Austenitic stainless steel with improved hydrogen embrittlement resistance and method for manufacturing the same

Abstract

By optimizing the steel composition and controlling the manufacturing process, we provide austenitic stainless steel that is cost-competitive while improving yield strength and hydrogen embrittlement resistance, and a manufacturing method thereof. [Solution] The alloy contains, in weight percent, C: more than 0% and not more than 0.03%, N: 0.15% or more and 0.25% or less, Si: more than 0% and not more than 1.0%, Mn: more than 0% and not more than 10.0%, Cr: 16.0% or more and not more than 22.0%, Ni: more than 0% and not more than 6.0%, Cu: more than 0% and not more than 1.6%, Mo: 0% or more and not more than 0.8%, and the remainder being Fe and unavoidable impurities, An austenitic stainless steel having improved resistance to hydrogen embrittlement, characterized in that the value of the following formula (1) is 250 or more: Formula (1): Ni eq ×D c

Description

[Technical Field]

[0001] The present invention relates to austenitic stainless steel with improved hydrogen embrittlement resistance and a manufacturing method therefor, and more particularly to austenitic stainless steel with improved hydrogen embrittlement resistance that is cost-competitive while improving yield strength and hydrogen embrittlement resistance by optimizing steel components and controlling the manufacturing process, and a manufacturing method therefor. [Background technology]

[0002] Austenitic stainless steel has excellent resistance to hydrogen embrittlement and has been used in various parts, machinery, and structural materials that are directly exposed to hydrogen. In addition, austenitic stainless steel is less susceptible to low-temperature embrittlement, making it suitable for use in cryogenic environments, and is therefore used in storage parts for LNG, liquefied hydrogen, liquefied ammonium, liquefied nitrogen, liquefied carbon dioxide, etc. However, austenitic stainless steels have a yield strength of 250 MPa or less, making them difficult to use in stress-resistant environments. In addition, the martensitic phase transformation phenomenon that occurs in some metastable austenitic stainless steels can rapidly deteriorate their resistance to hydrogen embrittlement.

[0003] Previous attempts to solve this problem have been made to improve austenite stabilization by using expensive elements such as Ni, but this has the problem of reducing cost competitiveness. Also, while martensitic phase transformation theoretically does not occur when only the austenitic phase stabilization of a metal is considered, martensitic phase transformation due to segregation may occur in actual environments. Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide an austenitic stainless steel that is cost-competitive while improving yield strength and hydrogen embrittlement resistance by optimizing the steel composition and controlling the manufacturing process, and a manufacturing method thereof. [Means for solving the problem]

[0005] The austenitic stainless steel with improved hydrogen embrittlement resistance contains, by weight, C: more than 0% and not more than 0.03%, N: 0.15% or more and 0.25% or less, Si: more than 0% and not more than 1.0%, Mn: more than 0% and not more than 10.0%, Cr: 16.0% or more and not more than 22.0%, Ni: more than 0% and not more than 6.0%, Cu: more than 0% and not more than 1.6%, Mo: 0% or more and not more than 0.8%, with the remainder being Fe and unavoidable impurities, and is characterized by having a value of 250 or more for the following formula (1):

[0006] Formula (1): Ni eq ×D c In formula (1), Ni eq (Ni equivalent) is Ni + 0.65Cr + 0.98Mo + 1.05Mn + 0.35Si + 12.6C + 33.6N, and D c (Normalized diffusion coefficient) is 3.1(Mn / (Mn+Ni+Cr+Cu+Mo))+0.8(Ni / (Mn+Ni+Cr+Cu+Mo))+12.5(Cr / (Mn+Ni+Cr+Cu+Mo))+0 .6(Cu / (Mn+Ni+Cr+Cu+Mo))+0.1(Mo / (Mn+Ni+Cr+Cu+Mo)), and C, N, Si, Mn, Cr, Ni, Cu, and Mo are the contents (% by weight) of each component.

