A method for improving the high-temperature thermal stability of ferritic martensitic steel and its application

Abstract

The present invention relates to a method for improving the high-temperature thermal stability of ferritic-martensitic steel and its application, belonging to the technical field of nuclear structural materials. The method specifically includes the following steps: forging, starting rolling, rolling, quenching and air cooling an alloy steel ingot in sequence to obtain an alloy blank with a ferritic-martensitic structure; subjecting the above alloy blank to austenitization at 1020-1080°C, quenching, tempering at 700-750°C and air cooling in sequence to maintain the ferritic-martensitic structure in the alloy blank while increasing the solute element concentration in the alloy blank; finally, performing severe plastic deformation processing on the alloy blank after the secondary heat treatment. This method can maintain good plasticity while increasing the high-temperature tensile strength of ferritic-martensitic steel, realizing the improvement of high-temperature thermal stability, and is beneficial to enhancing the application prospect of ferritic-martensitic steel in nuclear structural materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of nuclear structural materials, and particularly relates to a method for improving the high-temperature thermal stability of ferritic-martensitic steel and its application. Background Art

[0002] Ferritic-martensitic (F / M) steel is considered to be one of the most promising candidate structural materials for nuclear applications due to its excellent thermophysical, mechanical, and anti-irradiation swelling properties. However, whether as a structural material for a fusion reactor or a nuclear reactor, it faces the combined effects of neutron irradiation, liquid metal corrosion, and high temperature (500 - 600 °C). Therefore, there is an urgent need to develop ferritic-martensitic steel with better high-temperature resistance, radiation resistance, and corrosion resistance.

[0003] In the prior art, Patent CN117431370A discloses a high-temperature high-strength and high-plasticity ferritic-martensitic steel and its preparation method. First, the steel ingot is heat-treated to obtain the original ferritic-martensitic steel, and then the obtained original ferritic-martensitic steel is subjected to cold plastic deformation processing with a total strain ≥ 1 at a low temperature (not higher than 50 °C) to obtain a nanocrystalline or ultrafine-grained ferritic-martensitic steel with a large number of prefabricated dislocations. Subsequently, the dislocation behavior is controlled by controlling the heat treatment process, so that a large number of prefabricated dislocations evolve into substructures such as dislocation cell structures or subgrains, thereby enabling the obtained ferritic-martensitic steel to have both high strength and plasticity at high temperature (550 °C).

[0004] Severe plastic deformation to refine grains is a common means to strengthen the material properties, which can significantly increase the volume density of grain boundaries. On the one hand, grain boundaries can absorb point defects generated by neutron irradiation and improve the radiation resistance of the material. On the other hand, as a rapid diffusion channel for elements, it can improve the corrosion resistance of the material. However, materials with severe plastic deformation at low temperature usually have poor thermal stability, making it difficult for the deformed materials to meet the requirements of high-temperature service conditions in fusion reactors or nuclear fission reactors. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for improving the high-temperature thermal stability of ferritic-martensitic steel and its application in view of the problems existing in the background art.

[0006] The present invention achieves the above purpose through the following technical solutions:

[0007] The present invention provides a method for improving the high-temperature thermal stability of ferritic-martensitic steel, and the method includes the following steps:

[0008] (1) Forging, starting rolling, rolling, quenching, and air cooling the alloy steel ingot in sequence to obtain an alloy blank with a ferritic-martensitic structure;

[0009] (2) The alloy blank processed in step (1) is successively subjected to austenitization at 1020 - 1080 °C, quenching, tempering at 700 - 750 °C, and air cooling, so as to maintain the ferrite-martensite structure in the alloy blank while increasing the concentration of solute elements in the alloy blank;

[0010] (3) The alloy blank processed in step (2) is subjected to severe plastic deformation processing.

[0011] As a further optimized solution, the alloying elements of the alloy steel ingot include Fe, C, Cr, W, Si, Mn, V, Ta, and Zr, wherein the content of Fe element is ≥ 80%.

