EP4606925A1

EP4606925A1 - Austenitic stainless steel with improved hydrogen embrittlement resistance and manufacturing method therefor

Info

Publication number: EP4606925A1
Application number: EP23903777.3A
Authority: EP
Inventors: Seokweon SONG; Kwangmin Kim; Minam PARK
Original assignee: Posco Co Ltd
Current assignee: Posco Holdings Inc
Priority date: 2022-12-16
Filing date: 2023-11-13
Publication date: 2025-08-27
Also published as: EP4606925A4; WO2024128574A1; KR20240094448A; CN120418472A; JP2025542023A

Abstract

Provided are an austenitic stainless steel with improved hydrogen embrittlement resistance and a method for manufacturing the same.

The austenitic stainless steel with improved hydrogen embrittlement resistance according to an embodiment of the present disclosure may include: in percent by weight (wt%), more than 0% and 0.03% or less of carbon (C), 0.15% or more and 0.25% or less of nitrogen (N), more than 0% and 1.0% or less of silicon (Si), more than 0% and 10.0% or less of manganese (Mn), 16.0% or more and 22.0% or less of chromium (Cr), more than 0% and 6.0% or less of nickel (Ni), more than 0% and 1.6% or less of copper (Cu), 0% or more and 0.8% or less of molybdenum (Mo), the remainder of iron (Fe), and inevitable impurities.

Description

[Technical Field]

The present disclosure relates to an austenitic stainless steel with improved hydrogen embrittlement resistance and a manufacturing method therefor.

[Background Art]

Austenitic stainless steels have excellent hydrogen embrittlement resistance and have been used in various parts, equipment, and structural materials that are directly exposed to hydrogen. In addition, austenitic stainless steel is suitable for use in extremely low-temperature environments due to its low occurrence of low-temperature embrittlement, and is employed in storage components for liquefied natural gas (LNG), liquefied hydrogen, liquefied ammonium, liquefied nitrogen, and liquefied carbon dioxide.
However, austenitic stainless steel has a yield strength of 250 MPa or less, which limits its use in stress-bearing environments. In addition, martensite phase transformation observed in metastable austenitic stainless steels causes a deterioration in hydrogen embrittlement resistance.
Conventionally, expensive elements such as nickel (Ni) have been used to improve austenite stability in order to overcome the above limitation, but the cost competitiveness is low. Furthermore, although martensite phase transformation does not theoretically occur when only the stability of an austenite phase of a metal is considered, martensite phase transformation may occur due to segregation in an actual environment.

[Disclosure]

[Technical Problem]

The present disclosure provides an austenitic stainless steel with improved hydrogen embrittlement resistance and improved yield strength as well as excellent cost competitiveness by optimizing steel composition and controlling a manufacturing process, and a method for manufacturing the same.

[Technical Solution]

According to an embodiment of the present disclosure, an austenitic stainless steel with improved hydrogen embrittlement resistance may include, in percent by weight (wt%), more than 0% and 0.03% or less of carbon (C), 0.15% or more and 0.25% or less of nitrogen (N), more than 0% and 1.0% or less of silicon (Si), more than 0% and 10.0% or less of manganese (Mn), 16.0% or more and 22.0% or less of chromium (Cr), more than 0% and 6.0% or less of nickel (Ni), more than 0% and 1.6% or less of copper (Cu), 0% or more and 0.8% or less of molybdenum (Mo), the remainder of iron (Fe), and inevitable impurities, wherein a value of Formula (1) below may be 250 or more.

Formula (1): Ni_eq X D_c
In Formula (1), Ni_eq (Ni equivalent) is Ni + 0.65 Cr + 0.98 Mo + 1.05 Mn + 0.35 Si + 12.6 C + 33.6 N, 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 represent the content (wt%) of the respective elements.
The austenitic stainless steel with improved hydrogen embrittlement resistance according to an embodiment may have a value of Formula (2) below of 16 or more.