[0007] The austenitic stainless steel with improved hydrogen embrittlement resistance may have a value of 16 or more in the following formula (2).

[0008] Formula (2):4.4+23(C+N)+1.3Si+0.24(Cr+Ni+Mn) In formula (2), C, N, Si, Mn, Cr, and Ni represent the content (wt %) of each component.

[0009] In the austenitic stainless steel with improved hydrogen embrittlement resistance, the value of the following formula (3) may be 2.0 or less. Formula (3): Ni / Mn In formula (3), Ni and Mn are the contents (wt %) of each component.

[0010] The austenitic stainless steel with improved hydrogen embrittlement resistance may have an RNTS (relative notch tensile strength) value of 0.90 or more.

[0011] The austenitic stainless steel with improved hydrogen embrittlement resistance may have a yield strength of 300 MPa or more.

[0012] A method for producing austenitic stainless steel with improved hydrogen embrittlement resistance includes the steps of producing a slab containing, by weight, C: more than 0% and 0.03% or less, N: 0.15% or more and 0.25% or less, Si: more than 0% and 1.0% or less, Mn: more than 0% and 10.0% or less, Cr: 16.0% or more and 22.0% or less, Ni: more than 0% and 6.0% or less, Cu: more than 0% and 1.6% or less, Mo: 0% or more and 0.8% or less, with the remainder being Fe and unavoidable impurities, and hot rolling the slab and then hot-rolling and annealing the slab at 1050 to 1150°C to produce a hot-rolled steel sheet, wherein the slab is characterized in that the value of the following formula (1) is 250 or more.

[0013] Formula (1): Ni eq ×D c In formula (1), Ni eq (Ni equivalent) is Ni + 0.65Cr + 0.98Mo + 1.05Mn + 0.35Si + 12.6C + 33.6N, and D c(Normalized diffusion coefficient) is 3.1(Mn / (Mn+Ni+Cr+Cu+Mo))+0.8(Ni / (Mn+Ni+Cr+Cu+Mo))+12.5(Cr / (Mn+Ni+Cr+Cu+Mo))+0 .6(Cu / (Mn+Ni+Cr+Cu+Mo))+0.1(Mo / (Mn+Ni+Cr+Cu+Mo)), and C, N, Si, Mn, Cr, Ni, Cu, and Mo are the contents (% by weight) of each component.

[0014] The slab may have a value of 16 or more in the following formula (2), and a value of 2.0 or less in the following formula (3).

[0015] Formula (2):4.4+23(C+N)+1.3Si+0.24(Cr+Ni+Mn)

[0016] Formula (3): Ni / Mn

[0017] In formula (2), C, N, Si, Mn, Cr, and Ni represent the content (wt %) of each component.

[0018] In formula (3), Ni and Mn are the contents (wt %) of each component.

[0019] The method may further include cold rolling the hot-rolled steel sheet and cold-rolling annealing the hot-rolled steel sheet at 1050 to 1150°C to manufacture a cold-rolled steel sheet. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide an austenitic stainless steel and a manufacturing method thereof that are cost-competitive while improving yield strength and hydrogen embrittlement resistance by controlling the alloy components and manufacturing method. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention will now be described in detail with reference to the accompanying drawings. The following examples are presented to fully convey the spirit of the disclosed invention to those skilled in the art to which the present invention pertains. The disclosed invention is not limited to the embodiments presented herein and may be embodied in other forms. In the drawings, parts irrelevant to the description may be omitted to clarify the disclosed invention, and the sizes of components may be somewhat exaggerated to facilitate understanding. Throughout the specification, when a part is said to "comprise" certain elements, this means that it may further include other elements, rather than excluding other elements, unless specifically stated to the contrary. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0022] The reasons for limiting the alloying element contents in the present invention will be explained below. Unless otherwise specified, the units are % by weight.