[0012] As a further optimized solution, the time of austenitization is 40 - 60 min, and the tempering time is 1 - 2 h.

[0013] As a further optimized solution, the temperature of the severe plastic deformation processing is lower than 300 °C.

[0014] As a further optimized solution, the severe plastic deformation processing selects at least one of rotary forging and equal-channel angular pressing. The total processing strain is ≥ 3, and the total number of processing passes and strain are determined according to the achievable total processing strain. The purpose of the total processing strain ≥ 3 is to introduce a high density of dislocations in the alloy blank to ensure the interaction between dislocations and solute atoms in the alloy blank at high temperatures, achieving the effect of dynamic strain aging.

[0015] As the second aspect of the present invention, there is also provided a high-temperature thermal stability ferrite-martensite steel prepared by any of the above methods.

[0016] As a further optimized solution, the high-temperature thermal stability means that at 600 °C, the tensile strength of the ferrite-martensite steel is 500 - 515 MPa, and the total elongation is 45 - 50%.

[0017] As the third aspect of the present invention, there is also provided an application of the high-temperature thermal stability ferrite-martensite steel as described above in nuclear structural materials.

[0018] As a further optimized solution, the operating temperature of the nuclear structural material is 600 °C.

[0019] The working principle of the present invention is as follows:

[0020] Different from the prior art which first introduces a large number of dislocations into the original ferritic-martensitic steel (F / M steel) through cold plastic deformation and then anneals at 300 °C to allow the dislocations to undergo a recovery process to form dislocation cells with high-temperature thermal stability, thereby achieving an improvement in high-temperature strength and plasticity. The present invention uses a commercial ingot as the raw material, and first obtains an alloy blank with a ferritic-martensitic structure, that is, the original ferritic-martensitic steel (F / M steel), through a primary heat treatment including forging, rough rolling, rolling, quenching and air cooling. Subsequently, the F / M steel is subjected to a secondary heat treatment including austenitization, quenching and tempering to obtain F / M-R steel, so that the M 23 C6 carbides in the F / M steel dissolve and then reprecipitate, increasing the solute element concentration in the F / M-R steel. At the same time, it is ensured that the structure of the F / M-R steel remains ferritic-martensitic. On this basis, the F / M-R steel is further subjected to severe plastic deformation with a total processing strain of ≥3 to introduce a high density of dislocations, so that the dislocations interact with the solute atoms in the F / M-R steel at high temperatures, achieving the effect of dynamic strain aging. As a result, compared with the F / M-E steel, the F / M-R-E steel improves the high-temperature strength of the material at the expense of a certain amount of plasticity (or total elongation), and realizes the improvement of the high-temperature thermal stability of the ferritic-martensitic steel.

[0021] The beneficial effects of the present invention are as follows:

[0022] For nuclear reactor structural materials, especially nuclear fuel cladding, their operating temperature can reach 600 °C. Therefore, being able to maintain excellent strength and plasticity at 600 °C is more beneficial to the safety of the nuclear reactor system. In addition, during the service process of nuclear structural materials, they will also face neutron irradiation, which will cause irradiation embrittlement of the materials and exacerbate material failure. The ferritic-martensitic steel obtained by the method of the present invention has a total elongation of about 50% at 600 °C, which is nearly 80% higher than that of the original ferritic-martensitic steel. This provides a very sufficient space for resisting the irradiation embrittlement of the materials, further improving its service life, and is conducive to enhancing the application prospect of ferritic-martensitic steel in nuclear structural materials. Description of the Drawings

[0023] Figure 1 It is a process flow chart for improving the high-temperature thermal stability of ferritic-martensitic steel provided by the present invention.

