High-strength maraging stainless steel adopting multi-stage aging process as well as preparation method and application of high-strength maraging stainless steel

Abstract

The invention discloses high-strength maraging stainless steel adopting a multi-stage aging process and a preparation method and application of the high-strength maraging stainless steel, and belongs to the field of maraging stainless steel. The high-strength maraging stainless steel comprises the following components in percentage by mass: 7.0%-10.0% of Ni, 12.0%-18.0% of Cr, 0.5%-2.5% of Al, 0.5%-2.5% of Ti, 0.5%-3% of Mo, 0.5%-2.5% of Cu, 0.5%-1.5% of Mn, 0.5%-1.5% of Si, less than or equal to 0.005% of C, less than or equal to 0.003% of P, less than or equal to 0.003% of S, less than or equal to 0.003% of O and the balance of Fe, and a precipitated phase is a composite structure of a Cu-rich phase, a NiAl phase and a Ni3Ti phase. The Cu-NiAl-Ni3Ti composite precipitated phase disclosed by the invention has remarkable advantages in the aspects of strengthening effect synergy, thermal stability improvement and structure optimization.

Description

Technical Field

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

[0002] As a high-strength stainless steel, maraging stainless steel has high strength and excellent corrosion resistance, making it an important material for many applications such as aerospace, nuclear industry, ships, military machinery, and chemical industry. Maraging stainless steel forms a supersaturated matrix microstructure during solution treatment and then undergoes aging treatment to produce precipitation. According to different steel grades, these precipitation strengthening phases include Cu-rich phases, NiAl phases, Ni3Ti phases, and carbides, etc. The improvement of the strength of maraging stainless steel brought about by a single strengthening phase gradually fails to meet people's requirements for high-performance stainless steel, so composite precipitation strengthening emerges as the times require. On the one hand, composite precipitation strengthening can further improve the precipitation strengthening level of maraging stainless steel. On the other hand, the preferential precipitation of Cu during the aging process can also serve as the nucleation sites for subsequent precipitation phases, further promoting the nucleation of precipitation phases.

[0003] The strengthening effect of the precipitated phase depends on the size, number density, and volume fraction of the precipitated phase. For the heat treatment process of single-temperature aging, on the one hand, the optimal precipitation temperatures of the precipitated phases in maraging stainless steel are different, and using single-temperature aging cannot exert the maximum strengthening effect of the precipitated phase. On the other hand, the precipitation rates of the precipitated phases are different. The precipitated phase with a faster nucleation rate first segregates from the matrix to form clusters. Subsequently, the remaining precipitated phases aggregate and segregate near the pre-precipitated phase to form a composite structure. Using single-temperature aging cannot effectively control the composite precipitation process, so it is difficult to achieve the maximum precipitation strengthening effect. Chinese Patent CN119736560A discloses a super-high-strength and high-toughness steel component and its preparation method. This patent uses the Ni3(Ti,Mo) phase precipitated during aging to strengthen the martensite matrix. However, this method uses arc additive manufacturing to prepare maraging stainless steel, and there are many defects in this process. Chinese Patent CN116065101A discloses a cobalt-free steel and its preparation method and application. This patent uses the NiAl phase precipitated during aging to strengthen the martensite matrix. However, a certain amount of carbon element is added to the steel composition of this patent, resulting in the formation of relatively coarse carbides during aging, which is not conducive to the improvement of precipitation strengthening. Chinese Patent CN118639126A discloses a nano-precipitation-strengthened weldable high-strength steel, marine steel plate and preparation method. This steel promotes the precipitation of Cu-rich + NiAl nano-composite phases by adding Cu, Ni, and Al. The nano-composite precipitated phases with a semi-coherent / non-coherent relationship between the matrix can improve the strength of the heat-affected zone through the precipitation strengthening effect. However, the contents of Ti and Ni in the steel of this patent are relatively low, which limits the precipitation strengthening effect. Chinese Patent CN114150232A discloses a super-high-strength maraging steel with composite strengthening of coherent and non-coherent nano-phases and its manufacturing method. This super-high-strength maraging steel uses the martensite matrix and the coherent NiAl nano-phase, coherent Cu-rich nano-phase, and non-coherent Ni3Ti nano-phase dispersed in the martensite matrix to complete the preparation of the super-high-strength maraging steel through composite precipitation, wherein at least one of the coherent NiAl nano-phase and the coherent Cu-rich nano-phase is compounded with the non-coherent Ni3Ti nano-phase. However, the holding time during the aging process of this patent is relatively long. On the one hand, it is easy to form brittle Mo-rich clusters, leading to brittle fracture of the steel. On the other hand, a long holding time will cause coarsening of the precipitated phase, weakening the precipitation strengthening effect. Using single-temperature aging cannot achieve the best precipitation strengthening effect and mechanical properties. Summary of the Invention

