Austenitic stainless steel and manufacturing method therefor

Abstract

The present invention provides an ultra-low cost austenitic stainless steel ensuring excellent toughness and appropriate corrosion resistance, and thus can be used widely and in a variety of ways across industries including eco-friendly energy transfer and transport. The provided austenitic stainless steel comprises, by wt%, 0.08% or less of carbon (C), 1.0% or less of silicon (Si), 18.0-33.0% of manganese (Mn), 9.0-19.0% of chromium (Cr), 0.5% or less of nickel (Ni), 0.1% or less of nitrogen (N), and the balance of iron (Fe) and other inevitable impurities, wherein parameter α for ensuring manufacturability has the value of 23.0 or greater, and parameter β for ensuring material properties has the value of 0.12 or less. (1) 23.0 ≤ α = Ni + 0.65Cr + 0.81Mn + 0.35Si + 12.6C + 18.6N (2) β = C + N ≤ 0.12 (amount of alloy elements are in wt%)

Description

Austenitic stainless steel and method of manufacturing the same

[0001] The present invention relates to a low-cost austenitic stainless steel material and a method for manufacturing the same, which is universally applicable in industries requiring excellent toughness but not relatively high corrosion resistance.

[0002] Austenitic stainless steel is a type of steel widely utilized across various industries due to its excellent formability and elongation, which allow it to be used in shapes and environments that meet diverse customer needs without issue. Representative austenitic stainless steel grades include Stainless 304 and 304L, which are the most universally used steels. They are well known for their versatility, being utilized in a wide range of environments from cryogenic to high temperatures, and are widely used in industries ranging from kitchenware to shipbuilding and construction.

[0003] However, there are many industries that do not require the corrosion resistance typically exhibited by standard stainless steel. A representative market is the infrastructure market for the transportation and storage of eco-friendly energy sources (such as hydrogen, ammonia, and natural gas), the use of which has recently increased to achieve carbon neutrality. Tanks and equipment manufactured in this sector do not actually require the corrosion resistance of the 304 grade. The properties required by this industry are formability, represented by the elongation of austenitic steel, as well as toughness at cryogenic temperatures and weldability. In these markets, corrosion resistance is required merely to the minimum extent necessary to prevent rust from forming during various tests and manufacturing processes. Furthermore, the architectural interior materials market often does not require 304-level corrosion resistance, and markets requiring non-magnetism frequently do not demand superior corrosion resistance.

[0004] In response to these industrial demands, the development of low-cost austenitic stainless steel, represented by 200-series stainless steel, is actively underway. However, to reduce raw material costs, these materials generally utilize high levels of carbon and nitrogen, resulting in the development of high-strength materials. While such high strength offers advantages in terms of application, such as reduced thickness, it presents various disadvantages in terms of manufacturing. High-strength materials not only place a burden on the rolling process during production but also cause manufacturing costs by making shape correction difficult, requiring additional straightening equipment. Furthermore, this steel grade has the disadvantage of requiring additional equipment investment and modifications because it is difficult to utilize existing equipment designed for general-purpose 304(L), and it also causes the problem of drastically shortening the lifespan of molds.

[0005] One aspect of the present invention aims to provide an ultra-low-cost austenitic stainless steel with material characteristics similar to those of a general-purpose austenitic stainless steel that has excellent manufacturability and secures minimal corrosion resistance, and a method for manufacturing the same.

[0006] An austenitic stainless steel according to one embodiment of the present invention comprises, in weight percent, carbon (C): 0.08% or less (excluding 0), silicon (Si): 1.0% or less (excluding 0), manganese (Mn): 18.0~33.0%, chromium (Cr): 9.0~19.0%, nickel (Ni): 0.5% or less (excluding 0), nitrogen (N): 0.10% or less (excluding 0), the remainder being Fe and unavoidable impurities, and may satisfy the following parameter α value of 23.0 or more and the following parameter β value of 0.12 or less.

