Austenitic steel material and its manufacturing method

Abstract

Provided are austenitic steel materials with excellent ultra-low temperature toughness and a method for producing the same. [Solution] The austenitic steel of the present invention contains, by weight, 10-45% manganese (Mn), carbon (C) in a range satisfying 24 × [C] + [Mn] ≥ 25 and 33.5 × [C] - [Mn] ≤ 18, 10% or less (excluding 0%) chromium (Cr), one or more of 5% or less (excluding 0%) Ni, 5% or less (excluding 0%) Cu, 5% or less (excluding 0%) Si, 5% or less (excluding 0%) Al, and 1% or less (excluding 0%) N, with the remainder being iron (Fe) and unavoidable impurities. The microstructure contains, by area, 95% or more (including 100%) austenite and 5% or less (including 0%) carbides. The austenitic steel of the present invention is suitable as a structural material for use in ultra-low temperature environments, such as liquefied gas storage tanks and liquefied gas transportation facilities.

Description

[Technical Field]

[0001] The present invention relates to an austenitic steel material and a manufacturing method thereof, and more particularly to an austenitic steel material that can be suitably applied to structural materials used in ultra-low temperature environments such as liquefied gas storage tanks and liquefied gas transport facilities, and a manufacturing method thereof. [Background technology]

[0002] Liquefied gases such as liquefied hydrogen (boiling point: -253°C), liquefied natural gas (LNG, boiling point: -164°C), liquefied oxygen (boiling point: -183°C), and liquefied nitrogen (boiling point: -196°C) require cryogenic storage. Therefore, to store these gases, structures such as pressure vessels made of materials with sufficient toughness and strength at cryogenic temperatures are required.

[0003] Materials that can be used at low temperatures in liquefied gas atmospheres include Cr-Ni stainless steel alloys such as AISI 304, 9% Ni steel, and 5000-series aluminum alloys. However, aluminum alloys are limited in use due to their high alloy costs, low strength, which increases the design thickness of structures, and poor weldability. While Cr-Ni stainless steel and 9% nickel (Ni) steel have significantly improved the physical properties of aluminum, they contain large amounts of expensive nickel (Ni), making them undesirable from an economic standpoint. Summary of the Invention [Problem to be solved by the invention]

[0004] One aspect of the present invention is to provide an austenitic steel material and a method for producing the same.

[0005] A preferred aspect of the present invention is to provide an austenitic steel material having excellent ultra-low temperature toughness and a method for producing the same. [Means for solving the problem]

[0006] One embodiment of the present invention provides an austenitic steel material containing, by weight%, 10 to 45% manganese (Mn), carbon (C) in a range satisfying 24 × [C] + [Mn] ≧ 25 and 33.5 × [C] - [Mn] ≦ 18, 10% or less (excluding 0%) chromium (Cr), one or more of 5% or less (excluding 0%) Ni, 5% or less (excluding 0%) Cu, 5% or less (excluding 0%) Si, 5% or less (excluding 0%) Al, and 1% or less (excluding 0%) N, with the remainder being iron (Fe) and unavoidable impurities, and having a microstructure containing, by area%, 95% or more (including 100%) austenite and 5% or less (including 0%) carbides.

[0007] The above-mentioned microstructure may be maintained even after a 20% deformation is applied by a uniaxial tensile test at room temperature, followed by holding at -253°C and measurement at room temperature.

[0008] The austenite may have an average crystal grain size of 5 to 200 μm.

[0009] The steel may have a lateral expansion of 0.32 mm or more after a Charpy impact test at -253°C.

[0010] The steel material may have a Charpy impact energy of 27 J or more at −253° C.

[0011] The steel material may have a room temperature yield strength of 245 MPa or more and less than 400 MPa.

[0012] Another embodiment of the present invention provides a method for producing an austenitic steel material, the method including the steps of heating a slab containing, in weight percent, 10 to 45% manganese (Mn), carbon (C) in a range satisfying 24 × [C] + [Mn] ≧ 25 and 33.5 × [C] − [Mn] ≦ 18, 10% or less (excluding 0%) chromium (Cr), one or more of 5% or less (excluding 0%) Ni, 5% or less (excluding 0%) Cu, 5% or less (excluding 0%) Si, 5% or less (excluding 0%) Al, and 1% or less (excluding 0%) N, with the remainder being iron (Fe) and unavoidable impurities, at 1000 to 1300°C, and finish hot rolling the heated slab at 800 to 1050°C to obtain a hot-rolled steel sheet. [Effects of the Invention]

[0013] According to one aspect of the present invention, an austenitic steel material and a method for producing the same can be provided.

