Production process of nuclear austenitic stainless steel capable of improving high-temperature performance

Abstract

The invention discloses a production process of nuclear austenitic stainless steel capable of improving high-temperature performance. The production process comprises component design and process design. According to the component design, the nuclear austenitic stainless steel comprises, by weight, less than or equal to 0.03% of C, less than or equal to 0.75% of Si, 1.40-1.60% of Mn, less than or equal to 0.035% of P, less than or equal to 0.020% of S, 8.4-8.6% of Ni, 18.00-18.50% of Cr, 0.040-0.055% of N and the balance Fe and residual elements. The process comprises the steps of smelting, continuous casting, heating, rolling, solution treatment and acid pickling. The production process has the characteristics of low production risk and high success rate; by reasonably controlling the content of C, Mn, N and other elements and optimizing the process design, on the basis of not increasing the smelting production difficulty, the produced nuclear stainless steel meets the high-temperature scene performance requirements that the yield strength is not smaller than 149 MPa under the condition of 100 DEG C and the tensile strength is not smaller than 419 MPa under the condition of 150 DEG C.

Description

Technical Field

[0001] This invention belongs to the field of nuclear austenitic stainless steel production technology, specifically relating to a production process for nuclear austenitic stainless steel that can improve high-temperature performance. Background Technology

[0002] Austenitic stainless steel is currently widely used in nuclear power projects. However, some components in nuclear power projects (such as the internal support structure of the reactor pressure vessel) need to withstand high temperatures and certain loads, and the high-temperature strength of conventional austenitic stainless steel cannot meet the corresponding requirements. During the design process of nuclear power projects, minimum strength indicators for materials at high temperatures are usually specified based on the specific operating temperature and stress conditions of the components. Currently, some components require a yield strength of not less than 149 MPa at 100°C and a tensile strength of not less than 419 MPa at 150°C. Existing austenitic stainless steel cannot meet these requirements; therefore, its composition and manufacturing process need to be optimized to ensure the safe operation of nuclear facilities.

[0003] Chinese patent application CN116479232A discloses a method for controlling the grain corrosion performance and high-temperature strength of thick plates of nitrogen-controlled austenitic stainless steel for nuclear power. This method is aimed at nuclear stainless steel with a thickness of ≥50mm and a yield strength of not less than 135MPa at 350℃. It mainly improves high-temperature strength and resistance to intergranular corrosion by controlling the carbon content, rolling with large deformation, and slowly heating the furnace. However, since the nitrogen content is controlled between 0.06% and 0.08%, excessively high nitrogen content is prone to porosity and delamination defects due to the limited dissolution capacity of molten steel, which places extremely high demands on smelting.

[0004] Chinese patent application CN114318137B discloses "an austenitic stainless steel plate for nuclear power and its method". It mainly increases the carbon content and adds a certain amount of Zr. However, excessive carbon content will have an adverse effect on corrosion resistance. Adding a certain amount of precious metal Zr will significantly increase production costs. At the same time, the nitrogen content is controlled between 0.15% and 0.20%, which makes it very easy to have porosity and delamination defects. Summary of the Invention

[0005] The purpose of this invention is to provide a production process for nuclear austenitic stainless steel that can improve high-temperature performance, and to develop nuclear austenitic stainless steel that is easy to smelt, has low production cost and excellent high-temperature performance, so as to solve the current situation that the high-temperature strength of conventional austenitic stainless steel cannot meet the requirements of high-temperature components.

[0006] To achieve its purpose, the present invention adopts the following technical solution: A production process for nuclear austenitic stainless steel that can improve high-temperature performance, including composition design and process design; The composition is designed to adjust the weight percentage of the austenitic stainless steel for nuclear applications to: C≤0.03%, Si≤0.75%, Mn 1.40~1.60%, P≤0.035%, S≤0.020%, Ni 8.4~8.6%, Cr 18.00~18.50%, N 0.040~0.055%, the rest being Fe and residual elements; The process design, which involves adjusting the process method, includes the following steps: (1) Smelting: Pure iron and electrolytic nickel are smelted in an AOD furnace to obtain molten steel that meets the composition requirements; (2) Continuous casting: The superheat of the continuous casting process is controlled to be ≤40℃ to obtain a continuous casting billet with a thickness of 220mm, and then rough and fine finishing and grinding are carried out. (3) Heating: Heat the ground continuous casting billet to 1180~1250℃; (4) Rolling: The continuous casting billet heated to the target temperature in step (3) is rolled by large deformation rolling process, and then rapidly cooled to 650~700℃; (5) Solution treatment: The continuously cast billet cooled in step four is subjected to solution treatment at a temperature of 1000~1050℃, with a heating coefficient of 0.8~1.0 and a heat homogenization coefficient of 1.0~1.2; (6) Pickling: The continuous casting billet after solution treatment in step (5) is pickled with a mixture of nitric acid and hydrofluoric acid to obtain austenitic stainless steel for nuclear applications with excellent high-temperature performance.

