An austenitic stainless steel, a method for producing the same and use thereof

Abstract

The application relates to the technical field of stainless steel materials, in particular to an austenitic stainless steel and a preparation method and application thereof. The austenitic stainless steel is composed of the following elements: chromium 18.5-19.5%, nickel 30.0-40.0%, aluminum 1.0-5.0%, manganese 0.45-0.55%, niobium 0.45-0.55%, carbon 0.02-0.03%, sulfur 0-0.01% and iron in a residual amount, with the total mass of the austenitic stainless steel being 100%. The austenitic stainless steel has excellent high-temperature mechanical properties, high-temperature oxidation resistance and organizational stability, and can be stably adapted to a high-temperature gas cooled reactor one-loop over-800 DEG C working condition environment.

Description

Technical Field

[0001] This invention relates to the field of stainless steel materials technology, and in particular to an austenitic stainless steel, its preparation method, and its application. Background Technology

[0002] As an important development direction of fourth-generation nuclear power technology, high-temperature gas-cooled reactors have significant advantages in terms of inherent high safety, high thermal efficiency, and high fuel utilization. Its core components, such as primary circuit pressure boundary components (e.g., in-core components, heat exchange equipment, process piping), will be in long-term service in a high-temperature helium (He) environment exceeding 800°C. In this environment, materials must withstand extreme environmental effects such as high temperature, high pressure, and corrosion. Therefore, extremely high requirements are placed on the high-temperature mechanical properties, high-temperature corrosion resistance, and structural stability of the materials.

[0003] Currently, austenitic stainless steel is commonly used as the pressure boundary material for the primary circuit of high-temperature gas-cooled reactors (HTGRs). It primarily withstands temperatures below 700°C. However, significant technical challenges arise in the future helium environment of HTGRs exceeding 750°C: First, its high-temperature strength is insufficient; the yield strength and tensile strength are insufficient to meet the load-bearing requirements of pressure boundary components, leading to deformation and failure during long-term service. Second, its high-temperature oxidation resistance is limited, relying mainly on the protective Cr2O3 oxide film formed on the surface. This oxide film is prone to thickening, cracking, and peeling in the 800°C helium environment, resulting in a significant upper limit to the material's corrosion resistance. Existing austenitic stainless steel patents are mostly geared towards service environments below 650°C, lacking dedicated austenitic stainless steel materials for higher-temperature helium environments, thus failing to meet the long-term safe service requirements of the pressure boundary components in the primary circuit of HTGRs. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides an austenitic stainless steel, its preparation method, and its application. The austenitic stainless steel provided by this invention possesses excellent high-temperature mechanical properties, high-temperature oxidation resistance, and structural stability, and can be stably adapted to the operating environment of a high-temperature gas-cooled reactor primary circuit exceeding 800°C.

[0005] In a first aspect, the present invention provides an austenitic stainless steel, wherein, based on 100% of the total mass of the austenitic stainless steel, the austenitic stainless steel is composed of the following elements: Chromium 18.5-19.5%, Nickel 30.0-40.0%, Aluminum 1.0-5.0%, Manganese 0.45-0.55%, Niobium 0.45-0.55%, Carbon 0.02-0.03%, Sulfur 0-0.01%, and Iron balance.

[0006] The austenitic stainless steel provided by this invention possesses excellent high-temperature mechanical properties, high-temperature oxidation resistance, and structural stability, and can be stably adapted to the operating environment of high-temperature gas-cooled reactors with primary circuit temperatures exceeding 800°C. Specifically: The austenitic stainless steel provided by this invention contains only eight elements: iron (Fe), chromium (Cr), nickel (Ni), aluminum (Al), manganese (Mn), niobium (Nb), carbon (C), and sulfur (S). Among them, Al is the core corrosion-resistant and strengthening element, which can significantly improve the high-temperature mechanical properties, high-temperature strength, and structural stability of austenitic stainless steel materials. It also promotes the formation of a dense and stable Al2O3 protective film in a high-temperature helium environment exceeding 800°C. The high-temperature stability of this protective film is far superior to that of the traditional Cr2O3 oxide film, which can effectively resist the corrosion in a high-temperature helium environment. This solves the problems of insufficient high-temperature corrosion resistance and limited service temperature of traditional austenitic stainless steel. At the same time, it forms a strengthening phase with Nb, Ni, C, and other elements, further improving the high-temperature strength and structural stability of the material, thus making it suitable for the high-temperature helium environment exceeding 800°C in the primary loop of a high-temperature gas-cooled reactor.

