Niobium-containing 304 austenitic stainless steel plate for nuclear power and preparation method thereof

Abstract

The invention relates to the field of metal materials, in particular to a niobium-containing 304 austenitic stainless steel plate for nuclear power and a preparation method of the niobium-containing 304 austenitic stainless steel plate for nuclear power, and the niobium-containing 304 austenitic stainless steel plate comprises the following components in percentage by mass: 0.02%-0.06% of C, 1.00%-2.00% of Mn, 0.20%-0.75% of Si, 0-0.030% of P, 0-0.005% of S, 18.00%-19.50% of Cr, 8.00%-10.50% of Ni, 0.2%-0.8% of Nb, 0-0.10% of Cu, 0-0.10% of Co, 0-0.10% of N and the balance of Fe and other inevitable impurities. The 304 austenitic stainless steel is improved, and the niobium element is added, so that stable production of the 304 austenitic stainless steel plate for nuclear power can be ensured, the 304 austenitic stainless steel plate has excellent grain size, intergranular corrosion resistance and mechanical property, and the design requirements of steel for nuclear power are met.

Description

Technical Field

[0001] This invention relates to the field of metallic materials, and more specifically, to a 304 austenitic stainless steel sheet for nuclear power and its preparation method. Technical Background

[0002] Austenitic stainless steel is a non-magnetic stainless steel with high chromium and nickel content and low carbon content, and it is the most widely used stainless steel. In the nuclear power field, material selection is crucial, directly affecting the safe, reliable operation, and service life of nuclear power plants. Austenitic stainless steels 304, 316, 321, and 347 play an important role in the construction and operation of nuclear power plants due to their excellent corrosion resistance, mechanical properties, weldability, and radiation resistance, and are widely used in nuclear reactor pressure vessels, steam generators, primary loop piping systems, and control rod assemblies.

[0003] The relevant technologies for austenitic stainless steel in the nuclear power field are as follows: Patent CN117802404A, "A Production Method of High-Purity Austenitic Stainless Steel Billet for Nuclear Power", effectively avoids the infiltration of impurity elements through strict selection of raw materials and precise control of the production process, keeping various impurity elements at extremely low levels. It also optimizes the production process and adds a vacuum degassing process to ensure the inclusion level, and can produce high-purity austenitic stainless steel billets that meet the requirements of nuclear power steel. However, the production of such high-purity steel billets requires high standards for production equipment and process control, leading to increased production costs. Patent CN117428130A, "A Forging Method for Large-Size Irregular T-Way Forgings of High-Performance Austenitic Stainless Steel for Nuclear Power Plants," describes a technical solution that uses specific forging process steps and parameter control, including billet upsetting, drawing, punching, mandrel reaming, and mandrel drawing, as well as strict control of the forging ratio and reheating temperature for each step. This improves the alloy's deformation force and grain size, thereby enhancing the performance of the forgings and meeting the requirements for large-size irregular t-way forgings of high-performance austenitic stainless steel for nuclear power plants. However, the process is relatively complex, requiring strict adherence to each step and parameter, demanding high levels of technical skill and experience from production personnel, and potentially leading to longer production cycles, increased costs, and a certain impact on production efficiency. Patent CN202310621123.6, "A Stress Corrosion Resistant Austenitic Stainless Steel for Nuclear Power Plants and Its Manufacturing Method," features a rationally designed chemical composition. The addition of Nb, Mg, and Zn strengthens the steel and increases the Al content, significantly improving its high-temperature performance and stress corrosion resistance. The manufacturing method has clearly defined process parameters for smelting, continuous casting, heating, rolling, and heat treatment, offering strong operability. The produced stainless steel effectively balances stress corrosion resistance and the mechanical properties of nuclear power steel. However, the composition control and process requirements are relatively strict, making production more difficult and increasing production and quality control costs. Patent CN116695024B, "A High-Temperature Corrosion Resistant Austenitic Stainless Steel for Nuclear Power Plants and Its Manufacturing Method," is specifically developed for high-temperature corrosion resistance, meeting the requirements for use in high-temperature corrosive environments in nuclear power equipment and improving the safety and reliability of nuclear power equipment. The disadvantage is poor machinability, leading to increased production costs. Patent CN202310621125.5, "A High-Strength, High-Toughness, High-Corrosion-Resistant Austenitic Stainless Steel for Nuclear Power Plants and Its Manufacturing Method," features an optimized chemical composition, containing higher levels of elements such as Ni, Cr, and Mo, and rationally controlling the proportions of each element to give the steel excellent comprehensive properties such as high strength, high toughness, and high corrosion resistance. Its manufacturing process is meticulously designed, employing induction furnace + LF + RH smelting, specific heated rolling, and solution heat treatment processes to ensure the stability of product quality and performance. However, due to the addition of numerous alloying elements and the complex manufacturing process, production costs may be high, and the requirements for production equipment and technical personnel are high, hindering large-scale promotion and application. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the above-mentioned deficiencies of the prior art and provide a niobium-containing 304 austenitic stainless steel plate for nuclear power and its preparation method. By optimizing the alloy composition and adopting the processes of electric furnace smelting, hot forging, hot rolling and solution treatment, a niobium-containing austenitic stainless steel with good grain size, resistance to intergranular corrosion and mechanical properties is finally obtained to meet the requirements of niobium-containing austenitic stainless steel for nuclear power 304 steel.

