Austenitic stainless steel and hydrogen-resistant components

Abstract

The present disclosure relates to an austenitic stainless steel containing C ≤ 0.10 mass%, Si ≤ 0.50 mass%, 3.0 mass% ≤ Mn ≤ 8.0 mass%, P ≤ 0.30 mass%, S ≤ 0.30 mass%, 7.0 mass% ≤ Ni ≤ 12.0 mass%, 18.0 mass% ≤ Cr ≤ 28.0 mass%, 1.0 mass% ≤ Mo ≤ 3.0 mass%, 0.03 mass% ≤ V ≤ 0.50 mass%, 0.0003 mass% ≤ B ≤ 0.0300 mass%, 0.0001 mass% ≤ Ca ≤ 0.0300 mass%, 0.35 mass% ≤ N ≤ 0.80 mass%, W ≤ 2.0 mass%, Zr ≤ 0.20 mass%, Cu ≤ 0.5 mass%, Al ≤ 0.10 mass%, and O ≤ 0.050 mass%, with the balance being Fe and unavoidable impurities. The austenitic stainless steel has a number density of 3 × 10 5 mm 2 The following coarse alloyed carbonitrides.

Description

Technical Field

[0001] The present disclosure relates to austenitic stainless steel and hydrogen-resistant parts, and more particularly, to austenitic stainless steel excellent in strength and hydrogen embrittlement resistance, and hydrogen-resistant parts using the austenitic stainless steel. Background Art

[0002] In recent years, fuel cell vehicles using hydrogen as fuel and hydrogen stations that supply hydrogen to fuel cell vehicles have been developed. Because the various devices used in fuel cell vehicles, hydrogen stations, and the like (hereinafter collectively referred to as "high-pressure hydrogen devices") operate in high-pressure hydrogen environments, the materials used in these devices are required to have excellent resistance to hydrogen embrittlement. Stainless steel, particularly austenitic stainless steel with an increased nickel equivalent, has excellent resistance to hydrogen embrittlement and is therefore suitable for such applications.

[0003] Among austenitic stainless steels, SUS316L is considered to be a material with excellent resistance to hydrogen embrittlement. Currently, according to the standards for compressed hydrogen containers for vehicles stipulated in Japan's High-Pressure Gas Safety Law, SUS316L is approved as stainless steel with excellent resistance to hydrogen embrittlement. However, since SUS316L has low strength, in the case where SUS316L is used for structural components of high-pressure hydrogen devices, the structural components need to be designed to be thick. As a result, there is an unavoidable problem of increasing the size and weight of the device. In order to reduce the weight of fuel cell vehicles, miniaturize hydrogen stations, and achieve high-pressure operation in hydrogen stations, it is preferred that the stainless steel used for these applications has high strength.

[0004] Therefore, in order to solve this problem, various proposals have been made in the related art.

[0005] For example, Patent Document 1 discloses a stainless steel for high-pressure hydrogen, which is required to (a) contain predetermined contents of C, Si, Mn, Cr, Ni, V, N and Al, with the balance being Fe and impurities, and (b) satisfy 2.5Cr+3.4Mn<300N.

[0006] The same document describes that (A) solid solution strengthening with N is most effective for improving the strength of austenitic stainless steel, and that as the added N content increases, the strength improves but the ductility and toughness decrease, and (B) when the composition is adjusted to meet 2.5Cr+3.4Mn<300N, the tensile strength is improved and the elongation is also improved.

[0007] Patent Document 2 discloses an austenitic stainless steel for high-pressure hydrogen gas, which is required to (a) contain a predetermined content of C, Si, Mn, Cr, Ni, Al, N, and at least one of V and Nb, with the balance being Fe and impurities, (b) have a tensile strength of 800 MPa or more, (c) have a grain size of 8 or more, and (d) have a content of 0.4 alloy carbonitrides with a maximum diameter of 50 nm to 1,000 nm per μm. 2 above.

[0008] The same document describes that (A) when nitrogen is used as a solute element, the strength of stainless steel can be improved, but the stacking fault energy is reduced and, therefore, the durability to hydrogen environment embrittlement is reduced, (B) when V and / or Nb are added to the steel, fine alloy carbides are precipitated during solution heat treatment and the grains are refined due to the pinning effect, and (C) when the grains are refined, the hydrogen environment embrittlement resistance of high nitrogen steel can be improved.

[0009] Patent document 3 discloses an austenitic stainless steel which is required to (a) contain predetermined contents of C, Si, Mn, P, S, Ni, Cr, Mo, N, Nb and V, with the balance being Fe and impurities, (b) satisfy 15≤12.6C+1.05Mn+Ni+15N, (c) have a grain size grade number of less than 8.0, and (d) have a tensile strength of 690 MPa or more.

[0010] The same document describes that (A) excellent workability can be obtained when the grain size number is 8.0 or less, (B) C, N, Mn, and Ni are all austenite stabilizing elements, and when the contents of these elements are optimized, austenite is stabilized and hydrogen embrittlement resistance is improved even with coarse grains, and (C) when 1.0% or more of Mo is added, high tensile strength can be obtained even with a grain size number of less than 8.0.

[0011] In addition, Patent Document 4 discloses an austenitic stainless steel material which is required to (a) contain predetermined contents of C, Si, Mn, P, S, Ni, Cr, N, Mo, V, and Nb, with the balance being Fe and impurities, (b) have a grain size grade number of 6.0 or more, (c) have a tensile strength of 800 MPa or more, (d) have a difference between the maximum and minimum values ​​of the tensile strength of 50 MPa or less, and (e) have an alloy carbonitride number of 10 pieces / mm each having an equivalent circle diameter of more than 1,000 nm. 2 (f) the difference between the maximum value and the minimum value of the grain size grade number is 1.5 or less.

[0012] The same document describes that (A) when the grain size number is 6.0 or more and the difference between the maximum and minimum values ​​of the grain size number (ΔGS) is 1.5 or less, the difference between the maximum and minimum values ​​of the tensile strength is 50 MPa or less, (B) when the difference between the initial temperature and the final temperature during hot working is 100°C or less, ΔGS can be controlled to be 1.5 or less, and (C) when the grain size number is 6.0 or more and the number of alloy carbonitrides exceeding 1,000 nm is 10 pieces / mm 2 When the tensile strength is greater than 800 MPa, a tensile strength of 800 MPa or more can be obtained.

[0013] When using materials with excellent hydrogen embrittlement resistance as structural components for high-pressure hydrogen devices, the materials are typically processed, such as cutting, cold working, and welding. Therefore, this type of material is required to have not only excellent strength and hydrogen embrittlement resistance, but also excellent machinability, such as machinability, cold working, and weldability.

