A high-strength maraging stainless steel with a multi-stage aging process and its preparation method and application

Abstract

The present invention discloses a high-strength martensitic aging stainless steel using a multi-stage aging process, a preparation method thereof, and an application thereof, belonging to the field of martensitic stainless steel. The high-strength martensitic aging stainless steel using a multi-stage aging process comprises the following components, calculated by mass percentage: Ni: 7.0%-10.0%, Cr: 12.0%-18.0%, Al: 0.5%-2.5%, Ti: 0.5%-2.5%, Mo: 0.5%-3%, Cu: 0.5%-2.5%, Mn: 0.5%-1.5%, Si: 0.5%-1.5%, C≤0.005%, P≤0.003%, S≤0.003%, O≤0.003%, and the balance being Fe. The precipitated phase is a composite structure of a Cu-rich phase, NiAl, and Ni3Ti phases. The Cu-NiAl-Ni3Ti composite precipitate of the present invention has significant advantages in synergistic strengthening effects, improved thermal stability, and optimized structure.

Description

Technical Field

[0001] The present invention belongs to the field of martensitic stainless steel, and in particular relates to a high-strength martensitic aging stainless steel with a multi-stage aging process, a preparation method thereof, and an application thereof. Background Art

[0002] Maraging stainless steel, a high-strength stainless steel, possesses both high strength and excellent corrosion resistance, making it an important material for numerous applications, including aerospace, nuclear industry, shipbuilding, military machinery, and the chemical industry. Maraging stainless steel forms a supersaturated matrix microstructure during solution treatment, followed by aging to produce precipitation. Depending on the steel grade, these precipitation-strengthening phases include Cu-rich phases, NiAl phases, Ni3Ti phases, and carbides. The strength gains of maraging stainless steel provided by a single strengthening phase are increasingly unable to meet the demand for high-performance stainless steel, leading to the development of composite precipitation strengthening. Composite precipitation strengthening can further enhance the precipitation strengthening level of maraging stainless steel. Furthermore, the preferential precipitation of Cu during aging can serve as a nucleation site for subsequent precipitation phases, further promoting their formation.

[0003] The strengthening effect of precipitates depends on their size, number density, and volume fraction. For a single-temperature aging heat treatment, on the one hand, the optimal precipitation temperatures of each precipitate in maraging stainless steel vary, making a single-temperature aging process incapable of achieving the maximum strengthening effect of the precipitates. On the other hand, the precipitation rates of each precipitate vary, and the precipitate with the faster nucleation rate segregates from the matrix first to form clusters. Subsequently, the remaining precipitates aggregate and segregate near the earlier precipitates, forming a composite structure. Using a single-temperature aging process, it is impossible to effectively control the composite precipitation process, making it difficult to achieve maximum precipitation strengthening. Chinese patent CN119736560A discloses an ultra-high-strength and high-toughness steel component and a method for preparing the same. This patent utilizes the Ni3(Ti,Mo) phase precipitated during the aging process to strengthen the martensitic matrix. However, this method utilizes arc additive manufacturing to prepare martensitic aged stainless steel, and this process produces many defects. Chinese patent CN116065101A discloses a cobalt-free steel and a method for preparing and using the same. This patent utilizes the NiAl phase precipitated during the aging process to strengthen the martensitic matrix. However, a certain amount of carbon is added to the steel composition of this patent, resulting in the formation of relatively coarse carbides during the aging process, which is not conducive to the improvement of precipitation strengthening. Chinese patent CN118639126A discloses a nano-precipitation-strengthened weldable high-strength steel, a shipbuilding steel plate, and a preparation method. This steel promotes the precipitation of a Cu+NiAl-rich nanocomposite phase by adding Cu, Ni, and Al. The nanocomposite precipitates in a semi-coherent / incoherent matrix, enhancing the strength of the heat-affected zone through precipitation strengthening. However, the low Ti and Ni content in this patented steel limits the precipitation strengthening effect. Chinese patent CN114150232A discloses an ultra-high-strength maraging steel reinforced with coherent and incoherent nanophases and a preparation method. This ultra-high-strength maraging steel is prepared by composite precipitation of a martensitic matrix with coherent NiAl nanophases, coherent Cu-rich nanophases, and incoherent Ni3Ti nanophases dispersed within the martensitic matrix. At least one of the coherent NiAl nanophase and the coherent Cu-rich nanophase is compositely precipitated with the incoherent Ni3Ti nanophase. However, the patented method uses a long holding time during the aging process. This, on the one hand, easily forms brittle Mo-rich clusters, leading to brittle fracture of the steel. On the other hand, the long holding time causes the precipitate phase to coarsen, weakening the precipitation strengthening effect. Using a single temperature for aging cannot achieve the optimal precipitation strengthening effect and mechanical properties. Summary of the Invention