[0005] The technical problem it aims to solve can be addressed through the following technical solutions.

[0006] A niobium-containing 304 austenitic stainless steel for nuclear power applications, wherein the chemical composition of the stainless steel by weight percentage is: C: 0.02%–0.06%, Mn: 1.00–2.00%, Si: 0.20–0.75%, P: 0–0.030%, S: 0–0.005%, Cr: 18.00–19.50%, Ni: 8.00–10.50%, Nb: 0.2–0.8%, Cu: 0–0.10%, Co: 0–0.10%, N: 0–0.10%, with the balance being Fe and other unavoidable impurities;

[0007] The preferred chemical composition of this stainless steel is: C: 0.03–0.05%, Mn: 1.20–1.40%, Si: 0.30–0.60%, Cr: 18.30–18.90%, Ni: 8.20–9.90%, Nb: 0.40–0.55% (Nb = 8*C%), Cu: 0.01–0.05%, Co: 0–0.04%, N: 0.06–0.07%.

[0008] This invention mainly involves elements such as carbon (C), manganese (Mn), silicon (Si), phosphorus (P), sulfur (S), chromium (Cr), nickel (Ni), niobium (Nb), copper (Cu), cobalt (Co), and nitrogen (N), and their effects on this invention are as follows:

[0009] Carbon (C) is an interstitial solid solution element that can significantly improve the mechanical properties of steel. As a strong austenite forming element, it can stabilize the austenite phase and inhibit ferrite formation. However, excessively high carbon content will reduce the toughness of steel and will combine with chromium (Cr) in the steel to form M23C6 type carbides, reducing the steel's resistance to intergranular corrosion. Therefore, in this invention, the carbon content is controlled at C: 0.02%–0.06%.

[0010] Manganese (Mn) is an austenite-forming element that can expand the austenite phase region and is also a good deoxidizer and desulfurizer. In stainless steel, manganese can replace some nickel to stabilize austenite, reduce production costs, and increase the nitrogen content in the steel, ensuring its strength. However, excessive manganese content will significantly reduce the steel's corrosion resistance, especially its resistance to pitting and intergranular corrosion. Therefore, the manganese content in this invention is controlled at 1.00–2.00%.

[0011] Silicon (Si) is primarily used as a deoxidizer during smelting, and it can strengthen the matrix and improve the corrosion resistance and high-temperature oxidation resistance of steel. However, excessive silicon content can lead to the precipitation of harmful phases (intermetallic compounds), reducing the hot workability and toughness of the steel. Therefore, the silicon content in this invention is controlled at Si: 0.20–0.75%.

