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  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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  • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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  • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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  • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt

Definitions

• This disclosure relates to alloy materials, and more specifically, to alloy materials that can be used in high-temperature environments.
• Alloy materials used in steam reformers, ethylene cracking furnaces, heating furnace tubes for oil refining and petrochemical plants, and polycrystalline silicon manufacturing equipment are used in high-temperature environments of 500 to 1000°C. Therefore, alloy materials used in such high-temperature environments are required to have excellent corrosion resistance and high creep strength in high-temperature environments.
• Alloy 800, Alloy 800H, and Alloy 800HT are known alloy materials used in such high-temperature environments.
• Alloy 800, Alloy 800H, and Alloy 800HT contain large amounts of Cr and Ni. Therefore, these alloy materials have excellent corrosion resistance at high temperatures. These alloy materials also contain Al and Ti. Therefore, in these alloy materials, gamma prime ( ⁇ ') phase (Ni 3 (Al, Ti)) is generated during use in high temperature environments. Precipitation strengthening by the ⁇ ' phase allows these alloy materials to obtain high creep strength.
• Alloy 800, Alloy 800H, and Alloy 800HT which contain Al and Ti
• welding hot cracking is likely to occur in the heat-affected zone (HAZ) during welding.
• these alloy materials are manufactured by hot working in a temperature range of around 900°C, and are prone to cracking due to embrittlement during hot working. For this reason, these alloy materials are required to have excellent resistance to welding hot cracking and excellent hot workability.
• Patent Document 1 JP 2022-163425 A
• Patent Document 2 JP 2022-163585 A
• Patent Document 3 JP 2022-163586 A
• the alloy material disclosed in Patent Document 1 has a chemical composition containing, by mass%, C: 0.15% or less, Si: 0.05 to 2.0%, Mn: 0.05 to 2.0%, P: 0.035% or less, S: 0.0015% or less, Cr: 16 to 30%, Ni: 18 to 50%, Al: 0.01 to 1.0%, Ti: 0.01 to 1.5%, N: 0.35% or less, O: 0.003% or less, Mo: 8% or less, Cu: 4% or less, Co: 3% or less, Ca: 0.0003 to 0.0050%, and Mg: 0.0045% or less, with the balance being Fe and impurities.
• the mass ratio of CaO, MgO and Al 2 O 3 in the inclusions calculated from the average Ca concentration, average Mg concentration and average Al concentration of the inclusions in which O or S is detected satisfies [CaO-0.6 ⁇ MgO]/[CaO+MgO+Al 2 O 3 ] ⁇ 0.20.
• the mass ratio of oxide-based inclusions (CaO, MgO and Al 2 O 3 ) in the alloy material is appropriately controlled. This suppresses the generation of coarse TiC and improves the weld hot cracking resistance of the alloy material.
• the alloy material disclosed in Patent Document 2 has a chemical composition containing, by mass%, C: 0.15% or less, Si: 0.05 to 2.0%, Mn: 0.05 to 2.0%, P: 0.035% or less, S: 0.0015% or less, Cr: 16 to 30%, Ni: 18 to 50%, Al: 0.01 to 1.0%, Ti: 0.01 to 1.5%, N: 0.35% or less, O: 0.003% or less, Mo: 8% or less, Cu: 4% or less, Co: 3% or less, Ca: 0.0003 to 0.0050%, and Mg: 0.0060% or less, with the balance being Fe and impurities.
• the number density of TiC-based precipitates having a circle equivalent diameter of 1.0 ⁇ m or more and the Mg content in the steel satisfy the following: TiC number density (particles/mm 2 ) ⁇ 463 ⁇ 9.5 ⁇ Mg concentration in steel (ppm by mass).
• the amount of coarse TiC precipitates is appropriately controlled according to the Mg concentration in the alloy material. This enhances the weld hot cracking resistance of the alloy material.
• the alloy material disclosed in Patent Document 3 has a chemical composition containing, by mass%, C: 0.15% or less, Si: 0.05-2.0%, Mn: 0.05-2.0%, P: 0.035% or less, S: 0.0015% or less, O: 0.0020% or less, with the sum of O+S being 0.0020% or less, Cr: 16-30%, Ni: 18-50%, Al: 0.01-1.0%, Ti: 0.01-1.5%, N: 0.02% or less, Mo: 8% or less, Cu: 4% or less, Co: 3% or less, Ca: 0.0010-0.0050%, and Mg: 0.0010-0.0050%, with the balance being Fe and impurities.
• the average concentration of S in the oxide-based inclusions and sulfide-based inclusions is 0.70% or more by mass.
• S which reduces the grain boundary strength and the melting point of the grain boundary, is fixed in the inclusions. This increases the resistance of the alloy to hot welding cracking.
• Patent Document 4 JP 2021-070838 A
• the alloy material disclosed in Patent Document 4 has a chemical composition containing, by mass%, C: 0.10% or less, Si: 0.05-1.0%, Mn: 0.05-2.0%, P: 0.035% or less, S: 0.0015% or less, Cr: 18-25%, Ni: 18-50%, Al: 0.05-1.0%, Ti: 0.15-1.5%, N: 0.02% or less, O: 0.003% or less, Mo: 5% or less, W: 2% or less, Cu: 3% or less, Co: 2.0% or less, Ca: 0.0003-0.005%, and Mg: 0.006% or less, with the balance being Fe and unavoidable impurities. Furthermore, the Ca/Al mass ratio in the oxide-based inclusions is 1.0-15.
• ⁇ Ca in the alloy material is appropriately controlled. This improves the hot workability of the alloy material.
• Patent Documents 1 to 3 provide excellent resistance to hot welding cracking, but these documents do not examine the hot workability of the alloy materials.
• the alloy material described in Patent Document 4 provides excellent hot workability, but does not examine the resistance to hot welding cracking.
• the objective of this disclosure is to provide an alloy material that has high creep strength, as well as excellent resistance to hot welding cracking and excellent hot workability.
• the alloy material according to the present disclosure comprises: The chemical composition, in mass%, is C: 0.050-0.100%, Si: 1.00% or less, Mn: 1.50% or less, P: 0.035% or less, S: 0.0015% or less, Cr: 19.00-23.00%, Ni: 30.00-35.00%, N: 0.010% or less, Al: 0.15-0.70%, Ti: 0.15-0.70%, B: 0.0001 to 0.0030%, Nb: 0.0010 to 0.5000%, Mo: 0.01-1.00%, Ca: 0.0001-0.0200%, Ta: 0 to 0.50%, V: 0-1.00%, Zr: 0 to 0.100%, Hf: 0-0.10%, Cu: 0 to 1.00%, W: 0-1.00%, Co: 0-1.00%, Rare earth elements: 0 to 0.1000%, Mg: 0 to 0.0200%, and The balance is Fe and impurities.
