4-point bending test.
  • a mixed aqueous solution of 5.0 mass% sodium chloride and 0.5 mass% acetic acid (NACE solution A) at 4° C. is used for the test bath.
  • a test piece taken from a steel material is immersed in a test bath under a stress equivalent to 90% of the actual yield stress. Subsequently, the test bath is degassed, and 1 atm of H 2 S gas is blown into the test bath to saturate it. The test bath saturated with H 2 S gas is kept at 4° C. for 720 hours.
  • the stress applied to the test piece taken from the steel material should be 90% of the actual yield stress of the steel material.
  • Stress is applied by four-point bending.
  • a 5.0 mass% sodium chloride aqueous solution at 24° C. is used for the test bath.
  • the stressed test piece is immersed in a test bath in an autoclave. After deaeration of the test bath, 20 atm of H 2 S gas is pressurized and sealed in the autoclave. After sealing the autoclave, the test bath is stirred at 24° C. for 720 hours.
  • Mn 0.01-1.00%
  • Manganese (Mn) deoxidizes steel. Mn further enhances the hardenability of the steel material and enhances the yield strength of the steel material. If the Mn content is too low, these effects cannot be obtained. On the other hand, if the Mn content is too high, Mn segregates at the grain boundaries together with impurities such as P and S. In this case, the SSC resistance of the steel material decreases. Therefore, the Mn content is 0.01 to 1.00%.
  • the preferable lower limit of the Mn content is 0.02%, more preferably 0.03%, and further preferably 0.10%.
  • the preferable upper limit of the Mn content is 0.80%, more preferably 0.70%, further preferably 0.65%, further preferably less than 0.60%, further preferably 0. 55%.
  • S 0.0050% or less Sulfur (S) is an impurity. That is, the S content is more than 0%. S segregates at the grain boundaries and reduces the SSC resistance of the steel material. Therefore, the S content is 0.0050% or less.
  • the preferable upper limit of the S content is 0.0040%, more preferably 0.0030%, and further preferably 0.0020%. It is preferable that the S content is as low as possible. However, the extreme reduction of the S content significantly increases the manufacturing cost. Therefore, when industrial production is taken into consideration, the preferable lower limit of the S content is 0.0001%, more preferably 0.0003%.
  • Mo over 1.00 to 2.00% Molybdenum (Mo) enhances the hardenability of steel and enhances the yield strength of steel. Further, Mo is solid-dissolved in the steel material, and a part thereof is segregated at the austenite grain boundaries during heating during quenching. As a result, the old ⁇ grain size of the steel material after tempering becomes small due to the pinning effect. In this case, the SSC resistance of the steel material is enhanced. If the Mo content is too low, these effects cannot be obtained. On the other hand, if the Mo content is too high, coarse carbides are generated at the old ⁇ grain boundaries in the steel material. In this case, the SSC resistance of the steel material decreases. Therefore, the Mo content is more than 1.00 to 2.00%.
  • the preferable lower limit of the Mo content is 1.01%, more preferably 1.05%, further preferably 1.10%, further preferably 1.15%, further preferably 1.20. %.
  • the preferable upper limit of the Mo content is 1.90%, more preferably 1.80%, further preferably 1.75%, further preferably 1.70%, further preferably 1.65. %.
  • the Mo content is preferably less than 2.00 times the Cr content. If the Mo content is too high relative to the Cr content, the old ⁇ grains of the steel material may become coarse. The reason for this is unknown. However, in the steel material having the chemical composition according to the present embodiment, if the Mo content is less than 2.00 times the Cr content, the old ⁇ grain size of the steel material can be stably reduced to 11.0 ⁇ m or less. Therefore, in the chemical composition of the steel material according to the present embodiment, the Mo content is preferably less than 2.00 times the Cr content.
  • the more preferable upper limit of the ratio of Mo content to Cr content is 1.98, more preferably 1.95, and further preferably 1.90.
  • the lower limit of the Mo/Cr ratio is not particularly limited, the chemical composition of the steel material according to the present embodiment is substantially 0.67 or more.
  • Titanium (Ti) forms a nitride and refines the structure of the steel material by the pinning effect. As a result, the SSC resistance of the steel material is enhanced. If the Ti content is too low, this effect cannot be obtained. On the other hand, if the Ti content is too high, a large amount of Ti nitride is formed. As a result, the SSC resistance of the steel material decreases. Therefore, the Ti content is 0.002 to 0.020%.
  • the preferable lower limit of the Ti content is 0.003%, more preferably 0.004%.
  • the preferable upper limit of the Ti content is 0.018%, more preferably 0.015%.