[0012] Phosphorus (P) is generally considered a harmful element in steel, primarily manifesting as the precipitated brittle compound Fe3P. At room temperature, phosphorus drastically reduces the plasticity and toughness of steel, causing low-temperature brittleness, a phenomenon known as "cold brittleness." Therefore, the phosphorus content in this invention is controlled below 0.030%.

[0013] Sulfur (S) exists in steel in the form of FeS, which causes "hot brittleness" in steel. Sulfur also significantly reduces the weldability of steel, causes high-temperature cracking, and generates many pores and porosity in the metal weld, thereby reducing the strength of the weld. Therefore, the sulfur content in this invention is controlled below 0.005%.

[0014] Chromium (Cr) is the most important element for improving the corrosion resistance of stainless steel, and its corrosion resistance increases with increasing Cr content. However, excessively high Cr content can promote the formation of harmful phases (Sigma phase and intermetallic compounds), reduce the hot workability of stainless steel, and easily lead to metal segregation during smelting. Therefore, the chromium content in this invention is controlled at 18.00-19.50%.

[0015] Nickel (Ni) is an austenite-forming element that can expand the austenite phase region and reduce the ferrite content. Nickel can improve the composition, structure, and properties of chromium oxide films, thereby enhancing the corrosion resistance of austenitic stainless steel. Furthermore, it can significantly reduce the cold work hardening tendency of austenitic stainless steel and prevent the formation of deformed martensite during cold working. However, excessively high nickel content leads to increased production costs. Considering all factors, the nickel content in this invention is controlled at Ni: 8.00-10.50%.

[0016] Niobium (Nb) is a very important element in austenitic stainless steel:

[0017] (i) Solid solution strengthening is achieved by solid solution in the matrix;

[0018] (ii) Nb is a strong carbide-forming element. The addition of Nb, C and N can precipitate a dispersed MX phase, which plays a role in dispersion strengthening. The MX phase can pin dislocations and grain boundaries, and it has good thermal stability and is not easy to coarsen. It is the main strengthening phase in this steel.

[0019] Therefore, the niobium content in this invention is controlled at 0.2-0.8%.

[0020] In austenitic stainless steel, copper (Cu) acts as an alloying element to significantly reduce the cold work hardening tendency of chromium-nickel austenitic stainless steel and improve its cold working formability. Copper can significantly improve the corrosion resistance of austenitic stainless steel to reducing media, such as sulfuric acid and phosphoric acid. Therefore, the copper content in this invention is controlled below 0.10%.

[0021] Cobalt (Co), an austenitic stabilizing element, primarily dissolves in the matrix, exerting a strong solid solution strengthening effect and improving the structural stability of steel during high-temperature heating. Co can also increase the relative Cr content in the oxide film, promoting the formation of a continuous protective oxide film in the alloy. Simultaneously, it enhances the adhesion and density of the oxide film, delays its rupture time, and prolongs the incubation period for hot corrosion. However, Co is a precious metal, resulting in high alloying costs, and excessive Co can make processing difficult. Therefore, the Co content in this invention is controlled below 0.10%.

[0022] Nitrogen (N), like carbon, is a strong austenite-forming element and can replace nickel's austenitizing effect along with manganese. However, if the nitrogen content is too high, it will precipitate from the molten steel in the form of nitrogen pores during smelting, causing product scrap and increasing the deformation resistance during hot working, leading to difficulties in hot working. In this invention, the nitrogen content is limited to within 0.10%.

