A dual peak heterogeneous structure maraging steel and a preparation method thereof

Abstract

The application belongs to the field of metal structural materials, and particularly relates to a bimodal heterogeneous structure maraging steel and a preparation method thereof. The alloy components of the bimodal heterogeneous structure maraging steel are as follows in percentage by weight: Ni: 18.0-21.0%, Mo: 2.5-3.5%, Ti: 1.0-1.8%, 0.01<=Y<=0.2, C<=0.01%, Si<=0.10%, Mn<=0.10%, S<=0.008%, P<=0.008%, and Fe balance. The preparation method has a process route of: atomization spraying-powdering, low-energy ball milling, packaging and air extraction, hot isostatic pressing solidification molding, forging and rolling, solid solution + aging heat treatment. Pure Y powder is added in the low-energy ball milling process, and by controlling the rotation speed and ball milling time, the powder particles form a bimodal grain size core-shell structure with fine crystals on the surface and coarse crystals in the center. The oxide formed by the Y element pins the grain boundary, and the stability of the grain boundary is ensured, so that the bimodal grain size structure characteristics can be guaranteed even after the later hot isostatic pressing solidification molding, heat treatment and heat treatment.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metallic structural materials, and particularly relates to a bimodal heterogeneous structure of a maraging steel and a preparation method thereof. BACKGROUND

[0002] At present, super high strength steel is widely used in aircraft landing gear, high-end bearing steel, precision gear, warship, rocket engine shell and other structural parts. Among them, the maraging steel is a kind of super high strength steel with carbon-free (or ultra-low carbon) iron-nickel martensite as the matrix, and intermetallic compound precipitation hardening is generated by aging. With the increasingly harsh service environment, higher requirements are put forward for the strength and plasticity of the material.

[0003] Grain refinement is an effective means to achieve high yield strength. However, due to the difficulty of opening the grain boundary rotation and creep at room temperature, with the decrease of grain size, the dislocation accommodation space will be compressed, and the dislocation nucleation will also be inhibited. Microstructure nanocrystallization is a new way to develop high strength / ultra high strength structural materials, and the yield strength is usually several times or even dozens of times higher than that of traditional coarse grain structure metal. However, the nanostructured metal material has almost no room temperature tensile plasticity, and the realization of bimodal distribution of grain size can effectively improve the strength and toughness of the material. The design idea of this bimodal grain structure is to use fine grains to ensure the high strength of the material, and to provide strain hardening capacity by using coarse grains, so that the plasticity of the material is improved without reducing the strength.

[0004] At present, the methods for preparing bimodal heterogeneous structure alloy mainly include large plastic deformation method and powder metallurgy method. Large plastic deformation mainly includes equal channel angular extrusion and high pressure torsion, wherein: equal channel angular extrusion is to obtain ultra-fine crystal nanocrystalline by equal channel angular extrusion, and then annealing treatment is carried out to produce microcrystalline and nanocrystalline bimodal heterogeneous structure, and the microcrystalline grains are embedded in the nanocrystalline matrix. High pressure torsion is also a large plastic deformation method, which is different from equal channel angular extrusion, and the sample is deformed under hydrostatic pressure to obtain bimodal heterogeneous structure. The powder metallurgy process is to mix, compact and sinter the microcrystalline and nanocrystalline powders to form a bimodal heterogeneous structure. However, the grain boundaries of these bimodal structures are not stable, and the structure will change under the influence of heat treatment process. SUMMARY

[0005] The purpose of the present application is to provide a bimodal heterogeneous structure of a maraging steel and a preparation method thereof, based on the characteristics of the bimodal grain size, the material has not only high strength, but also good plasticity.

[0006] The technical scheme of the present application is:

[0007] A bimodal heterogeneous structure maraging steel, the alloying components of which are as follows in percentage by weight: Ni: 18.0-21.0%, Mo: 2.5-3.5%, Ti: 1.0-1.8%, 0.01≤Y≤0.2, C≤0.01%, Si≤0.10%, Mn≤0.10%, S≤0.008%, P≤0.008%, Fe balance.