  • V 0.05 to 0.30% Vanadium (V) combines with C and/or N to form a carbide, a nitride, or a carbonitride (hereinafter, referred to as “carbonitride or the like”). Carbonitride and the like refine the structure of the steel material by the pinning effect. As a result, the SSC resistance of the steel material is enhanced. V further combines with C to form fine carbides. As a result, the yield strength of the steel material increases. If the V content is too low, these effects cannot be obtained. On the other hand, if the V content is too high, carbonitrides and the like are excessively generated, and the SSC resistance of the steel material deteriorates. Therefore, the V content is 0.05 to 0.30%.
  • the preferable lower limit of the V content is more than 0.05%, more preferably 0.06%, further preferably 0.07%, and further preferably 0.09%.
  • the preferable upper limit of the V content is 0.25%, more preferably 0.20%, and further preferably 0.15%.
  • B 0.0005 to 0.0040% Boron (B) forms a solid solution in steel to enhance the hardenability of the steel material and enhance the yield strength of the steel material. If the B content is too low, this effect cannot be obtained. On the other hand, if the B content is too high, coarse nitrides are generated, and the SSC resistance of the steel material deteriorates. Therefore, the B content is 0.0005 to 0.0040%.
  • the preferable lower limit of the B content is 0.0007%, more preferably 0.0010%, and further preferably 0.0012%.
  • the preferable upper limit of the B content is 0.0035%, more preferably 0.0030%, and further preferably 0.0025%.
  • Oxygen (O) is an impurity. That is, the O content is more than 0%. O forms a coarse oxide and reduces the SSC resistance of the steel material. Therefore, the O content is less than 0.0020%.
  • the preferable upper limit of the O content is 0.0018%, and more preferably 0.0015%.
  • the O content is preferably as low as possible. However, the extreme reduction of the O content significantly increases the manufacturing cost. Therefore, when industrial production is taken into consideration, the preferable lower limit of the O content is 0.0001%, and more preferably 0.0003%.
  • the balance of the chemical composition of the steel material according to this embodiment is Fe and impurities.
  • the impurities are ores as raw materials when industrially manufacturing a steel material, scrap, or those that are mixed from the manufacturing environment, etc. within a range that does not adversely affect the steel material according to the present embodiment. Means acceptable.
  • the chemical composition of the above-described steel material may further contain, in place of part of Fe, one or more selected from the group consisting of Ca, Mg, Zr, and a rare earth element (REM).
  • REM rare earth element
  • Ca 0 to 0.0100% Calcium (Ca) is an optional element and may not be contained. That is, the Ca content may be 0%. When included, Ca renders S in the steel material harmless as a sulfide and enhances the SSC resistance of the steel material. This effect can be obtained to some extent if even a small amount of Ca is contained. However, if the Ca content is too high, the oxides in the steel material become coarse, and the SSC resistance of the steel material decreases. Therefore, the Ca content is 0 to 0.0100%.
  • the preferable lower limit of the Ca content is more than 0%, more preferably 0.0001%, further preferably 0.0003%, further preferably 0.0006%, further preferably 0.0010%. Is.
  • the preferable upper limit of the Ca content is 0.0040%, more preferably 0.0030%, further preferably 0.0025%, and further preferably 0.0020%.
  • Mg 0 to 0.0100%
  • Magnesium (Mg) is an optional element and may not be contained. That is, the Mg content may be 0%. When contained, Mg makes S in the steel material harmless as a sulfide and enhances the SSC resistance of the steel material. This effect can be obtained to some extent if Mg is contained at all. However, if the Mg content is too high, the oxides in the steel material become coarse, and the SSC resistance of the steel material decreases. Therefore, the Mg content is 0 to 0.0100%.
  • the preferable lower limit of the Mg content is more than 0%, more preferably 0.0001%, further preferably 0.0003%, further preferably 0.0006%, further preferably 0.0010%. Is.
  • the preferable upper limit of the Mg content is 0.0040%, more preferably 0.0030%, further preferably 0.0025%, and further preferably 0.0020%.
  • Zr Zirconium
  • Zr Zirconium
  • the Zr content may be 0%.
  • Zr renders S in the steel material harmless as a sulfide and enhances the SSC resistance of the steel material. This effect can be obtained to some extent if Zr is contained even in a small amount.
  • the Zr content is 0 to 0.0100%.
  • the preferable lower limit of the Zr content is more than 0%, more preferably 0.0001%, further preferably 0.0003%, further preferably 0.0006%, further preferably 0.0010%. Is.
  • the preferable upper limit of the Zr content is 0.0040%, more preferably 0.0030%, further preferably 0.0025%, and further preferably 0.0020%.
