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 0.12 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 0.35 wt% V; 0.02 wt% to 0.60 wt% of a strong carbonitride element, including at least one of Ta, Ti, and Zr; the balance being Fe and unavoidable impurities; the precipitated phase of the low-activation steel includes Mn. 23 C6 phase and M'X phase, M 23 The average equivalent diameter of the C6 phase is 50 nm to 90 nm. M includes Cr, W, Mn, or V; M' includes Ti, Ta, Zr, or V; and X includes C or N. Using the above chemical composition ratio in the preparation method of low-activation steel, combined with a multi-temperature, multi-step tempering process, can reduce the concentration of M... 23 The average equivalent diameter of the C6 phase is controlled to be 50nm–90nm. Therefore, the low-activation steel of this invention possesses excellent strength, toughness, high-temperature creep life, and radiation resistance. The preparation method is compatible with existing processes and is conducive to its widespread 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 power produces almost no carbon emissions and, compared to other clean energy sources such as wind and solar power, offers the advantage of stable power generation. It also eliminates the need for energy storage for peak shaving and valley filling, making the development of nuclear energy an essential path to clean power generation. Nuclear power generation includes controlled nuclear fission and controlled nuclear fusion. Currently, fission reactors are relatively mature, while fourth-generation reactors are under development. Both fourth-generation fission reactors and fusion demonstration reactors place higher demands on the high-temperature performance and radiation resistance of structural materials, making related fields a research hotspot both domestically and internationally. Low-activation steel possesses excellent radiation resistance, including a small swelling rate after irradiation and high thermal conductivity, and has a strong research and industrial foundation, making it considered the preferred structural material for fusion demonstration reactors and an important structural material for fourth-generation fission reactors.

[0003] Low-activation steel is an improvement upon traditional heat-resistant steel, possessing similar composition and production processes. The production process generally includes smelting, forging, hot working, and heat treatment. The classic heat treatment is normalizing followed by high-temperature tempering, with a typical microstructure being tempered martensite. During 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 100–500 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, forming continuous precipitation at the martensite lath bundle boundaries, severely impairing the material's high-temperature strength and toughness, and causing material failure.

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

[0005] One object of the present invention is to provide a low-activation steel, its preparation method and application, wherein M in the low-activation steel 23 The C6 phase is small in size and uniformly distributed, which effectively improves the strength, toughness, high-temperature creep life and radiation resistance of 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 0.12 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 0.35 wt% V; 0.02 wt% to 0.60 wt% of a strong carbonitride element, said strong carbonitride element including at least one of Ta, Ti, and Zr; 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 M 23 The average equivalent diameter of the C6 phase is 50 nm to 90 nm. M includes Cr, W, Mn or V, M' includes Ti, Ta, Zr 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 elements (i.e., Ta, Ti, Zr) 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 the M'X precipitate. 23 C6 precipitates act as precipitation strengthening, improving the strength and toughness of the low-activation steel. Si enhances the oxidation and corrosion resistance of the low-activation steel, while Mn combines with impurities such as P and S to reduce their detrimental effects on the performance of the low-activation steel and improves its hot working properties, impact resistance, and corrosion resistance. W provides solid solution strengthening, and Cr enhances the oxidation and corrosion resistance of the low-activation steel. Furthermore, the Mn in the low-activation steel of this invention... 23 The average equivalent diameter of the C6 phase is controlled within the range of 50nm to 90nm, resulting in a relatively smaller size and more uniform distribution, which enhances its precipitation strengthening effect. Therefore, the low-activation steel with the above-mentioned composition and content range, as well as the above-mentioned precipitate size range, exhibits a more uniform precipitate distribution, and M... 23 The smaller size of the C6 phase enhances 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 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 elements is not less than 0.05 wt%, the content of Ti is not less than 0.02 wt%, and the content of Zr 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 0.02% to 0.15%. This enhances the ability of the precipitated phases 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) melting, removing impurities and forming the low-activation steel raw material to obtain a steel ingot; (2) hot working the steel ingot to obtain a hot-worked part; (3) austenitizing the hot-worked part and then cooling it; (4) tempering the workpiece obtained in step (3), the tempering comprising heating the workpiece to 600℃~700℃ and holding it at that temperature for 0.5h~3h, then raising the temperature to 720℃~800℃ and holding it at that temperature for 0.5h~3h and then cooling it, or holding the workpiece at 720℃~800℃ for 15min~45min and then cooling it, and repeating this process 3~6 times.