[0007] α = [Ni] + 0.65*[Cr] + 0.81*[Mn] + 0.35*[Si] + 12.6*[C] + 18.6*[N]

[0008] β = [C] + [N]

[0009] (Here, [Ni], [Cr], [Mn], [Si], [C], and [N] represent the content of each element in weight percent)

[0010] In addition, an austenitic stainless steel according to another embodiment of the present invention may further include one or more of phosphorus (P): 0.035% or less and sulfur (S): 0.01% or less in weight%.

[0011] In addition, an austenitic stainless steel according to another embodiment of the present invention may contain 95% or more of an austenite phase in terms of area fraction.

[0012] In addition, an austenitic stainless steel according to another embodiment of the present invention may contain an ε-martensite phase in an area fraction of 5% or less.

[0013] In addition, according to another embodiment of the present invention, the austenitic stainless steel may have a room temperature yield strength of 270 MPa or less.

[0014] In addition, according to another embodiment of the present invention, the austenitic stainless steel may have a room temperature tensile strength of 700 MPa or less.

[0015] In addition, according to another embodiment of the present invention, the austenitic stainless steel may have an elongation of 30% or more.

[0016] A method for manufacturing an austenitic stainless steel according to one embodiment of the present invention comprises the steps of: providing a steel material comprising, in weight%, carbon (C): 0.08% or less (excluding 0), silicon (Si): 1.0% or less (excluding 0), manganese (Mn): 18.0~33.0%, chromium (Cr): 9.0~19.0%, nickel (Ni): 0.5% or less (excluding 0), nitrogen (N): 0.10% or less (excluding 0), the remainder being Fe and unavoidable impurities, satisfying the following parameter α value of 23.0 or more and the following parameter β value of 0.12 or less; and performing hot working.

[0017] α = [Ni] + 0.65*[Cr] + 0.81*[Mn] + 0.35*[Si] + 12.6*[C] + 18.6*[N]

[0018] β = [C] + [N]

[0019] (Here, [Ni], [Cr], [Mn], [Si], [C], and [N] represent the content of each element in weight percent)

[0020] In addition, in a method for manufacturing austenitic stainless steel according to another embodiment of the present invention, the hot working may be performed by any one of hot forging, hot extrusion, or hot rolling.

[0021] In addition, a method for manufacturing austenitic stainless steel according to another embodiment of the present invention may include the step of reheating the steel material to 1000 to 1300°C during hot rolling; and the step of finishing the hot rolling at a temperature of 800°C or higher with a total reduction rate of 60% or more.

[0022] In addition, a method for manufacturing austenitic stainless steel according to another embodiment of the present invention may include a step of performing a first solution heat treatment at 900 to 1150°C for 1 to 180 minutes after the hot rolling; and a step of cooling to 500°C.

[0023] In addition, a method for manufacturing austenitic stainless steel according to another embodiment of the present invention may further include the steps of cold rolling with a reduction rate of 50% after the cooling step and performing a secondary solution heat treatment at 00 to 1150°C for 20 to 600 seconds.

[0024] According to the present invention, an ultra-low-cost austenitic stainless steel can be provided that has excellent manufacturability due to phase stability and manufacturing method, secures minimum corrosion resistance required for eco-friendly energy transfer and transportation applications, has a room temperature yield strength of 270 MPa or less and a tensile strength of 700 MPa or less, and can be immediately applied to various industrial sites without changing equipment or making additional investments that use 304(L).

[0025] Preferred embodiments of the present invention are described below. However, embodiments of the present invention may be modified in various other forms, and the technical concept of the present invention is not limited to the embodiments described below. Furthermore, the embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the relevant technical field.

[0026] The terms used in this application are used merely to describe specific examples. For this reason, singular expressions include plural expressions unless the context clearly requires them to be singular. Additionally, it should be noted that terms such as “comprising” or “comprising” used in this application are used to clearly indicate the presence of features, steps, functions, components, or combinations thereof described in the specification, and are not used to preliminarily exclude the existence of other features, steps, functions, components, or combinations thereof.

[0027] Meanwhile, unless otherwise defined, all terms used in this specification shall be understood to have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Accordingly, unless explicitly defined in this specification, specific terms should not be interpreted in an overly ideal or formal sense.