[0004] Aiming at the problem that the single-temperature aging heat treatment method of existing high-strength maraging stainless steel cannot fully exert the strengthening effect of the precipitated phase, resulting in insufficient mechanical properties, the purpose of the present invention is to provide a high-strength maraging stainless steel with a multi-stage aging process, and in combination with the nucleation and growth characteristics of different precipitated phases during the aging treatment, a preparation method of a high-strength maraging stainless steel with a multi-stage aging heat treatment process is proposed. By regulating the behavior of nano-scale precipitate phases at different aging stages and controlling the size of the precipitate phases on the premise of maintaining the number density of the precipitate phases, a maraging stainless steel with excellent properties can be obtained.

[0005] The purpose of the present invention is achieved through the following technical solutions: The present invention provides a high-strength maraging stainless steel with a multi-stage aging process, which includes the following components 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 precipitated phase of the high-strength maraging stainless steel with the multi-stage aging process is a composite structure of Cu-rich phase, NiAl and Ni3Ti phases, and the synergistic strengthening realizes the improvement of the strength of the maraging stainless steel.

[0006] Further, the tensile strength of the high-strength maraging stainless steel with the multi-stage aging process is 1932 MPa - 2301 MPa, the yield strength is 1755 MPa - 2156 MPa, the hardness is 556 HV - 633 HV. When the tensile strength is in the range of 2051 MPa - 2301 MPa, the total elongation is 3.1% - 10.2%, the equivalent radius of the composite precipitate phase 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 in the range of 1932 MPa - 2051 MPa, the total elongation is 10.2% - 11.7%, the equivalent radius of the composite precipitate phase is 3.6 nm - 4.4 nm, and the number density is 1.0×10 24 m -3 -1.1×10 24 m -3 .

[0007] The present invention provides a preparation method of a high-strength maraging stainless steel with a multi-stage aging process, which includes the following steps: (1)Smelt by vacuum melting and vacuum degassing treatment according to the proportion of each component, and pour to obtain an ingot after meeting the requirements of the designed composition; (2)Conduct homogenization and hot rolling treatment on the ingot to obtain a steel plate; (3)Conduct solution treatment on the steel plate; (4)Conduct cold rolling treatment after solution treatment; (5)Conduct multi-stage aging treatment after cold rolling. The aging temperature is subjected to three-stage aging treatment in sequence from low to high to obtain a high-strength maraging stainless steel with a multi-stage aging process.

[0008] Further, in step (2), the ingot is heated in the furnace in a vacuum, inert protective atmosphere or air, taken out of the furnace for hot rolling after holding at 1000°C - 1200°C for 2h - 6h, the initial rolling temperature is 950°C - 1050°C, the final rolling temperature ≥ 900°C, the total reduction is 30% - 75%, and it is cooled to room temperature after hot rolling.

[0009] Further, in step (3), the steel plate is heated in the furnace in a vacuum, inert protective atmosphere or air, the solution treatment temperature is 850°C - 950°C, the holding time is 1h - 4h, and it is cooled to room temperature after solution treatment.

[0010] Further, in step (4), at room temperature, the steel plate after solution treatment is subjected to cold rolling deformation, and the total reduction is 30% - 70%.