[0007] As a further preferred embodiment of the technical solution of the present invention, in step (4), the single-pass reduction rate in the longitudinal rolling stage of the large deformation rolling process is greater than 12%.

[0008] Furthermore, in step (4), the cooling temperature is 650~700℃.

[0009] Furthermore, in step (6), the concentration of nitric acid is 120~150g / l and the concentration of hydrofluoric acid is 20~30g / l.

[0010] By adopting the above technical solution, the present invention has the following beneficial effects: The production process of this invention features low production risk and high success rate. By rationally controlling the content of elements such as C, Mn, and N, and by using a large deformation rolling process with a low solution treatment temperature, a product with uniform and fine grains is finally obtained. Without increasing the difficulty of smelting and production, the nuclear stainless steel produced meets the high-temperature performance requirements of a yield strength of not less than 149 MPa at 100℃ and a tensile strength of not less than 419 MPa at 150℃. Attached Figure Description

[0011] Figure 1 A photograph of the finished austenitic stainless steel for nuclear applications obtained using the method of Example 1 of this invention. Detailed Implementation

[0012] The following detailed description of a production process for nuclear austenitic stainless steel with improved high-temperature performance, based on specific embodiments, illustrates the present invention in further detail. It is understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0013] Example 1 This embodiment provides a production process for nuclear austenitic stainless steel that can improve high-temperature performance, including the following steps: (1) Smelting: Pure iron and electrolytic nickel are smelted in an AOD furnace to obtain molten steel that meets the composition requirements; the composition of the molten steel is shown in the table below.

[0014] (2) Continuous casting: The superheat of the continuous casting process is controlled at 40℃ to obtain a continuous casting billet with a thickness of 220mm, and rough and fine finishing and grinding are carried out. (3) Heating: Heat the ground continuous casting billet to 1220℃; (4) Rolling: The continuous casting billet heated to the target temperature in step (3) is rolled by large deformation rolling process (minimum reduction rate of 13.5% per pass in the longitudinal rolling stage), and then rapidly cooled to 700℃ after rolling. The final product thickness is 15mm. (5) Solution treatment: The continuously cast billet cooled in step four is subjected to solution treatment at a temperature of 1050℃, with a heating coefficient of 0.8 and a heat homogenization coefficient of 1.0. (6) Pickling: The continuously cast billet after solution treatment in step (5) is pickled with a mixture of nitric acid and hydrofluoric acid (nitric acid concentration 150 g / L, hydrofluoric acid concentration 30 g / L) to obtain austenitic stainless steel for nuclear applications with excellent high-temperature performance. Figure 1 ).

[0015] The final product has a yield strength of 204 MPa at 100℃ and a tensile strength of 453 MPa at 150℃, which meets the requirements for use in the nuclear stainless steel industry (Table 1).

[0016] Example 2 This embodiment provides a production process for nuclear austenitic stainless steel that can improve high-temperature performance, including the following steps: (1) Smelting: Pure iron and electrolytic nickel are smelted in an AOD furnace to obtain molten steel that meets the composition requirements; the composition of the molten steel is shown in the table below.

[0017] (2) Continuous casting: The superheat of the continuous casting process is controlled at 32℃ to obtain a continuous casting billet with a thickness of 220mm, and then rough and fine finishing and grinding are carried out. (3) Heating: Heat the ground continuous casting billet to 1210℃; (4) Rolling: The continuous casting billet heated to the target temperature in step (3) is rolled by large deformation rolling process (minimum reduction rate of 12.2% per pass in the longitudinal rolling stage), and then rapidly cooled to 650°C. The final product thickness is 30mm. (5) Solution treatment: The continuously cast billet cooled in step four is subjected to solution treatment at a temperature of 1000℃, with a heating coefficient of 0.8 and a heat homogenization coefficient of 1.0. (6) Pickling: The continuous casting billet after solution treatment in step (5) is pickled with a mixture of nitric acid and hydrofluoric acid (nitric acid concentration 120g / l, hydrofluoric acid concentration 20g / l) to obtain nuclear austenitic stainless steel with excellent high-temperature performance.