[0024] Figure 2 It is the engineering stress-strain curves of the ferritic-martensitic steel (F / M) blank and the ferritic-martensitic steel (F / M-R) after secondary heat treatment at high temperatures of 500 °C (a) and 600 °C (b) before and after 4 passes of room temperature extrusion provided in Example 1 of the present invention. Detailed Embodiments

[0025] The present invention will be further described in detail below in conjunction with the accompanying drawings. It is necessary to point out here that the following specific embodiments are only used to further illustrate the present invention and should not be construed as limiting the protection scope of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above application content.

[0026] The methods used in the present invention are all conventional methods known to those skilled in the art unless otherwise specified. For those without specific conditions indicated, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For materials or instruments without the manufacturer indicated, they are all products that can be obtained through commercial purchase.

[0027] In the present invention, the alloy steel ingot is first subjected to a primary heat treatment to obtain a ferrite-martensite steel (F / M) blank with a ferrite-martensite structure. The primary heat treatment method adopted in the present invention is (but not limited to this process): The alloy steel ingot is homogenized at 1100°C for 3 h and then forged. The forging deformation ratio is 5:1 to obtain a steel billet. The steel billet is put into a heating furnace at 1100°C and held for 1 h and then rolled. The deformation amount is 50%. The rolled sample is put into a heating furnace at 800°C and held for 1 h and then rolled. The deformation amount is 30%. It is rolled for 2 passes. Subsequently, the rolled sample is held at 1020°C for 1 h and then quenched in water. Finally, it is held at 700°C for 1.5 h and then air-cooled to obtain a ferrite-martensite steel (F / M) blank.

[0028] In the present invention, the alloy steel ingot is a commercially available commercial steel ingot, and its alloying elements include: Fe, C, Cr, W, Si, Mn, V, Ta, and Zr. Among them, the Fe content is ≥80%. The alloying element composition and ratio (but not limited to this alloying element composition and ratio) of the alloy steel ingot selected in the embodiment of the present invention are 0.04 - 0.14% C, 7 - 12% Cr, 1.0 - 2.0% W, 0 - 1.0% Si, 0.2 - 0.6% Mn, 0.1 - 0.3% V, 0 - 0.2% Ta, 0 - 0.03% Zr, and the balance is Fe.

[0029] The process flow charts for improving the high-temperature thermal stability of the ferrite-martensite steel provided in Examples 1 - 4 are all as Figure 1 shown.

[0030] Example 1

[0031] The method for improving the high-temperature thermal stability of ferritic-martensitic steel disclosed in this embodiment is specifically as follows: The ferritic-martensitic steel (F / M) blank is subjected to secondary heat treatment, that is, it is austenitized at 1020 °C for 1 h and then quenched in water, and then tempered at 700 °C for 1.5 h. After tempering, it is cooled to room temperature in the air outside the heating furnace. The ferritic-martensitic steel after secondary heat treatment is denoted as F / M-R. Then, at room temperature, equal-channel angular pressing with a total strain of 4.12 is carried out on F / M-R for 4 passes, and the ferritic-martensitic steel obtained through the above treatment is denoted as F / M-R-E. In addition, the ferritic-martensitic steel obtained by directly performing equal-channel angular pressing with a total strain of 4.12 for 4 passes without secondary heat treatment is denoted as F / M-E.

[0032] High-temperature tensile tests are carried out on F / M, F / M-R, F / M-R-E, and F / M-E at 500 °C and 600 °C.

[0033] Figure 2 a shows the high-temperature (500 °C) engineering stress-strain curves of the ferritic-martensitic steel (F / M) blank and the ferritic-martensitic steel (F / M-R) after secondary heat treatment before and after equal-channel angular pressing at room temperature for 4 passes. It is measured that the tensile strength of the ferritic-martensitic steel (F / M-R-E) obtained by the method of the present invention at 500 °C is about 864 MPa, and the total elongation is about 19%. Compared with the ferritic-martensitic steel (F / M-E) that has not undergone secondary heat treatment but has been equal-channel angular pressed for 4 passes, the tensile strength is increased (from about 802 MPa to about 864 MPa), and the plasticity is decreased (from about 23% to about 19%). Compared with the ferritic-martensitic steel (F / M-R) that has not been deformed by equal-channel angular pressing for 4 passes after secondary heat treatment, the strength is significantly increased (the tensile strength is increased from about 618 MPa to about 864 MPa), and the total elongation is decreased from about 22% to about 19%. Compared with the ferritic-martensitic steel (F / M) blank, the tensile strength is significantly increased (significantly increased from about 681 MPa to about 864 MPa), and the total elongation is decreased (from about 21% to about 19%).