[0011] Further, in step (5), the steel product in step (4) is heated in the furnace in a vacuum, inert protective atmosphere or air. 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 it is cooled to room temperature after multi-stage aging treatment;

[0012] When performing multi-stage aging treatment in step (5), control the primary aging temperature and holding time to promote the precipitation of Cu atoms and the formation of clusters, forming a Cu-rich precipitation phase. Since the primary aging temperature is relatively low, the annihilation rate of dislocations is slow, and the equilibrium volume fraction of the precipitation phase is high, which increases the nucleation driving force of the Cu precipitation phase, facilitating the massive precipitation of Cu atoms in the steel and the formation of clusters, while the nucleation number of NiAl or Ni3Ti is small; control the secondary aging temperature and holding time to promote the precipitation of the 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 precipitation phase also rapidly nucleates near dislocations. The secondary aging temperature (450°C - 550°C) is the optimal precipitation temperature for the NiAl phase, and a small amount of the Ni3Ti phase precipitates; control the tertiary aging temperature and holding time to promote the precipitation of the Ni3Ti phase. Ni and Ti atoms segregate near the Cu-rich phase and rapidly nucleate, forming small-sized Ni3Ti precipitation phases, while the NiAl precipitation phase continues to grow, ultimately forming a composite precipitation structure of Cu-NiAl-Ni3Ti. The tertiary aging temperature (500°C - 650°C) is the optimal precipitation temperature for Ni3Ti. Due to the consumption of Ni atoms in the steel by the NiAl precipitation phase during the secondary aging stage, even when held at a relatively high temperature, Ni3Ti can maintain a small size, and the previously precipitated NiAl precipitation phase can also grow moderately.

[0013] Furthermore, the cooling methods in step (2), step (3) and step (5) are air cooling or oil cooling.

[0014] The present invention provides an application of a high-strength maraging stainless steel with a multi-stage aging process, which is used for key structures such as ships, ocean engineering, aerospace engineering, etc.

[0015] Advantages and effects of the present invention: The preparation method of the high-strength maraging stainless steel with the multi-stage aging process of the present invention adopts a novel multi-stage aging heat treatment process. The preparation process is simple, the manufacturing cost is low, and it is easy to realize industrial production; The present invention can regulate the behavior of precipitation phases at different aging stages at the nanoscale, enabling the precipitates to maintain a small size while keeping a large number density. Compared with a single precipitate phase, the Cu-NiAl-Ni3Ti composite precipitate phase has significant advantages, mainly reflected in aspects such as synergistic strengthening effect, improved thermal stability, and microstructure optimization. The Cu phase itself is difficult to significantly improve the alloy strength, but when eutectoid with NiAl and Ni3Ti, it can serve as a nucleation core, promoting the fine and uniform precipitation of NiAl / Ni3Ti, significantly enhancing the precipitation density and dispersion, and achieving a stronger precipitation strengthening effect. In addition, the composite precipitation can also inhibit the coarsening of a single phase and delay the tissue aging, thereby improving the thermal stability and long-term service performance of maraging stainless steel. Therefore, the Cu-NiAl-Ni3Ti composite precipitation mechanism exhibits more excellent comprehensive mechanical properties and microstructural stability in maraging stainless steel. The high-strength maraging stainless steel with the multi-stage aging process of the present invention has excellent mechanical properties, with a tensile strength ≥ 1932 MPa, a yield strength ≥ 1755 MPa, a hardness ≥ 556 HV, a total elongation ≥ 3.1%, an equivalent radius of the composite precipitate phase ≤ 4.4 nm, and a number density ≥ 1.0×10 24 m -3 . BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is the heat treatment process route diagram of Example 1; Figure 2 is the engineering stress-strain curve of the high-strength maraging stainless steel with the multi-stage aging process of Example 1 and the high-strength maraging stainless steel of Comparative Example 1; Figure 3 is the transmission electron microscope (TEM) image of Example 3 after multi-stage aging treatment, where: (a) is the bright field image of the distribution of precipitate phases in the martensite matrix, and (b) is the corresponding selected area diffraction; Figure 4 is the precipitate phase size distribution diagram 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 OF THE INVENTION

[0017] The present invention will be described in detail below with reference to the embodiments.

[0018] Example 1 The present invention provides a high-strength maraging stainless steel with a multi-stage aging process. By mass percentage, it includes the following components: 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 inevitable impurities; the precipitation phase of this high-strength maraging stainless steel is a composite structure of Cu-rich phase, NiAl, and Ni3Ti phases; the yield strength is 2020 MPa, the tensile strength is 2253 MPa, the hardness is 620 HV, and the elongation is 3.8%; the equivalent radius of the composite precipitation phase is 1.9 ± 0.4 nm, and the number density is about 1.2×10 24 m -3 .