[0004] To address the problem that existing high-strength maraging stainless steels, characterized by single-temperature aging heat treatments, fail to fully utilize the strengthening effects of precipitates, resulting in insufficient mechanical properties, the present invention aims to provide a high-strength maraging stainless steel using a multi-stage aging process. By integrating the nucleation and growth characteristics of different precipitates during the aging process, a method for preparing high-strength maraging stainless steel using a multi-stage aging heat treatment process is proposed. By regulating the behavior of nanoscale precipitates at different aging stages, the size of the precipitates can be controlled while maintaining the number density of the precipitates, resulting in a maraging stainless steel with excellent performance.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] The present invention provides a high-strength maraging stainless steel subjected to a multi-stage aging process. The high-strength maraging stainless steel comprises the following components, calculated by mass percentage: Ni: 7.0%-10.0%, Cr: 12.0%-18.0%, Al: 0.5%-2.5%, Ti: 0.5%-2.5%, Mo: 0.5%-3%, Cu: 0.5%-2.5%, Mn: 0.5%-1.5%, Si: 0.5%-1.5%, C≤0.005%, P≤0.003%, S≤0.003%, O≤0.003%, and the balance is Fe. The high-strength maraging stainless steel subjected to the multi-stage aging process has a precipitated phase comprising a composite structure of a Cu-rich phase, NiAl, and Ni3Ti phases, and synergistic strengthening is employed to improve the strength of the maraging stainless steel.

[0007] Furthermore, the tensile strength of the high-strength martensitic aging stainless steel obtained by the multi-stage aging process is 1932MPa-2301MPa, the yield strength is 1755MPa-2156MPa, and the hardness is 556HV-633HV. When the tensile strength is 2051MPa-2301MPa, the total elongation is 3.1%-10.2%, the equivalent radius of the composite precipitate phase is 2.3nm-4.4nm, and the number density is 1.1×10 24 m -3 -3.5×10 24 m -3 When the tensile strength is between 1932MPa and 2051MPa, the total elongation is 10.2% to 11.7%, the equivalent radius of the composite precipitate is 3.6nm to 4.4nm, and the number density is 1.0×10 24 m -3 -1.1×10 24 m -3 .

[0008] The present invention provides a method for preparing high-strength maraging stainless steel using a multi-stage aging process, comprising the following steps:

[0009] (1) According to the proportion of each component, smelting is carried out through vacuum melting and vacuum degassing treatment, and after meeting the design composition requirements, steel ingots are cast;

[0010] (2) homogenizing and hot rolling the steel ingot to obtain steel plates;

[0011] (3) Solution treatment of the steel plate;

[0012] (4) Cold rolling after solution treatment;

[0013] (5) After cold rolling, multi-stage aging treatment is performed, and the aging temperature is sequentially increased to three levels to obtain high-strength martensitic aging stainless steel with multi-stage aging process.

[0014] Furthermore, in step (2), the steel ingot is heated in a vacuum, inert protective atmosphere or in air, kept at 1000°C-1200°C for 2h-6h, and then taken out of the furnace for hot rolling, with an initial rolling temperature of 950°C-1050°C, a final rolling temperature ≥900°C, a total reduction amount of 30%-75%, and cooled to room temperature after hot rolling.

[0015] Furthermore, in step (3), the steel plate is heated in a vacuum, inert protective atmosphere or air in a furnace, the solution treatment temperature is 850°C-950°C, the holding time is 1h-4h, and the steel plate is cooled to room temperature after the solution treatment.

[0016] Furthermore, in step (4), the solution treated steel plate is subjected to cold rolling deformation at room temperature, with a total reduction amount of 30%-70%.

[0017] Furthermore, in step (5), the steel product of step (4) is furnace-heated in a vacuum, inert protective atmosphere or air, with the first-stage aging temperature being 350°C-500°C and the holding time being 0.5h-6h, the second-stage aging temperature being 450°C-550°C and the holding time being 0.5h-4h, and the third-stage aging temperature being 500°C-650°C and the holding time being 0.5h-4h, and cooling to room temperature after the multi-stage aging treatment;

[0018] When the multi-stage aging treatment is carried out in step (5), the primary aging temperature and holding time are controlled to promote the precipitation of Cu atoms and the formation of clusters to form a Cu-rich precipitate phase. The primary aging temperature is low, the annihilation rate of dislocations is slow, and the equilibrium volume fraction of the precipitate phase is high, which increases the nucleation driving force of the Cu precipitate phase, and is conducive to the precipitation of a large number of Cu atoms in the steel and the formation of clusters, while the number of NiAl or Ni3Ti nuclei is small; the secondary aging temperature and holding time are controlled to promote the precipitation of NiAl phase. Ni and Al atoms segregate at the interface between the Cu-rich phase and the matrix and then rapidly nucleate and grow. The NiAl precipitate phase also rapidly nucleates near the dislocation. The secondary aging temperature (450℃-550℃) is The optimal precipitation temperature of the NiAl phase causes a small amount of Ni3Ti phase to precipitate. The three-stage aging temperature and holding time are controlled to promote the precipitation of the Ni3Ti phase. Ni and Ti atoms segregate near the Cu-rich phase and rapidly nucleate to form a small-sized Ni3Ti precipitate phase. The NiAl precipitate phase continues to grow, eventually forming a Cu-NiAl-Ni3Ti composite precipitation structure. The three-stage aging temperature (500℃-650℃) is the optimal precipitation temperature for Ni3Ti. Due to the consumption of Ni atoms in the steel by the NiAl precipitate phase in the secondary aging stage, the Ni3Ti can maintain a small size even when holding at a higher temperature, and the NiAl precipitate phase that precipitated first can also grow moderately.

[0019] Furthermore, the cooling method of step (2), step (3) and step (5) is air cooling or oil cooling.