  • the rare earth element (REM) is an optional element and may not be contained. That is, the REM content may be 0%. When contained, REM renders S in the steel material harmless as a sulfide and enhances the SSC resistance of the steel material. REM further binds to P in the steel material and suppresses the segregation of P at the grain boundaries. Therefore, the deterioration of the low temperature toughness and SSC resistance of the steel material due to the segregation of P is suppressed. These effects can be obtained to some extent if REM is contained in any amount. However, if the REM content is too high, the oxide is coarsened, and the low temperature toughness and SSC resistance of the steel material deteriorate.
  • the REM content is 0 to 0.0100%.
  • the preferable lower limit of the REM content is more than 0%, more preferably 0.0001%, further preferably 0.0003%, further preferably 0.0006%, further preferably 0.0010%. Is.
  • the preferable upper limit of the REM content is 0.0040%, more preferably 0.0030%, further preferably 0.0025%, and further preferably 0.0020%.
  • REM in this specification means scandium (Sc) having an atomic number of 21, an yttrium (Y) having an atomic number of 39, and a lanthanide (lanthanum (La) having an atomic number of 57 to an atomic number of 71). It is one or more elements selected from the group consisting of lutetium (Lu).
  • the REM content in the present specification is the total content of these elements.
  • the chemical composition of the above-mentioned steel material may further contain one or more selected from the group consisting of Cu and Ni, instead of part of Fe. All of these elements are optional elements and enhance the hardenability of steel materials.
  • Cu 0 to 0.50% Copper (Cu) is an optional element and may not be contained. That is, the Cu content may be 0%. When contained, Cu enhances the hardenability of the steel material and enhances the yield strength of the steel material. This effect can be obtained to some extent if Cu is contained in a small amount. However, if the Cu content is too high, the hardenability of the steel material becomes too high, and the SSC resistance of the steel material deteriorates. Therefore, the Cu content is 0 to 0.50%.
  • the preferable lower limit of the Cu content is more than 0%, more preferably 0.02%, further preferably 0.03%, further preferably 0.05%.
  • the preferable upper limit of the Cu content is 0.35%, more preferably 0.25%.
  • Nickel (Ni) is an optional element and may not be contained. That is, the Ni content may be 0%. When contained, Ni enhances the hardenability of the steel material and enhances the yield strength of the steel material. This effect can be obtained to some extent if Ni is contained at all. However, if the Ni content is too high, localized corrosion is promoted and the SSC resistance of the steel material deteriorates. Therefore, the Ni content is 0 to 0.50%.
  • the preferable lower limit of the Ni content is more than 0%, more preferably 0.02%, further preferably 0.03%, further preferably 0.05%.
  • the preferable upper limit of the Ni content is 0.35%, more preferably 0.25%.
  • the chemical composition of the above-mentioned steel material may further contain one or more selected from the group consisting of Co and W instead of part of Fe.
  • Each of these elements is an arbitrary element and forms a protective corrosive film in a hydrogen sulfide environment to suppress hydrogen invasion. Thereby, these elements enhance the SSC resistance of the steel material.
  • Co is an optional element and may not be contained. That is, the Co content may be 0%. When contained, Co forms a protective corrosion film in a hydrogen sulfide environment and suppresses hydrogen invasion. As a result, the SSC resistance of the steel material is enhanced. This effect can be obtained to some extent if Co is contained in a small amount. However, if the Co content is too high, the hardenability of the steel material deteriorates, and the yield strength of the steel material decreases. Therefore, the Co content is 0 to 0.50%.
  • the preferable lower limit of the Co content is more than 0%, more preferably 0.02%, further preferably 0.03%, further preferably 0.05%.
  • the preferable upper limit of the Co content is 0.45%, and more preferably 0.40%.
  • W 0 to 0.50%
  • Tungsten (W) is an optional element and may not be contained. That is, the W content may be 0%. When contained, W forms a protective corrosion film in a hydrogen sulfide environment and suppresses hydrogen invasion. As a result, the SSC resistance of the steel material is enhanced. If W is contained even a little, this effect can be obtained to some extent. However, if the W content is too high, coarse carbides are generated in the steel material, and the SSC resistance of the steel material deteriorates. Therefore, the W content is 0 to 0.50%.
  • the preferable lower limit of the W content is more than 0%, more preferably 0.02%, further preferably 0.03%, further preferably 0.05%.
  • the preferable upper limit of the W content is 0.45%, more preferably 0.40%.
  • F1 is less than 3.90, sufficient hardenability cannot be obtained and yield strength of steel cannot be obtained. Therefore, the steel material according to the present embodiment has F1 of 3.90 or more.
  • the preferable lower limit of F1 is 3.93, and more preferably 4.00.
