Low activation steel and method of making and using same

Abstract

This invention provides a low-activation steel, its preparation method, and its applications. The low-activation steel comprises: 0.03 wt% to 0.15 wt% C; 0.1 wt% to 2.5 wt% Si; 0.2 wt% to 1.2 wt% Mn; 0.5 wt% to 3.5 wt% W; 8 wt% to 12 wt% Cr; 0.05 wt% to 0.6 wt% V; 0.02 wt% to 0.6 wt% of a strong carbonitride forming element, which includes at least one of Ta and Ti; the balance being Fe and unavoidable impurities; the precipitated phase of the low-activation steel includes Mn. 23 The C6 phase and M'X phase, where M includes Cr, W, Mn, or V, M' includes Ti, Ta, or V, and X includes C or N, are used in the preparation method of low-activation steel. By employing the above chemical composition ratio and a pre-precipitation process, the number density of the M'X phase can be controlled to 10. 20 / m 3 ~10 21 / m 3 Therefore, the low-activation steel of this invention has excellent strength, toughness, high-temperature creep life, and radiation resistance. The preparation method is compatible with existing processes and is conducive to its industrial application.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a low-activation steel, its preparation method, and its application. Background Technology

[0002] Nuclear energy, as a clean energy source that produces almost no carbon emissions during construction and operation, has gained popularity. Low-activation steel is considered the preferred structural material for fusion reactors and an important structural material for fourth-generation fission reactors. The high-temperature and high-energy neutron irradiation service environment requires low-activation steel to have good high-temperature mechanical properties and radiation resistance.

[0003] Low-activation steel exhibits a tempered martensitic structure, and the classic heat treatment process involves normalizing followed by high-temperature tempering. During this heat treatment, M'X and M precipitate. 23 The C6 phase precipitates as a Laves (Fe2W) phase during prolonged high-temperature service. It is generally believed that coarser M phases precipitate primarily at the martensite lath interface. 23 The C6 (M = Cr, Fe, W, V) phase, with an equivalent diameter of 100 nm to 500 nm, primarily functions to hinder the migration of martensite lath boundaries, stabilize the martensite lath structure, and thus achieve better high-temperature stability. 23 C6 coarsens faster at high temperatures, and M 23 C6 is enriched with a large amount of W, and is the nucleation site for the main deteriorating phase, Laves (Fe2W). The Laves phase is attached to a large amount of M. 23 After nucleation, C6 rapidly grows to the micrometer scale, absorbing the main solid-solution strengthening element W in the matrix and forming continuous precipitates at the martensite lath boundaries, severely impairing the material's high-temperature performance and toughness, leading to material failure. In contrast, the M'X phase (M' = Ta, Ti, V, X = C, N) can disperse in the martensite matrix, with smaller sizes, typically 20 nm to 50 nm. Furthermore, it grows very slowly under high-temperature aging conditions, exhibiting excellent dimensional stability. It can hinder dislocation movement in high-temperature environments, improving creep life, and also acts as a reaction site for irradiation defects, absorbing nearby point defects and inhibiting irradiation swelling and hardening. In traditional low-activation steels, the M'X phase cannot be fully precipitated; V (C / N) often segregates at grain boundaries, Ta (C / N) is less abundant, and M... 23 The C6 phase is relatively large, resulting in poor precipitation strengthening effect, and its creep resistance and radiation resistance cannot meet the requirements for use in fusion reactors.

[0004] Therefore, in order to improve the service performance of low-activation steel and achieve optimization and control of precipitated phases, there is an urgent need in this field to propose new alloy designs and preparation processes. Summary of the Invention

[0005] One objective of this invention is to provide a low-activation steel, its preparation method, and its application. The low-activation steel has a high M'X phase precipitation density and uniform distribution, which effectively improves the strength, toughness, high-temperature creep life, and radiation resistance of the low-activation steel.

[0006] In one aspect of the invention, a low-activation steel is provided. According to an embodiment of the invention, the low-activation steel comprises: 0.03 wt% to 0.15 wt% C; 0.1 wt% to 2.5 wt% Si; 0.2 wt% to 1.2 wt% Mn; 0.5 wt% to 3.5 wt% W; 8 wt% to 12 wt% Cr; 0.05 wt% to 0.6 wt% V; 0.02 wt% to 0.6 wt% of a strong carbonitride forming element, said strong carbonitride forming element including at least one of Ta and Ti; the balance being Fe and unavoidable impurities; the precipitated phase of the low-activation steel includes Mn. 23 C6 phase and M'X phase, wherein the number density of the M'X phase is 10. 20 / m 3 ~10 21 / m 3 M includes Cr, W, Mn or V, M' includes Ti, Ta or V, and X includes C or N.

[0007] Therefore, the low-activation steel of the present invention includes the components with the above-mentioned content and the above-mentioned precipitates. On the one hand, in the components with the above-mentioned content, the C element can combine with strong carbonitride forming elements (i.e., Ta, Ti) and V elements to form the M'X precipitate, and the C element can also combine with Mn, W, Cr, Fe, and V elements to form M 23 The C6 precipitate plays a precipitation strengthening role, improving the strength and toughness of the low-activation steel. Furthermore, the content of strong carbonitride forming elements is controlled within the range of 0.02wt% to 0.6wt%, which can increase the number density of the M'X precipitate and improve its distribution. Si element can improve the oxidation and corrosion resistance of the low-activation steel, while Mn element can combine with impurity elements such as P and S to reduce their damage to the properties of the low-activation steel and improve its hot working properties, impact resistance, and corrosion resistance. W element can play a solid solution strengthening role, and Cr element can improve the oxidation and corrosion resistance of the low-activation steel. On the other hand, the number density of the M'X phase in the low-activation steel of this invention is controlled to 10. 20 / m 3 ~10 21 / m 3 Within the range, the size of the M'X phase relative to M 23 The smaller size of the C6 phase enhances the ability of the precipitates to stabilize the matrix and pin dislocations by increasing the number density of the M'X phase. Furthermore, the smaller and more uniform spacing of the M'X phases allows for greater consumption of M'X phases.23 C6 phase formation element C, realizing M 23 The refinement of the C6 phase further enhances the precipitation strengthening effect. Therefore, in low-activation steels with the aforementioned composition and content ranges, as well as the aforementioned precipitate density ranges, the M'X phase precipitation is more complete and uniformly distributed. This enhances the ability of the precipitates to stabilize the matrix and pin dislocations, thereby effectively improving the strength, toughness, high-temperature creep life, and radiation resistance of the low-activation steel.

[0008] In addition, the low-activation steel according to the above embodiments of the present invention may also have the following additional technical features:

[0009] According to an embodiment of the present invention, the content of Ta in the strong carbonitride forming elements is not less than 0.06 wt%, and the content of Ti is not less than 0.02 wt%. This achieves a better precipitation effect, thereby improving the strength, toughness, high-temperature creep life, and radiation resistance of the low-activation steel.

[0010] According to an embodiment of the present invention, the low-activation steel further includes 0.02 wt% to 0.06 wt% N. Thus, the N element can combine with the V element to form a beneficial precipitate phase, thereby improving the strength and toughness of the low-activation steel.

[0011] According to an embodiment of the present invention, the low-activation steel further includes 0.05 wt% to 0.3 wt% of rare earth elements, wherein the rare earth elements include at least one of Y, La, and Ce. This avoids the introduction of the highly activating element Al and further improves the toughness and high-temperature creep properties of the low-activation steel.

[0012] According to an embodiment of the present invention, based on the total volume of the low-activation steel, the M 23 The volume fraction of the C6 phase is 0.5% to 3%, and the volume fraction of the M'X phase is 0.05% to 0.45%. This enhances the ability of the precipitated phase to stabilize the matrix and pin dislocations, thereby improving the strength, toughness, high-temperature creep life, and radiation resistance of the low-activation steel.

[0013] In another aspect of the present invention, the present invention provides a method for preparing the aforementioned low-activation steel, the method comprising: (1) smelting, removing impurities and forming the low-activation steel raw material to obtain a steel ingot; (2) heating the steel ingot and forging it to obtain a hot-worked part; (3) heating the hot-worked part to 850°C to 950°C and holding it at that temperature for 0.5h to 12h, then cooling it and repeating the process 1 to 3 times; (4) subjecting the workpiece obtained in step (3) to austenitization treatment, cooling it, and then tempering it.