[0020] The present invention provides an application of high-strength martensitic aged stainless steel with a multi-stage aging process, which is used in key structures such as ships, marine engineering, and aerospace engineering.

[0021] Advantages and effects of the present invention:

[0022] The method for preparing high-strength martensitic aging stainless steel by the multi-stage aging process of the present invention adopts a novel multi-stage aging heat treatment process, which has a simple preparation process, low production cost, and is easy to realize industrial production;

[0023] The present invention can regulate the behavior of the precipitated phase at different aging stages from the nanoscale, so that the precipitated phase maintains a smaller size while maintaining a larger number density. Compared with a single precipitated phase, the Cu-NiAl-Ni3Ti composite precipitated phase has significant advantages, which are mainly reflected in the synergistic strengthening effect, improved thermal stability and organizational optimization. The Cu phase itself is difficult to significantly improve the alloy strength, but when it is eutectic with NiAl and Ni3Ti, it can serve as a nucleation core to promote the fine and uniform precipitation of NiAl / Ni3Ti, significantly improve the precipitation density and dispersibility, and achieve a stronger precipitation strengthening effect. In addition, Composite precipitation can also inhibit the coarsening of a single phase and delay microstructure aging, thereby improving the thermal stability and long-term service performance of maraging stainless steel. Therefore, the Cu-NiAl-Ni3Ti composite precipitation mechanism exhibits better comprehensive mechanical properties and microstructure stability in maraging stainless steel. The high-strength maraging stainless steel produced by the multi-stage aging process of the present invention has excellent mechanical properties, with a tensile strength of ≥1932 MPa, a yield strength of ≥1755 MPa, a hardness of ≥556 HV, a total elongation of ≥3.1%, an equivalent radius of the composite precipitate phase of ≤4.4 nm, and a number density of ≥1.0×10 24 m -3 . BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the heat treatment process roadmap of Example 1;

[0025] Figure 2 The engineering stress-strain curves of the high-strength martensitic stainless steel subjected to the multi-stage aging process in Example 1 and the high-strength martensitic stainless steel in Comparative Example 1;

[0026] Figure 3 Transmission electron microscopy (TEM) images of Example 3 after multi-stage aging treatment, where: (a) is a bright field image of the distribution of the precipitate phase in the martensite matrix, and (b) is the corresponding selected area diffraction;

[0027] Figure 4 The precipitate size distribution diagrams of the multi-stage aging treatment of Example 3 and the traditional aging treatment of Comparative Example 1, where: (a) is the traditional aging treatment, and (b) is the multi-stage aging treatment. DETAILED DESCRIPTION

[0028] The present invention is described in detail below with reference to the embodiments.

[0029] Example 1

[0030] The present invention provides a high-strength maraging stainless steel subjected to a multi-stage aging process. The high-strength maraging stainless steel comprises the following components, calculated by mass percentage: Ni: 10.0%, Cr: 18.0%, Al: 2.5%, Ti: 0.5%, Mo: 3.0%, Cu: 0.5%, Mn: 1.0%, Si: 1.0%, C≤0.005%, P≤0.003%, S≤0.003%, O≤0.003%, and the balance is Fe. C, P, and S are unavoidable impurities. The high-strength maraging stainless steel has a precipitated phase comprising a Cu-rich phase, NiAl, and Ni3Ti phases. The high-strength maraging stainless steel has a yield strength of 2020 MPa, a tensile strength of 2253 MPa, a hardness of 620 HV, and an elongation of 3.8%. The equivalent radius of the composite precipitated phase is 1.9±0.4 nm, and the number density is approximately 1.2×10 24 m -3 .

[0031] The present invention provides a method for preparing high-strength maraging stainless steel by multi-stage aging process. The heat treatment process route is as follows: Figure 1 As shown, the specific steps include:

[0032] (1) According to the following mass percentages: Ni: 10.0%, Cr: 18.0%, Al: 2.5%, Ti: 0.5%, Mo: 3.0%, Cu: 0.5%, Mn: 1.0%, Si: 1.0%, C≤0.005%, P≤0.003%, S≤0.003%, O≤0.003%, and the balance is Fe, metal Fe, metal Cr, metal Ni, metal Ti, metal Mn, metal Mo, metal Cu, metal Al and silicon with a purity greater than 99.5 wt.% are selected as raw materials, and smelted through vacuum melting and vacuum degassing treatment. After meeting the design composition requirements, steel ingots are cast;

[0033] (2) The steel ingot is homogenized and hot rolled. The steel ingot is heated in an inert protective atmosphere. The homogenization treatment is carried out at 1200 ° C for 2 hours. Then it is taken out of the furnace and hot rolled. The initial rolling temperature is 1050 ° C, the final rolling temperature is ≥ 950 ° C, and the total reduction is 75% to obtain a steel plate. Then it is cooled to room temperature by air cooling;

[0034] (3) The steel plate is subjected to solution treatment. The steel plate is heated in an inert protective atmosphere. The solution treatment is carried out at 850 ° C for 4 hours and then cooled to room temperature by oil cooling.