[0014] In addition, in order to reduce the manufacturing cost and maintenance cost of the high-pressure hydrogen device, it is preferred that the materials used in the device can be used in a solution treated (solution heat treated) state or a welded state, and the content of expensive elements such as Ni is small.

[0015] In this regard, the stainless steel for high-pressure hydrogen described in Patent Document 1 has a strength of 700 MPa or more after solution treatment. However, since the stainless steel described in the same document has a large Mn content, excellent workability may not be achieved.

[0016] The austenitic stainless steel for high-pressure hydrogen described in Patent Document 2 achieves grain refinement and high strength by performing solution heat treatment, cold working, and secondary heat treatment. However, cold working and secondary heat treatment increase manufacturing costs.

[0017] Furthermore, the premise of the austenitic stainless steel described in Patent Document 3 is to use it in a hot-worked state. Therefore, the stainless steel described in the same document has an excessive amount of carbonitrides in the steel and has low workability.

[0018] Similarly, in Patent Document 4, a relatively large amount of relatively coarse alloy carbonitrides are precipitated by subjecting austenitic stainless steel after hot working to a low-temperature heat treatment (from 930°C to less than 1000°C). Therefore, it is believed that the stainless steel described in Patent Document 4 also has low workability.

[0019] Patent Document 1: WO2004 / 083477A

[0020] Patent Document 2: WO2012 / 132992A

[0021] Patent Document 3: WO2015 / 159554A

[0022] Patent Document 4: WO2017 / 175739A Summary of the Invention

[0023] A problem to be solved by the present disclosure is to provide an austenitic stainless steel having excellent hydrogen embrittlement resistance, high strength, and excellent workability.

[0024] In addition, another problem to be solved by the present disclosure is to provide hydrogen-resistant parts using such austenitic stainless steel.

[0025] The points of the present disclosure in solving the above-mentioned problems are as follows.

[0026] [1] Austenitic stainless steel consisting of:

[0027] C≤0.10% by mass,

[0028] Si≤0.50 mass%,

[0029] 3.0 mass%≤Mn≤8.0 mass%,

[0030] P≤0.30 mass%,

[0031] S≤0.30 mass%,

[0032] 7.0 mass%≤Ni≤12.0 mass%,

[0033] 18.0 mass% ≤ Cr ≤ 28.0 mass%,

[0034] 1.0 mass%≤Mo≤3.0 mass%,

[0035] 0.03 mass%≤V≤0.50 mass%,

[0036] 0.0003 mass% ≤ B ≤ 0.0300 mass%,

[0037] 0.0001 mass%≤Ca≤0.0300 mass%,

[0038] 0.35 mass%≤N≤0.80 mass%,

[0039] W≤2.0% by mass,

[0040] Zr≤0.20 mass%,

[0041] Cu≤0.5% by mass,

[0042] Al≤0.10 mass% and

[0043] O≤0.050% by mass,

[0044] The balance is iron and unavoidable impurities, and

[0045] With a number density of 3×10 5 Pieces / mm 2 The following coarse alloy carbonitrides.

[0046] Here, "coarse alloy carbonitrides" refer to alloy carbonitrides having an equivalent circle diameter greater than 1,000 nm.

[0047] [2] The austenitic stainless steel according to [1], which satisfies:

[0048] 0.3 mass% ≤ W ≤ 2.0 mass%, and / or

[0049] 0.01 mass%≤Zr≤0.20 mass%.

[0050] [3] The austenitic stainless steel according to [1] or [2],

[0051] The tensile strength of this austenitic stainless steel measured at 25° C. is 690 MPa or more.

[0052] [4] The austenitic stainless steel according to any one of [1] to [3],

[0053] The austenitic stainless steel has a grain size number of austenite grains less than 8.0.

[0054] [5] The austenitic stainless steel according to any one of [1] to [4],

[0055] The austenitic stainless steel has a reduction of area measured at 25° C. of 30% or more.

[0056] [6] A hydrogen-resistant component comprising the austenitic stainless steel according to any one of [1] to [5].

[0057] [7] The hydrogen-resistant component according to [6], wherein

[0058] The austenitic stainless steel includes a portion in a solution treated state.

[0059] [8] The hydrogen-resistant component according to [6] or [7], comprising a butt-welded portion, wherein

[0060] The as-welded tensile strength of the butt welded portion measured at 25°C is 690 MPa or more.

[0061] N is an austenite stabilizing element and a solid solution strengthening element, but is also an element that reduces stacking fault energy. On the other hand, for example, Si is an element that reduces grain boundary strength, and B is an element that improves grain boundary strength. Therefore, when a relatively large amount of N is added to steel and the components are optimized at the same time (specifically, the content of the element that reduces grain boundary strength is limited, and the element that improves grain boundary strength of an appropriate amount is added), it is possible to obtain austenitic stainless steel with excellent hydrogen embrittlement resistance and high strength. In addition, since the content of Ni contained in the steel can be reduced, the cost of raw materials can be reduced.

[0062] Furthermore, the austenitic stainless steel according to the present disclosure exhibits high strength, for example, even in a solution-treated or welded state. Furthermore, due to the relatively low Mn content and the low number density of coarse alloy carbides, the austenitic stainless steel according to the present disclosure exhibits excellent workability. Furthermore, when manufacturing conditions are optimized, the grains are moderately coarsened, further improving workability. DETAILED DESCRIPTION

[0063] Embodiments of the present disclosure will be described in detail below.

[0064] [1. Austenitic stainless steel]

[0065] [1.1. Main component elements]

[0066] The austenitic stainless steel according to the present disclosure contains the following elements, with the balance being iron and inevitable impurities. The types of the added elements, their content ranges, and the reasons for their limitations are as follows.

[0067] (1) C≤0.10 mass%:

[0068] In the present disclosure, C is an impurity. Excessive C content can lead to the precipitation of large amounts of carbides, resulting in deterioration of toughness, ductility, and corrosion resistance. Therefore, the C content should be 0.10% by mass or less. The C content is preferably less than 0.05% by mass, and more preferably 0.03% by mass or less.

[0069] In the present disclosure, the lower the C content, the better. However, an extreme reduction in the C content will lead to an increase in manufacturing costs. Considering manufacturing costs, the C content is preferably 0.0005% by mass or more. The C content is more preferably 0.001% by mass or more.

[0070] (2) Si≤0.50 mass%

[0071] In the present disclosure, Si is an impurity. Si combines with Ni and Cr to form intermetallic compounds. Si further promotes the growth of intermetallic compounds such as σ phase. These intermetallic compounds reduce the hot workability of the steel. Furthermore, excessive Si content can reduce grain boundary strength and lower hydrogen embrittlement resistance. Therefore, the Si content needs to be 0.50 mass% or less. The Si content is preferably 0.20 mass% or less, and more preferably 0.09 mass% or less.