[0014] Therefore, this invention involves melting, impurity removal, forming, and hot forging low-activation steel raw materials, then pre-precipitating the resulting hot-worked parts, and finally austenitizing and tempering the pre-precipitated parts. Before the austenitizing process, a pre-precipitation process is added to adjust the main precipitation process of the M'X phase to the austenite phase region. Firstly, in the pre-precipitation process, a lower temperature is used to reduce the amount of M precipitated during heating. 23 The dissolution rate of C6 preserves the M atoms located at the grain boundaries and martensite laths of the original microstructure. 23 At the C6 / austenitic phase interface, M'X phase-forming elements such as Ti, Ta, and V in the matrix diffuse to the interface and combine with the high concentration of C to form the M'X phase. The martensite laths have a high density and uniform distribution, thus promoting the full dispersion and precipitation of the M'X phase, thereby increasing the number density of the M'X phase (from 10...). 18 ~10 19 / m 3 Upgraded to 10 20 ~10 21 / m 3 Then, in the austenitizing process, new austenite is formed, causing the M'X phase obtained in the pre-precipitation process to be distributed within the grains. The average spacing of the precipitates is reduced from 5000 nm to 100 nm to 500 nm, resulting in a relatively low average size and a significantly improved number density compared to traditional heat treatment processes. Finally, the abundant M'X phase dispersed in the tempering process can serve as M... 23 The nucleation site of the C6 phase promotes the formation of some M... 23 The precipitation of C6 phase within the crystal, attached to the precipitated M... 23 The C6 phase size is between 30 nm and 50 nm. The large-scale precipitation of the M'X phase also consumes M... 23 The C6 phase-forming element C, and the M precipitated at grain boundaries and lath boundaries during tempering. 23 The C6 phase was also refined to a certain extent, with its average size reduced to 70 nm–120 nm. Therefore, the preparation method of this invention can realize the M'X phase and M... 23 The method involves multifaceted control of the quantity, distribution, and size of C6 phase precipitates. Low-activation steel obtained using this method exhibits a higher quantity and more uniform distribution of the M'X phase precipitates. Simultaneously, M... 23 The C6 phase is also refined to a certain extent, thereby effectively enhancing the ability of the precipitated phase to stabilize the matrix and pin dislocations, thus giving the resulting low-activation steel excellent strength, toughness, high-temperature creep life, and radiation resistance.

[0015] In addition, the method for preparing the low-activation steel according to the above embodiments of the present invention may also have the following additional technical features:

[0016] According to an embodiment of the present invention, in step (1), the impurity removal process uses rare earth elements for impurity removal. This avoids the introduction of highly activated element Al, which is beneficial for improving the strength, toughness, and high-temperature creep life of low-activated steel.

[0017] According to an embodiment of the present invention, in step (2), the steel ingot is heated to 1150°C to 1250°C and held for 2 to 6 hours before forging begins. The forging ratio is not less than 3, and the final forging temperature is not less than 850°C, preferably not less than 1000°C. This improves the strength and toughness of the low-activation steel.

[0018] According to an embodiment of the present invention, in step (2), the hot-worked part is a plate, and the hot-worked part is subjected to hot rolling treatment. The initial rolling temperature is 1130℃~1180℃, and the final rolling temperature is not less than 850℃, preferably not less than 1000℃. This improves the strength and toughness of the low-activation steel.

[0019] According to an embodiment of the present invention, in step (2), the hot-worked part is a sheet metal, and the hot-worked part is subjected to hot rolling treatment, with a total reduction of not less than 50% and a single reduction of not more than 20% below 1000°C. This prevents cracking of the hot-worked part, thereby improving the strength and toughness of the low-activation steel.

[0020] According to an embodiment of the present invention, in step (2), the strain rate of the hot working is not higher than 0.08 / s. This prevents plastic instability of the hot-worked part during the hot working process, thereby improving the strength and toughness of the low-activation steel.

[0021] According to an embodiment of the present invention, in step (4), the workpiece obtained in step (3) is heated to 980°C to 1080°C and held at that temperature for 0.5h to 12h for austenitization treatment, and then cooled. This improves the strength and toughness of the low-activation steel.

[0022] According to an embodiment of the present invention, in step (4), the tempering includes heating the cooled workpiece to 700°C to 800°C, holding it at that temperature for 0.5h to 3h, and then cooling it. This can improve the strength and toughness of the low-activation steel.

[0023] In another aspect, the present invention provides the application of the aforementioned low-activation steel or low-activation steel obtained by the aforementioned method in the field of nuclear power generation. By employing the above-mentioned chemical composition and increasing the number density of the M'X phase, the low-activation steel of the present invention effectively improves its strength, toughness, high-temperature creep resistance, and radiation resistance, enabling it to meet the higher requirements for low-activation steel materials in related nuclear power generation fields such as fourth-generation fission reactors and fusion demonstration reactors.

[0024] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0025] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0026] Figure 1 This is a schematic diagram of the process for preparing low-activation steel in one embodiment of the present invention;

[0027] Figure 2 This is a hot working diagram of the low-activation steel prepared in Example 1 of the present invention;

[0028] Figure 3 This is a TEM image of the tempered microstructure of the low-activation steel prepared in Example 1 of this invention;

[0029] Figure 4 This is a TEM image of the tempered microstructure of the low-activation steel prepared in Comparative Example 1 of this invention;

[0030] Figure 5 This is a STEM image of the normalized microstructure of the low-activation steel prepared in Example 2 of this invention;

[0031] Figure 6 This is a TEM image of the tempered microstructure of the low-activation steel prepared in Example 2 of this invention;

[0032] Figure 7 This is a TEM image of the tempered microstructure of the low-activation steel prepared in Comparative Example 2 of this invention;

[0033] Figure 8 This is the creep curve of the low-activation steel prepared in Example 3 of the present invention under various stresses at 550℃;

[0034] Figure 9 This is an OM diagram of the tempered microstructure of the low-activation steel prepared in Example 3 of this invention;

[0035] Figure 10 This is a SEM image of the tempered microstructure of the low-activation steel prepared in Example 3 of this invention;

[0036] Figure 11 This is a TEM image of the tempered microstructure of the low-activation steel prepared in Example 4 of this invention;

[0037] Figure 12 These are SEM images of the low-activation steel prepared in Comparative Example 2 and Example 5 of the present invention after normalizing process, wherein (a) corresponds to Comparative Example 2 and (b) corresponds to Example 5;

[0038] Figure 13These are SEM images of the low-activation steel prepared in Comparative Example 2 and Example 5 of the present invention after tempering, wherein (a) and (c) correspond to Comparative Example 2, and (b) and (d) correspond to Example 5. Detailed Implementation

[0039] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0040] In one aspect of the invention, a low-activation steel is provided. According to an embodiment of the invention, the low-activation steel comprises: 0.03 wt% to 0.15 wt% C; 0.1 wt% to 2.5 wt% Si; 0.2 wt% to 1.2 wt% Mn; 0.5 wt% to 3.5 wt% W; 8 wt% to 12 wt% Cr; 0.05 wt% to 0.6 wt% V; 0.02 wt% to 0.6 wt% of a strong carbonitride forming element, said strong carbonitride forming element including at least one of Ta and Ti; the balance being Fe and unavoidable impurities; the precipitated phase of the low-activation steel includes Mn. 23 C6 phase and M'X phase, wherein the number density of the M'X phase is 10. 20 / m 3 ~10 21 / m 3 M includes Cr, W, Mn or V, M' includes Ti, Ta or V, and X includes C or N.

[0041] Therefore, the low-activation steel of the present invention includes the components with the above-mentioned content and the above-mentioned precipitates. On the one hand, in the components with the above-mentioned content, the C element can combine with strong carbonitride forming elements (i.e., Ta, Ti) and V elements to form the M'X precipitate, and the C element can also combine with Mn, W, Cr, Fe, and V elements to form M 23 The C6 precipitate plays a precipitation strengthening role, improving the strength and toughness of the low-activation steel. Furthermore, the content of strong carbonitride forming elements is controlled within the range of 0.02wt% to 0.6wt%, which can increase the number density of the M'X precipitate and improve its distribution. Si element can improve the oxidation and corrosion resistance of the low-activation steel, while Mn element can combine with impurity elements such as P and S to reduce their damage to the properties of the low-activation steel and improve its hot working properties, impact resistance, and corrosion resistance. W element can play a solid solution strengthening role, and Cr element can improve the oxidation and corrosion resistance of the low-activation steel. On the other hand, the number density of the M'X phase in the low-activation steel of this invention is controlled to 10. 20 / m 3 ~10 21 / m 3 Within a certain range (e.g., the number density of phase M'X is 1×10),20 / m 3 3×10 20 / m 3 5×10 20 / m 3 7×10 20 / m 3 9×10 20 / m 3 1×10 21 / m 3 (etc.), the size of the M'X phase relative to M 23 The smaller size of the C6 phase enhances its ability to stabilize the matrix and pin dislocations by increasing the number density and precipitation amount of the M'X phase. Furthermore, the smaller precipitation spacing and more uniform distribution of the M'X phase, combined with the increased M'X phase concentration, also contribute to the reduction of M... 23 C6 phase formation element C, realizing M 23 The refinement of the C6 phase further enhances the precipitation strengthening effect. Therefore, in the low-activation steel with the above-mentioned composition and content range and the above-mentioned precipitate number density range, the M'X phase precipitation is more complete and uniformly distributed, thereby enhancing the ability of the precipitate phase to stabilize the matrix and pin dislocations, effectively improving the strength, toughness, high-temperature creep life, and radiation resistance of the low-activation steel. According to embodiments of the present invention, the mechanical properties of the low-activation steel of the present invention satisfy: Room temperature mechanical properties: σ 0.2 ≥550MPa, σ b ≥650MPa, A≥10%, Ψ≥65%, KV2≥150J; High-temperature mechanical properties: at a test temperature of 550℃, σ 0.2 ≥300MPa, σ b ≥350MPa, A≥20%, Ψ≥70%; High-temperature performance degradation: Performance remains stable after aging at 550℃ for 10000h, KV2≥70J; High-temperature creep life: Under high-temperature conditions of 550℃, creep life ≥20h at 270MPa, creep life ≥400h at 240MPa, creep life ≥2000h at 210MPa, and creep life ≥10000h at 180MPa. According to embodiments of the present invention, the selection principle of the types and contents of components in the low-activation steel of the present invention will be specifically explained below:

[0042] First, the carbon (C) content in the low-activation steel of this invention is 0.03 wt% to 0.15 wt%. C can combine with strong carbide-forming elements such as Ti, Ta, Nb, and V to form an FCC (face-centered cubic) precipitate M'X, and with weak carbide-forming elements such as Cr, W, Mn, and Fe to form a carbide precipitate M. 23C6 and these two precipitates are the main precipitates in ferrite / martensite low-activation steels, playing a role in precipitation strengthening and being one of the main strengthening methods under high-temperature conditions. The selection of C content should ensure that after fully participating in the formation of the M'X phase, a portion still combines with Cr, W, etc., to form M... 23 C6 phase, but this portion of C should not be excessive, otherwise it will cause M. 23 The excessively large size of the C6 phase and its continuous precipitation at grain boundaries consume excessive amounts of Cr and W, leading to a decrease in the corrosion resistance and creep resistance of the low-activation steel, respectively. Furthermore, considering that excessively high C content can degrade weldability, the C content of the low-activation steel in this invention is controlled within the range of 0.03wt% to 0.15wt% (for example, C content can be 0.03wt%, 0.04wt%, 0.05wt%, 0.06wt%, 0.07wt%, 0.08wt%, 0.10wt%, 0.12wt%, 0.14wt%, 0.15wt%, etc.). This allows for the precipitation of M in the low-activation steel... 23 The C6 and M'X phases have small sizes, effectively improving the strength and toughness of the low-activation steel, while also giving it better creep resistance and weldability. In some specific embodiments of the present invention, the specific content of C can be dynamically adjusted within the range of 0.03wt% to 0.15wt% based on the content of other alloying elements, in order to further improve the high-temperature service performance of the low-activation steel of the present invention.

[0043] Second, the Si content in the low-activation steel of this invention is 0.1wt% to 2.5wt%. Si can improve the hardenability of steel, thereby affecting the matrix strength, and can also improve the oxidation and corrosion resistance of steel. However, under high-dose neutron irradiation conditions, Ni, Si, and P elements in the steel will combine at the grain boundaries, causing severe irradiation embrittlement. Therefore, this invention controls the Si content within the range of 0.1wt% to 2.5wt% (for example, the Si content can be 0.1wt%, 0.3wt%, 0.5wt%, 0.7wt%, 0.9wt%, 1.0wt%, 1.2wt%, 1.5wt%, 1.7wt%, 1.9wt%, 2.0wt%, 2.2wt%, 2.5wt%, etc.). In practical applications, the Si content can be further restricted within the range of 0.1wt% to 2.5wt% depending on the specific application of the low-activation steel. When low-activation steel is used in fusion reactors, it needs to withstand a high neutron irradiation dose, and the service environment is free of oxygen and water vapor. Therefore, the silicon content is low, limited to the range of 0.1wt% to 0.5wt%. When low-activation steel is used in Generation IV reactors and ADS reactors (accelerator-driven reactors), it comes into direct contact with liquid Pb-Bi, liquid Na, or high-temperature gases or water vapor. Therefore, in order to improve the oxidation and corrosion resistance of low-activation steel, the Si content in the low-activation steel can be appropriately increased, up to a maximum of 2.5wt%.

[0044] Third, the Mn content in the low-activation steel of this invention is 0.2wt% to 1.2wt%. Mn is an important alloying element in low-activation steel, which can combine with elements such as P and S that remain after impurity removal, reducing their damage to the properties of the low-activation steel. In addition, increasing the Mn content can improve the hot working properties, impact properties, and corrosion resistance of the low-activation steel. However, excessively high Mn content will increase the M content in the low-activation steel. 23 The C6 phase coarsening rate impairs the creep properties of low-activation steel, and the formation of clusters under neutron irradiation leads to radiation hardening. Therefore, this invention controls the Mn content within the range of 0.2wt% to 1.2wt% (e.g., Mn content can be 0.2wt%, 0.4wt%, 0.8wt%, 1.0wt%, 1.2wt%, etc.). This improves the hot workability and impact resistance of the low-activation steel without compromising its creep properties. In practical applications, the Mn content can be further restricted within the 0.2wt% to 1.2wt% range depending on the specific application of the low-activation steel. When the low-activation steel is used in fusion reactors, the Mn content is controlled between 0.2wt% and 0.8wt%. When the low-activation steel is used in fourth-generation reactors, the upper limit of the Mn content can be increased to 1.2wt%, meaning the Mn element content is controlled within the range of 0.2wt% to 1.2wt%.

[0045] Fourth, the W content in the low-activation steel of this invention is 0.5wt% to 3.5wt%. The W content has a decisive influence on the high-temperature strength and creep life of the low-activation steel. The solid solution strengthening effect of W is one of the main high-temperature strengthening methods of low-activation steel. However, excessive W content will reduce the austenite phase region of the low-activation steel, resulting in the absence of a fully austenite phase region in the alloy system. During processing, δ-ferrite will inevitably be generated, which will impair the processing performance and creep resistance of the low-activation steel. In addition, during long-term high-temperature service, the W element in the low-activation steel will form large-sized Laves phase (Fe2W), which will seriously impair the impact toughness of the low-activation steel. Furthermore, the large-sized Laves phase will debond from the matrix interface and form microcracks, thereby causing creep fracture of the low-activation steel. Therefore, this invention controls the W content within the range of 0.5wt% to 3.5wt% (for example, the W content can be 0.5wt%, 0.7wt%, 1.0wt%, 1.3wt%, 1.5wt%, 1.7wt%, 2.0wt%, 2.3wt%, 2.5wt%, 2.7wt%, 3.0wt%, 3.3wt%, 3.5wt%, etc.), which can improve the high-temperature strength and high-temperature creep life of the low-activation steel. In practical applications, the W content can be further restricted within the range of 0.5wt% to 3.5wt% according to the service temperature and stress conditions of the low-activation steel. For example, low-activation steel used at lower temperatures and lower stresses can use a lower W content, selected in the range of 0.5wt% to 2.0wt%, while low-activation steel used at higher temperatures and stresses needs to increase the W content, selected in the range of 2.0wt% to 3.5wt%. In addition, the W content in this application is controlled at a maximum of 3.5 wt%, which can ensure a fully austenitized phase region with a sufficient temperature window.

[0046] Fifth, the Cr content in the low-activation steel of this invention is 8wt% to 12wt%. On the one hand, Cr can increase the electrode potential of the low-activation steel, and Cr can form a dense oxide film after oxidation. Therefore, increasing the Cr content in the low-activation steel can improve the steel's oxidation resistance and corrosion resistance. On the other hand, Cr is a key element in metallurgy. 23The C6 phase is a major forming element and plays a crucial role in stabilizing the martensitic structure. Furthermore, when the Cr content is 9 wt%, the low-activation steel exhibits the smallest ΔDBTT (ductile-brittle transition temperature change) under neutron irradiation. Therefore, when low-activation steel is used in fusion reactors, limiting the Cr content to the range of 8 wt% to 10 wt% allows it to possess good oxidation and corrosion resistance, while also exhibiting good strength and toughness. Further, since low-activation steel in contact with liquid metal requires even higher corrosion resistance, it is necessary to further increase the Cr content. Therefore, considering the above reasons, the Cr content in this invention is controlled within the range of 8 wt% to 12 wt% (for example, Cr content can be 8 wt%, 8.5 wt%, 9 wt%, 9.5 wt%, 10 wt%, 10.5 wt%, 11 wt%, 11.5 wt%, 12 wt%, etc.). This allows the low-activation steel to simultaneously possess excellent oxidation and corrosion resistance, as well as good strength and toughness.

[0047] Sixth, the content of V in the activated steel of this invention is 0.05wt% to 0.6wt%, and the content of strong carbonitride forming elements is 0.02wt% to 0.6wt%, wherein the strong carbonitride forming elements include at least one of Ta and Ti. Ta, Ti, and V are all M'X phase forming elements. Among them, Ti and Ta have strong bonding ability with C and N, and their initial precipitation temperature is between 1100℃ and 1250℃. In some embodiments of this invention, a pre-precipitation process can be used to promote their large-scale dispersion precipitation. To achieve a better precipitation effect, the content of Ti is not less than 0.02wt%, while the content of Ta, which has a higher atomic mass, is not less than 0.06wt%. Increasing the content of Ti and Ta can improve the precipitation effect, but excessively high Ti and Ta content will increase the difficulty of metallurgy. Therefore, in this invention, the content of strong carbonitride forming elements is controlled within the range of 0.02wt% to 0.6wt%. For example, the content of strong carbonitride forming elements can be 0.02wt%, 0.04wt%, 0.08wt%, 0.12wt%, 0.16wt%, 0.2wt%, 0.25wt%, 0.3wt%, 0.35wt%, 0.4wt%, 0.45wt%, 0.5wt%, 0.53wt%, 0.58wt%, 0.6wt%, etc. This can achieve a better precipitation effect of M'X phase, increase the number density of M'X phase, and thus improve the strength, toughness, high-temperature creep life, and radiation resistance of low-activation steel.

[0048] V has a relatively poor affinity for combining with C and N, and its initial precipitation temperature is between 950℃ and 1050℃. With the addition of V, some V can form a dispersed M'X phase under pre-precipitation conditions, while the remaining V can combine with M during the tempering process. 23The C6 phase precipitates at both grain boundaries and martensite lath interfaces. The addition of V promotes the precipitation of the M'X phase and increases its number density. Simultaneously, the precipitation of the M'X phase at grain boundaries can inhibit the precipitation of M... 23 The increase in the C6 phase refines the M phase to some extent. 23 C6 phase. Furthermore, to avoid the formation of δ-ferrite, the V content cannot be too high; the maximum V content should not exceed 0.6 wt%. Therefore, in this invention, the V content is controlled within the range of 0.05 wt% to 0.6 wt%, for example, V content can be 0.05 wt%, 0.08 wt%, 0.12 wt%, 0.16 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.45 wt%, 0.5 wt%, 0.53 wt%, 0.58 wt%, 0.6 wt%, etc., which can better promote the precipitation of the M'X phase, increase its number density, and simultaneously prevent M... 23 The C6 phase grows, achieving a better precipitation effect, which can improve the strength, toughness, high-temperature creep life, and radiation resistance of low-activation steel. To further improve the precipitation effect, the V content can be adjusted within the range of 0.05wt% to 0.6wt% based on the content of strong carbonitride forming elements. When the Ta content is high (≥0.2%) or the Ti content is high (≥0.1%), the V content can be reduced, and the V content can be 0.05wt% to 0.2wt%. Conversely, when the Ta and Ti contents are low, the V content can be increased, and the V content can be 0.05wt% to 0.6wt%.

[0049] For the reasons mentioned above, this invention achieves the desired balance between the M'X phase and M in low-activation steel by controlling the composition and content of the low-activation steel. 23 Comprehensive regulation of the C6 phase promotes the precipitation of the M'X phase while inhibiting the M phase. 23 The size increase of the C6 phase enhances precipitation strengthening; on the other hand, this invention increases the number density of the smaller M'X phase to 10. 20 / m 3 ~10 21 / m 3 Within this range, it can effectively enhance the ability of precipitated phases to stabilize the matrix and pin dislocations, thereby effectively improving the strength, toughness, high-temperature creep life, and radiation resistance of low-activation steel.

[0050] In some embodiments of the present invention, the low-activation steel further includes 0.02wt% to 0.06wt% of nitrogen (N). Nitrogen (N) and carbon (C) jointly participate in the formation of M'X-type precipitates. TiN typically forms during smelting, is large in size, and is difficult to dissolve; therefore, nitrogen addition should be avoided when Ti is added, i.e., no nitrogen is added. VN (VN) is a beneficial precipitate. Therefore, based on the content of Ti, Ta, and V alloying elements, when adding nitrogen to the low-activation steel, the present invention controls the N content within the range of 0.02wt% to 0.06wt% (e.g., the N content can be 0.02wt%, 0.03wt%, 0.04wt%, 0.05wt%, 0.06wt%, etc.), thus achieving a better precipitation effect. Furthermore, since excessive interstitial alloying elements can impair weldability, in some specific embodiments of the present invention, when C and N are added together, to ensure weldability, the C and N content is controlled within the range of (C+N) ≤ 0.15wt%.

[0051] In some embodiments of the present invention, M is based on the total volume of the low-activation steel. 23 The volume fraction of the C6 phase is 0.5% to 3% (e.g., 0.5%, 0.7%, 1%, 1.3%, 1.5%, 1.7%, 2%, 2.3%, 2.5%, 2.7%, 3%, etc.), and the volume fraction of the M'X phase is 0.05% to 0.45% (e.g., 0.05%, 0.07%, 0.1%, 0.13%, 0.16%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.43%, 0.45%, etc.). Specifically, in some embodiments of the present invention, the precipitated M... 23 C6 phase is distributed at the interface, and M phase is distributed at the martensite lath boundary. 23 C6 is rod-shaped or ellipsoidal, with an aspect ratio between 2 and 10, and a size between 30 nm and 150 nm. M is present at the original austenite grain boundaries. 23 C6 is rod-shaped or polygonal, with dimensions ranging from 50 nm to 300 nm. 23 In the C6 phase, M includes Cr, W, Mn, or V; the precipitated M'X phase is distributed inside the matrix and at the interface, mostly in spherical or ellipsoidal shapes, with an equivalent diameter between 5 nm and 50 nm. In the M'X phase, M' includes Ti, Ta, or V, and X includes C or N. Therefore, this invention optimizes M... 23 The precipitation of C6 and M'X phases increases the content of the smaller M'X phase and optimizes the distribution of precipitates, effectively enhancing the ability of precipitates to stabilize the matrix and pin dislocations, thereby improving the strength and creep resistance of low-activation steel and its high-temperature service performance.

[0052] In some embodiments of the present invention, the low-activation steel further includes 0.05wt% to 0.3wt% of rare earth elements, wherein the rare earth elements include at least one of Y, La, and Ce. On the one hand, rare earth elements such as Y, La, and Ce serve as a final impurity removal slag to replace Al, avoiding the introduction of highly activated Al, and possess superior ability to remove impurities such as Sn, Pb, Sb, and As. On the other hand, Y, La, and Ce can be added to the low-activation steel as alloying elements, combining with elements such as S and O that are still difficult to completely remove after impurity removal and remelting to form small-sized spherical rare earth sulfur oxides with strength matching the low-activation steel matrix, thereby improving the hot working performance of the low-activation steel. Simultaneously, they can reduce the debonding of inclusion interfaces during the high-temperature creep process of the low-activation steel, thus extending the creep life of the low-activation steel. Furthermore, rare earth elements segregated to grain boundaries also have the effect of inhibiting the segregation of P and S at grain boundaries, thereby improving the fracture toughness of the low-activation steel. Although rare earth elements have high solubility in molten steel, their addition during smelting is difficult. High rare earth element content can result in a large amount of rare earth compounds that are difficult to float, thus affecting the casting of steel and causing drastic fluctuations in performance. Therefore, the amount of rare earth elements added in this invention does not exceed 0.3 wt%. The content of rare earth elements in this invention is controlled within the range of 0.05 wt% to 0.3 wt%, such as 0.05 wt%, 0.06 wt%, 0.08 wt%, 0.1 wt%, 0.14 wt%, 0.18 wt%, 0.2 wt%, 0.24 wt%, 0.28 wt%, 0.3 wt%, etc., preferably 0.05 wt% to 0.1 wt%. In this way, the influence of impurity elements in low-activation steel on the performance of low-activation steel can be effectively reduced, and the fracture toughness and high-temperature creep performance of low-activation steel can be further improved.

[0053] In some embodiments of the present invention, the unavoidable impurities in the low-activation steel of the present invention are mainly at least one of O, P, and S elements, and also include at least one of Co, Ni, Cu, Al, Nb, B, and other impurity elements. During the preparation of the low-activation steel, the impurity content needs to be minimized through methods such as impurity removal. In the low-activation steel of the present invention, the O content is no higher than 0.002 wt%, the P content is no higher than 0.005 wt%, and the S content is no higher than 0.003 wt%, thus minimizing the impact of impurities on the performance of the low-activation steel. For impurity elements such as Co, Ni, Cu, Al, Nb, and B, because they are highly activated elements under fusion neutron irradiation, their content in the low-activation steel should be limited. In the activated steel of the present invention, the Co content is no higher than 0.01 wt%, the Ni content is no higher than 0.01 wt%, the Cu content is no higher than 0.01 wt%, the Al content is no higher than 0.01 wt%, the Nb content is no higher than 0.01 wt%, and the B content is no higher than 0.001 wt%. In this way, the radiation resistance of low-activation steel can be guaranteed to the greatest extent and the radiation swelling can be reduced. In addition, other harmful elements commonly found in low-activation steel, such as As, Pb, Sn, Sb, and Bi, also need to be controlled to the lowest possible level to prevent them from damaging the high-temperature creep resistance of low-activation steel.

[0054] According to embodiments of the present invention, it should be noted that the content of each component mentioned in the present invention refers to the mass percentage of the chemical composition of the steel grade elements in low-activation steel.

[0055] In another aspect of the invention, a method for preparing the aforementioned low-activation steel is provided, referring to... Figure 1 The method includes:

[0056] S100: Melting, impurity removal, and forming of low-activation steel raw materials.

[0057] In this step, based on the composition of the final low-activation steel, low-activation steel raw materials are added. The smelting method can be electric arc furnace smelting or vacuum induction smelting. Among them, the electric arc furnace smelting method can adopt AOD (argon-oxygen decarburization), LF (ladle refining), VD (vacuum degassing) and other methods. The impurity removal method can be atmosphere-protected electroslag remelting or vacuum self-consumption smelting.

[0058] In some embodiments of the present invention, the low-activation steel raw material can be an intermediate alloy (master alloy) of alloying elements and iron, which can reduce the burning loss of alloying elements and the formation of oxide and nitride inclusions.

[0059] In some embodiments of the present invention, rare earth elements (at least one of Y, La, and Ce) are used to replace Al for deoxygenation in the impurity removal process. This avoids the introduction of highly active Al, and rare earth elements Y, La, and Ce have superior ability to remove impurities such as Sn, Pb, Sb, and As. On the other hand, rare earth elements Y, La, and Ce, when added as alloying elements to low-activation steel, can combine with elements such as S and O that are still difficult to completely remove after impurity removal and remelting, forming small-sized spherical rare earth sulfur oxides with strength matching the low-activation steel matrix, thereby improving the hot working performance of the low-activation steel. In addition, the addition of rare earth elements during the high-temperature creep process of low-activation steel can reduce the debonding of inclusion interfaces, thereby extending the creep life of low-activation steel. Rare earth elements segregated to the grain boundaries also have the effect of inhibiting the segregation of P and S at the grain boundaries, thereby improving the fracture toughness of low-activation steel. The amount of rare earth elements added can be based on the impurity content in the low-activation steel raw material and the rare earth element content in the final composition of the low-activation steel.

[0060] It should be noted that if Al is used for deoxygenation and inclusion removal, the final Al content should be less than 0.01 wt%.

[0061] After the above-mentioned smelting, impurity removal and forming processes, steel ingots can be obtained. It should be noted that those skilled in the art can choose the forming method according to actual needs.

[0062] S200: The steel ingot obtained in step S100 is heated and then forged.

[0063] In this step, the heating temperature of the steel ingot is 1150℃~1250℃ (for example, it can be 1150℃, 1170℃, 1190℃, 1200℃, 1230℃, 1250℃, etc.); after the steel ingot is heated, it is homogenized and held at a constant temperature. The holding time can be determined according to the difference in alloy element content and workpiece size. In some embodiments of the present invention, the homogenization holding time is 2h~6h (for example, the holding time can be 2h, 3h, 4h, 5h, 6h, etc.), and then forging is performed.

[0064] In some embodiments of the present invention, during the forging process, the forging ratio is not less than 3, thus achieving better forging results and obtaining higher quality hot-worked parts. Furthermore, the hot deformation rate during forging is not higher than 0.08 / s to prevent plastic instability during forging. Even further, the final forging temperature is not less than 850°C, preferably not less than 1000°C (especially when the W content in the low-activation steel is between 1.3wt% and 3.5wt%, the final forging temperature should be higher than 1000°C), thus preventing cracking of the steel ingot during forging. In this way, better forging results can be achieved, and better hot-worked parts can be obtained.

[0065] According to embodiments of the present invention, the shape of the heat-treated part is not particularly limited, and those skilled in the art can select it according to actual production needs. In some embodiments of the present invention, the heat-treated part can be a plate or a bar (for example, a plate with a thickness of 12mm to 20mm or a bar with a diameter of 12mm to 20mm).

[0066] In some specific embodiments of the present invention, the hot-worked part is a plate. The steel ingot is heated and forged, then hot-rolled. The initial rolling temperature is 1130℃~1180℃ (e.g., 1130℃, 1140℃, 1150℃, 1160℃, 1170℃, 1180℃, etc.), and the final rolling temperature is not less than 850℃, preferably not less than 1000℃ (especially when the W content in the low-activation steel is between 1.3wt% and 3.5wt%, the final rolling temperature should be higher than 1000℃) to prevent cracking of the steel ingot during hot rolling. Furthermore, the total reduction during hot rolling is not less than 50% to fully crush the as-cast structure and refine the austenite grain size. Additionally, during hot rolling, when the temperature is below 1000℃, the reduction in a single rolling pass is not more than 20% to prevent cracking of the plate.

[0067] S300: Pre-precipitate the hot-worked part obtained in step S200.

[0068] In this step, the pre-precipitation process includes heating the hot-worked part to 850℃~950℃ (e.g., heating to 850℃, 860℃, 870℃, 880℃, 890℃, 900℃, 910℃, 920℃, 930℃, 940℃, 950℃, etc.) and holding it at that temperature for 0.5h~12h (e.g., holding for 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 10.5h, 11h, 11.5h, 12h, etc.) followed by cooling. This process is repeated 1~3 times (e.g., 2 or 3 times) depending on the holding time. The cooling method can be water cooling or air cooling. If water cooling is used, the next heat treatment must be performed within 12 hours after cooling to prevent the cooled workpiece from cracking due to stress release.

[0069] According to an embodiment of the present invention, in the above-described pre-precipitation step, during the heating process of the hot-worked part, the M'X phase and M 23 The C6 phase inevitably precipitates, but M 23 The precipitation and growth rate of the C6 phase is much higher than that of the M'X phase, with a large amount of C preferentially combining with elements such as Cr, W, and Mn to form M. 23C6 precipitates, resulting in a low volume fraction and number density of the M'X phase during heating. As the temperature continues to rise and reaches the aforementioned temperature range (850℃~950℃), the diffusion rate of alloying elements such as Ta accelerates, leading to faster segregation towards the interface, while M... 23 The concentration of the C6 phase gradually decreases as it dissolves, releasing carbon (C) elements. These released C elements combine with alloying elements segregated at the interface to form the M'X phase. With increasing holding time, M... 23 The complete dissolution of the C6 phase allows the carbon element in the alloy system to be fully released and combine with elements such as Ti, Ta, and V to precipitate the M'X phase, thereby promoting the precipitation of the M'X phase and increasing its final volume fraction and number density. Furthermore, in the subsequent austenitization process, austenite and martensite are regenerated in the low-activation steel. Therefore, most of the M'X phase precipitated in the pre-precipitation process will be located within the martensite matrix, thus improving the distribution of the M'X phase. On the other hand, when the total content of Ti, Ta, and V is high, for example, above 0.3 wt%, the high-density M'X phase has a strong ability to pin the original austenite grain boundaries, and the austenite grain growth rate is very slow. Therefore, excessively long holding times can actually cause the MX phase precipitated on the austenite grain boundaries to grow. Therefore, this invention employs a short pretreatment process in the pre-precipitation process and repeats it multiple times to avoid the growth of the M'X phase.

[0070] Therefore, in the method for preparing low-activation steel of the present invention, the use of multiple short-time pre-precipitation processes can promote the precipitation of the M'X phase at the interfaces of different original microstructures and at the interfaces of austenite grain migration, thereby making the distribution of the M'X phase more uniform. Furthermore, while promoting the precipitation of the M'X phase, it can also prevent the growth of the M'X phase, ensuring that it has a small size. This can effectively enhance the ability of the precipitated phase to stabilize the matrix and pin dislocations, thereby effectively improving the strength, toughness, high-temperature creep life, and radiation resistance of the low-activation steel.

[0071] S400: After austenitizing the workpiece obtained in step S300, cool it and then temper it.

[0072] In this step, the austenitizing process includes heating the workpiece obtained in step S300 to 980℃~1080℃ (e.g., heating to 980℃, 1000℃, 1020℃, 1040℃, 1060℃, 1080℃, etc.) and holding it at that temperature for 0.5h~12h (e.g., holding for 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 10.5h, 11h, 11.5h, 12h, etc.) to perform austenitizing treatment, followed by cooling.