[0028] Additionally, terms such as "about," "substantially," etc., in this specification are used to mean at or near the stated value when inherent manufacturing and material tolerances are presented in the said sense, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosed content in which precise or absolute values ​​are mentioned to aid in understanding the invention.

[0029] Unless otherwise specifically stated in this specification, the % indicating the content of each element is based on weight.

[0030] First, an austenitic stainless steel according to one aspect of the present invention will be described.

[0031] An austenitic stainless steel according to one embodiment of the present invention comprises, in weight percent, carbon (C): 0.08% or less (excluding 0), silicon (Si): 1.0% or less (excluding 0), manganese (Mn): 18.0~33.0%, chromium (Cr): 9.0~19.0%, nickel (Ni): 0.5% or less (excluding 0), nitrogen (N): 0.10% or less (excluding 0), the remainder being Fe and unavoidable impurities.

[0032] Hereinafter, the reason for the numerical limitation of the alloy component content in the embodiments of the present invention will be explained.

[0033] C: 0.08% or less (excluding 0)

[0034] The carbon (C) content is 0.08% or less (excluding 0). Carbon is an element effective for stabilizing the austenite phase and can be added to secure the yield strength of austenitic stainless steel. However, if the content is excessive, it may induce intergranular precipitation of Cr carbides, which may adversely affect ductility, toughness, corrosion resistance, etc., so the upper limit may be limited to 0.08%. Preferably, it may be 0.07% or less, and more preferably, 0.05% or less.

[0035] Si: 1.0% or less (excluding 0)

[0036] The silicon (Si) content is 1.0% or less (excluding 0). Silicon can be added as an element effective in improving the strength of the material while acting as a deoxidizer during the steelmaking process. However, since Si is an element effective in stabilizing the ferrite phase, excessive addition can promote the formation of delta (δ) ferrite, thereby reducing manufacturability and adversely affecting the ductility and low-temperature impact properties of the material; therefore, the upper limit may be limited to 1.0%. Preferably, it may be 0.5% or less.

[0037] Mn: 18.0 to 33.0%

[0038] The manganese (Mn) content is 18.0% or more and 33.0% or less. Manganese is the most critical component in the present invention and corresponds to an austenite phase stabilizing element; it can be added in an amount of 18.0% or more to secure the austenite phase. However, if the content is excessive, it may form an excessive amount of sulfur-based inclusions (MnS), which can reduce the ductility, toughness, and corrosion resistance of the austenitic stainless steel. Furthermore, it may generate Mn fumes during the steelmaking process, which entails manufacturing risks, and lower the melting point of the molten steel, which can drastically reduce hot rolling performance; therefore, the upper limit may be restricted to 33.0%. Preferably, it may be 20.0% or more and 30% or less, and more preferably, 25.0% or more and 30.0% or less.

[0039] Cr: 9.0 to 19.0%

[0040] The chromium (Cr) content is 9.0% or more and 19.0% or less. Although chromium is a ferrite-stabilizing element, it effectively provides a positive effect on manufacturability by suppressing the formation of martensite phases and can be added in an amount of 9.0% or more as a basic element to secure the corrosion resistance required for stainless steel. However, if the content is excessive, manufacturing costs increase, and as a large amount of delta (δ) ferrite is formed in the slab, causing a decrease in hot workability and adverse effects on material properties, the upper limit may be limited to 19.0%. Preferably, it may be 9.0% to 17.0%, and more preferably, it may be 9.0% to 15.0%.

[0041] Ni: 0.5% or less (excluding 0)

[0042] The nickel (Ni) content is 0.5% or less. Nickel is a strong austenite phase stabilizing element that provides good material properties, but as it is an expensive element, adding a large amount leads to an increase in raw material costs. Therefore, the upper limit can be limited to 0.5%. Preferably, it can be 0.4% or less, and more preferably, 0.2% or less.