[0014] According to a preferred aspect of the present invention, it is possible to provide an austenitic steel material having excellent ultra-low temperature toughness and a method for producing the same. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram showing the correlation between the carbon content and the manganese content of an austenitic steel according to one aspect of the present invention. [Figure 2] FIG. 1 is a diagram illustrating a method for measuring the transverse expansion value of an austenitic steel material according to one aspect of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] An austenitic steel material according to one embodiment of the present invention will be described below. First, the alloy composition will be described. The contents of the alloy composition described below are in weight percent unless otherwise specified.

[0017] Manganese (Mn): 10-45% Manganese is an element that plays an important role in stabilizing austenite. To stabilize austenite at ultralow temperatures, a manganese (Mn) content of 10% or more is preferred. If the manganese (Mn) content is less than this, a metastable epsilon martensite phase is formed, which easily transforms to alpha martensite through strain-induced transformation at ultralow temperatures, resulting in poor toughness. While increasing the carbon (C) content to suppress the formation of epsilon martensite can stabilize austenite, this can result in the precipitation of a large amount of carbides, which can rapidly deteriorate physical properties. Therefore, a manganese (Mn) content of 10% or more is preferred. A manganese (Mn) content of 15% or more is preferred, and a manganese (Mn) content of 18% or more is even more preferred. Excessive manganese (Mn) content not only reduces the corrosion rate of the steel but is also undesirable from an economic standpoint. Therefore, a manganese (Mn) content of 45% or less is preferred. A preferred manganese (Mn) content may be 40% or less, and a more preferred manganese (Mn) content may be 35% or less.

[0018] Carbon (C): 24 × [C] + [Mn] ≥ 25 and 33.5 × [C] - [Mn] ≤ 18 Carbon (C) stabilizes austenite and increases its strength. In particular, carbon (C) lowers the Ms or Md, the transformation point from austenite to epsilon- or alpha-martensite, during cooling or processing. Therefore, carbon (C) effectively stabilizes austenite. Insufficient carbon (C) content can lead to insufficient austenite stability at ultralow temperatures, preventing stable austenite from being obtained. External stress can easily induce strain-induced transformation to epsilon- or alpha-martensite, potentially reducing the toughness or strength of the steel. On the other hand, excessive carbon (C) content can rapidly degrade the toughness of the steel due to carbide precipitation, and excessive strength can lead to reduced workability.

[0019] The inventors of the present invention have conducted extensive research into the relative behavior of carbon (C) and manganese (Mn) contents with respect to carbide formation. As a result, they have concluded that by determining the relative content relationship of carbon (C) and manganese (Mn), it is possible to effectively stabilize austenite while effectively controlling the amount of carbide precipitation, as shown in Figure 1. Although carbides are formed by carbon (C), carbon (C) does not affect carbide formation independently, but rather acts in combination with manganese (Mn) to affect carbide formation.

[0020] To stabilize austenite, it is preferable to control the value of 24 × [C] + [Mn] (where [C] and [Mn] represent the contents of each component in weight percent) to 25 or greater, provided that the other components satisfy the ranges specified in this invention. This boundary refers to the inclined left boundary of the parallelogram region shown in Figure 1. If 24 × [C] + [Mn] is less than 25, the stability of austenite decreases, and deformation-induced transformation occurs upon impact at ultralow temperatures, which may result in a decrease in the impact toughness of the steel. On the other hand, to suppress the formation of carbides, it is preferable to control the value of 33.5 × [C] - [Mn] (where [C] and [Mn] represent the contents of each component in weight percent) to 18 or less, provided that the other components satisfy the ranges specified in this invention. If 33.5 × [C] - [Mn] exceeds 18, the addition of excess carbon (C) may cause carbide precipitation, resulting in a decrease in the low-temperature impact toughness of the steel. Therefore, in the present invention, carbon (C) is preferably added so as to satisfy the conditions 24 × [C] + [Mn] ≥ 25 and 33.5 × [C] - [Mn] ≤ 18. As can be seen from Figure 1, the lowest limit of the carbon (C) content within the range that satisfies the above formula is 0%.