[0072] In the present disclosure, the lower the Si content, the better. However, an extreme reduction in the Si content will lead to an increase in manufacturing costs. Considering manufacturing costs, the Si content is preferably 0.001% by mass or more. The Si content is more preferably 0.01% by mass or more.

[0073] (3) 3.0 mass% ≤ Mn ≤ 8.0 mass%:

[0074] Mn stabilizes austenite and prevents the formation of martensite, which is highly susceptible to hydrogen embrittlement. Furthermore, Mn increases the solubility of nitrogen in the molten metal, thereby contributing to increased strength. To achieve this effect, the Mn content needs to be 3.0% by mass or greater. The Mn content is preferably 5.1% by mass or greater, and more preferably 5.5% by mass or greater.

[0075] On the other hand, when the Mn content is too high, the stacking fault energy and grain boundary strength decrease, and the hydrogen embrittlement resistance decreases. In addition, when the Mn content is too high, the toughness, ductility, and hot workability of the steel also decrease. Therefore, the Mn content needs to be 8.0% by mass or less. The Mn content is preferably 6.9% by mass or less, and more preferably 6.5% by mass or less.

[0076] (4) P≤0.30 mass%:

[0077] In the present disclosure, phosphorus (P) is an impurity. Excessive P content reduces the hot workability, toughness, and ductility of the steel. Furthermore, excessive P content increases the risk of hardening cracking during welding. Therefore, the P content should be 0.30% by mass or less. The P content is preferably less than 0.10% by mass, and more preferably 0.03% by mass or less.

[0078] In the present disclosure, the lower the P content, the better. However, an extreme reduction in the P content will lead to an increase in manufacturing costs. Considering manufacturing costs, the P content is preferably 0.0005% by mass or more. The P content is more preferably 0.001% by mass or more.

[0079] (5) S≤0.30 mass%

[0080] In the present disclosure, S is an impurity. Excessive S content reduces the toughness, ductility, and hot workability of the steel. Furthermore, excessive S content increases the risk of cracking during welding. Therefore, the S content should be 0.30% by mass or less. The S content is preferably less than 0.10% by mass, and more preferably 0.09% by mass or less.

[0081] In the present disclosure, the lower the S content, the better. However, an extreme reduction in the S content will lead to an increase in manufacturing costs. Considering manufacturing costs, the S content is preferably 0.0005% by mass or more. The S content is more preferably 0.001% by mass or more.

[0082] (6) 7.0 mass% ≤ Ni ≤ 12.0 mass%:

[0083] Ni stabilizes austenite and increases stacking fault energy, thereby improving hydrogen embrittlement resistance. To achieve this effect, the Ni content needs to be 7.0% by mass or more. The Ni content is preferably 9.0% by mass or more, and more preferably 9.5% by mass or more.

[0084] On the other hand, excessive Ni content increases raw material costs. Furthermore, excessive Ni content reduces the solubility of N in the molten metal, thereby degrading strength. Therefore, the Ni content needs to be 12.0% by mass or less. The Ni content is preferably 10.5% by mass or less, and more preferably 9.9% by mass or less.

[0085] (7) 18.0 mass% ≤ Cr ≤ 28.0 mass%:

[0086] Cr improves the corrosion resistance of steel. Furthermore, Cr increases the solubility of nitrogen in the molten metal, contributing to increased strength. To achieve these effects, the Cr content must be 18.0% by mass or greater. The Cr content is preferably 20.0% by mass or greater, and more preferably 22.0% by mass or greater.

[0087] On the other hand, if the Cr content is too high, intermetallic compounds or carbonitrides may precipitate excessively, and the toughness, ductility, and corrosion resistance of the steel may decrease. Therefore, the Cr content needs to be 28.0% by mass or less. The Cr content is preferably 26.0% by mass or less, and more preferably 25.0% by mass or less.

[0088] (8) 1.0 mass% ≤ Mo ≤ 3.0 mass%:

[0089] Mo contributes to increased strength by solid solution strengthening austenite or forming carbonitrides. Furthermore, Mo improves the corrosion resistance of steel. To achieve this effect, the Mo content needs to be 1.0% by mass or greater. The Mo content is preferably 1.5% by mass or greater, and more preferably 1.8% by mass or greater.

[0090] On the other hand, if the Mo content is too high, intermetallic compounds or carbonitrides may precipitate excessively, reducing the toughness and ductility of the steel. Furthermore, if the Mo content is too high, raw material costs may increase. Therefore, the Mo content should be 3.0% by mass or less. The Mo content is preferably 2.5% by mass or less, and more preferably 2.2% by mass or less.

[0091] (9) 0.03 mass% ≤ V ≤ 0.50 mass%:

[0092] V forms hard alloy carbonitrides to increase the strength of steel. To achieve this effect, the V content needs to be 0.03% by mass or more. The V content is preferably 0.05% by mass or more, and more preferably 0.08% by mass or more.

[0093] On the other hand, if the V content is too high, alloy carbonitrides precipitate excessively, and the toughness and ductility of the steel decrease. Therefore, the V content needs to be 0.50% by mass or less. The V content is preferably 0.30% by mass or less, and more preferably 0.20% by mass or less.

[0094] (10) 0.0003 mass% ≤ B ≤ 0.0300 mass%:

[0095] Boron segregates at grain boundaries, increasing the grain boundary anchoring force and thereby improving the strength of the steel. Furthermore, Boron prevents embrittlement of the steel in a hydrogen environment, thereby improving hydrogen embrittlement resistance. Furthermore, Boron improves the hot workability of the steel. To achieve these effects, the Boron content must be at least 0.0003 mass%. The Boron content is preferably at least 0.0005 mass%, and more preferably at least 0.0010 mass%.

[0096] On the other hand, if the B content is too high, the molten metal's hardening cracking sensitivity increases when welding is performed without using filler metal. Therefore, the B content needs to be 0.0300 mass% or less. The B content is preferably 0.0100 mass% or less, and more preferably 0.0050 mass% or less.

[0097] (11) 0.0001 mass% ≤ Ca ≤ 0.0300 mass%:

[0098] Ca improves the hot workability of steel. To achieve this effect, the Ca content needs to be 0.0001 mass % or more. The Ca content is preferably 0.0003 mass % or more, and more preferably 0.0005 mass % or more.

[0099] On the other hand, if the Ca content is too high, Ca combines with O, reducing the purity of the steel. As a result, hot workability is reduced, and toughness and ductility are also reduced. Therefore, the Ca content needs to be 0.0300 mass% or less. The Ca content is preferably 0.0150 mass% or less, and more preferably 0.0100 mass% or less.