[0073] The tempering process involves heating the austenitized and cooled workpiece to 700℃~800℃ (e.g., heating to 700℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, etc.) and holding it at that temperature for 0.5h~3h (e.g., holding for 0.5h, 0.7h, 0.9h, 1.1h, 1.3h, 1.6h, 1.9h, 2.2h, 2.6h, 2.8h, 3h, etc.) and then cooling it.

[0074] In the process of preparing low-activation steel according to the present invention, since the original austenite grains in the low-activation steel after the pre-precipitation process are small, which is not conducive to the high-temperature creep performance of the low-activation steel, the present invention performs an austenitizing treatment process and a tempering process after the pre-precipitation process, and adopts a holding time of 0.5h to 12h in the austenitizing treatment process according to the required original austenite grain size of 10μm to 200μm, so as to further improve the high-temperature service performance of the low-activation steel.

[0075] According to embodiments of the present invention, in the above-described austenitizing process, new austenite can be formed in the low-activation steel, causing the M'X phase obtained in the pre-precipitation process to be distributed within the grains. The average spacing of the precipitates is reduced from 5000 nm to 100 nm to 500 nm, resulting in a relatively low average size and a significantly higher number density compared to conventional heat treatment processes. In the above-described tempering process, the abundant dispersed M'X phase can serve as M... 23 The nucleation site of the C6 phase promotes the formation of some M... 23 The precipitation of C6 phase within the crystal, attached to the precipitated M... 23 The C6 phase size is between 30 nm and 50 nm. The large-scale precipitation of the M'X phase also consumes M... 23 The C6 phase-forming element C, and the M precipitated at grain boundaries and lath boundaries during tempering. 23 The C6 phase was also refined to a certain extent, with the average size reduced to 70nm~120nm.

[0076] Therefore, according to embodiments of the present invention, the preparation method of the present invention involves melting, removing impurities, and forming low-activation steel raw materials, hot forging, and hot rolling, then pre-precipitating the resulting hot-worked parts, and finally austenitizing and tempering the pre-precipitated parts. This method can achieve the treatment of M'X phase and M in low-activation steel. 23 The method involves multi-faceted control of the number, distribution, and average size of C6 phase precipitates. Low-activation steel obtained using this method exhibits a higher number of M'X phase precipitates, with a number density significantly higher than that obtained using traditional heat treatment processes (10). 18 / m 3 ~10 19 / m 3 Upgraded to 10 20 / m 3 ~1021 / m 3 And the distribution is more uniform, while M 23 The C6 phase is also refined to a certain extent, which can effectively enhance the ability of the precipitated phase to stabilize the matrix and pin dislocations, thus giving the resulting low-activation steel excellent strength, toughness, high-temperature creep life and radiation resistance.

[0077] In another aspect, the present invention provides the application of the aforementioned low-activation steel, or low-activation steel obtained by the aforementioned method, in the field of nuclear power generation. The low-activation steel of the present invention uses the above-mentioned chemical composition, combined with a pre-precipitation process, to reduce the number density of the M'X phase in the low-activation steel from 10... 18 ~10 19 / m 3 Upgraded to 10 20 ~10 21 / m 3 This improves the strength, toughness, high-temperature creep performance, and radiation resistance of low-activation steel, thus meeting the higher requirements for low-activation steel materials in nuclear power generation fields such as fourth-generation fission reactors and fusion demonstration reactors.

[0078] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0079] Example 1

[0080] The composition of the low-activation steel in Example 1 is shown in Table 1, #1. The preparation process of the low-activation steel is as follows:

[0081] (1) Low-activation steel raw materials are added according to the chemical composition ratio, wherein the low-activation steel raw materials are made of intermediate alloys. The low-activation steel raw materials are vacuum induction melted, and then refined and impurities are removed by electroslag remelting under atmosphere protection. Finally, the steel ingots are cast into shape.

[0082] (2) Heat the steel ingot to 1200℃, homogenize and hold for 2 hours, then forge it. The final forging temperature is 1000℃, and it is prepared into a bar with a diameter of 20mm.

[0083] (3) Heat the bar obtained in step (2) to 900℃ and keep it at that temperature for 2 hours, then air cool it to room temperature;

[0084] (4) The workpiece obtained by cooling in step (3) is heated to 1030°C and held for 0.5 h, then air-cooled to room temperature (normalizing), and then heated to 760°C and held for 1.5 h for tempering. After cooling, the low-activation steel of the present invention is obtained. The obtained low-activation steel includes M. 23 The C6 phase and the M'X phase, with the M'X phase having a number density of 1.6 × 10⁻⁶. 20 / m 3 .

[0085] The room temperature mechanical properties of the low-activation steel prepared in Example 1: σ 0.2 =583MPa, σ b =737MPa, KV2=198J, creep life=33h

[0086] (σ 0.2 For yield strength, σ b (KV2 is the tensile stress, and KV2 is the impact energy)

[0087] Comparative Example 1

[0088] The composition of the low-activation steel in Comparative Example 1 is shown in Table 1, #1. The preparation process of the low-activation steel is as follows:

[0089] (1) Low-activation steel raw materials are added according to the chemical composition ratio, wherein the low-activation steel raw materials are made of intermediate alloys. The low-activation steel raw materials are vacuum induction melted, and then refined and impurities are removed by electroslag remelting under atmosphere protection. Finally, the steel ingots are cast into shape.

[0090] (2) Heat the steel ingot to 1200℃, homogenize and hold for 2 hours, then forge it. The final forging temperature is 1000℃, and it is prepared into a bar with a diameter of 20mm.

[0091] (3) The bar obtained in step (2) is heated to 1030°C and held for 0.5 h, then air-cooled to room temperature (normalizing), and then heated to 760°C and held for 1.5 h for tempering. After cooling, the low-activation steel of the present invention is obtained. The obtained low-activation steel includes M. 23 The C6 phase and the M'X phase, wherein the number density of the M'X phase is 9 × 10⁻⁶. 18 / m 3 .

[0092] Room temperature mechanical properties of the low-activation steel prepared in Comparative Example 1: σ 0.2 =532MPa, σ b =682MPa, KV2=220J, creep life=9h.

[0093] The performance comparison between the low-activation steels prepared in Example 1 and Comparative Example 1 is as follows:

[0094] <![CDATA[σ 0.2 (MPa)]]> <![CDATA[σ b (MPa)]]> <![CDATA[KV2(J)]]> <![CDATA[M’X number density ( / m 3 )]]> Creep life (h) Comparative Example 1 532 682 220 <![CDATA[9×10 18 ]]> 9 Example 1 583 737 198 <![CDATA[1.6×10 20 ]]> 33

[0095] Hot compression experiments were conducted using the low-activation steel sample prepared in Example 1. Based on the obtained hot compression curves, a hot working diagram suitable for the composition of #1 steel was plotted, as follows: Figure 2 As shown, by Figure 2 It can be seen that the low-activation steel prepared in Example 1 has good hot working properties.

[0096] Figure 3and Figure 4 The images shown are TEM (transmission electron microscopy) images of the tempered microstructure of the low-activation steel samples prepared in Example 1 and Comparative Example 1, respectively. Figure 3 and Figure 4 As can be seen, a large number of fine and dispersed M'X phases precipitated inside the matrix in Example 1, with an average equivalent diameter of 23 nm and a precipitation spacing of 100 nm. This indicates that the preparation process in Example 1 effectively promoted the precipitation of M'X phase in the low-activation steel, increased the number density of M'X phase, and thus improved the strength, toughness, high-temperature creep life and radiation resistance of the low-activation steel in Example 1.

[0097] Example 2

[0098] The composition of the low-activation steel in Example 2 is shown in Table 1, #4. The preparation process of the low-activation steel is as follows:

[0099] (1) Low-activation steel raw materials are added according to the chemical composition ratio, wherein the low-activation steel raw materials are made of intermediate alloys. The low-activation steel raw materials are vacuum induction melted, and then refined and impurities are removed by electroslag remelting under atmosphere protection. Finally, the steel ingots are cast into shape.

[0100] (2) Heat the steel ingot to 1200℃, homogenize and hold for 2 hours, then forge and hot roll. The final rolling temperature is 1000℃, and the plate is prepared with a thickness of 20mm.

[0101] (3) Heat the board obtained in step (2) to 930℃ and keep it at that temperature for 2 hours, then air cool it to room temperature;

[0102] (4) The workpiece obtained by cooling in step (3) is heated to 1030°C and held for 0.5 h, then air-cooled to room temperature (normalizing), and then heated to 760°C and held for 0.5 h for tempering. After cooling, the low-activation steel of the present invention is obtained. The obtained low-activation steel includes M. 23 The C6 phase and the M'X phase, with the M'X phase having a number density of 4.1 × 10⁻⁶. 20 / m 3 .