[0008] The preparation method of the bimodal heterogeneous structure maraging steel comprises the following steps:

[0009] (1) smelting of master alloy;

[0010] (2) gas atomization powder spraying;

[0011] (3) low-energy ball milling;

[0012] (4) encapsulation and air extraction;

[0013] (5) hot isostatic pressing solidification molding;

[0014] (6) forging and rolling;

[0015] (7) solid solution + aging heat treatment;

[0016] In the low-energy ball milling process, pure Y powder is added, and by controlling the rotation speed and ball milling time, the powder particles form a bimodal grain size core-shell structure with a fine crystal zone on the surface wrapping a coarse crystal zone in the center.

[0017] In the preparation method of the bimodal heterogeneous structure maraging steel, in steps (1) and (2), the components obtained by smelting of master alloy are as follows in percentage by weight: Ni: 18.0-21.0%, Mo: 2.5-3.5%, Ti: 1.0-1.8%, C≤0.01%, Si≤0.10%, Mn≤0.10%, S≤0.008%, P≤0.008%, Fe balance; the master alloy is subjected to gas atomization powder spraying, the powder particle size is <75 μm, the atomization gas pressure is ≥3.5 MPa, the superheat is ≥200 ℃, and the protective atmosphere is argon with a volume purity of ≥99.99%.

[0018] In the preparation method of the bimodal heterogeneous structure maraging steel, in step (3), 0.01≤Y≤0.2 is subjected to low-energy ball milling with the master alloy atomized powder in percentage by weight, the particle size of Y powder is <45 μm, and the process parameters of low-energy ball milling are controlled as follows: the ball milling atmosphere is argon with a volume purity of ≥99.99%, the ball-to-material mass ratio is (3-8):1, the ball milling time is 10-50 h, and the rotation speed is 40-180 r / min.

[0019] The preparation method of the bimodal heterogeneous structure maraging steel, in step (4), in order to remove the gas adsorbed on the surface of the powder particles and reduce the porosity, the powder loaded in the capsule is < 200 mu m in particle size; the capsule is pumped out under the following parameters: the vacuum air pressure is <= 10 -2 Pa, the temperature is 150-450 DEG C, and the time is 3-8 h.

[0020] The preparation method of the bimodal heterogeneous structure maraging steel, in step (5), the hot isostatic pressing solidification forming process of the capsule is as follows: the pressure is 100-180 MPa, the temperature is 1000-1200 DEG C, and the holding time is 3-8 h.

[0021] The preparation method of the bimodal heterogeneous structure maraging steel, in step (6), in order to further improve the density and mechanical properties of the maraging steel after solidification forming, first, the forging process is as follows: the open forging temperature is 1100-1200 DEG C, and the final forging temperature is 850-950 DEG C; then the hot rolling process of the forged blank is as follows: the open rolling temperature is 1100-1200 DEG C, the final rolling temperature is 900-950 DEG C, the rolling pass is 3-10 times, the deformation amount of each pass is 10-30 %, and the total deformation amount is 50-70 %.

[0022] The preparation method of the bimodal heterogeneous structure maraging steel, in step (7), the heat treatment process is as follows: the solid solution process parameters are 800-950 DEG C for 60-90 min, and then water cooling, and the aging process parameters are 450-550 DEG C for 3-6 h, and then air cooling.

[0023] The preparation method of the bimodal heterogeneous structure maraging steel, the microstructure of the maraging steel has a bimodal grain size, the center of the original particle is a coarse grain region, the average grain size of the coarse grain region is 2-10 mu m, and the edge of the original particle is a fine grain region, and the average grain size of the fine grain region is <= 250 nm; wherein, the volume fraction of the fine grain region is 30 %-90 %.

[0024] The preparation method of the bimodal heterogeneous structure maraging steel, the maraging steel has a room temperature yield strength >= 1850 MPa, a tensile strength >= 1900 MPa, and an elongation >= 10 %.

[0025] The design idea of the application is:

[0026] 1, the application adopts an ultra-high strength maraging steel as a base material, utilizes a low-energy ball milling process, controls the rotation speed and ball milling time, so that the powder particles form a bimodal grain size core-shell structure in which the surface fine grain region wraps the center coarse grain region.

[0027] 2、The application pins the grain boundary by adding pure Y powder in the ball milling process, using the oxide formed by Y element and O mixed in the preparation process to pin the grain boundary, and increases the stability of the grain boundary. Even after the heat isostatic pressing solidification forming, heat processing and heat treatment in the later stage, the structure characteristics of the bimodal grain size can be ensured.