[0019] The present invention provides a preparation method of a high-strength maraging stainless steel with a multi-stage aging process. The heat treatment process route is as Figure 1 shown, and specifically includes the following steps: (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, select 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.% as raw materials, and conduct smelting through vacuum melting and vacuum degassing treatment. After meeting the requirements of the designed composition, pour to obtain an ingot; (2) Conduct homogenization and hot rolling treatment on the ingot. The ingot is heated in the furnace under an inert protective atmosphere. The homogenization treatment is carried out at 1200 °C for 2 h, and then taken out of the furnace for hot rolling. 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, and then air-cooled to room temperature; (3) Conduct solution treatment on the steel plate. The steel plate is heated in the furnace under an inert protective atmosphere. The solution treatment is carried out at 850 °C for 4 h, and then oil-cooled to room temperature; (4) Conduct cold rolling deformation on the solution-treated steel plate at room temperature, with a total reduction of 30%; (5) After cold rolling, conduct multi-stage aging treatment. The cold-rolled sheet is heated in the furnace in a vacuum. The first-stage aging temperature is 350 °C, the holding time is 0.5 h, the second-stage aging temperature is 500 °C, the holding time is 1 h, the third-stage aging temperature is 650 °C, the holding time is 0.5 h, and then oil-cooled to room temperature to obtain a high-strength maraging stainless steel with a multi-stage aging process.

[0020] As Figure 2 shown, the high-strength maraging stainless steel with a multi-stage aging process prepared in Example 1 was tested for mechanical properties. The yield strength was 2020 MPa, the tensile strength was 2253 MPa, and the elongation was 3.8%. The hardness was tested using an HVS-1000 SPTA type micro-Vickers hardness tester with a loading load of 500 g and a time of 15 s. After 10 tests, the average hardness was 620 HV. Compared with the high-strength maraging stainless steel under the traditional aging process in Comparative Example 1, the tensile strength increased by 22.38%, the yield strength increased by 18.75%, the elongation increased by 18.75%, and the hardness increased by 14.39%. This is because the multi-stage aging treatment process adopted in this example realizes the synergistic strengthening of three precipitation phases, namely Cu, NiAl, and Ni3Ti, in the maraging stainless steel through a "segmented control" mechanism that promotes nucleation at low temperature first and triggers the precipitation of new phases at medium and high temperatures. It not only effectively restricts the growth and coarsening of the precipitation phases during aging but also significantly improves the mechanical properties of the material through multi-scale and multi-mechanism composite strengthening, which is superior to the traditional isothermal aging method. The equivalent radius of the composite precipitation phase is 1.9 ± 0.4 nm, and the number density is about 1.2×10 24 m -3 .

[0021] Example 2 The present invention provides a high-strength maraging stainless steel with a multi-stage aging process, which includes the following components 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 inevitable impurities. The precipitation phase of this high-strength maraging stainless steel is a composite structure of a Cu-rich phase, NiAl, and Ni3Ti phases. The yield strength is 2156 MPa, the tensile strength is 2208 MPa, the hardness is 608 HV, and the elongation is 3.5%. The equivalent radius of the composite precipitation phase is 2.6 ± 0.3 nm, and the number density is about 2.1×10 24 m -3 .

[0022] The present invention provides a method for preparing a high-strength maraging stainless steel with a multi-stage aging process, which includes the following steps: (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%, with the balance being Fe, select metallic Fe, metallic Cr, metallic Ni, metallic Ti, metallic Mn, metallic Mo, metallic Cu, metallic Al, and silicon with a purity greater than 99.5 wt.% as raw materials, and conduct smelting through vacuum melting and vacuum degassing treatment. After meeting the requirements of the designed composition, pour to obtain an ingot; (2) Conduct homogenization and hot rolling treatment on the ingot. The ingot is heated in the furnace in vacuum. The homogenization treatment is carried out at 1010 °C for 6 h, then taken out of the furnace for hot rolling. The initial rolling temperature is 950 °C, the final rolling temperature ≥ 900 °C, and the total reduction is 50% to obtain a steel plate, and then it is cooled to room temperature by oil cooling; (3) Conduct solution treatment on the steel plate. The steel plate is heated in the furnace in vacuum. The solution treatment is carried out at 950 °C for 1 h, and then it is cooled to room temperature by oil cooling; (4) Conduct cold rolling deformation on the solution-treated steel plate at room temperature, with a total reduction of 70%; (5) After cold rolling, conduct multi-stage aging treatment. The cold-rolled sheet is heated in the furnace in vacuum. 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, the third-stage aging temperature is 550 °C, the holding time is 0.5 h, and then it is cooled to room temperature by air cooling to obtain a high-strength maraging stainless steel with a multi-stage aging process.

[0023] The high-strength maraging stainless steel with a multi-stage aging process prepared in this Example 2 is subjected to mechanical property tests. The yield strength is 2156 MPa, the tensile strength is 2208 MPa, and the elongation is 3.5%; the hardness is tested using an HVS-1000 SPTA type micro-Vickers hardness tester with a loading load of 500 g and a time of 15 s. After 10 tests, the average hardness is 608 HV; the equivalent radius of the composite precipitate phase is 2.6 ± 0.3 nm, and the number density is about 2.1×10 24 m -3 .

[0024] Example 3 The present invention provides a high-strength maraging stainless steel with a multi-stage aging process. By mass percentage, it includes the following components: 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 inevitable impurities; the precipitation phase of this high-strength maraging stainless steel is a composite structure of Cu-rich phase, NiAl, and Ni3Ti phases; the yield strength is 2088 MPa, the tensile strength is 2213 MPa, the hardness is 633 HV, and the elongation is 5.5%; the equivalent radius of the composite precipitation phase is 2.8 ± 0.2 nm, and the number density is about 3.5×10 24 m -3 。

[0025] The present invention provides a preparation method of a high-strength maraging stainless steel with a multi-stage aging process, including the following steps: (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, select metallic Fe, metallic Cr, metallic Ni, metallic Ti, metallic Mn, metallic Mo, metallic Cu, metallic Al, and silicon with a purity greater than 99.5 wt.% as raw materials, and conduct smelting through vacuum melting and vacuum degassing treatment. After meeting the requirements of the designed composition, pour to obtain an ingot; (2) Conduct homogenization and hot rolling treatment on the ingot. The ingot is heated in the furnace in air. The homogenization treatment is to hold at 1000 °C for 4 h, then take it out of the furnace for hot rolling. The initial rolling temperature is 980 °C, the final rolling temperature is ≥950 °C, and the total reduction is 30% to obtain a steel plate, and then air-cool it to room temperature; (3) Conduct solution treatment on the steel plate. The steel plate is heated in the furnace in air. The solution treatment is to hold at 900 °C for 2 h, and then air-cool it to room temperature; (4) Conduct cold rolling deformation on the solution-treated steel plate at room temperature, with a total reduction of 50%; (5) Conduct multi-stage aging treatment after cold rolling. The cold-rolled sheet is heated in the furnace in an inert protective atmosphere. 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, the third-stage aging temperature is 500 °C, the holding time is 4 h, and then air-cool it to room temperature to obtain a high-strength maraging stainless steel with a multi-stage aging process.

[0026] Such as Figure 3As shown, the high-strength maraging stainless steel with a multi-step aging process prepared in this example was observed by transmission electron microscopy. As Figure 3 shown in (a), it was found that fine and dispersed precipitation phases were distributed in the martensite matrix. Figure 3 (b) is Figure 3 the selected area diffraction pattern of (a). The superlattice diffraction spots prove that the precipitation phase is completely coherent with the martensite matrix. As Figure 4 shown is the precipitation phase size statistics of Example 3 and Comparative Example 1 in this example. From Figure 4 (a), it can be seen that the equivalent radius of the precipitation phase in Comparative Example 1 with traditional aging treatment is 3.3 ± 0.5 nm. From Figure 4 (b), it can be seen that after the multi-step aging treatment in this example, the equivalent radius of the precipitation phase is 2.8 ± 0.2 nm, indicating that the multi-step aging effectively restricts the growth and coarsening of the precipitation phase.