[0007] The chromium content can be 18.5%, 18.8%, 19.0%, 19.2%, 19.5%, etc.

[0008] The nickel content can be 30.0%, 32.0%, 34.0%, 36.0%, 38.0%, 40.0%, etc.

[0009] The aluminum content can be 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, etc.

[0010] The manganese content can be 0.45%, 0.48%, 0.5%, 0.52%, 0.55%, etc.

[0011] The niobium content can be 0.45%, 0.48%, 0.5%, 0.52%, 0.55%, etc.

[0012] The carbon content can be 0.02%, 0.022%, 0.025%, 0.028%, 0.03%, etc.

[0013] The sulfur content can be 0.001%, 0.002%, 0.005%, 0.008%, 0.01%, etc.

[0014] As a preferred embodiment of the present invention, the austenitic stainless steel, with a total mass of 100%, is composed of the following elements: Chromium 18.5-19.5%, Nickel 31.5-32.5%, Aluminum 1.0-5.0%, Manganese 0.45-0.55%, Niobium 0.45-0.55%, Carbon 0.02-0.03%, Sulfur 0-0.01%, and Iron balance.

[0015] As a preferred embodiment of the present invention, the austenitic stainless steel, with a total mass of 100%, is composed of the following elements: Chromium 19%, Nickel 32%, Aluminum 1.0-5.0%, Manganese 0.5%, Niobium 0.5%, Carbon 0.02%, Sulfur 0-0.01%, and Iron balance.

[0016] With the above-mentioned preferred elemental composition, the austenitic stainless steel of the present invention has superior high-temperature mechanical properties, high-temperature oxidation resistance, and structural stability.

[0017] As a preferred embodiment of the present invention, the austenitic stainless steel contains NbC strengthening phase and NiAl strengthening phase.

[0018] As a preferred embodiment of the present invention, the particle size of the NbC reinforced phase is 10-30 nm, such as 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, etc.

[0019] As a preferred embodiment of the present invention, the particle size of the NiAl reinforcing phase is 200-800 nm, such as 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, etc.

[0020] The austenitic stainless steel of this invention contains NbC strengthening phase and NiAl strengthening phase, which can further improve the high-temperature strength, corrosion resistance and microstructure stability of austenitic stainless steel materials.

[0021] As a preferred embodiment of the present invention, the austenitic stainless steel, under a helium atmosphere at 800°C, has a tensile strength greater than or equal to 450 MPa, a yield strength greater than or equal to 250 MPa, and an elongation at break of 25-30%, such as 25%, 26%, 27%, 28%, 29%, 30%, etc.

[0022] The austenitic stainless steel provided by this invention has excellent high-temperature mechanical properties, combining high strength and good plasticity, and can be adapted to service conditions with higher temperatures and higher pressures.

[0023] As a preferred embodiment of the present invention, the austenitic stainless steel exhibits an oxidation weight gain of less than 45 mg / dm³ under helium atmosphere at 800°C for 1000 hours. 2 .

[0024] The austenitic stainless steel provided by this invention has excellent high-temperature oxidation resistance, significantly improves the corrosion resistance stability of austenitic stainless steel materials in a high-temperature helium environment exceeding 800℃, and extends the service life of the materials.

[0025] In a second aspect, the present invention provides a method for preparing the austenitic stainless steel described in the first aspect, the method comprising the following steps: (1) The iron, chromium, nickel and niobium metal raw materials are vacuum melted until completely liquefied and clarified, carbon raw materials are added for refining, and then manganese and aluminum metal raw materials are added and mixed evenly, and then cast into shape to obtain steel ingots. (2) The steel ingot is forged into a stainless steel forging billet, and then heat-treated to obtain the austenitic stainless steel.

[0026] Among them, the purity of iron, chromium, nickel, niobium, manganese and aluminum metal raw materials is all above 99.99%.

[0027] The preparation method provided by this invention optimizes the heat treatment process parameters to effectively improve the structural stability, mechanical properties and corrosion resistance of austenitic stainless steel in a high-temperature helium environment above 800℃. At the same time, this invention adopts conventional mature processes such as vacuum melting, forging and heat treatment, without the need for additional special production equipment. All processes can be realized on existing production lines, the difficulty of composition control is moderate, and the production cost is comparable to that of traditional austenitic stainless steel, enabling large-scale mass production.

