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WO2025041848A1 - Matériau d'acier inoxydable à base d'austénite - Google Patents

Matériau d'acier inoxydable à base d'austénite Download PDF

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Publication number
WO2025041848A1
WO2025041848A1 PCT/JP2024/029955 JP2024029955W WO2025041848A1 WO 2025041848 A1 WO2025041848 A1 WO 2025041848A1 JP 2024029955 W JP2024029955 W JP 2024029955W WO 2025041848 A1 WO2025041848 A1 WO 2025041848A1
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content
steel material
austenitic stainless
stainless steel
less
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Japanese (ja)
Inventor
健登 羽仁
孝裕 小薄
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Nippon Steel Corp
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Nippon Steel Corp
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C30/00—Alloys containing less than 50% by weight of each constituent
    • C22C30/04—Alloys containing less than 50% by weight of each constituent containing tin or lead
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon

Definitions

  • This disclosure relates to austenitic stainless steel materials.
  • Hydrogen embrittlement is a problem for tanks and piping for high-pressure hydrogen. Hydrogen embrittlement is a phenomenon in which hydrogen penetration into steel material significantly reduces its ductility and toughness. In other words, austenitic stainless steel materials used for tanks and piping for high-pressure hydrogen are required to have excellent resistance to hydrogen embrittlement in a high-pressure hydrogen gas environment.
  • the austenitic stainless steel materials used in tanks and piping for high-pressure hydrogen also require high strength to withstand high-pressure hydrogen.
  • Patent Document 1 JP Patent Publication No. 2018-135592 (Patent Document 1) and JP Patent Publication No. 2021-139007 (Patent Document 2) propose technologies to improve the hydrogen embrittlement resistance and strength of austenitic stainless steel materials.
  • the austenitic stainless steel material disclosed in Patent Document 1 is an austenitic stainless steel for high pressure hydrogen, which contains, by mass%, C: 0.40-1.00%, Si: 1.00% or less, Mn: 2.00% or less, P: 0.040% or less, S: 0.030% or less, Ni: 8.00-14.00%, Cr: 16.00-21.00%, N: 0.09% or less, with the balance being Fe and impurity elements, and further satisfies formula 1 (54.8C + 3.7Ni + 2.5Mn-1.6Cr-0.9Si + 266N-39.6>0), is used as is after solution heat treatment, and is characterized in that Cr carbides are present in the steel at an area ratio of 23% or more.
  • This austenitic stainless steel material is inexpensive in terms of its components, and can achieve excellent yield strength and hardness without relying on cold working to improve strength, and it also has excellent resistance to hydrogen embrittlement at low temperatures, as disclosed in Patent Document 1.
  • the austenitic stainless steel material disclosed in Patent Document 2 contains, in mass %, C: 0.100% or less, Si: 1.00% or less, Mn: 1.50 to 6.00%, P: 0.050% or less, S: 0.030% or less, Ni: 4.0 to 12.0%, Cr: 17.0 to 19.0%, N: 0.12 to 0.30%, Nb: 0.01 to 0.20%, V: 0.01 to 0.10%, Mo: 0 to 0.10%, Cu: 0.
  • the austenitic stainless steel material contains up to 0.5% Fe, with the remainder consisting of Fe and impurities, satisfies formulas (1) to (3), and is characterized in that in a cross section perpendicular to the longitudinal direction of the austenitic stainless steel material, the ratio A0/A1 of the austenite area fraction A0 (%) at the center of the cross section to the austenite area fraction A1 (%) at a depth of 5 mm from the surface of the austenitic stainless steel material is 0.990 to 1.010.
  • Patent Document 2 discloses that this austenitic stainless steel material is capable of achieving both high strength and excellent hydrogen embrittlement resistance, and has stable yield strength.
  • the austenitic stainless steel materials disclosed in the above-mentioned Patent Documents 1 and 2 achieve both high strength and improved resistance to hydrogen embrittlement.
  • austenitic stainless steel materials having high strength and excellent resistance to hydrogen embrittlement in a high-pressure hydrogen gas environment may be obtained by means other than those disclosed in Patent Documents 1 and 2.
  • the objective of this disclosure is to provide an austenitic stainless steel material that has high strength and excellent resistance to hydrogen embrittlement in a high-pressure hydrogen gas environment.
  • the austenitic stainless steel material according to the present disclosure has The chemical composition, in mass%, is C: 0.100% or less, Si: 1.000% or less, Mn: 8.00-20.00%, P: 0.050% or less, S: 0.0050% or less, Cr: 18.00-30.00%, Ni: 10.00-25.00%, N: 0.700-1.000%, V: 0.010-0.200%, Nb: 0.010-0.300%, Al: 0.200% or less, O: 0.0100% or less, Mo: 0-1.00%, W: 0-2.00%, Ti: 0 to 0.100%, Zr: 0 to 0.100%, Hf: 0-0.100%, Ta: 0-0.200%, Cu: 0 to 1.00%, Sn: 0 to 0.05%, Co: 0-2.00%, B: 0 to 0.020%, Mg: 0 to 0.0050%, Ca: 0-0.0050%, Rare earth elements: 0 to 0.5000%, and The balance is Fe and impurities.
  • the austenitic stainless steel material disclosed herein has high strength and excellent resistance to hydrogen embrittlement in high-pressure hydrogen gas environments.
  • the inventors first investigated, from the standpoint of chemical composition, how to obtain high strength and excellent resistance to hydrogen embrittlement for austenitic stainless steel materials intended for use in high-pressure hydrogen gas environments.
  • C 0.100% or less, Si: 1.000% or less, Mn: 8.00-20.00%, P: 0.050% or less, S: 0.0050% or less, Cr: 18.00-30.00%, Ni: 10.00-25.00%, N: 0.700-1.000%, V: 0.010-0.200%, Nb: 0.010-0.300%, Al: 0.200% or less, O: 0.0100% or less, Mo: 0-1.00%, W: 0-2.00%, Ti: 0-0.100%, Austenitic stainless steel materials with a chemical composition of Zr: 0-0.100%, Hf: 0-0.100%, Ta: 0-0.200%, Cu: 0-1.00%, Sn: 0-0.05%, Co: 0-2.00%, B: 0-0.020%, Mg: 0-0.0050%, Ca: 0-0.0050%, rare earth elements: 0-0.5000%, and the balance being Fe and impurities may be able to achieve both high strength and excellent resistance to hydrogen embrittlement in
  • the present inventors considered stabilizing austenite in an austenitic stainless steel material with low stacking fault energy by satisfying the above-mentioned chemical composition containing a high N content. If austenite is stabilized, it may be possible to achieve both high strength and excellent resistance to hydrogen embrittlement in a high-pressure hydrogen gas environment, even if stacking fault energy is reduced by satisfying the above-mentioned chemical composition containing a high N content.
  • the present inventors have focused on the stability of austenite in the microstructure of an austenitic stainless steel material having the above-mentioned chemical composition and have conducted detailed studies on a method for improving hydrogen embrittlement resistance in a high-pressure hydrogen gas environment while maintaining strength.
  • Fn1 defined by the following formula (1) satisfies a predetermined value depending on the Ni content, hydrogen embrittlement resistance in a high-pressure hydrogen gas environment can be improved, provided that the other configurations of this embodiment are satisfied.
  • Fn1 Ni+0.02 ⁇ Cr+0.52 ⁇ Mn-0.48 ⁇ Mo (1)
  • the content of the corresponding element in the chemical composition is substituted for each element symbol in formula (1) in mass %.
  • the corresponding element symbol is substituted with "0".
  • Fn1 defined in formula (1) is an index of austenite stability in an austenitic stainless steel material having the above-mentioned chemical composition.
  • the austenitic stainless steel material according to this embodiment satisfies the above-mentioned chemical composition, and furthermore, Fn1 is set to 18.0 or more, or 22.0 or more depending on the Ni content.
  • the austenitic stainless steel material according to this embodiment can achieve both high strength and excellent hydrogen embrittlement resistance in a high-pressure hydrogen gas environment.