Formula (2): 4.4 + 23 (C + N) + 1.3 Si + 0.24 (Cr + Ni + Mn)
In Formula (2), C, N, Si, Mn, Cr, and Ni represent the content (wt%) of the respective elements.
The austenitic stainless steel with improved hydrogen embrittlement resistance according to an embodiment may have a value of Formula (3) below of 2.0 or less.

Formula (3): Ni / Mn
In Formula (3), Ni and Mn represent the content (wt%) of the respective elements.
The austenitic stainless steel with improved hydrogen embrittlement resistance according to an embodiment may have a relative notch tensile strength (RNTS) value of 0.90 or more.
The austenitic stainless steel with improved hydrogen embrittlement resistance according to an embodiment may have a yield strength of 300 MPa or more.
According to an embodiment of the present disclosure, a method for manufacturing an austenitic stainless steel with improved hydrogen embrittlement resistance may include: manufacturing a slab including, in percent by weight (wt%), more than 0% and 0.03% or less of carbon (C), 0.15% or more and 0.25% or less of nitrogen (N), more than 0% and 1.0% or less of silicon (Si), more than 0% and 10.0% or less of manganese (Mn), 16.0% or more and 22.0% or less of chromium (Cr), more than 0% and 6.0% or less of nickel (Ni), more than 0% and 1.6% or less of copper (Cu), 0% or more and 0.8% or less of molybdenum (Mo), the remainder of iron (Fe), and inevitable impurities; and hot rolling the slab, and then hot annealing at 1050 to 1150°C to manufacture a hot-rolled steel sheet, wherein the slab may have a value of Formula (1) below of 250 or more.

Formula (1): Ni_eq X D_c
In Formula (1), Ni_eq (Ni equivalent) is Ni + 0.65 Cr + 0.98 Mo + 1.05 Mn + 0.35 Si + 12.6 C + 33.6 N, 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 represent the content (wt%) of the respective elements.
The slab may have a value of Formula (2) below of 16 or more, and have a value of Formula (3) below of 2.0 or less.

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

Formula (3): Ni / Mn
In Formula (2), C, N, Si, Mn, Cr, and Ni represent the content (wt%) of the respective elements.
In Formula (3), Ni and Mn represent the content (wt%) of the respective elements.
The method may further include: cold rolling the hot-rolled steel sheet, and cold annealing at 1500 to 1150°C to manufacture a cold-rolled steel sheet.

[Advantageous Effects]

According to an embodiment of the present disclosure, an austenitic stainless steel with improved hydrogen embrittlement resistance and improved yield strength as well as excellent cost competitiveness by controlling alloy components and a manufacturing process, and a method for manufacturing the same may be provided.

[Mode for Invention]