[0028] As a preferred technical solution of the present invention, the carbon raw material in step (1) includes carbon powder and / or graphite powder.

[0029] As a preferred technical solution of the present invention, the temperature of vacuum melting in step (1) is 1500-1700℃, such as 1500℃, 1550℃, 1600℃, 1650℃, 1700℃, etc.

[0030] As a preferred embodiment of the present invention, the refining temperature is 1800-2000℃, such as 1800℃, 1850℃, 1900℃, 1950℃, 2000℃, etc.

[0031] As a preferred embodiment of the present invention, the operation of adding manganese and aluminum metal raw materials and mixing them is carried out under an inert gas atmosphere, wherein the inert gas includes argon and helium.

[0032] As a preferred embodiment of the present invention, the forging method in step (2) includes: Heat to 1180-1220℃ (e.g., 1190℃, 1200℃, 1210℃, 1220℃) at a heating rate of 100-150℃ / h (e.g., 100℃ / h, 110℃ / h, 120℃ / h, 130℃ / h, 140℃ / h, 150℃ / h, etc.), and hold at that temperature for 4-6 hours (e.g., 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours). After cooling to 1150-1180℃ (e.g., 1150℃, 1160℃, 1170℃, 1180℃, etc.), forging begins. The initial forging temperature is 1150-1220℃ (e.g., 1150℃, 1180℃, 1200℃, 1220℃, etc.), and the final forging temperature is greater than or equal to 930℃. Forging is completed in 2-3 hours, followed by air cooling to room temperature to obtain a stainless steel forging billet.

[0033] As a preferred embodiment of the present invention, the stainless steel forging billet is further polished before the heat treatment to remove the oxide layer and defects on the surface.

[0034] As a preferred embodiment of the present invention, the heat treatment in step (2) includes a solution treatment and an aging treatment performed sequentially: The solution treatment method involves holding the stainless steel billet at 1200-1250℃ (e.g., 1200℃, 1210℃, 1220℃, 1230℃, 1240℃, 1250℃, etc.) for 60-90 min (e.g., 60 min, 70 min, 80 min, 90 min, etc.) and then water cooling it to room temperature to ensure the uniformity of the microstructure of the stainless steel forging billet. The aging treatment method involves holding the temperature at 725-775℃ (e.g., 725℃, 735℃, 745℃, 755℃, 765℃, 775℃, etc.) for 100-120 h (e.g., 100 h, 105 h, 110 h, 115 h, 120 h, etc.) and then cooling it to room temperature.

[0035] This invention effectively improves the structural stability, mechanical properties, and corrosion resistance of austenitic stainless steel in a high-temperature helium environment above 800℃ by optimizing the solution treatment and aging process parameters.

[0036] Thirdly, the present invention provides the application of the austenitic stainless steel described in the first aspect or the austenitic stainless steel prepared by the preparation method described in the second aspect in the material for the pressure boundary of the primary loop of a high-temperature gas-cooled reactor.

[0037] The technical solution provided by the embodiments of the present invention has the following advantages compared with the prior art: The austenitic stainless steel provided by this invention has excellent high-temperature mechanical properties, high-temperature oxidation resistance and structural stability, and can be stably adapted to the operating environment of high-temperature gas-cooled reactor primary circuit exceeding 800°C. Attached Figure Description

[0038] The drawings herein are incorporated into and constitute a part of this specification, show embodiments in accordance with the present invention, and serve to explain the principles of the present invention together with the specification.

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following briefly introduces the accompanying drawings required for describing the embodiments or the prior art. Obviously, for those skilled in the art, other drawings can be obtained from these drawings without creative labor.

[0040] Figure 1 is a preparation flow chart of the austenitic stainless steel described in Embodiment 1 of the present invention. Detailed Description

[0041] In order to more clearly understand the above objects, features and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0042] Many specific details are set forth in the following description to facilitate a full understanding of the present invention, but the present invention can also be implemented in other ways different from those described herein. Obviously, the embodiments in the specification are only part of the embodiments of the present invention, not all of them.

[0043] Embodiment 1 The present embodiment provides an austenitic stainless steel and a preparation method thereof. Based on the total mass of the austenitic stainless steel as 100%, the austenitic stainless steel consists of the following elements: Cr=19.0%, Ni=32.0%, Al=1.0%, Mn=0.50%, Nb=0.50%, C=0.02%, 0%<S≤0.01wt%, and the balance is Fe.

