Low-activation ferrite / martensitic steel clf-1 for nuclear fusion blanket and preparation method and application thereof

Abstract

This invention relates to the field of nuclear fusion reactor materials technology, specifically to a low-activation ferritic / martensitic steel CLF-1 for nuclear fusion reactor blankets, its preparation method, and its applications. The steel's chemical composition, by mass percentage, is: Cr: 8.0-9.0%, W: 1.4-1.6%, V: 0.2-0.3%, Ta: 0.06-0.1%, Mn: 0.3-0.5%, C: 0.07-0.12%, Gd: 0.03-0.06%, N≤0.02%, with the balance being Fe and unavoidable impurities of a specific content. The microstructure is tempered lath martensite, possessing excellent room-temperature and high-temperature mechanical properties, thermal properties, and radiation resistance. This steel is effectively adapted to the extreme working environment of nuclear fusion reactor blankets and is suitable for manufacturing structural components for nuclear fusion reactor blankets.

Description

Technical Field

[0001] This invention relates to the field of nuclear fusion reactor materials technology, specifically to a low-activation ferritic / martensitic steel CLF-1 for nuclear fusion blankets, its preparation method, and its application. Background Technology

[0002] Nuclear fusion energy, due to its cleanliness, safety, and abundant resources, is considered one of the ultimate solutions to future energy problems. In a fusion reactor, the blanket is a core component located on the inner wall of the plasma chamber, directly exposed to high-flux, high-energy (14.1 MeV) neutron radiation, extremely high heat flux density, and complex mechanical loads. The blanket structure material not only needs to constitute and support this critical component but also needs to accommodate the tritium breeder and coolant, and provide radiation shielding.

[0003] The extreme nature of their operating environment places stringent requirements on materials: they must simultaneously possess low activation (for easy decommissioning), excellent resistance to radiation swelling and embrittlement, high-temperature mechanical strength, good thermal conductivity, and compatibility with tritium breeders / coolants. Traditional austenitic stainless steels (such as 316L) are prone to radiation swelling and embrittlement under high neutron flux, and their activation products have long half-lives, making them unsuitable for the needs of future commercial fusion reactors.

[0004] Low-activation ferritic / martensitic steel is internationally recognized as the preferred structural material for fusion reactor blankets due to its high thermal conductivity, low coefficient of thermal expansion, and good resistance to radiation swelling. Recent studies have shown that the addition of trace rare earth elements can purify grain boundaries, refine the microstructure, and stabilize precipitates, providing an effective way to further improve the overall performance of RAFM steel. Among these, gadolinium (Gd), a heavy rare earth element, possesses a unique neutron absorption cross section and microalloying properties, and is expected to enhance the material's mechanical properties and radiation resistance while providing additional neutron modulation capabilities for the blanket. However, how to synergistically design the rare earth element Gd with matrix elements and optimize its existence form and distribution in the steel to maximize performance remains a pressing technical challenge. Summary of the Invention

[0005] This invention provides a low-activation ferritic / martensitic steel CLF-1 for nuclear fusion blankets, its preparation method and application, solving the technical problems of insufficient high-temperature strength, need to improve radiation resistance, and difficulty in effectively microalloying rare earth elements in traditional low-activation steels.

[0006] To achieve the above objectives, the main technical solutions adopted by the present invention include: In a first aspect, this application provides a low-activation ferritic / martensitic steel CLF-1 for nuclear fusion blankets, the chemical composition of which, by mass percentage, is: Cr: 8.0-9.0%, W: 1.4-1.6%, V: 0.2-0.3%, Ta: 0.06-0.1%, Mn: 0.3-0.5%, C: 0.07-0.12%, Gd: 0.03-0.06%, N≤0.02%, with the balance being Fe and unavoidable impurities.

[0007] In a further embodiment, the unavoidable impurities include P, S, B, Ni, Cu, Mo, Nb, Al, Ti, O, and H, and the contents of the unavoidable impurities, by mass percentage, respectively satisfy the following: P≤0.005%, S≤0.002%, B≤0.003%, Ni≤0.01%, Cu≤0.01%, Mo≤0.01%, Nb≤0.01%, Al≤0.02%, Ti≤0.01%, O≤0.01%, and H≤0.0005%, and the total content of the impurity elements is ≤0.1%.

[0008] Cr (chromium): A Cr content of 8.0-9.0% aims to ensure the steel's oxidation resistance and high-temperature strength while avoiding the formation of excessive δ-ferrite. It preferentially oxidizes at grain boundaries to form a continuous and dense Cr2O3 passivation film, which can reduce the oxidation rate by more than 60%.

[0009] W (tungsten): 1.4-1.6% W mainly strengthens the matrix through solid solution, inhibits dislocation climb, and synergistically forms fine Laves phase (Fe2W) with Cr, effectively hindering the migration of irradiation defects, thereby reducing the high-temperature creep rate and irradiation hardening increment.

[0010] Mn (manganese): 0.3-0.5% Mn mainly plays the role of deoxidation, desulfurization, and purification of molten steel, forming MnS spherical inclusions, which improves the hot working performance of the material.