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The following embodiments are presented to fully convey the spirit of the present disclosure to those skilled in the art to which the present disclosure pertains, and are not limited to those shown herein, but may be embodied in other forms. The drawings may omit figures not pertinent to the description in order to clarify the present disclosure, and the sizes of configurations may be exaggerated for the purpose of illustration.
Throughout the specification, when a part "includes" a certain component, this means that the part may further include other components, rather than excluding other components, unless specifically stated otherwise.
It is to be understood that the singular forms are intended to include the plural forms as well, unless the context clearly dictates otherwise.
Hereinafter, reasons for numerical limitations on the contents of alloy components in the embodiments of the present disclosure will be described. Hereinafter, unless otherwise specified, the unit is percent by weight (wt%).
According to an embodiment, an austenitic stainless steel with improved hydrogen embrittlement resistance may include, in percent by weight (wt%), more than 0% and 0.03% or less of carbon (C), 0.15% or more and 0.25% or less of nitrogen (N), more than 0% and 1.0% or less of silicon (Si), more than 0% and 10.0% or less of manganese (Mn), 16.0% or more and 22.0% or less of chromium (Cr), more than 0% and 6.0% or less of nickel (Ni), more than 0% and 1.6% or less of copper (Cu), 0% or more and 0.8% or less of molybdenum (Mo), the remainder of iron (Fe), and inevitable impurities.
The content of C (carbon) may be more than 0% and 0.03% or less.
C is an element effective for austenite phase stabilization, and may be added to obtain yield strength of the austenitic stainless steel. However, an excessive C content may induce grain boundary precipitation of a Cr carbide, which may adversely affect ductility, toughness, corrosion resistance, and the like. Accordingly, an upper limit of the C content may be 0.03% or less. Preferably, the content of C may be 0.02% or more and 0.03% or less.
The content of N (nitrogen) may be 0.15% or more and 0.25% or less.
N is a strong austenite-stabilizing element and is effective for improving the yield strength of the austenitic stainless steel. Considering the above, N may be added in an amount of 0.15% or more. However, an excess of N may impair toughness in cryogenic environments, and pin holes may occur. Accordingly, an upper limit of the N content may be controlled to 0.25%. Preferably, N may be 0.19% or more and 0.23% or less.
The content of Si (silicon) may be more than 0% and 1.0% or less.
Si is an element effective for improving a strength of material and serves as a deoxidizer during a steelmaking process. However, Si is an effective element for stabilization of a ferrite phase, and an excess of Si may promote formation of delta ferrite in a cast slab. In addition, an excess of Si may impair ductility and impact properties of a steel material. Considering the above, an upper limit of the Si content may be controlled to 1.0%.
The content of Mn (manganese) may be more than 0% and 10.0% or less.
The content of Mn (manganese) may be more than 0 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, as an austenite phase-stabilizing element added as a Ni substitute, is effective for improving austenite stability. Considering the above, Mn may be added in an amount of more than 0% or 0.1% or more. For example, a lower limit value of Mn may be 0.1% or more, 0.3% or more, 0.8% or more, 0.9% or more, 1.1% or more, 1.3% or more, 1.5% or more, 2.0% or more, 3.0% or more, 3.5% or more, 4.0% or more, 4.5% or more, 5% or more, or 5.5% or more. In this case, the austenitic stainless steel according to an embodiment of the present disclosure may have further improved austenite stability, and also more excellent ductility, toughness, and corrosion resistance. However, an excess of Mn may cause excessive formation of S-based inclusions (MnS), which impairs the ductility, toughness, and corrosion resistance of the austenitic stainless steel. In addition, an excess of Mn may generate Mn fume during a steelmaking process to cause manufacturing risks. Furthermore, an excess of Mn may cause grain boundary embrittlement, leading to sequential deterioration of hydrogen embrittlement resistance. Accordingly, an upper limit of the Mn content may be controlled to 10.0%. Preferably, the content of Mn may be 5.9% or more and 10.0% or less.
The content of Cr (chromium) may be 16.0% or more and 22.0% or less.
Although Cr is a ferrite-stabilizing element, Cr is an effective element for inhibiting formation of a martensite phase. In addition, Cr is a basic element for obtaining corrosion resistance required in stainless steels. Considering the above, Cr may be added in an amount of 16.0% or more. However, an excess of Cr may increase manufacturing costs and form a large amount of delta ferrite in a slab, which impairs hot workability and adversely affects properties. Accordingly, an upper limit of the Cr content may be controlled to 22.0%. Preferably, the content of Cr may be 16.5% or more and 21.8% or less.
The content of Ni (nickel) may be more than 0% and 6.0% or less.
Ni is a strong austenite phase-stabilizing element and is an essential element for obtaining excellent workability. However, because Ni is a high-priced element, adding a large amount of Ni may increase manufacturing costs. Considering the above, an upper limit of the Ni content may be controlled to 6.0%. Preferably, the content of Ni may be 0.1 to 6.0%, and more preferably, 3.5% or more and 6.0% or less.
The content of Cu (copper) may be more than 0% and 1.6% or less.
Cu, as an austenite phase-stabilizing element, may be added as a Ni substitute. In addition, Cu may be added to enhance corrosion resistance under a reducing environment. However, an excess of Cu may impair corrosion resistance, strength, and properties, and decrease productivity. Considering the above, an upper limit of the Cu content may be controlled to 1.6%. Preferably, the content of Cu may be 0.4% or more and 1.6% or less.
The content of Mo (molybdenum) may be 0% or more and 0.8% or less.
Mo may be selectively added to obtain corrosion resistance together with Cr and contribute to a solid solution strengthening effect. However, an excess of Mo may not only impair hot workability but also reduce cost competitiveness. Considering the above, an upper limit of the Mo content may be controlled to 0.8%. For example, the content of Mo may be more than 0% and 0.8% or less.
The remaining component of the present disclosure is iron (Fe). However, since unintended impurities may inevitably be introduced from raw materials or the surrounding environment during a typical manufacturing process, this may not be excluded. Since such impurities may be well known to those skilled in the art during a typical manufacturing process, details thereof are not described in this specification.
The austenitic stainless steel with improved hydrogen embrittlement resistance according to an embodiment may have a value of Formula (1) below of 250 or more.