[0018] The final product has a yield strength of 202 MPa at 100℃ and a tensile strength of 448 MPa at 150℃, which meets the requirements for use in the nuclear stainless steel industry (Table 1).

[0019] Example 3 This embodiment provides a production process for nuclear austenitic stainless steel that can improve high-temperature performance, including the following steps: (1) Smelting: Pure iron and electrolytic nickel are smelted in an AOD furnace to obtain molten steel that meets the composition requirements; the composition of the molten steel is shown in the table below.

[0020] (2) Continuous casting: The superheat of the continuous casting process is controlled at 36℃ to obtain a continuous casting billet with a thickness of 220mm, and then rough and fine finishing and grinding are carried out. (3) Heating: Heat the ground continuous casting billet to 1215℃; (4) Rolling: The continuous casting billet heated to the target temperature in step (3) is rolled by large deformation rolling process (minimum reduction rate of 12.8% per pass in the longitudinal rolling stage), and then rapidly cooled to 680℃ after rolling. The final product thickness is 20mm. (5) Solution treatment: The continuously cast billet cooled in step four is subjected to solution treatment at a temperature of 1030℃, with a heating coefficient of 0.9 and a heat homogenization coefficient of 1.1. (6) Pickling: The continuous casting billet after solution treatment in step (5) is pickled with a mixture of nitric acid and hydrofluoric acid (nitric acid concentration 130g / l, hydrofluoric acid concentration 25g / l) to obtain austenitic stainless steel for nuclear applications with excellent high-temperature performance.

[0021] The final product has a yield strength of 212 MPa at 100℃ and a tensile strength of 454 MPa at 150℃, which meets the requirements for use in the nuclear stainless steel industry (Table 1).

[0022] Table 1. Performance test results of products in each embodiment.

Claims

1. A production process for nuclear-grade austenitic stainless steel that can improve high-temperature performance, characterized in that, The production method includes component design and process design; The composition is designed to adjust the weight percentage of the austenitic stainless steel for nuclear applications to: C≤0.03%, Si≤0.75%, Mn 1.40~1.60%, P≤0.035%, S≤0.020%, Ni 8.4~8.6%, Cr 18.00~18.50%, N 0.040~0.055%, the rest being Fe and residual elements; The process design, which involves adjusting the process method, includes the following steps: (1) Smelting: Pure iron and electrolytic nickel are smelted in an AOD furnace to obtain molten steel that meets the composition requirements; (2) Continuous casting: The superheat of the continuous casting process is controlled to be ≤40℃ to obtain a continuous casting billet with a thickness of 220mm, and then rough and fine finishing and grinding are carried out. (3) Heating: Heat the ground continuous casting billet to 1180~1250℃; (4) Rolling: The continuous casting billet heated to the target temperature in step (3) is rolled by large deformation rolling process, and then rapidly cooled to 650~700℃; (5) Solution treatment: The continuously cast billet cooled in step four is subjected to solution treatment at a temperature of 1000~1050℃, with a heating coefficient of 0.8~1.0 and a heat homogenization coefficient of 1.0~1.2; (6) Pickling: The continuous casting billet after solution treatment in step (5) is pickled with a mixture of nitric acid and hydrofluoric acid to obtain austenitic stainless steel for nuclear applications with excellent high-temperature performance.

2. The production process of nuclear austenitic stainless steel with improved high-temperature performance as described in claim 1, characterized in that, In step (4), the single-pass reduction rate in the longitudinal rolling stage of the large deformation rolling process is greater than 12%.

3. The production process of nuclear austenitic stainless steel with improved high-temperature performance as described in claim 1, characterized in that, In step (4), the cooling temperature is 650~700℃.

4. The production process of nuclear austenitic stainless steel with improved high-temperature performance as described in claim 1, characterized in that, In step (6), the concentration of nitric acid is 120~150g / l and the concentration of hydrofluoric acid is 20~30g / l.

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