[0044] The flow chart of the preparation method is shown in Figure 1 and includes the following steps: (1) Raw material preparation and smelting: after pure metal raw materials Fe, Cr, Ni and Nb are uniformly mixed according to the above proportion in this embodiment, the mixture is placed in a crucible of a vacuum smelting furnace, after vacuum pumping, power is supplied for temperature rise to carry out smelting, the smelting temperature is controlled at 1600°C, after all the metal raw materials in the furnace are completely liquefied and clarified, C powder is added for refining treatment, and the refining temperature is 1900°C.

[0045] (2) Casting molding: after refining is completed, 0.03-0.05MPa argon is introduced into the vacuum smelting furnace as an inert protective gas, then Mn and Al metal raw materials are added, after stirring uniformly to ensure that the distribution of each element is uniform, the molten metal in the furnace is cast and molded to obtain a stainless steel ingot.

[0046] (3) Forging forming: placing the smelted stainless steel ingot into a heating furnace for gradient heating, controlling the heating rate at 120°C / h, heating up to 1200°C, holding the temperature for 5 hours, cooling down to 1160-1180°C before starting forging, wherein the initial forging temperature is not lower than 1150°C and not higher than 1220°C, the final forging temperature is not lower than 930°C, forging is carried out for 2 h, and after forging is completed, the product is air-cooled to room temperature to obtain a stainless steel forging blank; the surface of the forging blank is ground to completely remove oxide scale on the surface of the forging blank and defects generated during forging, so as to obtain a forging blank with a smooth surface.

[0047] (4) Heat treatment: subjecting the descaled stainless steel forging blank to heat treatment: first carrying out solution treatment, controlling the solution temperature at 1200°C, holding the temperature for 60 minutes, then water-cooling to room temperature to ensure homogenization of the structure of the forging blank; then carrying out aging treatment, controlling the aging temperature at 750°C, holding the temperature for 100 hours, and naturally cooling to room temperature after heat preservation is completed, so as to obtain a stable austenite structure and NbC and NiAl strengthening phases, wherein the particle size of the NbC strengthening phase is 10-30 nm and the particle size of the NiAl strengthening phase is 200-800 nm, that is the austenitic stainless steel.

[0048] Example 2 This example provides an austenitic stainless steel and a preparation method thereof, based on the total mass of the austenitic stainless steel being 100%, the austenitic stainless steel consists of the following elements: Cr=19.0%, Ni=32.0%, Al=2.0%, Mn=0.50%, Nb=0.50%, C=0.02%, 0% < S ≤ 0.01 wt%, and the balance is Fe.

[0049] The preparation method is the same as that in Example 1.

[0050] Example 3 This example provides an austenitic stainless steel and a preparation method thereof, based on the total mass of the austenitic stainless steel being 100%, the austenitic stainless steel consists of the following elements: Cr=19.0%, Ni=32.0%, Al=3.0%, Mn=0.50%, Nb=0.50%, C=0.02%, 0% < S ≤ 0.01 wt%, and the balance is Fe.

[0051] The preparation method is the same as that in Example 1.

[0052] Example 4 This example provides an austenitic stainless steel and a preparation method thereof, based on the total mass of the austenitic stainless steel being 100%, the austenitic stainless steel consists of the following elements: Cr=19.0%, Ni=32.0%, Al=4.0%, Mn=0.50%, Nb=0.50%, C=0.02%, 0%<S≤0.01wt%, with the balance being Fe.

[0053] The preparation method is the same as that in Example 1.

[0054] Example 5 This example provides an austenitic stainless steel and a preparation method thereof. Based on 100% of the total mass of the austenitic stainless steel, the austenitic stainless steel consists of the following elements: Cr=19.0%, Ni=32.0%, Al=5.0%, Mn=0.50%, Nb=0.50%, C=0.02%, 0%<S≤0.01wt%, with the balance being Fe.

[0055] The preparation method is the same as that in Example 1.

[0056] Example 6 This example provides an austenitic stainless steel and a preparation method thereof. Based on 100% of the total mass of the austenitic stainless steel, the austenitic stainless steel consists of the following elements: Cr=18.5%, Ni=40%, Al=1.0%, Mn=0.55%, Nb=0.45%, C=0.03%, 0%<S≤0.01wt%, with the balance being Fe.