Formula (1): Ni_eq X D_c
In Formula (1), Ni_eq (Ni equivalent) is Ni + 0.65 Cr + 0.98 Mo + 1.05 Mn + 0.35 Si + 12.6 C + 33.6 N, 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 represent the content (wt%) of the respective elements.
The Formula (1) consists of Ni_eq (Ni equivalent) and Dc (normalized diffusion coefficient).
In the case where the Ni_eq (Ni equivalent) value is low, a theoretical austenite phase stability is low, and thus martensite phase transformation may occur depending on an environment such as external stress or external temperature, causing hydrogen embrittlement resistance to deteriorate.
In the case where the D_c (normalized diffusion coefficient) value is low, segregation may occur during a slab manufacturing process, causing the austenite phase stability to drop sharply. Accordingly, even when the D_c (normalized diffusion coefficient) value is low, martensite phase transformation may occur depending on an external environment, causing hydrogen embrittlement resistance to deteriorate.
Thus, in the case where Formula (1) consisting of Ni_eq (Ni equivalent) and D_c (normalized diffusion coefficient) is less than 250, it may be difficult to realize an austenitic stainless steel with excellent cost competitiveness while improving hydrogen embrittlement resistance. Preferably, the value of Formula (1) may be 250 to 311.84, more preferably 250 to 300, and even more preferably 260 to 295. Within the above range, the austenitic stainless steel with improved hydrogen embrittlement resistance according to an embodiment of the present disclosure may have an excellent balance between yield strength and tensile strength, and a relative notch tensile strength (RNTS) value may be further increased.
The austenitic stainless steel with improved hydrogen embrittlement resistance according to an embodiment may have a value of Formula (2) below of 16 or more.

Formula (2): 4.4 + 23 (C + N) + 1.3 Si + 0.24 (Cr + Ni + Mn)
In Formula (2), C, N, Si, Mn, Cr, and Ni represent the content (wt%) of the respective elements.
The Formula (2) was derived in consideration of the improvement of yield strength by a stress field of the steel material to obtain a high yield strength of the austenitic stainless steel.
As the value of Formula (2) increases, a stress field between lattices may increase due to the difference in atomic size between alloying elements. Accordingly, as the value of Formula (2) increases, limits of plastic deformation while resisting external stress may increase. In the case where the value of Formula (2) is less than 16, it may be difficult to obtain a desired yield strength of the present disclosure. Preferably, the value of the Formula (2) may be 16 to 19.24, more preferably 16 to 18.5, and even more preferably 17 to 18. The austenitic stainless steel with improved hydrogen embrittlement resistance according to an embodiment of the present disclosure may have an excellent balance between yield strength and tensile strength, and the RNTS value may be further increased.
The austenitic stainless steel with improved hydrogen embrittlement resistance according to an embodiment may have a value of Formula (3) below of 2.0 or less.