[0043] N: 0.10% or less (excluding 0)

[0044] The nitrogen (N) content is 0.10% or less. Nitrogen is a powerful austenite-stabilizing element and can be added as an effective element for improving the yield strength of austenitic stainless steel. However, if the content is excessive, there are problems that make manufacturability difficult, such as causing pinholes. In addition, the strength of the steel increases rapidly, making cold rolling or product forming difficult, reducing the lifespan of the mold, and potentially inducing additional equipment investment; therefore, the upper limit can be restricted to 0.10%. Preferably, it can be 0.07% or less, and more preferably, 0.05% or less.

[0045] In addition, the austenitic stainless steel according to one embodiment of the present invention may further include one or more of P: 0.035% or less and S: 0.01% or less.

[0046] P: 0.035% or less

[0047] Phosphorus (P) is an impurity inevitably contained in steel and is a major cause of intergranular corrosion or impaired hot workability, so it is desirable to control its content to be as low as possible. In the present invention, the upper limit of the P content is managed to be 0.035% or less.

[0048] S: 0.01% or less

[0049] Sulfur (S) is an impurity inevitably contained in steel and is an element that causes segregation at grain boundaries and hinders hot workability, so it is desirable to control its content to be as low as possible. In the present invention, the upper limit of the S content is managed to be 0.01% or less.

[0050] The remaining component of the present invention is iron (Fe). However, since unintended impurities from raw materials or the surrounding environment may inevitably be incorporated during the ordinary manufacturing process, they cannot be excluded. As these impurities are known to any person skilled in the ordinary manufacturing process, all details thereof are not specifically mentioned in this specification.

[0051] The austenitic stainless steel according to the present invention satisfies the aforementioned alloy composition, and at the same time satisfies the following parameter α value being 23.0 or higher and the following parameter β value being 0.12 or lower.

[0052] α = [Ni] + 0.65*[Cr] + 0.81*[Mn] + 0.35*[Si] + 12.6*[C] + 18.6*[N]

[0053] β = [C] + [N]

[0054] (Here, [Ni], [Cr], [Mn], [Si], [C], and [N] represent the content of each element in weight percent)

[0055] The above α is an essential formula for securing the manufacturability to be achieved in the present invention, and is an indicator representing the stabilization of the austenite phase of the material. In order to secure the physical properties intended in the present invention, the α value must be 23.0 or higher to ensure sufficient stability of the austenite phase. If the α value is less than 23.0, the austenite phase rapidly transforms into the martensite phase during cold rolling or the forming process of the product, causing cracks in the product or, in severe cases, fracture. Therefore, the lower limit of the above α value is set to 23.0, preferably 26.0 or higher, and more preferably 30.0 or higher. Accordingly, the austenitic stainless steel according to one embodiment of the present invention may contain an austenite phase of 95% or more in area fraction, and preferably 99% or more. In addition, the above austenitic stainless steel may contain an ε-martensite phase of 5% or less in area fraction. In addition, ε-martensite has a hexagonal close-packed (HCP) structure, and compared to austenite, which has a face-centered cubic (FCC) structure, the slip system is limited and the lattice structure itself is formed asymmetrically, resulting in very inferior ductility and formability. If formed excessively, it can reduce the overall ductility of the steel and make it susceptible to stress corrosion cracking, so it is controlled to be 5% or less.

[0056] The above β is an essential requirement for securing strengths similar to 304 and 304L, and is an indicator that quantifies the increase in material strength due to the addition of interstitial components. In order to control the strength and other properties intended in the present invention, the β value must be maintained at 0.12 or less to maintain the material characteristics of stainless steel 304(L), which is the most widely used, thereby enabling immediate application to equipment currently in use across various industries. Therefore, the upper limit of the β value is set to 0.12, and preferably, it may be 0.1% or less.

[0057] The austenitic stainless steel of the present invention satisfying the above composition and parameter values ​​α and β may have a room temperature yield strength of 270 MPa or less. In addition, the room temperature tensile strength may be 700 MPa or less, and the elongation may be 30% or more.

[0058] Next, a method for manufacturing austenitic stainless steel according to another aspect of the present invention will be described.

[0059] A method for manufacturing an austenitic stainless steel according to one embodiment of the present invention comprises the steps of: providing a steel material comprising, in weight%, carbon (C): 0.08% or less (excluding 0), silicon (Si): 1.0% or less (excluding 0), manganese (Mn): 18.0~33.0%, chromium (Cr): 9.0~19.0%, nickel (Ni): 0.5% or less (excluding 0), nitrogen (N): 0.10% or less (excluding 0), the remainder being Fe and unavoidable impurities, satisfying the following parameter α value of 23.0 or more and the following parameter β value of 0.12 or less; and performing hot working.

[0060] α = [Ni] + 0.65*[Cr] + 0.81*[Mn] + 0.35*[Si] + 12.6*[C] + 18.6*[N]

[0061] β = [C] + [N]

[0062] (Here, [Ni], [Cr], [Mn], [Si], [C], and [N] represent the content of each element in weight percent)

[0063] The above composition and parameters α and β are as described above.

[0064] The step of preparing the steel involves producing molten steel that satisfies the above parameters α and β, and producing a material using the produced molten steel. The material may be, for example, a cast billet or an ingot. Specifically, a cast billet may be produced by a continuous casting method using the molten steel, and the cast billet may be in the form of a slab, bloom, billet, etc. In addition, an ingot may be made using the molten steel, and a billet may be produced by performing hot forging or rolling, etc., on the cast billet or ingot.

[0065] The manufactured slabs, etc. are subjected to well-known hot working to produce intermediate steel. When the final product is a steel pipe, the intermediate steel is a small pipe; when the final product is a round steel, the intermediate steel may be a bar; and when the final product is a steel plate, the intermediate steel may be a plate.

[0066] Hot working can be performed by any one of hot forging, hot extrusion, or hot rolling. The hot working method is not particularly limited and includes well-known methods. When the final product is a steel sheet, the hot working process can be performed as follows.

[0067] First, the material is heated in a furnace. A method for manufacturing austenitic stainless steel according to one embodiment of the present invention may include a step of reheating to 1000 to 1300°C. Subsequently, hot rolling is performed on the material extracted from the furnace using a reverse mill and a tandem mill to produce a plate-shaped intermediate steel. Additionally, hot forging may be performed, and after hot forging, the material may be reheated to 1000 to 1300°C and then hot rolling may be performed on the material to produce a plate-shaped intermediate steel. If the reheating temperature is below 1000°C, sufficient thermal energy cannot be secured, resulting in high strength of the material and poor rolling performance; if it exceeds 1300°C, melting of some low-melting point inclusions occurs, and quality defects such as surface cracks occur; therefore, reheating is performed at 1000 to 1300°C.

[0068] Subsequently, the process may include a step of completing hot rolling at a temperature of 800°C or higher with a total reduction ratio of 60% or more. If the total reduction ratio is less than 60%, sufficient stress is not transferred to the interior of the material, resulting in the presence of segregation zones or cast structures within the material, which causes quality problems. If the final rolling temperature is less than 800°C, the rolling resistance increases and the shape of the material becomes distorted. Therefore, hot rolling is performed under the above conditions.

[0069] The method may include a step of performing a first solution heat treatment at 900 to 1150°C for 1 to 180 minutes after the above hot rolling; and a step of cooling to 500°C.

[0070] Specifically, the manufactured hot-worked intermediate material undergoes solution heat treatment. The intermediate steel can be loaded into a heat treatment furnace, maintained at a desired temperature, and then rapidly cooled. The solution temperature is not specifically limited, but can be carried out at 900 to 1150°C for 1 to 180 minutes, and the rapid cooling method in the solution treatment may include water cooling and forced air cooling. If the solution temperature is below 900°C, the recrystallization and the resolution of dislocations generated during rolling are not completed, which may result in material degradation; if it exceeds 1150°C, the structure becomes too coarse, which may result in material degradation. In addition, if the solution heat treatment time exceeds 180 minutes, the microstructure may become too coarse, which may cause the material to deteriorate and is inefficient in terms of raw materials, and if it is performed for less than 1 minute, there may be a problem in that sufficient recrystallization does not occur inside the product, so the solution heat treatment can be performed at 900 to 1150°C for 1 to 180 minutes.

[0071] Subsequently, a cold working process may be performed. Cold working may be, for example, cold drawing or cold rolling. The cold rolling may be performed at room temperature with a reduction rate of 50%, and the manufactured cold working material may undergo additional solution heat treatment. If the reduction rate is less than 50%, sufficient stress cannot be transferred to the interior of the material, and there is a high possibility that an uneven microstructure will develop after annealing; therefore, the reduction rate is controlled to be 50% or more. In addition, the solution heat treatment of the cold working material may be performed at 900 to 1150°C for 20 to 600 seconds. If the solution temperature is below 900°C, the recrystallization and the resolution of dislocations generated during rolling are not completed, which may result in material degradation; if it exceeds 1150°C, the microstructure becomes too coarse, which may result in material degradation. In addition, if the solution heat treatment time exceeds 600 seconds, the microstructure may become too coarse, which may cause material degradation and is inefficient in terms of raw materials, and if it is performed for less than 20 seconds, there may be a problem where sufficient recrystallization does not occur inside the product, so the solution heat treatment can be performed at 900 to 1150°C for 20 to 600 seconds.

[0072] According to the results of the present invention, it is possible to obtain an austenitic stainless steel capable of general-purpose application that possesses manufacturability and excellent toughness, while ensuring minimal corrosion resistance.

[0073] The present invention will be explained in more detail below through examples. However, it should be noted that the following examples are intended merely to illustrate and explain the invention in more detail, and are not intended to limit the scope of the invention. This is because the scope of the invention is determined by the matters described in the patent claims and matters reasonably inferred therefrom.

[0074] (Example)

[0075] After preparing a slab having the alloy composition listed in Table 1 below, hot rolling, solution heat treatment, and cold rolling were performed. For hot rolling, the heating temperature was controlled at 1200℃, the heating time at 200 minutes, the total reduction ratio at 0.85, and the cooling rate after hot rolling at 30℃ / s or less; after cooling, the solution heat treatment was performed at 1100℃ for 20 minutes. The cold rolling reduction ratio was 0.75, and the solution heat treatment after cold rolling was performed at 1050℃ for 5 minutes.

[0076] Table 1 shows the main components and calculated parameter values ​​of the comparative example and example of austenitic stainless steel.

[0077] Composition (Weight%) αβCSiPSMnNiCrN Example 10.07 0.4 0.032 0.00218.10.114.10.0425.7 0.11 Example 20.03 0.5 0.033 0.00223.20.210.10.0426.9 0.07 Example 30.05 0.4 0.03 0.00327 0.110.20.043 0.10.09 Example 40.06 0.4 0.0310.00229.10.2100.0431.9 0.1 Example 50.07 0.4 0.0310.00232.10.1100.0434.4 0.11 Example 60.030.40.0330.00324.30.19.10.0427.00.07 Example 70.050.50.0290.00326.10.112.20.0430.70.09 Example 80.060.50.0280.00226.90.213.10.0432.20.1 Example 90.020.40.0280.003270.113.90.0432.10.06 Example 100.060.30.0310.00329.50.114.80.0435.20.1 Example 110.020.40.0340.00223.10.111.10.0827.90.1 Comparative Example 10.070.40.0330.0021.28.618.10.0523.30.12 Comparative Example 20.020.50.0310.0021.39.518.20.0523.70.07 Comparative Example 30.050.40.0270.00315.20.110.10.0420.50.09 Comparative Example 40.060.50.0260.00317.10.110.20.0422.30.1 Comparative Example 50.060.40.0320.00217.90.110.10.0422.80.1 Comparative Example 60.060.40.0320.00333.80.1100.0435.60.1 Comparative Example 70.070.60.0340.00236.20.29.90.0437.80.11 Comparative Example 80.050.40.0290.00235.10.18.10.0435.30.09 Comparative Example 90.060.40.030.00324.20.280.0426.60.1 Comparative Example 100.020.30.0290.00219.50.19.10.0222.50.04Comparative Example 110.040.40.0310.00223.80.111.10.129.10.14Comparative Example 120.080.40.0330.00323.40.1110.129.20.18Comparative Example 130.080.50.0310.00223.50.180.127.40.18.