[0021] Chromium (Cr): 10% or less (excluding 0%) Chromium (Cr) is an austenite-stabilizing element. Up to an appropriate addition level, it stabilizes austenite, improving the low-temperature impact toughness of steel and dissolving in austenite to increase the strength of steel. Chromium (Cr) also effectively contributes to improving the corrosion resistance of steel. Therefore, the present invention adds chromium (Cr) as an essential element. A preferred lower limit of the chromium (Cr) content is 1%, and a more preferred lower limit is 2%. However, chromium (Cr) is a carbide-forming element, and it can form carbides, especially at austenite grain boundaries, thereby reducing the low-temperature impact toughness of steel. Furthermore, if the amount of chromium (Cr) added exceeds a certain level, excessive carbides may precipitate in the heat-affected zone (HAZ), potentially degrading the ultra-low temperature toughness. Therefore, the present invention limits the upper limit of chromium (Cr) to 10%. A preferred upper limit for the chromium (Cr) content may be 8%, and a more preferred upper limit for the chromium (Cr) content may be 7%.

[0022] At least one of the following: Ni: 5% or less (excluding 0%), Cu: 5% or less (excluding 0%), Si: 5% or less (excluding 0%), Al: 5% or less (excluding 0%), and N: 1% or less (excluding 0%)

[0023] Ni: 5% or less (excluding 0%) Nickel (Ni) is an effective austenite stabilizing element and improves the toughness of steel by lowering the Ms and Md, the transformation points from austenite to epsilon- or alpha-martensite during cooling or processing. It is particularly well known as an element that increases the stacking fault energy of steel and promotes slip. However, if Ni is added in an amount exceeding 5%, economic viability may be reduced. The upper limit of the nickel (Ni) content may be preferably 4%, and more preferably 3.5%. The lower limit of the nickel (Ni) content may be preferably 0.3%, and more preferably 0.5%.

[0024] Cu: 5% or less (excluding 0%) Copper (Cu) has very low solid solubility in carbides and slow diffusion in austenite, so it concentrates at the interface between austenite and nucleated carbides. This effectively slows carbide growth by blocking carbon diffusion, ultimately suppressing carbide formation. Copper also stabilizes austenite and improves cryogenic toughness. However, because a Cu content exceeding 5% can degrade the hot workability of steel, it is preferable to limit the Cu content to 5% by weight. The preferred upper limit of the Cu content may be 3%, and more preferably 2%. The preferred lower limit of the Cu content may be 0.1%, and more preferably 0.3%.

[0025] Si: 5% or less (excluding 0%) Silicon (Si) improves the castability of molten steel. When added to austenitic steel, it dissolves in the steel, effectively increasing its strength. It also affects the activity of carbon in the steel, effectively suppressing the formation of carbides and increasing its toughness. However, if added in amounts exceeding 5%, it reduces stacking fault energy and promotes twinning, potentially resulting in a decrease in toughness due to increased strength. Therefore, the upper limit of the silicon (Si) content is preferably 5%. The upper limit of the silicon (Si) content may be preferably 3%, and more preferably 2.5%. The lower limit of the silicon (Si) content may be preferably 0.1%, and more preferably 0.3%.

[0026] Aluminum (Al): 5% or less (excluding 0%) Aluminum (Al) stabilizes austenite within an appropriate range of addition and lowers the Ms and Md, the transformation points from austenite to epsilon- or alpha-martensite during cooling or processing, thereby improving the toughness of steel. It also dissolves in steel to increase strength. It specifically affects the activity of carbon in steel, effectively suppressing carbide formation and increasing toughness. It is particularly well known for effectively increasing stacking fault energy and promoting slip. However, adding more than 5% aluminum can lead to problems such as the formation of oxides and nitrides, which can degrade the castability and surface quality of steel. Therefore, the upper limit of the aluminum (Al) content is preferably 5% by weight. The preferred upper limit of the aluminum (Al) content may be 3%, and more preferably 2.5%. The preferred lower limit of the aluminum (Al) content may be 0.2%, and more preferably 0.3%.