[0035] (4) The solution treated steel plate is cold rolled at room temperature with a total reduction of 30%;

[0036] (5) After cold rolling, multi-stage aging treatment is performed. The cold-rolled plate is heated in a vacuum furnace. The first-stage aging temperature is 350°C and the holding time is 0.5h. The second-stage aging temperature is 500°C and the holding time is 1h. The third-stage aging temperature is 650°C and the holding time is 0.5h. Then, it is cooled to room temperature by oil cooling to obtain high-strength martensitic aging stainless steel with multi-stage aging process.

[0037] like Figure 2 As shown, the high-strength maraging stainless steel prepared by the multi-stage aging process in Example 1 was tested for mechanical properties, and the yield strength was 2020 MPa, the tensile strength was 2253 MPa, and the elongation was 3.8%; The hardness was tested using an SPTA micro Vickers hardness tester with a load of 500 g for 15 seconds. After 10 tests, the average hardness was 620 HV. Compared with the high-strength maraging stainless steel treated with the conventional aging process in Comparative Example 1, the tensile strength, yield strength, elongation, and hardness were increased by 22.38%, 18.75%, and 14.39%, respectively. This is because the multi-stage aging treatment process adopted in this embodiment achieves synergistic strengthening of the three precipitates of Cu, NiAl, and Ni3Ti in the maraging stainless steel through a "segmented control" mechanism of first promoting nucleation at low temperature and then inducing precipitation of new phases at medium and high temperatures. This not only effectively limits the growth and coarsening of the precipitates during the aging process, but also significantly improves the mechanical properties of the material through multi-scale and multi-mechanism composite strengthening, which is superior to the conventional constant temperature aging method. The equivalent radius of the composite precipitate is 1.9±0.4 nm, and the number density is approximately 1.2×10 24 m -3 .

[0038] Example 2

[0039] The present invention provides a high-strength maraging stainless steel subjected to a multi-stage aging process. The stainless steel comprises the following components, calculated by mass percentage: Ni: 7.0%, Cr: 12.0%, Al: 2%, Ti: 2.5%, Mo: 2.0%, Cu: 1.2%, Mn: 0.5%, Si: 0.5%, C≤0.005%, P≤0.003%, S≤0.003%, O≤0.003%, and the balance is Fe. C, P, and S are unavoidable impurities. The precipitated phase of the high-strength maraging stainless steel is a composite structure of a Cu-rich phase, NiAl, and Ni3Ti phases. The stainless steel has a yield strength of 2156 MPa, a tensile strength of 2208 MPa, a hardness of 608 HV, and an elongation of 3.5%. The equivalent radius of the composite precipitated phase is 2.6±0.3 nm, and the number density is approximately 2.1×10 24 m -3 .

[0040] The present invention provides a method for preparing high-strength maraging stainless steel using a multi-stage aging process, comprising the following steps:

[0041] (1) According to the following mass percentages: Ni: 7.0%, Cr: 12.0%, Al: 2%, Ti: 2.5%, Mo: 2.0%, Cu: 1.2%, Mn: 0.5%, Si: 0.5%, C≤0.005%, P≤0.003%, S≤0.003%, O≤0.003%, and the balance is Fe, metal Fe, metal Cr, metal Ni, metal Ti, metal Mn, metal Mo, metal Cu, metal Al and silicon with a purity greater than 99.5wt.% are selected as raw materials, and smelted through vacuum melting and vacuum degassing treatment. After meeting the design composition requirements, steel ingots are cast;

[0042] (2) The steel ingot is homogenized and hot rolled. The steel ingot is heated in a vacuum furnace. The homogenization treatment is carried out by keeping the temperature at 1010℃ for 6 hours. Then the steel ingot is taken out of the furnace and hot rolled. The initial rolling temperature is 950℃, the final rolling temperature is ≥900℃, and the total reduction is 50%. The steel plate is obtained and then cooled to room temperature by oil cooling.

[0043] (3) The steel plate is subjected to solution treatment. The steel plate is heated in a vacuum furnace. The solution treatment is carried out at 950 ° C for 1 hour and then cooled to room temperature by oil cooling.

[0044] (4) The solution treated steel plate is cold rolled at room temperature with a total reduction of 70%;

[0045] (5) After cold rolling, multi-stage aging treatment is performed. The cold-rolled plate is heated in a vacuum furnace. The first-stage aging temperature is 400 ° C, the holding time is 3 h, the second-stage aging temperature is 500 ° C, the holding time is 1 h, and the third-stage aging temperature is 550 ° C, the holding time is 0.5 h. Then, it is cooled to room temperature by air cooling to obtain high-strength martensitic aging stainless steel with a multi-stage aging process.

[0046] The high-strength martensitic aging stainless steel prepared by the multi-stage aging process in Example 2 was subjected to mechanical property tests, and the yield strength was 2156 MPa, the tensile strength was 2208 MPa, and the elongation was 3.5%. The hardness was tested using an HVS-1000 SPTA micro Vickers hardness tester with a load of 500 g for 15 s. After 10 tests, the average hardness was 608 HV. The equivalent radius of the composite precipitate phase was 2.6 ± 0.3 nm, and the number density was approximately 2.1 × 10 24 m -3 .