[0023] An austenitic stainless steel with improved hydrogen embrittlement resistance may contain, in weight percent, C: more than 0% and not more than 0.03%, N: 0.15% or more and not more than 0.25%, Si: more than 0% and not more than 1.0%, Mn: more than 0% and not more than 10.0%, Cr: 16.0% or more and not more than 22.0%, Ni: more than 0% and not more than 6.0%, Cu: more than 0% and not more than 1.6%, Mo: 0% or more and not more than 0.8%, with the remainder consisting of Fe and unavoidable impurities.

[0024] The C (carbon) content may be more than 0% and not more than 0.03%. C is an element effective in stabilizing the austenite phase and can be added to ensure the yield strength of austenitic stainless steel. However, excessive C content can induce grain boundary precipitation of Cr carbides, which can adversely affect ductility, toughness, corrosion resistance, and the like. In consideration of this, the upper limit of the C content can be 0.03% or less. Preferably, the C content can be 0.02% or more and 0.03% or less.

[0025] The N (nitrogen) content may be 0.15% or more and 0.25% or less. N is a strong austenite-stabilizing element and is effective in improving the yield strength of austenitic stainless steel. In consideration of this, N can be added in an amount of 0.15% or more. However, if the N content is excessive, the cryogenic impact toughness may decrease and pinholes may occur. In consideration of this, the upper limit of the N content can be limited to 0.25%. Preferably, N can be 0.19% or more and 0.23% or less.

[0026] The Si (silicon) content may be more than 0% and not more than 1.0%. Silicon acts as a deoxidizer during the steelmaking process and is an effective element for improving the strength of the material. However, silicon is also an effective element for stabilizing the ferrite phase, and excessive addition can promote the formation of delta ferrite in the cast slab. Furthermore, excessive addition of silicon can adversely affect the ductility and impact properties of the material. Taking this into consideration, the upper limit of silicon content can be limited to 1.0%.

[0027] The Mn (manganese) content may be more than 0% and not more than 10.0%. The Mn (manganese) content can be greater than 0 and up to 10.0%, specifically 0.1% to 10.0%, more specifically 0.3% to 10.0%, and even more specifically 5.5% or more and 10.0% or less. Mn is an austenite phase stabilizer added in place of Ni and is effective in improving austenite stability. Taking this into consideration, Mn can be added in an amount greater than 0% or 0.1% or greater. For example, the lower limit of Mn can be 0.1% or greater, 0.3% or greater, 0.8% or greater, 0.9% or greater, 1.1% or greater, 1.3% or greater, 1.5% or greater, 2.0% or greater, 3.0% or greater, 3.5% or greater, 4.0% or greater, 4.5% or greater, 5% or greater, or 5.5% or greater. In this case, the austenitic stainless steel of the present invention can have improved austenite stability and superior ductility, toughness, and corrosion resistance. However, excessive Mn content can result in excessive formation of S-based inclusions (MnS), potentially reducing the ductility, toughness, and corrosion resistance of the steel. Furthermore, excessive Mn content can generate Mn fumes during the steelmaking process, which can be dangerous in manufacturing, and can induce grain boundary embrittlement, resulting in a chain reaction of deterioration in hydrogen embrittlement resistance. In consideration of this, the upper limit of the Mn content can be set to 10.0%. Preferably, the Mn content can be 5.9% or more and 10.0% or less.

[0028] The Cr (chromium) content may be 16.0% or more and 22.0% or less. Cr is a ferrite stabilizing element and is effective in suppressing the formation of martensite. Cr is also a key element for ensuring the corrosion resistance required of stainless steel. Taking this into consideration, Cr can be added in an amount of 16.0% or more. However, excessive Cr content can increase manufacturing costs and adversely affect material properties by forming a large amount of delta ferrite in the slab, which can reduce hot workability. Taking this into consideration, the upper limit of the Cr content can be limited to 22.0%. Preferably, the Cr content can be 16.5% or more and 21.8% or less.

