Austenitic stainless steel material

Abstract

To provide an austenitic stainless steel material which exhibits superior tensile strength in a hydrogen environment, and demonstrates superior resistance to hydrogen embrittlement, while reducing the use of high-cost alloy elements.SOLUTION: An austenitic stainless steel material has a predetermined chemical composition, and contains inclusions having a particle diameter of 0.1 to 5.0 μm. The number of inclusions is 75 to 250 pieces / mm2 per unit area. The inclusions have an average aspect ratio of more than 1.0 and less than 3.0. Among these inclusions, those having an Al concentration of 50 wt.% or more are regarded as Al-based inclusions, where the ratio of the number of Al-based inclusions to the total number of inclusions is 0.50 or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an austenitic stainless steel material. [Background technology]

[0002] In recent years, hydrogen has been attracting attention as a new energy source to replace fossil fuels. 2 Hydrogen is a clean energy source that does not emit CO2. However, hydrogen can cause hydrogen embrittlement, which weakens materials. Patent Document 1 discloses an austenitic stainless steel with improved resistance to hydrogen embrittlement. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-196842 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, the austenitic stainless steel disclosed in Patent Document 1 contains many expensive alloy elements to improve hydrogen embrittlement resistance, which increases the alloy cost. Therefore, there is a problem that it is difficult to improve hydrogen embrittlement resistance while reducing the amount of expensive alloy elements in austenitic stainless steel.

[0005] Another problem is that tensile strength is lower in a hydrogen environment than in air. For this reason, there is a demand for austenitic stainless steel materials that have tensile strength equivalent to that in air while reducing the amount of expensive alloying elements.

[0006] In view of the above, an object of the present invention is to solve the above problems and provide an austenitic stainless steel material that has good tensile strength and excellent hydrogen embrittlement resistance in a hydrogen environment while reducing expensive alloy elements. [Means for solving the problem]

[0007] The present invention has been made to solve the above problems, and the gist of the present invention is the following austenitic stainless steel material.

[0008] (1) Chemical composition, in mass%, C: 0.080% or less, Si: 1.00% or less, Mn: 2.00% or less, P: 0.050% or less, S: 0.020% or less, Cr: 17.0-19.5%, Ni: 8.0-10.5%, Al: 0.05-0.40%, N: 0.100% or less, Nb: 0-0.20%, Ti: 0 to 0.20%, Mo: 0-1.0%, Cu: 0-1.0%, Co: 0-0.50%, V: 0~0.50%, W: 0 to 0.50%, B: 0~0.0050%, Ca: 0 to 0.0100%, Mg: 0 to 0.010%, Zr: 0-0.50%, Ga: 0 to 0.050%, Hf: 0~0.10%, La: 0 to 0.10%, Y: 0~0.10%, REM: 0~0.10%, The balance is Fe and impurities. Contains inclusions with particle sizes of 0.1 to 5.0 μm. The number of inclusions per unit area is 75 to 250 pieces / mm 2 and The average aspect ratio of the inclusions is greater than 1.0 and less than 3.0; When the inclusions having an Al concentration of 50 wt% or more are defined as Al-based inclusions, An austenitic stainless steel material, wherein a ratio of the number of the Al-based inclusions to the number of the other inclusions is 0.50 or more.

[0009] (2) the average particle size of the Al-based inclusions is 1.0 to 2.0 μm; The austenitic stainless steel material according to (1) above, wherein the ratio of the number of Al-based inclusions having an N concentration of 5 wt% or more to the number of the Al-based inclusions is less than 0.35.

[0010] (3) The chemical composition is, in mass%, Nb: 0.03 to 0.20%, Ti: 0.01 to 0.20%, Mo: 0.1-1.0%, Cu: 0.1-1.0%, Co: 0.10-0.50%, V: 0.05~0.50%, W: 0.05 to 0.50%, B: 0.0002~0.0050%, Ca: 0.0002~0.0100%, Mg: 0.0002~0.010%, Zr: 0.01 to 0.50%, Ga: 0.001 to 0.050%, Hf: 0.01 to 0.10%, La: 0.01 to 0.10%, Y: 0.01 to 0.10%, and REM: 0.01~0.10%, The austenitic stainless steel material according to the above (1) or (2), comprising one or more selected from the following:

[0011] (4) An austenitic stainless steel material according to any one of (1) to (3) above, which is used in a hydrogen environment.