[0057] The preparation method comprises the following steps: (1) Raw material preparation and smelting: after uniformly mixing pure metal raw materials Fe, Cr, Ni and Nb according to the above proportion in this example, place the mixture in a crucible of a vacuum smelting furnace, evacuate the vacuum and then power on to raise the temperature for smelting, control the smelting temperature at 1500°C. After all the metal raw materials in the furnace are completely liquefied and clarified, add graphite powder for refining treatment, and the refining temperature is 2000°C.

[0058] (2) Casting molding: after refining is completed, feed 0.03-0.05MPa argon as inert protective gas into the vacuum smelting furnace, then add Mn and Al metal raw materials, stir uniformly to ensure uniform distribution of each element, then cast and mold the molten metal in the furnace to obtain a stainless steel ingot.

[0059] (3) Forging forming: placing the smelted stainless steel ingot into a heating furnace for gradient heating, controlling the heating rate at 150°C / h, heating to 1220°C, keeping the temperature for 6 hours, cooling to 1160-1180°C and then starting forging, wherein the initial forging temperature is not lower than 1150°C and not higher than 1220°C, the final forging temperature is not lower than 930°C, forging is performed for 3 h, and after forging is completed, air cooling is performed to room temperature to obtain a stainless steel forging blank; polishing the surface of the forging blank to thoroughly remove oxide scale on the surface of the forging blank and defects generated during forging, so as to obtain a forging blank with a smooth surface.

[0060] (4) Heat treatment: subjecting the descaled stainless steel forging blank to heat treatment: first performing solution treatment, controlling the solution temperature at 1250°C, keeping the temperature for 80 minutes, then water cooling to room temperature to ensure homogenization of the structure of the forging blank; then performing aging treatment, controlling the aging temperature at 725°C, keeping the temperature for 120 hours, after heat preservation is completed, naturally cooling to room temperature to obtain a stable austenite structure and NbC and NiAl strengthening phases, wherein the particle size of the NbC strengthening phase is 10-30 nm, and the particle size of the NiAl strengthening phase is 200-800 nm, that is the austenitic stainless steel.

[0061] Example 7 This example provides an austenitic stainless steel and a preparation method thereof. Based on 100% of the total mass of the austenitic stainless steel, the austenitic stainless steel consists of the following elements: Cr=19.5%, Ni=30%, Al=1.0%, Mn=0.45%, Nb=0.55%, C=0.02%, 0%<S≤0.01wt%, and the balance is Fe.

[0062] The preparation method comprises the following steps: (1) Raw material preparation and smelting: after uniformly mixing pure metal raw materials Fe, Cr, Ni and Nb according to the above proportion in this example, placing the mixture in a crucible of a vacuum smelting furnace, evacuating the vacuum and then powering on to raise the temperature for smelting, controlling the smelting temperature at 1700°C, after all the metal raw materials in the furnace are liquefied and clarified, adding C powder for refining treatment, wherein the refining temperature is 1800°C.

[0063] (2) Casting forming: after refining is completed, introducing 0.03-0.05MPa argon as an inert protective gas into the vacuum smelting furnace, then adding Mn and Al metal raw materials, stirring uniformly to ensure uniform distribution of each element component, then casting and forming the molten metal in the furnace to obtain a stainless steel ingot.

[0064] (3) Forging forming: placing the smelted stainless steel ingot into a heating furnace for gradient heating, controlling the heating rate at 100°C / h, heating to 1180°C, keeping the temperature for 6 hours, cooling to 1160-1180°C and then starting forging, wherein the initial forging temperature is not lower than 1150°C and not higher than 1220°C, the final forging temperature is not lower than 930°C, forging is performed for 2 h, and air cooling to room temperature after forging is completed to obtain a stainless steel forging billet; grinding the surface of the forging billet to thoroughly remove oxide scale on the surface of the forging billet and defects generated during forging, so as to obtain a forging billet with a smooth surface.

[0065] (4) Heat treatment: subjecting the descaled stainless steel forging billet to heat treatment: first performing solution treatment, controlling the solution temperature at 1230°C, keeping the temperature for 90 minutes, then water cooling to room temperature to ensure homogenization of the structure of the forging billet; then performing aging treatment, controlling the aging temperature at 740°C, keeping the temperature for 110 hours, and naturally cooling to room temperature after heat preservation is completed, so as to obtain a stable austenite structure and NbC and NiAl strengthening phases, wherein the particle size of the NbC strengthening phase is 10-30 nm, and the particle size of the NiAl strengthening phase is 200-800 nm, that is the austenitic stainless steel.