• formula (3) is further satisfied. 0.60 ⁇ Al+Ti ⁇ 1.20 (1) 3.3-41C-Si+2Mo+3Ti+245B-12Nb ⁇ 2.00 (2) 0.4+67C+1.3Si+5.5Mo+5.2Ti+13.4Nb ⁇ 8.25 (3)
• the content of the corresponding element in the chemical composition is substituted for each element symbol in formulas (1) to (3) in terms of mass %.
• the alloy material disclosed herein provides high creep strength, as well as excellent resistance to hot welding cracking and excellent hot workability.
• the inventors first conducted a study from the viewpoint of chemical composition on an alloy material that provides high creep strength, excellent resistance to weld hot cracking, and excellent hot workability. As a result, the inventors found that the alloy material contains, in mass%, C: 0.050-0.100%, Si: 1.00% or less, Mn: 1.50% or less, P: 0.035% or less, S: 0.0015% or less, Cr: 19.00-23.00%, Ni: 30.00-35.00%, N: 0.010% or less, Al: 0.15-0.70%, Ti: 0.15-0.70%, B: 0.0001-0.0030%, Nb: 0.0010-0.5000%, Mo: 0.01-1.00%, Ca: 0.
• an alloy material with a chemical composition of 0.0001-0.0200%, Ta: 0-0.50%, V: 0-1.00%, Zr: 0-0.100%, Hf: 0-0.10%, Cu: 0-1.00%, W: 0-1.00%, Co: 0-1.00%, rare earth elements: 0-0.1000%, Mg: 0-0.0200%, and the balance being Fe and impurities, could be used in high-temperature environments and could potentially achieve excellent resistance to weld hot cracking and excellent hot workability.
• the inventors therefore further investigated the creep strength, resistance to hot welding cracking, and hot workability of alloy materials that satisfy the above-mentioned chemical composition. As a result, the inventors obtained the following findings.
• the present inventors have investigated means for increasing creep strength in high-temperature environments in alloy materials that satisfy the above-mentioned chemical composition.
• Al and Ti form a gamma prime ( ⁇ ') phase ( Ni3 (Al,Ti)) in the alloy material during use in high-temperature environments.
• the ⁇ ' phase increases creep strength. Therefore, the total content of Al and Ti affects creep strength.
• sufficient creep strength can be obtained if the following formula (1) is satisfied: 0.60 ⁇ Al+Ti ⁇ 1.20 (1)
• each element symbol in formula (1) is substituted with the content of the corresponding element in the chemical composition of the alloy material in mass %.
• the inventors therefore investigated ways to improve hot workability while also improving resistance to welding hot cracking by including B.
• it is effective to (A) increase the melting and solidification temperatures of Ti-based precipitates that precipitate at the grain boundaries, and (B) increase the solidification temperature of the grain boundaries that melt due to the compositional liquation phenomenon during the heating process during welding.
• the Ti-based precipitate means a precipitate containing Ti.
• the Ti-based precipitate is mainly a carbide containing Ti.
• the Ti-based precipitate may contain elements other than Ti (e.g., Si, Nb, etc.).
• C, Si and Nb increase the melting and solidification temperatures of Ti-based precipitates.
• C and Si increase the stability of Ti-based precipitates at high temperatures. This increases the melting and solidification temperatures of Ti-based precipitates.
• Nb is contained in Ti-based precipitates and increases the melting and solidification temperatures of Ti-based precipitates. Therefore, C, Si and Nb are elements that increase the melting and solidification temperatures of Ti-based precipitates that precipitate at grain boundaries.
• Grain boundaries where compositional liquefaction occurs become the starting point of cracks. Therefore, in order to improve resistance to hot welding cracking, it is effective not only to increase the melting temperature and solidification temperature of Ti-based precipitates, but also to increase the solidification temperature of grain boundaries where compositional liquefaction occurs. Therefore, the inventors investigated means for increasing the solidification temperature of grain boundaries where compositional liquefaction occurs. As a result, they found that Mo, Ti, and B promote compositional liquefaction at grain boundaries. When Mo, Ti, or B is contained in the grain boundaries where compositional liquefaction occurs, the solidification temperature of the grain boundaries where compositional liquefaction occurs decreases. If the solidification temperature of the grain boundaries where compositional liquefaction occurs decreases, hot welding cracking becomes more likely to occur.
• Ti-based precipitates may be present within the crystal grains during hot working at approximately 900°C.
• the Ti-based precipitates harden the alloy material.
• the hot workability of the alloy material decreases. Therefore, in order to improve the hot workability at approximately 900°C, it is effective to suppress the hardening of the alloy material caused by Ti-based precipitates.
• the inventors therefore investigated means for sufficiently suppressing hardening of the alloy material caused by Ti-based precipitates during hot working when the B content is 0.0010% or less. As a result, the inventors obtained the following findings.
• C, Ti, Si and Nb promote the formation of Ti-based precipitates.
• C and Ti directly contribute to the formation of Ti-based precipitates.
• Si increases the diffusion rate of C and Ti, contributing to the formation of Ti-based precipitates.
• Nb substitutes for the Ti sites of Ti-based precipitates (i.e., lattice points occupied by Ti atoms in Ti-based precipitates), promoting the formation of Ti-based precipitates (composite precipitates) containing Nb.
• Mo strengthens the grain interior with solid solution, hardening the alloy material even in the hot working temperature range.
• the inventors believed that when the B content is 0.0010% or less, the hot workability at approximately 900°C can be improved by appropriately controlling the C content, Ti content, Si content, Nb content, and Mo content.
• the alloy material of the first configuration is The chemical composition, in mass%, is C: 0.050-0.100%, Si: 1.00% or less, Mn: 1.50% or less, P: 0.035% or less, S: 0.0015% or less, Cr: 19.00-23.00%, Ni: 30.00-35.00%, N: 0.010% or less, Al: 0.15-0.70%, Ti: 0.15-0.70%, B: 0.0001 to 0.0030%, Nb: 0.0010-0.5000%, Mo: 0.01-1.00%, Ca: 0.0001-0.0200%, Ta: 0 to 0.50%, V: 0-1.00%, Zr: 0 to 0.100%, Hf: 0-0.10%, Cu: 0 to 1.00%, W: 0-1.00%, Co: 0-1.00%, Rare earth elements: 0 to 0.1000%, Mg: 0 to 0.0200%, and The balance is Fe and impurities.
• formula (3) is further satisfied. 0.60 ⁇ Al+Ti ⁇ 1.20 (1) 3.3-41C-Si+2Mo+3Ti+245B-12Nb ⁇ 2.00 (2) 0.4+67C+1.3Si+5.5Mo+5.2Ti+13.4Nb ⁇ 8.25 (3)
• the content of the corresponding element in the chemical composition is substituted for each element symbol in formulas (1) to (3) in terms of mass %.
• the alloy material of the second configuration is 1.