[0027] The high-strength maraging stainless steel with a multi-step aging process prepared in Example 3 was tested for mechanical properties. 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 type micro-Vickers hardness tester with a loading load of 500 g and a time of 15 s. After 10 tests, the average hardness was 633 HV. The equivalent radius of the composite precipitation phase was 2.8 ± 0.2 nm, and the number density was approximately 3.5×10 24 m -3 .

[0028] Example 4 The present invention provides a high-strength maraging stainless steel with a multi-step aging process, which includes the following components 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 inevitable impurities. The precipitation phase of this high-strength maraging stainless steel is a composite structure of Cu-rich phase, NiAl, and Ni3Ti phases. The yield strength is 2001 MPa, the tensile strength is 2301 MPa, the hardness is 601 HV, and the elongation is 3.1%. The equivalent radius of the composite precipitation phase is 2.5 ± 0.2 nm, and the number density is approximately 2.2×10 24 m -3 .

[0029] The present invention provides a preparation method for a high-strength maraging stainless steel with a multi-step aging process, which includes the following steps: (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%, with the balance being Fe, select metallic Fe, metallic Cr, metallic Ni, metallic Ti, metallic Mn, metallic Mo, metallic Cu, metallic Al, and silicon with a purity greater than 99.5 wt.% as raw materials, and conduct smelting through vacuum melting and vacuum degassing treatment. After meeting the requirements of the designed composition, pour to obtain an ingot; (2) Conduct homogenization and hot rolling treatment on the ingot. The ingot is heated in the furnace in air. The homogenization treatment is carried out at 1000 °C for 4 h, and then taken out of the furnace for hot rolling. The initial rolling temperature is 1000 °C, the final rolling temperature is ≥ 950 °C, and the total reduction is 30% to obtain a steel plate, and then air-cooled to room temperature; (3) Conduct solution treatment on the steel plate. The steel plate is heated in the furnace in air. The solution treatment is carried out at 900 °C for 2 h, and then air-cooled to room temperature; (4) Conduct cold rolling deformation on the solution-treated steel plate at room temperature, with a total reduction of 50%; (5) Conduct multi-stage aging treatment after cold rolling. The cold-rolled sheet is heated in the furnace in air. The first-stage aging temperature is 500 °C, the holding time is 2 h, the second-stage aging temperature is 550 °C, the holding time is 0.5 h, the third-stage aging temperature is 560 °C, the holding time is 2 h, and then air-cooled to room temperature to obtain a high-strength maraging stainless steel with a multi-stage aging process.

[0030] The high-strength maraging stainless steel with a multi-stage aging process prepared in Example 4 of the present invention was subjected to mechanical property tests. 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 type micro-Vickers hardness tester with a loading load of 500 g and a time of 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 。

[0031] Example 5 The present invention provides a high-strength maraging stainless steel with a multi-stage aging process. By mass percentage, it includes the following components: 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 inevitable impurities. The precipitation phase of this high-strength maraging stainless steel is a composite structure of Cu-rich phase, NiAl, and Ni3Ti phases. The yield strength is 1807 MPa, the tensile strength is 2051 MPa, the hardness is 588 HV, and the elongation is 10.2%. The equivalent radius of the composite precipitation phase is 4.0 ± 0.4 nm, and the number density is about 1.1×10 24 m -3 .

[0032] The present invention provides a preparation method for a high-strength maraging stainless steel with a multi-stage aging process, which specifically includes the following steps: (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, select 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.% as raw materials, and carry out smelting through vacuum melting and vacuum degassing treatment. After meeting the requirements of the designed composition, pour to obtain an ingot; (2) Carry out homogenization and hot rolling treatment on the ingot. The ingot is heated in a furnace under an inert protective atmosphere. The homogenization treatment is to hold at 1200 °C for 6 h, then take it out of the furnace for hot rolling. 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, and then air-cool it to room temperature; (3) Carry out solution treatment on the steel plate. The steel plate is heated in a furnace under an inert protective atmosphere. The solution treatment is to hold at 950 °C for 2 h, and then oil-cool it to room temperature; (4) Carry out cold rolling deformation on the solution-treated steel plate at room temperature with a total reduction of 30%; (5) After cold rolling, carry out multi-stage aging treatment. The cold-rolled sheet is heated in a furnace under vacuum. The first-stage aging temperature is 450 °C, the holding time is 0.5 h, the second-stage aging temperature is 500 °C, the holding time is 3 h, the third-stage aging temperature is 550 °C, the holding time is 2.5 h, and then oil-cool it to room temperature to obtain a high-strength maraging stainless steel with a multi-stage aging process.