[0028] 3、The bimodal heterogeneous structure martensite aging steel prepared by the application can precipitate a large number of short rod-shaped Ni3Ti precipitates with an average length of 2-5 nm after solid solution + aging heat treatment, and greatly improves the room temperature strength of the material.

[0029] 4、The bimodal heterogeneous structure martensite aging steel prepared by the application has a mixed distribution of high-strength, high-hardness ultra-fine grains and low-strength, low-hardness micron-sized grains. When plastic deformation is performed, the small grains with high hardness and the large grains with low hardness have different deformation degrees, thereby generating a plastic deformation strain gradient. A large number of geometrically necessary dislocations are gathered in the heterogeneous structure, so that the overall strength and plasticity of the material are improved.

[0030] The advantages and beneficial effects of the application are as follows:

[0031] 1、The process route of the preparation method of the martensite aging steel is: atomization powder spraying-low energy ball milling-sealing and air extraction-heat isostatic pressing solidification forming-forging and rolling-solid solution + aging heat treatment. The martensite aging steel with a bimodal heterogeneous structure is prepared by using a mechanical alloying method. The key is to add pure Y powder in the low-energy ball milling process. By controlling the rotation speed and ball milling time, the powder particles form a bimodal grain size core-shell structure with fine grains on the surface and coarse grains in the center. The oxide formed by the Y element pins the grain boundary and ensures the stability of the grain boundary.

[0032] 2、The bimodal heterogeneous structure martensite aging steel with mixed distribution of high-strength, high-hardness ultra-fine grains and low-strength, low-hardness micron-sized grains is realized by component and preparation process design and organization regulation, and the strength and plasticity of the material are improved, so that the performance indicators of the material are as follows: room temperature yield strength ≥1850MPa, tensile strength ≥1900MPa, elongation ≥10%. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The metallographic phase diagram of the bimodal heterogeneous structure martensite aging steel of Example 1 prepared by the application.

[0034] Figure 2 The EBSD diagram of the bimodal heterogeneous structure martensite aging steel of Example 1 prepared by the application.

[0035] Figure 3 The metallographic phase diagram of the bimodal heterogeneous structure martensite aging steel of Example 2 prepared by the application.

[0036] Figure 4 This is the metallographic phase diagram of Example 3 of the maraging steel with a bimodal heterogeneous structure prepared in the present invention.

[0037] Figure 5 This is a metallographic diagram of Example 4 of the maraging steel with a bimodal heterogeneous structure prepared in the present invention.

[0038] Figure 6 This is the metallographic phase diagram of the maraging steel prepared in Comparative Example 1.

[0039] Figure 7 This is the metallographic phase diagram of the maraging steel prepared in Comparative Example 2. DETAILED DESCRIPTION

[0040] The technical solution of the present invention is further described below in conjunction with specific implementation examples.

[0041] Example 1

[0042] In this embodiment, a method for preparing a maraging steel with a bimodal heterogeneous structure is as follows:

[0043] (1) Preparation of master alloy powder

[0044] A master alloy was prepared in a vacuum induction melting furnace. The master alloy's composition, by weight, was 18.3% Ni, 2.93% Mo, 1.72% Ti, 0.0078% C, 0.009% Si, 0.005% Mn, 0.0058% S, 0.006% P, and the balance was Fe. The master alloy powder was atomized and sprayed with the following requirements: a powder size of <75 μm, an atomizing pressure of 4.0 MPa, a superheat of 200°C, and a protective atmosphere of argon with a purity of at least 99.99% by volume.

[0045] (2) Low-energy ball milling

[0046] In order to disperse the nano-oxides in the material, high-energy ball milling is performed with 0.1% by weight of Y and master alloy atomized powder. The particle size of the Y powder is less than 45 μm. The process parameters of low-energy ball milling are controlled as follows: the ball milling atmosphere is argon with a volume purity of more than 99.99%, the ball-to-material mass ratio is 6:1, the ball milling time is 30 hours, and the rotation speed is 120 r / min.