[0012] (5) The austenitic stainless steel material according to any one of (1) to (3) above, which is used for a component of a hydrogen facility or hydrogen equipment. Effect of the Invention

[0013] According to the present invention, it is possible to obtain an austenitic stainless steel material that has good tensile strength in a hydrogen environment and is excellent in resistance to hydrogen embrittlement while reducing expensive alloying elements. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present inventors have conducted research into austenitic stainless steel materials that have good tensile strength and excellent hydrogen embrittlement resistance in a hydrogen environment while reducing expensive alloying elements, and have obtained the following findings.

[0015] (a) When expensive alloying elements are reduced, the γ (also called "austenite") phase is easily transformed into the α' phase even at room temperature. As a result, hydrogen embrittlement is likely to occur in a hydrogen environment. Furthermore, when tensile stress is applied in a hydrogen environment, hardening occurs at the work hardening stage, and the same tensile strength as in air cannot be secured.

[0016] (b) For this reason, the inventors have found that it is effective to add a certain amount of Al to austenitic stainless steel material and dissolve Al in the steel. Dissolving Al in the steel increases stacking fault energy, suppresses the generation of stacking faults, and suppresses the transformation from the γ phase to the α' phase. As a result, hydrogen embrittlement can be suppressed.

[0017] (c) In addition, inclusions are formed in austenitic stainless steel materials. In particular, it is effective to set the number and average aspect ratio of inclusions having a certain particle size within a specified range, and to reduce inclusions with a high N concentration that contain a certain amount of Al. By controlling the inclusions in this way, the inclusions trap hydrogen, making it possible to maintain the tensile strength in air even in a hydrogen environment.

[0018] An embodiment of the present invention has been made based on the above findings. Each requirement of the austenitic stainless steel material of this embodiment will be described in detail below.

[0019] 1.Chemical composition The reasons for limiting the content of each element are as follows. In the following description, "%" for the content means "mass %."

[0020] C: 0.080% or less C (carbon) is an element effective in stabilizing the austenite phase and has the effect of improving strength. However, if C is contained in excess, toughness decreases. For this reason, the C content is 0.080% or less. The C content is preferably 0.070% or less, and more preferably 0.065% or less. On the other hand, in order to obtain the above effect, the C content is preferably 0.010% or more.

[0021] Si: 1.00% or less Silicon (Si) is an effective element for deoxidization and improves hydrogen embrittlement resistance. However, excessive Si content promotes the formation of intermetallic compounds such as σ phase, reducing toughness. For this reason, the Si content is 1.00% or less. The Si content is preferably 0.90% or less. On the other hand, in order to obtain the above effect, the Si content is preferably 0.10% or more.

[0022] Mn: 2.00% or less Manganese (Mn) is an element effective in stabilizing the austenite phase and improving hydrogen embrittlement resistance, but excessive Mn content increases the alloy cost. For this reason, the Mn content is 2.00% or less. The Mn content is preferably 1.90% or less. On the other hand, in order to obtain the above effects, the Mn content is preferably 0.50% or more.

[0023] P:0.050% or less P (phosphorus) is an impurity element contained in steel, and it reduces mechanical properties. For this reason, the P content is 0.050% or less. It is preferable to reduce the P content as much as possible, but excessive reduction of P increases refining costs. For this reason, the P content is preferably 0.010% or more.

[0024] S: 0.020% or less S (sulfur) is an impurity element contained in steel and reduces mechanical properties. For this reason, the S content is preferably 0.020% or less. It is preferable to reduce the S content as much as possible, but excessive reduction of S increases refining costs. For this reason, the S content is preferably 0.0002% or more.