  • the upper limit of F1 is not particularly limited. However, in the steel material according to the present embodiment having the above chemical composition, the upper limit of F1 is, for example, 8.27.
  • the preferable upper limit of F1 is 8.20, more preferably 8.10, and further preferably 8.00.
  • the former austenite grain size (former ⁇ grain size) is 11.0 ⁇ m or less.
  • the crystal grain size of old austenite grains means the crystal grain size of old austenite grains, which is obtained in accordance with the comparison method of ASTM E112-10. If the old ⁇ grains of the steel material are fine, the yield strength and SSC resistance are stably enhanced. Therefore, in the present embodiment, the old ⁇ grains of the steel material are made fine by including Mo in the steel material in an amount of more than 1.00%.
  • the preferable upper limit of the old ⁇ grain size of the steel material according to the present embodiment is 10.5 ⁇ m, more preferably 10.0 ⁇ m.
  • the lower limit of the old ⁇ grain size of the steel material according to the present embodiment is not particularly limited.
  • the lower limit of the old ⁇ grain size of the steel material according to the present embodiment is, for example, 4.5 ⁇ m.
  • the old ⁇ particle size can be determined according to the comparison method of ASTM E112-10. More specifically, it can be determined by the following method.
  • the steel material is a steel plate
  • a test piece having an observation surface perpendicular to the rolling direction is cut out from the center part of the plate thickness.
  • the steel material is a steel pipe
  • a test piece having an observation surface perpendicular to the pipe axis direction is cut out from the central portion of the wall thickness. After the observation surface is mirror-polished, it is embedded in a resin and immersed in a 2% Nital etchant for about 10 seconds to expose old ⁇ grain boundaries by etching.
  • the etched observation surface with a secondary electron image using a scanning electron microscope (SEM: Scanning Electron Microscope) to generate a photographic image.
  • the observation magnification is, for example, 200 times.
  • the grain size number is evaluated by comparison with the grain size standard diagram specified in ASTM E112-10. From the evaluated grain size number, the average grain size of the old ⁇ grains in each visual field is determined. The arithmetic average value of the average crystal grain size of the old ⁇ grains obtained in the 10 fields of view is defined as the crystal grain size of the old ⁇ grains (old ⁇ grain size) ( ⁇ m).
  • the average area of the precipitates precipitated at the former austenite grain boundaries is 10.0 ⁇ 10 ⁇ 3 ⁇ m 2 or less.
  • the precipitate deposited on the old ⁇ grain boundary is also referred to as “specific precipitate”. If the average area of the specific precipitate is 10.0 ⁇ 10 ⁇ 3 ⁇ m 2 or less, 110 ksi class yield strength and excellent SSC resistance are provided, provided that the other requirements of the steel material according to the present embodiment are satisfied. Can be compatible.
  • the average area of the precipitates (specific precipitates) that precipitate at the old ⁇ grain boundaries is 10.0 ⁇ 10 ⁇ 3 ⁇ m 2 or less. If the average area of the specific precipitates exceeds 10.0 ⁇ 10 ⁇ 3 ⁇ m 2 , the SSC resistance of the steel material may deteriorate. If the average area of the specific precipitates exceeds 10.0 ⁇ 10 ⁇ 3 ⁇ m 2 , the yield strength of 758 to 862 MPa (110 ksi class) may not be obtained.
  • the average area of the precipitates precipitated at the old ⁇ grain boundary is 10.0 ⁇ 10 ⁇ 3 ⁇ m 2 or less.
  • the preferable upper limit of the average area of the specific precipitate is 9.9 ⁇ 10 ⁇ 3 ⁇ m 2 , and more preferably 9.7 ⁇ 10 ⁇ 3 ⁇ m 2 .
  • the lower limit of the average area of the specific precipitate is not particularly limited and may be 0.0 ⁇ 10 ⁇ 3 ⁇ m 2 .
  • the lower limit of the average area of specific precipitates is, for example, 3.0 ⁇ 10 ⁇ 3 ⁇ m 2 .
  • the average area of specific precipitates can be obtained by the following method.
  • a test piece is cut out from the steel material in the same manner as the above-described method for measuring the old ⁇ particle size. Specifically, when the steel material is a steel plate, a test piece having an observation surface perpendicular to the rolling direction is cut out from the center part of the plate thickness. When the steel material is a steel pipe, a test piece having an observation surface perpendicular to the pipe axis direction is cut out from the central portion of the wall thickness. After the observation surface is mirror-polished, it is embedded in a resin and immersed in a 2% Nital etchant for about 10 seconds to expose old ⁇ grain boundaries by etching. The observation surface of the test piece is observed in 10 fields of view with a secondary electron image by SEM to generate a photographic image. The observation magnification is, for example, 10,000 times.