[0047] (3) Powder filling and bag extraction

[0048] In order to remove the gas adsorbed on the surface of the powder particles and reduce the porosity, the particle size of the powder after ball milling is less than 200μm. The exhaust process of the package is as follows: the vacuum pressure is 10 -2 Pa, temperature is 400℃, time is 8h.

[0049] (4) Hot isostatic pressing

[0050] The canning hot isostatic pressing solidification forming process is as follows: the pressure is 170 MPa, the temperature is 1150℃, and the holding time is 4h.

[0051] (5) forging and hot rolling

[0052] In order to further improve the density and mechanical properties of the martensite-aging steel after solidification forming, the material is forged into a plate, and the forging process is controlled as follows: the open forging temperature is 1150℃, and the final forging temperature is 850℃. The forged plate is hot rolled, and the hot rolling process is controlled as follows: the open rolling temperature is 1150℃, the final rolling temperature is 900℃, the rolling pass is 4, and the deformation amount of each pass is 12%, 13%, 15% and 15% respectively, and the total deformation amount is 55%.

[0053] (6) The heat treatment process of the martensite-aging steel is as follows: the solid solution process parameters are 850℃ for 60min, and then water cooling to room temperature, and the aging process parameters are 480℃ for 5h, and then air cooling to room temperature.

[0054] Example 2

[0055] In this embodiment, a preparation method of a bimodal heterogeneous structure martensite-aging steel is as follows:

[0056] (1) Preparation of master alloy powder

[0057] The master alloy is prepared by a vacuum induction melting furnace, and the composition of the master alloy is as follows: Ni: 18.3%, Mo: 2.93%, Ti: 1.72%, C: 0.0078%, Si: 0.009%, Mn: 0.005%, S: 0.0058%, P: 0.006%, and Fe balance. The master alloy powder is subjected to gas atomization spraying, and the requirements are as follows: powder particle size <75μm, atomization gas pressure 4.0MPa, superheat 200℃, and protective atmosphere is argon with a volume purity of more than 99.99%.

[0058] (2) Low-energy ball milling

[0059] In order to disperse the nanometer oxides in the material, Y with a weight percentage of 0.1% is high-energy ball milled with the master alloy atomized powder, and the particle size of Y powder is <45μm. The process parameters of low-energy ball milling are controlled as follows: the ball milling atmosphere is argon with a volume purity of more than 99.99%, the ball-to-material mass ratio is 6:1, the ball milling time is 30h, and the rotation speed is 90r / min.

[0060] (3) Powder loading and canning vacuum pumping

[0061] In order to remove the gas adsorbed on the surface of the powder particles and reduce the porosity, the particle size of the ball milled powder loaded in the canning is <200μm. The vacuum pumping process of the canning is as follows: the vacuum pressure is 10-2 Pa, temperature is 400℃, time is 8h.

[0062] (4) Hot isostatic pressing

[0063] The hot isostatic pressing curing molding process of the package is as follows: pressure is 170MPa, temperature is 1150℃, and heat preservation and pressure holding time is 4h.

[0064] (5) Forging and hot rolling

[0065] To further improve the density and mechanical properties of the solidified maraging steel, the material was forged into plates using the following forging process: an initial forging temperature of 1150°C and a final forging temperature of 850°C. The forged plates were then hot-rolled using the following hot-rolling process: an initial rolling temperature of 1150°C and a final rolling temperature of 900°C. Four rolling passes were performed, with deformations of 12%, 13%, 15%, and 15% per pass, for a total deformation of 55%.

[0066] (6) The heat treatment process of the maraging steel is as follows: the solution process parameters are 850℃ for 60min and then water-cooled to room temperature; the aging process parameters are 480℃ for 5h and then air-cooled to room temperature.

[0067] Example 3

[0068] In this embodiment, a method for preparing a maraging steel with a bimodal heterogeneous structure is as follows:

[0069] (1) Preparation of master alloy powder

[0070] A master alloy was prepared in a vacuum induction melting furnace. The master alloy's composition, by weight, was 18.3% Ni, 2.93% Mo, 1.72% Ti, 0.0078% C, 0.009% Si, 0.005% Mn, 0.0058% S, 0.006% P, and the balance was Fe. The master alloy powder was atomized and sprayed with the following requirements: a powder size of <75 μm, an atomizing pressure of 4.0 MPa, a superheat of 200°C, and a protective atmosphere of argon with a purity of at least 99.99% by volume.