[0100] (12) 0.35 mass% ≤ N ≤ 0.80 mass%:

[0101] Nitrogen stabilizes austenite and improves resistance to hydrogen embrittlement. Furthermore, nitrogen increases the strength of steel through solid solution strengthening and the formation of nitrides. Furthermore, nitrogen improves the corrosion resistance of steel. To achieve these effects, the nitrogen content must be 0.35% by mass or greater. The nitrogen content is preferably 0.40% by mass or greater, and more preferably 0.46% by mass or greater.

[0102] On the other hand, excessive N content can produce coarse nitrides, reducing the toughness and ductility of the steel. Furthermore, excessive N content can reduce the hot workability of the steel, or can lead to the formation of pores (defects) during welding. Furthermore, excessive N content can reduce stacking fault energy and hydrogen embrittlement resistance. Therefore, the N content should be 0.80% by mass or less. The N content is preferably 0.60% by mass or less, and more preferably 0.53% by mass or less.

[0103] It should be noted that in high nitrogen steel, hydrogen embrittlement resistance may decrease due to deterioration of grain boundary strength, but in the present disclosure, since the grain boundary strength is improved by optimizing the Si content, B content, etc., deterioration of hydrogen embrittlement resistance can be prevented.

[0104] [1.2. Auxiliary components]

[0105] In addition to the above-mentioned main component elements, the austenitic stainless steel according to the present disclosure may further contain one or two or more of the following elements: The types of the added elements, their content ranges, and the reasons for their limitation are as follows.

[0106] (1) W≤2.0 mass%:

[0107] W has the effect of improving corrosion resistance and strength through solid solution or the formation of carbonitrides. Therefore, the austenitic stainless steel according to the present disclosure may further contain W. To achieve these effects, the W content is preferably 0.3% by mass or greater. The W content is more preferably 0.8% by mass or greater.

[0108] On the other hand, if the W content is too high, the raw material cost increases. Therefore, the W content is preferably 2.0% by mass or less. The W content is more preferably 1.5% by mass or less.

[0109] (2) Zr≤0.20 mass%

[0110] Zr forms crystalline carbides. Since crystalline carbides serve as a starting point for the formation of inclusions such as MnS and carbonitrides, the size of inclusions can be reduced, and toughness and ductility can be improved. Therefore, the austenitic stainless steel according to the present disclosure may further contain Zr in place of or in addition to W. To achieve this effect, the Zr content is preferably 0.01% by mass or greater. More preferably, the Zr content is 0.05% by mass or greater.

[0111] On the other hand, if the Zr content is too high, coarse oxides may be formed, and toughness and ductility may be reduced. Therefore, the Zr content is preferably 0.20% by mass or less. The Zr content is more preferably 0.15% by mass or less.

[0112] [1.3. Unavoidable impurities]

[0113] The inevitable impurities refer to elements mixed in from ore or scrap used as a raw material for steel or from the environment during the manufacturing process, etc. Specific examples of the inevitable impurities include the following elements in addition to C, Si, P, and S mentioned above.

[0114] (1) Cu≤0.5 mass%:

[0115] In the present disclosure, Cu is an impurity. Excessive Cu content increases the risk of hardening cracking during welding. Therefore, the Cu content is preferably 0.5% by mass or less. More preferably, the Cu content is 0.4% by mass or less.

[0116] In the present disclosure, the lower the Cu content, the better. However, an extreme reduction in the Cu content will lead to an increase in manufacturing costs. Considering manufacturing costs, the Cu content is preferably 0.005% by mass or more. The Cu content is more preferably 0.010% by mass or more.

[0117] (2) Al≤0.10 mass%

[0118] In this disclosure, Al is an impurity. Similar to Si, Al has the effect of deoxidizing steel. However, excessive Al content can lead to excessive nitride formation, reducing the toughness and ductility of the steel. Furthermore, excessive Al content can reduce the penetration depth during welding. Therefore, the Al content is preferably 0.10% by mass or less. More preferably, the Al content is 0.05% by mass or less.

[0119] In the present disclosure, the lower the Al content, the better. However, an extreme reduction in the Al content will lead to an increase in manufacturing costs. Considering manufacturing costs, the Al content is preferably 0.0005% by mass or more. The Al content is more preferably 0.001% by mass or more.

[0120] (3) O≤0.050 mass%:

[0121] In the present disclosure, O is an impurity. O reduces the hot workability of the base material during manufacturing. Furthermore, O reduces the purity of steel and reduces its toughness and ductility. Therefore, the O content is preferably 0.050 mass% or less. The O content is more preferably 0.030 mass% or less, and even more preferably 0.010 mass% or less.

[0122] In the present disclosure, the lower the O content, the better. However, an extreme reduction in the O content leads to an increase in manufacturing costs. Considering manufacturing costs, the O content is preferably 0.0005% by mass or more. The O content is more preferably 0.001% by mass or more, and even more preferably 0.002% by mass or more.

[0123] [1.4. Features]

[0124] [1.4.1. Number density of coarse alloy carbonitrides]

[0125] “Coarse alloy carbonitrides” refer to alloy carbonitrides having an equivalent circle diameter greater than 1,000 nm.

[0126] The “number density of coarse alloy carbonitrides” refers to the number of coarse alloy carbonitrides per unit area (number / mm 2 ). Specifically, the number density is determined by the following method.

[0127] Specifically, a sample of austenitic stainless steel material is obtained, including the central portion of a cross section perpendicular to the rolling or forging elongation direction. The aforementioned observation area of ​​the sample is mirror-polished. Subsequently, observation is performed using a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS) in an arbitrary 10 fields of view (200 μm × 200 μm) of observation area, and alloy carbonitrides are identified from the precipitates and inclusions in each field of view. In the present disclosure, alloy carbonitrides are defined as those containing C or N, or both C and N, in the precipitates and inclusions.

[0128] The equivalent circle diameter of the alloy carbonitride specified in each field of view is obtained by image analysis. The equivalent circle diameter refers to the diameter (nm) when the area of ​​the alloy carbonitride in the field of view is converted into a circle. The number of each alloy carbonitride with an equivalent circle diameter greater than 1,000 nm (coarse alloy carbonitride) is counted. In the present disclosure, the average number of coarse alloy carbonitrides obtained in 10 fields of view is defined as the "number density of coarse alloy carbonitrides (numbers / mm 2 )”.