[0047] Example 3

[0048] The present invention provides a high-strength maraging stainless steel subjected to a multi-stage aging process. The stainless steel comprises the following components, calculated by mass percentage: Ni: 8.0%, Cr: 15.0%, Al: 0.5%, Ti: 2.5%, Mo: 0.5%, Cu: 2.5%, Mn: 1.5%, Si: 1.5%, C≤0.005%, P≤0.003%, S≤0.003%, O≤0.003%, and the balance is Fe. C, P, and S are unavoidable impurities. The precipitated phase of the high-strength maraging stainless steel is a composite structure of a Cu-rich phase, NiAl, and Ni3Ti phases. The stainless steel has a yield strength of 2088 MPa, a tensile strength of 2213 MPa, a hardness of 633 HV, and an elongation of 5.5%. The equivalent radius of the composite precipitated phase is 2.8±0.2 nm, and the number density is approximately 3.5×10 24 m -3 .

[0049] The present invention provides a method for preparing high-strength maraging stainless steel using a multi-stage aging process, comprising the following steps:

[0050] (1) According to the following mass percentages: Ni: 8.0%, Cr: 15.0%, Al: 0.5%, Ti: 2.5%, Mo: 0.5%, Cu: 2.5%, Mn: 1.5%, Si: 1.5%, C≤0.005%, P≤0.003%, S≤0.003%, O≤0.003%, and the balance is Fe, metal Fe, metal Cr, metal Ni, metal Ti, metal Mn, metal Mo, metal Cu, metal Al and silicon with a purity greater than 99.5wt.% are selected as raw materials, and smelted through vacuum melting and vacuum degassing treatment. After meeting the design composition requirements, steel ingots are cast;

[0051] (2) The steel ingot is homogenized and hot rolled. The steel ingot is heated in the air. The homogenization treatment is to keep the temperature at 1000℃ for 4 hours. Then it is taken out of the furnace and hot rolled. The initial rolling temperature is 980℃, the final rolling temperature is ≥950℃, and the total reduction is 30%. The steel plate is obtained and then cooled to room temperature by air cooling.

[0052] (3) The steel plate is subjected to solution treatment. The steel plate is heated in the air with the furnace. The solution treatment is carried out at 900 ° C for 2 hours and then cooled to room temperature by air cooling.

[0053] (4) The solution treated steel plate is cold rolled at room temperature with a total reduction of 50%;

[0054] (5) After cold rolling, multi-stage aging treatment is performed. The cold-rolled plate is heated in an inert protective atmosphere with a furnace. The first-stage aging temperature is 400 ° C, the holding time is 6 h, the second-stage aging temperature is 450 ° C, the holding time is 4 h, and the third-stage aging temperature is 500 ° C, the holding time is 4 h. Then, it is cooled to room temperature by air cooling to obtain a high-strength martensitic aging stainless steel with a multi-stage aging process.

[0055] like Figure 3 As shown, the high strength maraging stainless steel prepared by the multi-stage aging process in this embodiment was observed by transmission electron microscopy. Figure 3 As shown in (a), it is found that fine dispersed precipitates are distributed in the martensite matrix. Figure 3 (b) Yes Figure 3 (a) The selected area diffraction pattern shows that the superlattice diffraction spots prove that the precipitated phase is completely coherent with the martensite matrix. Figure 4 The precipitate size statistics of Example 3 and Comparative Example 1 are shown. Figure 4 (a) It can be seen that the equivalent radius of the precipitate phase in the conventional aging treatment of comparative example 1 is 3.3±0.5nm. Figure 4 (b) It can be seen that after the multi-stage aging treatment in this embodiment, the equivalent radius of the precipitate phase is 2.8±0.2nm, indicating that the multi-stage aging effectively limits the growth and coarsening of the precipitate phase.

[0056] The high-strength martensitic aging stainless steel prepared by the multi-stage aging process in Example 3 was subjected to mechanical property tests, and the yield strength was 2088 MPa, the tensile strength was 2213 MPa, and the elongation was 5.5%. The hardness was tested using an HVS-1000 SPTA micro Vickers hardness tester with a load of 500 g for 15 s. After 10 tests, the average hardness was 633 HV. The equivalent radius of the composite precipitate phase was 2.8 ± 0.2 nm, and the number density was approximately 3.5 × 10 24 m -3 .

[0057] Example 4

[0058] The present invention provides a high-strength maraging stainless steel subjected to a multi-stage aging process. The high-strength maraging stainless steel comprises the following components, calculated by mass percentage: Ni: 8.0%, Cr: 15.0%, Al: 2.0%, Ti: 2.0%, Mo: 3.0%, Cu: 2.5%, Mn: 1.5%, Si: 1.0%, C≤0.005%, P≤0.003%, S≤0.003%, O≤0.003%, and the balance is Fe. C, P, and S are unavoidable impurities. The precipitated phase of the high-strength maraging stainless steel is a composite structure of a Cu-rich phase, NiAl, and Ni3Ti phases. The high-strength maraging stainless steel has a yield strength of 2001 MPa, a tensile strength of 2301 MPa, a hardness of 601 HV, and an elongation of 3.1%. The equivalent radius of the composite precipitated phase is 2.5±0.2 nm, and the number density is approximately 2.2×10 24 m -3 .