• An alloy material of a first configuration comprising: The chemical composition is, in mass%, Ta: 0.01 to 0.50%, V: 0.01-1.00%, Zr: 0.001 to 0.100%, Hf: 0.01-0.10%, Cu: 0.01 to 1.00%, W: 0.01-1.00%, Co: 0.01 to 1.00%, Rare earth elements: 0.0001 to 0.1000%, and Mg: 0.0001 to 0.0200%.
• the alloy material of the third configuration is An alloy material having a first or second configuration,
• the chemical composition is, in mass%, B: contains more than 0.0010 to 0.0030%;
• the Ti content [Ti] in mass% in the residue obtained by the extraction residue method is less than 0.020%, or The [Ti] is 0.020% or more, the Nb content [Nb] in mass% in the residue is 0.015% or more, and the [Ti] and the [Nb] satisfy formula (4).
• the alloy material of the fourth configuration is An alloy material having a first or second configuration,
• the chemical composition is, in mass%, B: 0.0001 to 0.0010%;
• the Ti content [Ti] in mass% in the residue obtained by the extraction residue method is 0.031% or less, or The [Ti] exceeds 0.031%, and the Nb content [Nb] in mass % in the residue is 0.3 ⁇ [Ti]% or more.
• the alloy material of this embodiment satisfies the following characteristics 1 to 4.
• the chemical composition is, in mass%, C: 0.050-0.100%, Si: 1.00% or less, Mn: 1.50% or less, P: 0.035% or less, S: 0.0015% or less, Cr: 19.00-23.00%, Ni: 30.00-35.00%, N: 0.010% or less, Al: 0.15-0.70%, Ti: 0.15-0.70%, B: 0.0001-0.0030%, Nb: 0.00 10-0.5000%, Mo: 0.01-1.00%, Ca: 0.0001-0.0200%, Ta: 0-0.50%, V: 0-1.00%, Zr: 0-0.100%, Hf: 0-0.10%, Cu: 0-1.00%, W: 0-1.00%, Co: 0-1.00%, rare earth elements: 0-0.1000%, Mg: 0-0.0200%, and the balance is Fe and impurities.
• the alloy material of this embodiment satisfies the above-mentioned features 1 to 4. Therefore, the alloy material of this embodiment has high creep strength, and further has excellent resistance to hot welding cracking and excellent hot workability. Features 1 to 4 are explained below.
• Carbon (C) enhances the creep strength of the alloy material in a high-temperature environment. If the C content is less than 0.050%, the above effect can be obtained even if the contents of other elements are within the range of this embodiment. is not being obtained sufficiently. On the other hand, if the C content exceeds 0.100 %, M23C6 type Cr carbides are formed at the grain boundaries. In this case, Cr-depleted regions are formed at the grain boundaries. Therefore, the content of other elements is Even within the range of this embodiment, the stress relaxation cracking resistance of the alloy material is reduced. Therefore, the C content is 0.050 to 0.100%.
• the lower limit of the C content is preferably 0.055%, more preferably 0.060%, further preferably 0.065%, and further preferably 0.070%.
• the upper limit of the C content is preferably 0.097%, more preferably 0.095%, still more preferably 0.093%, still more preferably 0.090%, and still more preferably 0.085%. %, and more preferably 0.080%.
• Si 1.00% or less Silicon (Si) deoxidizes the alloy in the steelmaking process. Si also enhances the oxidation resistance of the alloy material in a high-temperature environment. If even a small amount of Si is contained, the above effect can be obtained to a certain extent even if the contents of other elements are within the range of this embodiment. However, if the Si content exceeds 1.00%, even if the contents of other elements are within the ranges of this embodiment, the resistance to weld hot cracking and the hot workability are reduced. Therefore, the Si content is 1.00% or less.
• the lower limit of the Si content is preferably more than 0%, more preferably 0.01%, more preferably 0.05%, more preferably 0.10%, more preferably 0.15%, and more preferably 0.20%.
• the upper limit of the Si content is preferably 0.90%, more preferably 0.80%, more preferably 0.70%, more preferably 0.65%, more preferably 0.60%, more preferably 0.55%, and more preferably 0.50%.
• Mn 1.50% or less
• Manganese (Mn) deoxidizes the welded portion of the alloy material during welding. Mn also stabilizes austenite. Even if even a small amount of Mn is contained, the above effect can be obtained to some extent. However, if the Mn content exceeds 1.50%, sigma phase ( ⁇ phase) is likely to be generated when used in a high-temperature environment. The ⁇ phase reduces the toughness and creep ductility of the alloy material in a high-temperature environment. Therefore, the Mn content is 1.50% or less.
• the lower limit of the Mn content is preferably more than 0%, more preferably 0.01%, more preferably 0.05%, more preferably 0.10%, more preferably 0.40%, more preferably 0.50%, and more preferably 0.60%.
• the upper limit of the Mn content is preferably 1.45%, more preferably 1.40%, still more preferably 1.35%, still more preferably 1.30%, still more preferably 1.25%, and still more preferably 1.20%.
• Phosphorus (P) is an unavoidable impurity.
• the P content is more than 0%.
• P segregates at the grain boundaries of the alloy material during welding, reducing stress relaxation cracking resistance. P also segregates at the grain boundaries, reducing hot workability. Therefore, the P content is 0.035% or less.
• the P content is preferably as low as possible. However, excessive reduction in the P content significantly increases the production cost. Therefore, in consideration of normal industrial production, the lower limit of the P content is preferably 0.001%, more preferably 0.002%, and even more preferably 0.005%.
• the upper limit of the P content is preferably 0.030%, more preferably 0.025%, further preferably 0.020%, and further preferably 0.015%.
• S 0.0015% or less Sulfur (S) is an unavoidable impurity.
• the S content is more than 0%.
• S segregates at grain boundaries of alloy materials during welding and hot working, and reduces resistance to welding hot cracking and hot workability. Therefore, the S content is 0.0015% or less.
• the S content is preferably as low as possible. However, excessive reduction in the S content significantly increases the production cost. Therefore, in consideration of normal industrial production, the preferred lower limit of the S content is more than 0%, more preferably 0.0001%, and even more preferably 0.0002%.
• the upper limit of the S content is preferably 0.0012%, more preferably 0.0010%, further preferably 0.0008%, and further preferably 0.0006%.
• Chromium (Cr) enhances the corrosion resistance of the alloy material in a high-temperature environment. If the Cr content is less than 19.00%, the above effect can be obtained even if the contents of other elements are within the range of this embodiment. Can't get enough. On the other hand, if the Cr content exceeds 23.00%, the stability of austenite in a high temperature environment is reduced. In this case, even if the contents of other elements are within the range of this embodiment, the creep strength of the alloy material is reduced. decreases. Therefore, the Cr content is 19.00 to 23.00%.
• the lower limit of the Cr content is preferably 19.20%, more preferably 19.40%, and further preferably 19.60%.