[0034] Figure 2b shows the high-temperature (600 °C) engineering stress-strain curves of the ferritic-martensitic steel (F / M) billet and the ferritic-martensitic steel after secondary heat treatment (F / M-R) before and after 4 passes of room-temperature extrusion. The tensile strength of the ferritic-martensitic steel (F / M-R-E) obtained by the method of the present invention at 600 °C is about 515 MPa, and the total elongation is about 50%. Compared with the ferritic-martensitic steel (F / M-E) that has not undergone secondary heat treatment but has been extruded 4 times, the tensile strength is significantly improved (significantly increased from about 373 MPa to about 515 MPa), and the plasticity decreases (decreased from about 64% to about 50%). Although the total elongation of the F / M-E steel is relatively high at this time, its low tensile strength obviously makes it no longer suitable for nuclear structural materials. Compared with the ferritic-martensitic steel (F / M-R) that has not been extruded 4 times after secondary heat treatment, both the strength and plasticity are significantly improved (the tensile strength is increased from about 433 MPa to about 515 MPa; the total elongation is significantly increased from about 28% to about 50%). Compared with the ferritic-martensitic steel (F / M) billet, the tensile strength is slightly increased (slightly increased from about 505 MPa to about 515 MPa), and the total elongation is significantly increased (significantly increased from about 28% to about 50%).

[0035] Generally speaking, the ferritic-martensitic steel (F / M-R-E) obtained by the method of the present invention realizes the improvement of high-temperature thermal stability.

[0036] Example 2

[0037] The method for improving the high-temperature thermal stability of ferritic-martensitic steel disclosed in this example is specifically as follows: The ferritic-martensitic steel (F / M) billet is subjected to secondary heat treatment, that is, it is austenitized at 1020 °C for 1 h and then quenched in water, and then tempered at 700 °C for 1.5 h. After tempering, it is cooled to room temperature in the air outside the heating furnace. The ferritic-martensitic steel after secondary heat treatment is denoted as F / M-R. Then, at room temperature, equal-channel angular extrusion with a total strain of 3.09 is carried out on F / M-R for 3 passes. The ferritic-martensitic steel obtained through the above treatment is denoted as F / M-R-E. In addition, the ferritic-martensitic steel obtained by directly performing equal-channel angular extrusion treatment with a total strain of 3.09 for 3 passes without secondary heat treatment is denoted as F / M-E.

[0038] Perform high-temperature tensile tests at 500 °C - 600 °C on F / M, F / M-R, F / M-R-E and F / M-E of this example.

[0039] The tensile strength of the ferrite-martensite steel (F / M-R-E) measured at 500 °C is approximately 821 MPa, and the total elongation is approximately 24%. Compared with the ferrite-martensite steel (F / M-E) that has not undergone secondary heat treatment but has been extruded 3 times, the strength of F / M-R-E has increased (from approximately 726 MPa to approximately 821 MPa), and the plasticity remains basically unchanged (approximately 24%). Compared with the ferrite-martensite steel (F / M-R) that has not been extruded 3 times after secondary heat treatment, both the strength and plasticity of F / M-R-E have increased (the tensile strength has increased from approximately 618 MPa to approximately 821 MPa, and the total elongation has increased from approximately 22% to approximately 24%). Compared with the ferrite-martensite steel (F / M) billet, the tensile strength of F / M-R-E has increased significantly (from approximately 681 MPa to approximately 821 MPa), and the total elongation has increased (from approximately 21% to approximately 24%).

[0040] The tensile strength of the ferrite-martensite steel (F / M-R-E) measured at 600 °C is approximately 500 MPa, and the total elongation is approximately 46%. Compared with the ferrite-martensite steel (F / M-E) that has not undergone secondary heat treatment but has been extruded 3 times, the strength of F / M-R-E has increased significantly (from approximately 387 MPa to approximately 500 MPa), and the plasticity has decreased (from approximately 57% to approximately 45%). Although the total elongation of F / M-E is higher at this time, its lower tensile strength obviously makes it no longer suitable for nuclear structural materials. Compared with the ferrite-martensite steel (F / M-R) that has not been extruded 3 times after secondary heat treatment, both the strength and plasticity of F / M-R-E have increased significantly (the tensile strength has increased from approximately 433 MPa to approximately 500 MPa, and the total elongation has increased significantly from approximately 28% to approximately 46%). Compared with the ferrite-martensite steel (F / M) billet, the tensile strength of F / M-R-E has decreased slightly (from approximately 505 MPa to approximately 500 MPa), and the total elongation has increased significantly (from approximately 28% to approximately 46%).

[0041] Example 3

[0042] The method for improving the high-temperature thermal stability of ferrite-martensite steel disclosed in this example is specifically as follows: The ferrite-martensite steel (F / M) billet is subjected to secondary heat treatment, that is, it is austenitized at 1040 °C for 50 min and then quenched in water, followed by tempering at 720 °C for 1 h. After tempering, it is cooled to room temperature in the air outside the heating furnace. The ferrite-martensite steel after secondary heat treatment is denoted as F / M-R. Then, F / M-R is subjected to rotary forging at 200 °C for 13 passes to achieve a total equivalent strain of approximately 3.2. The ferrite-martensite steel obtained through the above treatment is denoted as F / M-R-E. In addition, the ferrite-martensite steel obtained by directly performing rotary forging treatment at 200 °C for 13 passes to achieve a total equivalent strain of approximately 3.2 without secondary heat treatment is denoted as F / M-E.

[0043] The high-temperature tensile tests of F / M, F / M-R, F / M-R-E and F / M-E of this embodiment were carried out at 500 °C and 600 °C.

[0044] The tensile strength of ferritic martensitic steel (F / M-R-E) at 500 °C was measured to be approximately 830 MPa, and the total elongation was approximately 23%. Compared with the ferritic martensitic steel (F / M-E) without secondary heat treatment but subjected to 13 passes of rotary forging, the tensile strength of F / M-R-E at 500 °C was significantly increased (from approximately 740 MPa to approximately 830 MPa), and the plasticity decreased slightly (from approximately 24% to approximately 23%). Compared with the ferritic martensitic steel (F / M-R) without 13 passes of rotary forging deformation after secondary heat treatment, the strength of F / M-R-E was significantly increased (the tensile strength increased from approximately 627 MPa to approximately 830 MPa), and the total elongation increased slightly (from approximately 21% to approximately 23%). Compared with the ferritic martensitic steel (F / M) billet, the tensile strength was significantly increased (the tensile strength increased from approximately 681 MPa to approximately 830 MPa), and the total elongation increased slightly (from approximately 21% to approximately 23%).

[0045] The tensile strength of ferritic martensitic steel (F / M-R-E) at 600 °C was measured to be approximately 504 MPa, and the total elongation was approximately 48%. Compared with the ferritic martensitic steel (F / M-E) without secondary heat treatment but subjected to 13 passes of rotary forging, the tensile strength of F / M-R-E at 600 °C was significantly increased (significantly increased from approximately 383 MPa to approximately 504 MPa), and the plasticity decreased (from approximately 60% to approximately 48%). Although the total elongation of the steel was relatively high at this time, its low tensile strength obviously made it no longer suitable for nuclear structural materials. Compared with the ferritic martensitic steel (F / M-R) without 13 passes of rotary forging deformation after secondary heat treatment, both the strength and plasticity of F / M-R-E were significantly increased (the tensile strength increased from approximately 453 MPa to approximately 504 MPa, and the total elongation increased significantly from approximately 26% to approximately 48%). Compared with the ferritic martensitic steel (F / M) billet, the tensile strength remained basically unchanged, and the total elongation increased significantly (significantly increased from approximately 28% to approximately 48%).

[0046] Example 4

[0047] The method for improving the high-temperature thermal stability of ferritic martensitic steel disclosed in this embodiment is specifically as follows: subject the ferritic martensitic steel (F / M) blank to secondary heat treatment, that is, austenitize at 1080 °C for 40 min and then quench in water, subsequently temper at 750 °C for 2 h, and after tempering, cool to room temperature in air outside the heating furnace. Denote the ferritic martensitic steel after secondary heat treatment as F / M-R. Then, perform equal-channel angular pressing on F / M-R at room temperature with a total strain of 3.09 in 3 passes, and denote the ferritic martensitic steel obtained through the above treatment as F / M-R-E. Additionally, denote the ferritic martensitic steel obtained by directly performing equal-channel angular pressing treatment with a total strain of 3.09 in 3 passes without secondary heat treatment as F / M-E.

[0048] Perform high-temperature tensile tests on F / M, F / M-R, F / M-R-E, and F / M-E of this embodiment at 500 °C and 600 °C.

[0049] It is measured that the tensile strength of the ferritic martensitic steel (F / M-R-E) at 500 °C is approximately 839 MPa, and the total elongation is approximately 21%. Compared with the ferritic martensitic steel (F / M-E) that has not undergone secondary heat treatment but has been extruded 3 times, the strength of F / M-R-E is increased (significantly increased from approximately 781 MPa to approximately 839 MPa), and the plasticity is decreased (decreased from approximately 23% to approximately 21%). Compared with the ferritic martensitic steel (F / M-R) that has not been extruded 3 times after secondary heat treatment, the strength of F / M-R-E is significantly increased (the tensile strength is increased from approximately 670 MPa to approximately 839 MPa), and the total elongation is slightly increased (increased from approximately 20% to approximately 21%). Compared with the ferritic martensitic steel (F / M) blank, the tensile strength is significantly increased (increased from approximately 681 MPa to approximately 839 MPa), and the total elongation remains basically unchanged.

[0050] It is measured that the tensile strength of the ferritic martensitic steel (F / M-R-E) at 600 °C is approximately 506 MPa, and the total elongation is approximately 45%. Compared with the ferritic martensitic steel (F / M-E) that has not undergone secondary heat treatment but has been extruded 3 times, the strength of F / M-R-E is significantly increased (significantly increased from approximately 380 MPa to approximately 506 MPa), and the plasticity is decreased (decreased from approximately 60% to approximately 45%). Although the total elongation of F / M-E is higher at this time, its lower tensile strength obviously makes it no longer suitable for nuclear structural materials. Compared with the ferritic martensitic steel (F / M-R) that has not been extruded 3 times after secondary heat treatment, both the strength and plasticity of F / M-R-E are significantly increased (the tensile strength is increased from approximately 460 MPa to approximately 506 MPa, and the total elongation is significantly increased from approximately 25% to approximately 45%). Compared with the ferritic martensitic steel (F / M) blank, the tensile strength remains basically unchanged, and the total elongation is significantly increased (significantly increased from approximately 28% to approximately 45%).

[0051] Comparative Example 1

[0052] The method for improving the high-temperature thermal stability of ferritic martensitic steel disclosed in this comparative example is specifically as follows: The ferritic martensitic steel (F / M) blank is subjected to equal-channel angular pressing with a total strain of about 4.12 in 4 passes at room temperature, then austenitized at 1020°C for 1 h and quenched in water, immediately tempered at 700°C for 1.5 h, and cooled to room temperature in air outside the heating furnace after tempering. The F / M-R-E obtained in this comparative example is subjected to a high-temperature tensile test at 600°C. The results show that the tensile strength of F / M-R-E at 500°C is about 681 MPa, the total elongation is about 22%, the tensile strength at 600°C is about 503 MPa, and the total elongation is about 29%, which is close to that of the ferritic martensitic steel (F / M) blank, and the improvement of the high-temperature thermal stability of the ferritic martensitic steel cannot be achieved.

[0053] Comparative Example 2

[0054] The method for improving the high-temperature thermal stability of ferritic martensitic steel disclosed in this comparative example is specifically as follows: The ferritic martensitic steel (F / M) blank is subjected to rotary forging deformation with a total strain of about 3.2 at 200°C, then austenitized at 1020°C for 1 h and quenched in water, immediately tempered at 700°C for 1.5 h, and cooled to room temperature in air outside the furnace after tempering. The F / M-R-E obtained in this comparative example is subjected to a high-temperature tensile test at 600°C. The results show that the tensile strength of F / M-R-E at 500°C is about 683 MPa, the total elongation is about 20%, the tensile strength at 600°C is about 505 MPa, and the total elongation is about 27%, which is close to that of the ferritic martensitic steel (F / M) blank, and the improvement of the high-temperature thermal stability of the ferritic martensitic steel cannot be achieved.

[0055] The high-temperature tensile test results of the intermediate products and final products in Examples 1-4 and Comparative Examples 1-2 are summarized in Tables 1-2 as follows.

[0056] Table 1 Tensile Test Results at 500°C

[0057] ;

[0058] Table 2 Tensile Test Results at 600°C

[0059] ;

[0060] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation to the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention.

Claims

1. A method for improving the high-temperature thermal stability of ferritic martensitic steel, characterized in that, The method includes the following steps: (1) Forging, starting rolling, rolling, quenching and air cooling an alloy steel ingot in sequence to obtain an alloy blank with a ferrite-martensite structure; (2) Austenitizing the alloy blank processed in step (1) at 1020 - 1080 °C, quenching, tempering at 700 - 750 °C and air cooling to maintain the ferrite-martensite structure in the alloy blank while increasing the concentration of solute elements in the alloy blank; (3) Subjecting the alloy blank processed in step (2) to severe plastic deformation processing.

2. The method for improving the high-temperature thermal stability of ferritic martensitic steel according to claim 1, characterized in that: The alloying elements of the alloy steel ingot include Fe, C, Cr, W, Si, Mn, V, Ta and Zr, wherein the content of the Fe element is ≥ 80%.

3. A method for improving the high-temperature thermal stability of ferritic martensitic steel according to claim 1, characterized in that, The time for austenitizing is 40 - 60 min, and the tempering time is 1 - 2 h.

4. A method for improving the high-temperature thermal stability of ferritic martensitic steel according to claim 1, characterized in that, The temperature of the severe plastic deformation processing is lower than 300 °C.

5. A method for improving the high-temperature thermal stability of ferritic martensitic steel according to claim 1, characterized in that, The severe plastic deformation processing selects at least one of rotary forging and equal-channel angular pressing, and the total processing strain is ≥ 3.

6. A high-temperature thermally stable ferritic martensitic steel, characterized in that, Prepared by the method according to any one of claims 1 - 5.

7. The high-temperature thermal stability ferritic martensitic steel according to claim 6, characterized in that, The high-temperature thermal stability means that at 600 °C, the tensile strength of the ferrite-martensite steel is 500 - 515 MPa and the total elongation is 45 - 50%.

8. Application of a high-temperature thermal stability ferrite-martensite steel according to any one of claims 6 - 7 in nuclear structural materials.

9. The application according to claim 8, wherein The operating temperature of the nuclear structural materials is 600 °C.

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