  • the observation magnification is, for example, 10,000 times in the observation of the specific precipitate. Therefore, if the precipitate has a circle equivalent diameter of 50 nm or more, it can be specified based on the contrast from the observation visual field.
  • the upper limit of the equivalent circle diameter of the specified precipitate is not particularly limited. In the steel material having the above chemical composition, the upper limit of the equivalent circle diameter of the identified precipitate is, for example, 1000 nm. Therefore, in the present embodiment, the equivalent circle diameter of the specific precipitate is, for example, 50 to 1000 nm.
  • the yield strength is 758, provided that the other regulations of this embodiment are satisfied. Up to 862 MPa (110 ksi class).
  • the total volume ratio of tempered martensite and tempered bainite can be obtained by microstructure observation.
  • the microstructure a photographic image generated when obtaining the above-mentioned old ⁇ grain size is used.
  • the tempered martensite and tempered bainite and the other phases can be distinguished from the contrast. Therefore, tempered martensite and tempered bainite are specified based on the contrast in each visual field.
  • the arithmetic average value of the total area ratios of tempered martensite and tempered bainite obtained from all fields of view is taken as the volume ratio of tempered martensite and tempered bainite.
  • the yield strength of the steel material according to this embodiment is 758 to 862 MPa (110 ksi class).
  • the yield strength as used herein means the stress at 0.7% elongation (0.7% proof stress) obtained in a tensile test.
  • the steel material according to the present embodiment has excellent SSC resistance even if the yield strength is 110 ksi class, by satisfying the above-mentioned chemical composition, old ⁇ grain size, and average area of the specific precipitate.
  • the yield strength of the steel material according to this embodiment can be obtained by the following method. Perform a tensile test by the method based on ASTM E8/E8M (2013).
  • a round bar test piece is sampled from the steel material according to the present embodiment.
  • the steel material is a steel plate
  • a round bar test piece is taken from the center part of the plate thickness. If the steel material is a steel pipe, collect a round bar test piece from the center of the wall thickness.
  • the size of the round bar test piece is, for example, the parallel portion diameter 8.9 mm and the parallel portion length 35.6 mm.
  • the axial direction of the round bar test piece is parallel to the rolling direction of the steel material.
  • a tensile test is carried out at room temperature (25° C.) in the atmosphere, and the stress at 0.7% elongation obtained is defined as the yield strength (MPa).
  • a round bar test piece is collected from the steel material according to this embodiment.
  • the steel material is a steel plate
  • a round bar test piece is taken from the center part of the plate thickness. If the steel material is a steel pipe, collect a round bar test piece from the center of the wall thickness.
  • the size of the round bar test piece is, for example, a diameter of 6.35 mm and a parallel portion length of 25.4 mm.
  • the axial direction of the round bar test piece is parallel to the rolling direction of the steel material.
  • the test solution is a mixed aqueous solution (NACE solution A) of 5.0% by mass sodium chloride and 0.5% by mass acetic acid at 4°C.
  • NACE solution A a mixed aqueous solution
  • a stress equivalent to 90% of the actual yield stress is applied to the round bar test piece.
  • a test solution at 4° C. is poured into a test container so that a stress-loaded round bar test piece is immersed therein to form a test bath. After deaeration of the test bath, 1 atm of H 2 S gas is blown into the test bath to saturate the test bath with H 2 S gas. The test bath saturated with H 2 S gas is kept at 4° C. for 720 hours.
  • test pieces are taken from the steel material according to the present embodiment.
  • the steel material is a steel plate
  • a test piece is taken from the center part of the plate thickness.
  • the steel material is a steel pipe
  • the size of the test piece is, for example, 2 mm in thickness, 10 mm in width, and 75 mm in length.
  • the length direction of the test piece is parallel to the rolling direction of the steel material.
  • the shape of the steel material according to the present embodiment is not particularly limited.
  • the steel material is, for example, a steel pipe or a steel plate.
  • the preferable wall thickness is 9 to 60 mm.
  • the steel material according to the present embodiment is suitable for use as a thick-walled seamless steel pipe. More specifically, even if the steel material according to the present embodiment is a seamless steel pipe having a thickness of 15 mm or more and further 20 mm or more, it exhibits a yield strength of 110 ksi class and excellent SSC resistance.
  • the method for manufacturing a steel material according to this embodiment will be described.
  • the manufacturing method described below is a method for manufacturing a seamless steel pipe as an example of the steel material according to the present embodiment.
  • the manufacturing method of the steel material according to the present embodiment is not limited to the manufacturing method described below.
