Precipitation-strengthened austenitic stainless steel, method for producing same, and member for hydrogen environment

Abstract

Provided are: a precipitation-strengthened austenitic stainless steel in which the anisotropy of elongation and shrinkage in the material is reduced and the hydrogen brittleness resistance is expected to be improved; and a method for producing the precipitation-strengthened austenitic stainless steel. A precipitation-strengthened austenitic stainless steel characterized by comprising, in mass%, 0.08% or less of C, 1.00% or less of Si, 2.00% or less of Mn, 0.040% or less of P, 0.030% or less of S, 24.00-27.00% of Ni, 13.50-16.00% of Cr, 1.00-1.50% of Mo, 1.90-2.35% of Ti, 0.35% or less of Al, 0.10-0.50% of V, and 0.001-0.010% of B, the remainder being Fe and unavoidable impurities, and the Ti segregation ratio in the material being 1.25 or less, a method for producing the same, and a member for hydrogen environments.

Description

Technical Field

[0001] This invention relates to precipitation-strengthened austenitic stainless steel, its manufacturing method, and components for hydrogen environments. Background Technology

[0002] Against the backdrop of recent environmental issues, efforts have been made worldwide toward achieving a decarbonized society. Among these efforts, the practical application of fuel cell vehicles that efficiently utilize hydrogen without emitting carbon dioxide, and hydrogen stations as their infrastructure, has attracted significant attention.

[0003] To make fuel cell vehicles and hydrogen stations practical, containers, piping, and metering instruments for storing hydrogen are needed, requiring high-strength metallic materials with resistance to hydrogen embrittlement. The metallic materials eligible for these applications are regulated by the High Pressure Gas Safety Law. Based on general high pressure gas safety regulations, materials such as SUS316, SUS316L, SCM435, SUH660, and XM-19 are selected. These materials were selected by comparing their mechanical properties in the atmosphere with those in hydrogen and evaluating their performance. The evaluation results confirmed their excellent resistance to hydrogen embrittlement.

[0004] For components requiring exceptional strength in hydrogen environments, SUH660, the strongest of these metallic materials, is used. SUH660 is a precipitation-strengthened austenitic steel as defined in the Japanese Industrial Standard (JIS). This material achieves high strength by incorporating the γ′ phase into the matrix through solution treatment and aging. While originally developed as a heat-resistant alloy steel, it is known to exhibit excellent resistance to hydrogen embrittlement in a temperature range of -253°C to 120°C and a hydrogen pressure of 82 MPa or less. Furthermore, existing technical literature has proposed inventions to further improve the mechanical properties of SUH660-equivalent steels and alloy steels with similar compositions.

[0005] For example, the applicant proposed a manufacturing method in Patent Document 1 for hot forging raw materials for precipitation-strengthened austenitic alloys in such a way that the total forging ratio is 30 or more. According to the present invention, mechanical properties can be improved, and the service life of components under high-pressure hydrogen environments can be expected.

[0006] In Patent Document 2, dislocations are introduced into the Fe-Ni based alloy through cold working, thereby increasing the tensile strength to over 1000 MPa and limiting the upper limit of the tensile strength to 1300 MPa, thus achieving both high strength and resistance to hydrogen embrittlement.

[0007] In Patent Document 3, austenitic stainless steel contains Ti, with a grain size of 8 or higher, and the η phase precipitated at the grain boundaries is controlled to achieve high strength, stably obtaining a tensile strength of 1150 MPa or higher without hydrogen embrittlement.