[0033] The high-strength maraging stainless steel with a multi-stage aging process prepared in Example 5 was tested for mechanical properties. 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 type micro-Vickers hardness tester with a loading load of 500 g and a time of 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 .

[0034] Example 6 The present invention provides a high-strength maraging stainless steel with a multi-stage aging process. By mass percentage, it includes the following components: 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 inevitable impurities. The precipitate phase of this high-strength maraging stainless steel is a composite structure of Cu-rich phase, NiAl, and Ni3Ti phases. The yield strength is 1755 MPa, the tensile strength is 1932 MPa, the hardness is 556 HV, and the elongation is 11.7%. The equivalent radius of the composite precipitate phase is 3.9 ± 0.3 nm, and the number density is approximately 1.0×10 24 m -3 .

[0035] The present invention provides a preparation method for a high-strength maraging stainless steel with a multi-stage aging process, which specifically includes the following steps: (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, select 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.% as raw materials, and conduct smelting through vacuum melting and vacuum degassing treatment. After meeting the requirements of the designed composition, pour to obtain an ingot; (2) Conduct homogenization and hot rolling treatment on the ingot. The ingot is heated in a furnace under an inert protective atmosphere. The homogenization treatment is carried out at 1200 °C for 6 h, and then taken out of the furnace for hot rolling. 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, and then air-cooled to room temperature; (3) Solution treatment is carried out on the steel plate. The steel plate is heated in the furnace in an inert protective atmosphere. The solution treatment is carried out at 950 °C for 2 h, and then cooled to room temperature by oil quenching; (4) Cold rolling deformation is carried out on the solution-treated steel plate at room temperature, and the total reduction is 30%; (5) Multi-stage aging treatment is carried out after cold rolling. The cold-rolled plate is heated in the furnace in a vacuum. The first-stage aging temperature is 450 °C, the holding time is 1.5 h, the second-stage aging temperature is 500 °C, the holding time is 4 h, the third-stage aging temperature is 550 °C, the holding time is 2.5 h, and then cooled to room temperature by oil quenching to obtain high-strength maraging stainless steel with a multi-stage aging process.

[0036] The high-strength maraging stainless steel with a multi-stage aging process prepared in Example 6 of the present invention is tested for mechanical properties. The yield strength is 1755 MPa, the tensile strength is 1932 MPa, and the elongation is 11.7%; the hardness is tested by an HVS-1000 SPTA type micro-Vickers hardness tester with a loading load of 500 g and a time of 15 s. After 10 tests, the average hardness is 556 HV; the equivalent radius of the composite precipitate is 3.9 ± 0.3 nm, and the number density is about 1.0×10 24 m -3 。

[0037] In summary, the present invention combines a multi-stage aging process with different aging temperature-holding time, and utilizes the characteristics of different precipitation rates of precipitates to regulate the number density of nano-scale composite precipitates in the martensite matrix while controlling the size of the precipitates, and successfully prepares high-strength maraging stainless steel with excellent properties. The tensile strength is as high as 2156 MPa, which can be used in key structures such as ships, ocean engineering, and aerospace engineering.