[0103] The room temperature mechanical properties of the low-activation steel prepared in Example 2: σ 0.2 =632MPa, σ b =760MPa, KV2=204J.

[0104] Comparative Example 2

[0105] The composition of the low-activation steel in Comparative Example 2 is shown in Table 1, #4. The preparation process of the low-activation steel is as follows:

[0106] (1) Low-activation steel raw materials are added according to the chemical composition ratio, wherein the low-activation steel raw materials are made of intermediate alloys. The low-activation steel raw materials are vacuum induction melted, and then refined and impurities are removed by electroslag remelting under atmosphere protection. Finally, the steel ingots are cast into shape.

[0107] (2) Heat the steel ingot to 1200℃, homogenize and hold for 2 hours, then forge and hot roll. The final rolling temperature is 1000℃, and the plate is prepared with a thickness of 20mm.

[0108] (3) The plate obtained in step (2) is heated to 1030°C and held for 0.5 hours, then air-cooled to room temperature (normalizing), and then heated to 760°C and held for 0.5 hours for tempering. After cooling, the low-activation steel of the present invention is obtained. The obtained low-activation steel includes M. 23 The C6 phase and the M'X phase, with the M'X phase having a number density of 2.6 × 10⁻⁶. 19 / m 3 .

[0109] Room temperature mechanical properties of the low-activation steel prepared in Comparative Example 2: σ 0.2 =574MPa, σ b =723MPa, KV2=212J.

[0110] The performance comparison between the low-activation steels prepared in Example 2 and Comparative Example 2 is as follows:

[0111] <![CDATA[σ 0.2 (MPa)]]> <![CDATA[σ b (MPa)]]> <![CDATA[KV2(J)]]> <![CDATA[M’X number density ( / m 3 )]]> Example 2 632 760 204 <![CDATA[4.1×10 20 ]]> Comparative Example 2 574 723 212 <![CDATA[2.6×10 19 ]]>

[0112] Figure 5 This is a STEM (scanning transmission electron microscope) image of the normalized microstructure of the low-activation steel sample prepared in Example 2. Figure 6 and Figure 7 The images show TEM images of the tempered microstructure of the low-activation steel samples prepared in Example 2 and Comparative Example 2, respectively. Figures 5-7 As can be seen from the data, the precipitation density of the M'X phase in the low-activation steel prepared in Example 2 is significantly increased. The average equivalent diameter of the M'X phase is 32 nm, the column spacing is approximately 250 nm, and the precipitation spacing is approximately 100 nm. In the tempered microstructure, the M'X phase... 23 The average equivalent diameter of the C6 phase was reduced to 80 nm. This indicates that the preparation process in Example 2 effectively promoted the precipitation of the M'X phase in the low-activation steel, increased the number density of the M'X phase, and reduced the size of the M'X phase, thereby improving the strength, toughness, high-temperature creep life, and radiation resistance of the low-activation steel in Example 2.

[0113] Example 3

[0114] The composition of the low-activation steel in Example 3 is shown in Table 1, #1. The preparation process of the low-activation steel is as follows:

[0115] (1) Low-activation steel raw materials are added according to the chemical composition ratio, wherein the low-activation steel raw materials are made of intermediate alloys. The low-activation steel raw materials are vacuum induction melted, and then refined and impurities are removed by electroslag remelting under atmosphere protection. Finally, the steel ingots are cast into shape.

[0116] (2) Heat the steel ingot to 1200℃, homogenize and hold for 2 hours, then forge it. The final forging temperature is 1000℃, and it is prepared into a bar with a diameter of 20mm.

[0117] (3) Heat the bar obtained in step (2) to 900℃ and keep it at that temperature for 2 hours, then air cool it to room temperature;

[0118] (4) The workpiece obtained by cooling in step (3) is heated to 1030°C and held for 0.5 h, then air-cooled to room temperature (normalizing), and then heated to 760°C and held for 0.5 h for tempering. After cooling, the low-activation steel of the present invention is obtained. The obtained low-activation steel includes M. 23 The C6 phase and the M'X phase, with the M'X phase having a number density of 1.6 × 10⁻⁶. 20 / m 3 .

[0119] The room temperature mechanical properties of the low-activation steel prepared in Example 3: σ 0.2 =665MPa, σ b =790MPa, A=16%, Ψ=72%, KV2=185J. (A is elongation after fracture, Ψ is reduction of area)

[0120] The low-activation steel prepared in Example 3 was subjected to high-temperature aging tests at 550℃ for over 10,000 hours. The low-activation steel of Example 3 maintained stable properties after aging at 550℃ for more than 10,000 hours. 0.2 ≥550MPa, KV2≥150J, no significant decrease in toughness, matrix structure remains lath martensite, no polygonization occurs.

[0121] Figure 8 The creep curves of the low-activation steel prepared in Example 3 under various stresses at 550℃ show the following creep lifetimes: ≥20h at 270MPa, ≥420h at 240MPa, ≥2490h at 210MPa, and ≥10000h at 180MPa and 150MPa. This demonstrates that the creep resistance of the low-activation steel in Example 3 was effectively improved.

[0122] Figure 9 and Figure 10 The images shown are optical microscopy (OM) images and scanning electron microscopy (SEM) images of the tempered microstructure of the low-activation steel sample prepared in Example 3. Figure 9 and Figure 10A large number of fine and dispersed M'X phases can be seen precipitated inside the matrix, thereby improving the strength, toughness, high-temperature creep life and radiation resistance of the low-activation steel in Example 3.

[0123] Example 4

[0124] The composition of the low-activation steel in Example 4 is shown in Table 1, #7. The preparation process of the low-activation steel is as follows:

[0125] (1) Low-activation steel raw materials are added according to the chemical composition ratio, wherein the low-activation steel raw materials are made of intermediate alloys. The low-activation steel raw materials are vacuum induction melted, and then refined and impurities are removed by electroslag remelting under atmosphere protection. Finally, the steel ingots are cast into shape.

[0126] (2) Heat the steel ingot to 1200℃, homogenize and hold for 2 hours, then forge it. The final forging temperature is 1000℃, and it is prepared into a bar with a diameter of 20mm.

[0127] (3) Heat the bar obtained in step (2) to 930℃ and keep it at that temperature for 2 hours, then air cool it to room temperature;

[0128] (4) The workpiece obtained by cooling in step (3) is heated to 1030°C and held for 0.5 h, then air-cooled to room temperature (normalizing), and then heated to 760°C and held for 1.5 h for tempering. After cooling, the low-activation steel of the present invention is obtained. The obtained low-activation steel includes M. 23 The C6 phase and the M'X phase, with the M'X phase having a number density of 2.1 × 10⁻⁶. 20 / m 3 .

[0129] The room temperature mechanical properties of the low-activation steel prepared in Example 4: σ 0.2 =553MPa, σ b =660MPa, A=20%, Ψ=76%, KV2=221J.

[0130] Figure 11 The image shows a TEM image of the tempered microstructure of the low-activation steel sample prepared in Example 4. As can be seen from the image, the low-activation steel prepared in Example 4 exhibits good precipitation performance. The average equivalent diameter of the M'X phase is approximately 20 nm, the intragranular precipitate spacing is 80 nm, and the precipitate array spacing is approximately 200 nm.

[0131] Example 5

[0132] The composition of the low-activation steel in Example 5 is shown in Table 1, #13. The preparation process of the low-activation steel is as follows:

[0133] (1) Low-activation steel raw materials are added according to the chemical composition ratio, wherein the low-activation steel raw materials are made of intermediate alloys. The low-activation steel raw materials are vacuum induction melted, and then refined and impurities are removed by electroslag remelting under atmosphere protection. Finally, the steel ingots are cast into shape.

[0134] (2) Heat the steel ingot to 1200℃, homogenize and hold for 2 hours, then forge and hot roll. The final rolling temperature is 1000℃, and the plate is prepared with a thickness of 20mm.

[0135] (3) Heat the board obtained in step (2) to 930℃ and keep it at that temperature for 2 hours, then air cool it to room temperature;

[0136] (4) The workpiece obtained by cooling in step (3) is heated to 1030°C and held for 0.5 h, then air-cooled to room temperature (normalizing), and then heated to 760°C and held for 0.5 h for tempering. After cooling, the low-activation steel of the present invention is obtained. The obtained low-activation steel includes M. 23 The C6 phase and the M'X phase, with the M'X phase having a number density of 3.5 × 10⁻⁶. 20 / m 3 .

[0137] The room temperature mechanical properties of the low-activation steel prepared in Example 5: σ 0.2 =625MPa, σ b =755MPa, KV2=254J.