[0008] In Patent Document 4, rare earth elements are added to stainless steel to achieve a balance between hot workability, tensile strength, and resistance to hydrogen embrittlement.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: International Publication No. 2023 / 145423

[0012] Patent Document 2: Japanese Patent Application Publication No. 2011-68919

[0013] Patent Document 3: Japanese Patent Application Publication No. 2014-47409

[0014] Patent Document 4: Japanese Patent Application Publication No. 2018-95929 Summary of the Invention

[0015] The problem the invention aims to solve

[0016] The aforementioned prior art documents all focus on SUH660 equivalent steel and similar precipitation-strengthened austenitic stainless steels, aiming to improve their mechanical properties as one of the effects of the invention. Furthermore, these inventions evaluate mechanical properties by taking tensile test pieces from specific locations on the raw material and conducting tensile tests. Additionally, the evaluation results are expressed as representative values ​​for the material. Therefore, it is desirable that the representative value of this mechanical property does not significantly depend on the sampling location and direction of the test piece from the raw material. Moreover, when evaluating the mechanical properties of an alloy by tensile testing, the length of the tensile test piece is usually considered, and test pieces are mostly taken along the length of the raw material. That is, this aligns with the forging direction during the hot forging process of manufacturing the raw material, and the mechanical properties along the forging direction are tended to be used as representative values ​​for the material.

[0017] However, in order to confirm the anisotropy of the mechanical properties in the raw materials, the inventors collected tensile test pieces from the same raw materials in both the compression and forging directions, and compared and evaluated the mechanical properties of the two materials in ambient air at room temperature. The results showed that even raw materials for which anisotropy was not confirmed in the 0.2% yield strength and tensile strength tests exhibited anisotropy in elongation and shrinkage.

[0018] When anisotropy is confirmed in elongation and contraction under ambient temperature and atmospheric pressure, a relatively large safety factor relative to the representative value of mechanical properties is required, which may pose significant obstacles to the design of products using this material. Furthermore, as mentioned above, resistance to hydrogen embrittlement is evaluated by comparing the mechanical properties in the atmosphere with those in hydrogen. Therefore, if anisotropy is confirmed in the elongation and contraction of the raw material, it means that anisotropy also exists in resistance to hydrogen embrittlement. This could become a major problem when the material is used in hydrogen environments. The aforementioned issues related to anisotropy in elongation / contraction are not recognized in existing technical literature, leaving room for further research. Therefore, the object of the present invention is to provide a precipitation-strengthened austenitic stainless steel with low anisotropy in elongation and contraction and the potential for improved resistance to hydrogen embrittlement.

[0019] Solution for solving the problem

[0020] To address the anisotropy of elongation and shrinkage in SUH660 material, the inventors conducted detailed observations and analyses of the material's microstructure, investigating the causes of this anisotropy. The results revealed the presence of striation-like segregation in the microstructure of the hot-forged steel sheet (billet) after solution treatment and aging. Further investigation revealed that reducing this striation-like segregation significantly improves the anisotropy of elongation and shrinkage, and an effective manufacturing method for reducing striation-like segregation was also discovered, thus completing this invention.

[0021] That is, one aspect of the present invention is a precipitation-strengthened austenitic stainless steel, characterized in that, by mass%, C is less than 0.08%, Si is less than 1.00%, Mn is less than 2.00%, P is less than 0.040%, S is less than 0.030%, Ni is 24.00~27.00%, Cr is 13.50~16.00%, Mo is 1.00~1.50%, Ti is 1.90~2.35%, Al is less than 0.35%, V is 0.10~0.50%, B is 0.001~0.010%, and the balance consists of Fe and unavoidable impurities, wherein the Ti segregation ratio in the steel is less than 1.25.

[0022] Another aspect of the present invention is a method for manufacturing precipitation-strengthened austenitic stainless steel, which is the same as the above-mentioned method for manufacturing precipitation-strengthened austenitic stainless steel. The manufacturing method includes the following steps: a first homogenization heat treatment step, in which a prepared steel ingot is subjected to homogenization heat treatment at a heating temperature of 980~1270°C to obtain raw material for hot forging; a hot forging step, in which the raw material for hot forging is hot forged to obtain steel sheet; and a solution / aging treatment step, in which the steel sheet is subjected to solution treatment and aging treatment, wherein the heat treatment time of the first homogenization heat treatment is 25~150 hours.