[0059] The present invention provides a method for preparing high-strength maraging stainless steel using a multi-stage aging process, comprising the following steps:

[0060] (1) According to the following mass percentages: Ni: 8.0%, Cr: 15.0%, Al: 2.0%, Ti: 2.0%, Mo: 3.0%, Cu: 2.5%, Mn: 1.5%, Si: 1.0%, C≤0.005%, P≤0.003%, S≤0.003%, O≤0.003%, and the balance is Fe, metal Fe, metal Cr, metal Ni, metal Ti, metal Mn, metal Mo, metal Cu, metal Al and silicon with a purity greater than 99.5 wt.% are selected as raw materials, and smelted through vacuum melting and vacuum degassing treatment. After meeting the design composition requirements, steel ingots are cast;

[0061] (2) The steel ingot is homogenized and hot rolled. The steel ingot is heated in the air with the furnace. The homogenization treatment is to keep the temperature at 1000℃ for 4 hours, then the steel ingot is taken out of the furnace for hot rolling. The initial rolling temperature is 1000℃, the final rolling temperature is ≥950℃, and the total reduction is 30% to obtain the steel plate. The steel plate is then cooled to room temperature by air cooling.

[0062] (3) The steel plate is subjected to solution treatment. The steel plate is heated in the air with the furnace. The solution treatment is carried out at 900 ° C for 2 hours and then cooled to room temperature by air cooling.

[0063] (4) The solution treated steel plate is cold rolled at room temperature with a total reduction of 50%;

[0064] (5) After cold rolling, multi-stage aging treatment is performed. The cold-rolled plate is heated in the air with the furnace. The first-stage aging temperature is 500℃, the holding time is 2h, the second-stage aging temperature is 550℃, the holding time is 0.5h, and the third-stage aging temperature is 560℃, the holding time is 2h. Then, it is cooled to room temperature by air cooling to obtain high-strength martensitic aging stainless steel with multi-stage aging process.

[0065] The high-strength martensitic aging stainless steel prepared by the multi-stage aging process in Example 4 was subjected to mechanical property tests, and the yield strength was 2001 MPa, the tensile strength was 2301 MPa, and the elongation was 3.1%. The hardness was tested using an HVS-1000 SPTA micro Vickers hardness tester with a load of 500 g for 15 s. After 10 tests, the average hardness was 601 HV. The equivalent radius of the composite precipitate phase was 2.5 ± 0.2 nm, and the number density was approximately 2.2 × 10 24 m -3 .

[0066] Example 5

[0067] The present invention provides a high-strength maraging stainless steel subjected to a multi-stage aging process. The high-strength maraging stainless steel comprises the following components, calculated by mass percentage: Ni: 10.0%, Cr: 14.0%, Al: 1.5%, Ti: 1.5%, Mo: 0.5%, Cu: 2.5%, Mn: 1.0%, Si: 1.0%, C≤0.005%, P≤0.003%, S≤0.003%, O≤0.003%, and the balance is Fe. C, P, and S are unavoidable impurities. The precipitated phase of the high-strength maraging stainless steel is a composite structure of a Cu-rich phase, NiAl, and Ni3Ti phases. The high-strength maraging stainless steel has a yield strength of 1807 MPa, a tensile strength of 2051 MPa, a hardness of 588 HV, and an elongation of 10.2%. The equivalent radius of the composite precipitated phase is 4.0±0.4 nm, and the number density is approximately 1.1×10 24 m -3 .

[0068] The present invention provides a method for preparing high-strength maraging stainless steel using a multi-stage aging process, which specifically comprises the following steps:

[0069] (1) According to the following mass percentages: Ni: 10.0%, Cr: 14.0%, Al: 1.5%, Ti: 1.5%, Mo: 0.5%, Cu: 2.5%, Mn: 1.0%, Si: 1.0%, C≤0.005%, P≤0.003%, S≤0.003%, O≤0.003%, and the balance is Fe, metal Fe, metal Cr, metal Ni, metal Ti, metal Mn, metal Mo, metal Cu, metal Al and silicon with a purity greater than 99.5 wt.% are selected as raw materials, smelted through vacuum melting and vacuum degassing treatment, and cast to obtain steel ingots after meeting the design composition requirements;

[0070] (2) The steel ingot is homogenized and hot rolled. The steel ingot is heated in an inert protective atmosphere. The homogenization treatment is carried out at 1200 ° C for 6 hours. Then it is taken out of the furnace and hot rolled. The initial rolling temperature is 1050 ° C, the final rolling temperature is ≥ 950 ° C, and the total reduction is 35% to obtain a steel plate. Then it is cooled to room temperature by air cooling;

[0071] (3) The steel plate is subjected to solution treatment. The steel plate is heated in an inert protective atmosphere. The solution treatment is carried out at 950 ° C for 2 hours and then cooled to room temperature by oil cooling.

[0072] (4) The solution treated steel plate is cold rolled at room temperature with a total reduction of 30%;

[0073] (5) After cold rolling, multi-stage aging treatment is performed. The cold-rolled plate is heated in a vacuum furnace. The first-stage aging temperature is 450℃, the holding time is 0.5h, the second-stage aging temperature is 500℃, the holding time is 3h, and the third-stage aging temperature is 550℃, the holding time is 2.5h. Then, it is cooled to room temperature by oil cooling to obtain high-strength martensitic aging stainless steel with multi-stage aging process.

[0074] The high-strength martensitic aging stainless steel prepared by the multi-stage aging process in Example 5 was subjected to mechanical property tests, and the yield strength was 1807 MPa, the tensile strength was 2051 MPa, and the elongation was 10.2%. The hardness was tested using an HVS-1000 SPTA micro Vickers hardness tester with a load of 500 g for 15 s. After 10 tests, the average hardness was 588 HV. The equivalent radius of the composite precipitate phase was 4.0 ± 0.4 nm, and the number density was approximately 1.1 × 10 24 m -3 .

[0075] Example 6

[0076] The present invention provides a high-strength maraging stainless steel subjected to a multi-stage aging process. The stainless steel comprises the following components, calculated by mass percentage: Ni: 10.0%, Cr: 14.0%, Al: 2.5%, Ti: 2.5%, Mo: 0.5%, Cu: 2.5%, Mn: 1.0%, Si: 1.0%, C≤0.005%, P≤0.003%, S≤0.003%, O≤0.003%, and the balance is Fe. C, P, and S are unavoidable impurities. The precipitated phase of the high-strength maraging stainless steel is a composite structure of a Cu-rich phase, NiAl, and Ni3Ti phases. The stainless steel has a yield strength of 1755 MPa, a tensile strength of 1932 MPa, a hardness of 556 HV, and an elongation of 11.7%. The equivalent radius of the composite precipitated phase is 3.9±0.3 nm, and the number density is approximately 1.0×10 24 m -3 .

[0077] The present invention provides a method for preparing high-strength maraging stainless steel using a multi-stage aging process, which specifically comprises the following steps:

[0078] (1) According to the following mass percentages: Ni: 10.0%, Cr: 14.0%, Al: 2.5%, Ti: 2.5%, Mo: 0.5%, Cu: 2.5%, Mn: 1.0%, Si: 1.0%, C≤0.005%, P≤0.003%, S≤0.003%, O≤0.003%, and the balance is Fe, metal Fe, metal Cr, metal Ni, metal Ti, metal Mn, metal Mo, metal Cu, metal Al and silicon with a purity greater than 99.5 wt.% are selected as raw materials, and smelted through vacuum melting and vacuum degassing treatment. After meeting the design composition requirements, steel ingots are cast;

[0079] (2) The steel ingot is homogenized and hot rolled. The steel ingot is heated in an inert protective atmosphere. The homogenization treatment is carried out at 1200 ° C for 6 hours. Then it is taken out of the furnace and hot rolled. The initial rolling temperature is 1050 ° C, the final rolling temperature is ≥ 950 ° C, and the total reduction is 35% to obtain a steel plate. Then it is cooled to room temperature by air cooling;

[0080] (3) The steel plate is subjected to solution treatment. The steel plate is heated in an inert protective atmosphere. The solution treatment is carried out at 950 ° C for 2 hours and then cooled to room temperature by oil cooling.

[0081] (4) The solution treated steel plate is cold rolled at room temperature with a total reduction of 30%;

[0082] (5) After cold rolling, multi-stage aging treatment is performed. The cold-rolled plate is heated in a vacuum furnace. The first-stage aging temperature is 450℃, the holding time is 1.5h, the second-stage aging temperature is 500℃, the holding time is 4h, and the third-stage aging temperature is 550℃, the holding time is 2.5h. Then, it is cooled to room temperature by oil cooling to obtain high-strength martensitic aging stainless steel with multi-stage aging process.

[0083] The high-strength martensitic aging stainless steel prepared by the multi-stage aging process in Example 6 was subjected to mechanical property tests, and the yield strength was 1755 MPa, the tensile strength was 1932 MPa, and the elongation was 11.7%. The hardness was tested using an HVS-1000 SPTA micro Vickers hardness tester with a load of 500 g for 15 s. After 10 tests, the average hardness was 556 HV. The equivalent radius of the composite precipitate phase was 3.9 ± 0.3 nm, and the number density was approximately 1.0 × 10 24 m -3 .

[0084] In summary, the present invention successfully prepared high-strength martensitic aged stainless steel with excellent performance, a tensile strength of up to 2156 MPa, by combining a multi-stage aging process with different aging temperatures and holding times, utilizing the different precipitation rates of the precipitates, regulating the number density of the nanoscale composite precipitates in the martensitic matrix, and controlling the size of the precipitates. The stainless steel has been used for key structures such as ships, marine engineering, and aerospace engineering.

[0085] Comparative Example 1

[0086] A method for preparing high-strength maraging stainless steel, which differs from Example 1 in that a conventional aging treatment is performed instead of a multi-stage aging treatment after cold rolling, comprising the following steps:

[0087] (1) According to the following mass percentages: Ni: 10.0%, Cr: 18.0%, Al: 2.5%, Ti: 0.5%, Mo: 3.0%, Cu: 0.5%, Mn: 1.0%, Si: 1.0%, C≤0.005%, P≤0.003%, S≤0.003%, O≤0.003%, and the balance is Fe, metal Fe, metal Cr, metal Ni, metal Ti, metal Mn, metal Mo, metal Cu, metal Al and silicon with a purity greater than 99.5 wt.% are selected as raw materials, and smelted through vacuum melting and vacuum degassing treatment. After meeting the design composition requirements, steel ingots are cast;

[0088] (2) The steel ingot is homogenized and hot rolled. The steel ingot is heated in an inert protective atmosphere. The homogenization treatment is carried out at 1200 ° C for 2 hours. Then it is taken out of the furnace and hot rolled. The initial rolling temperature is 1050 ° C, the final rolling temperature is ≥ 950 ° C, and the total reduction is 75% to obtain a steel plate. Then it is cooled to room temperature by air cooling;

[0089] (3) The steel plate is subjected to solution treatment. The steel plate is heated in an inert protective atmosphere. The solution treatment is carried out at 850 ° C for 4 hours and then cooled to room temperature by oil cooling.