[0029] The Ni (nickel) content may be more than 0% and not more than 6.0%. Ni is a strong austenite phase stabilizing element and is an essential element for ensuring good workability. However, Ni is an expensive element, and adding a large amount of Ni increases raw material costs. In consideration of this, the upper limit of the Ni content can be limited to 6.0%. Preferably, the Ni content is 0.1 to 6.0%, and more preferably, it can be 3.5% or more and 6.0% or less.

[0030] The Cu (copper) content may be more than 0% and not more than 1.6%. Cu is an element that can be added in place of Ni to stabilize the austenite phase and improve corrosion resistance in a reducing environment. However, if the Cu content is excessive, the corrosion resistance, strength, and material properties may be deteriorated, and productivity may decrease. In consideration of this, the upper limit of the Cu content may be limited to 1.6%. Preferably, the Cu content may be 0.4% or more and 1.6% or less.

[0031] The content of Mo (molybdenum) may be 0% or more and 0.8% or less. Mo, along with Cr, is an element that can be selectively added to ensure the corrosion resistance of steel and contributes to the solid solution strengthening effect. However, if the Mo content is excessive, hot workability may be deteriorated and price competitiveness may decrease. In consideration of this, the upper limit of the Mo content can be limited to 0.8%. For example, the Mo content can be more than 0% and less than or equal to 0.8%. The remaining component of the present invention is iron (Fe). However, in a normal manufacturing process, unintentional impurities may inevitably be mixed in from raw materials or the surrounding environment, and this cannot be excluded. Since these impurities are known to anyone skilled in normal manufacturing processes, not all of the contents of these impurities will be specifically mentioned in this specification.

[0032] Austenitic stainless steel with improved hydrogen embrittlement resistance may have a value of 250 or more in the following formula (1).

[0033] Equation (1): Nieq × Dc In formula (1), Ni eq (Ni equivalent) is Ni + 0.65Cr + 0.98Mo + 1.05Mn + 0.35Si + 12.6C + 33.6N, and D c (Normalized diffusion coefficient) is 3.1(Mn / (Mn+Ni+Cr+Cu+Mo))+0.8(Ni / (Mn+Ni+Cr+Cu+Mo))+12.5(Cr / (Mn+Ni+Cr+Cu+Mo))+0 .6(Cu / (Mn+Ni+Cr+Cu+Mo))+0.1(Mo / (Mn+Ni+Cr+Cu+Mo)), and C, N, Si, Mn, Cr, Ni, Cu, and Mo are the contents (% by weight) of each component. The above formula (1) is Ni eq (Ni equivalent) and D c (Normalized diffusion coefficient). Ni eq If the (Ni equivalent) value is low, the theoretical austenite phase stability is low, and martensite phase transformation occurs due to environmental factors such as external stress and external temperature, resulting in poor hydrogen embrittlement resistance.

[0034] D c If the normalized diffusion coefficient (D) value is low, segregation may occur during the slab manufacturing process, and the austenite phase stability may decrease rapidly. c Even if the normalized diffusion coefficient (DDC) value is low, martensitic phase transformation may occur due to the external environment, resulting in a deterioration of hydrogen embrittlement resistance.

[0035] Therefore, Ni eq (Ni equivalent) and D cIf the value of formula (1), which is the normalized diffusion coefficient (r), is less than 250, it is difficult to realize an austenitic stainless steel that has improved hydrogen embrittlement resistance and is cost-competitive. Preferably, the value of formula (1) is 250 to 311.84, more preferably 250 to 300, and even more preferably 260 to 295. Within the above ranges, the austenitic stainless steel of the present invention with improved hydrogen embrittlement resistance can achieve a higher RNTS value while maintaining an excellent balance between yield strength and tensile strength.

[0036] Austenitic stainless steel with improved hydrogen embrittlement resistance may have a value of 16 or more in the following formula (2).