[0023] Preferably, the process includes a second homogenization heat treatment step, in which at least one of the steel sheet and the intermediate material during hot forging is subjected to homogenization heat treatment at a heating temperature of 980~1270°C, and the total heat treatment time of the first homogenization heat treatment and the second homogenization heat treatment is 25~150 hours.

[0024] Another aspect of the present invention is a component for a hydrogen environment, which uses the aforementioned precipitation-strengthened austenitic stainless steel.

[0025] The effects of the invention

[0026] According to the present invention, it is possible to provide precipitation-strengthened austenitic stainless steels with low anisotropy in elongation and contraction and improved resistance to hydrogen embrittlement. Attached Figure Description

[0027] Figure 1 This is a schematic diagram showing the sampling location and direction of the tensile test specimen collected from the steel sheet.

[0028] Figure 2 This is a graph showing the relationship between the total homogenization heat treatment time and the Ti segregation ratio.

[0029] Figure 3 This is a graph showing the relationship between the Ti segregation ratio and the elongation anisotropy ratio.

[0030] Figure 4 This is a graph showing the relationship between the Ti segregation ratio and the shrinkage anisotropy ratio. Detailed Implementation

[0031] The following is a detailed description of the methods for implementing the present invention. First, the precipitation-strengthened austenitic steel of the present invention will be described. The precipitation-strengthened austenitic steel of the present invention refers to an alloy equivalent to SUH660 in JIS (Japanese Industrial Standard) G-4311 with the following composition: by mass%, C is 0.08% or less, Si is 1.00% or less, Mn is 2.00% or less, P is 0.040% or less, S is 0.030% or less, Ni is 24.00 to 27.00%, Cr is 13.50 to 16.00%, Mo is 1.00 to 1.50%, Ti is 1.90 to 2.35%, Al is 0.35% or less, V is 0.10 to 0.50%, B is 0.001 to 0.010%, and the balance consists of Fe and unavoidable impurities. Unless otherwise specified, the precipitation-strengthened austenitic stainless steel of this embodiment refers to an alloy equivalent to the above-described SUH660.

[0032] The main characteristic of the precipitation-strengthened austenitic steel of the present invention is that the Ti segregation ratio in the material is 1.25 or less. The significance of limiting the Ti segregation ratio will be explained. According to the analysis of the present inventors, stripe-like segregation sometimes exists in the metal structure of steel sheets (semi-finished products obtained by blanking steel ingots, also referred to as steel billets) of precipitation-strengthened austenitic steel after solution treatment and aging. Generally, it is known that stripe-like segregation is formed when the solidified structure (dendritic structure) in the steel ingot (cast ingot) is compressed during hot forging. Because the dendritic structure has micro-segregation, it is stretched in the forging direction during hot working, forming a stripe-like segregation layer.

[0033] When this stripe-like segregation forms in precipitation-strengthened austenitic steel, the distribution of Ni, Ti, Al, etc., forming the γ′ phase becomes non-uniform. After aging treatment, it becomes impossible to make the γ′ phase distribute isotropically, resulting in anisotropy in mechanical properties in both the compression and forging directions. Especially in the compression direction, the depth of the γ′ distribution is continuously generated due to the stripe-like segregation layer, which may be a cause of deterioration in mechanical properties. In terms of anisotropy in mechanical properties at 0.2% yield strength and tensile strength, the influence of grain size is greater than that of the γ′ phase distribution at room temperature. Therefore, if the grains are isotropic, they tend to be almost unaffected by the stripe-like segregation. On the other hand, elongation and shrinkage are significantly affected by the distribution of the γ′ phase, thus the anisotropy is considered to be significant. Therefore, by reducing the aforementioned stripe-like segregation, it is expected to reduce the anisotropy of elongation and shrinkage in precipitation-strengthened austenitic steel.