[0066] Comparative Example 1 This comparative example provides an austenitic stainless steel and a preparation method thereof. The composition of the austenitic stainless steel is the same as that of Example 1, and the difference from Example 1 is that the austenitic stainless steel of this comparative example does not contain Al element, that is, based on the total mass of the austenitic stainless steel being 100%, the austenitic stainless steel consists of the following elements: Cr=19.0%, Ni=32.0%, Al=0%, Mn=0.50%, Nb=0.50%, C=0.02%, 0%<S≤0.01wt%, and the balance is Fe.

[0067] The preparation method is carried out with reference to Example 1.

[0068] Comparative Example 2 This comparative example provides an austenitic stainless steel and a preparation method thereof. The composition of the austenitic stainless steel is the same as that of Example 1, and the difference from Example 1 is that the austenitic stainless steel in this comparative example does not contain Al element, and the content of Mn element is adjusted to 0.70%, that is, based on the total mass of the austenitic stainless steel being 100%, the austenitic stainless steel consists of the following elements: Cr=19.0%, Ni=32.0%, Al=0%, Mn=0.70%, Nb=0.50%, C=0.02%, 0%<S≤0.01wt%, and the balance is Fe.

[0069] The preparation method is carried out with reference to Example 1.

[0070] Comparative Example 3 This comparative example provides an austenitic stainless steel and a preparation method thereof. The composition of the austenitic stainless steel is the same as that in Example 1. The difference from Example 1 is that the austenitic stainless steel in this comparative example does not contain Al, and the content of Mn is adjusted to 0.20%. That is, based on the total mass of the austenitic stainless steel as 100%, the austenitic stainless steel consists of the following elements: Cr=19.0%, Ni=32.0%, Al=0%, Mn=0.20%, Nb=0.50%, C=0.02%, 0%<S≤0.01wt%, and the balance is Fe.

[0071] The preparation method is carried out with reference to Example 1.

[0072] Comparative Example 4 This comparative example provides an austenitic stainless steel and a preparation method thereof. The composition of the austenitic stainless steel is the same as that in Example 1. The difference from Example 1 is that the austenitic stainless steel in this comparative example does not contain Al, and the content of Nb is adjusted to 0.70%. That is, based on the total mass of the austenitic stainless steel as 100%, the austenitic stainless steel consists of the following elements: Cr=19.0%, Ni=32.0%, Al=0%, Mn=0.50%, Nb=0.70%, C=0.02%, 0%<S≤0.01wt%, and the balance is Fe.

[0073] The preparation method is carried out with reference to Example 1.

[0074] Comparative Example 5 This comparative example provides an austenitic stainless steel and a preparation method thereof. The composition of the austenitic stainless steel is the same as that in Example 1. The difference from Example 1 is that the austenitic stainless steel in this comparative example does not contain Al, and the content of Nb is adjusted to 0.20%. That is, based on the total mass of the austenitic stainless steel as 100%, the austenitic stainless steel consists of the following elements: Cr=19.0%, Ni=32.0%, Al=0%, Mn=0.50%, Nb=0.20%, C=0.02%, 0%<S≤0.01wt%, and the balance is Fe.

[0075] The preparation method is carried out with reference to Example 1.

[0076] Performance Test Conventional performance testing equipment for metallic materials is used to test the performance of the finished austenitic stainless steels prepared in each example and comparative example, and the test working conditions strictly meet the service requirements of the primary circuit pressure boundary of a high-temperature gas-cooled reactor.

[0077] 1. An oxidation weight gain test was conducted at 800℃ in a helium atmosphere for 1000 h. Sampling points were set at 200 h, 400 h, 600 h, 800 h, and 1000 h. After each test, the sample was cleaned with alcohol, dried in an oven for at least 3 hours, and then weighed. Except for some samples that were retained for subsequent analysis, the remaining samples were returned to the test environment to continue the test until the 1000 h test cycle ended.

[0078] 2. Tensile properties were tested at 800℃, determining the tensile strength, yield strength, and elongation at break. Standard tensile specimens were used for the tensile property tests, and the strain rate was 1×10⁻⁶. -4 / s, with a test temperature of 800℃, to ensure accurate and reliable test data.