Formula (3): Ni / Mn
In Formula (3), Ni and Mn represent the content (wt%) of the respective elements.
The Formula (3) was derived to obtain an excellent austenite phase stability relative to cost.
Ni and Mn are representative elements that may increase an austenite phase stability. However, assuming that austenite phase stabilities are the same, cost competitiveness may increase at a lower Ni/Mn value. Preferably, the value of the Formula (3) may be 0.025 to 2.0, more preferably 0.4 to 2.0, and even more preferably 0.4 to 0.9. Within the above range, the austenitic stainless steel with improved hydrogen embrittlement resistance according to an embodiment of the present disclosure may have further improved yield strength and tensile strength, and at the same time, the RNTS value may be further increased.
The austenitic stainless steel with improved hydrogen embrittlement resistance according to an embodiment of the present disclosure may have an RNTS value, which is an index of hydrogen embrittlement resistance, of 0.90 or more by controlling alloy composition and manufacturing method. The RNTS may preferably be 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 with improved hydrogen embrittlement resistance according to an embodiment of the present disclosure may be advantageous for improving cost competitiveness while having excellent hydrogen embrittlement resistance; and yield strength or tensile strength.
In addition, the austenitic stainless steel with improved hydrogen embrittlement resistance according to an embodiment may have a yield strength of 300 MPa or more by realizing high strength.
Next, a method for manufacturing an austenitic stainless steel with improved hydrogen embrittlement resistance according to another aspect of the present disclosure is described.
According to an embodiment of the present disclosure, the method for manufacturing an austenitic stainless steel with improved hydrogen embrittlement resistance may include: manufacturing a slab including, in percent by weight (wt%), more than 0% and 0.03% or less of carbon (C), 0.15% or more and 0.25% or less of nitrogen (N), more than 0% and 1.0% or less of silicon (Si), more than 0% and 10.0% or less of manganese (Mn), 16.0% or more and 22.0% or less of chromium (Cr), more than 0% and 6.0% or less of nickel (Ni), more than 0% and 1.6% or less of copper (Cu), 0% or more and 0.8% or less of molybdenum (Mo), the remainder of iron (Fe), and inevitable impurities; and hot rolling the slab and then hot annealing at 1050 to 1150°C to manufacture a hot-rolled steel sheet, wherein the slab may have a value of Formula (1) of 250 or more. Preferably, the value of Formula (1) below may be 250 to 311.84, more preferably 250 to 300, and even more preferably 260 to 295.

Formula (1): Ni_eq X D_c
In Formula (1), Ni_eq (Ni equivalent) is Ni + 0.65 Cr + 0.98 Mo + 1.05 Mn + 0.35 Si + 12.6 C + 33.6 N, 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 represent the content (wt%) of the respective elements.
The slab may have a value of Formula (2) of 16 or more. Preferably, the value of the Formula (2) may be 16 to 19.24, more preferably 16 to 18.5, and even more preferably 17 to 18.

Formula (2): 4.4 + 23 (C + N) + 1.3 Si + 0.24 (Cr + Ni + Mn)
In Formula (2), C, N, Si, Mn, Cr, and Ni represent the content (wt%) of the respective elements.
The slab may have a value of Formula (3) of 2.0 or less. Preferably, the value of the Formula (3) may be 0.025 to 2.0, more preferably 0.4 to 2.0, and even more preferably 0.4 to 0.9.

Formula (3): Ni / Mn
In Formula (3), Ni and Mn represent the content (wt%) of the respective elements.
The reasons for numerical limitations of the component ranges of the respective alloy compositions, Formula (1), Formula (2), and Formula (3) are as described above, and each manufacturing step is described in more detail below.
The method for manufacturing an austenitic stainless steel with improved hydrogen embrittlement resistance according to an embodiment may include manufacturing a slab that satisfies the above alloy composition, Formula (1), Formula (2), and Formula (3), and then performing a series of hot rolling and hot annealing. In addition, if required, the method for manufacturing an austenitic stainless steel with improved hydrogen embrittlement resistance according to an embodiment may further include cold rolling and cold annealing processes.
First, the slab may be hot-rolled, and hot-annealed at 1050 to 1150°C to manufacture a hot-rolled steel sheet.
In the case where the hot annealing temperature is low, a residual martensite fraction may be high, causing elongation to deteriorate. However, in the case where the hot annealing temperature is excessively high, strength may be reduced due to grain coarsening.
Thereafter, if required, the method may further include cold rolling the hot-rolled steel sheet, and cold annealing at 1050 to 1150°C to manufacture a cold-rolled steel sheet.
In the case where the cold annealing temperature is low, recrystallization may not be sufficient, causing elongation to decrease. However, in the case where the cold annealing temperature is excessively high, crystal grains coarsen, and the depth of oxides formed at grain boundaries deepens, and thus surface quality after pickling may become inferior.
Hereinafter, the present disclosure is described in more detail through embodiments. However, the descriptions of the embodiments are only for illustrating the implementation of the present disclosure, and the present disclosure is not limited by the descriptions of the embodiments. This is because the scope of the rights of the present disclosure is determined by matters described in the scope of claims and matters reasonably inferred therefrom.

{Embodiments}

With respect to the various alloy component ranges shown in Table 1 below, a slab was manufactured in a vacuum induction melting furnace. The manufactured slab was hot-rolled, and hot-annealed at 1100°C to manufacture a hot-rolled steel sheet. The hot-rolled steel sheet was cold-rolled, and cold-annealed at 1100°C to manufacture specimens.

[Table 1]

Classification	Alloy component (wt%)
Classification	C	Si	Mn	Ni	Cr	Cu	Mo	N
Example 1	0.03	0.4	10.0	3.5	16.5	1.0	0.0	0.23
Example2	0.02	0.4	7.6	6.0	17.4	0.4	0.0	0.19
Example3	0.02	0.4	7.6	5.5	17.5	0.4	0.0	0.21
Example4	0.02	0.4	9.8	5.4	17.6	0.4	0.0	0.19
Example5	0.02	0.4	5.9	5.6	18.0	0.4	0.0	0.19
Example6	0.02	0.4	7.8	5.9	18.2	0.4	0.0	0.21
Example7	0.02	0.4	7.0	6.0	21.8	0.4	0.0	0.19
Example8	0.02	0.4	6.5	5.6	18.1	1.6	0.0	0.21
Comparative Example 1	0.02	0.5	0.9	8.0	18.8	0.3	0.0	0.02
Comparative Example2	0.06	0.5	0.9	7.8	17.8	0.2	0.0	0.04
Comparative Example3	0.02	0.6	1.1	10.2	16.1	0.3	2.1	0.02
Comparative Example4	0.02	0.5	1.3	10.1	16.7	0.3	2.1	0.07
Comparative Example5	0.03	0.4	10.0	2.5	16.2	1.0	0.0	0.22
Comparative Example6	0.02	0.4	7.9	5.0	16.8	0.4	0.0	0.18
Comparative Example7	0.02	0.4	5.6	5.5	16.5	0.4	0.0	0.15
Comparative Example8	0.02	0.4	5.7	5.6	17.3	0.4	0.0	0.18
Comparative Example9	0.02	0.4	3.0	6.2	17.9	1.2	0.0	0.19
Comparative Example 10	0.02	0.4	4.5	6.0	18.0	1.2	0.0	0.20
Comparative Example 11	0.02	0.4	4.5	8.0	18.3	0.4	0.0	0.17
Comparative Example12	0.02	0.4	1.2	10.3	19.4	0.4	0.0	0.11
Comparative Example13	0.02	0.5	8.9	2.8	16.8	1.9	0.0	0.22
Comparative Example14	0.02	0.4	6.6	5.6	17.9	1.6	0.0	0.16

Table 2 below shows Ni_eq, D_c, the value of Formula (1), the value of Formula (2), the value of Formula (3), yield strength, tensile strength, and RNTS.
Ni_eq (Ni equivalent) was calculated by the formula below.
Ni_eq: Ni + 0.65 Cr + 0.98 Mo + 1.05 Mn + 0.35 Si + 12.6 C + 33.6 N
D_c (normalized diffusion coefficient) was calculated by the formula below.
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))
The value of Formula (1) was calculated by Formula (1) below.

Formula (1): Ni_eq X D_c
In Formula (1), Ni_eq (Ni equivalent) is Ni + 0.65 Cr + 0.98 Mo + 1.05 Mn + 0.35 Si + 12.6 C + 33.6 N, 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 represent the content (wt%) of the respective elements.
The value of Formula (2) was calculated by Formula (2) below.