[0071] (2) Low-energy ball milling

[0072] In order to disperse the nano-oxides in the material, high-energy ball milling is performed with 0.1% by weight of Y and master alloy atomized powder. The particle size of the Y powder is less than 45 μm. The process parameters of low-energy ball milling are controlled as follows: the ball milling atmosphere is argon with a volume purity of more than 99.99%, the ball-to-material mass ratio is 6:1, the ball milling time is 40 hours, and the rotation speed is 60 r / min.

[0073] (3) Powder filling and bag extraction

[0074] In order to remove the gas adsorbed on the surface of the powder particles and reduce the porosity, the powder particle size after the canning ball milling is <200 μm. The canning degassing process is as follows: the vacuum air pressure is 10 -2 Pa, the temperature is 400℃, and the time is 8h.

[0075] (4) Hot isostatic pressing

[0076] The canning hot isostatic pressing solidification forming process is as follows: the pressure is 170 MPa, the temperature is 1150℃, and the holding time is 4h.

[0077] (5) Forging and hot rolling

[0078] In order to further improve the density and mechanical properties of the maraging steel after solidification forming, the material is forged into a plate, and the forging process is controlled as follows: the open forging temperature is 1150℃, and the final forging temperature is 850℃. The forged plate is hot rolled, and the hot rolling process is controlled as follows: the open rolling temperature is 1150℃, the final rolling temperature is 900℃, the rolling pass is 4, and the deformation amount of each pass is 12%, 13%, 15%, and 15% respectively, and the total deformation amount is 55%.

[0079] (6) The heat treatment process of the maraging steel is as follows: the solid solution process parameters are 850℃ for 60min, and then water cooled to room temperature, and the aging process parameters are 480℃ for 5h, and then air cooled to room temperature.

[0080] Example 4

[0081] In this embodiment, a preparation method of a bimodal heterogeneous structure maraging steel is as follows:

[0082] (1) Preparation of master alloy powder

[0083] The master alloy is prepared by a vacuum induction melting furnace, and the composition of the master alloy is as follows in terms of weight percentage: Ni: 18.3%, Mo: 2.93%, Ti: 1.72%, C: 0.0078%, Si: 0.009%, Mn: 0.005%, S: 0.0058%, P: 0.006%, and Fe: balance. The master alloy powder is subjected to gas atomization spraying, and the requirements are as follows: the powder particle size is <75 μm, the atomization gas pressure is 4.0 MPa, the superheat degree is 200℃, and the protective atmosphere is argon with a volume purity of more than 99.99%.

[0084] (2) Low-energy ball milling

[0085] In order to disperse the nano-oxide in the material, the Y powder with particle size <45 μm is high-energy ball milled with the master alloy atomized powder at 0.1% by weight. The process parameters of the low-energy ball milling are as follows: the ball milling atmosphere is argon with purity of more than 99.99% by volume, the ball-to-material mass ratio is 4:1, the ball milling time is 30 h, and the rotating speed is 90 r / min.

[0086] (3) Powder loading and jacket evacuation

[0087] In order to remove the gas adsorbed on the surface of the powder particles and reduce the porosity, the powder with a particle size <200 μm is loaded into the jacket after the ball milling. The evacuation process of the jacket is as follows: the vacuum air pressure is 10 -2 Pa, the temperature is 400 °C, and the time is 8 h.

[0088] (4) Hot isostatic pressing

[0089] The solidification forming process of the jacket by the hot isostatic pressing is as follows: the pressure is 170 MPa, the temperature is 1150 °C, and the holding time is 4 h.

[0090] (5) Forging and hot rolling

[0091] In order to further improve the density and mechanical properties of the maraging steel after the solidification forming, the material is forged into a plate. The forging process is controlled as follows: the open forging temperature is 1150 °C, and the final forging temperature is 850 °C. The forged plate is hot rolled. The hot rolling process is controlled as follows: the open rolling temperature is 1150 °C, the final rolling temperature is 900 °C, the rolling passes are 4, the deformation amount of each pass is 12%, 13%, 15%, and 15% respectively, and the total deformation amount is 55%.