[0129] When coarse alloy carbonitrides are excessively precipitated in the matrix phase, the coarse alloy carbonitrides cause tool wear, thereby deteriorating machinability. On the other hand, when the composition of austenitic stainless steel is optimized and hot working and / or solution treatment is performed under appropriate conditions, the number density of coarse alloy carbonitrides can be reduced. In order to obtain excellent machinability, the number density of coarse alloy carbonitrides is preferably 3×10 5 Pieces / mm 2 The number density is more preferably 1×10 4 Pieces / mm 2 Below, and further more preferably 1×10 3 Pieces / mm 2 the following.

[0130] On the other hand, since coarse alloy carbonitrides also contribute to tensile strength, if austenitic stainless steel with higher strength is desired, the number density is preferably 1 per mm. 2 More than 10 pieces / mm 2 above.

[0131] [1.4.2. Tensile strength]

[0132] The “tensile strength” refers to the tensile strength obtained by a tensile test using a No. 14A test piece having a parallel portion diameter of 6 mm in accordance with JIS Z2241:2011.

[0133] By optimizing hot working conditions and / or solution treatment conditions, the tensile strength of the austenitic stainless steel according to the present disclosure reaches 690 MPa or more when measured at 25° C. When the components are further optimized, the tensile strength can be 750 MPa or more, or 800 MPa or more.

[0134] [1.4.3. Grain size level]

[0135] The "grain size fraction number" is a value measured according to JIS G0551 (2005). Specifically, the grain size fraction number is determined by the following method.

[0136] Specifically, a sample for microscopic observation was obtained from austenitic stainless steel, and the grain size grade was evaluated by performing a microscopic test method for grain size specified in JIS G0551 (2005) using the sample.

[0137] More specifically, the surface of the sample is etched using a well-known etchant (Glyceregia, Kalling's reagent, Marbles' reagent, etc.) to reveal the grain boundaries on the surface. The grain size number is obtained for each of 10 fields of view on the etched surface. The area of ​​each field of view is about 40 mm. 2 The grain size number of each field of view was evaluated by comparison with the grain size reference diagram defined in 7.1.2 of JIS G0551 (2005). The average grain size number of these fields of view was defined as the grain size number of the austenitic stainless steel according to the present disclosure.

[0138] In the austenitic stainless steel disclosed herein, due to the optimized composition, the grain size of the austenite grains can be less than 8.0 by optimizing the hot working conditions and / or the solution treatment conditions. When the grain size is less than 8.0, the grain size is moderately increased and the cutting resistance is reduced. In addition, during the cutting process, the chips can be easily separated from the workpiece material and the cutting tool, and the processability of the chips is improved. In other words, when the grain size is less than 8.0, the machinability of the steel is improved. The grain size is preferably 7.0 or less.

[0139] On the other hand, if the grain size number is too small, the size of the grains increases excessively, which may reduce the tensile strength of the steel. Therefore, the grain size number is preferably 2.0 or more. The grain size number is more preferably 3.0 or more.

[0140] [1.4.4. Sectional reduction]

[0141] “Reduction of area” refers to the difference between the original cross-sectional area (S0) of the tensile specimen before the test and the cross-sectional area (S0) of the tensile specimen after the test when a tensile test is performed using a No.14A specimen with a parallel portion diameter of 6 mm in accordance with JIS Z2241:2011. u ) relative to the original cross-sectional area (S0) (=(S0-S u )×100 / S0).

[0142] By optimizing hot working conditions and / or solution treatment conditions, the austenitic stainless steel according to the present disclosure can have a reduction in area of ​​30% or more measured at 25° C. When the composition is further optimized, the reduction in area can be 40% or more, or 50% or more.

[0143] Here, in the present disclosure, "solution treatment" refers to a process of heating a steel material at 800 to 1200°C for 1 minute or more and cooling the steel material at a cooling rate of water cooling, oil cooling, or air cooling, or an equivalent cooling rate thereof.

[0144] [1.4.5. Hydrogen embrittlement resistance]

[0145] The quality of hydrogen embrittlement resistance can be evaluated based on the magnitude of the relative reduction of area.

[0146] Here, the "relative reduction of area" refers to a value expressed by the following equation (1): The larger the value of the relative reduction of area expressed by equation (1), the better the hydrogen embrittlement resistance.

[0147] Relative area reduction = A / B (1)

[0148] in:

[0149] A is the reduction of area of ​​a round bar tensile specimen when a low strain rate test is conducted under conditions including a test temperature of room temperature and a test atmosphere of hydrogen at 87.5 MPa, and

[0150] B is the reduction of area of ​​the round bar tensile specimen when a low strain rate test is performed under conditions including a test temperature of room temperature and a test atmosphere of helium at 87.5 MPa.

[0151] It should be noted that in each measurement of A and B, a round bar tensile specimen with a parallel portion diameter of 4 mm was used, and the strain rate was 7 × 10 -5 / s.

[0152] Furthermore, it is known that relative reduction of area, which is an indicator of hydrogen embrittlement resistance, is worse in low-temperature low-strain rate tests than in low-strain rate tests at room temperature. Even in low-temperature low-strain rate tests, the austenitic stainless steel according to the present disclosure exhibits excellent relative reduction of area.

[0153] The relative reduction of area in the low strain rate test at low temperature refers to a value expressed by the following equation (2): The larger the value of the relative reduction of area expressed by equation (2), the better the hydrogen embrittlement resistance.

[0154] Relative area reduction = C / D(2)

[0155] C is the reduction of area of ​​a round bar tensile specimen when subjected to a low strain rate test under conditions including a test temperature of -60°C and a test atmosphere of 87.5 MPa of hydrogen, and

[0156] D is the reduction of area of ​​the round bar tensile test specimen when a low strain rate test is performed under conditions including a test temperature of -60°C and a test atmosphere of helium at 87.5 MPa.

[0157] It should be noted that in each measurement of C and D, a round bar tensile specimen with a parallel portion diameter of 4 mm was used, and the strain rate was 7 × 10 -5 / s.

[0158] Due to its optimized composition, the austenitic stainless steel according to the present disclosure is excellent in hydrogen embrittlement resistance. With further optimization of the composition and microstructure, the austenitic stainless steel according to the present disclosure can achieve a relative reduction in area of ​​0.8 or greater. Further optimization of the composition and / or microstructure can achieve a relative reduction in area of ​​0.9 or greater.

[0159] [1.5. Application]

[0160] Since the austenitic stainless steel according to the present disclosure has excellent hydrogen embrittlement resistance, the austenitic stainless steel can be used (a) as austenitic stainless steel for high-pressure hydrogen gas or (b) as austenitic stainless steel for liquid hydrogen environments.