Formula (2): 4.4 + 23 (C + N) + 1.3 Si + 0.24 (Cr + Ni + Mn)
In Formula (2), C, N, Si, Mn, Cr, and Ni represent the content (wt%) of the respective elements.
The value of Formula (3) was calculated by Formula (3) below.

Formula (3): Ni / Mn
In Formula (3), Ni and Mn represent the content (wt%) of the respective elements.
Yield strength and tensile strength were measured by conducting a tensile test on specimens according to the JIS13B standards at room temperature at a tensile speed of 15 mm per minute, using a tensile tester from Zwick Roell.
RNTS was calculated by Formula (4) below. Meanwhile, RNTS was measured by conducting a test on a notched tensile test specimen in a high-pressure hydrogen environment of 1000 bar or less at room temperature under the condition of a crosshead speed of 0.05 mm/min or less.
Formula (4): (notch tensile strength (MPa) in high-pressure hydrogen atmosphere of 1000 bar or less χ notch tensile strength (MPa) in normal atmospheric atmosphere)

Meanwhile, it may be determined that the higher the RNTS, the more improved the hydrogen embrittlement resistance.

[Table 2]

Classification	Ni_eq	D_c	Formula (1)	Formula (2)	Formula (3)	Yield strength (MPa)	Tensile strength (MPa)	RNTS
Example 1	32.97	7.76	255.8	18.1	0.4	348	677	0.913
Example2	32.07	7.84	251.4	17.2	0.8	314	651	0.914
Example3	32.30	7.97	257.4	17.6	0.7	325	662	0.912
Example4	33.91	7.68	260.4	17.6	0.6	346	659	0.983
Example5	30.27	8.29	250.9	16.8	0.9	353	683	0.920
Example6	33.37	7.95	265.3	17.9	0.8	359	673	0.968
Example7	34.30	8.50	291.6	18.1	0.9	348	667	0.999
Example8	31.64	7.92	250.6	17.5	0.9	359	659	0.908
Comparative Example 1	22.26	8.73	194.3	12.6	8.9	265	661	0.753
Comparative Example2	22.59	8.68	196.1	13.7	8.7	247	623	0.756
Comparative Example3	25.01	7.15	178.8	12.7	9.3	238	556	0.794
Comparative Example4	27.16	7.25	196.9	13.9	7.8	277	615	0.827
Comparative Example5	31.44	7.95	249.9	17.6	0.3	355	692	0.870
Comparative Example6	30.66	7.93	243.1	16.6	0.6	338	675	0.894
Comparative Example7	27.54	8.15	224.5	15.5	1.0	284	682	0.794
Comparative Example8	29.27	8.23	240.9	16.4	1.0	335	684	0.855
Comparative Example9	27.76	8.44	234.3	16.3	2.1	330	657	0.810
Comparative Example 10	29.54	8.23	243.1	16.8	1.3	347	656	0.821
Comparative Example 11	30.72	7.99	245.5	16.7	1.8	315	631	0.888
Comparative Example12	28.26	8.14	230.0	15.3	8.6	282	586	0.785
Comparative Example 13	30.88	7.93	244.9	17.4	0.3	374	677	0.861
Comparative Example14	29.93	7.88	235.8	16.3	0.8	323	627	0.799