[0092] (6) The heat treatment process of the maraging steel is as follows: the solid solution process parameters are 850 °C for 60 min, water cooling to room temperature, and the aging process parameters are 480 °C for 5 h, air cooling to room temperature.

[0093] Comparative Example 1

[0094] In the comparative example, the preparation method of a maraging steel is as follows:

[0095] (1) Preparation of master alloy powder

[0096] The master alloy is prepared by a vacuum induction melting furnace. The composition of the master alloy is as follows: Ni: 18.3%, Mo: 2.93%, Ti: 1.72%, C: 0.0078%, Si: 0.009%, Mn: 0.005%, S: 0.0058%, P: 0.006%, and Fe: balance. The master alloy powder is atomized by gas spraying. The requirements are as follows: the powder particle size is <75 μm, the atomization gas pressure is 4.0 MPa, the superheat degree is 200 °C, and the protective atmosphere is argon with purity of more than 99.99% by volume.

[0097] (2) Low-energy ball milling

[0098] The process parameters are controlled as follows: the ball milling atmosphere is argon with a volume purity of more than 99.99%, the ball-to-material mass ratio is 6:1, the ball milling time is 30 h, and the rotation speed is 120 r / min.

[0099] (3) Powder loading and jacket evacuation

[0100] In order to remove the gas adsorbed on the surface of the powder particles and reduce the porosity, the powder particles with a size of less than 200 μm are loaded into the jacket after the ball milling. The evacuation process of the jacket is as follows: the vacuum air pressure is 10 -2 Pa, the temperature is 400 ℃, and the time is 8 h.

[0101] (4) Hot isostatic pressing molding

[0102] The hot isostatic pressing solidification molding process of the jacket is as follows: the pressure is 170 MPa, the temperature is 1150 ℃, and the holding time is 4 h.

[0103] (5) Forging and hot rolling

[0104] In order to further improve the density and mechanical properties of the maraging steel after the solidification molding, the material is forged into a plate, and the forging process is controlled as follows: the open forging temperature is 1150 ℃, and the final forging temperature is 850 ℃. The forged plate is subjected to hot rolling, and the hot rolling process is controlled as follows: the open rolling temperature is 1150 ℃, the final rolling temperature is 900 ℃, the rolling passes are 4, and the deformation amount of each pass is 12%, 13%, 15%, and 15% respectively, and the total deformation amount is 55%.

[0105] (6) The heat treatment process of the maraging steel is as follows: the solid solution process parameters are 850 ℃ for 60 min, and then water cooling to room temperature, and the aging process parameters are 480 ℃ for 5 h, and then air cooling to room temperature.

[0106] Comparative Example 2

[0107] In the present comparative example, a maraging steel is prepared by the following method:

[0108] (1) The maraging steel is prepared by a vacuum induction melting furnace, and the composition of the alloy is as follows in terms of weight percentage: Ni: 17.9%, Mo: 2.98%, Ti: 1.42%, C: 0.001%, Si: 0.010%, Mn: 0.010%, S: 0.004%, P: 0.005%, and Fe: the balance.

[0109] (2) The forging process is controlled as follows: the open forging temperature is 1150 ℃, and the final forging temperature is 850 ℃.

[0110] (3) The heat treatment process of the maraging steel is as follows: the solid solution process parameters are 850℃ for 60min, and then water cooling to room temperature; the aging process parameters are 480℃ for 5h, and then air cooling to room temperature.

[0111] Comparative Example 3

[0112] In the present comparative example, the preparation method of a maraging steel is as follows:

[0113] (1) The maraging steel is prepared by a vacuum induction melting furnace, and the alloy composition is as follows in percentage by weight: Ni: 17.9%, Mo: 2.98%, Ti: 1.42%, C: 0.001%, Si: 0.010%, Mn: 0.010%, S: 0.004%, P: 0.005%, and Fe: balance.

[0114] (2) The forging process is controlled as follows: the open forging temperature is 1150℃, and the final forging temperature is 850℃.

[0115] (3) The heat treatment process of the maraging steel is as follows: the solid solution process parameters are 900℃ for 60min, and then water cooling to room temperature; the aging process parameters are 480℃ for 5h, and then air cooling to room temperature.

[0116] Table 1 Mechanical properties of each example and comparative example at room temperature

[0117] No. Tensile strength / MPa Yield strength / MPa Elongation / % