Method for improving structure and performance stability of copper-containing precipitation strengthened steel by using rare earth elements

Abstract

The invention discloses a method for improving the structure and performance stability of copper-containing precipitation strengthened steel through rare earth elements, and relates to the technical field of copper-containing precipitation strengthened steel machining. According to the method provided by the invention, the stabilizing element which can be combined with the vacancy to form the stabilizing element-Vac complex is introduced into the steel, so that the stabilizing element-Vac complex generates a pinning effect on the Cu precipitated phase, and the structural transformation and coarsening of the Cu precipitated phase are inhibited. By the adoption of the method, the proportion of the 9R-Cu phase in the precipitation phase can be greatly increased, the alloying cost of the copper-containing precipitation strengthened steel can be remarkably reduced, the welding process performance can be improved, the application temperature range can be expanded, and the service life of the steel can be prolonged.

Description

Technical Field

[0001] This invention relates to the field of copper precipitation-strengthened steel processing technology, and particularly to a method for improving the microstructure and property stability of copper precipitation-strengthened steel using rare earth elements. Background Technology

[0002] Copper precipitation-strengthened steel, as an important class of high-performance structural materials, is widely used in engineering structures with extremely high requirements for strength and durability, such as nuclear reactor pressure vessels, offshore platforms, and bridges. Copper significantly improves the mechanical properties of steel through a precipitation strengthening mechanism, with the Cu content typically controlled between 0.1% and 4.0%. After quenching and tempering (DQT) treatment, Cu-containing steel can achieve a strength increase of 150-250 MPa through the synergistic effect of grain refinement strengthening, dislocation strengthening, and precipitation strengthening.

[0003] However, Cu precipitates undergo complex structural evolution during heat treatment and long-term service, directly affecting the long-term performance stability of the material. According to existing research, the structural evolution of Cu precipitates follows a specific sequence: first, they precipitate from the supersaturated matrix, forming BCC (Body-Centered Cubic) clusters that are coherent with the matrix; as the size of the precipitate increases, the BCC structure transforms into a 9R structure with orthorhombic lattice characteristics, and finally evolves into a thermodynamically stable FCC (Face-Centered Cubic) structure.

[0004] In existing technologies, heat treatment process parameters have a decisive influence on Cu precipitation behavior. Studies have shown that aging at 425℃ can obtain coherent BCC Cu precipitates and achieve peak hardness. However, when the aging temperature exceeds 450℃, continuous recovery and dislocation annihilation occur in the matrix, while the Cu precipitates coarsen, leading to a continuous decrease in material hardness. More seriously, during long-term aging at 600℃, the size of the Cu precipitates increases significantly from the initial 20 nm to over 100 nm. Accompanied by the irreversible transformation of the 9R-Cu phase to the FCC structure, the strengthening effect of the material is greatly reduced.

[0005] To address the high-temperature instability of Cu precipitates, existing technologies primarily employ a strategy of adding large amounts of alloying elements. For example, Chinese patent application CN102011061A discloses a high-performance Cu-containing steel and its heat treatment process, which reduces the Cu matrix interfacial energy and promotes Cu precipitate nucleation by adding 1.00%-3.60% Ni. Chinese patent ZL2023104809584 describes a method for preparing mold steel with excellent heat loss resistance, in which Mo is added at a level of 2.8%-3.3%, aiming to promote Cu precipitate nucleation and inhibit its coarsening through Mo, and to improve the high-temperature stability of the material by utilizing the formation of M2C precipitates. Chinese patent ZL2015103700471 discloses Cu-reinforced Co-free secondary hardening ultra-high strength steel and its preparation method. In this Cu-reinforced Co-free secondary hardening ultra-high strength steel, the amount of Mo added is 1.0%-5.0%, and the amount of Ni added is as high as 8.0%-30.0%. Both of these methods attempt to improve the service stability of Cu-containing steel by using rare and precious metals such as Ni and Mo.

[0006] While the aforementioned existing technologies have improved the performance of Cu precipitation-strengthened steel to some extent, significant limitations remain. First, even with high-Ni, high-Mo alloying strategies, although the material reaches peak hardness at 425℃, its hardness inevitably continues to decline above 450℃. This indicates that existing technologies have failed to fundamentally solve the high-temperature stability problem of Cu precipitates, thus failing to fully utilize 9R-Cu to improve the material's service performance. Second, the addition of numerous expensive alloying elements significantly increases material costs; the high content of Mo and Ni results in a total alloying element content exceeding 10%, complicating the process and hindering economic efficiency. Third, during high-temperature processes such as welding, pre-existing Cu nanoparticles dissolve, leading to strength loss in the molten zone and heat-affected zone. Therefore, existing alloying strategies have limited effectiveness in addressing this problem.

[0007] More importantly, existing technologies, such as the method for preparing 440MPa grade ship hull structural steel based on Cu age strengthening disclosed in Chinese patent application CN118854155A, and the rolling and heat treatment strengthening method for copper-containing steel for marine engineering provided in Chinese patent application CN120082704A, do not fully consider the impact of Cu precipitate phase structure evolution on the long-term service performance of materials, and lack effective means to control the stability of the 9R-Cu phase.

[0008] In applications such as the nuclear industry, where the long-term stability of materials is extremely critical, the evolution of Cu precipitates is one of the main factors leading to irradiation embrittlement of reactor pressure vessel steel, severely impacting the safe operation and service life of nuclear power plants. Existing copper precipitation-strengthened steel materials, when subjected to long-term service at temperatures above 300°C, suffer from a significant decline in material strength due to the unstable transformation of the 9R-Cu phase, a problem that remains unresolved.

[0009] Therefore, how to effectively stabilize the Cu precipitate structure, especially the 9R-Cu phase with excellent strengthening effect, without significantly increasing the cost of the alloy, and prevent it from transforming into the FCC structure and coarsening, so as to achieve the microstructure stability and performance stability of the material under long-term high-temperature service conditions, remains a key technical challenge in the field of Cu precipitation-strengthened steel. Summary of the Invention

[0010] In existing technologies, Cu precipitates undergo an uncontrollable structural evolution from BCC to 9R to 3R to FCC. In particular, the 9R-Cu phase, which exhibits excellent strengthening effects, irreversibly transforms into an FCC structure above 450°C, accompanied by a coarsening of the precipitate from 10-20 nm to over 100 nm, leading to a significant reduction in the material's strengthening effect. While existing high-Ni and high-Mo alloying strategies can delay this process to some extent, they still cannot overcome the 450°C temperature limit, and the addition of large amounts of precious elements significantly increases costs. Therefore, to address the microstructural instability and performance degradation issues of existing Cu-containing precipitation-strengthened steels during high temperatures and long-term service, this invention provides a method for improving the microstructure and performance stability of copper-containing precipitation-strengthened steel using rare earth elements. This method utilizes rare earth elements such as Ce to regulate the structural stability of the Cu precipitate, thereby improving the long-term service performance of the steel. This invention is specifically implemented through the following techniques.

[0011] In a first aspect, the present invention provides a method for improving the microstructure and performance stability of copper precipitation-strengthened steel using rare earth elements. By introducing stabilizing elements into the steel that can combine with vacancies to form stabilizing element-Vac complexes, the stabilizing element-Vac complexes exert a pinning effect on the Cu precipitates, thereby inhibiting the structural transformation and coarsening of the Cu precipitates.

[0012] In this invention, the contents of Cu and Ce are precisely controlled to ensure they are within a range conducive to the formation of an effective Ce-Vac complex. The formation mechanism of the Ce-Vac complex is as follows: Ce atoms have a large atomic radius and extremely low solid solubility in steel, making them readily combine with vacancies generated during hot working to form the Ce-Vac complex. This complex possesses high binding energy and thermodynamic stability, remaining stable during subsequent heat treatment. The 9R-Cu phase stabilization mechanism utilizes the combination of Ce atoms with vacancies (Vac) generated during hot working to form the Ce-Vac complex. Through pinning and anchoring effects, the vacancies are fixed, causing the diffusion barrier of Cu atoms to jump from 0.585 eV to 1.498 eV, inhibiting Cu from completing long-range diffusion and Ostwald ripening processes via vacancies. Therefore, the method provided by this invention effectively regulates the transformation and coarsening process of the 9R-Cu precipitate phase towards the FCC structure.

[0013] Furthermore, the Cu precipitates include various structures such as B2, BCC, 9R, 3R, and FCC. The pinning effect can inhibit the transformation of the 9R-Cu precipitate into the FCC structure and increase the proportion of the 9R-Cu phase in the precipitates.

[0014] Furthermore, the 9R-Cu phase accounts for no less than 50% of the precipitated phase.

[0015] Furthermore, the stabilizing element-Vac complex is distributed around the Cu precipitate phase.

[0016] Furthermore, by mass percentage, the content of the stabilizing element in the copper precipitation-strengthened steel is 0.005-0.20%.

[0017] Furthermore, the content of the stabilizing element is 0.01-0.02%.

[0018] Furthermore, the stabilizing element is Ce.

[0019] In a second aspect, the present invention also provides a copper precipitation-strengthened steel with stable structure and properties, wherein the copper precipitation-strengthened steel comprises 0.8-1.2% Cu and 0.005-0.20% stabilizing elements by mass percentage.

[0020] Furthermore, the copper precipitation-strengthened steel contains 0.95% Cu and 0.01-0.02% stabilizing elements.

[0021] Furthermore, by mass percentage, the elements of the copper precipitation-strengthened steel also include: C 0.03-0.25%, Mn 0.5-2.0%, Si 0.1-0.8%, Ni 0.3-0.5%, Cr 0.3-0.5%, Nb 0.01-0.02%, P≤0.020%, S≤0.010%, with the balance being Fe and unavoidable impurities.

[0022] Furthermore, the elements in the copper precipitation-strengthened steel also include: C 0.085%, Mn 0.92%, Si 0.3%, Ni 0.49%, Cr 0.48%, Nb 0.01-0.03%, P≤0.020%, S≤0.010%, with the balance being Fe and unavoidable impurities.

[0023] A third aspect of the present invention provides a method for preparing the above-mentioned copper precipitation-strengthened steel, comprising the following steps:

[0024] The billet of copper precipitation-strengthened steel is hot-rolled and controlled-cooled, then coiled or air-cooled to room temperature;

[0025] The steel billet undergoes aging and stabilization treatment.

[0026] Furthermore, the cumulative deformation amount of the heat deformation treatment is ≥50%, preferably ≥70%, to promote the combination of stabilizing elements and vacancies to form a stabilizing element-Vac complex.

[0027] Optionally, the billet of copper precipitation-strengthened steel is heated to 1100-1200°C, preferably to 1120-1180°C, before hot rolling.

[0028] Optionally, the hot rolling process has an initial rolling temperature of 1050-1150℃, preferably 1080-1120℃, and a final rolling temperature of 850-950℃, preferably 880-920℃.

[0029] Optionally, the cooling method is to cool to 500-600℃ at a cooling rate of 5-15℃ / s.

[0030] Furthermore, the aging treatment method involves holding the temperature at 425-500℃ for 0.1-3 h, then air-cooling to room temperature to stabilize the 9R-Cu precipitate phase using the pinning effect of the stabilizing element-Vac complex.

[0031] Furthermore, the aging treatment method involves holding the temperature at 450-480℃ for 0.2-1 h.

[0032] Furthermore, the stabilization treatment method involves holding the temperature at 300-400℃ for 0.1-1 h to further enhance the pinning effect of the stabilizing element-Vac complex.

[0033] Furthermore, the stabilization treatment method is to keep the temperature at 360-380℃ for 0.2-0.5 h.

[0034] In a fourth aspect, the present invention also provides the application of the above-mentioned copper precipitation-strengthened steel for the manufacture of structural components for nuclear reactor pressure vessels, deep-earth energy storage equipment, antibacterial medical equipment, marine engineering equipment, or high-temperature power equipment.

[0035] Compared with the prior art, the advantages of the present invention are:

[0036] 1. Increase the proportion of 9R-Cu in the precipitate: Through the stabilizing effect of Ce-Vac complex, the proportion of 9R-Cu phase in the precipitate is increased from 32.6% to 58.5%.

[0037] 2. Significantly reduces the alloying cost of copper precipitation-strengthened steel: The Ce addition is only 0.01-0.10%, compared with the existing high alloying strategy of Ni addition of 1.0-30.0% and Mo addition of 1.0-5.0%, the raw material cost increases by no more than 5% compared with steel without any alloying elements, while the cost increase of existing high alloying schemes usually exceeds 30%.

[0038] 3. Improved welding process performance: The presence of Ce-Vac composite helps to inhibit the complete dissolution of Cu precipitates during welding, reduce strength loss in the molten zone and heat-affected zone, and promote the rapid re-precipitation of Cu precipitates after welding, thereby improving the recovery efficiency of joint performance.

[0039] 4. Expanded application temperature range: Enables Cu precipitation-strengthened steel to operate stably for extended periods in higher temperature environments such as nuclear reactor pressure vessels, high-temperature marine engineering equipment, and power equipment, with an expected service life extension of 1.5-3 times. Attached Figure Description

[0040] Figure 1 The images show the metallographic and scanning microstructures of copper precipitation-strengthened steels from Examples 1, 2, and Comparative Example 1. Figures (a) and (d) show the steel sample from Comparative Example 1 (containing no Ce), Figures (b) and (e) show the steel sample from Example 1 (Ce content 0.013%), and Figures (c) and (f) show the steel sample from Example 2 (Ce content 0.019%).

[0041] Figure 2Figure 1 shows the IPF (Integrated Precipitation Factor) diagrams of copper precipitation-strengthened steels from Examples 1, 2, and Comparative Example 1, along with the corresponding grain boundary fractions and average grain diameters. Specifically, Figure (a) shows the IPF diagram of the steel sample from Comparative Example 1 (Ce-free), Figure (b) shows the IPF diagram of the steel sample from Example 1 (Ce content 0.013%), Figure (c) shows the IPF diagram of the steel sample from Example 2 (Ce-free, 0.019%), and Figure (d) shows the corresponding grain boundary fractions and average grain diameters of the steel samples from Examples 1, 2, and Comparative Example 1.

[0042] Figure 3 The figures show the statistical distribution of precipitated phase size. In Figure (e), 0 Ce is observed; in Figure (f), 1.3 Ce is observed; and in Figure (g), 1.9 Ce is observed. Detailed Implementation

[0043] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] In some embodiments of the present invention, a method is provided to improve the microstructure and performance stability of copper precipitation-strengthened steel by using rare earth elements. By introducing stabilizing elements into the steel that can combine with vacancies to form stabilizing element-Vac complexes, the stabilizing element-Vac complexes pin the Cu precipitates, thereby inhibiting the structural transformation and coarsening of the Cu precipitates.

[0045] The pinning effect inhibits the transformation of the 9R-Cu precipitate into the FCC structure in the Cu precipitate, thereby increasing the proportion of the 9R-Cu phase in the precipitate. Preferably, in the final copper precipitation-strengthened steel, the proportion of the 9R-Cu phase in the precipitate is not less than 50%.

[0046] The content of stabilizing elements in copper precipitation-strengthened steel is 0.005-0.20% by mass, preferably 0.01-0.02%.

[0047] Furthermore, the stabilizing element is Ce.

[0048] In other embodiments of the present invention, the copper precipitation-strengthened steel provided contains, by mass percentage, 0.8-1.2% Cu and 0.005-0.20% stabilizing elements. Preferably, it contains 0.95% Cu and 0.01-0.02% stabilizing elements.

[0049] Optionally, by mass percentage, the elements of the copper precipitation-strengthened steel further include: C 0.03-0.25%, Mn 0.5-2.0%, Si 0.1-0.8%, Ni 0.3-0.5%, Cr 0.3-0.5%, Nb 0.01-0.03%, P≤0.020%, S≤0.010%, with the balance being Fe and unavoidable impurities.

[0050] Preferably, the elements of the copper precipitation-strengthened steel further include: C 0.085%, Mn 0.92%, Si 0.3%, Ni 0.49%, Cr 0.48%, Nb 0.01-0.02%, P≤0.020%, S≤0.010%, with the balance being Fe and unavoidable impurities.

[0051] In some embodiments of the present invention, the method for preparing copper precipitation-strengthened steel includes the following steps:

[0052] The billet of copper precipitation-strengthened steel is hot-rolled and controlled-cooled, then coiled or air-cooled to room temperature;

[0053] The steel billet undergoes aging and stabilization treatment.

[0054] In the above preparation method, the cumulative deformation amount of the heat deformation treatment is ≥50%, preferably ≥70%, to promote the combination of stabilizing elements and vacancies to form a stabilizing element-Vac complex.

[0055] In the above preparation method, the steel billet containing copper precipitation strengthening steel is heated to 1100-1200℃ before hot rolling, preferably to 1120-1180℃.

[0056] In the above preparation method, the hot rolling process has an initial rolling temperature of 1050-1150℃, preferably 1080-1120℃; and a final rolling temperature of 850-950℃, preferably 880-920℃.

[0057] In the above preparation method, the cooling method is to cool to 500-600℃ at a cooling rate of 5-15℃ / s.

[0058] In the above preparation method, the aging treatment can be performed by holding at 425-500℃ for 0.1-3 h and then air-cooling to room temperature. Preferably, the aging treatment is performed by holding at 450-480℃ for 0.2-1 h. Through aging treatment, the formation of the 9R-Cu precipitate can be promoted, and the Ce-Vac complex can be used to stabilize the precipitate structure.

[0059] In the above preparation method, the stabilization treatment can be selected as holding at 300-400℃ for 0.1-1 h. Preferably, the stabilization treatment is held at 360-380℃ for 0.2-0.5 h. Through stabilization treatment, the anchoring effect of Ce-Vac complex can be further enhanced, and the stability of 9R-Cu phase can be improved.

[0060] In the above preparation method, the steel billet can be heated to 1100-1200℃, preferably 1120-1180℃, before hot rolling.

[0061] In the above preparation method, the hot rolling process can be selected with an initial rolling temperature of 1050-1150℃, preferably 1080-1120℃; a final rolling temperature of 850-950℃, preferably 880-920℃; and a cumulative deformation of ≥50%, preferably ≥70%. The above hot rolling process can promote the formation of Ce-Vac composites.

[0062] In the above preparation method, the cooling method can be selected as follows: cooling to 500-600℃ at a cooling rate of 5-15 ℃ / s.

[0063] Example 1: Steel with 0.013% Ce added

[0064] The copper-containing precipitation-strengthened steel provided in this embodiment has the following elemental composition by mass percentage: C: 0.088%, Cu: 0.93%, Ce: 0.013%, Mn: 0.90%, Si: 0.29%, Ni: 0.52%, Cr: 0.50%, Nb: 0.017%, P≤0.020%, S≤0.010%, with the balance being Fe. The specific steps of its preparation method are as follows:

[0065] 1. Hot working process:

[0066] The billet is heated to 1100℃ for initial rolling and 900℃ for final rolling, with a cumulative deformation of 75%; then cooled to 550℃ at 10℃ / s.

[0067] 2. Heat treatment process

[0068] (1) Aging treatment: heat treatment at 450℃ for 1 h, followed by air cooling to room temperature;

[0069] (2) Stabilization treatment: heat treatment at 300℃ for 0.2 h, then air-cooled to room temperature.

[0070] Example 2: Steel with 0.019% Ce added

[0071] The copper precipitation-strengthened steel provided in this embodiment has the following elemental composition by mass percentage: C: 0.095%, Cu: 0.96%, Ce: 0.019%, Mn: 0.89%, Si: 0.31%, Ni: 0.41%, Cr: 0.55%, Nb: 0.021%, P≤0.020%, S≤0.010%, with the balance being Fe. The specific preparation method of the copper precipitation-strengthened steel is the same as in Example 1.

[0072] Comparative Example 1: Base steel without Ce addition

[0073] The copper precipitation-strengthened steel provided in this comparative example does not contain Ce. Its elements, by mass percentage, are: C: 0.09%, Cu: 0.99%, Mn: 0.90%, Si: 0.30%, Ni: 0.22%, Cr: 0.54%, Nb: 0.02%, P≤0.020%, S≤0.010%, with the balance being Fe. The specific preparation method for the copper precipitation-strengthened steel is the same as in Example 1.

[0074] Experimental Example: Microstructure Analysis of Copper Precipitation Strengthened Steels in Examples and Comparative Cases

[0075] Microstructures such as Figure 1 As shown, Figures (a) and (d) are steel samples of Comparative Example 1 (containing no Ce), referred to as "0Ce steel"; Figures (b) and (e) are steel samples of Example 1 (Ce content 0.013%), referred to as "1.3Ce steel"; Figures (c) and (f) are steel samples of Example 2 (Ce content 0.019%), referred to as "1.9Ce steel".

[0076] As the Ce content increases, the ferrite grains become more refined and their orientation more uniform, while the pearlite exhibits a regular distribution. This indicates that Ce plays a role in grain refinement in steel, improving the uniformity of the steel's microstructure. This is because the addition of Ce alters the phase transformation temperature. Grain refinement increases the number of grain boundaries, homogenizing the ferrite and pearlite matrix.

[0077] Figure 2 The IPF diagrams, corresponding grain boundary fractions, and average grain diameters of steels with different Ce contents are shown. It can be seen that 0Ce steel, which contains no Ce, generally exhibits large grain sizes and irregular shapes. This non-uniform grain structure may lead to steel failure. However, with the addition of Ce, the grain size becomes significantly finer, and the grains tend to become more homogeneous. Therefore, the refined and uniform microstructure of Ce-containing steel is beneficial to improving its mechanical properties and hydrogen resistance.

[0078] Statistical results are as follows Figure 2As shown in (d), the average grain diameters of 0Ce steel, 1.3Ce steel, and 1.9Ce steel are 5.11 μm, 3.41 μm, and 3.56 μm, respectively, with corresponding small-angle grain boundary ratios of 14.5%, 16.9%, and 15.5%. It is evident that the addition of Ce significantly reduces the grain size from 5.11 μm to 3.41 μm, and increases the small-angle grain boundary ratio from 14.5% to 16.9%.

[0079] Figure 3 This is a statistical chart showing the size and distribution of precipitated phases. From... Figure 3 As can be seen, the number of precipitates in 1.3Ce increases from 1.23 × 10⁻⁶ to that in the absence of Ce. 15 / m 2 Increased to 2.35 × 10 15 / m 2 .

[0080] The above detailed embodiments describe the implementation of the present invention; however, the present invention is not limited to the specific details described in the above embodiments. Within the scope of the claims and technical concept of the present invention, various simple modifications and changes can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A method for improving the microstructure and property stability of copper precipitation-strengthened steel using rare earth elements, characterized in that, By introducing stabilizing elements into steel that can combine with vacancies to form stabilizing element-Vac complexes, the stabilizing element-Vac complexes can pin Cu precipitates, thereby inhibiting the structural transformation and coarsening of Cu precipitates.

2. The method for improving the microstructure and property stability of copper-containing precipitation-strengthened steel using rare earth elements according to claim 1, characterized in that, The pinning effect inhibits the transformation of the 9R-Cu precipitate to the FCC structure in the Cu precipitate, thereby increasing the proportion of the 9R-Cu phase in the precipitate.

3. The method for improving the microstructure and property stability of copper-containing precipitation-strengthened steel using rare earth elements according to claim 2, characterized in that, The proportion of the 9R-Cu phase in the precipitated phase is not less than 50%.

4. The method for improving the microstructure and property stability of copper-containing precipitation-strengthened steel using rare earth elements according to claim 1, characterized in that, The stabilizing element-Vac complex is distributed around the Cu precipitate phase.

5. The method for improving the microstructure and property stability of copper precipitation-strengthened steel using rare earth elements according to claim 1, characterized in that, By mass percentage, the content of the stabilizing element in the copper precipitation-strengthened steel is 0.005-0.20%; Furthermore, the content of the stabilizing element is 0.01-0.02%.

6. The method for improving the microstructure and property stability of copper-containing precipitation-strengthened steel using rare earth elements according to claim 1, characterized in that, The stabilizing element is Ce.

7. A copper precipitation-strengthened steel with stable microstructure and properties, characterized in that, By mass percentage, the elements contained include Cu 0.8-1.2% and stabilizing elements 0.005-0.20%; Furthermore, the elements contained include 0.95% Cu and 0.01-0.02% stabilizing elements.

8. The copper precipitation-strengthened steel with stable microstructure and properties according to claim 7, characterized in that, By mass percentage, the elements contained also include: C 0.03-0.25%, Mn 0.5-2.0%, Si 0.1-0.8%, Ni 0.3-0.5%, Cr 0.3-0.5%, Nb 0.01-0.02%, P≤0.020%, S≤0.010%, with the balance being Fe and unavoidable impurities; Furthermore, the elements contained include: C 0.085%, Mn 0.92%, Si 0.3%, Ni 0.49%, Cr 0.48%, Nb 0.01-0.03%, P≤0.020%, S≤0.010%, with the balance being Fe and unavoidable impurities.

9. The method for preparing copper precipitation-strengthened steel with stable microstructure and properties as described in claim 7 or 8, characterized in that, Includes the following steps: The billet of copper precipitation-strengthened steel is hot-rolled and controlled-cooled, then coiled or air-cooled to room temperature; The steel billet undergoes aging and stabilization treatment.

10. The method for preparing copper precipitation-strengthened steel with stable microstructure and properties according to claim 9, characterized in that, The cumulative deformation amount of the heat deformation treatment is ≥50%, which promotes the combination of stabilizing elements and vacancies to form stabilizing element-Vac complexes; the aging treatment method is to hold at 425-500℃ for 0.1-3 h and air cool to room temperature, using the pinning effect of the stabilizing element-Vac complex to stabilize the 9R-Cu precipitate phase; the stabilization treatment method is to hold at 300-400℃ for 0.1-1 h, which further enhances the pinning effect of the stabilizing element-Vac complex; Furthermore, the aging treatment method is to keep the temperature at 450-480℃ for 0.2-1 h; the stabilization treatment method is to keep the temperature at 360-380℃ for 0.2-0.5 h.

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