• the upper limit of the Cr content is preferably 22.50%, more preferably 22.00%, still more preferably 21.50%, still more preferably 21.00%, and still more preferably 20.50%. %, and more preferably 20.00%.
• Ni 30.00-35.00%
• Nickel (Ni) stabilizes austenite and enhances the creep strength of the alloy in high temperature environments. If the Ni content is less than 30.00%, the other element contents are within the ranges of this embodiment. However, the above effects cannot be sufficiently obtained. On the other hand, if the Ni content exceeds 35.00%, the above effects are saturated, and furthermore, the raw material cost increases. Therefore, the Ni content is 30.00 to 35.00%.
• the lower limit of the Ni content is preferably 30.20%, more preferably 30.40%, further preferably 30.60%, and further preferably 30.80%.
• the upper limit of the Ni content is preferably 34.70%, more preferably 34.50%, still more preferably 34.00%, still more preferably 33.50%, and still more preferably 33.00%. %, more preferably 32.50%, more preferably 32.00%, more preferably 31.50%, and even more preferably 31.00%.
• N 0.010% or less Nitrogen (N) is an impurity. N is dissolved in the matrix (parent phase) to stabilize austenite. The dissolved N further forms fine nitrides in the alloy material during use in a high-temperature environment. The fine nitrides strengthen the Cr-deficient region, thereby improving the stress relaxation cracking resistance of the alloy material. The fine nitrides formed during use in a high-temperature environment further improve creep strength by precipitation strengthening. 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 0.010%, Ti nitrides are excessively formed and coarsened.
• the N content is 0.010% or less.
• the lower limit of the N content is preferably 0.001%.
• the upper limit of the N content is preferably 0.007%, more preferably 0.006%, and further preferably 0.005%.
• Al 0.15-0.70%
• Aluminum (Al) deoxidizes the alloy during the steelmaking process. It also increases the oxidation resistance of the alloy in high-temperature environments. It also generates the ⁇ ' phase in high-temperature environments. If the Al content is less than 0.15%, 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 Al content exceeds 0.70%, a large amount of ⁇ ' phase is generated during the manufacturing process of the alloy material. In this case, even if the contents of other elements are within the range of this embodiment, The hot workability during the manufacturing process of the alloy material is reduced. Therefore, the Al content is 0.15 to 0.70%.
• the lower limit of the Al content is preferably 0.17%, more preferably 0.19%, still more preferably 0.21%, still more preferably 0.23%, and still more preferably 0.30%. %.
• the upper limit of the Al content is preferably 0.65%, more preferably 0.60%, still more preferably 0.57%, still more preferably 0.55%, and still more preferably 0.53%. %, more preferably 0.51%, more preferably 0.45%, and even more preferably 0.40%.
• the Al content is the so-called total Al content (mass %).
• Titanium (Ti) combines with Ni and Al to form the ⁇ ' phase in high temperature environments, improving the creep strength of alloy materials in high temperature environments. If the Ti content is less than 0.15%, other Even if the element contents are within the ranges of this embodiment, the above effects cannot be sufficiently obtained. On the other hand, if the Ti content exceeds 0.70%, the Ti-based precipitates become coarse and a large amount of ⁇ ' phase is generated during the manufacturing process of the alloy material. Even within the range of this embodiment, resistance to hot welding cracking and hot workability are deteriorated. Therefore, the Ti content is 0.15 to 0.70%.
• the lower limit of the Ti content is preferably 0.16%, more preferably 0.17%, further preferably 0.18%, and further preferably 0.20%.
• the upper limit of the Ti content is preferably 0.65%, more preferably 0.60%, still more preferably 0.57%, still more preferably 0.55%, and still more preferably 0.50%. %, and more preferably 0.45%.
• B 0.0001-0.0030% Boron (B) segregates at grain boundaries in a high-temperature environment of about 900°C, increasing grain boundary strength. This improves the hot workability of the alloy material. If the B content is less than 0.0001%, Even if the contents of other elements are within the ranges of this embodiment, the above effects cannot be sufficiently obtained. On the other hand, if the B content exceeds 0.0030%, B lowers the solidification temperature of the grain boundary melted during welding heating. In this case, even if the contents of other elements are within the range of this embodiment, the resistance Weld hot cracking resistance decreases. Therefore, the B content is 0.0001 to 0.0030%.
• the lower limit of the B content is preferably 0.0003%, more preferably 0.0005%, and further preferably 0.0010%.
• the upper limit of the B content is preferably 0.0028%, more preferably 0.0025%, further preferably 0.0023%, and further preferably 0.0020%.
• Niobium (Nb) when contained in Ti-based precipitates, increases the melting and solidification temperatures of the Ti-based precipitates, thereby improving the resistance to hot weld cracking of the alloy material. Nb also has the effect of increasing the resistance to hot weld cracking in high temperature environments. Fine precipitates are formed in the alloy material, thereby improving the creep strength of the alloy material. If the Nb content is less than 0.0010%, even if the contents of other elements are within the ranges of this embodiment, , the above-mentioned effects cannot be obtained sufficiently. On the other hand, if the Nb content exceeds 0.5000%, the hot workability of the alloy material decreases even if the contents of other elements are within the ranges of this embodiment.
• the Nb content is 0.0010 to 0.5000%.
• the lower limit of the Nb content is preferably 0.0020%, more preferably 0.0050%, further preferably 0.0080%, and further preferably 0.0100%.
• the upper limit of the Nb content is preferably 0.4500%, more preferably 0.4000%, still more preferably 0.3000%, still more preferably 0.2500%, and still more preferably 0.2400%. %.
• Mo Molybdenum
• B Molybdenum
• the Mo content If the amount is less than 0.01%, the above effects cannot be obtained sufficiently.
• the Mo content exceeds 1.00%, intermetallic compounds such as LAVES phases are generated within the crystal grains. In this case, the strength difference between the crystal grains and the grain boundaries becomes large.
• the B content is 0.0010% or less, not only the above-mentioned effect of Mo is reduced, but also the hardness within the grains increases due to solid solution strengthening of Mo. The hot workability around 1000°C decreases.
• the Mo content is 0.01 to 1.00%.
• the lower limit of the Mo content is preferably 0.02%, more preferably 0.03%, further preferably 0.04%, and further preferably 0.05%.
• the upper limit of the Mo content is preferably 0.90%, more preferably 0.80%, still more preferably 0.70%, still more preferably 0.60%, and still more preferably 0.50%. %.
• the lower limit of the Ca content is preferably 0.0002%, more preferably 0.0005%, and further preferably 0.0010%.
• the upper limit of the Ca content is preferably 0.0150%, more preferably 0.0100%, still more preferably 0.0080%, still more preferably 0.0050%, and still more preferably 0.0040%. %, and more preferably 0.0030%.
• Tantalum (Ta) is an optional element and may not be contained, that is, the Ta content may be 0%.