[0027] N: 1% or less (excluding 0%) Nitrogen (N) is an element that stabilizes austenite together with carbon to improve toughness. Like carbon, it is particularly advantageous for improving strength through solid solution strengthening. It is particularly well known for effectively increasing stacking fault energy and promoting slip. However, if added in excess of 1%, coarse nitrides are formed, deteriorating the surface quality and physical properties of the steel. Therefore, the upper limit of the nitrogen (N) content is preferably 1 wt%. The upper limit of the nitrogen (N) content may be preferably 0.5%, and more preferably 0.2%. The lower limit of the nitrogen (N) content may be preferably 0.005%, and more preferably 0.007%.

[0028] In addition to the aforementioned components, the austenitic steel according to one aspect of the present invention may contain the remaining Fe and other inevitable impurities. However, since unintended impurities may be inevitably mixed in from raw materials or the surrounding environment during normal manufacturing processes, it is not possible to completely eliminate these impurities. Since these impurities are known to anyone with ordinary skill in the art, not all of their contents are specifically mentioned in this specification. Furthermore, the addition of additional effective components other than the aforementioned components is not completely excluded.

[0029] The austenitic steel according to one aspect of the present invention may contain 95 area% or more of austenite as a microstructure in order to ensure the desired physical properties. The preferred austenite fraction may be 97 area% or more, including a case where the austenite fraction is 100 area%. Meanwhile, the austenitic steel according to one aspect of the present invention may actively suppress the carbide fraction to 5 area% or less in order to prevent a decrease in cryogenic impact toughness. The preferred carbide fraction may be 3 area% or less, including a case where the carbide fraction is 0 area%. In the present invention, the methods for measuring the austenite fraction and carbide fraction are not particularly limited, and can be easily confirmed by a measurement method commonly used by a person of ordinary skill in the art to which the present invention pertains for measuring microstructures and carbides.

[0030] In steels, austenite is an unstable structure at room temperature. To retain austenite, which is stable at high temperatures, at room temperature, austenite-stabilizing elements are typically added. Even if austenite is obtained at room temperature, it can transform into epsilon martensite or alpha martensite with additional cooling or processing, depending on the alloy composition, cooling temperature, and processing amount. Steels used for liquefied gas storage tanks and other structures require cold processing. Therefore, even if the microstructure of the rolled material is austenite, a phase transformation may occur during deformation during the fabrication of the structure or during cooling at ultra-low temperatures after deformation. If brittle epsilon or alpha martensite is formed as a result of this phase transformation, impact toughness may be reduced, potentially making the material unsuitable for use as a liquefied gas container.

[0031] Therefore, austenite must remain stable even after cold working at room temperature and holding at -253°C, the service temperature. Typically, structures such as storage tanks are processed within a maximum of 20% of the uniaxial deformation during cold forming. Therefore, after 20% cold working and holding at -253°C, austenite must be maintained without the formation of epsilon or alpha martensite. However, since carbides are not related to phase transformation, there is no problem if they are controlled within the 5% range controlled in the present invention. In other words, the microstructure of the present invention is maintained even after 20% deformation in a uniaxial tensile test at room temperature, holding at -253°C, and then measuring at room temperature.

[0032] The austenite may have an average grain size of 5 to 200 μm. If the average grain size of the austenite exceeds 200 μm, the strength decreases due to coarsening of the austenite. Furthermore, the processing-induced transformation temperature increases, and transformation to epsilon martensite or martensite easily occurs during processing, which may result in a drawback of reduced impact toughness. On the other hand, if the average grain size of the austenite is less than 5 μm, the strength may increase excessively, which may result in a drawback of reduced toughness. The lower limit of the average grain size of the austenite is more preferably 7 μm, and even more preferably 10 μm. The upper limit of the average grain size of the austenite is more preferably 180 μm, and even more preferably 150 μm.

[0033] The steel material of the present invention may have a lateral expansion of 0.32 mm or more after a Charpy impact test at −253°C. However, in the present invention, the higher the lateral expansion value, the more advantageous it is, so there is no particular upper limit. However, the upper limit of the lateral expansion value may be 2.30 mm, for example.

[0034] The inventors of the present invention have found that for steel materials to be used in cryogenic environments, plastic deformation characteristics are a key factor in ensuring safety. That is, after extensive research, the inventors of the present invention have confirmed that for steel materials that satisfy the chemical composition proposed in the present invention, the lateral expansion value (mm) is a more important factor in ensuring the safety of the base metal than the Charpy impact energy value (J).

[0035] The transverse expansion value refers to the average value of the transverse plastic deformation of a test piece subjected to a Charpy impact test at -253°C. Figure 2 shows a photograph of a test piece subjected to a standard Charpy impact test at -253°C. As shown in Figure 2, the transverse expansion value can be calculated by calculating the increase in transverse length (△X1 + △X2) near the fracture surface. If the transverse expansion value is 0.32 mm or more, it can be determined that the minimum low-temperature safety required for cryogenic structures is met.

[0036] According to the research results of the present inventors, it has been confirmed that the -253°C standard Charpy impact energy (J) and the lateral expansion value (mm) of the test piece generally show a tendency similar to that of the following relational expression 1, and that the lateral expansion value (mm) is preferably 0.32 mm or more. It has been found that the larger the lateral expansion value (mm), the better the low-temperature impact toughness, and a value of 0.72 to 1.4 mm is more effective.

[0037] [Equation 1] Lateral expansion value (mm) = 0.0088 x Charpy impact energy value (J) + 0.0893

[0038] In an austenitic steel according to one aspect of the present invention, a test piece subjected to a −253°C standard Charpy impact test using the steel as a base material has a lateral expansion value of 0.32 mm or more, and therefore, when the steel is used to fabricate a structure for use at cryogenic temperatures, excellent structural safety can be ensured.

[0039] The austenitic steel material of the present invention may have a Charpy impact energy of 27 J or more at -253°C. By ensuring such a high level of cryogenic Charpy impact energy, ductile fracture occurs when the structure is destroyed, thereby ensuring the fracture stability of the cryogenic structure. Meanwhile, in the present invention, the higher the cryogenic Charpy impact energy, the more advantageous it is, so there is no particular restriction on the upper limit. However, the upper limit of the cryogenic Charpy impact energy may be 250 J, for example.

[0040] The room-temperature yield strength of the austenitic steel according to one aspect of the present invention may be 245 MPa or more but less than 400 MPa. As the strength of the steel increases, its low-temperature impact toughness decreases. In particular, in the case of steels intended for use at ultra-low temperatures of -253°C, such as those of the present invention, an excessively high yield strength may result in failure to achieve the desired impact toughness. Furthermore, since it is generally difficult for commercial austenitic welding materials to exceed the strength of the base metal, maintaining the strength of the base metal high may result in a strength difference between the weld and the base metal, potentially reducing structural stability. Therefore, the room-temperature yield strength of the austenitic steel according to one aspect of the present invention is preferably less than 400 MPa. However, if the room-temperature yield strength of the steel is too low, the thickness of the base metal may be excessively increased to ensure the stability of the structure, which may result in an excessive increase in the weight of the structure. Therefore, the lower limit of the room-temperature yield strength of the austenitic steel according to one aspect of the present invention may be limited to 245 MPa.

[0041] Hereinafter, a method for producing an austenitic steel material according to one embodiment of the present invention will be described.

[0042] First, a slab having the above-mentioned alloy composition is heated at 1000 to 1300°C. If the slab heating temperature is less than 1100°C, there are drawbacks, such as the alloy components not being redissolved and homogenized, or it taking a considerable amount of time for the center of the slab to reach the target temperature. If the slab heating temperature exceeds 1300°C, there are drawbacks, such as partial melting occurring in the alloy component segregation portion of the slab, or severe surface oxidation occurring. The lower limit of the slab heating temperature is more preferably 1030°C, even more preferably 1070°C, and most preferably 1100°C. The upper limit of the slab heating temperature is more preferably 1250°C, even more preferably 1230°C, and most preferably 1200°C.

[0043] The heated slab is then finish hot-rolled at 800 to 1050°C to obtain a hot-rolled steel sheet. If the finish hot-rolling temperature is less than 800°C, the high high-temperature strength of the material makes rolling difficult, and rolling in the unrecrystallized region results in an excessive increase in the material's strength and reduced impact toughness. If the finish hot-rolling temperature exceeds 1050°C, the austenite grains become coarse, resulting in a decrease in strength. The lower limit of the finish hot-rolling temperature is more preferably 820°C, even more preferably 850°C, and most preferably 870°C. The upper limit of the finish hot-rolling temperature of the slab is more preferably 1030°C, even more preferably 1000°C, and most preferably 980°C. Meanwhile, the reduction ratio during the hot rolling can be applied within an appropriate range depending on the target plate thickness. As a non-limiting example, the final thickness of the hot-rolled hot-rolled steel sheet may be 5 to 80 mm.