[0078] Table 2 shows the values ​​for manufacturability, corrosion resistance, room temperature yield strength, room temperature tensile strength, and room temperature elongation obtained as a result of the invention. Manufacturability was judged to be excellent if no edge cracks or fractures occurred and no surface cracks appeared when performing well-known hot and cold working processes. Corrosion resistance was judged to be acceptable if the rust area was 5% or less after 3 cycles under ISO 14993 cyclic corrosion test conditions. The room temperature tensile test was conducted in accordance with ASTM E8-M.

[0079] Manufacturability Corrosion Resistance Yield Strength (MPa) Tensile Strength (MPa) Elongation (%) Example 1 Excellent Pass 246.1652.549.8 Example 2 Excellent Pass 239.1659.454.3 Example 3 Excellent Pass 245.266552.2 Example 4 Excellent Pass 248.3667.756.7 Example 5 Excellent Pass 252.9671.951.8 Example 6 Excellent Pass 236.9645.157.1 Example 7 Excellent Pass 248662.755.8 Example 8 Excellent Pass 259.1656.856.1 Example 9 Excellent Pass 241.5661.454.9 Example 10 Excellent Pass 253.9655.357.3 Implementation Example 11 Excellent Pass 230.5665.853.8 Comparative Example 1 Excellent Pass 255.3660.555.8 Comparative Example 2 Excellent Pass 232.8635.856.1 Comparative Example 3 Poor (Cold Rolled Defect) Pass 209.2371.3 Hot Rolled Material: 7.3 Cold Rolled Material: Unmeasurable Comparative Example 4 Poor (Cold Rolled Defect) Pass 239.8619.8 Hot Rolled Material: 20.6 Cold Rolled Material: Unmeasurable Comparative Example 5 Poor (Cold Rolled Defect) Pass 225.8520.3 Hot Rolled Material: 17.5 Cold Rolled Material: Unmeasurable Comparative Example 6 Poor (Hot Rolled Defect) Pass--Unmeasurable Comparative Example 7 Poor (Hot-rolled Defect) Pass -- Unmeasurable Comparative Example 8 Inferior (Hot-rolled Defect) Pass -- Unmeasurable Comparative Example 9 Excellent Fail 233.2661.155.8 Comparative Example 10 Inferior (Cold-rolled Defect) Pass 238.5600.7 Cold-rolled material: Unmeasurable Comparative Example 11 Excellent Pass 280.2715.542.8 Comparative Example 12 Excellent Pass 295.5719.643.5 Comparative Example 13 Excellent Fail 301.1711.644.1

[0080] Examples 1 to 11 are ultra-low-cost austenitic stainless steels that satisfy both composition and parameters, having excellent manufacturability and securing the minimum corrosion resistance required for eco-friendly energy transfer and transportation applications, and having material properties similar to 304(L), the most commonly used stainless steel, such as a room temperature yield strength of 270 MPa or less and a tensile strength of 700 MPa or less, allowing for immediate application in various industrial sites without changing existing equipment or making additional investments. Comparative Example 1 satisfies all manufacturability, corrosion resistance, and room temperature tensile properties with the composition of general-purpose stainless steel 304, but has the problem of high raw material costs due to the high addition of Ni and Cr.

[0081] Comparative Example 2 is a general-purpose stainless steel 304L component that satisfies manufacturability, corrosion resistance, and room temperature tensile properties, but has the problem of high raw material costs due to the addition of high Ni and Cr.

[0082] Comparative Examples 3 and 4 have a Mn value of less than 18, making it difficult to secure the stability of the austenitic phase, and the parameter α value is 23 or less, resulting in cracks and fractures occurring during cold rolling, which causes problems with inferior manufacturability.

[0083] Comparative Examples 5 and 10 have a parameter α value of 23 or less, and have a problem of poor manufacturability due to cracks and fractures occurring during cold rolling caused by excessive formation of martensite phase during deformation.

[0084] Comparative Examples 6, 7, and 8 have a lower melting point and inferior hot workability due to the Mn content exceeding 33, resulting in edge cracks and fractures occurring during hot rolling, which causes problems with poor manufacturability.