[0034] The aforementioned stripe-like segregation is formed during the forging of dendritic structures and their compression deformation, thus the thickness of one layer of the stripe becomes smaller than that of the dendritic structure. For example, the secondary dendrite arm spacing, which is a representative size of the dendritic structure, is tens to hundreds of μm, and it is assumed that the stripe-like segregation formed by compression has a concentration depth of at least a few μm intervals. Therefore, in this invention, EPMA (electron probe microanalysis) is used to evaluate the local concentration distribution in the material. Furthermore, the element being analyzed is a γ′ phase-forming element and a major constituent element of precipitation-strengthened austenitic steel. Additionally, Ti is chosen because it has a small equilibrium distribution coefficient and is prone to segregation. After multi-point analysis of the local concentration of Ti using EPMA, the Ti segregation ratio is calculated from the ratio of the maximum concentration to the minimum concentration (maximum concentration / minimum concentration). In this invention, the degree of stripe-like segregation in the material can be quantitatively evaluated using this Ti segregation ratio.

[0035] In this embodiment, when determining the local component concentration using EPMA, the probe diameter of the EPMA is determined based on the distance interval between the depths of the streak segregation concentration. To avoid compositional variations caused by products other than γ′ phase solidification segregation, a probe diameter in the range of 0.5 to 1.0 μm is preferred. Furthermore, to improve the accuracy of the analytical results, it is preferable to obtain more than 100 data points from the target material. Then, the maximum and minimum values ​​of Ti concentration after removing outliers from the analytical results are calculated, and their ratio is derived as the segregation ratio. Here, outliers refer to data points where the EPMA analytical probe contacts Ti carbides and Ti nitrides such as TiC and TiN present within the grains and grain boundaries, rather than contacting the matrix in the metallic structure of the material, resulting in an abnormally high Ti concentration.

[0036] The main characteristic of the precipitation-strengthened austenitic stainless steel of the present invention is that the Ti segregation ratio is 1.25 or less. When the Ti segregation ratio is 1.25 or less, the striation-like segregation in the material is sufficiently neutralized, and consequently, the anisotropy of elongation and shrinkage, indicators of ductility, can be sufficiently reduced. In the case of the precipitation-strengthened austenitic stainless steel of this embodiment, which includes hot forging in the manufacturing process, the anisotropy of mechanical properties is evaluated as the ratio of the forging direction characteristic to the compression direction characteristic. That is, the elongation anisotropy is evaluated using the elongation anisotropy ratio obtained by elongation in the forging direction / elongation in the compression direction, and the shrinkage anisotropy is evaluated using the shrinkage anisotropy ratio obtained by shrinkage in the forging direction / shrinkage in the compression direction. The elongation anisotropy ratio and shrinkage anisotropy ratio of the precipitation-strengthened austenitic stainless steel of this embodiment are both 1.60 or less, indicating that anisotropy is sufficiently reduced. The preferred upper limit for the elongation anisotropy ratio is 1.50, and a more preferred upper limit is 1.45. Additionally, the preferred upper limit for the shrinkage anisotropy ratio is 1.58.

[0037] Next, the manufacturing method for obtaining the precipitation-strengthened austenitic stainless steel of the present invention will be described.

[0038] First, steel ingots (cast ingots) are prepared by melting to serve as raw materials for hot forging. In this embodiment, vacuum melting is preferably used for the casting. In addition, in order to prevent the occurrence of macrosegregation that is difficult to neutralize in subsequent processes, it is preferable to use the melted ingot as a consumable electrode for remelting and remelt it using electroslag remelting or vacuum arc remelting.