[0161] In particular, since the austenitic stainless steel according to the present disclosure has excellent toughness at extremely low temperatures in addition to resistance to hydrogen embrittlement, the austenitic stainless steel can be used, for example, as a material for (a) components of a liquid hydrogen pump pressurizing hydrogen station and (b) components used in a liquid hydrogen environment (such as liquid hydrogen valves and pump components).

[0162] [2. Manufacturing method of austenitic stainless steel]

[0163] The austenitic stainless steel according to the present disclosure can be obtained by: (a) melting and casting raw materials mixed to obtain a predetermined composition to prepare an ingot, (b) performing primary hot working on the obtained ingot, (c) performing secondary hot working on the material obtained by the primary hot working, (d) if necessary, cold working the material after the secondary hot working or after the cold working, and (e) if necessary, post-treating the material after the secondary hot working, after the cold working, or after the solution treatment.

[0164] [2.1. Melting and Casting Process]

[0165] First, raw materials mixed to obtain a predetermined composition are melted and cast to produce an ingot. The melting and casting methods and conditions are not particularly limited, and the optimal method and conditions can be selected according to the intended purpose. For example, an electric furnace, an argon oxygen decarburization (AOD) furnace, a vacuum oxygen decarburization (VOD) furnace, or the like can be used to produce molten steel.

[0166] It should be noted that, if necessary, the obtained ingot may be subjected to a homogenization heat treatment to eliminate segregation.

[0167] [2.2. Initial hot working process]

[0168] Next, the resulting ingot is subjected to primary hot working. This primary hot working is performed to break down the coarse cast structure and refine the structure, while converting the ingot into steel materials such as slabs, billets, and bars. There are no particular limitations on the primary hot working method, and the optimal method can be selected based on the intended purpose. Examples of primary hot working methods include hot forging and hot rolling.

[0169] It should be noted that steel materials such as slabs, billets and billets can be directly made from the molten steel produced by a continuous casting process, in which case the initial hot working step can be omitted.

[0170] [2.3. Secondary heat treatment process]

[0171] Next, the material obtained in the primary hot working step is subjected to secondary hot working. Secondary hot working is performed to process the material obtained in the primary hot working step into the final product shape (e.g., steel plate, steel bar, wire rod, and steel pipe) or a shape close thereto. There are no particular limitations on the secondary hot working method, and the optimal method can be selected depending on the intended purpose. Examples of secondary hot working methods include hot rolling, hot extrusion, and hot piercing rolling.

[0172] There are no particular restrictions on the conditions for secondary hot working, and optimal conditions can be selected according to the intended purpose. Furthermore, secondary hot working can be performed multiple times depending on the intended purpose. The heating temperature of the steel material prior to secondary hot working is preferably 900°C or higher and 1,300°C or lower.

[0173] Furthermore, when secondary hot working is performed multiple times, the temperature of the steel material at the completion of the last secondary hot working is preferably 800° C. to 1200° C. This is to optimize the crystal grains and the number density of coarse alloy carbonitrides.

[0174] [2.4. Cold working process]

[0175] Next, if necessary, the material can be cold worked after the secondary hot working. There are no particular restrictions on the cold working method, and the optimal method can be selected based on the intended purpose. For example, when cold working the material into steel pipe, cold drawing is preferred. Alternatively, when processing the material into steel plate, cold rolling is preferred.

[0176] [2.5. Solution treatment process]

[0177] Next, if necessary, the material that has been subjected to secondary hot working or the material that has been cold worked may be solution treated. Solution treatment may be performed only once or may be performed multiple times.

[0178] The solution treatment temperature affects the material's properties. Without solution treatment, or at too low a temperature, the number density of coarse alloy carbonitrides may increase excessively, and the reduction of area may decrease. Furthermore, grain refinement may become excessive, and machinability may decrease. Therefore, the solution treatment temperature is preferably 800°C or higher. More preferably, it is 1,000°C or higher.

[0179] On the other hand, if the solution treatment temperature is too high, there is a concern that local melting may occur. Therefore, the solution treatment temperature is preferably 1,200°C or lower.

[0180] The optimal hold time for the solution treatment temperature can be selected depending on the intended purpose. Generally, the longer the hold time at the solution treatment temperature, the lower the number density of coarse alloy carbonitrides. On the other hand, if the hold time is extended beyond necessary, the grains may become excessively coarsened. The optimal hold time depends on the solution treatment temperature, but is typically between 1 minute and 3 hours. After the hold time expires, the material is cooled at a cooling rate of water, oil, or air cooling, or an equivalent cooling rate.

[0181] [2.6. Post-processing process]

[0182] If necessary, the material that has undergone secondary hot working, cold working, or solution treatment can be further post-processed. Examples of post-processing include cutting, welding, and cold working. The resulting components are used in various applications.

[0183] [3. Hydrogen-resistant parts]

[0184] A hydrogen-resistant component according to the present disclosure includes the austenitic stainless steel according to the present disclosure.

[0185] [3.1. Materials]

[0186] Since the austenitic stainless steel according to the present disclosure has a predetermined composition, the austenitic stainless steel has excellent hydrogen embrittlement resistance. Since other aspects regarding the composition of the austenitic stainless steel are as described above, description thereof is omitted.

[0187] The austenitic stainless steel constituting the hydrogen-resistant component may be in any of the following states: hot-worked, cold-worked, solution-treated, or solution-treated and subjected to necessary post-treatment. To reduce the number density of coarse alloy carbonitrides and lower manufacturing costs, the austenitic stainless steel constituting the hydrogen-resistant component preferably includes a portion in a solution-treated state.

[0188] Here, "including a portion in a solution-treated state" means (a) the case where all of the austenitic stainless steel constituting the hydrogen-resistant component is in a solution-treated state, or (b) the case where a portion of the austenitic stainless steel constituting the hydrogen-resistant component undergoes necessary post-treatment (e.g., cutting and welding) while the other portion is in a solution-treated state.

[0189] [3.2. Shape]

[0190] There is no particular limitation on the shape of the hydrogen resistant member, and an optimal shape can be selected according to the purpose. Examples of the shape of the hydrogen resistant member include tubes, rods, wires, plates, and the like.

[0191] The hydrogen-resistant component may include a welded portion formed by welding components each having a predetermined shape. The type of joint in the welded portion (i.e., welded joint) is not particularly limited, and the optimal welded joint can be selected according to the intended purpose. Examples of welded joints include butt joints, T-joints, corner joints, lap joints, and end joints.

[0192] When the hydrogen-resistant component includes welded portions, there are no particular limitations on the welding method, and the optimal method can be selected based on the intended purpose. The welding method may be either soldering or solder-free. Examples of solder include YS316L, YS309LMo, YS308L, YS308H, YS308N2, and YS308LN.

[0193] Examples of the welding method using solder include TIG welding, plasma welding, laser welding, MIG welding, MAG welding, and shielded metal arc welding.