[0025] Cr: 17.0~19.5% Cr (chromium) is an element necessary for maintaining the corrosion resistance of stainless steel. Cr also has the effect of increasing stacking fault energy and improving tensile strength in a hydrogen environment. For this reason, the Cr content is 17.0% or more. The Cr content is preferably 17.5% or more, and more preferably 18.0% or more. However, if Cr is contained in excess, the N concentration in the Al-based inclusions becomes high. As a result, the tensile strength in a hydrogen environment is likely to decrease. For this reason, the Cr content is 19.5% or less.

[0026] Ni: 8.0~10.5% Ni (nickel) has the effect of increasing stacking fault energy and improving hydrogen embrittlement resistance. It also has the effect of improving strength. For this reason, the Ni content is 8.0% or more. The Ni content is preferably 8.5% or more. However, since Ni is an expensive element, if Ni is contained in excess, the alloy cost increases. For this reason, the Ni content is 10.5% or less. The Ni content is preferably 10.0% or less.

[0027] Al: 0.05 to 0.40% In the austenitic stainless steel material of this embodiment, Al (aluminum) is an important element for increasing stacking fault energy, enhancing hydrogen embrittlement resistance, and obtaining desired inclusions. Therefore, the Al content is 0.05% or more. The Al content is preferably 0.10% or more, and more preferably 0.15% or more. However, if Al is contained excessively, inclusions are formed excessively, and the tensile strength in a hydrogen environment is reduced. Therefore, the Al content is 0.40% or less. The Al content is preferably 0.35% or less, and more preferably 0.30% or less.

[0028] N: 0.100% or less Like Mn and Ni, N (nitrogen) is an element effective in improving hydrogen embrittlement resistance. However, if N is contained in excess, the N concentration in the inclusions becomes high, making it difficult to form the desired inclusions. As a result, the tensile strength in a hydrogen environment decreases. For this reason, the N content is 0.100% or less. The N content is preferably 0.080% or less, and more preferably 0.050% or less. On the other hand, in order to obtain the above effect, the N content is preferably 0.010% or more.

[0029] In addition to the above elements, one or more selected from Nb, Ti, Mo, Cu, Co, V, W, B, Ca, Mg, Zr, Ga, Hf, La, Y and REM may be contained within the ranges shown below. In other words, the lower limit of the above elements is 0%. The reasons for limiting each element will be explained below.

[0030] Nb: 0 to 0.20% Nb (niobium) has the effect of forming fine precipitates and enhancing the function of trapping hydrogen. Therefore, it may be contained as necessary. However, since Nb is an expensive element, if Nb is contained in excess, the alloy cost increases. Furthermore, the formation of excessive precipitates reduces toughness. For this reason, the Nb content is 0.20% or less. The Nb content is preferably 0.18% or less, and more preferably 0.15% or less. On the other hand, in order to obtain the above effect, the Nb content is preferably 0.03% or more.

[0031] Ti: 0 to 0.20% Ti (titanium), like Nb, forms fine precipitates and has the effect of enhancing the hydrogen trapping action. Therefore, it may be contained as necessary. However, since Ti is an expensive element, if Ti is contained in excess, the alloy cost increases. Therefore, the Ti content is 0.20% or less. The Ti content is preferably 0.18% or less, and more preferably 0.15% or less. On the other hand, in order to obtain the above effect, the Ti content is preferably 0.01% or more.

[0032] Mo: 0-1.0% Mo (molybdenum) has the effect of improving strength and corrosion resistance. Therefore, it may be contained as necessary. However, Mo is an expensive element, and if Mo is contained in excess, the alloy cost increases. For this reason, the Mo content is 1.0% or less. The Mo content is preferably 0.5% or less. On the other hand, in order to obtain the above effect, the Mo content is preferably 0.1% or more.

[0033] Cu: 0-1.0% Cu (copper) has the effect of improving strength and corrosion resistance. Therefore, it may be contained as necessary. However, Cu is an expensive element, and if Cu is contained in excess, the alloy cost increases. In addition, the steel becomes excessively hard, and mechanical properties such as toughness decrease. For this reason, the Cu content is 1.0% or less. The Cu content is preferably 0.9% or less, and more preferably 0.6% or less. On the other hand, in order to obtain the above effect, the Cu content is preferably 0.1% or more.