[0014] Therefore, this invention involves melting, removing impurities, and shaping low-activation steel raw materials, then hot-working and austenitizing the resulting steel ingots, followed by tempering the cooled workpiece as described above. This is achieved using a combination of high and low temperature tempering or multiple short-time high-temperature tempering processes (i.e., multi-temperature, multi-step tempering). During the tempering process, M... 23 The C6 phase exhibits a higher precipitation driving force at lower temperatures, which can promote the precipitation of M. 23 C6 phase precipitates at the martensite lath boundaries, utilizing the fine M precipitates. 23The C6 phase inhibits martensite lath coalescence and dislocation recovery, improves the stability of the martensite matrix, increases the interfacial density of the matrix, and provides more M for the high-temperature tempering process. 23 C6 nucleation site. Multi-temperature, multi-step tempering process increases interfacial density by more than 20%, from (0.7–1.2) × 10⁻⁶. 6 / m increased to (1.2~5)×10 6 / m, a greater number of nucleation sites also cause M 23 The refinement of C6 reduces the average equivalent diameter by more than 20%, from 80nm-150nm to 50nm-90nm, thereby achieving M 23 The C6 phase size is refined, and the uniformity of the precipitated phase distribution is improved. Therefore, this method can yield M with uniform distribution and refined size. 23 Low-activation steel with C6 phase, uniformly distributed and finely sized M 23 The C6 phase has the ability to enhance the stability of 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 strain rate of the hot-worked part during forging and rolling is not higher than 0.08 / s. This prevents plastic instability of the hot-worked part during hot working, thereby improving 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 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.

[0020] According to an embodiment of the present invention, in step (2), the hot-worked part is a plate, 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. As a result, a uniform austenitic structure can be obtained, plastic instability and banded structure can be avoided, cracking of the hot-worked part can be prevented, thereby improving the strength and toughness of the low-activation steel.

[0021] According to an embodiment of the present invention, in step (3) of the above method, the hot-worked part is heated to 980°C to 1080°C and held at that temperature for 0.5h to 12h for austenitization treatment, followed by cooling. This improves the strength and toughness of the low-activation steel.

[0022] 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 possesses high strength and toughness, excellent high-temperature creep resistance, and radiation resistance, thus meeting the higher requirements for low-activation steel materials in related nuclear power generation fields such as fourth-generation fission reactors and fusion demonstration reactors.

[0023] 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

[0024] 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:

[0025] Figure 1 This is a schematic diagram of the process for preparing low-activation steel in one embodiment of the present invention;

[0026] Figure 2 These are SEM images of the low-activation steels prepared in Comparative Example 1 and Example 1, where a is Comparative Example 1 and b is Example 1.

[0027] Figure 3 The creep curves of the low-activation steel prepared in Comparative Example 1 and Example 1 under conditions of 650°C and 120MPa are shown.

[0028] Figure 4 These are TEM images of the low-activation steel prepared in Comparative Example 2 and Example 2, where a is Comparative Example 2 and b is Example 2;

[0029] Figure 5 This is an EBSD characterization diagram of the interfacial density of the low-activation steel prepared in Comparative Example 2.

[0030] Figure 6 This is an EBSD characterization diagram of the interfacial density of the low-activation steel prepared in Example 2;

[0031] Figure 7 This is a TEM image of the low-activation steel prepared in Example 3. Detailed Implementation

[0032] The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention.

[0033] 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 0.12 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 0.35 wt% V; 0.02 wt% to 0.60 wt% of a strong carbonitride element, said strong carbonitride element including at least one of Ta, Ti, and Zr; 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 M 23 The average equivalent diameter of the C6 phase is 50 nm to 90 nm. M includes Cr, W, Mn or V, M' includes Ti, Ta, Zr or V, and X includes C or N.

[0034] 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 elements (i.e., Ta, Ti, Zr) and V elements to form the M'X precipitate, and the C element can also combine with Mn, W, and Cr elements to form the M'X precipitate. 23 C6 precipitates act as precipitation strengthening, improving the strength and toughness of the low-activation steel. Si enhances the oxidation and corrosion resistance of the low-activation steel, while Mn combines with impurities such as P and S to reduce their detrimental effects on the performance of the low-activation steel and improves its hot working properties, impact resistance, and corrosion resistance. W provides solid solution strengthening, and Cr enhances the oxidation and corrosion resistance of the low-activation steel. Furthermore, the Mn in the low-activation steel of this invention... 23 The average equivalent diameter of the C6 phase was controlled within the range of 50 nm to 90 nm (e.g., M). 23 The average equivalent diameter of the C6 phase can be 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, etc., which is relatively smaller and more uniformly distributed, thus enhancing its precipitation strengthening effect. Therefore, the low-activation steel with the above-mentioned composition and content range, as well as the above-mentioned precipitate size range, exhibits a more uniform precipitate distribution, and M... 23The smaller size of the C6 phase enhances 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. According to embodiments of the present invention, the mechanical properties of the low-activation steel satisfy the following: 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; High-temperature creep life: Creep life ≥120h under 650℃ and 120MPa conditions.

[0035] 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:

[0036] First, the carbon content in the low-activation steel of this invention is 0.03wt% to 0.12wt%. C can combine with strong carbide-forming elements such as Ti, Zr, 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. 23 C6 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 0.12wt% (for example, C content can be 0.03wt%, 0.04wt%, 0.05wt%, 0.06wt%, 0.07wt%, 0.08wt%, 0.09wt%, 0.10wt%, 0.11wt%, 0.12wt%, etc.). This allows for the precipitation of M in the low-activation steel... 23 The C6 and M'X phases have small size and relatively uniform distribution, effectively improving the strength and toughness of the low-activation steel. They also give the low-activation steel better corrosion resistance, 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 0.12wt% 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.

[0037] 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 low-activation 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 oxygen-free, so 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, it comes into direct contact with liquid Pb-Bi, liquid Na, or high-temperature gas 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%.

[0038] 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 low-activation steel. In addition, increasing the Mn content can improve the hot working properties, impact properties, and corrosion resistance of low-activation steel. However, excessively high Mn content will cause segregation in low-activation steel, prolong its homogenization time, impair its economic efficiency, and increase the M content in low-activation steel. 23The 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, impact resistance, and corrosion resistance of the low-activation steel without compromising its creep properties. In practical applications, the Mn content can be further limited 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 Generation IV 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%.

[0039] 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 strength, toughness, 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 within 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 within 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.

[0040] 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. 23 The 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.

[0041] Sixth, the content of V in the activated steel of this invention is 0.05wt% to 0.35wt%, and the content of strong carbonitride elements is 0.02wt% to 0.60wt%, wherein the strong carbonitride elements include at least one of Ta, Ti, and Zr. Ta, Ti, Zr, and V are all M'X phase forming elements. Ta, Ti, and Zr have strong bonding ability with C and N, while V has relatively poor bonding ability with C. The addition of V and C alone cannot form the M'X phase thermodynamically. The combined action of strengthening elements (i.e., Ta, Ti, Zr) and N is required to form V(C,N). Therefore, at least one of the three elements Ta, Ti, and Zr must be added. The initial precipitation temperature of the M'X precipitate, formed by the combination of strong carbonitride elements with C and N, is between 1100℃ and 1250℃. For Ti and Zr to achieve relatively good precipitation, the minimum addition amount is 0.02wt%. Due to its large atomic mass, Ta requires a minimum addition amount of 0.05wt% for relatively good precipitation. That is to say, when Ti is added to low-activation steel, the amount of Ti added should not be less than 0.02wt%, and similarly, when Zr is added to low-activation steel, the amount of Zr added should not be less than 0.02wt%, and when Ta is present in low-activation steel, the Ta content should not be less than 0.05wt%. However, excessively high contents of Ta, Ti, and Zr will increase the difficulty of smelting low-activation steel. Therefore, considering the above reasons, in this invention, the content of strong carbonitride elements is controlled within the range of 0.02wt% to 0.60wt% (for example, strong carbonitride elements can be 0.02wt%, 0.05wt%, 0.10wt%, 0.15wt%, 0.20wt%, 0.30wt%, 0.40wt%, 0.50wt%, 0.55wt%, 0.60wt%, etc.). Specifically, if Ta is present, the Ta content is not less than 0.05wt%; if Ti is present, the Ti content is not less than 0.02wt%; and if Zr is present, the Zr content is not less than 0.02wt%. This enhances precipitation strengthening, thereby improving the strength, toughness, high-temperature creep life, and radiation resistance of the low-activation steel. Furthermore, within the above-mentioned content range, i.e., 0.02wt% to 0.60wt%, increasing the content of Ta, Ti, and Zr can increase the volume fraction of the M'X phase and reduce the M... 23 The volume fraction and size of the C6 phase enhance the ability of the precipitated phase to stabilize the matrix and pin dislocations. Therefore, as a preferred embodiment, the content of Ta is not less than 0.12 wt%, the content of Ti is not less than 0.06 wt%, and the content of Zr is not less than 0.06 wt%, which can better refine the M... 23 The size of the C6 phase improves the strength, toughness, high-temperature creep life, and radiation resistance of low-activation steel.

[0042] The initial precipitation temperature of V(C,N) is between 950℃ and 1050℃. In actual heat treatment processes, V reacts with M during tempering. 23 The C6 phase precipitates at both grain boundaries and martensite lath interfaces. The V content is adjusted based on the concentration of strong carbonitride elements. When the concentration of strong carbonitride elements is high (≥0.2 wt%), less V can be added, with the V content controlled between 0.05 wt% and 0.15 wt%. When the concentration of strong carbonitride elements is low (<0.2 wt%), more V can be added, with the V content between 0.05 wt% and 0.35 wt% (e.g., 0.05 wt%, 0.07 wt%, 0.10 wt%, 0.12 wt%, 0.15 wt%, 0.18 wt%, 0.20 wt%, 0.22 wt%, 0.25 wt%, 0.28 wt%, 0.30 wt%, 0.33 wt%, 0.35 wt%). This is because higher V additions will form a mass close to M at the martensite lath interface. 23 V(C,N) of the C6 phase, and V also participates in M. 23 The formation of the C6 phase increases its average size, so further increasing the V content has no practical significance for M'X phase precipitation strengthening. Therefore, the V content should not exceed 0.35 wt%. In this way, a better precipitation effect can be achieved, thereby improving the strength, toughness, high-temperature creep life, and radiation resistance of low-activation steel.

[0043] For the reasons mentioned above, this invention designs the optimal chemical composition for low-activation steel, adding multiple strong carbide-forming elements, namely strong carbonitride elements (Ta, Ti, and Zr) and V, to form multiple M'X phase composite strengthening, and controlling the content of chemical components to achieve M 23 The C6 phase is refined in size and uniformly distributed, improving M 23 The precipitation of C6 phase enhances the strength, toughness, high-temperature creep life, and radiation resistance of the low-activation steel of this invention.

[0044] In some embodiments of the present invention, the low-activation steel of the present invention further includes 0.02wt% to 0.06wt% N. N and C jointly participate in the formation of M'X type precipitates. TiN is usually formed during the smelting process, is large in size and difficult to dissolve, therefore, when Ti is added, N addition should be avoided, i.e., no N element is added. VN has a low precipitation temperature and is a beneficial precipitate phase. Therefore, depending on the content of Ti, Zr, Ta, and V elements, when N element is added to the activated steel, controlling the N content range to 0.02wt% to 0.06wt% (for example, the N content can be 0.02wt%, 0.03wt%, 0.04wt%, 0.05wt%, 0.06wt%, etc.) can achieve better precipitation effect. Furthermore, excessive interstitial alloying elements will impair the weldability of the low-activation steel. Therefore, in some specific embodiments of the present invention, when C and N are added together, in order to ensure its weldability, their mass percentage is controlled within the range of (C+N) ≤ 0.15wt%.

[0045] 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., M). 23 The volume fraction of the C6 phase can be 0.5%, 0.8%, 1%, 1.2%, 1.4%, 1.8%, 2.2%, 2.5%, 2.7%, 3%, etc., and the volume fraction of the M'X phase is 0.02% to 0.15% (for example, the volume fraction of the M'X phase can be 0.02%, 0.04%, 0.06%, 0.08%, 0.1%, 0.12%, 0.14%, 0.15%, etc.). Specifically, in some embodiments of the present invention, the M'X phase in the low-activation steel of the present invention... 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 120 nm. M is present at the original austenite grain boundaries. 23 C6 is rod-shaped or polygonal, with dimensions ranging from 50 nm to 200 nm. 23 In the C6 phase, M includes Cr, W, Mn, or V; in the low-activation steel of this invention, the M'X phase is distributed within 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, Zr, or V, and X is C or N. Therefore, this invention optimizes M... 23 The precipitation ratio of C6 phase and M'X phase can be adjusted to optimize M to a certain extent. 23 The distribution and size of the C6 phase, i.e., the refinement of M 23The C6 phase and the uniform distribution of the precipitate in the matrix effectively enhance the ability of the precipitate to stabilize the matrix and pin dislocations, thereby improving the strength and creep resistance of the low-activation steel and its high-temperature service performance.

[0046] 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, 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%. This can effectively reduce the influence of impurity elements in low-activation steel on the performance of low-activation steel and further improve the fracture toughness and high-temperature creep performance of low-activation steel.

[0047] 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. 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.

[0048] According to embodiments of the present invention, it should be noted that the mass percentage mentioned in the present invention refers to the mass percentage of the chemical composition of steel grade elements in low-activation steel.

[0049] In another aspect of the invention, a method for preparing the aforementioned low-activation steel is provided, referring to... Figure 1 The method includes:

[0050] S100: Melting, impurity removal, and forming of low-activation steel raw materials.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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%.

[0055] 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.

[0056] S200: The steel ingot obtained in step S100 is heated and then forged.

[0057] 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. 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 1.5wt% 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.

[0058] 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).

[0059] 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 1.5wt% 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.

[0060] S300: The hot-worked part obtained in step S200 is subjected to austenitizing treatment and then cooled.

[0061] In this step, the hot-worked part is first heated to 980℃~1080℃ (e.g., to 980℃, 1000℃, 1020℃, 1040℃, 1060℃, 1080℃, etc.) to induce austenitization, and then held at this temperature. The holding time can be selected according to the desired original austenite grain size. In some embodiments of the present invention, the desired original austenite grain size is 10μm~200μm, therefore the holding time is selected as 0.5h~12h (e.g., 0.5h, 2h, 4h, 6h, 8h, 10h, 12h, etc.). After the austenitization is fully achieved, cooling is performed. Cooling can be done by water cooling or air cooling to room temperature. If water cooling is used, the next heat treatment should be carried out within 12 hours to prevent the workpiece from cracking due to stress release. If air cooling is used, there is no time limit.

[0062] S400: Temper the workpiece obtained in step S300.

[0063] In this step, the tempering process can employ either a combination of high and low temperature tempering or multiple short-duration high-temperature tempering. Specifically, the combination of high and low temperature tempering involves heating the workpiece to 600℃~700℃ (e.g., heating to 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, 660℃, 670℃, 680℃, 690℃, 700℃, etc.) and holding it at that temperature for 0.5h~3h (e.g., holding for 0.5h, 0.6h, 0.8h, 1h, 1.2h, 1.6h, 1.9h, 2.1h, 2.3h, 2.5h, 2.7h, 2.9h, 3h, etc.), and then raising the temperature to 720℃~800℃ (e.g., raising the temperature to 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, 790℃, etc.). The process involves holding the workpiece at 720℃ to 800℃ (for example, temperatures can be 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, etc.) for 15min to 45min (for example, temperatures can be 15min, 17min, 20min, 25min, 27min, 30min, 35min, 37min, 40min, 42min, 45min, etc.) and then cooling it, and repeating this process 3 to 6 times.

[0064] According to embodiments of the present invention, the workpiece is tempered using a combination of high and low temperature tempering or multiple short-time high-temperature tempering processes. Since M 23 The C6 phase exhibits a strong driving force for precipitation at lower temperatures, therefore, during the heating process of low-temperature tempering or multiple tempering, M... 23 The C6 phase can precipitate at martensite lath boundaries, thereby stabilizing the martensite lath structure, suppressing dislocation recovery and martensite lath coalescence, and increasing the grain boundary density of the matrix by more than 20%, from (0.7–1.2) × 10⁻⁶. 6 / m increased to (1.2~5)×10 6 / m, in addition, M 23 The nucleation sites of the C6 phase are thus significantly increased, and the increased number of nucleation sites also enables M... 23 Refinement of C6 phase, M 23 The average equivalent diameter of the C6 phase is reduced by more than 20%, from 80nm-150nm to 50nm-90nm. This enhances 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 low-activation steel.

[0065] According to embodiments of the present invention, both of the above-mentioned tempering processes can achieve the technical effects of the present invention. Among them, the high and low temperature combined tempering process has a wider range of applications and is simpler to use in industry. It can achieve better M in both high carbon content and low carbon content low activation steel. 23 The C6 phase refinement effect can be achieved, while multiple short-time high-temperature tempering processes can be used in systems with low (C+N) content.

[0066] According to an embodiment of the present invention, the present invention employs the above-described preparation process to melt, remove impurities from, and shape low-activation steel raw materials, then performs hot working and austenitizing treatment on the resulting steel ingots, and then performs the above-described tempering on the cooled workpieces. During the tempering process, a high-low temperature combined tempering process or a multiple short-time high-temperature tempering process is used to improve the efficiency of M... 23 The C6 phase exhibits a higher precipitation driving force at lower temperatures, promoting the precipitation of M. 23 C6 phase precipitates at the martensite lath boundaries, utilizing the fine M precipitates. 23 The C6 phase inhibits the recovery of dislocations and martensite laths in low-activation steel, improves the stability of the martensite matrix, and increases the interfacial density in low-activation steel (interfacial density increases by more than 20%, from (0.7~1.2)×10⁻⁶). 6 / m increased to (1.2~5)×10 6 / m), providing more M for the high-temperature tempering process. 23 The C6 nucleation site, along with numerous nucleation locations, also contributes to M. 23 Refining C6 reduces its average equivalent diameter by more than 20%, from 80nm-150nm to 50nm-90nm, and the size refinement also makes its distribution more uniform. Therefore, this method can be used to obtain M. 23 Low-activation steel with refined and uniform C6 phase size and distribution, and M phase with refined and uniform size and distribution. 23 The C6 phase enhances the stability of the matrix and the ability to pin dislocations, resulting in low-activation steel with excellent strength, toughness, high-temperature creep life, and radiation resistance. Furthermore, the preparation method of the low-activation steel of this invention is compatible with existing processes, can be mass-produced, and is suitable for widespread application in industrial production.

[0067] 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. Compared with traditional low-activation steel, the low-activation steel of the present invention has improved strength, toughness, high-temperature creep performance, and radiation resistance, which can meet the higher requirements of the nuclear power generation field for low-activation steel materials.

[0068] 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.

[0069] Example 1

[0070] 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:

[0071] (1) Add low-activation steel raw materials according to the chemical composition ratio, perform vacuum induction melting on the low-activation steel raw materials, refine and remove impurities by electroslag remelting under atmosphere protection, and then cast into steel ingots.

[0072] (2) Heat the steel ingot to 1200℃, homogenize and hold for 4 hours, then forge it. The forging ratio is >3, the final forging temperature is 1000℃, and it is prepared into a bar with a diameter of 20mm.

[0073] (3) Heat the bar obtained in step (2) to 1030℃ for austenitization, hold for 0.5h and then air cool to room temperature;

[0074] (4) The workpiece obtained in step (3) is heated to 650°C and held for 1.5 hours, then heated to 760°C in the furnace and held for 1.5 hours, and then air-cooled to room temperature to obtain the low-activation steel of the present invention. The obtained low-activation steel includes M. 23 C6 phase and M'X phase, where M 23 The average equivalent diameter of the C6 phase is 89 nm.

[0075] Example 2

[0076] The composition of the low-activation steel in Example 2 is shown in Table 1, #2. The preparation process of the low-activation steel is as follows:

[0077] (1) Use intermediate alloy batching to feed low activation steel raw materials, vacuum induction melting of low activation steel raw materials, refining and removing impurities by electroslag remelting under atmosphere protection, and then casting to obtain steel ingots.

[0078] (2) Heat the steel ingot to 1200℃, homogenize and hold for 2 hours, then forge it. The forging ratio is >3, the final forging temperature is 1000℃, and it is prepared into a bar with a diameter of 20mm.

[0079] (3) Heat the bar obtained in step (2) to 1030℃ for austenitization, hold for 0.5h and then air cool to room temperature;

[0080] (4) The workpiece obtained in step (3) is heated to 760°C and held at that temperature for 0.5 hours, then air-cooled to room temperature. This process is repeated three times to obtain the low-activation steel of the present invention. The obtained low-activation steel includes M. 23 C6 phase and M'X phase, where M 23 The average equivalent diameter of the C6 phase is 70 nm.

[0081] Example 3

[0082] The composition of the low-activation steel in Example 3 is shown in Table 1, #3. The preparation process of the low-activation steel is as follows:

[0083] (1) Use intermediate alloy batching to feed low activation steel raw materials, vacuum induction melting of low activation steel raw materials, refining and removing impurities by electroslag remelting under atmosphere protection, and then casting to obtain steel ingots.

[0084] (2) Heat the steel ingot to 1200℃, homogenize and hold for 2 hours, then forge it. The forging ratio is >3, the final forging temperature is 1000℃, and it is prepared into a bar with a diameter of 20mm.

[0085] (3) Heat the bar obtained in step (2) to 1030℃ for austenitization, hold for 0.5h and then air cool to room temperature;

[0086] (4) The workpiece obtained in step (3) is heated to 760°C and held at that temperature for 0.5 hours, then air-cooled to room temperature. This process is repeated three times to obtain the low-activation steel of the present invention. The obtained low-activation steel includes M. 23 C6 phase and M'X phase, where M 23 The average equivalent diameter of the C6 phase is 65 nm.

[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) Use intermediate alloy batching to feed low activation steel raw materials, vacuum induction melting of low activation steel raw materials, refining and removing impurities by electroslag remelting under atmosphere protection, and then casting to obtain steel ingots.

[0090] (2) Heat the steel ingot to 1200℃, homogenize and hold for 2 hours, then forge it. The forging ratio is >3, the final forging temperature is 1000℃, and it is prepared into a bar with a diameter of 20mm.

[0091] (3) Heat the bar obtained in step (2) to 1030℃ for austenitization, hold for 0.5h and then air cool to room temperature;

[0092] (4) The workpiece obtained in step (3) is heated to 760℃ and held for 1.5 hours, then air-cooled to room temperature to obtain low-activation steel. The obtained low-activation steel includes M. 23 C6 phase and M'X phase, where M 23 The average equivalent diameter of the C6 phase is 103 nm.

[0093] Comparative Example 2

[0094] The composition of the low-activation steel in Comparative Example 2 is shown in Table 1, #2. The preparation process of the low-activation steel is as follows:

[0095] (1) Use intermediate alloy batching to feed low activation steel raw materials, vacuum induction melting of low activation steel raw materials, refining and removing impurities by electroslag remelting under atmosphere protection, and then casting to obtain steel ingots.

[0096] (2) Heat the steel ingot to 1200℃, homogenize and hold for 2 hours, then forge it. The forging ratio is >3, the final forging temperature is 1000℃, and it is prepared into a bar with a diameter of 20mm.

[0097] (3) Heat the bar obtained in step (2) to 1030℃ for austenitization, hold for 0.5h and then air cool to room temperature;

[0098] (4) The workpiece obtained in step (3) is heated to 760℃ and held at that temperature for 1.5 hours, then air-cooled to room temperature to obtain low-activation steel. The obtained low-activation steel includes M. 23 C6 phase and M'X phase, where M 23 The average equivalent diameter of the C6 phase is 106 nm.

[0099] Table 2 lists the grain boundary density and M0 of the low-activation steels obtained in Examples 1-3 and Comparative Examples 1-2. 23 Average size of C6 phase and test data on the properties of low-activation steel, including σ 0.2 (Yield Strength), σ b (Tensile stress) and KV2 (impact energy) are the mechanical property test results of low-activation steel at room temperature. The tensile test standard is GB / T288, the impact test uses standard specimens with V-notch, and the creep test conditions are 650℃ and 120MPa, with the creep test standard being GB / T2039. As can be seen from the data in Table 2, the performance of the low-activation steel in Examples 1-3 was effectively improved.