• Ta is contained, that is, when the Ta content is more than 0%, Ta is combined with Ti and C and is contained in the Ti-based precipitates. The melting temperature and solidification temperature are increased. Therefore, the solidification temperature of the grain boundary melted during welding is increased. As a result, resistance to hot cracking during welding is improved. If even a small amount of Ta is contained, the above effect can be obtained to a certain extent. . However, if the Ta content exceeds 0.50%, the resistance to hot cracking during welding of the alloy material is reduced in the weld heat affected zone of the alloy material. Furthermore, the hot workability is reduced.
• the Ta content is 0 to 0.50%.
• the lower limit of the Ta content is preferably 0.01%, more preferably 0.02%, further preferably 0.05%, and further preferably 0.08%.
• the upper limit of the Ta content is preferably 0.45%, more preferably 0.40%, further preferably 0.35%, and further preferably 0.30%.
• the V content is 0 to 1.00%.
• the lower limit of the V content is preferably 0.01%, more preferably 0.02%, still more preferably 0.04%, and still more preferably 0.06%.
• the upper limit of the V content is preferably 0.80%, more preferably 0.50%, still more preferably 0.40%, still more preferably 0.35%, and still more preferably 0.30%.
• Zr Zirconium (Zr) is an optional element and may not be contained, that is, the Zr content may be 0%.
• Zr is contained, that is, when the Zr content is more than 0%, Zr is combined with Ti and C and is contained in Ti carbide. Melting temperature of Ti-based precipitates containing Zr The solidification temperature of the grain boundary melted during welding is increased. As a result, resistance to hot cracking during welding is improved. The above effect can be obtained to a certain extent if even a small amount of Zr is contained. However, if the Zr content exceeds 0.100%, the resistance to hot weld cracking in the weld heat affected zone of the alloy material is rather reduced during welding of the alloy material.
• Hf 0-0.10%
• Hafnium (Hf) is an optional element and may not be contained. In other words, the Hf content may be 0%.
• Hf is contained, that is, when the Hf content is more than 0%, Hf is combined with Ti and C and is contained in Ti-based precipitates.
• the melting and solidification temperatures of Ti-based precipitates containing Hf are high. Therefore, the solidification of the grain boundaries melted during welding is difficult. As a result, resistance to hot cracking during welding is improved. Even if even a small amount of Hf is contained, the above effect can be obtained to a certain extent.
• the Hf content is 0 to 0.10%.
• the lower limit of the Hf content is preferably 0.01%, and more preferably 0.02%.
• the upper limit of the Hf content is preferably 0.09%, more preferably 0.08%, further preferably 0.07%, and further preferably 0.06%.
• the chemical composition of the alloy material according to the present embodiment may further contain, in place of a portion of Fe, one or more elements selected from the group consisting of Cu, W, and Co. These elements are optional elements, and all of them increase the creep strength of the alloy material.
• Cu 0-1.00% 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 precipitates as a Cu phase in grains during use of the alloy material in a high-temperature environment. The creep strength is improved. If even a small amount of Cu is contained, the above effect can be obtained to some extent. However, if the Cu content exceeds 1.00%, the Cu phase is excessively precipitated in the crystal grains. In this case, the strength difference between the crystal grains and the grain boundaries becomes large. Therefore, the stress relaxation resistance is deteriorated. The crack resistance decreases. Therefore, the Cu content is 0 to 1.00%.
• the lower limit of the Cu 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%. %, and more preferably 0.20%.
• the upper limit of the Cu content is preferably 0.90%, more preferably 0.80%, still more preferably 0.70%, still more preferably 0.60%, and still more preferably 0.55%. %, and more preferably 0.50%.
• the lower limit of the W content is preferably 0.01%, more preferably 0.02%, more preferably 0.03%, more preferably 0.04%, more preferably 0.05%, and more preferably 0.10%.
• the upper limit of the W content is preferably 0.90%, more preferably 0.80%, more preferably 0.70%, more preferably 0.65%, more preferably 0.60%, and even more preferably 0.50%.
• Co is an optional element and may not be contained, that is, the Co content may be 0%.
• Co When Co is contained, that is, when the Co content is more than 0%, Co stabilizes austenite and increases the creep strength of the alloy material in a high-temperature environment. The effect is achieved to some extent. However, if the Co content exceeds 1.00%, the raw material cost increases. Therefore, the Co content is 0 to 1.00%.
• the lower limit of the Co content is preferably 0.01%, more preferably 0.02%, still more preferably 0.03%, still more preferably 0.05%, and still more preferably 0.10%. %.
• the upper limit of the Co content is preferably 0.90%, more preferably 0.80%, still more preferably 0.70%, still more preferably 0.60%, and still more preferably 0.50%. %.
• the chemical composition of the alloy material according to this embodiment may further contain rare earth elements (REM) in place of a portion of Fe.
• the rare earth elements are optional elements and may not be contained, i.e., the REM content may be 0%.
• REM When REM is contained, that is, when the REM content is more than 0%, REM fixes S (sulfur) as an inclusion, improving the hot workability of the alloy material. This fixes the REM content and suppresses the grain boundary segregation of S. In this case, resistance to hot welding cracking is improved.
• the above effect can be obtained to a certain extent if even a small amount of REM is contained. However, if the REM content exceeds 0.1000%, the cleanliness of the alloy material is reduced, and in this case, the hot workability of the alloy material is rather reduced.
• the REM content is 0 to 0.1000%.
• the lower limit of the REM content is preferably 0.0001%, more preferably 0.0005%, further preferably 0.0010%, and further preferably 0.0020%.
• the upper limit of the REM content is preferably 0.0800%, more preferably 0.0600%, and further preferably 0.0400%.
• REM contains at least one of the elements Sc, Y, and lanthanides (La with atomic number 57 to Lu with atomic number 71), and the REM content refers to the total content of these elements.
• the chemical composition of the alloy material according to this embodiment may further contain Mg instead of a portion of Fe.
• Mg 0 to 0.0200%
• Magnesium (Mg) is an impurity and does not necessarily need to be contained.
• the Mg content may be 0%. If the Mg content exceeds 0.0200%, Mg segregates at grain boundaries in a high-temperature environment of about 900° C., embrittling the grain boundaries, and in this case, the hot workability of the alloy material decreases. Therefore, the Mg content is 0 to 0.0200%.
• the Mg content is preferably as low as possible. However, excessive reduction in the Mg content significantly increases the production cost. Therefore, in consideration of normal industrial production, the lower limit of the Mg content is preferably more than 0%, more preferably 0.0001%, and even more preferably 0.0002%.
• the upper limit of the Mg content is preferably 0.0150%, more preferably 0.0100%, still more preferably 0.0080%, still more preferably 0.0050%, and still more preferably 0.0040%.
• F1 is defined as Al + Ti.
• F1 is an index of the amount of ⁇ ' phase generated during use of the alloy material of this embodiment in a high-temperature environment.