[0034] Co: 0 to 0.50% Co (cobalt) has the effect of improving strength and corrosion resistance. It also has the effect of improving hydrogen embrittlement resistance by stabilizing the γ phase. Therefore, it may be contained as necessary. However, Co is an expensive element, and if it is contained in excess, the alloy cost increases. In addition, the workability and toughness are also reduced. For this reason, the Co content is 0.50% or less. On the other hand, in order to obtain the above effects, the Co content is preferably 0.10% or more.

[0035] V: 0~0.50% V (vanadium) has the effect of improving strength by dissolving in steel or precipitating as carbonitride. Therefore, it may be contained as necessary. However, if V is contained in excess, excessive carbonitrides are formed, which reduces manufacturability during hot rolling. For this reason, the V content is 0.50% or less. The V content is preferably 0.30% or less. On the other hand, in order to obtain the above effect, the V content is preferably 0.05% or more.

[0036] W: 0~0.50% W (tungsten) has the effect of improving strength and corrosion resistance. Therefore, it may be contained as necessary. However, if W is contained in excess, the alloy cost increases. Therefore, the W content is 0.50% or less. The W content is preferably 0.30% or less. On the other hand, in order to obtain the above effect, the W content is preferably 0.05% or more.

[0037] B: 0 to 0.0050% B (boron) has the effect of strengthening grain boundaries and improving strength. Therefore, it may be contained as necessary. However, if B is contained in excess, workability decreases. For this reason, the B content is 0.0050% or less. The B content is preferably 0.0030% or less. On the other hand, in order to obtain the above effect, the B content is preferably 0.0002% or more.

[0038] Ca: 0 to 0.0100% Ca (calcium) has the effect of suppressing the grain boundary segregation of low melting point elements and strengthening the grain boundary. Therefore, it may be contained as necessary. However, if Ca is contained in excess, segregation is likely to occur and toughness is reduced. For this reason, the Ca content is 0.0100% or less. The Ca content is preferably 0.0050% or less. On the other hand, in order to obtain the above effect, the Ca content is preferably 0.0002% or more.

[0039] Magnesium: 0 to 0.010% Mg (magnesium) has the effect of suppressing the grain boundary segregation of low melting point elements and strengthening the grain boundary. Therefore, it may be contained as necessary. However, if Mg is contained in excess, a large amount of inclusions are formed, which tend to become the starting point of fracture, and as a result, the toughness may decrease. For this reason, the Mg content is 0.010% or less. The Mg content is preferably 0.005% or less. On the other hand, in order to obtain the above effect, the Mg content is preferably 0.0002% or more.

[0040] Zr: 0 to 0.50% Zr (zirconium) has a deoxidizing effect. It also has an effect of improving corrosion resistance. Therefore, it may be contained as necessary. However, if Zr is contained in excess, toughness and workability decrease. Therefore, the Zr content is 0.50% or less. The Zr content is preferably 0.30% or less. On the other hand, in order to obtain the above effects, the Zr content is preferably 0.01% or more.

[0041] Ga: 0 to 0.050% Ga (gallium) has the effect of improving hot workability. Therefore, it may be contained as necessary. However, if Ga is contained in excess, it reduces manufacturability. Therefore, the Ga content is 0.050% or less. The Ga content is preferably 0.020% or less. On the other hand, in order to obtain the above effect, the Ga content is preferably 0.001% or more.

[0042] Hf: 0~0.10% Hf has the effect of improving strength and hydrogen embrittlement resistance. Therefore, it may be contained as necessary. However, if Hf is contained in excess, workability decreases. Therefore, the Hf content is 0.10% or less. The Hf content is preferably 0.07% or less. On the other hand, in order to obtain the above effect, the Hf content is preferably 0.01% or more.

[0043] La: 0 to 0.10% Y: 0~0.10% La and Y have the effect of improving hot workability. They also have the effect of improving corrosion resistance. Therefore, they may be contained as necessary. However, if these elements are contained in excess, not only will the effect saturate, but the hot workability will also decrease. For this reason, the La content is 0.10% or less. The La content is preferably 0.07% or less. Similarly, the Y content is 0.10% or less. The Y content is preferably 0.07% or less. On the other hand, in order to obtain the above effects, the La content is preferably 0.01% or more. Similarly, the Y content is preferably 0.01% or more.