[0011] C (carbon): The C content of 0.07-0.12% is used as a strengthening phase forming element, and its content is precisely controlled to generate an appropriate amount of M. 23 C6-type carbides and MX-type carbonitrides containing rare earth elements Gd, Ta, and V achieve the best balance between strength and toughness.

[0012] In a further embodiment, the microstructure of the low-activation ferrite / martensitic steel CLF-1 is tempered lath martensite with a lath width of 0.5-1.2 μm; M is dispersedly distributed at the lath boundaries. 23 C6 type carbides, with MX type carbonitrides rich in rare earth elements Gd, Ta and V dispersed inside the laths; and δ-ferrite with a volume fraction of <5% uniformly distributed in the matrix.

[0013] In a further embodiment, the M 23 The size of C6-type carbides is 60-120 nm, and the size of the rare earth-rich MX-type carbonitrides is 5-20 nm; some Gd elements exist in the form of nanoclusters or Gd-rich precipitates in the matrix and grain boundaries, which enhances the ability to capture irradiation defects.

[0014] In a further embodiment, the low-activation ferritic / martensitic steel CLF-1 has a yield strength ≥550MPa, a tensile strength ≥750MPa, and an impact toughness ≥80J / cm² at room temperature. 2 The yield strength at 550℃ is ≥350MPa.

[0015] In a further embodiment, its thermal conductivity at room temperature is ≥28 W / (m·K), and its average coefficient of linear expansion in the range of room temperature to 600°C is ≤1.1×10⁻⁶. -5 / ℃.

[0016] In a further embodiment, the irradiation swelling rate of the low-activation ferritic / martensitic steel CLF-1 at a neutron irradiation dose of 10 dpa is ≤1.5%.

[0017] Secondly, this application provides a heat treatment process for preparing the above-mentioned low-activation ferrite / martensitic steel CLF-1, the preparation process including the following steps: Step 1, Raw material preparation and smelting and rolling: Prepare the raw materials according to the above chemical composition, and after vacuum induction melting and electroslag remelting, forge and open the billet, and then hot roll it into plates or bars of the required specifications. Step 2, Normalizing treatment: Heat the steel after hot working to 980-1050℃ and hold for a period of time, then air cool it to achieve austenitization and obtain a uniform lath martensite structure.

[0018] Step 3, Tempering Treatment: The normalized steel is heated to 730-780℃ and held at that temperature, followed by air cooling. During this process, rare earth elements Gd, Ta, and V synergistically drive the precipitation of dispersed (Gd,Ta,VC,N) complex carbonitrides and M. 23 C6 carbides are used to eliminate quenching stress and obtain a tempered martensitic structure with a good balance of strength and toughness.

[0019] In a further embodiment, the holding time for the normalizing treatment in step 2 and the holding time for the tempering treatment in step 3 are both determined based on the effective thickness of the steel. The holding time for normalizing in step 2 is as follows: 0.5-1.5 hours when the effective thickness of the steel is ≤20mm; 1.5-3 hours when the effective thickness is >20mm and ≤50mm; and 3-5 hours when the effective thickness is >50mm. The holding time for tempering in step 3 is as follows: 1-2 hours when the effective thickness of the steel is ≤20mm; 2-3.5 hours when the effective thickness is >20mm and ≤50mm; and 3.5-6 hours when the effective thickness is >50mm, to ensure that the quenching stress is fully eliminated and that nano-sized carbonitrides are fully precipitated.

[0020] Thirdly, the application of the low-activation ferritic / martensitic steel CLF-1 in the preparation of nuclear fusion reactor blanket structural components.

[0021] Beneficial effects: Compared with existing technologies, the present invention provides CLF-1 steel with the following advantages by introducing rare earth element Gd with Ta and V for multi-element microalloying: The rare earth element-based strengthening effect is significant: the addition of Gd, Ta, and V forms high-density nanoscale (Gd,Ta,V)(C,N) composite precipitates and Gd-rich nanoclusters. These rare earth-rich precipitates exhibit high thermal stability, with a coarsening rate reduced to less than 10% of that of ordinary RAFM steel at 900℃, effectively pinning grain boundaries and dislocations and ensuring the microstructural stability of the material under high temperature and irradiation conditions.

[0022] Rare earth element Gd has a large thermal neutron absorption cross section. Its addition gives CLF-1 steel a certain neutron absorption or regulation capability, which can play a role in neutron shielding or flux regulation in local areas of the cladding. This provides new degrees of freedom for cladding neutronics design and helps to optimize tritium breeding ratio and shielding efficiency.

[0023] Thanks to the strong trapping ability of rare earth precipitation relative to irradiation defects and the purifying effect of Gd on grain boundaries, the irradiation swelling rate was effectively suppressed. At a neutron irradiation dose of 10 dPa, the irradiation swelling rate was less than 1.5%, which is further reduced compared to RAFM steel without Gd. After high-dose irradiation of 20 dPa, the martensitic lath structure remained intact, and the carbide distribution uniformity deviation was less than 10%.

[0024] With a room temperature thermal conductivity of 28 W / (m·K), it can effectively dissipate heat from the cladding. The average coefficient of linear expansion from room temperature to 600℃ is approximately 1.0 × 10⁻⁶. -5 At / ℃, when matched with ceramic tritium breeding materials such as Li4SiO4, the thermal stress between components can be reduced by more than 35%.

[0025] At a high temperature of 550℃, the yield strength can still be maintained above 360MPa. Under the conditions of 550℃ / 100MPa, after 10,000 hours of creep testing, the creep strain is only 0.45%, which is better than similar materials without added Gd. Its excellent fatigue performance enables it to withstand more than 5 million cycles of alternating load without failure.

[0026] Strict control over the types of alloying elements ensures that the material undergoes rapid radioactive decay after fusion neutron irradiation, meeting the stringent requirements of nuclear fusion reactors for low-activation materials, which is beneficial for reactor decommissioning and environmental safety. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a comparative schematic diagram of the microstructure of the low-activation ferrite / martensitic steel CLF-1 of the present invention.

[0029] Figure 2 This is a microstructure characterization diagram of the low-activation ferrite / martensitic steel CLF-1 obtained in Example 1 of the present invention. Detailed Implementation

[0030] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of the present invention by way of example, but should not be used to limit the scope of the present invention. The present invention can be implemented in many different forms and is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

[0031] Unless otherwise specified, the number of copies and percentages in this application refer to parts by weight and percentage by weight.

[0032] This application specifies that the low-activation ferritic / martensitic steel CLF-1 used for nuclear fusion blankets refers specifically to a low-activation ferritic / martensitic steel (RAFM steel) for nuclear fusion blanket systems, which is micro-alloyed with the rare earth element gadolinium (Gd). In particular, it refers to the rare earth-containing special structural material with the grade CLF-1 and its heat treatment preparation process.

[0033] The unique role of rare earth element Gd: As a heavy rare earth element, Gd has a large neutron absorption cross section, which can provide local neutron shielding or regulation in the cladding structure, helping to optimize the neutron performance of the cladding; as a surface-active element, Gd tends to segregate at grain boundaries, purifying grain boundaries, reducing interfacial energy, and inhibiting the segregation of harmful elements at grain boundaries; Gd has a strong affinity for elements such as C and N, and can form nanoscale Gd carbonitrides or composite precipitates, further pinning grain boundaries and dislocations, and improving high-temperature stability; the addition of Gd can improve the purity of molten steel, refine the solidification structure, and provide a good microstructure basis for subsequent heat treatment.

[0034] Synergistic strengthening of rare earth elements Ta and V: V and Ta, as key microalloying elements, complement Gd. Through combination with C and N, they precipitate nanoscale VC, VN, and (Ta,V)(C,N) composite carbonitrides during tempering. These nanoparticles not only pin dislocations and refine grains but also exhibit extremely high stability under high temperature and neutron irradiation conditions. The addition of Ta significantly slows down the coarsening rate of carbides, while V, by forming VC and VN nanoparticles, doubles the grain boundary area and increases the resistance to dislocation movement. The synergistic effect of these three elements provides a dual guarantee for rare earth element-based strengthening.

[0035] Example 1 The raw materials are precisely formulated according to the following mass percentages: Cr: 8.5%, W: 1.5%, V: 0.25%, Ta: 0.08%, Mn: 0.4%, C: 0.09%, Gd: 0.045%, P: 0.004%, S: 0.0015%, B: 0.002%, Ni: 0.008%, Cu: 0.007%, Mo: 0.006%, Nb: 0.005%, Al: 0.015%, Ti: 0.008%, N: 0.018%, O: 0.008%, H: 0.0003%, with the balance being Fe.

[0036] Smelting and rolling process: The prepared raw materials are added to a vacuum induction melting furnace, and the process is carried out under a vacuum degree ≤5×10⁻⁶. -3 Melting under Pa conditions, the ingot is cooled to room temperature and then purified by electroslag remelting. The electroslag remelting current is 3500A and the voltage is 55V. After remelting, the ingot is held at 1150℃ for 2.5 hours for homogenization treatment, and then forged into a billet at 1100℃ with a reduction of 15% per pass. Finally, it is hot rolled into a 20mm thick plate at 1000℃ and a final rolling temperature of 850℃.

[0037] Normalizing: Heat to 1000℃ at a rate of 10℃ / min, hold for 1 hour, and then air cool to room temperature.

[0038] Tempering: Heat to 750℃ at a rate of 8℃ / min, hold for 1.5 hours, and air cool to room temperature.

[0039] Performance testing and microstructure observation: Room temperature tensile properties: yield strength 558 MPa, tensile strength 755 MPa, elongation 21.5%, reduction of area 58%.

[0040] High-temperature tensile properties (550℃): Yield strength 375MPa, tensile strength 568MPa, elongation 18.2%.

[0041] Impact toughness, room temperature, V-notch: 87 J / cm 2 The impact toughness at -20℃ is 62 J / cm. 2 It exhibits excellent low-temperature toughness.

[0042] Thermal properties: Thermal conductivity at room temperature 28.3 W / (m·K), average coefficient of linear expansion from room temperature to 600℃ 1.05×10⁻⁶ -5 / ℃.

[0043] Radiation resistance: After simulating a neutron irradiation dose of 10 dpa, the irradiation swelling rate is 1.3%, the room temperature yield strength after irradiation is 582 MPa, the tensile strength is 783 MPa, and the impact toughness is 79 J / cm2.

[0044] Microstructure: Observed using transmission electron microscopy (TEM), the microstructure is typical tempered lath martensite, with lath width of 0.8 μm; M particles with a diameter of approximately 80 nm are diffusely distributed at the lath boundaries. 23 C6 carbide, with a large number of MX phase particles with a diameter of 10-20 nm evenly distributed inside the lath; the volume fraction of δ-ferrite in the matrix is ​​3.2%.

[0045] Atomic probe chromatography (APT) analysis confirmed that Gd was enriched in the MX phase particles with an enrichment factor of 8.6. Some Gd existed in the matrix in the form of nanoclusters, effectively playing a role in microalloying.

[0046] Performance under 20 dPa neutron irradiation: After irradiation with a high dose of 20 dPa neutrons, the martensitic lath structure remained intact, with no significant coarsening or distortion; the carbide distribution uniformity deviation was 8.2%. The irradiation swelling rate was 1.85%; the room temperature yield strength was 605 MPa, the tensile strength was 802 MPa, and the impact toughness was 72 J / cm. 2 .

[0047] High-temperature creep performance (550℃ / 100MPa, 10000h): creep strain 0.45%, steady-state creep rate 3.2×10⁻⁶. - 9 s -1.

[0048] High-cycle fatigue performance (room temperature, R=-1): under a stress level of 450MPa, it can withstand 5.26 million cycles of alternating load without fracture.

[0049] High-temperature oxidation performance (550℃, 1000h cycle oxidation): Oxidation weight gain 0.42mg / cm³ 2 Oxidation rate: 0.085 mg / (cm³) 2 ·h).

[0050] Example 2 The raw materials are precisely formulated according to the following mass percentages: Cr: 8%, W: 1.4%, V: 0.2%, Ta: 0.06%, Mn: 0.3%, C: 0.07%, Gd: 0.03%, P: 0.004%, S: 0.0015%, B: 0.001%, Ni: 0.007%, Cu: 0.008%, Mo: 0.007%, Nb: 0.006%, Al: 0.02%, Ti: 0.008%, N: 0.02%, O: 0.006%, H: 0.0003%, with the balance being Fe.

[0051] Add the prepared raw materials to a vacuum induction melting furnace, with a vacuum degree ≤ 5×10 -3 Melting under Pa conditions, the ingot is cooled to room temperature and then purified by electroslag remelting. The electroslag remelting current is 3500A and the voltage is 55V. After remelting, the ingot is held at 1150℃ for 2.5 hours for homogenization treatment, and then forged into a billet at 1100℃ with a reduction of 15% per pass. Finally, it is hot rolled into a 20mm thick plate at 1000℃ and a final rolling temperature of 850℃.

[0052] Normalizing: Heat to 980℃ at a rate of 10℃ / min, hold for 1 hour, and then air cool to room temperature.

[0053] Tempering: Heat to 730℃ at a rate of 8℃ / min, hold for 1.5 hours, and air cool to room temperature.

[0054] Performance test results: Room temperature tensile properties: yield strength 552 MPa, tensile strength 750 MPa, elongation 22.1%, reduction of area 59.2%.

[0055] High-temperature tensile properties (550℃): Yield strength 368MPa, tensile strength 560MPa, elongation 18.8%.

[0056] Impact toughness (room temperature, V-notch): 86 J / cm 2 Impact toughness at -20℃: 63.5 J / cm 2 .

[0057] Thermal properties: Thermal conductivity at room temperature 28.1 W / (m·K), average coefficient of linear expansion from room temperature to 600℃ 1.06 × 10⁻⁶ -5 / ℃.

[0058] Radiation resistance: After simulating a neutron irradiation dose of 10 dPa, the irradiation swelling rate is 1.45%; the room temperature yield strength after irradiation is 575 MPa, the tensile strength is 776 MPa, and the impact toughness is 78 J / cm. 2 .

[0059] Microstructure: The tempered laths exhibit a complete martensitic structure with a lath width of 0.85 μm; M 23 The C6 carbide particles have a diameter of 75-85 nm, while the MX phase particles have a diameter of 8-18 nm. The enrichment coefficient of Gd in the MX phase is 6.2, and the number of nanoclusters is relatively small, which is the main reason for its slightly lower radiation resistance.

[0060] Performance under 20 dPa neutron irradiation: After irradiation with 20 dPa, the martensitic lath structure remains intact, with a carbide distribution uniformity deviation of 9.5%. Irradiation swelling rate is 2.02%; room temperature yield strength is 596 MPa, tensile strength is 790 MPa, and impact toughness is 69 J / cm. 2 High-temperature creep performance (550℃ / 100MPa, 10000h): creep strain 0.51%, steady-state creep rate 3.8×10⁻⁶. -9 s -1 High-cycle fatigue performance (room temperature, R=-1): 5.01 million cycles under 450 MPa stress. High-temperature oxidation performance (550℃, 1000h): Oxidation weight gain 0.45 mg / cm³. 2 Oxidation rate: 0.091 mg / (cm³) 2 ·h).

[0061] Example 3 The raw materials are precisely formulated according to the following mass percentages: Cr: 9%, W: 1.6%, V: 0.3%, Ta: 0.1%, Mn: 0.5%, C: 0.12%, Gd: 0.06%, P: 0.004%, S: 0.001%, B: 0.001%, Ni: 0.01%, Cu: 0.009%, Mo: 0.007%, Nb: 0.007%, Al: 0.02%, Ti: 0.01%, N: 0.02%, O: 0.008%, H: 0.0003%, with the balance being Fe.

[0062] Add the prepared raw materials to a vacuum induction melting furnace, with a vacuum degree ≤ 5×10 -3Melting under Pa conditions, the ingot is cooled to room temperature and then purified by electroslag remelting. The electroslag remelting current is 3500A and the voltage is 55V. After remelting, the ingot is held at 1150℃ for 2.5 hours for homogenization treatment, and then forged into a billet at 1100℃ with a reduction of 18% per pass. Finally, it is hot rolled into a 20mm thick plate at 1000℃ and a final rolling temperature of 850℃.

[0063] Normalizing: Heat to 1050℃ at a rate of 10℃ / min, hold for 1 hour, and air cool to room temperature.

[0064] Tempering: Heat to 780℃ at a rate of 8℃ / min, hold for 1.5 hours, and air cool to room temperature.

[0065] Performance test results: Room temperature tensile properties: yield strength 562 MPa, tensile strength 760 MPa, elongation 20.8%, reduction of area 56.5%.

[0066] High-temperature tensile properties (550℃): Yield strength 382MPa, tensile strength 575MPa, elongation 17.6%.

[0067] Impact toughness, room temperature, V-notch: 84 J / cm 2 Impact toughness at -20℃: 59.8 J / cm 2 .

[0068] Thermal properties: Thermal conductivity at room temperature 28 W / (m·K); Average coefficient of linear expansion from room temperature to 600℃ 1.04 × 10⁻⁶ -5 It exhibits excellent thermal stability at / ℃.

[0069] Radiation resistance: After simulating a neutron irradiation dose of 10 dPa, the irradiation swelling rate was 1.25%, slightly lower than that of Example 1, indicating the best radiation resistance performance; the room temperature yield strength after irradiation was 588 MPa, the tensile strength was 790 MPa, and the impact toughness was 77 J / cm. 2 .

[0070] Microstructure: The width of the tempered lath martensitic laths is 0.75 μm, indicating a finer microstructure; M 23 C6 carbide particles have a diameter of 70-80 nm, while MX phase particles have a diameter of 12-20 nm. The enrichment coefficient of Gd in the MX phase is 9.3, and the number of nanoclusters increases, which effectively hinders dislocation movement during irradiation and improves radiation resistance.

[0071] Performance under 20 dPa neutron irradiation: After irradiation with 20 dPa, the martensitic lath structure is dense and intact, with a carbide distribution uniformity deviation of 7.6%. Irradiation swelling rate is 1.78%; room temperature yield strength is 612 MPa, tensile strength is 810 MPa, and impact toughness is 73 J / cm.2 High-temperature creep performance (550℃ / 100MPa, 10000h): creep strain 0.42%, steady-state creep rate 2.9×10⁻⁶. -9 s -1 High-cycle fatigue performance (room temperature, R=-1): 5.42 million cycles under 450 MPa stress. High-temperature oxidation performance (550℃, 1000h): Oxidation weight gain 0.40 mg / cm³. 2 Oxidation rate: 0.082 mg / (cm³) 2 ·h).

[0072] Comparative Example 1 It was prepared using the traditional low-activation ferritic / martensitic steel (RAFM steel) composition, without adding rare earth element Gd, adjusting the Ta content to 0.08% and the V content to 0.25%, and the mass percentage of other alloying elements and impurity control standards were consistent with those of Example 1 of this invention. The swelling rate after 10 dpa irradiation simulation was 1.8%, the high-temperature creep rate was higher than that of Example 1, the coarsening degree of grain boundary precipitates in the microstructure was slightly higher, and there was a lack of Gd-rich nanoclusters. The room temperature impact toughness decreased to 80 J / cm2, and the thermal conductivity decreased to 27.5 W / (m·K).

[0073] Neutron irradiation performance at 20 dPa: irradiation swelling rate 2.65%, carbide distribution uniformity deviation 16.8%; room temperature impact toughness reduced to 61 J / cm. 2 High-temperature creep performance (550℃ / 100MPa, 10000h): creep strain 0.78%, steady-state creep rate 6.5×10⁻⁶. -9 s -1 High-cycle fatigue performance (room temperature, R=-1): fatigue life of 3.85 million cycles under 450 MPa stress. High-temperature oxidation performance (550℃, 1000h): oxidation weight gain of 0.71 mg / cm³. 2 Oxidation rate: 0.224 mg / (cm³) 2 • h). 900℃ aging and roughening performance: After holding at 900℃ for 100 h, the roughening rate of the MX phase accelerated, reaching 10.8 times that of Example 1.

[0074] Comparative Example 2 This comparative example is the same as Example 1, except that the Gd content is 0.02%, while the contents of other alloying elements and the preparation process are the same as in Example 1. Test results show that its rare earth multi-element strengthening effect is insufficient, the swelling rate under 10 dPa irradiation is 1.65%, the room temperature yield strength drops to 545 MPa, the number of Gd-rich MX-type carbonitrides inside the lath is significantly reduced, and the neutron absorption regulation effect of Gd is not obvious.

[0075] Comparative Example 3 This comparative example is the same as Example 1, except that the Gd content is adjusted to 0.07%, while the contents of other alloying elements and the preparation process are the same as in Example 1. Test results show that excessive Gd leads to the formation of Gd-rich coarse precipitates at grain boundaries, causing grain boundary embrittlement and reducing the room temperature impact toughness to 75 J / cm. 2 The elongation rate dropped to 18.2%, and although the irradiation swelling rate dropped to 1.2%, the overall mechanical properties deteriorated, failing to meet the strength and toughness requirements of fusion blanket materials.

[0076] Comparative Example 4 This comparative example is the same as Example 1, except that the Cr content is adjusted to 7.5%, while the contents of other alloying elements and the preparation process are the same as in Example 1. Test results show that the steel's oxidation resistance is significantly reduced, the high-temperature oxidation rate increases by more than 80%, a continuous and dense Cr2O3 passivation film is not formed, and the high-temperature yield strength at 550℃ decreases to 340 MPa.

[0077] Comparative Example 5 This comparative example is the same as Example 1, except that the Cr content is adjusted to 9.5%, while the contents of other alloying elements and the preparation process are the same as in Example 1. Test results show that the increase in the volume fraction of δ-ferrite in the matrix to 8% leads to a decrease in room temperature impact toughness to 78 J / cm. 2 The high-temperature creep rate increases, and the stability of the microstructure decreases.

[0078] Comparative Example 6 This comparative example is the same as Example 1, except that the W content is adjusted to 1.3%, while the contents of other alloying elements and the preparation process are the same as in Example 1. Test results show that the solid solution strengthening effect is insufficient, the yield strength at 550℃ decreases to 335 MPa, the high-temperature creep rate is higher than in Example 1, the radiation hardening increment increases by 30%, and both radiation resistance and high-temperature mechanical properties do not meet the requirements.

[0079] Comparative Example 7 This comparative example is the same as Example 1, except that the V content is adjusted to 0.15%, while the contents of other alloying elements and the preparation process are the same as in Example 1. The test results show that the amount of MX-type carbonitride precipitation is reduced, the effect of pinned dislocations and grain boundaries is weakened, the room temperature yield strength is reduced to 538 MPa, and the 10 dpa irradiation swelling rate is increased to 1.7%, indicating that the radiation resistance is inferior to that of Example 1.

[0080] Comparative Example 8 This comparative example is the same as Example 1, except that the Ta content is adjusted to 0.05%, while the contents of other alloying elements and the preparation process are the same as in Example 1. Test results show that the carbide coarsening rate is accelerated, decreasing by only 40% at 800℃, and the carbide distribution uniformity deviation increases to 18% after 10 dpa irradiation, indicating insufficient microstructure stability.

[0081] Comparative Example 9 This comparative example is the same as Example 1, except that the normalizing temperature was adjusted to 950℃. The content of other alloying elements and the preparation process are the same as in Example 1. Test results show that austenitization is insufficient, a uniform lath martensite structure was not formed, the lath width is uneven (1.3-1.5μm), the room temperature tensile strength decreased to 730MPa, and the impact toughness decreased to 76J / cm. 2 Organizational defects are increasing.

[0082] Comparative Example 10 This comparative example is the same as Example 1, except that the tempering temperature was adjusted to 720℃. The content of other alloying elements and the preparation process are the same as in Example 1. The test results show that the quenching stress was not fully eliminated, and MX-type carbonitrides rich in Gd, Ta, and V were fully precipitated, with the precipitation amount reduced by 60%. The room temperature yield strength decreased to 542 MPa, the irradiation swelling rate increased to 1.75%, and the strength-toughness matching deteriorated.

[0083] Examples 1-3 of this invention, by adjusting the Gd content and synergistically combining it with Ta and V, demonstrated the improvement of material performance by an appropriate amount of Gd, while Comparative Examples 2 and 3 clarified the optimal range for Gd addition. In these examples, the addition of Gd led to the formation of rare-earth-rich MX-type carbonitrides and nanoclusters in the steel, effectively capturing irradiation defects and purifying grain boundaries. Simultaneously, it endowed the material with neutron absorption regulation capabilities, achieving synergistic optimization of radiation resistance, high-temperature strength, and thermal properties. Among these examples, those with moderate Gd content exhibited outstanding performance in high-temperature creep, radiation resistance, and fatigue properties, and demonstrated excellent microstructural stability. In Comparative Example 2, the insufficient addition of Gd significantly reduced the rare earth multi-element strengthening effect, decreased the precipitation of MX-type carbonitrides, and weakened the neutron absorption regulation and grain boundary purification effects of Gd. The material's radiation resistance swelling rate and high-temperature creep rate were inferior to those of the Example. In Comparative Example 3, the excessive addition of Gd led to the formation of coarse precipitates at the grain boundaries, causing grain boundary embrittlement and resulting in a decrease in mechanical properties, especially impact toughness, which violated the core requirement of matching strength and toughness in fusion reactor materials.

[0084] In Examples 1-3, the contents of core alloying elements such as Cr, W, V, and Ta were all within the optimal range set by the invention. However, Comparative Examples 4-8 deviated from the set values ​​for each key element. In Comparative Example 4, the Cr content was below the lower limit, resulting in a significant decrease in the steel's oxidation resistance, the inability to form a dense Cr2O3 passivation film, an increased high-temperature oxidation rate, and a failure to meet the high-temperature yield strength standard. In Comparative Example 5, the Cr content was too high, leading to an excessive volume fraction of δ-ferrite in the matrix, which damaged the integrity of the martensitic structure and deteriorated both impact toughness and microstructure stability. Regarding W, V, and Ta elements, the W content in Comparative Example 6 was insufficient, weakening the effects of solid solution strengthening and resistance to radiation defect migration, and failing to meet the requirements for high-temperature yield strength and radiation resistance. The V content in Comparative Example 7 was too low, resulting in a reduction in the precipitation of MX-type carbonitrides, a decrease in the ability to pin dislocations and grain boundaries, and a decrease in room temperature strength and radiation swelling resistance. The Ta content in Comparative Example 8 was insufficient, leading to an accelerated carbide coarsening rate, a significant decrease in the stability of the microstructure under high temperature and radiation conditions, and a deterioration in the uniformity of carbide distribution after irradiation.

[0085] The normalizing temperature, tempering temperature, and holding time in Examples 1-3 all conformed to the invention settings, achieving precise control of the microstructure and sufficient precipitation of the precipitated phases. Comparative Examples 9 and 10, by deviating from the process parameters, demonstrated that the heat treatment process cannot be arbitrarily adjusted. In Comparative Example 9, the normalizing temperature was below the lower limit, resulting in insufficient austenitization, failure to form a uniform lath martensite microstructure, uneven lath width, and increased microstructural defects, directly leading to a decrease in room temperature tensile strength and impact toughness. In Comparative Example 10, the tempering temperature was too low, quenching stress was not fully eliminated, and MX-type carbonitride precipitation was insufficient, not only reducing room temperature strength but also increasing the irradiation swelling rate and deteriorating the strength-toughness match. In contrast, the appropriate normalizing and tempering processes in the examples ensured both the uniformity of the martensite microstructure and the stable precipitation of nano-sized carbonitrides, laying the microstructural foundation for the material's excellent high-temperature mechanical properties and radiation resistance.

[0086] Compared to the traditional material in Example 1, which lacks the rare-earth multi-element strengthening effect of Gd and the synergistic effect of Gd-rich nanoclusters and MX-type carbonitrides, the traditional material is insufficient in grain boundary purification and high-temperature stabilization. It lags behind the embodiments of this invention in key indicators such as radiation resistance to swelling, high-temperature creep, thermal conductivity, and impact toughness. Furthermore, the traditional material exhibits a faster aging rate at 900℃, resulting in more pronounced microstructure coarsening and performance degradation after irradiation, failing to meet the requirements of fusion reactor blankets for material adaptability to extreme environments.

[0087] In summary, this invention has successfully solved the technical problems of insufficient high-temperature strength, poor radiation resistance, and difficulty in effectively microalloying rare earth elements in traditional low-activation steel by precisely controlling the amount of rare earth Gd added, optimizing the ratio of core alloying elements, and standardizing heat treatment processes. The CLF-1 steel prepared by this invention has achieved breakthroughs in microstructure stability, high-temperature mechanical properties, radiation resistance, and thermal properties, and is suitable for the use requirements of nuclear fusion reactor blankets.

[0088] Figure 1 (a) shows the microstructure of Comparative Example 1. Figure 1 (b) shows the microstructure of Embodiment 1 of the present invention. In the figure, M represents the martensite matrix, and Lathboundary represents the martensite lath boundary; the ellipse represents M. 23 C6 type carbides, with solid dots representing MX type carbonitrides rich in Gd, Ta, and V. Figure 1 In (a), M 23 C6 type carbides are coarse and unevenly distributed, while MX type carbonitrides inside the laths are few in number and poorly dispersed, with no Gd. Rich nanoclusters exhibit poor tissue stability. Figure 1 In (b), the microstructure is uniform tempered lath martensite, with M atoms of 60-120 nm dispersed at the lath boundaries. 23 C6 type carbides, with a large number of 5-20nm nano-MX type carbonitrides uniformly precipitated inside the laths, some Gd exists in the form of nano clusters, and the δ-ferrite content is low and uniform.

[0089] Figure 2 The accompanying figures are for illustrative purposes only. The top image shows a low-magnification scanning electron microscope (SEM) image of CLF-1 steel, labeled M as the martensite matrix. The microstructure is a uniform, dense tempered lath martensite structure, without obvious δ-ferrite aggregation, structural defects, or coarse precipitates. The bottom left image shows a bright-field transmission electron microscope (TEM) image of CLF-1 steel (scale bar 1 μm), labeled M as the martensite matrix. It clearly shows a complete and uniform tempered lath martensite structure, with lath widths of approximately 0.8 μm. The bottom right image shows a high-magnification TEM image of CLF-1 steel and the corresponding selected area electron diffraction (SAED) pattern, where white arrows indicate the diffusely distributed M at the lath boundaries. 23 C6 type carbides (size 60-120 nm), red circles indicate the diffusely precipitated MC type (i.e., Gd, Ta, V rich MX type) carbonitrides (size 5-20 nm) inside the strips; the diffraction spot above corresponds to M. 23 The

[100] zone axis of the C6 phase and the diffraction spot below it correspond to the

[110] zone axis of the MX-type carbonitride, which verifies the existence of two types of strengthening phases from a crystallographic perspective.

[0090] The various embodiments of the present invention have now been described in detail. To avoid obscuring the concept of the invention, some details known in the art have not been described. Those skilled in the art will fully understand how to implement the technical solutions disclosed herein based on the above description.

[0091] While specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art should understand that modifications can be made to the above embodiments or equivalent substitutions can be made to some technical features without departing from the scope and spirit of the invention.

Claims

1. A low-activation ferritic / martensitic steel CLF-1 for nuclear fusion blankets, characterized in that, Its chemical composition by mass percentage is as follows: Cr: 8.0-9.0%, W: 1.4-1.6%, V: 0.2-0.3%, Ta: 0.06-0.1%, Mn: 0.3-0.5%, C: 0.07-0.12%, Gd: 0.03-0.06%, N≤0.02%, with the balance being Fe and unavoidable impurities.

2. The low-activation ferritic / martensitic steel CLF-1 according to claim 1, characterized in that, The unavoidable impurities include P, S, B, Ni, Cu, Mo, Nb, Al, Ti, O, and H. The contents of the unavoidable impurities, by mass percentage, respectively satisfy the following: P≤0.005%, S≤0.002%, B≤0.003%, Ni≤0.01%, Cu≤0.01%, Mo≤0.01%, Nb≤0.01%, Al≤0.02%, Ti≤0.01%, O≤0.01%, and H≤0.0005%, and the total content of the impurity elements is ≤0.1%.

3. The low-activation ferritic / martensitic steel CLF-1 according to claim 1, characterized in that, The microstructure of the low-activation ferritic / martensitic steel CLF-1 is tempered lath martensite with a lath width of 0.5-1.2 μm; M is dispersed at the lath boundaries. 23 C6 type carbides, with MX type carbonitrides rich in rare earth elements Gd, Ta and V dispersed inside the laths; and δ-ferrite with a volume fraction of <5% uniformly distributed in the matrix.

4. The low-activation ferritic / martensitic steel CLF-1 according to claim 3, characterized in that, The M 23 The size of C6-type carbides is 60-120 nm, and the size of the rare earth-rich MX-type carbonitrides is 5-20 nm; some Gd elements exist in the matrix and grain boundaries in the form of nanoclusters or Gd-rich precipitates.

5. The low-activation ferritic / martensitic steel CLF-1 according to claim 1, characterized in that, The low-activation ferritic / martensitic steel CLF-1 has a yield strength ≥550MPa, tensile strength ≥750MPa, and impact toughness ≥80J / cm² at room temperature. 2 The yield strength at 550℃ is ≥350MPa.

6. The low-activation ferritic / martensitic steel CLF-1 according to claim 1, characterized in that, The low-activation ferritic / martensitic steel CLF-1 has a thermal conductivity ≥28 W / (m·K) at room temperature and an average coefficient of linear expansion ≤1.1×10⁻⁶ over the range of room temperature to 600℃. -5 / ℃.

7. The low-activation ferritic / martensitic steel CLF-1 according to claim 1, characterized in that, Its irradiation swelling rate at a neutron irradiation dose of 10 dpa is ≤1.5%.

8. A heat treatment process for preparing the low-activation ferritic / martensitic steel CLF-1 as described in any one of claims 1 to 7, characterized in that, The preparation process includes the following steps: Step 1, Raw material preparation and smelting and rolling: The raw materials are prepared according to the chemical composition described in claim 1, and after vacuum induction melting and electroslag remelting, they are forged and then hot rolled into plates or bars of the required specifications. Step 2, Normalizing treatment: Heat the hot-worked steel to 980-1050℃ and hold for a period of time, then air cool it. Step 3, tempering treatment: Heat the normalized steel to 730-780℃ and hold it at that temperature, then air cool it.

9. The heat treatment process according to claim 8, characterized in that, The holding time for the normalizing treatment in step 2 and the holding time for the tempering treatment in step 3 are both determined based on the effective thickness of the steel. Specifically, the holding time for normalizing in step 2 is as follows: 0.5-1.5 hours when the effective thickness of the steel is ≤20mm; 1.5-3 hours when the effective thickness is >20mm and ≤50mm; and 3-5 hours when the effective thickness is >50mm. The holding time for tempering in step 3 is as follows: 1-2 hours when the effective thickness of the steel is ≤20mm; 2-3.5 hours when the effective thickness is >20mm and ≤50mm; and 3.5-6 hours when the effective thickness is >50mm, to ensure that the quenching stress is fully eliminated and that nano-sized carbonitrides are fully precipitated.

10. The use of the low-activation ferritic / martensitic steel CLF-1 as described in any one of claims 1 to 7 in the preparation of components for the blanket structure of a nuclear fusion reactor.

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