[0039] In this embodiment, a first homogenization heat treatment is performed on the prepared ingot. This is to minimize microsegregation, which contributes to banded segregation, and to homogenize the component concentration distribution within the material. Performing the homogenization heat treatment during the ingot casting stage also helps prevent cracking during subsequent hot forging. The homogenization heat treatment temperature is set in a range below the solidus temperature and above the solution temperature. It is set below the solidus temperature because, at temperatures above that, localized melting may occur in the material. On the other hand, it is set above the solution temperature to ensure that precipitates formed during cooling after solidification are completely dissolved in the matrix. To fully obtain the effects of the present invention, the Ti segregation ratio needs to be 1.25 or less; therefore, a homogenization heat treatment temperature of 980°C to 1270°C is preferred, and more preferably 1100°C to 1200°C is preferred. Regarding the heat treatment time, the total heat treatment time (hereinafter also referred to as the total homogenization heat treatment time) is important for obtaining the effects of the present invention, including the second homogenization heat treatment time performed in the billet stage described later. The total homogenization heat treatment time is preferably 25 hours or more, more preferably 30 hours or more. The longer the total homogenization heat treatment time, the more saturated the effect of reducing striation segregation becomes. Furthermore, prolonged heat treatment deteriorates manufacturability; therefore, the total homogenization heat treatment time is preferably 150 hours or less, more preferably 100 hours or less. Here, the total homogenization heat treatment time is expressed by the following formula.

[0040] Total homogenization heat treatment time = Homogenization heat treatment time in ingot stage + Homogenization heat treatment time in billet stage

[0041] It should be noted that if the Ti segregation ratio can be reduced to below 1.25 through homogenization heat treatment alone at the ingot casting stage, the formation of striation segregation will be slight even when the metal structure is compressed during subsequent hot forging, thus fully achieving the effects of the present invention. Therefore, in this case, it is not necessarily necessary to perform homogenization heat treatment at the billet stage.

[0042] In this embodiment, the raw material for hot forging after the first homogenization heat treatment is hot-forged to produce a steel billet with a specified cross-sectional size. At this time, it is preferable to perform a second homogenization heat treatment as needed. This second homogenization heat treatment homogenizes the intermediate material during the hot forging process and the steel billet obtained after hot forging. Performing the second homogenization heat treatment allows for the compression deformation of the dendritic solidification structure of the ingot, shortening the diffusion distance of segregated solute elements. Therefore, even in large ingots with coarse dendritic structures such as those in the axial portion, a high homogenization effect can be obtained. The preferred homogenization heat treatment temperature for the steel billet stage is 980°C to 1270°C, more preferably 1100°C to 1200°C. Regarding the second homogenization heat treatment time, the required time can be set using the total homogenization heat treatment time described above. Whether the second homogenization heat treatment is performed during or after the hot forging process can be determined by considering the grain size required for the final raw material product. In cases where there are no subsequent raw material compression processes such as die forging or cold forging after hot forging, it is necessary to increase the grain size beforehand to impart strength. Therefore, it is preferable to perform a second homogenization heat treatment midway through hot forging. It should be noted that even with the second homogenization heat treatment, cracks may still occur during hot forging due to segregation if the first homogenization heat treatment applied to the ingot is not performed. Therefore, the first homogenization heat treatment must be performed in the manufacturing method of the present invention.

[0043] In this embodiment, solution treatment and aging treatment are performed on the steel billet to fully improve the strength of the material. Solution treatment is performed to temporarily dissolve precipitates formed during solidification cooling and hot forging cooling into the matrix. The subsequent aging treatment is performed to integrate and precipitate the γ′ phase in the matrix, thereby fully improving the strength of the material. A preferred heat treatment temperature for solution treatment is 850°C to 1050°C, more preferably 900°C to 1000°C. A preferred heat treatment temperature for aging treatment is 650°C to 800°C, more preferably 700°C to 760°C.

[0044] Components for hydrogen environments made using the precipitation-strengthened austenitic stainless steel of the present invention can be expected to exhibit excellent mechanical properties. Here, "for hydrogen environments" can be applied to components exposed to high-pressure hydrogen in fuel cell vehicles and hydrogen stations. Examples of such components include piping, tanks, valves, and distributor components.