[0079] The test results are shown in Table 1: Table 1

[0080] As can be seen from the test results in Table 1, the austenitic stainless steel prepared in the embodiments of the present invention has better high-temperature mechanical properties, high-temperature oxidation resistance and other properties than the comparative example.

[0081] In summary, through reasonable composition design and optimized preparation process, the austenitic stainless steel prepared by this invention can stably adapt to high-temperature helium working conditions exceeding 800℃, solving the problems of insufficient high-temperature strength, poor corrosion resistance, and weak microstructure stability of traditional austenitic stainless steel.

[0082] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0083] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An austenitic stainless steel, characterized in that, Based on the total mass of the austenitic stainless steel as 100%, the austenitic stainless steel is composed of the following elements: Chromium 18.5-19.5%, Nickel 30.0-40.0%, Aluminum 1.0-5.0%, Manganese 0.45-0.55%, Niobium 0.45-0.55%, Carbon 0.02-0.03%, Sulfur 0-0.01%, and Iron balance.

2. The austenitic stainless steel according to claim 1, characterized in that, Based on the total mass of the austenitic stainless steel as 100%, the austenitic stainless steel is composed of the following elements: Chromium 18.5-19.5%, Nickel 31.5-32.5%, Aluminum 1.0-5.0%, Manganese 0.45-0.55%, Niobium 0.45-0.55%, Carbon 0.02-0.03%, Sulfur 0-0.01%, and Iron balance.

3. The austenitic stainless steel according to claim 1 or 2, characterized in that, Based on the total mass of the austenitic stainless steel as 100%, the austenitic stainless steel is composed of the following elements: Chromium 19%, Nickel 32%, Aluminum 1.0-5.0%, Manganese 0.5%, Niobium 0.5%, Carbon 0.02%, Sulfur 0-0.01%, and Iron balance.

4. The austenitic stainless steel according to any one of claims 1-3, characterized in that, The austenitic stainless steel contains NbC strengthening phase and NiAl strengthening phase; Preferably, the particle size of the NbC reinforced phase is 10-30 nm; Preferably, the particle size of the NiAl reinforced phase is 200-800 nm.

5. The austenitic stainless steel according to any one of claims 1-4, characterized in that, The austenitic stainless steel, under a helium atmosphere at 800℃, has a tensile strength greater than or equal to 450 MPa, a yield strength greater than or equal to 250 MPa, and an elongation at break of 25-30%.

6. The method for preparing austenitic stainless steel according to any one of claims 1-5, characterized in that, The preparation method includes the following steps: (1) The iron, chromium, nickel and niobium metal raw materials are vacuum melted until completely liquefied and clarified, carbon raw materials are added for refining, and then manganese and aluminum metal raw materials are added and mixed evenly, and then cast into shape to obtain steel ingots. (2) The steel ingot is forged into a stainless steel forging billet, and then heat-treated to obtain the austenitic stainless steel.

7. The preparation method according to claim 6, characterized in that, The carbon raw material mentioned in step (1) includes carbon powder and / or graphite powder; And / or, the temperature of the vacuum melting in step (1) is 1500-1700℃; And / or, the refining temperature is 1800-2000℃; And / or, the operation of adding manganese and aluminum metal raw materials and mixing them is carried out under an inert gas atmosphere.

8. The preparation method according to claim 6 or 7, characterized in that, The forging method described in step (2) includes: Heating to 1180-1220℃ at a heating rate of 100-150℃ / h, holding at that temperature for 4-6 hours, cooling down to 1150-1180℃ and then forging begins. The initial forging temperature is 1150-1220℃, and the final forging temperature is greater than or equal to 930℃. Forging is completed in 2-3 hours, and the billet is air-cooled to room temperature to obtain a stainless steel forging billet.

9. The preparation method according to any one of claims 6-8, characterized in that, Before the heat treatment, a grinding process is performed to remove the oxide layer and defects on the surface of the stainless steel forging billet. And / or, the heat treatment in step (2) includes a solution treatment and an aging treatment performed sequentially: The solution treatment method involves holding the solution at 1200-1250℃ for 60-90 minutes and then cooling it to room temperature with water. The aging treatment method involves holding the temperature at 725-775℃ for 100-120 hours and then cooling it to room temperature.

10. The application of the austenitic stainless steel according to any one of claims 1-5 or the austenitic stainless steel prepared by the preparation method according to any one of claims 6-9 in the material for the pressure boundary of the primary loop of a high-temperature gas-cooled reactor.

Images