  • the preparation step may include a step of preparing a material (material preparation step) and a step of hot working the material to produce an intermediate steel material (hot working step).
  • material preparation step a step of preparing a material
  • hot working step a step of hot working the material to produce an intermediate steel material
  • the material is manufactured using the molten steel having the above chemical composition.
  • a slab slab, bloom, or billet
  • a slab, bloom or ingot may be slab-rolled to produce a billet.
  • a material is manufactured by the above steps.
  • the prepared raw material is hot worked to produce an intermediate steel material.
  • the steel material is a steel pipe
  • the intermediate steel material corresponds to a raw pipe.
  • the billet is heated in a heating furnace.
  • the heating temperature is not particularly limited, but is, for example, 1100 to 1300°C.
  • the billet extracted from the heating furnace is subjected to hot working to manufacture a raw pipe (seamless steel pipe).
  • the Mannesmann method may be carried out as hot working to manufacture a raw tube.
  • a round billet is perforated and rolled by a perforator.
  • 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 by a mandrel mill, reducer, sizing mill or the like to obtain a raw tube.
  • the cumulative area reduction rate in the hot working step is, for example, 20 to 70%.
  • the raw pipe may be manufactured from the billet by another hot working method.
  • forging such as the Erhard method may be carried out to manufacture the raw pipe.
  • a raw tube is manufactured by the above steps.
  • the wall thickness of the manufactured raw pipe is not particularly limited, but is, for example, 9 to 60 mm.
  • the raw pipe manufactured by hot working may be air-cooled (As-Rolled).
  • the blank produced by hot working may be directly quenched without cooling to room temperature, or may be supplemented (reheated) and then quenched.
  • cooling may be stopped or slow cooling may be performed during quenching. In this case, it is possible to suppress the occurrence of quench cracks in the raw pipe.
  • the stress relief annealing SR treatment
  • the quenching is performed directly or after the supplementary heat treatment
  • the stress relief annealing may be performed after the quenching and before the heat treatment (tempering etc.) in the next step. In this case, the residual stress of the raw pipe is removed.
  • the intermediate steel is prepared in the preparation process.
  • the intermediate steel material may be manufactured by the above-described preferable process, or the intermediate steel material manufactured by a third party, or a factory other than the factory where the quenching process and the tempering process described below are carried out, other establishments. You may prepare the intermediate steel material manufactured by.
  • heat treatment process In the heat treatment step, heat treatment is performed on the prepared intermediate steel material. Specifically, quenching and tempering are performed on the prepared intermediate steel material.
  • quenching means quenching of an intermediate steel material having a point A 3 or higher.
  • tempering means to reheat and hold the intermediate steel material after quenching at the A c1 point or less.
  • the heat treatment step according to the present embodiment may be performed by rapidly cooling the intermediate steel material at 800 to 1000° C. after hot working, or using the auxiliary steel furnace or the heat treatment furnace as the intermediate steel material after hot working. It may be carried out by heating to 800 to 1000° C. and then quenching, or by heating the intermediate steel material after tempering to 800 to 1000° C. using a heat treatment furnace and then quenching. Good.
  • the quenching temperature is preferably 800 to 1000°C. A more preferable upper limit of the quenching temperature is 950°C.
  • a preferable quenching time is 5 to 20 minutes.
  • the "quenching time” means the time from the charging of the intermediate steel material into the supplementary heat treatment furnace or the heat treatment furnace to the removal thereof.
  • the quenching time is preferably 5 to 20 minutes.
  • the quenching method is, for example, to continuously cool the raw pipe from the quenching start temperature and continuously lower the temperature of the raw pipe.
  • the method of continuous cooling treatment is not particularly limited, and a known method may be used.
  • the method of continuous cooling treatment is, for example, a method of immersing the base pipe in a water tank for cooling, or a method of accelerating the base pipe by shower water cooling or mist cooling.
  • a preferable cooling rate during quenching, CR 800-500 is 8° C./second or more.
  • the microstructure of the intermediate steel material (base pipe) after quenching stably becomes mainly martensite and bainite.
  • the more preferable lower limit of the cooling rate during quenching CR 800-500 is 10°C/sec.
  • the preferable upper limit of the cooling rate CR 800-500 during quenching is 500° C./sec.
  • the tempered intermediate steel material is tempered.
  • the tempering temperature and the tempering time were adjusted according to the chemical composition of the steel material and the yield strength to be obtained. In this case, only the final tempering is controlled, and for the non-final tempering, it has been conventionally considered that the tempering temperature should be A c1 point or less.