[0138] In Example 5, a higher content of rare earth elements was added. Figure 12 SEM images of the low-activation steel samples prepared in Comparative Example 2 and Example 5 after normalizing are shown, where (a) corresponds to Comparative Example 2 and (b) corresponds to Example 5. Figure 13 SEM images of the low-activation steel samples prepared in Comparative Example 2 and Example 5 after tempering are shown below, respectively. (a) and (c) correspond to Comparative Example 2, and (b) and (d) correspond to Example 5. Figure 12 and Figure 13 As can be seen, since both Example 5 and Comparative Example 2 used a refining process, neither had micron-sized inclusions. However, in Example 5 with added rare earth elements, the number of submicron-sized (large spherical white spots in the SEM image) tantalum oxide inclusions was much less than in Comparative Example 2.

[0139] Example 6

[0140] The composition of the low-activation steel in Example 6 is shown in Table 1, Item 10. The preparation process of the low-activation steel is as follows:

[0141] (1) Low-activation steel raw materials are added according to the chemical composition ratio, wherein the low-activation steel raw materials are made of intermediate alloys. The low-activation steel raw materials are vacuum induction melted, and then refined and impurities are removed by electroslag remelting under atmosphere protection. Finally, the steel ingots are cast into shape.

[0142] (2) Heat the steel ingot to 1200℃, homogenize and hold for 2 hours, then forge it. The final forging temperature is 1000℃, and it is prepared into a bar with a diameter of 16mm.

[0143] (3) Heat the bar obtained in step (2) to 900℃ and keep it at that temperature for 2 hours, then air cool it to room temperature;

[0144] (4) The workpiece obtained by cooling in step (3) is heated to 1030°C and held for 2 hours, then air-cooled to room temperature (normalizing), and then heated to 800°C and held for 3 hours for tempering. After cooling, the low-activation steel of the present invention is obtained. The obtained low-activation steel includes M. 23 The C6 phase and the M'X phase, with the M'X phase having a number density of 1.4 × 10⁻⁶. 20 / m 3 .

[0145] The room temperature mechanical properties of the low-activation steel prepared in Example 6: σ 0.2 =688MPa, σ b =812MPa, A=11%, Ψ=66%, KV2=155J. The creep rupture life reaches 100h under the conditions of 650℃ and 200MPa, and KV2=72J after aging at 550℃ for 10000h.

[0146] Example 7

[0147] The composition of the low-activation steel in Example 7 is shown in Table 1, #12. The preparation process of the low-activation steel is as follows:

[0148] (1) Low-activation steel raw materials are added according to the chemical composition ratio, wherein the low-activation steel raw materials are made of intermediate alloys. The low-activation steel raw materials are vacuum induction melted, and then refined and impurities are removed by electroslag remelting under atmosphere protection. Finally, the steel ingots are cast into shape.

[0149] (2) Heat the steel ingot to 1200℃, homogenize and hold for 2 hours, then forge it. The final forging temperature is 1000℃, and it is prepared into a bar with a diameter of 20mm.

[0150] (3) Heat the bar obtained in step (2) to 900℃ and keep it at that temperature for 2 hours, then air cool it to room temperature;

[0151] (4) The workpiece obtained by cooling in step (3) is heated to 1030°C and held for 1 hour, then air-cooled to room temperature (normalizing), and then heated to 760°C and held for 1.5 hours for tempering. After cooling, the low-activation steel of the present invention is obtained. The obtained low-activation steel includes M. 23 The C6 phase and the M'X phase, with the M'X phase having a number density of 1.2 × 10⁻⁶. 20 / m 3 .

[0152] The room temperature mechanical properties of the low-activation steel prepared in Example 7: σ 0.2 =583MPa, σ b =691MPa, A=20%, Ψ=78%, KV2=241J.

[0153] Examples 8-14

[0154] In Examples 8-14, the low-activation steel compositions used were 2#, 3#, 5#, 6#, 8#, 9#, and 11# from Table 1, respectively. The preparation process of the low-activation steel is as follows:

[0155] (1) Low-activation steel raw materials are added according to the chemical composition ratio, wherein the low-activation steel raw materials are made of intermediate alloys. The low-activation steel raw materials are vacuum induction melted, and then refined and impurities are removed by electroslag remelting under atmosphere protection. Finally, the steel ingots are cast into shape.

[0156] (2) Heat the steel ingot to 1200℃, homogenize and hold for 2 hours, then forge and hot roll. The final rolling temperature is 1000℃, and the plate is prepared with a thickness of 40mm.

[0157] (3) Heat the bar obtained in step (2) to 900℃ and keep it at that temperature for 2 hours, then air cool it to room temperature;

[0158] (4) The workpiece obtained by cooling in step (3) is heated to 1030°C and held for 1 hour, then air-cooled to room temperature (normalizing), and then heated to 760°C and held for 1.5 hours for tempering. After cooling, the low-activation steel of the present invention is obtained. The obtained low-activation steel includes M. 23 C6 phase and M'X phase, wherein the low-activation steels prepared in Examples 8-14 all satisfy the requirement that the M'X phase number density is ≥1.0×10 20 / m 3 .

[0159] The room temperature properties of the low-activation steels prepared in Examples 8-14 all meet the following requirement: σ 0.2 ≥550MPa, σ b ≥650MPa, A≥10%, Ψ≥65%, KV2≥150J.

[0160] As can be seen from the performance test results of the low-activation steel in Examples 1-14 and Comparative Examples 1-2, the overall performance of the low-activation steel of the present invention has been effectively improved.

[0161] Table 1

[0162]

[0163] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A low-activation steel, characterized in that, include: 0.03wt%~0.15wt% C; 0.1wt%~2.5wt% Si; 0.2wt%~1.2wt% Mn; 0.5wt%~3.5wt% W; 8wt%~12wt% Cr; 0.05wt%~0.6wt% V; 0.02wt% to 0.6wt% of a strong carbonitride forming element, wherein the strong carbonitride forming element includes at least one of Ta and Ti; The balance consists of Fe and unavoidable impurities; The low-activation steel precipitate includes M 23 C6 phase and M'X phase, wherein the number density of the M'X phase is 10. 20 / m 3 ~10 21 / m 3 M includes Cr, W, Mn or V, M' includes Ti, Ta or V, and X includes C or N.

2. The low-activation steel according to claim 1, characterized in that, The content of Ta in the strong carbonitride forming elements is not less than 0.06 wt%, and the content of Ti is not less than 0.02 wt%.

3. The low-activation steel according to claim 1 or 2, characterized in that, Also includes: 0.02wt%~0.06wt% N.

4. The low-activation steel according to claim 3, characterized in that, It also includes 0.05wt% to 0.3wt% of rare earth elements, wherein the rare earth elements include at least one of Y, La and Ce.

5. The low-activation steel according to claim 1, characterized in that, Based on the total volume of the low-activation steel, the M 23 The volume fraction of the C6 phase is 0.5% to 3%, and the volume fraction of the M'X phase is 0.05% to 0.45%.

6. A method for preparing the low-activation steel according to any one of claims 1 to 5, characterized in that, include: (1) The low-activation steel raw material is smelted, impurities removed and shaped to obtain steel ingots; (2) The steel ingot is hot-processed to obtain a hot-processed part; (3) Heat the hot-worked part to 850℃~950℃ and hold for 0.5h~12h, then cool it and repeat 1~3 times; (4) After the workpiece obtained in step (3) is austenitized, it is cooled and then tempered.

7. The method according to claim 6, characterized in that, In step (1), the impurity removal process uses rare earth elements for impurity removal.

8. The method according to claim 6 or 7, characterized in that, In step (2), the steel ingot is heated to 1150℃~1250℃ and held for 2h~6h before forging begins. The forging ratio is not less than 3 and the final forging temperature is not less than 850℃. Optionally, in step (2), the strain rate of the hot working is not higher than 0.08 / s; Optionally, in step (2), the hot-worked part is a plate, and the hot-worked part is hot-rolled with an initial rolling temperature of 1130℃~1180℃ and a final rolling temperature of not less than 850℃. Optionally, in step (2), the hot-worked part is a sheet metal, and the hot-worked part is hot-rolled, with a total reduction of not less than 50% and a single reduction of not more than 20% when rolling at a temperature below 1000°C.

9. The method according to claim 8, characterized in that, The final forging temperature is not less than 1000℃.

10. The method according to claim 8, characterized in that, The final rolling temperature is not less than 1000℃.

11. The method according to claim 6 or 7, characterized in that, In step (4), the workpiece obtained in step (3) is heated to 980℃~1080℃ and held for 0.5h~12h for austenitization treatment and then cooled. Optionally, in step (4), the tempering includes heating the cooled workpiece to 700°C~800°C, holding it at that temperature for 0.5h~3h, and then cooling it.

12. The application of the low-activation steel according to any one of claims 1 to 5 or the low-activation steel obtained by the method according to any one of claims 6 to 11 in the field of nuclear power generation.

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