[0037] Formula (2):4.4+23(C+N)+1.3Si+0.24(Cr+Ni+Mn) In formula (2), C, N, Si, Mn, Cr, and Ni represent the content (wt %) of each component. The above formula (2) was derived in consideration of the improvement in yield strength due to the stress field of the steel material in order to ensure high yield strength of austenitic stainless steel.

[0038] The larger the value of formula (2), the greater the interlattice stress field due to the atomic size difference between alloying elements. Therefore, the larger the value of formula (2), the greater the limit of resistance to plastic deformation against external stress. If the value of formula (2) is less than 16, it is difficult to ensure the desired yield strength in the disclosed invention. Preferably, the value of formula (2) is 16 to 19.24, more preferably 16 to 18.5, and even more preferably 17 to 18. The austenitic stainless steel of the present invention with improved hydrogen embrittlement resistance can further increase the RNTS value while maintaining an excellent balance between yield strength and tensile strength.

[0039] Austenitic stainless steel with improved hydrogen embrittlement resistance has a value of 2.0 or less in the following formula (3).

[0040] Formula (3): Ni / Mn In formula (3), Ni and Mn are the contents (wt %) of each component. The above formula (3) was derived to ensure excellent austenite phase stabilization relative to cost.

[0041] Ni and Mn are typical elements that can increase the austenite phase stabilization degree. However, when the austenite phase stabilization degree is the same, the lower the Ni / Mn value, the higher the cost competitiveness. Preferably, the value of the above formula (3) is 0.025 to 2.0, more preferably 0.4 to 2.0, and even more preferably 0.4 to 0.9. Within the above ranges, the austenitic stainless steel of the present invention with improved hydrogen embrittlement resistance can further improve the yield strength and tensile strength while simultaneously further increasing the RNTS value. By controlling the alloy composition and production method, the austenitic stainless steel of the present invention with improved hydrogen embrittlement resistance can have a relative notch tensile strength (RNTS) value, which is an index of hydrogen embrittlement resistance, of 0.90 or more. The RNTS is preferably 0.9 to 1.0, more preferably 0.91 to 1.0, and even more preferably 0.96 to 1.0. Within the above range, the austenitic stainless steel of the present invention with improved hydrogen embrittlement resistance can be advantageous in terms of improving cost competitiveness while also having superior hydrogen embrittlement resistance and yield strength or tensile strength.

[0042] In addition, austenitic stainless steel with improved hydrogen embrittlement resistance can have a yield strength of 300 MPa or more by realizing high strength. Next, a method for producing the austenitic stainless steel having improved hydrogen embrittlement resistance according to the present invention will be described.

[0043] A method for producing an austenitic stainless steel with improved hydrogen embrittlement resistance includes the steps of producing a slab containing, by weight, C: more than 0% and 0.03% or less, N: 0.15% to 0.25%, Si: more than 0% and 1.0% or less, Mn: more than 0% and 10.0% or less, Cr: 16.0% to 22.0%, Ni: more than 0% and 6.0%, Cu: more than 0% and 1.6%, Mo: 0% to 0.8%, and the remainder being Fe and unavoidable impurities, and hot rolling the slab and then hot-rolling and annealing the slab at 1050 to 1150°C to produce a hot-rolled steel sheet, wherein the slab has a value of the following formula (1) of 250 or more. Preferably, the value of the following formula (1) is 250 to 311.84, more preferably 250 to 300, and even more preferably 260 to 295.

[0044] Formula (1): Ni eq ×D c In formula (1), Ni eq (Ni equivalent) is Ni + 0.65Cr + 0.98Mo + 1.05Mn + 0.35Si + 12.6C + 33.6N, and D c (Normalized diffusion coefficient) is 3.1(Mn / (Mn+Ni+Cr+Cu+Mo))+0.8(Ni / (Mn+Ni+Cr+Cu+Mo))+12.5(Cr / (Mn+Ni+Cr+Cu+Mo))+0 .6(Cu / (Mn+Ni+Cr+Cu+Mo))+0.1(Mo / (Mn+Ni+Cr+Cu+Mo)), and C, N, Si, Mn, Cr, Ni, Cu, and Mo are the contents (% by weight) of each component.