  • the tempering parameter TMP 2 of the second to last tempering is 15000 to 19000, the old ⁇ grain size of the steel material after the final tempering is made fine. be able to. If the tempering parameter TMP 2 in the penultimate tempering is less than 15000, the tempering effect may not be sufficiently obtained, and the steel material may be subject to temper cracking or set cracking. On the other hand, if the tempering parameter TMP 2 in the penultimate tempering exceeds 19000, the amount of solute Mo is not sufficiently obtained during heating in the final quenching, and the old ⁇ grain size after the final tempering becomes coarse. There is.
  • the tempering temperature is 500 to less than 700°C.
  • the tempering time (holding time) is set to 10 to 60 minutes. That is, in the second to last tempering in the present embodiment, the tempering temperature is 500 to less than 700° C., the tempering time is 10 to 60 minutes, and the tempering parameter TMP 2 is 15,000 to 19000.
  • the "tempering temperature” corresponds to the temperature of the heat treatment furnace when heating and holding the intermediate steel after quenching.
  • the “tempering time (holding time)” means the time from heating the intermediate steel after quenching and holding the intermediate steel in the heat treatment furnace until holding it.
  • the steel material according to the present embodiment further reduces coarse specific precipitates among the precipitates (specific precipitates) precipitated at the old ⁇ grain boundaries.
  • the tempering parameter TMP 1 of the final tempering is 19100 to 19600, coarse specific precipitates can be reduced in the steel material after the final tempering. it can. If the tempering parameter TMP 1 in the final tempering is less than 19100, the tempering effect may not be sufficiently obtained, and the yield strength of the steel material after tempering may be too high. If the tempering parameter TMP 1 in the final tempering is less than 19100, a large number of coarse specific precipitates may be further precipitated.
  • the tempering parameter TMP 1 in the final tempering exceeds 19600, the yield strength of the steel material after tempering may be too low. If the tempering parameter TMP 1 in the final tempering exceeds 19600, a large number of coarse specific precipitates may be further precipitated.
  • the tempering temperature is 650 to 730°C.
  • the tempering time (holding time) is set to 10 to 90 minutes. That is, in the present embodiment, in the final tempering, the tempering temperature is 650 to 730° C., the tempering time is 10 to 90 minutes, and the tempering parameter TMP 1 is 19100 to 19600.
  • the tempering time is preferably 15 to 90 minutes. It is sufficiently possible for those skilled in the art to set the yield strength to 758 to 862 MPa (110 ksi class) by appropriately adjusting the tempering temperature and the tempering time in the steel material having the chemical composition of the present embodiment. ..
  • the steel material according to the present embodiment can be manufactured by the above manufacturing method.
  • the manufacturing method of the seamless steel pipe has been described as an example.
  • the steel material according to the present embodiment may be a steel plate or another shape.
  • the manufacturing method of a steel plate or another shape also includes, for example, a preparation step and a heat treatment step, similar to the above-described manufacturing method.
  • the above-described manufacturing method is an example, and the manufacturing method may be performed by another manufacturing method.
  • Billet was manufactured by continuous casting using the above molten steel. After holding the manufactured billet of each test number at 1250° C. for 1 hour, hot rolling (hot working) by a Mannesmann-mandrel system was performed to manufacture a raw pipe (seamless steel pipe) of each test number.
  • Heat treatment was performed twice for each hot-worked test tube of each test number. Specifically, heat treatment was performed on the raw tubes of each test number by the following method.
  • the raw pipe of each test number manufactured by hot working was held in a supplementary heating furnace at 950° C. for 5 minutes and then directly quenched (that is, the first quench).
  • the cooling rate during quenching CR 800-500 in the first quenching of each test number was in the range of 8 to 500° C./sec in all cases.
  • the cooling rate during quenching, CR 800-500 was determined by measuring the surface temperature of the raw pipe of each test number.
  • the first tempering that is, the second tempering from the last
  • tempering was performed on the raw tubes of each test number at the tempering temperature (° C.) shown in the “second tempering from the last” column in Table 2 for the tempering time (minutes).
  • the second quenching that is, the final quenching, was performed on the raw tubes of the respective test numbers for which the first tempering was performed. Specifically, for the test tubes of each test number, quenching was carried out after holding for the quenching time (minutes) at the quenching temperature (°C) described in the "final quenching" column of Table 2.
  • the cooling rate during quenching CR 800-500 of the second quenching of each test number was in the range of 8 to 500° C./sec in all cases.
  • the second tempering that is, the final tempering
  • the second tempering was performed on the raw pipe of each test number on which the final quenching was performed. Specifically, tempering was performed on the raw tubes of each test number at the tempering temperature (° C.) described in the “final tempering” column of Table 2 for the tempering time (minutes).