  • the gist of the austenitic stainless steel material according to this embodiment which was completed based on the above findings, is as follows:
  • An austenitic stainless steel material The chemical composition, in mass%, is C: 0.100% or less, Si: 1.000% or less, Mn: 8.00-20.00%, P: 0.050% or less, S: 0.0050% or less, Cr: 18.00-30.00%, Ni: 10.00-25.00%, N: 0.700-1.000%, V: 0.010-0.200%, Nb: 0.010-0.300%, Al: 0.200% or less, O: 0.0100% or less, Mo: 0-1.00%, W: 0-2.00%, Ti: 0 to 0.100%, Zr: 0 to 0.100%, Hf: 0-0.100%, Ta: 0-0.200%, Cu: 0 to 1.00%, Sn: 0 to 0.05%, Co: 0-2.00%, B: 0 to 0.020%, Mg: 0 to 0.0050%, Ca: 0-0.0050%, Rare earth elements: 0 to 0.5000%, and The balance is Fe and impurities.
  • the austenitic stainless steel material according to this embodiment will be described in detail below. Unless otherwise specified, “%” for elements means mass %. In the following description, the austenitic stainless steel material will also be simply referred to as “steel material.”
  • the chemical composition of the austenitic stainless steel material according to this embodiment contains the following elements.
  • C 0.100% or less Carbon (C) is inevitably contained. That is, the lower limit of the C content is more than 0%. C forms carbides to increase the strength of the steel material. C also dissolves in the steel material to increase the strength of the steel material. However, if the C content is too high, C forms excessive carbides at the grain boundaries, reducing the hydrogen embrittlement resistance of the steel material. Therefore, the C content is 0.100% or less.
  • the preferred upper limit of the C content is 0.090%, more preferably 0.080%, more preferably 0.070%, more preferably 0.060%, and more preferably 0.050%.
  • the preferred lower limit of the C content to more effectively obtain the above effects is 0.001%, more preferably 0.002%, and more preferably 0.003%.
  • Si Silicon (Si) is inevitably contained. That is, the lower limit of the Si content is more than 0%. Si deoxidizes the steel. However, if the Si content is too high, Si forms an excessive amount of intermetallic compounds, which reduces the hot workability and hydrogen embrittlement resistance of the steel. Therefore, the Si content is 1.000% or less.
  • the preferred upper limit of the Si content is 0.900%, more preferably 0.800%, more preferably 0.700%, and even more preferably 0.600%. On the other hand, excessive reduction of the Si content increases the manufacturing cost. Therefore, in consideration of normal industrial production, the preferred lower limit of the Si content is 0.001%, more preferably 0.005%, and even more preferably 0.010%.
  • Mn 8.00-20.00%
  • Manganese (Mn) increases the amount of dissolved N and increases the N content in the steel material. As a result, the strength of the steel material is increased. Mn also stabilizes austenite and increases the hydrogen embrittlement resistance of the steel material. If the Mn content is too low, the above effect cannot be obtained sufficiently. On the other hand, if the Mn content is too high, the hot workability of the steel material is reduced. Therefore, the Mn content is 8.00 to 20.00%.
  • the preferred lower limit of the Mn content is 8.01%, more preferably 8.10%, more preferably 8.30%, and more preferably 8.50%.
  • the preferred upper limit of the Mn content is 19.50%, more preferably 19.00%, more preferably 18.00%, more preferably 17.00%, and more preferably 16.00%.
  • P 0.050% or less Phosphorus (P) is an impurity that is inevitably contained.
  • the lower limit of the P content is more than 0%. P reduces the hot workability and hydrogen embrittlement resistance of the steel material. Therefore, the P content is 0.050% or less.
  • the preferred upper limit of the P content is 0.040%, more preferably 0.030%, and even more preferably 0.025%. It is preferable that the P content is as low as possible. However, excessive reduction of the P content increases the manufacturing cost. Therefore, in consideration of normal industrial production, the preferred lower limit of the P content is 0.001%, and even more preferably 0.002%.
  • S 0.0050% or less Sulfur (S) is an impurity that is inevitably contained. That is, the lower limit of the S content is more than 0%. S reduces the hot workability and hydrogen embrittlement resistance of the steel material. Therefore, the S content is 0.0050% or less.
  • the preferred upper limit of the S content is 0.0040%, more preferably 0.0030%, and even more preferably 0.0020%.
  • the S content is preferably as low as possible. However, excessive reduction of the S content increases the manufacturing cost. Therefore, in consideration of normal industrial production, the preferred lower limit of the S content is 0.0001%, more preferably 0.0002%, and even more preferably 0.0003%.
  • Chromium (Cr) increases the amount of dissolved N and increases the N content in the steel material. As a result, the strength of the steel material is increased. If the Cr content is too low, the above effect cannot be obtained sufficiently. On the other hand, if the Cr content is too high, Cr nitrides are formed and the hydrogen embrittlement resistance of the steel material is reduced. Therefore, the Cr content is 18.00 to 30.00%.
  • the lower limit of the Cr content is preferably 18.50%, more preferably 19.00%, and even more preferably 19.50%.
  • the upper limit of the Cr content is preferably 29.50%, more preferably 29.10%, and even more preferably 28.70%.
  • Ni 10.00-25.00%
  • Nickel (Ni) stabilizes austenite and enhances the hydrogen embrittlement resistance of steel. If the Ni content is too low, the above effect cannot be obtained sufficiently. On the other hand, if the Ni content is too high, the N content in the steel is not increased sufficiently, and the strength of the steel decreases. Therefore, the Ni content is 10.00 to 25.00%.
  • the preferred lower limit of the Ni content is 10.05%, more preferably 10.10%, and even more preferably 10.30%.
  • the preferred upper limit of the Ni content is 24.50%, more preferably 24.00%, more preferably 23.00%, more preferably 22.00%, and even more preferably 21.00%.
  • the value of Fn1 defined by formula (1) is adjusted according to the Ni content. Specifically, when the Ni content is less than 10.00-17.00%, Fn1 is set to 18.0 or more. When the Ni content is less than 10.00-17.00%, the preferred upper limit of the Ni content is 16.99%, more preferably 16.90%, more preferably 16.80%, more preferably 16.50%, and more preferably 16.30%. When the Ni content is 17.00-25.00%, Fn1 is set to 22.0 or more. When the Ni content is 17.00-25.00%, the preferred lower limit of the Ni content is 17.05%, more preferably 17.10%, and more preferably 17.30%.
  • N Nitrogen (N) dissolves in steel material to increase the strength of the steel material. If the N content is too low, the above effect cannot be obtained sufficiently. On the other hand, if the N content is too high, the hot workability of the steel material decreases. Therefore, the N content is 0.700 to 1.000%.
  • the lower limit of the N content is preferably 0.705%, more preferably 0.710%, and even more preferably 0.725%.
  • the upper limit of the N content is preferably 0.995%, more preferably 0.980%, more preferably 0.975%, and even more preferably 0.960%.
  • V Vanadium
  • V forms precipitates to increase the strength of steel. If the V content is too low, the above effect cannot be obtained sufficiently. On the other hand, if the V content is too high, coarse precipitates are formed, and the hydrogen embrittlement resistance of the steel decreases. Therefore, the V content is 0.010 to 0.200%.
  • the lower limit of the V content is preferably 0.015%, more preferably 0.020%, and even more preferably 0.025%.
  • the upper limit of the V content is preferably 0.180%, more preferably 0.150%, and even more preferably 0.120%.
  • Niobium (Nb) forms a (Cr, Nb) composite precipitate in the steel material, thereby increasing the strength of the steel material. If the Nb content is too low, the above effect cannot be obtained sufficiently. On the other hand, if the Nb content is too high, coarse precipitates are formed, and the hydrogen embrittlement resistance of the steel material decreases. Therefore, the Nb content is 0.010 to 0.300%.
  • the lower limit of the Nb content is preferably 0.015%, more preferably 0.020%, and even more preferably 0.025%.
  • the upper limit of the Nb content is preferably 0.250%, more preferably 0.200%, and even more preferably 0.150%.
  • Al 0.200% or less
  • Aluminum (Al) is inevitably contained. That is, the lower limit of the Al content is more than 0%. Al deoxidizes steel. If even a small amount of Al is contained, the above effect can be obtained to a certain extent. However, if the Al content is too high, oxides and intermetallic compounds are generated in the steel material. In this case, the hydrogen embrittlement resistance of the steel material decreases. Therefore, the Al content is 0.200% or less.
  • the preferred upper limit of the Al content is 0.190%, more preferably 0.180%, and even more preferably 0.170%.