[0045] Example

[0046] (Example 1)

[0047] Four ingots (raw materials No. 1 to 4), each weighing approximately 10 kg, with the chemical composition shown in Table 1, were melted in a vacuum melting furnace. This chemical composition falls within the range of SUH660 as specified in JIS. Next, for these ingots, a first homogenization heat treatment was performed, varying the heat treatment time between 1140°C and 1200°C, to reduce microsegregation. The heat treatment times were set as follows: 5 hours for raw material No. 1, 35 hours for raw material No. 2, 45 hours for raw material No. 3, and 20 hours for raw material No. 4.

[0048] [Table 1]

[0049]

[0050] Following the first homogenization heat treatment, the ingot raw materials No. 1 to 4 were hot-forged at temperatures above 1000°C to produce four rod-shaped steel billets, each approximately 30 mm in diameter and 1000 mm in length. Of these billets, only the billet made from the ingot of raw material No. 4 was transversely cut to obtain a total of seven steel billet raw materials. Furthermore, for six of these billets, a homogenization heat treatment was performed at 1100°C to 1200°C for 10 to 60 hours to reduce striation segregation. As a result, the total homogenization heat treatment time for the material undergoing homogenization heat treatment at the billet stage was 30 to 80 hours.

[0051] Next, all steel billets obtained from raw material ingots No. 1 to 4 were subjected to solution treatment and aging treatment to dissolve unwanted precipitates and precipitate the γ′ phase. The solution treatment was performed at a heat treatment temperature of 980°C for 1 hour, cooled by oil cooling. The aging treatment was performed at a heat treatment temperature of 718°C for 16 hours, cooled by air cooling.

[0052] From steel billets that have undergone solution treatment and aging, such as Figure 1Tensile test specimens were collected in both the compression and forging directions. The compression direction specimen was collected from the center point of the specimen, coinciding with the center point of the billet's cross-section. The forging direction specimen was collected from the D / 4 mark (D is the diameter) of the billet's cross-section, coinciding with the center point of the specimen's cross-section. The tensile test specimens were made with the same dimensions in both the compression and forging directions, and were machined into round bars with a parallel section diameter of 2.5 mm and a distance of 10 mm between measurement marks. The tensile test environment was set to ambient temperature, and the test conditions were selected according to ASTM E8 / E8M. Under these conditions, tensile tests were performed in both the compression and forging directions on a single billet. The elongation anisotropy ratio and shrinkage anisotropy ratio were then derived from the tensile test results. In this embodiment, the allowable levels for both the elongation and shrinkage anisotropy ratios were set to 1.50 or lower.

[0053] Next, to determine the Ti segregation ratio in the material, samples for EPMA analysis were collected from the solution-treated and aged steel billet raw material. The analytical surfaces were mirror-polished, and quantitative analysis of Ti concentration was performed using EPMA. The EPMA analysis conditions were set as follows: accelerating voltage of 15 kV, irradiation current of 100 nA, analysis time per point of 1 s, probe diameter of 1 μm, 100 analytical points in a square grid, and an analytical area of ​​1 mm × 1 mm. The segregation ratio was calculated as the ratio of the maximum to the minimum Ti concentration. However, when the analytical point came into contact with Ti carbides and Ti nitrides that crystallized during solidification and remained in the steel billet, extremely high Ti concentrations were obtained. Therefore, data showing Ti concentrations more than 0.24% higher than the Ti composition of the raw material shown in Table 1 were considered outliers and excluded from the data set for which the segregation ratio was determined. The results are presented in Table 2.

[0054] [Table 2]

[0055]

[0056] Samples No. 1 and No. 2 were comparative examples where homogenization heat treatment was performed for 5 or 20 hours during the ingot casting stage, but the total heat treatment time was less than 25 hours. As shown in Table 2, insufficient homogenization was confirmed, with the Ti segregation ratio exceeding 1.25, and both the elongation anisotropy ratio and shrinkage anisotropy ratio failing to meet the targets. In contrast, samples No. 4 and No. 6 also underwent homogenization heat treatment during the ingot casting stage, with a total homogenization heat treatment time of more than 25 hours, achieving sufficient homogenization, and the Ti segregation ratio was below 1.25. Therefore, both the elongation anisotropy ratio and shrinkage anisotropy ratio showed low values, below the allowable level of anisotropy of 1.60, achieving the target values. Therefore, the effects of the present invention were fully obtained.