[0044] REM: 0~0.10% REM has the effect of improving hot workability. It also has the effect of improving corrosion resistance. Therefore, it may be contained as necessary. However, if REM is contained in excess, not only will the effect saturate, but the hot workability will also decrease. For this reason, the REM content is 0.10% or less. The REM content is preferably 0.07% or less. On the other hand, in order to obtain the above effects, the REM content is preferably 0.01% or more.

[0045] REM refers to a total of 14 lanthanoid elements excluding Y and La, and the above REM content refers to the total content of these elements. In industry, REM is often added in the form of misch metal.

[0046] In the chemical composition of this embodiment, the balance is Fe and impurities. Here, the term "impurities" refers to components that are mixed in due to various factors in raw materials such as ores and scraps and manufacturing processes during industrial production of austenitic stainless steel materials, and are permissible within a range that does not adversely affect this embodiment.

[0047] 2.Inclusions The austenitic stainless steel material of this embodiment contains inclusions with a particle size of 0.1 to 5.0 μm. In the present application, particle sizes of less than 0.1 μm are not included in the inclusions because they are considered to be very small and do not affect the properties. In other words, inclusions with a particle size of 0.1 to 5.0 μm that affect the properties are observed and measured.

[0048] 2-1. Number of inclusions per unit area In addition, the number of inclusions with the above particle diameter per unit area is 75 to 250 pieces / mm 2 The number of the above inclusions per unit area is 75 pieces / mm 2 If the thickness is less than 75 mm, the inclusions are not sufficiently formed, and the Al-based inclusions described below are not sufficiently formed. 2 The number of the above inclusions per unit area is 90 pieces / mm 2It is preferable that the number of pieces is 150 pieces / mm or more. 2 More preferably, it is equal to or greater than this.

[0049] On the other hand, the number of the above inclusions per unit area is 250 pieces / mm 2 If the thickness exceeds 100 mm, the inclusions will be excessive. Therefore, the number of inclusions per unit area is 250 / mm 2 The number of the above inclusions per unit area is 230 / mm 2 It is preferable that the number of pieces is 210 pieces / mm or less. 2 More preferably, it is:

[0050] 2-2. Average aspect ratio of inclusions The average aspect ratio of the inclusions having the above particle size is more than 1.0 and less than 3.0. The aspect ratio of an inclusion is the ratio of thickness to length when the inclusion is equivalent to an ellipse, and is calculated as (length / thickness). In other words, it is calculated as (long side / short side). The average aspect ratio is the average value of the aspect ratios of the observed inclusions.

[0051] It is difficult to form inclusions having an average aspect ratio of 1.0 or less in terms of manufacturing. Therefore, the average aspect ratio is preferably greater than 1.0 and equal to or greater than 1.5. On the other hand, if the average aspect ratio is 3.0 or more, the inclusions are too elongated, making it difficult for the inclusions to function as hydrogen trapping sites. Therefore, the average aspect ratio is preferably less than 3.0 and equal to or less than 2.8.

[0052] 2-3.Al-based inclusions In this embodiment, it is particularly desirable to form many Al-enriched inclusions among the above-mentioned inclusions. This is because Al-enriched inclusions have the effect of maintaining tensile strength even in a hydrogen environment. Therefore, when inclusions having an Al (aluminum) concentration of 50 wt% or more among the above-mentioned inclusions are defined as Al-based inclusions, the number ratio of Al-based inclusions to the number of all inclusions is 0.50 or more.

[0053] If the number ratio of the Al-based inclusions is less than 0.50, a sufficient amount of the Al-based inclusions is not formed, making it difficult to sufficiently improve the tensile strength in a hydrogen environment. Therefore, the number ratio of the Al-based inclusions is 0.50 or more, and preferably 0.60 or more. The upper limit of the number ratio of the Al-based inclusions is not particularly limited, but is usually 0.95 due to constraints on manufacturing conditions, etc.