[0038] Comparative Example 1 A preparation method of high-strength maraging stainless steel, which is different from Example 1 in that after cold rolling, multi-stage aging treatment is not adopted, but traditional aging treatment is carried out, including the following steps: (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. Select 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.% as raw materials, and carry out smelting through vacuum melting and vacuum degassing treatment. After meeting the design composition requirements, pour to obtain an ingot; (2) Homogenize and hot-roll the ingot. Heat the ingot in a furnace under an inert protective atmosphere. The homogenization treatment is carried out by holding at 1200 °C for 2 h, then taking it out of the furnace for hot rolling. 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, and then air-cool it to room temperature; (3) Solution-treat the steel plate. Heat the steel plate in a furnace under an inert protective atmosphere. The solution treatment is carried out by holding at 850 °C for 4 h, and then oil-cool it to room temperature; (4) Cold-roll and deform the solution-treated steel plate at room temperature with a total reduction of 30%; (5) Conduct traditional aging treatment after cold rolling. Heat the cold-rolled sheet in a vacuum furnace. The aging temperature is 500 °C, and the holding time is 4 h, and then oil-cool it to room temperature to obtain high-strength maraging stainless steel.

[0039] As Figure 2 shown, the mechanical properties of the high-strength maraging stainless steel prepared in this Comparative Example 1 were tested. 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 type micro-Vickers hardness tester with a loading load of 500 g and a time of 15 s. After 10 tests, the average hardness was 542 HV; As Figure 4 shown in (a), the equivalent radius of the composite precipitate phase is 3.3 ± 0.5 nm, and the number density is about 9.8×10 23 m -3 .

Claims

1. A high-strength maraging stainless steel with a multi-stage aging process, characterized in that, By mass percentage, it 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%, and the balance is Fe; the precipitation phase of the high-strength maraging stainless steel with the multi-stage aging process is a composite structure of Cu-rich phase, NiAl and Ni3Ti phases.

2. The high-strength maraging stainless steel with a multi-stage aging process according to claim 1, characterized in that, The tensile strength of the high-strength maraging stainless steel with the multi-stage aging process is 1932 MPa - 2301 MPa, the yield strength is 1755 MPa - 2156 MPa, and the hardness is 556 HV - 633 HV. When the tensile strength is in the range of 2051 MPa - 2301 MPa, the total elongation is 3.1% - 10.2%, the equivalent radius of the composite precipitation phase 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 in the range of 1932 MPa - 2051 MPa, the total elongation is 10.2% - 11.7%, the equivalent radius of the composite precipitation phase is 3.6 nm - 4.4 nm, and the number density is 1.0×10 24 m -3 -1.1×10 24 m -3 .

3. A method for preparing high-strength maraging stainless steel with a multi-stage aging process according to claim 1, characterized in that, It includes the following steps: (1) According to the proportion of each component, smelt through vacuum melting and vacuum degassing treatment, and pour to obtain an ingot after meeting the requirements of the designed composition. (2) Carry out homogenization and hot rolling treatment on the ingot to obtain a steel plate. (3) Carry out solution treatment on the steel plate. (4) Carry out cold rolling treatment after solution treatment. (5) Carry out multi-stage aging treatment after cold rolling. The aging temperature is subjected to three-stage aging treatment in sequence from low to high to obtain the high-strength maraging stainless steel with the multi-stage aging process.

4. The preparation method of a high-strength maraging stainless steel with a multi-stage aging process according to claim 3, characterized in that, In step (2), the ingot is heated in the furnace in vacuum, inert protective atmosphere or air, taken out of the furnace for hot rolling after holding at 1000°C - 1200°C for 2h - 6h, the initial rolling temperature is 950°C - 1050°C, the final rolling temperature ≥ 900°C, the total reduction is 30% - 75%, and it is cooled to room temperature after hot rolling.

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

6. The preparation method of a high-strength maraging stainless steel with a multi-stage aging process according to claim 3, characterized in that, In step (4), at room temperature, the steel plate after solution treatment is subjected to cold rolling deformation, and the total reduction is 30% - 70%.

7. The preparation method of a high-strength maraging stainless steel with a multi-stage aging process according to claim 3, characterized in that, In step (5), the steel product in step (4) is heated in the furnace in vacuum, inert protective atmosphere or air. 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 it is cooled to room temperature after multi-stage aging treatment.

8. The preparation method of a high-strength maraging stainless steel with a multi-stage aging process as described in claim 3, characterized in that, The cooling methods in steps (2), (3) and (5) are air cooling or oil cooling.

9. Application of a high-strength maraging stainless steel with a multi-stage aging process as described in claim 1, characterized in that, It is used for key structures in ships, ocean engineering, and aerospace engineering.

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