[0023] Another technical problem to be solved by the present invention is to provide an austenitic stainless steel plate made of the aforementioned niobium-containing 304 austenitic stainless steel for nuclear power, the preparation method of which includes the following steps:

[0024] S1, Smelting, according to the composition ratio of the niobium-containing 304 austenitic stainless steel for nuclear power as described above in this invention, the raw materials are smelted in an electric furnace to obtain ingots;

[0025] S2, forging: After the ingot is heated, it is subjected to multiple upsetting and blank forging, followed by air cooling to obtain an intermediate forging blank;

[0026] S3, Rolling: After the intermediate forging billet is heat-treated, it is rolled to obtain a rolled steel billet, which is then air-cooled on a cooling bed.

[0027] S4, solution treatment: after solution treatment of the rolled steel billet, water cooling is performed;

[0028] Preferably, in step S1:

[0029] By employing EF primary refining, AOD refining, and LF refining, an ingot with the same composition as the austenitic stainless steel plate described earlier in this invention is obtained.

[0030] Preferably, in step S2:

[0031] During the heat treatment process, the heating temperature is 1160-1200℃, and the holding time after reaching the temperature is 8-10 hours.

[0032] During the multi-forging process, the initial forging temperature is 1050~1120℃, and the final forging temperature is 850~950℃.

[0033] Preferably, in step S3:

[0034] In the heat treatment, the heating temperature is 1100~1220℃;

[0035] During the rolling process, the initial rolling temperature is 1100~1160℃, and the final rolling temperature is 950~1000℃.

[0036] Preferably, in step S4:

[0037] In the solution treatment, the steel billet is loaded into a hot furnace and heated to 1050-1070℃ at a rate of 50-200℃ / h, with a holding time of 10-15min.

[0038] Preferably, during the forging and rolling process from the austenitic stainless steel ingot to the austenitic stainless steel plate, the total deformation ratio of the finished product is ≥5.

[0039] Compared with existing products and technologies, the beneficial effects of this invention are as follows:

[0040] The addition of niobium to austenitic stainless steel has three main functions: first, to improve resistance to intergranular corrosion; second, to improve high-temperature performance; and third, to refine the grain size.

[0041] Enhancing resistance to intergranular corrosion: Niobium is a strong carbide-forming element. In stainless steel, niobium preferentially combines with carbon to form niobium carbide (NbC). This prevents carbon from combining with chromium to form chromium carbide (Cr). 23 C6), thereby ensuring sufficient chromium content at the grain boundaries to maintain the integrity of the chromium oxide (Cr2O3) protective film and effectively improving the stainless steel's resistance to intergranular corrosion.

[0042] Improved High-Temperature Performance: (I) High-Temperature Strength: Under high-temperature conditions, niobium compounds such as niobium carbide (NbC) are finely dispersed in the stainless steel matrix. When the material is subjected to external forces, dislocations encounter these dispersed hard particles during their movement, thereby increasing the resistance to dislocation movement and enabling the material to withstand greater external forces without significant deformation, thus improving high-temperature strength. (II) High-Temperature Oxidation Resistance: At high temperatures, niobium oxides (such as Nb2O5) together with oxides of other alloying elements form a composite oxide film. This composite oxide film has better adhesion and anti-peeling properties, and can prevent oxygen from further diffusing into the material, thereby improving the high-temperature oxidation resistance of stainless steel.

[0043] Grain refinement: During the solidification process of stainless steel, niobium can act as a nucleation site for heterogeneous growth. When liquid stainless steel begins to solidify, niobium atoms or niobium compound particles can provide additional nuclei for grain growth, increasing the grain nucleation rate. Furthermore, the dispersed precipitation of niobium carbide (NbC) at austenite grain boundaries acts as a pinning agent, inhibiting austenite grain growth. According to the Hall-Petch relation, the yield strength of a material is inversely proportional to the square root of the grain size; that is, the smaller the grain size, the higher the material strength. Simultaneously, refined grains, when subjected to external forces, can effectively hinder crack propagation through grain boundaries, thereby improving the material's toughness.