[0054] The average particle size of the Al-based inclusions is preferably in the range of 1.0 to 2.0 μm. This is because when the average particle size of the Al-based inclusions is in the range of 1.0 to 2.0 μm, fine Al-based inclusions are formed in large numbers, and are more likely to function as hydrogen trapping sites.

[0055] Moreover, the Al-based inclusions preferably have a low N (nitrogen) concentration. When the N concentration is high, the inclusions are often precipitated as AlN, and tend to become the starting point of fracture. As a result, the tensile strength in a hydrogen environment tends to decrease. For this reason, the ratio of the number of Al-based inclusions having an N concentration of 5 wt% or more to the total number of Al-based inclusions is preferably less than 0.35. The ratio of the number of Al-based inclusions having an N concentration of 5 wt% or more is preferably 0.30 or less, and more preferably 0.25 or less. The lower limit of the ratio of the number of Al-based inclusions having an N concentration of 5 wt% or more is not particularly limited, but is usually 0.05 due to constraints such as chemical composition and manufacturing conditions.

[0056] 2-4.Measuring method for inclusions The observation and measurement of inclusions in item 2 above may be performed according to the following procedure. Preparation of samples for observing and measuring inclusions may be performed in accordance with JIS G 0555:2020. An automatic inclusion analyzer (Metal Quality Analyzer) is used for the measurement. Specifically, it is recommended to use Explorer4 MQA (manufactured by Thermo Fisher Scientific) with a measurement field of view of 225 mm. 2The measurement field of view is a mirror-polished area of ​​15 mm x 15 mm.

[0057] Then, using an automatic inclusion analyzer, inclusions of 0.1 to 5.0 μm in the measurement field of view are extracted, and the number per unit area and the average aspect ratio are calculated. Among the extracted inclusions, inclusions with an Al concentration of 50 wt% or more are also extracted and recognized as Al-based inclusions, and the number ratio of inclusions recognized as Al-based inclusions and their average particle diameter are also calculated. Similarly, among the Al-based inclusions, the number of inclusions with an N concentration of 5 wt% or more is also extracted, and the number ratio of the inclusions is calculated. The elements measured when measuring inclusions are C, N, O, Mg, Al, Si, P, S, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Nb, and Mo.

[0058] 3.Applications The austenitic stainless steel material of this embodiment is suitable for use in a hydrogen environment, and is particularly suitable for use in a hydrogen gas environment. It is also suitable for use as a component of hydrogen facilities or equipment. Examples of hydrogen facilities and equipment include hydrogen gas production facilities, hydrogen gas supply facilities, other hydrogen gas utilization facilities, hydrogen gas storage tanks, and hydrogen gas lorries and trailers.

[0059] The shape of the austenitic stainless steel material is not particularly limited, but examples thereof include steel plates, steel pipes, and wire rods.

[0060] 4. Manufacturing method The austenitic stainless steel material of this embodiment can be stably produced, for example, by the following production method.

[0061] 4-1.Casting Molten steel having the above chemical composition is cast by continuous casting to produce a slab. In this case, it is preferable to cast by vertical continuous casting. This is because the casting speed can be increased by vertical continuous casting. This makes it easier to control inclusions in the process described below. The slab is preferably forced air-cooled, and the cooling rate is preferably more than 0.01°C / s.

[0062] 4-2.Hot rolling The resulting slab is hot rolled. Here, the heating temperature of the slab during hot rolling is 1150°C or lower. Generally, the heating temperature of an austenitic stainless steel slab is often higher than 1150°C, but in the production of the austenitic stainless steel material of this embodiment, a relatively low heating temperature is used, which makes it easier to form fine inclusions and makes it easier for the average aspect ratio of the inclusions to be greater than 1.0 and less than 3.0. In addition, the number of inclusions per unit area increases, making it easier for Al-based inclusions to be formed. The heating temperature of the slab is It is preferable that the temperature is 1130° C. or lower.

[0063] After the hot rolling, coiling is performed. The coiling temperature is 950°C or less. This is to form a certain amount of Al-based inclusions. The coiling temperature is preferably 500°C or less. By setting the coiling temperature to 500°C or less, the Al-based inclusions become finer and N is less likely to concentrate. This further improves the tensile strength in a hydrogen environment. A hot-rolled sheet is manufactured through such a hot rolling process. Other conditions in the hot rolling are not particularly limited. Conventional methods may be followed as appropriate.