[0194] Examples of the welding method that does not use solder include TIG welding, plasma welding, and laser welding.

[0195] [3.3. Tensile strength of welded parts]

[0196] When the hydrogen-resistant component includes a welded portion, the component before welding is preferably solution treated and has a tensile strength of 690 MPa or greater, as measured at 25°C. The tensile strength measured at 25°C is more preferably 750 MPa or greater, and even more preferably 800 MPa or greater. When welding using a high-strength component, a high-strength hydrogen-resistant component can be obtained.

[0197] Furthermore, when the composition and structure of austenitic stainless steel, as well as the welding method and welding conditions, are optimized, hydrogen-resistant parts with high strength can be obtained even in the welded state.

[0198] For example, when butt welding is performed using TIG welding with or without filler metal at a heat input of 0.20 kJ / mm to 0.60 kJ / mm, a hydrogen-resistant component including the butt weld portion can be obtained. In this case, by optimizing the composition and microstructure of the austenitic stainless steel, a hydrogen-resistant component including the butt weld portion can be obtained, wherein the butt weld portion in the as-welded state has a tensile strength of 690 MPa or greater measured at 25°C. Further optimizing the composition and microstructure of the austenitic stainless steel can achieve a tensile strength of 750 MPa or greater, or 800 MPa or greater, in the as-welded state.

[0199] Here, the “tensile strength of the butt-welded portion” refers to the tensile strength when a tensile test is conducted using a No. 1A test piece having a parallel portion width of 12 mm and a plate thickness of 1.5 mm in accordance with JIS Z3121:2013.

[0200] [4. Function]

[0201] N is an austenite stabilizing element and a solid solution strengthening element, but is also an element that reduces stacking fault energy. On the other hand, for example, Si is an element that reduces grain boundary strength, and B is an element that improves grain boundary strength. Therefore, when a relatively large amount of N is added to steel and the components are optimized at the same time (specifically, the content of the element that reduces grain boundary strength is limited, and the element that improves grain boundary strength of an appropriate amount is added), it is possible to obtain austenitic stainless steel with excellent hydrogen embrittlement resistance and high strength. In addition, since the content of Ni contained in the steel can be reduced, the cost of raw materials can be reduced.

[0202] Furthermore, the austenitic stainless steel according to the present disclosure exhibits high strength, for example, even in a solution-treated or welded state. Furthermore, due to the relatively low Mn content and the low number density of coarse alloy carbides, the austenitic stainless steel exhibits excellent workability. Furthermore, when manufacturing conditions are optimized, the grains are appropriately coarsened, further improving workability.

[0203] [example]

[0204] (Examples 1 to 9, Comparative Examples 1 to 8)

[0205] [1. Sample preparation]

[0206] In a vacuum induction furnace, 50 kg of steel having the composition shown in Table 1 was melted and cast into ingots. The ingots were then hot forged, hot rolled, solution treated, and machined to produce steel bars with a diameter of 30 mm. In Table 1, the steels in Examples 5 to 7 have the same composition as the steel in Example 4, and the steel in Comparative Example 8 has the same composition as the steel in Comparative Example 7. It should be noted that in Example 7 and Comparative Example 7, solution treatment was not performed. In addition, in Comparative Example 8, the solution treatment temperature was 700°C. Except for Example 7 and Comparative Examples 7 and 8, the solution treatment temperature was 900°C to 1,100°C.

[0207] Furthermore, two steel plates were separately prepared and butt-welded by TIG welding without using filler metal at a heat input of 0.20 kJ / mm to 0.60 kJ / mm.

[0208]

[0209] [2. Test methods]

[0210] [2.1. Grain size measurement]

[0211] Each steel bar was cut parallel to the rolling direction. Samples were taken for grain size measurement, with the surface closest to the central axis of the steel bar used as the observation surface. The observation surface of each sample was subjected to well-known electrolytic polishing techniques. The grain size grade of the electrolytically polished observation surface was determined using the method described above.

[0212] [2.2. Determination of the number density of coarse alloy carbonitrides]

[0213] The number density of coarse alloy carbonitrides was determined by the method described above.

[0214] [2.3. Evaluation of area reduction and tensile strength]

[0215] A round bar tensile specimen was obtained from the center of each steel bar. The parallel portion of the round bar tensile specimen was parallel to the rolling direction of the steel bar. The diameter of the parallel portion was 6 mm. The tensile strength (TS) (MPa) was determined by performing a tensile test on the round bar tensile specimen at room temperature (25°C) in air.

[0216] In addition, a tensile test was performed on each butt-welded component. Specifically, a plate-shaped tensile specimen with a welded portion at the center of the parallel sections was prepared from the butt-welded component. The tensile test was performed on the plate-shaped tensile specimen at room temperature to determine the tensile strength (TS) (MPa) of the butt-welded portion.

[0217] In the tensile test using a round bar tensile specimen or a plate tensile specimen, the case where the measured tensile strength TS (MPa) is 690 MPa or more (this is the strength required for the substrate) is judged as "A (high strength)", and the case where the measured tensile strength TS (MPa) is less than 690 MPa is judged as "B".

[0218] The area reduction was calculated based on the fracture surface area of ​​the round bar tensile specimen after the tensile test. A reduction of 30% or more was rated "A (high reduction)" and a reduction of less than 30% was rated "B."

[0219] [2.4. Hydrogen embrittlement resistance evaluation]

[0220] Low strain rate tests were performed to evaluate hydrogen compatibility. The test temperature was room temperature or -60°C, and the test atmosphere was helium or hydrogen at 87.5 MPa. Round bar tensile specimens with a parallel section diameter of 4 mm were used as specimens. The strain rate was 7 × 10 -5 / s.

[0221] Based on the fracture surface area of ​​the round bar tensile specimen after the low strain rate test, the cross-sectional reduction ratio in hydrogen and the cross-sectional reduction ratio in helium were calculated. Furthermore, based on these cross-sectional reduction ratios, the cross-sectional reduction ratio at room temperature (=A / B) and the cross-sectional reduction ratio at -60°C (=C / D) were calculated. In all cases, a relative cross-sectional reduction ratio of 0.8 or greater was judged as "A (excellent hydrogen embrittlement resistance)", and a relative cross-sectional reduction ratio of less than 0.80 was judged as "B".

[0222] It should be noted that in austenitic stainless steel, a high-pressure hydrogen environment at -60°C is the environment that most significantly reduces the reduction of cross-sectional area.

[0223] [2.5. Relative wear evaluation]

[0224] A rod-shaped specimen was taken from the center portion of each steel bar. The parallel portion of the rod-shaped specimen was parallel to the rolling direction of the steel bar. The rod-shaped specimen had a circular cross section and a diameter of 8 mm.