[0045] The slab has a value of the following formula (2) of 16 or more. Preferably, the value of the above formula (2) is 16 to 19.24, more preferably 16 to 18.5, and even more preferably 17 to 18.

[0046] Formula (2):4.4+23(C+N)+1.3Si+0.24(Cr+Ni+Mn) In formula (2), C, N, Si, Mn, Cr, and Ni represent the content (wt %) of each component.

[0047] The slab may have a value of 2.0 or less in the following formula (3): Preferably, the value of the above formula (3) is 0.025 to 2.0, more preferably 0.4 to 2.0, and even more preferably 0.4 to 0.9.

[0048] Formula (3): Ni / Mn In formula (3), Ni and Mn are the contents (wt %) of each component. The component ranges of each alloy composition and the reasons for limiting the values ​​of formulas (1), (2) and (3) are as described above, and each manufacturing step will be described in more detail below.

[0049] The method for producing austenitic stainless steel with improved hydrogen embrittlement resistance can include producing a slab that satisfies the above alloy composition, formula (1), formula (2), and formula (3), followed by a series of hot rolling and hot rolling annealing steps. The method for producing austenitic stainless steel with improved hydrogen embrittlement resistance can further include cold rolling and cold rolling annealing steps, if necessary. First, the slab is hot rolled and hot rolled and annealed at 1050 to 1150°C to produce a hot rolled steel sheet.

[0050] If the hot rolling annealing temperature is low, the residual martensite fraction may be high and the elongation rate may be poor, but if the hot rolling annealing temperature is too high, the strength may decrease due to coarsening of the crystal grains. Next, if necessary, the method may further include a step of cold rolling the hot-rolled steel sheet and cold-rolling annealing the hot-rolled steel sheet at 1050 to 1150°C to manufacture a cold-rolled steel sheet.

[0051] If the cold rolling annealing temperature is too low, recrystallization may be insufficient, resulting in a low elongation ratio.However, if the cold rolling annealing temperature is too high, the crystal grains may become coarse and the oxides formed at the grain boundaries may become deep, which may result in a deterioration of the surface quality after pickling.

[0052] The present invention will be described in more detail below through examples. However, the description of these examples is intended to illustrate the implementation of the present invention, and the present invention is not limited by the description of these examples. The scope of the present invention is determined by the matters described in the claims and matters reasonably inferred therefrom. [Example]

[0053] Slabs were produced in a vacuum induction melting furnace for the various alloy composition ranges shown in Table 1 below. The produced slabs were hot rolled and hot rolled and annealed at 1100°C to produce hot rolled steel sheets. The hot rolled steel sheets were cold rolled and cold rolled and annealed at 1100°C to produce test specimens.

[0054] [Table 1]

[0055] Table 2 below shows Ni eq , D c The values ​​of formula (1), formula (2), formula (3), yield strength, tensile strength and RNTS (relative notch tensile strength) are shown. Ni eq (Ni equivalent) was calculated using the following formula.

[0056] Ni eq :Ni+0.65Cr+0.98Mo+1.05Mn+0.35Si+12.6C+33.6N

[0057] D c The normalized diffusion coefficient was calculated using the following formula: D c :3.1(Mn / (Mn+Ni+Cr+Cu+Mo))+0.8(Ni / (Mn+Ni+Cr+Cu+Mo))+12.5(Cr / (Mn+Ni+Cr+Cu+Mo))+0.6(Cu / (Mn+Ni+Cr+Cu+Mo))+0.1(Mo / (Mn+Ni+Cr+Cu+Mo))

[0058] The value of formula (1) was calculated using the following formula (1).