• the ⁇ ' phase is generated during use in a high-temperature environment. This ⁇ ' phase increases the creep strength of the alloy material in a high-temperature environment.
• the lower limit of F1 is preferably 0.61, more preferably 0.62, more preferably 0.64, more preferably 0.66, more preferably 0.68, and more preferably 0.70.
• the upper limit of F1 is preferably 1.15, more preferably 1.10, still more preferably 1.05, still more preferably 1.00, and still more preferably 0.95.
• the numerical value of F1 shall be the value obtained by rounding off to the second decimal place.
• F2 is defined as 3.3-41C-Si+2Mo+3Ti+245B-12Nb.
• F2 is an index of resistance to hot cracking during welding.
• the alloy material of this embodiment contains B.
• the solidification temperature of the grain boundaries of the alloy material is reduced due to the segregation of B to the grain boundaries. Therefore, resistance to hot cracking during welding is likely to decrease.
• C, Si, and Nb increase the solidification temperature of Ti-based precipitates after melting.
• Mo, Ti, and B promote the compositional liquefaction phenomenon, lowering the solidification temperature of the grain boundaries after melting. Therefore, by appropriately controlling the C content, Si content, Nb content, Mo content, Ti content, and B content, the above (A) and (B) are simultaneously achieved, increasing the solidification temperature of the grain boundaries after melting during welding, and as a result, improving resistance to welding hot cracking. Even if the alloy material satisfies features 1, 2, and 4, if F2 exceeds 2.00, the above effects cannot be sufficiently obtained. Therefore, F2 is 2.00 or less.
• the upper limit of F2 is preferably 1.97, more preferably 1.95, still more preferably 1.93, and still more preferably 1.90.
• the lower limit of F2 is not particularly limited, but is preferably ⁇ 7.00, more preferably ⁇ 6.00, even more preferably ⁇ 5.00, and even more preferably ⁇ 4.00.
• the numerical value of F2 shall be the value obtained by rounding off to the second decimal place.
• F3 is defined as 0.4 + 67C + 1.3Si + 5.5Mo + 5.2Ti + 13.4Nb. F3 is an index of hot workability when hot working is performed at approximately 900°C.
• the chemical composition of the alloy material is made to satisfy formula (2), thereby increasing the solidification temperature of the grain boundaries after melting during welding and improving resistance to hot welding cracking.
• an alloy material with high resistance to hot cracking is used.
• the B content in the alloy material may be adjusted to 0.0010% or less.
• the alloy material of this embodiment improves the hot workability by suppressing the hardening of the alloy material due to Ti-based precipitates.
• C, Si, Mo, Ti and Nb promote the formation of Ti-based precipitates. Therefore, when the B content in the chemical composition is set to 0.0010% or less, the value of F3 consisting of the C content, Si content, Mo content, Ti content and Nb content is appropriately adjusted to suppress the formation of Ti-based precipitates. This improves hot workability at around 900°C. Even if the alloy material satisfies Features 1 to 3, if F3 exceeds 8.25, the above effects cannot be sufficiently obtained. Therefore, F3 is 8.25 or less.
• the upper limit of F3 is preferably 8.20, more preferably 8.15, still more preferably 8.13, and still more preferably 8.10.
• the lower limit of F3 is not particularly limited, but is preferably 4.60, more preferably 4.80, more preferably 5.00, and even more preferably 5.50.
• the numerical value of F3 shall be the value obtained by rounding off to the second decimal place.
• the alloy material of this embodiment satisfies the above-mentioned features 1 to 4. As a result, the alloy material of this embodiment has sufficient creep strength in high-temperature environments, and can achieve both excellent resistance to weld hot cracking and excellent hot workability.
• the microstructure of the alloy material of this embodiment is made of austenite.
• the shape of the alloy material of this embodiment is not particularly limited.
• the alloy material may be an alloy tube or an alloy plate.
• the alloy material may be rod-shaped.
• the alloy material of this embodiment is an alloy tube or an alloy plate.
• the alloy material of this embodiment when the B content exceeds 0.0010%
• the alloy material of this embodiment further satisfies the following feature 5.
• the Ti content [Ti] in mass% in the residue obtained by the extraction residue method is less than 0.020%, or [Ti] is 0.020% or more, the Nb content [Nb] in terms of mass% in the residue is 0.015% or more, and [Ti] and [Nb] satisfy formula (4).
• [Ti]+[Nb] ⁇ 0.050 (4) Feature 5 will now be described.
• the alloy material of this embodiment when the B content in the chemical composition is more than 0.0010% and less than 0.0030%, by satisfying Features 1 to 3, the alloy material has sufficient creep strength in high-temperature environments and can achieve both excellent resistance to weld hot cracking and excellent hot workability.
• the alloy material of this embodiment a certain amount of Ti-based precipitates is contained in the alloy material before welding. Therefore, in the heating process when welding the alloy material, the Ti-based precipitates trapped at the grain boundaries are eutectic melted. Since the alloy material of this embodiment contains B, B is segregated at the grain boundaries. Therefore, the solidification temperature of the grain boundaries after melting is lowered by B. As a result, the resistance to welding hot cracking is reduced. Therefore, in the alloy material of this embodiment, when the B content is more than 0.0010% to 0.0030%, it is preferable to adopt either of the following two measures I and II.
• the alloy material of this embodiment preferably satisfies either the following requirement I or requirement II.
• the Ti content [Ti] in the residue is less than 0.020%.
• [Ti] in the residue obtained by the extraction residue method is 0.020% or more
• the Nb content [Nb] in the residue is 0.015% or more
• [Ti] and [Nb] satisfy formula (4). [Ti]+[Nb] ⁇ 0.050 (4)
• the preferred upper limit of the Ti content in the residue [Ti] is 0.019%, and more preferably 0.017%.
• the proportion of Ti-based precipitates containing Nb is high among the Ti-based precipitates present in the alloy material. Therefore, the solidification temperature of the grain boundary after eutectic melting of the Ti-based precipitates with the grain boundary is sufficiently high. As a result, even better resistance to hot welding cracking is obtained.
• the preferred lower limit of [Ti] + [Nb] in the residue is 0.052%, more preferably 0.060%, more preferably 0.070%, more preferably 0.080%, and even more preferably 0.090%.
• the alloy material of this embodiment when the B content is 0.0010% or less
• the alloy material of this embodiment further satisfies the following feature 6.
• the Ti content [Ti] in mass% in the residue obtained by the extraction residue method is 0.031% or less, or [Ti] exceeds 0.031%, and the Nb content [Nb] in mass % in the residue is 0.3 ⁇ [Ti]% or more.
• Feature 6 will now be described.
• the [Ti] and [Nb] in the residue of the alloy material are determined by the following extraction residue method.
• a test piece is taken from the alloy material.
• the cross section perpendicular to the longitudinal direction of the test piece may be circular or rectangular.