[0044] While niobium offers numerous benefits for stainless steel, it can also pose some potential risks in certain situations: First, its higher price increases production costs and the final product price. Second, during hot working, niobium raises the recrystallization temperature of stainless steel, and its carbides and nitrides reduce its thermoplasticity, increasing its resistance to deformation and leading to surface cracks and other defects during hot rolling, thus affecting the yield rate. Third, during welding, niobium forms large carbides or nitrides in the heat-affected zone, reducing the toughness of the weld joint. Furthermore, the presence of niobium alters the solidification behavior of the weld pool, increasing the probability of welding defects such as porosity and inclusions. Fourth, as a ferrite-forming element, the addition of niobium may produce small amounts of ferrite in austenitic steel.

[0045] This invention provides a niobium-containing 304 austenitic stainless steel plate for nuclear power and its preparation method. By optimizing the alloy composition and using electric furnace smelting, hot forging, hot rolling and solution treatment processes, a niobium-containing austenitic stainless steel with good grain size, resistance to intergranular corrosion and mechanical properties is finally obtained to meet the requirements of niobium-containing austenitic stainless steel for nuclear power 304 steel. Detailed Implementation

[0046] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with embodiments.

[0047] The niobium-containing 304 austenitic stainless steel for nuclear power provided by this invention has the following chemical composition by weight percentage: C: 0.02%–0.06%, Mn: 1.00–2.00%, Si: 0.20–0.75%, P: 0–0.030%, S: 0–0.005%, Cr: 18.00–19.50%, Ni: 8.00–10.50%, Nb: 0.2–0.8%, Cu: 0–0.10%, Co: 0–0.10%, N: 0–0.10%, with the balance being Fe and other unavoidable impurities.

[0048] Based on the above-mentioned austenitic stainless steel for nuclear power, niobium-containing 304 austenitic stainless steel plates for nuclear power can be manufactured. The preparation method includes the following steps:

[0049] S1, Smelting, according to the composition ratio of the niobium-containing 304 austenitic stainless steel for nuclear power as described above in this invention, the raw materials are smelted in an electric furnace to obtain ingots;

[0050] The specific process is as follows: EF primary refining, AOD refining, and LF refining are used to obtain ingots with the same composition as the niobium-containing 304 austenitic stainless steel plate for nuclear power plants described in this invention. The raw materials used are clean, rust-free, low-phosphorus, low-sulfur, low-copper, and low-boron scrap steel. During the EF primary refining process, the following parameters need to be controlled: C ≤ 3.0%, Si ≤ 0.30%, P ≤ 0.028%, Cr: 16.0-18.5%, Ni ≤ 8.00-9.50%, Cu ≤ 0.10%, Co ≤ 0.10%, and the EF tapping temperature ≥ 1600℃. Oxygen decarburization is performed in the AOD furnace, controlling the final C content to ≤ 0.03%. Al and Si composite deoxidation is used during the reduction period, and after reduction, alloys are added to achieve the target composition according to the composition requirements. Lime, fluorite, or synthetic slag is added to the LF furnace for appropriate slag formation, and the ladle temperature is 1515-1525℃. Ar gas is used for protection during casting, and the casting rate is controlled. Demolding is performed ≥ 20 hours after casting.

[0051] S2, forging: After the ingot is heated, it is subjected to multiple upsetting and blank forging, followed by air cooling to obtain an intermediate forging blank;

[0052] The specific process is as follows: The stainless steel ingot obtained from S1 is heated to 1160-1200℃ and held at that temperature for 8-10 hours. Then, it is upset on a high-speed forging mill, and after upset, it is reheated to a furnace at a holding temperature of 1160-1180℃ for 2-3 hours. Multiple forging processes are then performed, with an initial forging temperature of 1050-1120℃ and a final forging temperature of 850-950℃, followed by air cooling to obtain the final intermediate forged billet.

[0053] S3, Rolling: After the intermediate forging billet is heat-treated, it is rolled to obtain a rolled steel billet, which is then air-cooled on a cooling bed.