  • the preferred lower limit of the Al content for more effectively obtaining the above effect is 0.001%, and even more preferably 0.002%.
  • the Al content means the content of sol. Al (acid-soluble Al).
  • Oxygen (O) is an impurity that is inevitably contained.
  • the lower limit of the O content is more than 0%.
  • O reduces the hot workability of steel materials. Therefore, the O content is 0.0100% or less.
  • the O content is preferably as low as possible. However, excessive reduction of the O content increases manufacturing costs. Therefore, in consideration of normal industrial production, the preferred lower limit of the O content is 0.0001%, and more preferably 0.0002%.
  • the upper limit of the O content is preferably 0.0090%, more preferably 0.0080%, and even more preferably 0.0060%.
  • the remainder of the chemical composition of the austenitic stainless steel material according to this embodiment is composed of Fe and impurities.
  • impurities refer to substances that are mixed in from the raw materials, such as ore or scrap, or the manufacturing environment, during the industrial production of austenitic stainless steel material, and are not intentionally contained, but are permissible within a range that does not adversely affect the austenitic stainless steel material according to this embodiment.
  • the chemical composition of the austenitic stainless steel material according to this embodiment further comprises: Mo: 0-1.00%, W: 0-2.00%, Ti: 0 to 0.100%, Zr: 0 to 0.100%, Hf: 0-0.100%, Ta: 0-0.200%, Cu: 0 to 1.00%, Sn: 0 to 0.05%, Co: 0-2.00%, B: 0 to 0.020%, Mg: 0 to 0.0050%, Ca: 0 to 0.0050%, and Rare earth elements: 0 to 0.5000%. All of these elements are optional and may not be contained.
  • the chemical composition of the austenitic stainless steel material according to this embodiment is, in place of a part of Fe, Mo: 0.01-1.00%, W: 0.01-2.00%, Ti: 0.001 to 0.100%, Zr: 0.001 to 0.100%, Hf: 0.001-0.100%, Ta: 0.001 to 0.200%, Cu: 0.01 to 1.00%, Sn: 0.01-0.05%, Co: 0.01-2.00%, B: 0.001-0.020%, Mg: 0.0001 to 0.0050%, Ca: 0.0001 to 0.0050%, and Rare earth elements: 0.0001 to 0.5000%. These optional elements will be described below.
  • the chemical composition of the austenitic stainless steel material according to this embodiment may contain, instead of a part of Fe, one or more elements selected from the group consisting of Mo and W. Any of these elements increases the strength of the steel material.
  • Mo 0-1.00% Molybdenum (Mo) is an optional element and may not be contained. That is, the Mo content may be 0%. When contained, Mo dissolves in steel to increase the strength of the steel. If even a small amount of Mo is contained, the above effect can be obtained to some extent. However, if the Mo content is too high, the strength of the steel becomes too high, and the toughness of the steel decreases. Therefore, the Mo content is 0 to 1.00%, and when contained, the Mo content is 1.00% or less, that is, more than 0 to 1.00%.
  • the preferred lower limit of the Mo content is 0.01%, and more preferably 0.02%.
  • the preferred upper limit of the Mo content is 0.95%, more preferably 0.90%, more preferably 0.80%, and more preferably 0.70%.
  • W 0 to 2.00% Tungsten (W) is an optional element and may not be contained. In other words, the W content may be 0%. When contained, W dissolves in the steel to increase the strength of the steel. If even a small amount of W is contained, the above effect can be obtained to some extent. However, if the W content is too high, the strength of the steel becomes too high, and the toughness of the steel decreases. Therefore, the W content is 0 to 2.00%, and when contained, it is 2.00% or less, that is, more than 0 to 2.00%.
  • the preferred lower limit of the W content is 0.01%, more preferably 0.05%, and more preferably 0.10%.
  • the preferred upper limit of the W content is 1.90%, more preferably 1.80%, more preferably 1.70%, more preferably 1.60%, and more preferably 1.50%.
  • the chemical composition of the austenitic stainless steel material according to the present embodiment may contain one or more elements selected from the group consisting of Ti, Zr, Hf, and Ta in place of a portion of Fe. All of these elements increase the strength of the steel material.
  • Titanium (Ti) is an optional element and may not be contained. That is, the Ti content may be 0%. When contained, Ti forms nitrides and refines crystal grains by pinning effect. As a result, Ti enhances hydrogen embrittlement resistance of steel. If Ti is contained even a little, the above effect can be obtained to some extent. However, if the Ti content is too high, excessive nitrides are formed and the toughness of the steel decreases. Therefore, the Ti content is 0 to 0.100%, and when contained, it is 0.100% or less, that is, more than 0 to 0.100%.
  • the preferable lower limit of the Ti content is 0.001%, more preferably 0.005%, and more preferably 0.010%.
  • the preferable upper limit of the Ti content is 0.090%, more preferably 0.080%, more preferably 0.075%, and more preferably 0.060%.
  • Zr Zirconium
  • Zr Zirconium
  • the Zr content may be 0%.
  • Zr forms nitrides and refines crystal grains by pinning effect.
  • Zr enhances hydrogen embrittlement resistance of steel. If even a small amount of Zr is contained, the above effect can be obtained to some extent.
  • the Zr content is 0 to 0.100%, and when contained, it is 0.100% or less, that is, more than 0 to 0.100%.
  • the preferable lower limit of the Zr content is 0.001%, more preferably 0.005%, and more preferably 0.010%.
  • the preferable upper limit of the Zr content is 0.090%, more preferably 0.080%, more preferably 0.070%, and more preferably 0.060%.
  • Hf 0-0.100%
  • Hafnium (Hf) is an optional element and may not be contained. In other words, the Hf content may be 0%. When contained, Hf forms nitrides and refines crystal grains by pinning effect. As a result, Hf enhances hydrogen embrittlement resistance of steel. If even a small amount of Hf is contained, the above effect can be obtained to some extent. However, if the Hf content is too high, excessive nitrides are formed and the toughness of the steel decreases. Therefore, the Hf content is 0 to 0.100%, and when contained, it is 0.100% or less, that is, more than 0 to 0.100%.
  • the preferable lower limit of the Hf content is 0.001%, more preferably 0.003%, and more preferably 0.005%.
  • the preferable upper limit of the Hf content is 0.095%, more preferably 0.090%, and more preferably 0.080%.
  • Tantalum (Ta) is an optional element and may not be contained. That is, the Ta content may be 0%. When contained, Ta forms nitrides and refines crystal grains by pinning effect. As a result, Ta enhances the hydrogen embrittlement resistance of steel. If even a small amount of Ta is contained, the above effect can be obtained to some extent. However, if the Ta content is too high, excessive nitrides are formed and the toughness of the steel decreases. Therefore, the Ta content is 0 to 0.200%, and when contained, it is 0.200% or less, that is, more than 0 to 0.200%. The preferred lower limit of the Ta content is 0.001%, more preferably 0.003%, and more preferably 0.005%. The preferred upper limit of the Ta content is 0.190%, more preferably 0.180%, more preferably 0.170%, more preferably 0.160%, and more preferably 0.150%.
  • the chemical composition of the austenitic stainless steel material according to this embodiment may contain, instead of a part of Fe, one or more elements selected from the group consisting of Cu, Sn, and Co. Any of these elements stabilizes the austenite in the steel material and enhances the hydrogen embrittlement resistance of the steel material.
  • Cu 0-1.00% Copper (Cu) is an optional element and may not be contained. That is, the Cu content may be 0%. When contained, Cu stabilizes austenite and enhances the hydrogen embrittlement resistance of the steel. If even a small amount of Cu is contained, the above effect can be obtained to some extent. However, if the Cu content is too high, the hot workability of the steel is reduced. Therefore, the Cu content is 0 to 1.00%, and when contained, the Cu content is 1.00% or less, that is, more than 0 to 1.00%.
  • the preferred lower limit of the Cu content is 0.01%, more preferably 0.05%, and more preferably 0.10%.
  • the preferred upper limit of the Cu content is 0.90%, more preferably 0.85%, and more preferably 0.80%.
  • Tin (Sn) is an optional element and may not be contained.
  • the Sn content may be 0%.
  • Sn stabilizes austenite and enhances the hydrogen embrittlement resistance of the steel. Even if even a small amount of Sn is contained, the above effect can be obtained to a certain extent.
  • the Sn content is 0 to 0.05%, and when contained, the Sn content is 0.05% or less, that is, more than 0 to 0.05%.
  • the preferable lower limit of the Sn content is 0.01%, and more preferably 0.02%.
  • the preferable upper limit of the Sn content is 0.04%, and more preferably 0.03%.
  • Co is an optional element and may not be contained. That is, the Co content may be 0%. When contained, Co stabilizes austenite and enhances the hydrogen embrittlement resistance of the steel. If even a small amount of Co is contained, the above effect can be obtained to a certain extent. However, if the Co content is too high, the manufacturing cost of the steel increases. Therefore, the Co content is 0 to 2.00%, and when contained, the Co content is 2.00% or less, that is, more than 0 to 2.00%.
  • the preferred lower limit of the Co content is 0.01%, more preferably 0.10%, more preferably 0.50%, and more preferably 1.00%.
  • the preferred upper limit of the Co content is 1.90%, more preferably 1.80%, and more preferably 1.70%.
  • the chemical composition of the austenitic stainless steel material according to the present embodiment may contain one or more elements selected from the group consisting of B, Mg, Ca and rare earth elements in place of a portion of Fe. All of these elements improve the hot workability of the steel material.
  • B 0-0.020% Boron (B) is an optional element and may not be contained. In other words, the B content may be 0%. When contained, B fixes S in the steel as sulfides to render it harmless and improve the hot workability of the steel. If even a small amount of B is contained, the above effect can be obtained to a certain extent. However, if the B content is too high, a large number of nitrides are formed, and the hot workability of the steel is rather reduced. Therefore, the B content is 0 to 0.020%, and when contained, it is 0.020% or less, that is, more than 0 to 0.020%.
  • the preferred lower limit of the B content is 0.001%, more preferably 0.002%, and more preferably 0.003%.
  • the preferred upper limit of the B content is 0.018%, more preferably 0.015%, more preferably 0.010%, and more preferably 0.008%.
  • Mg 0-0.0050%
  • Mg Magnesium
  • the Mg content may be 0%.
  • Mg fixes S in the steel as sulfides to render it harmless and improve the hot workability of the steel. If even a small amount of Mg is contained, the above effect can be obtained to a certain extent. However, if the Mg content is too high, coarse oxides are formed, and the hot workability of the steel is rather reduced. Therefore, the Mg content is 0 to 0.0050%, and when contained, it is 0.0050% or less, that is, more than 0 to 0.0050%.
  • the preferable lower limit of the Mg content is 0.0001%.
  • the preferable upper limit of the Mg content is 0.0045%, more preferably 0.0040%, more preferably 0.0030%, more preferably 0.0020%, and more preferably 0.0010%.
  • Ca 0-0.0050% Calcium (Ca) is an optional element and may not be contained. In other words, the Ca content may be 0%. When contained, Ca fixes S in the steel as sulfides to render it harmless and improve the hot workability of the steel. If even a small amount of Ca is contained, the above effect can be obtained to a certain extent. However, if the Ca content is too high, coarse oxides are formed, and the hot workability of the steel is rather reduced. Therefore, the Ca content is 0 to 0.0050%, and when contained, it is 0.0050% or less, that is, more than 0 to 0.0050%. The preferred lower limit of the Ca content is 0.0001%. The preferred upper limit of the Ca content is 0.0045%, more preferably 0.0040%, more preferably 0.0030%, more preferably 0.0020%, and more preferably 0.0010%.
  • Rare earth elements are optional elements and may not be contained.
  • the REM content may be 0%.
  • REM fixes S in the steel as sulfides to render it harmless and improve the hot workability of the steel. If even a small amount of REM is contained, the above effect can be obtained to a certain extent. However, if the REM content is too high, coarse oxides are formed, and the hot workability of the steel is rather reduced. Therefore, the REM content is 0 to 0.5000%, and when contained, it is 0.5000% or less, that is, more than 0 to 0.5000%.
  • the preferable lower limit of the REM content is 0.0001%, more preferably 0.0005%, and more preferably 0.0010%.
  • the preferable upper limit of the REM content is 0.4900%, more preferably 0.4800%, more preferably 0.4500%, more preferably 0.4200%, and more preferably 0.4000%.
  • REM refers to one or more elements selected from the group consisting of scandium (Sc), atomic number 21; yttrium (Y), atomic number 39; and the lanthanides lanthanum (La), atomic number 57, to lutetium (Lu), atomic number 71.
  • the REM content refers to the total content of these elements.
  • the austenitic stainless steel material according to this embodiment has the above-mentioned chemical composition, and when the Ni content is 10.00 to less than 17.00%, Fn1 defined by formula (1) is 18.0 or more, and when the Ni content is 17.00 to 25.00%, Fn1 defined by formula (1) is 22.0 or more.
  • Fn1 Ni+0.02 ⁇ Cr+0.52 ⁇ Mn-0.48 ⁇ Mo (1)
  • the content of the corresponding element in the chemical composition is substituted for each element symbol in formula (1) in mass %. When an element is not contained, the corresponding element symbol is substituted with "0".
  • formula (1) can be modified to the following formula (1A).
  • Fn1A defined by formula (1A) when the Ni content is 10.00 to less than 17.00%, Fn1A defined by formula (1A) is 18.0 or more, and when the Ni content is 17.00 to 25.00%, Fn1A defined by formula (1A) is 22.0 or more.
  • Fn1A Ni+0.02 ⁇ Cr+0.52 ⁇ Mn (1A)
  • each element symbol in formula (1A) is substituted with the content of the corresponding element in the chemical composition in mass %.
  • the Ni content is less than 10.00-17.00%, increasing Fn1 to 18.0 or more can improve hydrogen embrittlement resistance in a high-pressure hydrogen gas environment while maintaining strength.
  • the Ni content is 17.00-25.00%
  • increasing Fn1 to 22.0 or more can improve hydrogen embrittlement resistance in a high-pressure hydrogen gas environment while maintaining strength.
  • Fn1 is too low, hydrogen embrittlement resistance in a high-pressure hydrogen gas environment decreases.
  • Fn1 when the Ni content is less than 10.00-17.00%, Fn1 is set to 18.0 or more, and when the Ni content is 17.00-25.00%, Fn1 is set to 22.0 or more.
  • the preferred lower limit of Fn1 is 18.1, more preferably 18.2, and even more preferably 18.3.
  • the preferred lower limit of Fn1 is 22.1, more preferably 22.2, and even more preferably 22.3.
  • the upper limit of Fn1 is substantially 36.0.
  • the upper limit of Fn1 may be 35.0, 33.0, 30.0, or 28.0.
  • the austenitic stainless steel material according to this embodiment has the above-mentioned chemical composition, and when the Ni content is 10.00 to less than 17.00%, Fn1 satisfies 18.0 or more, and when the Ni content is 17.00 to 25.00%, Fn1 satisfies 22.0 or more.
  • the austenitic stainless steel material according to this embodiment can achieve both high strength and excellent hydrogen embrittlement resistance in a high-pressure hydrogen gas environment.
  • the fact that the steel material has high strength specifically means that the tensile strength of the steel material is 950 MPa or more.
  • the preferred lower limit of the tensile strength is 955 MPa, more preferably 960 MPa, more preferably 970 MPa, and even more preferably 980 MPa.
  • the austenitic stainless steel material according to this embodiment contains (Cr, Nb) composite precipitates having a circle equivalent diameter of 50 to 500 nm, which will be described later, at a number density of 1.00 pieces/ ⁇ m2 or more , the tensile strength is further increased to 1150 MPa or more.
  • the more preferred lower limit of the tensile strength is 1155 MPa, more preferably 1160 MPa, and even more preferably 1170 MPa.
  • the upper limit of the tensile strength is not particularly limited, but is, for example, 1500 MPa.
  • the upper limit of the tensile strength may be 1480 MPa, 1460 MPa, 1450 MPa, 1430 MPa, or 1420 MPa.
  • the tensile strength of the austenitic stainless steel material is determined by the following method. Specifically, a round bar tensile test piece is prepared from the austenitic stainless steel material.
  • the austenitic stainless steel material is a steel pipe
  • the round bar tensile test piece is prepared from the center position of the wall thickness. In this case, the longitudinal direction of the round bar tensile test piece is parallel to the axial direction of the steel pipe.
  • the austenitic stainless steel material is a steel bar
  • the round bar tensile test piece is prepared from the R/2 position. In this case, the longitudinal direction of the round bar tensile test piece is parallel to the axial direction of the steel bar.
  • the round bar tensile test piece is prepared from the center position of the plate width and the center position of the plate thickness.
  • the longitudinal direction of the round bar tensile test piece is parallel to the rolling direction of the steel plate.
  • the size of the round bar tensile test piece is, for example, 8 mm in diameter at the parallel part.
  • the prepared round bar tensile test specimen is subjected to a tensile test in accordance with JIS Z 2241:2011 at room temperature in air to determine the tensile strength (MPa).
  • the tensile strength (MPa) is determined by rounding the obtained value to the nearest tenth.
  • the austenitic stainless steel material according to this embodiment has the above-mentioned chemical composition, and when the Ni content is 10.00 to less than 17.00%, Fn1 satisfies 18.0 or more, and when the Ni content is 17.00 to 25.00%, Fn1 satisfies 22.0 or more.
  • the austenitic stainless steel material according to this embodiment can achieve both high strength and excellent hydrogen embrittlement resistance in a high-pressure hydrogen gas environment.
  • the hydrogen embrittlement resistance of the steel material is evaluated according to the Ni content.
  • a round bar tensile test piece is prepared from the austenitic stainless steel material.
  • the austenitic stainless steel material is a steel pipe
  • the round bar tensile test piece is prepared from the center position of the wall thickness. In this case, the longitudinal direction of the round bar tensile test piece is parallel to the axial direction of the steel pipe.
  • the austenitic stainless steel material is a steel bar
  • the round bar tensile test piece is prepared from the R/2 position. In this case, the longitudinal direction of the round bar tensile test piece is parallel to the axial direction of the steel bar.
  • the round bar tensile test piece is prepared from the center position of the plate width and the center position of the plate thickness.
  • the longitudinal direction of the round bar tensile test piece is parallel to the rolling direction of the steel plate.
  • the size of the round bar tensile test piece is, for example, 3 mm in parallel part diameter.
  • the steel material when the Ni content is between 10.00 and less than 17.00%, if the relative fracture elongation L obtained under the above conditions is 0.70 or more, the steel material is evaluated as having excellent hydrogen embrittlement resistance in a high-pressure hydrogen gas environment.
  • the austenitic stainless steel material according to this embodiment has a relative fracture elongation L obtained under the above conditions of 0.70 or more.
  • a round bar tensile test piece is prepared from the austenitic stainless steel material in the same manner as when the Ni content is 10.00 to less than 17.00%.
  • a slow strain rate tensile test (SSRT) is performed on the prepared round bar tensile test piece.
  • the test is performed under the same conditions as when the Ni content is 10.00 to less than 17.00%, except that the hydrogen gas pressure is 85 MPa. That is, a tensile test is performed at room temperature in air at a strain rate of 3 ⁇ 10 ⁇ 6 /sec to determine the breaking elongation L0 (unit: %) in air.
  • a tensile test is performed at room temperature in 85 MPa hydrogen gas at a strain rate of 3 ⁇ 10 ⁇ 6 /sec to determine the breaking elongation L1 (unit: %) in 85 MPa hydrogen gas.
  • the ratio of the breaking elongation L1 (%) in high pressure hydrogen gas to the breaking elongation L0 (%) in air is defined as the relative breaking elongation L.
  • the steel material when the Ni content is 17.00-25.00%, if the relative fracture elongation L obtained under the above conditions is 0.70 or more, the steel material is evaluated as having excellent hydrogen embrittlement resistance in a high-pressure hydrogen gas environment. In other words, when the Ni content is 17.00-25.00%, the austenitic stainless steel material according to this embodiment has a relative fracture elongation L obtained under the above conditions of 0.70 or more.
  • the austenitic stainless steel material according to this embodiment has the above-mentioned chemical composition, and when the Ni content is less than 10.00 to 17.00%, Fn1 satisfies 18.0 or more, and when the Ni content is 17.00 to 25.00%, Fn1 satisfies 22.0 or more.
  • the austenitic stainless steel material according to this embodiment further preferably has a number density of (Cr, Nb) composite precipitates having a circle equivalent diameter of 50 to 500 nm in the steel material of 1.00 pieces/ ⁇ m 2 or more.
  • the austenitic stainless steel material according to this embodiment can achieve both higher strength and better hydrogen embrittlement resistance in a high-pressure hydrogen gas environment.
  • the (Cr, Nb) composite precipitates having a circle equivalent diameter of 50 to 500 nm are also referred to as "specific precipitates”.
  • the specific precipitates are finely dispersed in the austenitic stainless steel material to increase the strength of the steel material.
  • the specific precipitates further refine the crystal grains to increase the strength of the steel material and also increase the hydrogen embrittlement resistance of the steel material. Therefore, in an austenitic stainless steel material having the above-mentioned chemical composition, in which the Ni content is less than 10.00 to 17.00%, Fn1 satisfies 18.0 or more, and in which the Ni content is 17.00 to 25.00%, Fn1 satisfies 22.0 or more, even higher strength and even better hydrogen embrittlement resistance can be obtained if the number density of the specific precipitates is 1.00 precipitates/ ⁇ m2 or more .
  • the austenitic stainless steel material according to this embodiment has the above-mentioned chemical composition, and when the Ni content is 10.00 to less than 17.00%, Fn1 satisfies 18.0 or more, and when the Ni content is 17.00 to 25.00%, Fn1 satisfies 22.0 or more, and further, it is preferable that the number density of the specific precipitates in the austenitic stainless steel material is 1.00 precipitates/ ⁇ m 2 or more. As a result, the austenitic stainless steel material according to this embodiment can achieve both even higher strength and even better hydrogen embrittlement resistance.
  • the more preferable lower limit of the number density of the specific precipitates is 1.05 pieces/ ⁇ m 2 , more preferably 1.10 pieces/ ⁇ m 2 , and even more preferably 1.20 pieces/ ⁇ m 2.
  • the upper limit of the number density of the specific precipitates is not particularly limited, but is, for example, 5.00 pieces/ ⁇ m 2.
  • the upper limit of the number density of the specific precipitates may be 4.50 pieces/ ⁇ m 2 , 4.00 pieces/ ⁇ m 2 , or 3.50 pieces/ ⁇ m 2 .
  • the number density of the specific precipitates is preferably 1.00 pieces/ ⁇ m2 or more , and the amount of the specific precipitates is not particularly limited.
  • the amount of the specific precipitates is substantially 0.010 mass% or more.
  • a more preferable lower limit of the amount of the specific precipitates is 0.015 mass%, more preferably 0.020 mass%, and even more preferably 0.025 mass%.
  • the upper limit of the amount of the specific precipitates is not particularly limited, and may be, for example, 0.300 mass%, 0.250 mass%, or 0.200 mass%.
  • the specific precipitates are nitrides. That is, in the austenitic stainless steel material according to the present embodiment, the number density of the (Cr, Nb) composite nitrides having a circle equivalent diameter of 50 to 500 nm is 1.00 pieces/ ⁇ m 2 or more.
  • the (Cr, Nb) composite nitrides having a circle equivalent diameter of 50 to 500 nm precipitate in a temperature range of about 1060°C.
  • the (Cr, Nb) composite nitrides having a circle equivalent diameter of 50 to 500 nm are also relatively stable precipitates even at high temperatures. Therefore, the specific precipitates precipitated in the steel material refine the austenite grain size by the pinning effect. As a result, it is considered that the strength can be further increased and the resistance to hydrogen embrittlement can be improved.
  • the number density of specific precipitates in the austenitic stainless steel material is determined by the following method. Specifically, a micro-test piece for preparing an extraction replica is prepared from the austenitic stainless steel material. The size of the micro-test piece is, for example, 10 mm x 10 mm. After mirror-polishing the surface of the micro-test piece, the micro-test piece is immersed in a 3% nital etching solution for 10 minutes to etch the surface. The etched surface is covered with a carbon vapor deposition film. The micro-test piece with the surface covered with the vapor deposition film is immersed in a 5% nital etching solution for 20 minutes. The vapor deposition film is peeled off from the immersed micro-test piece. The vapor deposition film peeled off from the micro-test piece is washed with ethanol, scooped up with a sheet mesh, and dried. In this embodiment, a sheet mesh made of Cu is used.
  • This deposition film (replica film) is observed with a transmission electron microscope (TEM). Specifically, an arbitrary position is identified from the deposition film, and the observation is performed with an acceleration voltage of 200 kV.
  • the size of the observation field is, for example, 4.0 ⁇ m ⁇ 4.0 ⁇ m.
  • particles with a circle-equivalent diameter of 50 to 500 nm or less are identified.
  • the particles can be identified from the contrast.
  • the term "particle” is not limited to a circular (spherical) particle, but may be a small piece having an angular shape or an elongated elliptical piece.
  • the circle-equivalent diameter of the precipitate can be determined by image analysis of the observation image in the TEM observation.
  • Point analysis is performed using energy dispersive X-ray spectrometry (EDS) on the identified particles with an equivalent circle diameter of 50 to 500 nm or less.
  • EDS energy dispersive X-ray spectrometry
  • the acceleration voltage is 200 kV.
  • the target elements for point analysis are Fe, Nb, Cr, Si, Mn, V, Mo, Cu, and Ti.
  • particles with a total Cr and Nb content of 20 mass% or more are defined as "specific precipitates.”
  • the number density of the specific precipitates (numbers/ ⁇ m 2 ) is calculated based on the total number of the specific precipitates identified in any three visual fields and the total area of the visual fields observed. In this embodiment, the number density of the specific precipitates is calculated by rounding off the obtained value to two decimal places.
  • the amount of specific precipitates in the austenitic stainless steel material is determined by the following method. Specifically, a test piece is prepared from the austenitic stainless steel material. Note that the test piece is not particularly limited as long as it provides an observation surface as described below.
  • the observation surface of the test piece After polishing the observation surface of the test piece to a mirror finish, it is immersed in an electrolyte (10% acetylacetone-1% tetramethylammonium chloride-methanol solution) and electrolysis is performed.
  • the orientation of the observation surface is not particularly limited.
  • the difference in mass between the test piece before electrolysis and the test piece after electrolysis is defined as the amount of electrolysis.
  • the electrolyte after electrolysis is passed through a 0.2 ⁇ m filter to capture the residue. The mass of the captured residue is measured. Furthermore, the obtained residue is decomposed with acid and ICP (inductively coupled plasma) emission spectrometry is performed. The mass of Cr and Nb in the residue is quantified from the Cr and Nb concentrations in the residue and the mass of the residue.
  • the mass of Cr and Nb in the residue is divided by the amount of electrolysis to define the concentration (mass%) of Cr and Nb elements.
  • the obtained concentration (mass%) of Cr and Nb elements is defined as the precipitation amount (mass%) of a specific precipitate in the austenitic stainless steel material.
  • the circle equivalent diameter of the residue captured by the above-mentioned method is 50 to 500 nm.
  • the austenitic stainless steel material according to this embodiment has the above-mentioned chemical composition, and when the Ni content is less than 10.00 to 17.00%, Fn1 satisfies 18.0 or more, and when the Ni content is 17.00 to 25.00%, Fn1 satisfies 22.0 or more, and further, it is preferable that the number density of the specific precipitates in the austenitic stainless steel material is 1.00 pieces/ ⁇ m 2 or more.
  • the austenitic stainless steel material according to this embodiment can achieve both even higher strength and even better hydrogen embrittlement resistance.
  • "having even higher strength” means that the tensile strength is 1150 MPa or more.
  • "having even better hydrogen embrittlement resistance” means that the relative fracture elongation L obtained by the above-mentioned method is 0.80 or more.
  • the number density of the specific precipitates is 1.00 particles/ ⁇ m 2 or more, it is possible to achieve both a tensile strength of 1150 MPa or more and a relative fracture elongation L of 0.80 or more.
  • the austenitic stainless steel material according to this embodiment has the above-mentioned chemical composition, and when the Ni content is 10.00 to less than 17.00%, Fn1 satisfies 18.0 or more, and when the Ni content is 17.00 to 25.00%, Fn1 satisfies 22.0 or more, and further, it is preferable that the number density of specific precipitates in the austenitic stainless steel material is 1.00 particles/ ⁇ m 2 or more. More preferably, the crystal grain size of the austenite grains (austenite grain size) of the austenitic stainless steel material according to this embodiment is 20.0 ⁇ m or less.
  • a more preferred upper limit of the austenite grain size is 19.8 ⁇ m, more preferably 19.5 ⁇ m, and even more preferably 19.0 ⁇ m. In this embodiment, a smaller austenite grain size is preferred.
  • the lower limit of the austenite grain size is, for example, 4.0 ⁇ m.
  • the crystal grain size of the austenite grains in the austenitic stainless steel material is determined by the following method. Specifically, a test piece for microstructural observation is prepared from the austenitic stainless steel material.
  • the austenitic stainless steel material is a steel pipe
  • a test piece having an observation surface including the pipe axial direction and the wall thickness direction is prepared.
  • the austenitic stainless steel material is a steel bar
  • a test piece having an observation surface including the axial direction and the cross-sectional radial direction is prepared.
  • the austenitic stainless steel material is a steel plate
  • a test piece having an observation surface including the rolling direction and the plate thickness direction is prepared.
  • the size of the test piece is not particularly limited as long as it can provide the observation surface described below.
  • the observation surface of the prepared test piece is polished to a mirror finish, electrolytic corrosion is performed using 10% oxalic acid - 90% distilled water to reveal the austenite grain boundaries.
  • the observation surface is observed using an optical microscope.
  • the magnification in the microscope observation can be set appropriately depending on the grain size. Specifically, in the microscope observation, the magnification is set so that, for example, 50 or more austenite grains are included in the field of view.
  • the grain size ( ⁇ m) of the austenite grains is obtained by the optical microscope observation based on the average intercept length measurement method in accordance with JIS G 0551 (2020). In this embodiment, the grain size ( ⁇ m) of the austenite grains is obtained by rounding off the obtained value to one decimal place.
  • the shape of the austenitic stainless steel material of this embodiment is not particularly limited.
  • the austenitic stainless steel material of this embodiment may be a steel pipe, a steel plate, or a steel bar.
  • the austenitic stainless steel material according to this embodiment can be widely used in applications requiring high strength and hydrogen embrittlement resistance. Examples of such applications include steel materials for fuel tanks of transportation equipment that uses hydrogen as energy, steel materials for piping connecting a fuel tank to a combustion chamber, etc. Note that the austenitic stainless steel material according to this embodiment is not limited to applications for transportation equipment that uses high-pressure hydrogen gas as energy, or hydrogen stations that supply hydrogen gas to transportation equipment.
  • a method for producing an austenitic stainless steel material according to this embodiment will be described below.
  • the method for producing an austenitic stainless steel material described below is one example of the method for producing an austenitic stainless steel material according to this embodiment.
  • an austenitic stainless steel material having the above-mentioned configuration may be produced by a production method other than the production method described below.
  • the production method described below is a preferred example of the method for producing an austenitic stainless steel material according to this embodiment.
  • An example of a method for manufacturing an austenitic stainless steel material includes a process for preparing a material (preparation process), a process for performing hot working on the prepared material to manufacture an intermediate steel material (hot working process), a process for cooling the manufactured intermediate steel material (cooling process), and a process for performing a specific precipitate precipitation treatment on the cooled intermediate steel material (specific precipitate precipitation treatment process).
  • preparation process a process for preparing a material
  • hot working process a process for performing hot working on the prepared material to manufacture an intermediate steel material
  • cooling process a process for cooling the manufactured intermediate steel material
  • specific precipitate precipitation treatment process a process for performing a specific precipitate precipitation treatment on the cooled intermediate steel material
  • Molten steel having the above-mentioned chemical composition including Fn1 is produced by a known method.
  • the produced molten steel is used to produce a cast material by a known casting method.
  • an ingot is produced by an ingot casting method.
  • a cast piece (slab, bloom, billet, etc.) may be produced by a continuous casting method.
  • the ingot may be subjected to hot processing such as blooming and hot forging to produce a slab, bloom, or billet.
  • the material is produced by the above steps.
  • the prepared material is hot worked to produce an intermediate steel material.
  • the hot working is not particularly limited, and may be, for example, hot forging, hot rolling, hot extrusion, etc.
  • the hot forging may be, for example, stretch forging.
  • the hot rolling may be, for example, a reverse rolling mill or a tandem rolling mill, which performs rolling in multiple passes.
  • the hot extrusion may be, for example, hot extrusion by the Euither-Séjournet method.
  • the intermediate steel material is produced by the above manufacturing process.
  • the heating temperature before the hot working is, for example, 1250°C.
  • the temperature range from the start to the end of hot working is 1100 to 1250°C, and the time is 4 minutes or less.
  • "from the start to the end of hot working” means the time from when the material is extracted from the heating furnace to when the final hot working is completed.
  • the time from when the material is extracted from the heating furnace to when the final hot working is completed is 4 minutes or less, and that the temperature of the material is 1100 to 1250°C from when the material is extracted from the heating furnace to when the final hot working is completed.
  • (Cr, Nb) compound nitrides precipitate and coarsen in the intermediate steel material during hot working.
  • the amount of dissolved Nb in the steel material decreases, and the amount of fine (Cr, Nb) compound nitrides precipitated in the specific precipitate precipitation treatment process described below decreases.
  • the (Cr, Nb) compound nitrides precipitated during hot working further coarsen in the specific precipitate precipitation treatment process described below.
  • the number density of the specific precipitates decreases in the manufactured austenitic stainless steel material. Therefore, in the hot working process according to this embodiment, it is preferable to set the temperature range from the start to the end of hot working to 1100 to 1250°C and the time to 4 minutes or less.
  • the intermediate steel material produced is cooled.
  • the cooling method is not particularly limited, and may be a well-known method.
  • the intermediate steel material after hot working is quenched (water-cooled) using a water-cooling device. If the cooling rate is too slow, (Cr, Nb) compound nitrides may precipitate in the intermediate steel material during cooling. In this case, in the specific precipitate precipitation treatment step described later, the (Cr, Nb) compound nitrides become coarse, and the number density of the specific precipitates decreases in the produced austenitic stainless steel material. Therefore, the cooling rate of the intermediate steel material in the cooling step is preferably 15° C./min or more.
  • the cooling stop temperature is not particularly limited, but is, for example, room temperature.
  • Specific precipitate precipitation treatment step In the specific precipitate precipitation treatment step, the cooled intermediate steel material is subjected to a specific precipitate precipitation treatment. Specifically, the intermediate steel material is held at 1000 to 1230°C for 15 to 90 minutes. Thereafter, the intermediate steel material is quenched.
  • the quenching method is not particularly limited, and may be, for example, water cooling or oil cooling.
  • the holding temperature in the specific precipitate precipitation treatment process is too low, the specific precipitates do not precipitate sufficiently, and a large amount of Cr nitrides is formed. As a result, hydrogen embrittlement resistance is reduced.
  • the holding temperature is too high, the specific precipitates are dissolved in the steel material, and the amount of specific precipitates in the steel material decreases. As a result, the desired strength is not obtained.
  • the holding time in the specific precipitate precipitation treatment process is too short, the specific precipitates do not precipitate sufficiently, and a large amount of Cr nitrides is formed. As a result, hydrogen embrittlement resistance is reduced.
  • the holding time is too long, the austenite grains become coarse, and the desired strength is not obtained. Therefore, in the specific precipitate precipitation treatment process of this embodiment, it is preferable to hold at 1000 to 1230°C for 15 to 90 minutes.
  • the above manufacturing method allows the austenitic stainless steel material of this embodiment to be manufactured.
  • the above manufacturing method is one example, and the material may be manufactured by other manufacturing methods.
  • the effect of the austenitic stainless steel material of this embodiment will be explained in more detail below using an example.
  • the conditions in the following example are one example of conditions adopted to confirm the feasibility and effect of the austenitic stainless steel material of this embodiment. Therefore, the austenitic stainless steel material of this embodiment is not limited to this one example of conditions.
  • Example 1 the effect of the austenitic stainless steel material according to this embodiment was confirmed when the Ni content was 10.00 to less than 17.00%. Specifically, molten steel having the chemical composition shown in Tables 1-1 and 1-2 was melted in a high-frequency melting furnace to produce ingots. In addition, Fn1 calculated from the chemical composition of each test number and formula (1) is shown in Table 2.
  • the ingots of each test number produced were soaked at 1230°C for 1 hour, and then hot forged to produce blocks with a thickness of 70 mm.
  • the blocks of each test number were heated to 1230°C, and then hot rolled to produce plates (intermediate steel) with a thickness of 9 mm.
  • hot rolling if the temperature range from when the steel was extracted from the heating furnace until the end of the final hot rolling was 1100-1250°C, then "A” is shown in the "Temperature range” column of the "Hot processing” column in Table 2. If the temperature range from when the steel was extracted from the heating furnace until the end of the final hot rolling was 950-1250°C, then "B” is shown in the "Temperature range” column of the "Hot processing” column in Table 2.
  • the intermediate steel material of each test number was cooled to room temperature at a cooling rate of 15°C/min or more.
  • the intermediate steel material of each test number was then subjected to a specific precipitate precipitation treatment.
  • the holding temperature (°C) and holding time (min) of the specific precipitate precipitation treatment performed for each test number are shown in Table 2.
  • Steel plates of each test number were manufactured using the above process. Note that cracks occurred during forging or hot working in the steel plate of test number 1-61. Therefore, the specific precipitate precipitation treatment was not performed on this steel plate.
  • Specific precipitate amount measurement test A specific precipitate amount measurement test was carried out for the steel plate of each test number by the above-mentioned method. Specifically, a test piece was prepared from the center of the thickness of the steel plate of each test number by the above-mentioned method. The observation surface of the test piece was a surface perpendicular to the rolling direction of the steel plate. Electrolysis was carried out for the test piece of each test number by the above-mentioned method to capture the residue. At this time, the difference in mass between the test piece before electrolysis and the test piece after electrolysis was taken as the amount of electrolysis. The obtained residue was decomposed with acid, and ICP emission analysis was carried out to obtain the Cr and Nb concentrations in the residue.
  • the masses of Cr and Nb in the residue were quantified from the Cr and Nb concentrations in the residue and the mass of the residue, and the concentration (mass%) of Cr and Nb elements was obtained by dividing by the amount of electrolysis.
  • the obtained concentrations of Cr and Nb elements were defined as the amount of precipitation (mass%) of the specific precipitate.
  • the amount of precipitation of the specific precipitate (mass%) for each test number is shown in Table 2.
  • the hydrogen embrittlement resistance evaluation test was carried out for the steel plate of each test number by the above-mentioned method. Specifically, a round bar tensile test piece with a parallel part diameter of 3 mm was prepared from the center of the plate thickness of the steel plate of each test number. The axial direction of the round bar tensile test piece was parallel to the rolling direction of the steel plate. For the round bar tensile test piece of each test number, SSRT (slow strain rate tensile test) was carried out at room temperature in air to obtain the breaking elongation L0 (%) in air.
  • SSRT slow strain rate tensile test
  • the steel plates of test numbers 1-1 to 1-55 further had a number density of specific precipitates of 1.00 particles/ ⁇ m2 or more .
  • the tensile strength was 1150 MPa or more, and the steel plates had even higher strength.
  • the steel plates further had a relative fracture elongation L of 0.80 or more, and the steel plates had excellent hydrogen embrittlement resistance in a high-pressure hydrogen gas environment.
  • the steel plate with test number 1-58 had too high a Cr content.
  • the relative fracture elongation L of this steel plate was less than 0.70, and it did not have excellent hydrogen embrittlement resistance in a high-pressure hydrogen gas environment.
  • the steel plate with test number 1-59 had too low a Cr content and too low a N content. As a result, the tensile strength of this steel plate was less than 950 MPa and it did not have high strength.
  • the Ni content of the steel plate with test number 1-60 was too low. As a result, the relative fracture elongation L of this steel plate was less than 0.70, and it did not have excellent hydrogen embrittlement resistance in a high-pressure hydrogen gas environment.
  • the steel plate with test number 1-62 had too low a Mn content and too low a N content. As a result, the tensile strength of this steel plate was less than 950 MPa and it did not have high strength.
  • the steel plate with test number 1-63 had too high a Nb content.
  • the relative fracture elongation L of this steel plate was less than 0.70, and it did not have excellent hydrogen embrittlement resistance in a high-pressure hydrogen gas environment.