• the test piece is taken so that the center of a cross section perpendicular to the longitudinal direction of the test piece is the center position of the wall thickness of the alloy pipe, and the longitudinal direction of the test piece is the axial direction of the alloy pipe.
• the test piece is taken so that the center of a cross section perpendicular to the longitudinal direction of the test piece is the center position of the plate width and the center position of the plate thickness of the alloy plate, and the longitudinal direction of the test piece is the longitudinal direction of the alloy plate.
• the alloy material is a round bar
• the test piece is taken so that the center of a cross section perpendicular to the longitudinal direction of the test piece is at the R/2 position of the round bar (the center position of the radius in a cross section perpendicular to the longitudinal direction of the round bar) and the longitudinal direction of the test piece is the longitudinal direction of the round bar.
• the surface of the collected test piece is polished by about 50 ⁇ m by preliminary electrolytic polishing to obtain a new surface.
• the electrolytically polished test piece is electrolyzed (main electrolysis) with an electrolytic solution (10% acetylacetone + 1% tetraammonium + methanol).
• the electrolytic solution after the main electrolysis is passed through a 0.2 ⁇ m filter to capture the residue.
• the obtained residue is decomposed with acid, and the mass of Ti in the residue and the mass of Nb in the residue are determined by ICP (inductively coupled plasma) emission spectrometry.
• the mass of the electrolyzed alloy material is determined. Specifically, the mass of the test piece before the electrolysis and the mass of the test piece after the electrolysis are measured. The value obtained by subtracting the mass of the test piece after the electrolysis from the mass of the test piece before the electrolysis is defined as the mass of the electrolyzed alloy material.
• the Ti content [Ti] (mass%) in the residue is calculated by dividing the mass of the electrolytically processed alloy material. Furthermore, the Nb content [Nb] (mass%) in the residue is calculated by dividing the mass of the Nb in the residue by the mass of the electrolytically processed alloy material.
• a method for producing the alloy material of this embodiment will be described.
• the method for producing the alloy material of this embodiment will be described below as an example. Therefore, the alloy material of this embodiment may be produced by a method other than the method for producing the alloy material of this embodiment. However, the method for producing the alloy material of this embodiment will be described below as a preferred example.
• the method for producing the alloy material of this embodiment includes the following steps.
• Step 1) Preparation step (Step 2) Hot working step (Step 3) Cold working step (Step 4) Heat treatment step
• Step 3 Cold working step
• Step 4 Heat treatment step
• the above step 3 is an optional step and may not be performed. Each step will be described below.
• a material having a chemical composition that satisfies the above-mentioned features 1 to 4 is prepared.
• the material may be supplied from a third party or may be manufactured.
• the material may be an ingot. , slabs, blooms, or billets.
• the material is manufactured by the following method.
• a molten alloy having the above-mentioned chemical composition is manufactured.
• the manufactured molten alloy is used to manufacture an ingot by ingot casting.
• the manufactured molten alloy may be used to manufacture slabs, blooms, or billets by continuous casting.
• the manufactured ingots, slabs, or blooms may be subjected to hot processing to manufacture billets.
• an ingot may be subjected to hot forging to manufacture a cylindrical billet, and this billet may be used as the material.
• the temperature of the material immediately before the start of hot forging is not particularly limited, but is, for example, 1100 to 1300°C.
• the method of cooling the material after hot forging is not particularly limited.
• Step 2 Hot working step In the hot working step, the raw material prepared in the preparation step is subjected to hot working to produce an intermediate alloy material.
• the intermediate alloy material may be, for example, an alloy pipe, an alloy plate, or an alloy round bar.
• the hot working process involves the following steps: First, a cylindrical material is prepared. A through hole is formed along the central axis of the cylindrical material by machining. The cylindrical material with the through hole formed is heated. The heated cylindrical material is subjected to hot extrusion, typically the Euffer-Séjournet process, to produce the intermediate alloy material (alloy pipe).
• piercing and rolling by the Mannesmann method may be performed to manufacture alloy tubes.
• the cylindrical material is heated.
• the heating temperature is not particularly limited, but is, for example, 1100 to 1300°C.
• the heated cylindrical material is piercing and rolling using a piercing machine.
• the piercing ratio is not particularly limited, but is, for example, 1.0 to 4.0.
• the piercing and rolling cylindrical material is further hot rolled using a mandrel mill, reducer, sizing mill, etc. to form a hollow blank tube (alloy tube).
• the cumulative reduction in area in the hot working process is not particularly limited, but is, for example, 20 to 80%.
• the temperature (finishing temperature) of the hollow blank tube immediately after the hot working is completed is preferably 800°C or higher.
• the hot working process includes hot working at about 900°C.
• the hot working process uses, for example, one or more rolling mills equipped with a pair of work rolls.
• a material such as a slab is heated.
• the heated material is hot rolled using the rolling mill to produce an alloy plate.
• the heating temperature of the material before hot rolling is not particularly limited, but is, for example, 1100 to 1300°C.
• the hot working process includes hot working at about 900°C.
• the hot working process uses, for example, one or more rolling mills equipped with a pair of work rolls.
• the pair of work rolls are formed with a groove.
• a material such as a bloom is heated.
• the heated material is hot rolled using a rolling mill to produce a round bar.
• the heating temperature of the material before hot rolling is not particularly limited, but is, for example, 1100 to 1300°C.
• the hot working process includes hot working at about 900°C.
• the cold working step is carried out as necessary. In other words, the cold working step does not have to be carried out.
• the intermediate alloy material is subjected to pickling treatment and then cold working.
• the cold working is, for example, cold drawing.
• the intermediate alloy material is an alloy plate
• the cold working is, for example, cold rolling.
• the area reduction rate in the cold working step is not particularly limited, but is, for example, 10 to 90%.
• Step 4 Heat treatment step
• the intermediate alloy material after the hot working process or the cold working process is subjected to heat treatment to adjust the amount of solute Ti in the alloy material and the size of the crystal grains.
• the heat treatment temperature T1 is 1170 to 1300°C.
• the holding time at the heat treatment temperature T1 is not particularly limited, but is, for example, 5 to 30 minutes. After the holding time has elapsed, the intermediate alloy material is quenched.
• the above steps allow the alloy material of this embodiment to be manufactured.
• the above manufacturing method is one example of a method for manufacturing the alloy material of this embodiment. Therefore, the method for manufacturing the alloy material of this embodiment is not limited to the above manufacturing method. As long as Features 1 to 4 are satisfied, the method for manufacturing the alloy material is not limited to the above manufacturing method.
• the heat treatment temperature T1 in the heat treatment step satisfies the following formula (X).
• Nb content in the chemical composition of the alloy material is substituted for (Nb) in formula (X) in mass %.