[0064] 4-3.Hot-rolled sheet annealing It is preferable to anneal the obtained hot-rolled sheet. This annealing is called hot-rolled sheet annealing. The annealing temperature during hot-rolled sheet annealing is not particularly limited, but is usually in the range of 1000 to 1150°C. The annealing time during hot-rolled sheet annealing is also not particularly limited, but is usually in the range of 0.5 to 5 minutes. In addition, after hot-rolled sheet annealing, pickling may be performed as necessary.

[0065] 4-4.Cold rolling It is preferable to cold-roll the hot-rolled sheet to produce a cold-rolled sheet. The conditions for cold rolling are not particularly limited. Cold rolling may be performed to obtain a desired sheet thickness. Intermediate annealing and pickling may be performed during cold rolling. The annealing temperature for intermediate annealing is not particularly limited, but is generally in the range of 1000 to 1150°C. The annealing time is also not particularly limited, but is generally in the range of 0.1 to 3 minutes.

[0066] 4-5. Finish annealing After the cold rolling, final annealing may be performed. The annealing temperature and time of the final annealing are not particularly limited, but the annealing is generally performed at 1000 to 1150°C for 0.1 to 2 minutes. After the final annealing, the product is cooled and, if necessary, pickled to obtain an austenitic stainless steel material.

[0067] EXAMPLES Hereinafter, the austenitic stainless steel material according to the present invention will be described more specifically with reference to examples, but the present embodiment is not limited to these examples. EXAMPLES

[0068] Steel having the chemical composition shown in Table 1 was melted, and a slab was produced by vertical continuous casting. The obtained slab was hot-rolled and coiled under the conditions shown in Table 2 to produce a hot-rolled sheet having a thickness of 5.0 mm. The obtained hot-rolled sheet was annealed at an annealing temperature of 1100 ° C. and an annealing time of 1 minute, cooled, and then pickled. After pickling, it was cold-rolled to a thickness of 3.0 mm. Then, intermediate annealing was performed at an annealing temperature of 1080 ° C. and an annealing time of 1 minute, followed by pickling and cold rolling again to produce a cold-rolled sheet having a thickness of 1.2 mm. The obtained cold-rolled sheet was finish-annealed at an annealing temperature of 1050 ° C. and an annealing time of 0.5 minutes, cooled, and pickled to obtain an austenitic stainless steel sheet.

[0069] [Table 1]

[0070] The obtained steel sheets were measured for the number of inclusions, the characteristic values ​​in a hydrogen environment, etc., by the following procedures.

[0071] (Values ​​of each inclusion) The preparation of samples for observing and measuring inclusions was performed in accordance with JIS G 0555:2020. An automatic inclusion analyzer (Metal Quality Analyzer) was used for the measurements. Specifically, Explorer4 MQA (manufactured by Thermo Fisher Scientific) was used with a measurement field of view of 225 mm. 2 The measurement field of view was a mirror-polished area of ​​15 mm x 15 mm.

[0072] Then, using an automatic inclusion analyzer, inclusions of 0.1 to 5.0 μm in the measurement field were extracted, and the number per unit area and the average aspect ratio were calculated. Among the extracted inclusions, inclusions with an Al concentration of 50 wt% or more were also extracted and recognized as Al-based inclusions, and the number ratio of inclusions recognized as Al-based inclusions and their average particle diameter were also calculated. Similarly, among the Al-based inclusions, the number of inclusions with an N concentration of 5 wt% or more was also extracted, and the number ratio was calculated. The elements measured when measuring inclusions were C, N, O, Mg, Al, Si, P, S, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Nb, and Mo.

[0073] (Characteristic values ​​in a hydrogen environment) A slow strain rate tensile test (also called "SSRT test") was performed. The strain rate was 3×10 -5 / s at 25°C and 20 MPa H 2 Tests were conducted in air and in the atmosphere. 2 The tensile strength in air is called the relative tensile strength RTS, and the H 2 The relative elongation (REL) was calculated using the following formula: Relative tensile strength RTS=H 2 TS in the air / TS in the atmosphere Relative elongation REL=H 2 EL in / EL in air In addition, TS represents tensile strength and EL represents elongation.