[0054] The specific process is as follows: the hot rolling process involves heating the slab at a temperature of 1100–1220℃; during the rolling process, the initial rolling temperature is 1100–1160℃, and the final rolling temperature is 950–1000℃. The resulting rolled steel billet is then air-cooled on a cooling bed.

[0055] Wherein, during the forging and rolling process from the austenitic stainless steel ingot to the austenitic stainless steel plate, the total deformation ratio of the finished product is ≥5.

[0056] S4, solution treatment: after solution treatment of the rolled steel billet, water cooling is performed;

[0057] The specific process is as follows: the rolled steel billet is solution treated, heated to 1050-1070℃ at a rate of 50-200℃ / h and held for 10-15 minutes. The total heating time in the furnace is ≥ the thickness of the steel plate (mm) × 1.5 minutes (±2 minutes), and then water cooled.

[0058] The following section provides a further introduction to the niobium-containing 304 austenitic stainless steel for nuclear power and its preparation method, using specific examples.

[0059] Example 1:

[0060] The preparation process of the austenitic stainless steel sheet in this embodiment is as follows:

[0061] (1) Smelting: EF primary refining, AOD refining, and LF refining were used to obtain ingots with the same composition as the niobium-containing 304 austenitic stainless steel plate for nuclear power plants described in this invention, as shown in Table 1. The LF furnace ladle temperature was 1518℃. Demolding was performed 21 hours after casting.

[0062] (2) Forging: The stainless steel ingot is heated to 1180℃ and held at that temperature for 8 hours. Then, it is upset on a high-speed forging mill, and then reheated in the furnace at 1170℃ for 2.5 hours. Multi-fire forging is then performed, with the initial forging temperature at 1100℃ and the final forging temperature at 900℃, followed by air cooling to obtain the final intermediate forging billet.

[0063] (3) Rolling: The intermediate forging billet is heat-treated to a temperature of 1150°C; during the rolling process, the initial rolling temperature is 1120°C and the final rolling temperature is 980°C. The rolled steel billet is obtained and air-cooled on a cooling bed.

[0064] In the process of forging and rolling from the austenitic stainless steel ingot to the austenitic stainless steel plate, the total deformation ratio of the finished product is 6.

[0065] (4) Solution treatment: The rolled steel billet is solution treated by heating to 1060℃ at a rate of 80℃ / h and holding for 15 minutes, and then water cooling.

[0066] Example 2:

[0067] The preparation process of the austenitic stainless steel sheet in this embodiment is as follows:

[0068] (1) Smelting: EF primary refining, AOD refining, and LF refining were used to obtain ingots with the same composition as the niobium-containing 304 austenitic stainless steel plate for nuclear power plants described in this invention, as shown in Table 1. The LF furnace ladle temperature was 1520℃. Demolding was performed 23 hours after casting.

[0069] (2) Forging: The stainless steel ingot is heated to 1170℃ and held at that temperature for 8 hours. Then, it is upset on a high-speed forging mill, and then reheated in the furnace at 1165℃ for 3 hours. Multi-fire forging is performed, with an initial forging temperature of 1080℃ and a final forging temperature of 880℃, followed by air cooling to obtain the final intermediate forging billet.

[0070] (3) Rolling: The intermediate forging billet is heat-treated to a temperature of 1200℃; during the rolling process, the initial rolling temperature is 1150℃ and the final rolling temperature is 990℃. The rolled steel billet is obtained and air-cooled on a cooling bed.

[0071] In the process of forging and rolling from the austenitic stainless steel ingot to the austenitic stainless steel plate, the total deformation ratio of the finished product is 6.

[0072] (4) Solution treatment: The rolled steel billet is solution treated by heating to 1065°C at a rate of 75°C / h and holding for 13 minutes, and then water cooling.

[0073] Example 3:

[0074] The preparation process of the austenitic stainless steel sheet in this embodiment is as follows:

[0075] (1) Smelting: EF primary refining, AOD refining, and LF refining were used to obtain ingots with the same composition as the niobium-containing 304 austenitic stainless steel plate for nuclear power plants described in this invention, as shown in Table 1. The LF furnace ladle temperature was 15-15℃. Demolding was performed 20 hours after casting.

[0076] (2) Forging: The stainless steel ingot is heated to 1190℃ and held at that temperature for 8 hours. Then, it is upset on a high-speed forging mill, and then reheated in the furnace at 1175℃ for 2 hours. Multi-fire forging is performed, with an initial forging temperature of 1060℃ and a final forging temperature of 870℃, followed by air cooling to obtain the final intermediate forging billet.

[0077] (3) Rolling: The intermediate forging billet is heat-treated to a temperature of 1120°C; during the rolling process, the initial rolling temperature is 1110°C and the final rolling temperature is 960°C. The rolled steel billet is obtained and air-cooled on a cooling bed.

[0078] In the process of forging and rolling from the austenitic stainless steel ingot to the austenitic stainless steel plate, the total deformation ratio of the finished product is 6.

[0079] (4) Solution treatment: The rolled steel billet is solution treated by heating to 1055℃ at a rate of 80℃ / h and holding for 14 minutes, and then water cooling.

[0080] Example 4:

[0081] The preparation process of the austenitic stainless steel sheet in this embodiment is as follows:

[0082] (1) Smelting: EF primary refining, AOD refining, and LF refining were used to obtain ingots with the same composition as the niobium-containing 304 austenitic stainless steel plate for nuclear power plants described in this invention, as shown in Table 1. The LF furnace ladle temperature was 1523℃. Demolding was performed 22 hours after casting.

[0083] (2) Forging: The stainless steel ingot is heated to 1200℃ and held at that temperature for 8 hours. Then, it is upset on a high-speed forging mill, and then reheated in the furnace at 1180℃ for 2.5 hours. Multi-fire forging is then performed, with the initial forging temperature at 1100℃ and the final forging temperature at 810℃. After air cooling, an intermediate forging billet is finally obtained.

[0084] (3) Rolling: The intermediate forging billet is heat-treated to a temperature of 1180°C; during the rolling process, the initial rolling temperature is 1130°C and the final rolling temperature is 980°C. The rolled steel billet is obtained and air-cooled on a cooling bed.

[0085] In the process of forging and rolling from the austenitic stainless steel ingot to the austenitic stainless steel plate, the total deformation ratio of the finished product is 6.

[0086] (4) Solution treatment: The rolled steel billet is solution treated by heating it to 1060°C at a rate of 85°C / h and holding it for 14 minutes, and then water cooling.

[0087] Comparative example:

[0088] The comparative example is 304 steel, and its composition and mass fraction are shown in Table 1.

[0089] The grain size, intergranular corrosion resistance, and mechanical properties of the niobium-containing 304 austenitic stainless steel for nuclear power prepared above are shown in Tables 2 and 2.

[0090] Table 1. Chemical composition (wt.%) of austenitic stainless steel ingots

[0091] C Mn Si P S Cr Ni Nb Cu Co N Fe Example 1 0.04 1.34 0.53 0.018 0.003 18.88 9.85 0.44 0.04 0.03 0.07 Bal. Example 2 0.05 1.29 0.49 0.025 0.003 18.32 8.35 0.52 0.01 0.00 0.07 Bal. Example 3 0.03 1.26 0.42 0.020 0.001 18.35 8.30 0.47 0.03 0.04 0.06 Bal. Example 4 0.05 1.20 0.32 0.013 0.004 18.39 8.29 0.50 0.02 0.02 0.06 Bal. Comparative Example 0.04 1.16 0.37 0.015 0.003 18.54 8.20 0 0.03 0.02 0.06 Bal.