[0100] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 uses a one-step high-temperature long-time tempering process, while Example 1 uses a high-low temperature combined tempering process. Figure 2 The images show SEM (scanning electron microscope) images of the low-activation steels of Comparative Example 1 and Example 1 (a is Comparative Example 1, b is Example 1). Figure 3 The creep curves of the low-activation steels of Comparative Example 1 and Example 1 at 650°C and 120 MPa are shown below. Figure 2 , Figure 3 As can be seen from the data in Table 2, in Example 1, through a combination of high and low temperature tempering process, most of the martensitic lath structure was preserved, M 23 The C6 phase precipitates more fully at the lath boundary, M 23 The density of the C6 phase increases and its size decreases, while the M phase at lath boundaries and grain boundaries... 23The C6 phase is also refined accordingly, thereby effectively improving the strength, toughness, high-temperature creep properties and radiation resistance of the low-activation steel in Example 1.

[0101] The difference between Comparative Example 2 and Example 2 is that Comparative Example 2 uses a one-step high-temperature long-time tempering process, while Example 2 uses a multiple short-time high-temperature tempering process. Figure 4 The images show TEM (transmission electron microscopy) images of the low-activation steels of Comparative Example 2 and Example 2 (a is Comparative Example 2, b is Example 2). Figure 5 and Figure 6 The figures shown in Table 3 are EBSD (electron backscattering diffraction) characterization patterns of the interface density of the low-activation steels of Comparative Example 2 and Example 2, respectively. Figure 4 , Figure 5 and Figure 6 It can be seen that the low-activation steel in Example 2 has a higher grain boundary density, M 23 The C6 phase has a higher density and smaller size, which effectively improves the strength, toughness, high-temperature creep properties and radiation resistance of the low-activation steel in Example 2.

[0102] Figure 7 The image shows a TEM image of the low-activation steel obtained in Example 3. It can be seen from the image that the low-activation steel has a high grain boundary density and small and uniformly distributed precipitated phases.

[0103] Table 1

[0104]

[0105] Table 2

[0106]

[0107] 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 method for preparing low-activation steel, 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) The hot-worked part is cooled after undergoing austenitizing treatment; (4) Temper the workpiece obtained in step (3). The tempering includes heating the workpiece to 600℃~700℃ and holding it for 0.5h~3h, then raising the temperature to 720℃~800℃ and holding it for 0.5h~3h before cooling, or holding the workpiece at 720℃~800℃ for 15min~45min and then cooling, and repeating this process 3~6 times. The low-activation steel includes: 0.03wt%~0.12wt% C; 0.1wt%~2.5wt% Si; 0.2wt%~1.2wt% Mn; 0.5wt%~3.5wt% W; 8wt%~12wt% Cr; 0.05wt%~0.35wt% V; 0.02wt% to 0.60wt% of a strong carbonitride element, wherein the strong carbonitride element includes at least one of Ta, Ti and Zr; The balance consists of Fe and unavoidable impurities; The low-activation steel precipitate includes M 23 C6 phase and M'X phase, wherein M 23 The average equivalent diameter of the C6 phase is 50 nm to 90 nm. M includes Cr, W, Mn or V, M' includes Ti, Ta, Zr or V, and X includes C or N.

2. The method according to claim 1, characterized in that, The content of Ta in the strong carbonitride elements is not less than 0.05wt%, the content of Ti is not less than 0.02wt%, and the content of Zr is not less than 0.02wt%.

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

4. The method according to claim 3, characterized in that, The low-activation steel 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 method 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 0.02% to 0.15%.

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

7. The method according to claim 1, 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 below 1000°C.

8. The method according to claim 7, characterized in that, The final forging temperature shall not be less than 1000℃.

9. The method according to claim 7, characterized in that, The final rolling temperature shall not be less than 1000℃.

10. The method according to claim 1, characterized in that, In step (3), the hot-worked part is heated to 980℃~1080℃ and held for 0.5h~12h for austenitization treatment and then cooled.

11. The application of low-activation steel obtained by the method according to any one of claims 1 to 10 in the field of nuclear power generation.

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