[0085] Comparative Example 9 has a Cr content of less than 9, which fails to secure the minimum corrosion resistance required by the present invention and has the problem of significant rust formation after CCT.

[0086] Comparative Examples 11 and 12 have a parameter β value exceeding 0.12, which results in excessively high yield strength and tensile strength of the product, making it difficult to manufacture the product using existing industrial equipment or requiring separate investment.

[0087] Comparative Example 13 has a problem in that its corrosion resistance is inferior because the Cr content is less than 9, and its yield strength and tensile strength are excessively high because the β value exceeds 0.12.

[0088] Although exemplary embodiments of the present invention have been described above, the present invention is not limited thereto, and those skilled in the art will understand that various changes and modifications are possible within the scope and concept of the claims set forth below.

Claims

1. In wt%, carbon (C): 0.08% or less (excluding 0), silicon (Si): 1.0% or less (excluding 0), manganese (Mn): 18.0–33.0%, chromium (Cr): 9.0–19.0%, nickel (Ni): 0.5% or less (excluding 0), nitrogen (N): 0.10% or less (excluding 0), the remainder being Fe and unavoidable impurities, and The following parameter α value satisfies 23.0 or greater, and Austenitic stainless steel satisfying the following parameter β value of 0.12 or less. α = [Ni] + 0.65*[Cr] + 0.81*[Mn] + 0.35*[Si] + 12.6*[C] + 18.6*[N] β = [C] + [N] (Here, [Ni], [Cr], [Mn], [Si], [C], and [N] represent the content of each element in weight percent) 2. In Claim 1, The above austenitic stainless steel further comprises, in weight percent, one or more of phosphorus (P): 0.035% or less and sulfur (S): 0.01% or less.

3. In Claim 1, The above austenitic stainless steel is an austenitic stainless steel containing 95% or more of an austenite phase in terms of area fraction.

4. In Claim 3, The above austenitic stainless steel is an austenitic stainless steel containing an ε-martensite phase in an area fraction of 5% or less.

5. In Claim 1, The above austenitic stainless steel is an austenitic stainless steel having a room temperature yield strength of 270 MPa or less.

6. In Claim 1, The above austenitic stainless steel is an austenitic stainless steel having a room temperature tensile strength of 700 MPa or less.

7. In Claim 1, The above austenitic stainless steel is an austenitic stainless steel having an elongation of 30% or more.

8. A step of preparing a steel material comprising, in wt%, carbon (C): 0.08% or less (excluding 0), silicon (Si): 1.0% or less (excluding 0), manganese (Mn): 18.0~33.0%, chromium (Cr): 9.0~19.0%, nickel (Ni): 0.5% or less (excluding 0), nitrogen (N): 0.10% or less (excluding 0), and the remainder being Fe and unavoidable impurities, satisfying the following parameter α value of 23.0 or more and the following parameter β value of 0.12 or less; and Step of performing hot working; A method for manufacturing austenitic stainless steel including α = [Ni] + 0.65*[Cr] + 0.81*[Mn] + 0.35*[Si] + 12.6*[C] + 18.6*[N] β = [C] + [N] (Here, [Ni], [Cr], [Mn], [Si], [C], and [N] represent the content of each element in weight percent) 9. In Claim 8, A method for manufacturing austenitic stainless steel, wherein the above hot working is performed by any one of hot forging, hot extrusion, or hot rolling.

10. In Claim 9, The above hot rolling comprises the step of reheating the steel to 1000~1300℃; and A method for manufacturing austenitic stainless steel, comprising the step of finishing hot rolling at a temperature of 800°C or higher with a total reduction rate of 60% or more.

11. In Claim 10, A method for manufacturing austenitic stainless steel, comprising: a step of performing a first solution heat treatment at 900 to 1150°C for 1 to 180 minutes after the above hot rolling; and a step of cooling to 500°C.

12. In Claim 11, A method for manufacturing austenitic stainless steel, further comprising the steps of cold rolling with a reduction rate of 50% after the above cooling step, and performing a secondary solution heat treatment at 900 to 1150°C for 20 to 600 seconds.