[0059] Formula (1): Ni eq ×D c In formula (1), Ni eq (Ni equivalent) is Ni + 0.65Cr + 0.98Mo + 1.05Mn + 0.35Si + 12.6C + 33.6N, and D c (Normalized diffusion coefficient) is 3.1(Mn / (Mn+Ni+Cr+Cu+Mo))+0.8(Ni / (Mn+Ni+Cr+Cu+Mo))+12.5(Cr / (Mn+Ni+Cr+Cu+Mo))+0 .6(Cu / (Mn+Ni+Cr+Cu+Mo))+0.1(Mo / (Mn+Ni+Cr+Cu+Mo)), and C, N, Si, Mn, Cr, Ni, Cu, and Mo are the contents (% by weight) of each component.

[0060] The value of formula (2) was calculated using the following formula (2).

[0061] Formula (2):4.4+23(C+N)+1.3Si+0.24(Cr+Ni+Mn) In formula (2), C, N, Si, Mn, Cr, and Ni represent the content (wt %) of each component.

[0062] The value of formula (3) was calculated using the following formula (3).

[0063] Formula (3): Ni / Mn In formula (3), Ni and Mn are the contents (wt %) of each component.

[0064] The yield strength and tensile strength were measured using a tensile testing machine manufactured by Zwick Roell, using a JIS13B tensile test piece at a tension rate of 15 mm per minute at room temperature. RNTS (relative notch tensile strength) was calculated using the following formula (4). Meanwhile, RNTS was measured on notched tensile test pieces in a high-pressure hydrogen environment of 1000 bar or less at room temperature with a crosshead speed of 0.05 mm / min or less.

[0065] Equation (4): (Notched tensile strength in a high-pressure hydrogen atmosphere of 1000 bar or less (MPa) x Notched tensile strength in a general air atmosphere (MPa))

[0066] On the other hand, it can be determined that the higher the RNTS, the more improved the hydrogen embrittlement resistance.

[0067] [Table 2]

[0068] As shown in Table 2, Examples 1 to 8 satisfied the alloy components, values ​​of formula (1), values ​​of formula (2), values ​​of formula (3), and manufacturing methods indicated in the present invention. Therefore, Examples 1 to 8 satisfied the RNTS (relative notch tensile strength) value of 0.90 or more and the yield strength of 300 MPa or more. That is, Examples 1 to 8 can be evaluated as having excellent cost competitiveness while improving the yield strength and hydrogen embrittlement resistance.

[0069] However, Comparative Examples 1 to 14 did not satisfy the value of formula (1) of 250 or more. Therefore, Comparative Examples 1 to 14 did not satisfy the RNTS (relative notch tensile strength) value of 0.90 or more. In other words, Comparative Examples 1 to 14 can be evaluated as having relatively poor hydrogen embrittlement resistance.

[0070] Furthermore, Comparative Examples 1 to 4, 7, and 12 failed to satisfy the value of formula (1) of 250 or more, and at the same time failed to satisfy the value of formula (2) of 16 or more. Therefore, Comparative Examples 1 to 4, 7, and 12 had relatively poor hydrogen embrittlement resistance and failed to satisfy the yield strength of 300 MPa or more. In other words, Comparative Examples 1 to 4, 7, and 12 were poor in hydrogen embrittlement resistance and strength, and therefore can be evaluated as being difficult to apply to environments where stress is applied.

[0071] As described above, according to the present invention, it is possible to provide an austenitic stainless steel and a manufacturing method thereof that are cost-competitive while improving yield strength and hydrogen embrittlement resistance by controlling the alloy components and manufacturing method.