  • the steel plate with test number 1-64 had too low a Nb content.
  • the steel plate with test number 1-65 had an Fn1 of less than 18.0.
  • Steel plate No. 1-66 had an Fn1 of less than 18.0. As a result, this steel plate had a relative fracture elongation L of less than 0.70, and did not have excellent hydrogen embrittlement resistance in a high-pressure hydrogen gas environment.
  • Example 2 the effect of the austenitic stainless steel material according to this embodiment was confirmed when the Ni content was 17.00 to 25.00%. Specifically, molten steel having the chemical composition shown in Tables 3-1 and 3-2 was melted in a high-frequency melting furnace to produce ingots. In addition, Fn1 calculated from the chemical composition of each test number and formula (1) is shown in Table 4.
  • the ingots of each test number produced were soaked at 1230°C for 1 hour, and then hot forged to produce blocks with a thickness of 70 mm.
  • the blocks of each test number were heated to 1230°C, and then hot rolled to produce plates (intermediate steel) with a thickness of 9 mm.
  • hot rolling if the temperature range from when the steel was extracted from the heating furnace until the end of the final hot rolling was 1100-1250°C, then "A” is shown in the "Temperature range” column of the "Hot processing” column in Table 4. If the temperature range from when the steel was extracted from the heating furnace until the end of the final hot rolling was 950-1250°C, then "B” is shown in the "Temperature range” column of the "Hot processing” column in Table 4.
  • the intermediate steel material of each test number was cooled to room temperature at a cooling rate of 15°C/min or more.
  • the intermediate steel material of each test number was then subjected to a specific precipitate precipitation treatment.
  • the holding temperature (°C) and holding time (min) of the specific precipitate precipitation treatment performed for each test number are shown in Table 4.
  • the steel plate of each test number was manufactured using the above process. Note that cracks occurred during forging or hot working in the steel plate of test number 2-60. Therefore, the specific precipitate precipitation treatment was not performed on this steel plate.
  • Specific precipitate amount measurement test A specific precipitate amount measurement test was carried out for the steel plate of each test number by the above-mentioned method. Specifically, a test piece was prepared from the center of the thickness of the steel plate of each test number by the above-mentioned method. The observation surface of the test piece was a surface perpendicular to the rolling direction of the steel plate. Electrolysis was carried out for the test piece of each test number by the above-mentioned method to capture the residue. At this time, the difference in mass between the test piece before electrolysis and the test piece after electrolysis was taken as the amount of electrolysis. The obtained residue was decomposed with acid, and ICP emission analysis was carried out to obtain the Cr and Nb concentrations in the residue.
  • the masses of Cr and Nb in the residue were quantified from the Cr and Nb concentrations in the residue and the mass of the residue, and the concentration (mass%) of Cr and Nb elements was obtained by dividing by the amount of electrolysis.
  • the obtained concentrations of Cr and Nb elements were defined as the amount of precipitation (mass%) of the specific precipitate.
  • the amount of precipitation of the specific precipitate (mass%) for each test number is shown in Table 4.
  • the hydrogen embrittlement resistance evaluation test was carried out for the steel plate of each test number by the above-mentioned method. Specifically, a round bar tensile test piece with a parallel part diameter of 3 mm was prepared from the center of the plate thickness of the steel plate of each test number. The axial direction of the round bar tensile test piece was parallel to the rolling direction of the steel plate. For the round bar tensile test piece of each test number, SSRT (slow strain rate tensile test) was carried out at room temperature in air to obtain the breaking elongation L0 (%) in air.
  • SSRT slow strain rate tensile test
  • the steel plates of test numbers 2-1 to 2-54 had a number density of specific precipitates of 1.00 precipitates/ ⁇ m2 or more. As a result, these steel plates had a tensile strength of 1150 MPa or more and had even higher strength. As a result, these steel plates had a relative fracture elongation L of 0.80 or more and had even better hydrogen embrittlement resistance in a high-pressure hydrogen gas environment.
  • the steel plate of test number 2-57 had too high a Cr content, too low a Ni content, and too low an Fn1.
  • the relative fracture elongation L of this steel plate was less than 0.70, and it did not have excellent hydrogen embrittlement resistance in a high-pressure hydrogen gas environment.
  • the steel plate with test number 2-58 had too low a Cr content and too low a N content. As a result, the tensile strength of this steel plate was less than 950 MPa and it did not have high strength.
  • the steel plate with test number 2-59 had too high a Ni content and too low a N content.
  • the steel plate with test number 2-61 had too low a Mn content, too low a N content, and too low an Fn1. As a result, the tensile strength of this steel plate was less than 950 MPa, and it did not have high strength.
  • the steel plate with test number 2-62 had too high a Nb content.
  • the relative fracture elongation L of this steel plate was less than 0.70, and it did not have excellent hydrogen embrittlement resistance in a high-pressure hydrogen gas environment.
  • the Nb content of the steel plate with test number 2-63 was too low.
  • the steel plate with test number 2-64 had an Fn1 of less than 22.0.
  • the relative fracture elongation L of this steel plate was less than 0.70, and it did not have excellent hydrogen embrittlement resistance in a high-pressure hydrogen gas environment.

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Abstract

L'invention fournit un matériau d'acier inoxydable à base d'austénite qui présente une solidité élevée, et une excellente résistance à la fragilité due à l'hydrogène dans un environnement d'hydrogène gazeux à haute pression. Le matériau d'acier inoxydable à base d'austénite de l'invention présente une composition chimique telle que, en % en masse, Ｃ représente ０,１００％ ou moins, Ｓｉ représente １,０００％ ou moins, Ｍｎ représente ８,００ à ２０,００％, Ｐ représente ０,０５０％ ou moins, Ｓ représente ０,００５０％ ou moins, Ｃｒ représente １８,００ à ３０,００％, Ｎｉ représente １０,００ à ２５,００％, Ｎ représente ０,７００ à １,０００％, Ｖ représente ０,０１０ à ０,２００％, Ｎｂ représente ０,０１０ à ０,３００％, Ａｌ représente ０,２００％ ou moins et Ｏ représente ０,０１００％ ou moins, le reste étant constitué de Fe et d'impuretés. Fn1 défini par la formule (1) dans la description satisfait 18,0 ou plus lorsque la teneur en Ni est inférieure à 17,00, et satisfait 22,0 ou plus lorsque la teneur en Ni est supérieure ou égale à 17,00.
PCT/JP2024/029955 2023-08-23 2024-08-23 Matériau d'acier inoxydable à base d'austénite Pending WO2025041848A1 (fr)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2005281855A (ja) * 2004-03-04 2005-10-13 Daido Steel Co Ltd 耐熱オーステナイト系ステンレス鋼及びその製造方法
JP2008018115A (ja) * 2006-07-14 2008-01-31 Daido Castings:Kk ゴルフクラブヘッド
JP2015507697A (ja) * 2011-12-20 2015-03-12 エイティーアイ・プロパティーズ・インコーポレーテッド 高強度の耐腐食性オーステナイト系合金
JP2018534433A (ja) * 2015-09-29 2018-11-22 エクソンモービル リサーチ アンド エンジニアリング カンパニーＥｘｘｏｎ Ｒｅｓｅａｒｃｈ Ａｎｄ Ｅｎｇｉｎｅｅｒｉｎｇ Ｃｏｍｐａｎｙ 不動態化元素を含有する耐食性および耐割れ性の高マンガンオーステナイト鋼

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2005281855A (ja) * 2004-03-04 2005-10-13 Daido Steel Co Ltd 耐熱オーステナイト系ステンレス鋼及びその製造方法
JP2008018115A (ja) * 2006-07-14 2008-01-31 Daido Castings:Kk ゴルフクラブヘッド
JP2015507697A (ja) * 2011-12-20 2015-03-12 エイティーアイ・プロパティーズ・インコーポレーテッド 高強度の耐腐食性オーステナイト系合金
JP2018534433A (ja) * 2015-09-29 2018-11-22 エクソンモービル リサーチ アンド エンジニアリング カンパニーＥｘｘｏｎ Ｒｅｓｅａｒｃｈ Ａｎｄ Ｅｎｇｉｎｅｅｒｉｎｇ Ｃｏｍｐａｎｙ 不動態化元素を含有する耐食性および耐割れ性の高マンガンオーステナイト鋼

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