Referring to Table 2, Examples 1 to 8 satisfied the alloy components, the value of Formula (1), the value of Formula (2), the value of Formula (3), and the manufacturing method of the present disclosure. Accordingly, Examples 1 to 8 satisfied an RNTS value of 0.90 or more and a yield strength of 300 MPa or more. That is, Examples 1 to 8 may be evaluated as having excellent cost competitiveness while improving yield strength and hydrogen embrittlement resistance.
However, Comparative Examples 1 to 14 did not satisfy the value of Formula (1) of 250 or more. Accordingly, Comparative Examples 1 to 14 did not satisfy the RNTS value of 0.90 or more. That is, Comparative Examples 1 to 14 may be evaluated as having relatively inferior hydrogen embrittlement resistance.
In addition, Comparative Examples 1 to 4, 7, and 12 did not satisfy the value of Formula (1) of 250 or more, and at the same time did not satisfy the value of Formula (2) of 16 or more. Accordingly, Comparative Examples 1 to 4, 7, and 12 have relatively inferior hydrogen embrittlement resistance and did not satisfy the yield strength of 300 MPa or more. That is, Comparative Examples 1 to 4, 7, and 12 may be evaluated as being difficult to apply in an environment where stress acts due to their inferior hydrogen embrittlement resistance and strength.
As described above, according to an embodiment of the present disclosure, by controlling the alloy components and manufacturing method, an austenitic stainless steel with excellent cost competitiveness while improving yield strength and hydrogen embrittlement resistance, and a manufacturing method thereof may be provided.

Claims

An austenitic stainless steel with improved hydrogen embrittlement resistance, comprising, in percent by weight (wt%), more than 0% and 0.03% or less of carbon (C), 0.15% or more and 0.25% or less of nitrogen (N), more than 0% and 1.0% or less of silicon (Si), more than 0% and 10.0% or less of manganese (Mn), 16.0% or more and 22.0% or less of chromium (Cr), more than 0% and 6.0% or less of nickel (Ni), more than 0% and 1.6% or less of copper (Cu), 0% or more and 0.8% or less of molybdenum (Mo), the remainder of iron (Fe), and inevitable impurities, and
wherein a value of Formula (1) below is 250 or more,

Formula (1): Ni_eq X D_c

(wherein Ni_eq (Ni equivalent) is Ni + 0.65 Cr + 0.98 Mo + 1.05 Mn + 0.35 Si + 12.6 C + 33.6N,

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 represent the content (wt%) of the respective elements).
The austenitic stainless steel of claim 1, wherein a value of Formula (2) below is 16 or more,

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

(wherein C, N, Si, Mn, Cr, and Ni represent the content (wt%) of the respective elements).
The austenitic stainless steel of claim 1, wherein a value of Formula (3) below is 2.0 or less,

Formula (3): Ni / Mn

(wherein Ni and Mn represent the content (wt%) of the respective elements).
The austenitic stainless steel of claim 1, wherein a relative notch tensile strength (RNTS) value is 0.90 or more.
The austenitic stainless steel of claim 1, wherein a yield strength is 300 MPa or more.
A method for manufacturing an austenitic stainless steel with improved hydrogen embrittlement resistance, the method comprising:
manufacturing a slab including, in percent by weight (wt%), more than 0% and 0.03% or less of carbon (C), 0.15% or more and 0.25% or less of nitrogen (N), more than 0% and 1.0% or less of silicon (Si), more than 0% and 10.0% or less of manganese (Mn), 16.0% or more and 22.0% or less of chromium (Cr), more than 0% and 6.0% or less of nickel (Ni), more than 0% and 1.6% or less of copper (Cu), 0% or more and 0.8% or less of molybdenum (Mo), the remainder of iron (Fe), and inevitable impurities; and

hot rolling the slab, and then hot annealing at 1050 to 1150°C to manufacture a hot-rolled steel sheet,

wherein the slab has a value of Formula (1) below of 250 or more,

Formula (1): Ni_eq X D_c

(wherein Ni_eq (Ni equivalent) is Ni + 0.65 Cr + 0.98 Mo + 1.05 Mn + 0.35 Si + 12.6 C + 33.6 N,

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 represent the content (wt%) of the respective elements).
The method of claim 6, wherein the slab has a value of Formula (2) below of 16 or more,

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

(wherein C, N, Si, Mn, Cr, and Ni represent the content (wt%) of the respective elements).
The method of claim 6, wherein the slab has a value of Formula (3) below of 2.0 or less,

Formula (3): Ni / Mn

(wherein Ni and Mn represent the content (wt%) of the respective elements).
The method of claim 6, further comprising:
cold rolling the hot-rolled steel sheet, and cold annealing at 1500 to 1150°C to manufacture a cold-rolled steel sheet.