[0044] Thereafter, the hot-rolled steel sheet can be air-cooled to room temperature. [Example]

[0045] Hereinafter, an austenitic steel material and a manufacturing method thereof according to one aspect of the present invention will be described in more detail with reference to specific examples. It should be noted that the following examples are provided for the purpose of understanding the present invention and are not intended to define the scope of the present invention. The scope of the present invention can be determined by the matters set forth in the claims and matters that can be reasonably inferred therefrom.

[0046] (Example) A 250 mm thick slab having the alloy composition shown in Table 1 below was prepared, and then the slab was heated and hot rolled under the conditions shown in Table 2 below to produce a steel material.

[0047] The microstructure and physical properties of the steel material thus produced were measured, and the results are shown in Table 2 below.

[0048] The microstructure was measured using an optical microscope at room temperature. After applying a 20% deformation to the specimens through a uniaxial tensile test at room temperature, the specimens were held at -253°C for 15 minutes or more, and then the microstructure at room temperature was examined to see if it remained the same. In other words, the microstructures listed in Table 2 below are the microstructures at room temperature, as well as the microstructures at room temperature after deformation and cryogenic holding.

[0049] The average austenite grain size was measured by taking a photograph of the microstructure using an optical microscope and then performing image analysis.

[0050] The Charpy impact energy was measured using a Charpy impact tester after the test piece was kept at -253°C for 15 minutes or more.

[0051] The room temperature yield strength was measured using the uniaxial tensile test method.

[0052] The lateral expansion was calculated by calculating the average value of the amount of lateral plastic deformation of test pieces subjected to a Charpy impact test at -253°C.

[0053] [Table 1]

[0054] [Table 2]

[0055] In the case of Examples 1 to 5, which satisfy the alloy composition and manufacturing conditions of the present invention, the microstructure and average austenite grain size that the present invention aims to obtain are secured, and it is clear that excellent physical properties are secured.

[0056] In the case of Comparative Examples 1 to 6, which do not satisfy the alloy composition or manufacturing conditions of the present invention, it is clear that the physical properties are at a low level because the fine structure or average austenite grain size that the present invention aims to obtain cannot be secured.

Claims

1. In weight percent, manganese (Mn): 10 to 45%, carbon (C): in a range satisfying 24 x [C] + [Mn] ≥ 25 and 33.5 x [C] - [Mn] ≤ 18, chromium (Cr): 10% or less (excluding 0%), one or more of Ni: 5% or less (excluding 0%), Cu: 5% or less (excluding 0%), Si: 5% or less (excluding 0%), Al: 5% or less (excluding 0%) and N: 1% or less (excluding 0%), with the remainder being iron (Fe) and inevitable impurities, An austenitic steel material characterized in that the microstructure contains, by area percentage, 95% or more (including 100%) of austenite and 5% or less (including 0%) of carbides.

2. 2. The austenitic steel according to claim 1, wherein the microstructure is maintained even after a uniaxial tensile test is performed at room temperature to apply a 20% deformation, after which the microstructure is maintained at −253°C and then measured at room temperature.

3. 2. The austenitic steel material according to claim 1, wherein the austenite has an average grain size of 5 to 200 μm.

4. 2. The austenitic steel according to claim 1, wherein the steel has a lateral expansion of 0.32 mm or more after a Charpy impact test at −253° C.

5. 2. The austenitic steel according to claim 1, wherein the steel has a Charpy impact energy of 27 J or more at −253° C.

6. 2. The austenitic steel material according to claim 1, wherein the steel material has a room temperature yield strength of 245 MPa or more and less than 400 MPa.

7. A step of heating a slab consisting of, in weight percent, manganese (Mn): 10 to 45%, carbon (C): in a range satisfying 24 × [C] + [Mn] ≧ 25 and 33.5 × [C] - [Mn] ≦ 18, chromium (Cr): 10% or less (excluding 0%), one or more of Ni: 5% or less (excluding 0%), Cu: 5% or less (excluding 0%), Si: 5% or less (excluding 0%), Al: 5% or less (excluding 0%), and N: 1% or less (excluding 0%), with the remainder being iron (Fe) and inevitable impurities, at 1000 to 1300°C; The method for producing austenitic steel comprises the step of finish hot rolling the heated slab at 800 to 1050°C to obtain a hot-rolled steel sheet.

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