[0074] When the RTS was over 0.95 and the REL was 0.95 or more, the characteristics were evaluated as very good and were recorded as ◎. When the RTS was over 0.95 and the REL was less than 0.95, the characteristics were evaluated as good and were recorded as ◯. When the RTS was 0.95 or less, the characteristics were evaluated as poor and were recorded as ×. The results are summarized in Table 2 below.

[0075] [Table 2]

[0076] Nos. 1, 2, 4, 5, 7, 9, 10, 12, and 13, which satisfy the requirements for the austenitic stainless steel material of this embodiment, exhibited good properties, whereas Nos. 3, 6, 8, 11, and 14 to 18, which do not satisfy the requirements for the austenitic stainless steel material of this embodiment, exhibited poor properties.

Claims

1. The chemical composition, in mass%, is C: 0.080% or less, Si: 1.00% or less, Mn: 2.00% or less, P: 0.050% or less, S: 0.020% or less, Cr: 17.0-19.5%, Ni: 8.0 to 10.5%, Al: 0.05-0.40%, N: 0.100% or less, Nb: 0 to 0.20%, Ti: 0 to 0.20%, Mo: 0-1.0%, Cu: 0 to 1.0%, Co: 0 to 0.50%, V: 0-0.50%, W: 0-0.50%, B: 0 to 0.0050%, Ca: 0-0.0100%, Mg: 0 to 0.010%, Zr: 0 to 0.50%, Ga: 0 to 0.050%, Hf: 0-0.10%, La: 0 to 0.10%, Y: 0 to 0.10%, REM: 0-0.10%, The balance is Fe and impurities. Contains inclusions with a particle size of 0.1 to 5.0 μm, The number of inclusions per unit area is 75 to 250 pieces / mm ２ and The average aspect ratio of the inclusions is greater than 1.0 and less than 3.0; When the inclusions having an Al concentration of 50 wt% or more are defined as Al-based inclusions, An austenitic stainless steel material, wherein a ratio of the number of the Al-based inclusions to the number of the inclusions is 0.50 or more.

2. The average particle size of the Al-based inclusions is 1.0 to 2.0 μm, 2. The austenitic stainless steel material according to claim 1, wherein a ratio of the number of Al-based inclusions having an N concentration of 5 wt % or more to the number of the Al-based inclusions is less than 0.

35.

3. The chemical composition, in mass%, Nb: 0.03 to 0.20%, Ti: 0.01-0.20%, Mo: 0.1-1.0%, Cu: 0.1 to 1.0%, Co: 0.10-0.50%, V: 0.05-0.50%, W: 0.05-0.50%, B: 0.0002 to 0.0050%, Ca: 0.0002-0.0100%, Mg: 0.0002 to 0.010%, Zr: 0.01 to 0.50%, Ga: 0.001-0.050%, Hf: 0.01-0.10%, La: 0.01 to 0.10%, Y: 0.01 to 0.10%, and REM: 0.01-0.10%, The austenitic stainless steel material according to claim 1, comprising one or more selected from the following:

4. The chemical composition, in mass%, Nb: 0.03 to 0.20%, Ti: 0.01-0.20%, Mo: 0.1-1.0%, Cu: 0.1 to 1.0%, Co: 0.10-0.50%, V: 0.05-0.50%, W: 0.05-0.50%, B: 0.0002 to 0.0050%, Ca: 0.0002-0.0100%, Mg: 0.0002 to 0.010%, Zr: 0.01 to 0.50%, Ga: 0.001-0.050%, Hf: 0.01-0.10%, La: 0.01 to 0.10%, Y: 0.01 to 0.10%, and REM: 0.01-0.10%, The austenitic stainless steel material according to claim 2, comprising one or more selected from the following:

5. The austenitic stainless steel material according to any one of claims 1 to 4, which is used in a hydrogen environment.

6. The austenitic stainless steel material according to any one of claims 1 to 4, which is used as a component of hydrogen equipment or machinery.

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