[0090] (4) The solution treated steel plate is cold rolled at room temperature with a total reduction of 30%;

[0091] (5) After cold rolling, the traditional aging treatment is carried out. The cold-rolled plate is heated in a vacuum furnace at an aging temperature of 500 °C for 4 h, and then cooled to room temperature by oil cooling to obtain high-strength maraging stainless steel.

[0092] like Figure 2 As shown, the high-strength maraging stainless steel prepared in this comparative example 1 was subjected to mechanical property tests, and the yield strength was 1701 MPa, the tensile strength was 1841 MPa, and the elongation was 3.2%; the hardness was tested using an HVS-1000 SPTA micro Vickers hardness tester with a load of 500 g for 15 seconds. After 10 tests, the average hardness was 542 HV. Figure 4 As shown in (a), the equivalent radius of the composite precipitate phase is 3.3±0.5nm, and the number density is about 9.8×10 23 m -3 .

Claims

1. A method for preparing high-strength maraging stainless steel using a multi-stage aging process, characterized in that: The following steps are involved: (1) According to the proportion of each component, the steel is smelted through vacuum melting and vacuum degassing treatment, and after the design composition requirements are met, the steel ingot is cast; the design composition is calculated in percentage by mass and includes the following components: Ni: 7.0%-10.0%, Cr: 12.0%-18.0%, Al: 0.5%-2.5%, Ti: 0.5%-2.5%, Mo: 0.5%-3%, Cu: 0.5%-2.5%, Mn: 0.5%-1.5%, Si: 0.5%-1.5%, C≤0.005%, P≤0.003%, S≤0.003%, O≤0.003%, balance is Fe; (2) homogenizing and hot rolling the steel ingot to obtain steel plates; (3) Solution treatment of the steel plate; (4) Cold rolling after solution treatment; (5) after cold rolling, a multi-stage aging treatment is performed, wherein the aging temperature is sequentially increased to three-stage aging treatments; the steel product of step (4) is furnace-heated in a vacuum, inert protective atmosphere or air, wherein the first-stage aging temperature is 350°C-500°C, the holding time is 0.5h-6h, the second-stage aging temperature is 450°C-550°C, the holding time is 0.5h-4h, the third-stage aging temperature is 500°C-650°C, the holding time is 0.5h-4h, and the multi-stage aging treatment is followed by cooling to room temperature to obtain a high-strength martensitic aging stainless steel of the multi-stage aging process; The precipitated phase of the high-strength maraging stainless steel in the multi-stage aging process is a composite structure of Cu-rich phase, NiAl and Ni3Ti phase; The high-strength martensitic aging stainless steel obtained by the multi-stage aging process has a tensile strength of 1932 MPa-2301 MPa, a yield strength of 1755 MPa-2156 MPa, and a hardness of 556 HV-633 HV. When the tensile strength is between 2051 MPa and 2301 MPa, the total elongation is 3.1%-10.2%, the equivalent radius of the composite precipitate is 2.3 nm-4.4 nm, and the number density is 1.1 × 10 24 m -3 -3.5×10 24 m -3 When the tensile strength is between 1932MPa and 2051MPa, the total elongation is 10.2% to 11.7%, the equivalent radius of the composite precipitate is 3.6nm to 4.4nm, and the number density is 1.0×10 24 m -3 -1.1×10 24 m -3 .

2. The method for preparing high-strength maraging stainless steel by a multi-stage aging process according to claim 1, characterized in that: In step (2), the steel ingot is heated in a vacuum, inert protective atmosphere or air, kept at 1000°C-1200°C for 2h-6h and then taken out of the furnace for hot rolling, the initial rolling temperature is 950°C-1050°C, the final rolling temperature is ≥900°C, the total reduction is 30%-75%, and the steel ingot is cooled to room temperature after hot rolling.

3. The method for preparing high-strength maraging stainless steel by a multi-stage aging process according to claim 1, characterized in that: In step (3), the steel plate is heated in a vacuum, inert protective atmosphere or air in a furnace, the solution treatment temperature is 850°C-950°C, the holding time is 1h-4h, and the steel plate is cooled to room temperature after the solution treatment.

4. The method for preparing high-strength maraging stainless steel by a multi-stage aging process according to claim 1, characterized in that: In step (4), the solution treated steel plate is subjected to cold rolling deformation at room temperature, with a total reduction amount of 30% to 70%.

5. The method for preparing high-strength maraging stainless steel by a multi-stage aging process according to claim 1, characterized in that: The cooling method of step (2), step (3) and step (5) is air cooling or oil cooling.

6. An application of the high-strength maraging stainless steel obtained by the method for preparing high-strength maraging stainless steel by multi-stage aging according to claim 1, characterized in that: Used for key structures of ships, marine engineering, and aerospace engineering.

Images