[0225] A bar-shaped specimen was peeled for 5 minutes. An uncoated carbide tool (corresponding to P20 in the JIS standard) was used as the peeling tool. The cutting speed was 100 m / min, the feed was 0.2 mm / rev, and the cutting depth was 1.0 mm. No lubricant was used during the peeling process. The peeling process was performed under the above conditions, and the flank wear W1 (mm) of the carbide tool after the test was measured.

[0226] Furthermore, a rod-shaped specimen (hereinafter referred to as a "reference specimen") having a chemical composition corresponding to JIS SUS316 was prepared. The reference specimen had the same shape as the rod-shaped specimen. Peeling treatment was performed using the reference specimen under the same conditions as above, and the flank wear W0 (mm) of the cemented carbide tool after the test was measured.

[0227] Based on the measurement results, the relative wear ratio defined by the following equation (3) was obtained: The case where the relative wear ratio was 0.40 or more was judged as "A (excellent workability)", and the case where the relative wear ratio was less than 0.40 was judged as "B".

[0228] Relative wear ratio = W0 / W1(3)

[0229] [3. Results]

[0230] The results are shown in Table 2. The following results can be found in Table 2. (1) In Comparative Examples 1 and 2, the tensile strength is low. This is believed to be due to the low N content. (2) In Comparative Example 3, the hydrogen embrittlement resistance is low. This is believed to be due to the excessive Si content. (3) In Comparative Example 4, the hydrogen embrittlement resistance is low. This is believed to be due to the low B content.

[0231] (4) In Comparative Example 5, the number density of coarse alloy carbonitrides was high, and the machinability was poor. The reasons for this are believed to be that the number density of coarse alloy carbonitrides increased due to excessive Nb content, excessively promoted grain refinement, and that the coarse alloy carbonitrides promoted tool wear. (5) In Comparative Example 6, the number density of coarse alloy carbonitrides was high, and the machinability was poor. The reasons for this are believed to be that the number density of coarse alloy carbonitrides increased due to excessive Ti content, excessively promoted grain refinement, and that the coarse alloy carbonitrides promoted tool wear.

[0232] (6) In Comparative Example 7, the number density of coarse alloy carbonitrides is high, and the grain size grade number is large. Therefore, it is considered that the machinability is poor. It is considered that this is because the temperature at the time of completion of the final secondary heat treatment is low. (8) In Comparative Example 8, the number density of coarse alloy carbonitrides is high, and the grain size grade number is large. Therefore, it is considered that the machinability is poor. It is considered that this is because the solution treatment temperature is low. (9) In each of Examples 1 to 9, the grain size grade number is less than 8, and the hydrogen embrittlement resistance is excellent. In addition, the tensile strength is 690 MPa or more, and the cross-sectional reduction rate is also 30% or more. In addition, the relative wear ratio is 0.40 or more.

[0233] (10) Examples 1 to 4 had a smaller number density of coarse alloy carbonitrides than Examples 5 to 7. This is believed to be due to the optimization of hot working conditions and / or solution treatment conditions. (11) In Example 8, the inclusion of W improved the tensile strength compared to Examples 1 to 7. (12) In Example 9, the inclusion of Zr increased the number density of coarse alloy carbonitrides compared to Examples 1 to 8, thereby improving the reduction of area.

[0234]

[0235] Although the embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to the above-mentioned embodiments, and various modifications may be made thereto within the scope not departing from the gist of the present disclosure.

[0236] This application is based on Japanese patent application No. 2022-020161 filed on February 14, 2022 and Japanese patent application No. 2022-171286 filed on October 26, 2022.

[0237] Industrial Applicability

[0238] Austenitic stainless steel according to the present disclosure may be used as a structural component used in a high-pressure hydrogen device.

Claims

1. An austenitic stainless steel, comprising: C≤0.10% by mass, Si≤0.50 mass%, 3.0 mass%≤Mn≤8.0 mass%, P≤0.30 mass%, S≤0.30 mass%, 7.0 mass%≤Ni≤9.9 mass%, 18.0 mass% ≤ Cr ≤ 28.0 mass%, 1.0 mass%≤Mo≤3.0 mass%, 0.03 mass%≤V≤0.50 mass%, 0.0003 mass% ≤ B ≤ 0.0300 mass%, 0.0001 mass%≤Ca≤0.0300 mass%, 0.35 mass%≤N≤0.80 mass%, W≤2.0% by mass, Zr≤0.20 mass%, Cu≤0.5% by mass, Al≤0.10 mass% and O≤0.050% by mass, The balance is iron and unavoidable impurities, and With a number density of 3×10 5 Pieces / mm 2 The following coarse alloy carbonitrides, The austenitic stainless steel has a grain size of 6.8 or less, and The relative wear ratio is above 0.

40. in The "coarse alloy carbonitrides" are alloy carbonitrides with an equivalent circle diameter greater than 1,000 nm. The relative wear amount ratio is defined by W0 / W1, wherein W0 represents the flank wear amount of the cemented carbide tool when a peeling treatment is performed on a rod-shaped specimen having a chemical composition corresponding to SUS316 in the JIS standard using an uncoated cemented carbide tool corresponding to P20 in the cutting process at a cutting speed of 100 m / min, a feed of 0.2 mm / rev, a cutting distance of 1.0 mm, and no lubricating oil; and W1 represents the flank wear amount of the cemented carbide tool when the same peeling treatment is performed on a rod-shaped specimen made of the austenitic stainless steel using the same cemented carbide tool under the same conditions.

2. The austenitic stainless steel according to claim 1, satisfying: 0.3 mass% ≤ W ≤ 2.0 mass%, and / or 0.01 mass%≤Zr≤0.20 mass%.

3. Austenitic stainless steel according to claim 1 or 2, The austenitic stainless steel has a tensile strength of 690 MPa or more measured at 25°C.

4. Austenitic stainless steel according to claim 1 or 2, The austenitic stainless steel has a cross-sectional reduction rate of 30% or more measured at 25°C.

5. A hydrogen-resistant component comprising the austenitic stainless steel according to claim 1 or 2.

6. The hydrogen resistant component according to claim 5, wherein The austenitic stainless steel includes a portion in a solution treated state. 7 . The hydrogen resistant component according to claim 5 , comprising a butt-welded portion, wherein the butt-welded portion has an as-welded tensile strength measured at 25° C. of 690 MPa or more. 8 . The hydrogen resistant component according to claim 6 , comprising a butt-welded portion, wherein the butt-welded portion has an as-welded tensile strength measured at 25° C. of 690 MPa or more.

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