  • the temperature of the auxiliary heating furnace and the heat treatment furnace used for heating the quenching was set to the "quenching temperature (°C)". Further, the temperature of the heat treatment furnace used for tempering was defined as “tempering temperature (°C)”.
  • the time from the time the raw tube was charged into the supplementary heating furnace or the heat treatment furnace to the time it was taken out at the time of heating during quenching was defined as “quenching time (minutes)”. The time from the time the raw tube was put into the heat treatment furnace during tempering to the time it was taken out was defined as "tempering time (minutes)".
  • Step SSC resistance evaluation test Using the seamless steel pipe of each test number, a test based on NACE TM0177-2005 Method A and a 4-point bending test were carried out to evaluate SSC resistance. Specifically, the test based on NACE TM0177-2005 Method A was performed by the following method.
  • 3Three round bar test pieces with a diameter of 6.35 mm and a parallel length of 25.4 mm were taken from the center of the wall thickness of the seamless steel pipe of each test number.
  • the round bar test piece was sampled so that its axial direction was parallel to the axial direction of the seamless steel pipe.
  • Tensile stress was applied in the axial direction of the round bar test piece of each test number. At this time, the applied stress was adjusted to be 90% of the actual yield stress of the seamless steel pipe of each test number.
  • test solution a mixed aqueous solution of 5.0 mass% sodium chloride and 0.5 mass% acetic acid (NACE solution A) was used.
  • the test solution at 4° C. was poured into three test containers to prepare a test bath. Three stress-loaded round bar test pieces were immersed in the test baths of different test containers one by one. After deaeration of each test bath, 1 atm of H 2 S gas was blown thereinto to saturate the test bath. The test bath saturated with 1 atm of H 2 S gas was kept at 4° C. for 720 hours.
  • the 4-point bending test was carried out by the following method. Three test pieces each having a thickness of 2 mm, a width of 10 mm, and a length of 75 mm were collected from the central portion of the wall thickness of the seamless steel pipe of each test number. The test piece was sampled so that its longitudinal direction was parallel to the axial direction of the seamless steel pipe. In accordance with ASTM G39-99 (2011), the stress applied to each test piece of each test number is 90% of the actual yield stress of the seamless steel pipe of each test number. Stress was applied by 4-point bending. The stress-loaded test piece was enclosed together with the test jig in an autoclave.
  • test solution a 5.0 mass% sodium chloride aqueous solution was used.
  • the test solution was injected into the autoclave, leaving the gas phase, to prepare a test bath. After deaeration of the test bath, 20 atm of H 2 S gas was pressure-filled, and the test bath was stirred to saturate the test bath with H 2 S gas. After sealing the autoclave, the test bath was stirred at 24° C. for 720 hours.
  • Table 2 shows the test results. Regarding the SSC resistance test, the result of the test based on NACE TM0177-2005 Method A is shown in the “1 atmH 2 S” column, and the result of the four-point bending test is shown in the “20 atmH 2 S” column.
  • the seamless steel pipes of test numbers 1 to 8 have appropriate chemical compositions, yield strength of 758 to 862 MPa, old ⁇ grain size of 11.0 ⁇ m or less, and The average area of the specific precipitate was 10.0 ⁇ 10 ⁇ 3 ⁇ m 2 or less. As a result, excellent SSC resistance was exhibited in both the test based on NACE TM0177-2005 Method A and the 4-point bending test.
  • the tempering parameter TMP 1 in the final tempering was too large. Therefore, the average area of the specific precipitate exceeded 10.0 ⁇ 10 ⁇ 3 ⁇ m 2 . As a result, the yield strength was less than 758 MPa, and 110 ksi class yield strength was not obtained.
  • the steel material according to the present disclosure is widely applicable to steel materials used in harsh environments such as polar regions, preferably steel materials used in oil well environments, and more preferably casing, tubing, line pipes, etc. It can be used as a steel material.
PCT/JP2020/005617 2019-02-15 2020-02-13 サワー環境での使用に適した鋼材 WO2020166668A1 (ja)

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EP20755579.8A EP3926059A4 (de) 2019-02-15 2020-02-13 Stahlmaterial zur verwendung in einer sauren umgebung
US17/422,870 US20220098712A1 (en) 2019-02-15 2020-02-13 Steel material suitable for use in sour environment
BR112021013441-7A BR112021013441A2 (pt) 2019-02-15 2020-02-13 Material de aço adequado para uso em ambiente ácido
JP2020572313A JP7036237B2 (ja) 2019-02-15 2020-02-13 サワー環境での使用に適した鋼材
MX2021009588A MX2021009588A (es) 2019-02-15 2020-02-13 Material de acero para uso en ambientes amargos.

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