[0057] Furthermore, samples No. 3, No. 5, and Nos. 7 through 10 underwent homogenization heat treatment in both the ingot casting and billet stages, with a total homogenization heat treatment time of over 25 hours, achieving sufficient homogenization and resulting in Ti segregation ratios below 1.25. Consequently, both elongation and shrinkage anisotropy ratios exhibited low values, below the permissible anisotropy level of 1.60, achieving the target values. Therefore, the effects of the present invention can be fully confirmed.

[0058] Figure 2 The figure shows the relationship between the total homogenization heat treatment time and the Ti segregation ratio. Figure 2 It can be confirmed that the longer the total homogenization heat treatment time, the lower the Ti segregation ratio tends to be. In addition, by approximating the relationship between the total homogenization heat treatment time and the Ti segregation ratio with a quadratic polynomial, it can be confirmed that a total homogenization heat treatment time of at least 25 hours is required to achieve a Ti segregation ratio of 1.25 or less.

[0059] Figure 3 This indicates the relationship between the Ti segregation ratio and the elongation anisotropy ratio. Figure 4 This represents the relationship between the Ti segregation ratio and the shrinkage anisotropy ratio. (From...) Figure 3 It can be seen that the correlation coefficient between the Ti segregation ratio and the elongation anisotropy ratio is 0.72, indicating a positive correlation. The lower the Ti segregation ratio, the lower the elongation anisotropy ratio tends to be. Furthermore, from... Figure 4 It can be seen that the correlation coefficient between Ti segregation ratio and shrinkage anisotropy is 0.85, indicating a positive correlation. The lower the Ti segregation ratio, the lower the shrinkage anisotropy ratio tends to be. Based on the above, it can be confirmed that the precipitation-strengthened austenitic stainless steel of the present invention with a Ti segregation ratio of 1.25 or less has a small elongation anisotropy ratio and shrinkage anisotropy ratio, and possesses excellent anisotropic mechanical properties.

Claims

1. A precipitation-strengthened austenitic stainless steel, wherein, By mass%, C is less than 0.08%, Si is less than 1.00%, Mn is less than 2.00%, P is less than 0.040%, S is less than 0.030%, Ni is 24.00~27.00%, Cr is 13.50~16.00%, Mo is 1.00~1.50%, Ti is 1.90~2.35%, Al is less than 0.35%, V is 0.10~0.50%, B is 0.001~0.010%, and the balance consists of Fe and unavoidable impurities. The Ti segregation ratio in the steel is below 1.

25.

2. A method for manufacturing precipitation-strengthened austenitic stainless steel, which is the method for manufacturing precipitation-strengthened austenitic stainless steel according to claim 1, the method comprising the following steps: The first homogenization heat treatment process involves homogenizing the prepared steel ingot at a heating temperature of 980~1270℃ to obtain raw materials for hot forging. The hot forging process involves hot forging the raw materials for hot forging to obtain steel sheets. as well as The solution / aging treatment process involves performing solution treatment and aging treatment on the steel sheet. The heat treatment time for the first homogenization heat treatment is 25 to 150 hours.

3. The method for manufacturing precipitation-strengthened austenitic stainless steel according to claim 2, comprising: The second homogenization heat treatment process involves homogenizing at least one of the steel sheet and intermediate materials used in hot forging at a heating temperature of 980~1270℃. The total heat treatment time for the first homogenization heat treatment and the second homogenization heat treatment is 25 to 150 hours.

4. A component for use in a hydrogen environment, which uses the precipitation-strengthened austenitic stainless steel as described in claim 1.

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