• the heat treatment temperature T1 is FA or lower, and the B content in the alloy material is greater than 0.0010% and less than 0.0030%, characteristic 5 (requirement (I) or requirement (II)) is more likely to be satisfied. Also, if the B content in the alloy material is 0.0001% to 0.0010%, characteristic 6 (requirement (III) or requirement (IV)) is more likely to be satisfied.
• the welded joint of the alloy material of this embodiment can be manufactured by the following method.
• the alloy material of this embodiment is prepared as the base material.
• a groove is formed in the prepared base material. Specifically, a groove is formed at the end of the base material by a well-known processing method.
• the groove shape may be V-shaped, U-shaped, X-shaped, or any other shape other than V-shaped, U-shaped, or X-shaped.
• Welding is performed on the prepared base material to produce a welded joint.
• two base materials with grooves are prepared.
• the grooves of the prepared base materials are butted together.
• welding is performed on the pair of butted grooves using a known welding material to form a weld metal having the above-mentioned chemical composition.
• An example of the welding material is AWS standard name: ER NiCr-3.
• the welding material is not limited to this.
• the welding method may be a single layer of weld metal or a multi-layer welding method.
• Examples of the welding method include TIG welding (GTAW), shielded metal arc welding (SMAW), flux-cored wire arc welding (FCAW), gas metal arc welding (GMAW), and submerged arc welding (SAW).
• GTAW TIG welding
• SMAW shielded metal arc welding
• FCAW flux-cored wire arc welding
• GMAW gas metal arc welding
• SAW submerged arc welding
• alloy material of this embodiment will be explained in more detail using examples.
• the conditions in the following examples are one example of conditions adopted to confirm the feasibility and effects of the alloy material of this embodiment. Therefore, the alloy material of this embodiment is not limited to this one example of conditions.
• Greeble test pieces were taken from the produced ingots. After the Greeble test pieces were taken, hot forging was performed on the ingots to produce a material (alloy plate) with a thickness of 30 mm. The heating temperature of the ingot during hot forging was 1100-1300°C. The produced material was subjected to a hot working process. Specifically, the material was heated in a heating furnace. The heating temperature during the hot working process was 1200°C. The heated material was hot rolled to produce an intermediate alloy material (alloy plate) with a thickness of 15 mm.
• a heat treatment process was carried out on the intermediate alloy material.
• the heat treatment temperature T1 (°C) in the heat treatment process was as shown in the "T1 (°C)" column in Table 2.
• the holding time at the heat treatment temperature was 30 minutes. After the holding time had elapsed, the intermediate alloy material was water-cooled to room temperature. Through the above process, alloy materials (alloy plates) with each test number were manufactured.
• Test 1 Measurement test of Ti content [Ti] and Nb content [Nb] in the residue of the alloy material (Test 2) Gleeble test (evaluation of hot workability) (Test 3) Welding hot cracking resistance evaluation test (Test 4) Creep strength evaluation test Each test will be described below.
• Ti content [Ti] (mass%) and Nb content [Nb] (mass%) are shown in the “Ti (mass%)" and “Nb (mass%)” columns in Table 3.
• the 0.3 x [Ti] value and the [Ti] + [Nb] value are shown in the “0.3 x [Ti]” and “Ti + [Nb]” columns in Table 3.
• the Gleeble test piece was heated from room temperature to 1200°C in 60 seconds, and then held at 1200°C for 300 seconds. Then, using He gas, it was cooled to 900°C at a cooling rate of 100°C/min, and held at 900°C for 10 seconds. After the holding time had elapsed, a tensile test was performed on the Gleeble test piece at a displacement rate of 10 mm/sec to break the Gleeble test piece. The dimensions of the cross section of the Gleeble test piece after fracture were measured, and the reduction in area (%) was obtained.
• TIG bead-on welding was performed in the longitudinal direction of the center of the plate width of each test piece under welding conditions of a welding current of 200 A, a voltage of 12 V, and a welding speed of 15 cm/min. During the TIG welding, a bending stress was momentarily applied parallel to the welding direction so that a 2% distortion was applied to the surface layer.
• the area containing the weld crack caused by the application of bending stress was cut out to a size that could be observed with an optical microscope.
• the size of the cut sample was 12 mm thick, 30 mm wide, and 30 mm long.
• the scale on the surface of the welded part of the cut sample was removed by buffing. After that, the presence or absence of cracks in the HAZ and, if cracks had occurred, their length were measured using a 100x optical microscope. Specifically, the length of the crack that propagated in a direction perpendicular to the welding direction (length perpendicular to the welding direction) starting from the boundary between the weld metal and the HAZ was measured. The length of all cracks that occurred in the test piece in the direction perpendicular to the welding direction was determined. The sum of these crack lengths was defined as the total crack length (mm). The total crack length was determined for each of the two test pieces. The arithmetic mean value of the determined total crack lengths was defined as the average total crack length.
• the average total crack length was evaluated as follows: Evaluation E: The average total crack length is 1.5 mm or less. Evaluation G (Good): The average total crack length is more than 1.5 mm and 2.0 mm or less. Evaluation B: The average total crack length exceeds 2.0 mm. In the case of evaluation G or E, it was evaluated that the resistance to welding hot cracking was excellent (shown as "G” or “E” in the "resistance to welding hot cracking” column in Table 3). On the other hand, in the case of evaluation B, it was evaluated that sufficient resistance to welding hot cracking was not obtained (shown as "B” in the "resistance to welding hot cracking” column in Table 3).
• the collected creep rupture test specimens were used to conduct creep rupture tests in accordance with JIS Z2271:2019. Specifically, the creep rupture test specimens were heated to 700°C. The creep rupture test was then conducted. The test stress was 80 MPa. In the test, the creep rupture time (hours) was determined.
• test numbers 1 to 13 in which the B content was greater than 0.0010% and less than 0.0030%, test numbers 2 and 3 also met requirement I of characteristic 5, and test numbers 4 to 13 met requirement II of characteristic 5. Therefore, compared to test number 1, which did not meet characteristic 5, the resistance to hot welding cracking was even better.
• test numbers 14 to 30 which have a B content of 0.0001 to 0.0010%, test numbers 15 to 29 met requirement III of characteristic 6, and test number 30 met requirement IV of characteristic 6. Therefore, compared to test number 14, which did not meet characteristic 6, the resistance to hot welding cracking was even better.
• test numbers 31 to 34 although the content of each element in the chemical composition was appropriate, F1 was too low. As a result, sufficient creep strength was not obtained.
• test numbers 35 to 38 the content of each element in the chemical composition was appropriate, but F1 was too high. As a result, sufficient resistance to hot welding cracking was not obtained.
• test numbers 39 to 43 the content of each element in the chemical composition was appropriate, but F2 was too high. As a result, sufficient resistance to hot welding cracking was not obtained.
• test numbers 44 and 45 the content of each element in the chemical composition was appropriate, but the B content was 0.0010% or less and F3 was too high. As a result, sufficient hot workability was not obtained.

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