Claims

1. The steel sheet contains, in weight percent, C: more than 0% and 0.03% or less, N: 0.15% or more and 0.25% or less, Si: more than 0% and 1.0% or less, Mn: more than 0% and 10.0% or less, Cr: 16.0% or more and 22.0% or less, Ni: more than 0% and 6.0% or less, Cu: more than 0% and 1.6% or less, Mo: 0% or more and 0.8% or less, and the remainder being Fe and unavoidable impurities, An austenitic stainless steel having improved resistance to hydrogen embrittlement, characterized in that the value of the following formula (1) is 250 or more: Formula (1): Ni ｅｑ × D ｃ (In formula (1), Ni ｅｑ (Ni equivalent) is Ni + 0.65Cr + 0.98Mo + 1.05Mn + 0.35Si + 12.6C + 33.6N, D ｃ I coefficientt)は、3.1(7n / Mnnnkii+3rrokk o))+0.8((8i / (Mn+(ii)Cr+Cu+ooo)+125() / / n+i+Cr+u+Moo))+0.6((u / (+++++ Cu+Mo))+0.1(Mo / Mn+8i+(r+uu+ooo)、、 C, N, Si, Mn, Cr, Ni, Cu and Mo are the contents (wt%) of each component.

2. 2. The austenitic stainless steel with improved hydrogen embrittlement resistance according to claim 1, wherein the value of the following formula (2) is 16 or more: Formula (2): 4.4+23(C+N)+1.3Si+0.24(Cr+Ni+Mn) (In formula (2), C, N, Si, Mn, Cr, and Ni represent the contents (wt%) of each component.)

3. 2. The austenitic stainless steel with improved hydrogen embrittlement resistance according to claim 1, wherein the value of the following formula (3) is 2.0 or less: Formula (3): Ni / Mn (In formula (3), Ni and Mn are the contents (wt%) of each component.)

4. 2. The austenitic stainless steel with improved hydrogen embrittlement resistance according to claim 1, characterized in that the RNTS (relative notch tensile strength) value is 0.90 or more.

5. 2. The austenitic stainless steel with improved hydrogen embrittlement resistance according to claim 1, characterized in that the yield strength is 300 MPa or more.

6. producing a slab containing, by weight, C: more than 0% and not more than 0.03%, N: 0.15% to 0.25%, Si: more than 0% and not more than 1.0%, Mn: more than 0% and not more than 10.0%, Cr: 16.0% to 22.0%, Ni: more than 0% and not more than 6.0%, Cu: more than 0% and not more than 1.6%, Mo: 0% to 0.8%, with the remainder being Fe and unavoidable impurities; and hot rolling the slab and then hot-rolling and annealing the slab at 1050 to 1150°C to produce a hot-rolled steel sheet. The method for producing austenitic stainless steel with improved hydrogen embrittlement resistance is characterized in that the slab has a value of 250 or more in the following formula (1): Formula (1): Ni ｅｑ × D ｃ (In formula (1), Ni ｅｑ (Ni equivalent) is Ni + 0.65Cr + 0.98Mo + 1.05Mn + 0.35Si + 12.6C + 33.6N, D ｃ I coefficientt)は、3.1(7n / Mnnnkii+3rrokk o))+0.8((8i / (Mn+(ii)Cr+Cu+ooo)+125() / / n+i+Cr+u+Moo))+0.6((u / (+++++ Cu+Mo))+0.1(Mo / Mn+8i+(r+uu+ooo)、、 C, N, Si, Mn, Cr, Ni, Cu and Mo are the contents (wt%) of each component.

7. 7. The method for producing an austenitic stainless steel having improved hydrogen embrittlement resistance according to claim 6, wherein the slab has a value of the following formula (2) of 16 or more: Formula (2): 4.4+23(C+N)+1.3Si+0.24(Cr+Ni+Mn) (In formula (2), C, N, Si, Mn, Cr, and Ni represent the contents (wt%) of each component.)

8. 7. The method for producing an austenitic stainless steel having improved hydrogen embrittlement resistance according to claim 6, wherein the slab has a value of the following formula (3) of 2.0 or less: Formula (3): Ni / Mn (In formula (3), Ni and Mn are the contents (wt%) of each component.)

9. 7. The method of claim 6, further comprising cold-rolling the hot-rolled steel sheet and cold-rolling annealing the hot-rolled steel sheet at 1050 to 1150°C to produce a cold-rolled steel sheet.

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