[0092] Table 2 Grain size and intergranular corrosion

[0093] Grain size grade Intergranular corrosion Example 1 6.5 No tendency for intergranular corrosion Example 2 6.0 No tendency for intergranular corrosion Example 3 6.0 No tendency for intergranular corrosion Example 4 6.5 No tendency for intergranular corrosion Comparative Example 5.0 No tendency for intergranular corrosion

[0094] Table 3 Mechanical Properties

[0095] <![CDATA[R P0.2 (MPa)]]> <![CDATA[R m (MPa)]]> A(％) Z(％) Example 1 276 638 60.0 78 Example 2 278 628 59.5 77 Example 3 275 624 60.5 78 Example 4 266 611 60.5 78 Comparative Example 245 583 60 88

[0096] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A niobium-containing 304 austenitic stainless steel for nuclear power applications, characterized in that, It contains the following alloying elements: C, Mn, Si, P, S, Cr, Ni, Nb, Cu, Co, N, and Fe, with the following mass percentages for each element: C: 0.02%–0.06%, Mn: 1.00–2.00%, Si: 0.20–0.75%, P: 0–0.030%, S: 0–0.005%, Cr: 18.00–19.50%, Ni: 8.00–10.50%, Nb: 0.2–0.8%, Cu: 0–0.10%, Co: 0–0.10%, N: 0–0.10%, with the balance being Fe and other unavoidable impurities.

2. The niobium-containing 304 austenitic stainless steel for nuclear power plants according to claim 1, characterized in that, The niobium-containing 304 austenitic stainless steel for nuclear power has an alloy element composition of Nb = 8*C.

3. A sheet material formed from niobium-containing 304 austenitic stainless steel for nuclear power as described in claim 1 or 2.

4. A method for preparing the niobium-containing 304 austenitic stainless steel plate for nuclear power as described in claim 3, characterized in that, Includes the following steps: S1, Smelting, according to the composition ratio of the niobium-containing 304 austenitic stainless steel for nuclear power as described in claim 1, wherein the raw materials are smelted in an electric furnace to obtain ingots; S2, forging: After the ingot is heated, it is subjected to multiple upsetting and blank forging, followed by air cooling to obtain an intermediate forging blank; S3, Rolling: After the intermediate forging billet is heat-treated, it is rolled to obtain a rolled steel billet, which is then air-cooled on a cooling bed. S4, solution treatment: after solution treatment of the rolled steel billet, water cooling is performed.

5. The method for preparing niobium-containing 304 austenitic stainless steel plate for nuclear power plants according to claim 4, characterized in that, In step S1: An ingot with the same composition as the austenitic stainless steel plate described in claim 1 is obtained by using EF primary refining, AOD refining, and LF refining.

6. The method for preparing niobium-containing 304 austenitic stainless steel sheet for nuclear power plants according to claim 4, characterized in that, In step S2: During the heat treatment process, the heating temperature is 1160~1200℃, and the holding time after reaching the temperature is 8~10h; During the multi-forging process, the initial forging temperature is 1050~1120℃, and the final forging temperature is 850~950℃.

7. The method for preparing niobium-containing 304 austenitic stainless steel plate for nuclear power plants according to claim 4, characterized in that, In step S3: In the heat treatment, the heating temperature is 1100~1220℃; During the rolling process, the initial rolling temperature is 1100~1160℃, and the final rolling temperature is 950~1000℃.

8. The method for preparing niobium-containing 304 austenitic stainless steel plate for nuclear power plants according to claim 4, characterized in that, In step S4: In the solution treatment, the steel billet is loaded into a hot furnace and heated to 1050-1070℃ at a rate of 50-200℃ / h, with a holding time of 10-15min.

9. The method for preparing niobium-containing 304 austenitic stainless steel plate for nuclear power plants according to claim 4, characterized in that, From the austenitic stainless steel ingot to the austenitic stainless steel plate, the total deformation ratio of the finished product during forging and rolling is ≥5.