Austenitic stainless steel with improved hydrogen embrittlement resistance and low-temperature impact toughness and manufacturing method thereof

Abstract

The present invention provides an austenitic stainless steel having improved resistance to hydrogen embrittlement and low-temperature impact toughness by controlling the alloy components and manufacturing method, and a manufacturing method thereof. [Solution] The austenitic stainless steel with improved hydrogen embrittlement resistance and low-temperature impact toughness is composed, by weight, of C: more than 0% and 0.1% or less, Si: more than 0% and 1.5% or less, Cr: 12-23%, Ni: 1-12%, Mn: 10-25%, Cu: more than 0% and 1.2% or less, N: 0.1-0.3%, with the remainder being Fe and impurities, and is characterized by having a value of the following formula (1) of 1.0-12.3, a -196°C Charpy impact toughness of 50J or more, and a relative notch tensile strength (RNTS) of 0.8-1.0. Equation (1): (Ni + 15 × N) × (0.03 × Mn) In formula (1), Ni, N, and Mn represent the content (wt %) of each element.

Description

[Technical Field]

[0001] The present invention relates to an austenitic stainless steel having improved hydrogen embrittlement resistance and low-temperature impact toughness and a manufacturing method thereof, and more particularly to an austenitic stainless steel having improved hydrogen embrittlement resistance and low-temperature impact toughness by controlling alloy components and a manufacturing method thereof, and a manufacturing method thereof. [Background technology]

[0002] As the development and widespread use of hydrogen-powered fuel cell vehicles expands, there is a demand for the development of hydrogen storage containers and components. Hydrogen storage containers are divided into liquid hydrogen and gaseous hydrogen depending on the form of hydrogen, and the operating temperature varies depending on the form of hydrogen. Therefore, materials used for hydrogen storage containers must have minimal deterioration in their physical properties due to hydrogen at various temperatures.

[0003] Meanwhile, liquefied hydrogen storage methods are expected to be used in a variety of fields due to their higher storage efficiency compared to gas storage methods. Therefore, materials used in hydrogen storage containers must be designed to withstand deterioration in physical properties not only at room temperature but also at cryogenic temperatures.

[0004] In addition, hydrogen storage containers are often exposed to gaseous hydrogen, which can cause hydrogen embrittlement. Therefore, hydrogen storage containers must be made of materials that take into consideration hydrogen embrittlement caused by gaseous hydrogen.

[0005] In other words, materials used for hydrogen containers must be selected taking into consideration both the temperature-induced deterioration of physical properties and the hydrogen-induced deterioration of physical properties. However, it is not easy to achieve both the property of preventing the temperature-induced deterioration and the property of preventing the hydrogen-induced deterioration at the same time. Summary of the Invention [Problem to be solved by the invention]

[0006] In order to solve the above-mentioned problems, an object of the present invention is to provide an austenitic stainless steel having improved hydrogen embrittlement resistance and low-temperature impact toughness by controlling the alloy components and manufacturing method, and a manufacturing method thereof. [Means for solving the problem]

[0007] The austenitic stainless steel with improved hydrogen embrittlement resistance and low-temperature impact toughness contains, by weight, C: more than 0% and not more than 0.1%, Si: more than 0% and not more than 1.5%, Cr: 12 to 23%, Ni: 1 to 12%, Mn: 10 to 25%, Cu: more than 0% and not more than 1.2%, N: 0.1 to 0.3%, with the remainder being Fe and impurities, and is characterized in that the value of the following formula (1) is 1.0 to 12.3.

[0008] Equation (1): (Ni + 15 × N) × (0.03 × Mn)

[0009] In formula (1), Ni, N, and Mn represent the content (wt %) of each element.

[0010] Austenitic stainless steel with improved hydrogen embrittlement resistance and low-temperature impact toughness can have a Charpy impact toughness value of 50J or more at -196°C.

[0011] Austenitic stainless steel with improved hydrogen embrittlement resistance and low-temperature impact toughness may have a relative notch tensile strength (RNTS) of 0.8 to 1.0.

[0012] A method for producing austenitic stainless steel with improved hydrogen embrittlement resistance and low-temperature impact toughness includes the steps of producing a slab containing, by weight, more than 0% and 0.1% or less C, more than 0% and 1.5% or less Si, 12 to 23% Cr, 1 to 12% Ni, 10 to 25% Mn, more than 0% and 1.2% or less Cu, 0.1 to 0.3% N, and the remainder being Fe and impurities; hot-rolling the slab to produce a hot-rolled steel sheet; and annealing the hot-rolled steel sheet, wherein the slab is characterized in that the value of the following formula (1) is 1.0 to 12.3:

[0013] Equation (1): (Ni + 15 × N) × (0.03 × Mn) In formula (1), Ni, N, and Mn represent the content (wt %) of each element.

[0014] In the method for producing austenitic stainless steel with improved hydrogen embrittlement resistance and low-temperature impact toughness, the annealing can be carried out at 900°C to 1200°C. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide an austenitic stainless steel having improved resistance to hydrogen embrittlement and low-temperature impact toughness by controlling the alloy components and the manufacturing method, and a manufacturing method thereof. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be described in detail below. 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 present 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.

[0017] The reasons for limiting the numerical values ​​of the alloying element contents in the present invention will be explained below. In the following, the units are % by weight unless otherwise specified.

[0018] An austenitic stainless steel with improved hydrogen embrittlement resistance and low-temperature impact toughness may contain, by weight, C: more than 0% and not more than 0.1%, Si: more than 0% and not more than 1.5%, Cr: 12 to 23%, Ni: 1 to 12%, Mn: 10 to 25%, Cu: more than 0% and not more than 1.2%, N: 0.1 to 0.3%, and the remainder consisting of Fe and impurities.

[0019] The C (carbon) content may be more than 0% and 0.1% or less. C is an element that is effective in stabilizing austenite, suppressing δ-ferrite, and increasing strength through solid solution strengthening. However, excessive C content can easily combine with carbide-forming elements (Cr, Ti, Nb, etc.) and reduce the corrosion resistance, ductility, and toughness of the base material. In consideration of this, the C content may be 0.1% or less. Preferably, the C content may be 0.02 to 0.1%.

[0020] The Si (silicon) content may be more than 0% and not more than 1.5%. Silicon is an element effective in improving corrosion resistance and solid solution strengthening. However, excessive silicon content increases the stability of the ferrite phase, which can lead to the formation of intermetallic compounds such as sigma phases, reducing the ductility and toughness of the base material. In consideration of this, the silicon content may be greater than 0% and not more than 1.5%. Preferably, the silicon content is 0.4 to 1.5%, and more preferably 0.4 to 0.5%.

[0021] The Cr (chromium) content may be 12 to 23%. Cr is an element that must be added to improve the corrosion resistance of stainless steel. Taking this into consideration, Cr can be added in an amount of 12% or more. However, if the Cr content is excessive, excess δ-ferrite may remain in the steel, potentially reducing hot workability. Furthermore, if the Cr content is excessive, the austenite phase in the steel becomes unstable, and adding a large amount of Ni for phase stability may increase costs. Preferably, the Cr content may be 12 to 21.4%.

[0022] The Ni (nickel) content may be 1 to 12%. Ni, together with Mn and N, is a powerful austenite-stabilizing element. Ni is also an important element that directly affects hydrogen embrittlement and low-temperature toughness. Furthermore, Ni is an effective element for suppressing δ-ferrite formation. Taking this into consideration, Ni can be added in an amount of 1% or more. However, excessive Ni content increases the probability of surface bonding, potentially reducing price competitiveness. Taking this into consideration, the upper limit of the Ni content can be limited to 12%. Preferably, Ni is 1.0 to 12%, and more preferably, Ni is 1.3 to 5.0%.

[0023] The Mn (manganese) content may be 10 to 25%. Mn, along with Ni and N, is a powerful austenite-stabilizing element. Furthermore, Mn can replace expensive Ni and is an essential element for cost reduction. Furthermore, Mn is an effective element for increasing austenite phase stability and suppressing deterioration of physical properties in a hydrogen environment. Considering this, Mn can be added in an amount of 10% or more. However, if the Mn content is excessive, corrosion resistance may be rapidly reduced due to the formation of MnS inclusions. Furthermore, if the Mn content is excessive, problems may arise due to the increase in Mn. Considering this, the upper limit of the Mn content can be limited to 25%. Preferably, the Mn content is 10.6 to 25%, more preferably 10.6 to 19.3%.

[0024] The Cu (copper) content may be more than 0% and not more than 1.2%. Cu is an element useful for stabilizing the austenite phase and can be used in place of expensive Ni. However, excessive Cu content can lead to the formation of a low-melting-point phase, which can reduce hot workability and result in poor surface quality. In consideration of this, the Cu content can be more than 0% and not more than 1.2%, preferably 0.7% to 1.2%, and more preferably 0.7 to 0.9%.

[0025] The N (nitrogen) content may be 0.1 to 0.3%. N is an austenite stabilizing element and is an element that is effective in further improving strength through solid solution strengthening. In consideration of this, N can be added in an amount of 0.1% or more. However, if the N content is excessive, deterioration of surface quality may occur due to the generation of pores. In consideration of this, the upper limit of the N content can be limited to 0.3%. Preferably, the N content can be 0.1 to 0.2%.

[0026] The remaining component of the present invention is iron (Fe). However, in a normal manufacturing process, unintentional impurities may be inevitably mixed in from the 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 thereof will be specifically mentioned in this specification.

[0027] One of the main causes of embrittlement in steel materials is the hydrogen environment and the temperature the material is exposed to. Therefore, when considering the use of steel materials in cryogenic environments such as liquefied hydrogen, it is necessary to evaluate their toughness at cryogenic temperatures and their resistance to hydrogen embrittlement.

[0028] Steel materials exposed to hydrogen environments are likely to be exposed not only to hydrogen environments but also to a wide range of temperatures. Furthermore, as temperatures drop, general steel materials tend to lose toughness and become brittle. Therefore, even if general steel materials appear to be fine at room temperature, they may show a tendency for their physical properties to deteriorate as temperatures drop.

[0029] In general, it is known that an austenite structure is advantageous for low-temperature toughness, while a martensite structure, a ferrite structure, etc. are relatively disadvantageous for low-temperature toughness.

[0030] However, despite their relatively excellent low-temperature toughness, general-purpose austenitic stainless steels can suffer from extreme hydrogen embrittlement when exposed to a hydrogen environment, which can cause problems with the long-term durability of the material.

[0031] According to one example of the present invention, by controlling the value of the following formula (1), which consists of austenite stabilizing elements Ni, N, and Mn, to 1.0 to 12.3, it is possible to provide an austenitic stainless steel having simultaneously improved hydrogen embrittlement resistance and low-temperature impact toughness.

[0032] Equation (1): (Ni + 15 × N) × (0.03 × Mn) In formula (1), Ni, N, and Mn represent the content (wt %) of each element. The above formula (1) is a hydrogen property relational formula, and is composed of Ni, N, and Mn, which can have a direct effect on hydrogen-related properties.

[0033] Meanwhile, Mn is an element that can replace Ni and has a cost advantage. Therefore, it is necessary to adjust the content of Mn and Ni in order to improve hydrogen-related properties while ensuring price competitiveness.

[0034] Therefore, when the value of the above formula (1) is 1.0 to 12.3, the hydrogen embrittlement resistance and low-temperature impact toughness of the austenitic stainless steel can be improved at the same time while maintaining price competitiveness.

[0035] The value of the above formula (1) can be specifically 1.0 to 10, more specifically 1.0 to 5, and even more specifically 1.2 to 3.6. Within the above ranges, the austenitic stainless steel of the present invention with improved hydrogen embrittlement resistance and low-temperature impact toughness can further improve the balance between the property of preventing deterioration of physical properties due to temperature and the property of preventing deterioration of physical properties due to hydrogen, thereby further enhancing the effect of simultaneously improving hydrogen embrittlement resistance and low-temperature impact toughness.

[0036] By controlling the alloy composition and manufacturing method, austenitic stainless steel with improved hydrogen embrittlement resistance and low-temperature impact toughness can have a Charpy impact toughness value at -196°C of 50 J or more, specifically 60 J or more, more specifically 100 J or more. In other words, since the present invention has excellent low-temperature impact toughness, it can be used not only at room temperature but also in low-temperature environments.

[0037] Austenitic stainless steel with improved hydrogen embrittlement resistance and low-temperature impact toughness may have a relative notch tensile strength (RNTS) of 0.8 to 1.0. Relative notch tensile strength (RNTS) is the notch tensile strength in a hydrogen environment (NTS) H It can be expressed as the ratio of the notched tensile strength in air (NTSair) to the strength in air (NTS).

[0038] TIFF2025542025000001.tif16129

[0039] It can be interpreted that the closer the relative notch tensile strength (RNTS) value is to 1.0, the less hydrogen embrittlement due to hydrogen is observed.

[0040] According to the present invention, the relative notch tensile strength (RNTS) value is 0.8 to 1.0, specifically 0.81 to 0.99, more specifically 0.81 to 0.93, and the hydrogen embrittlement resistance is very excellent. Furthermore, within the above range, the austenitic stainless steel according to the present invention has both the property of preventing deterioration of physical properties due to temperature and the property of preventing deterioration of physical properties due to hydrogen, and can further improve the hydrogen embrittlement resistance and low-temperature impact toughness.

[0041] Next, the method of the present invention for producing an austenitic stainless steel having improved hydrogen embrittlement resistance and low-temperature impact toughness will be described.

[0042] A method for producing austenitic stainless steel with improved hydrogen embrittlement resistance and low-temperature impact toughness includes the steps of producing a slab containing, by weight, C: more than 0% and 0.1% or less, Si: more than 0% and 1.5% or less, Cr: 12 to 23%, Ni: 1 to 12%, Mn: 10 to 25%, Cu: more than 0% and 1.2% or less, N: 0.1 to 0.3%, and the remainder being Fe and impurities; hot-rolling the slab to produce a hot-rolled steel sheet; and annealing the hot-rolled steel sheet, wherein the slab may have a value of the following formula (1) of 1.0 to 12.3:

[0043] Equation (1): (Ni + 15 × N) × (0.03 × Mn) In formula (1), Ni, N, and Mn represent the content (wt %) of each element.

[0044] The ranges of the components of each alloy composition and the reasons for limiting the values ​​in formula (1) are as described above. Each manufacturing step will be described in more detail below.

[0045] After the slabs satisfying the alloy composition and equation (1) are produced, they can undergo a series of hot rolling and annealing steps.

[0046] The annealing can be carried out at a temperature of 900°C to 1200°C.

[0047] In the annealing process after hot rolling, the annealing temperature can have a significant effect on the residual stress release and the microstructure.

[0048] If the annealing temperature is less than 900°C, coarse carbides are formed, making the structure uneven, and Cr is generated around the grain boundaries. 23 C6 precipitates may form, which may cause intergranular corrosion. However, if the annealing temperature exceeds 1200°C, the grains may become excessively coarsened.

[0049] The present invention will be described in detail below. 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 that can be reasonably inferred from them. [Example]

[0050] Slabs were produced by melting the alloys having the various alloy composition ranges shown in Table 1 below in a vacuum melting furnace. The slabs were hot-rolled to produce hot-rolled steel sheets, which were then annealed at 1050°C to produce test specimens.

[0051] [Table 1] The formula (1) values, Charpy impact toughness, and relative notched tensile strength (RNTS) are shown in the following Table 2. The formula (1) values ​​are shown by calculation using the following formula (1).

[0052] Equation (1): (Ni + 15 × N) x (0.03 × Mn) In formula (1), Ni, N, and Mn represent the content (wt %) of each element.

[0053] Charpy impact toughness was determined by impact testing at a temperature of -196°C using ASTM E23 type A specimen specifications.

[0054] Relative notch tensile strength (RNTS) was measured by charging hydrogen into steel using an electrochemical method and then conducting a slow strain rate tensile (SSRT) test. The relative notch tensile strength specimen was prepared using the ASTM E8 test piece standard and the slow strain rate tensile test was conducted in accordance with ASTM G129. The relative notch tensile strength (RNTS) value was calculated using the following formula:

[0055] TIFF2025542025000003.tif16129

[0056] It can be interpreted that the closer the relative notch tensile strength (RNTS) value is to 1.0, the less hydrogen embrittlement due to hydrogen is observed.

[0057] [Table 2]

[0058] As shown in Table 2, Examples 1 to 20 satisfied the alloy composition, formula (1), and manufacturing method proposed in the disclosed invention. Therefore, Examples 1 to 20 had a −196°C Charpy impact toughness value of 50 J or more and a relative notch tensile strength (RNTS) value of 0.8 to 1.0. That is, Examples 1 to 20 were excellent in both hydrogen embrittlement resistance and low-temperature impact toughness, but had a low Ni content, making them price competitive. However, Comparative Examples 1 to 5 did not satisfy the formula (1) value of 1.0 to 12.3. Therefore, Comparative Examples 1 to 5 did not satisfy the relative notch tensile strength (RNTS) value of 0.8 to 1.0. That is, Comparative Examples 1 to 5 had inferior hydrogen embrittlement resistance. Furthermore, Comparative Examples 1 and 2 had a higher Ni content than Examples 1 to 20 and Comparative Examples 3 to 5. Therefore, Comparative Examples 1 and 2 had lower price competitiveness.

[0059] Furthermore, the Ni content was less than 1% and the Mn content was less than 10% in Comparative Example 5. Furthermore, the relative notch tensile strength (RNTS) value was the lowest in Comparative Example 5. In other words, Comparative Examples 1 to 5 were the most inferior in hydrogen embrittlement resistance.

[0060] According to the present invention, by controlling the alloy composition and manufacturing method, it is possible to provide an austenitic stainless steel having improved hydrogen embrittlement resistance and low-temperature impact toughness, and a manufacturing method thereof.

[0061] Furthermore, according to the present invention, by reducing the amount of expensive Ni element added, it is possible to provide an austenitic stainless steel that is very cost-competitive.

Claims

1. The alloy contains, by weight, C: more than 0% and 0.1% or less, Si: more than 0% and 1.5% or less, Cr: 12 to 23%, Ni: 1 to 12%, Mn: 10 to 25%, Cu: more than 0% and 1.2% or less, N: 0.1 to 0.3%, and the remainder being Fe and impurities; An austenitic stainless steel having improved hydrogen embrittlement resistance and low-temperature impact toughness, characterized in that the value of the following formula (1) is 1.0 to 12.3: Formula (1): (Ni + 15 × N) × (0.03 × Mn) (In formula (1), Ni, N, and Mn represent the content (wt%) of each element.)

2. 2. The austenitic stainless steel having improved resistance to hydrogen embrittlement and low-temperature impact toughness according to claim 1, characterized in that it has a -196°C Charpy impact toughness value of 50J or more.

3. 2. The austenitic stainless steel having improved hydrogen embrittlement resistance and low-temperature impact toughness according to claim 1, characterized in that the relative notch tensile strength (RNTS) is 0.8 to 1.

0.

4. A step of producing a slab containing, in weight percent, C: more than 0% to 0.1% or less, Si: more than 0% to 1.5% or less, Cr: 12 to 23%, Ni: 1 to 12%, Mn: 10 to 25%, Cu: more than 0% to 1.2% or less, N: 0.1 to 0.3%, with the remainder being Fe and impurities; hot rolling the slab to produce a hot rolled steel sheet; and Annealing the hot-rolled steel sheet; The slab has a value of the following formula (1) of 1.0 to 12.

3. Formula (1): (Ni + 15 × N) × (0.03 × Mn) (In formula (1), Ni, N, and Mn represent the content (wt%) of each element.)

5. 5. The method for producing austenitic stainless steel with improved hydrogen embrittlement resistance and low-temperature impact toughness according to claim 4, wherein the annealing is carried out at a temperature of 900 to 1200°C.

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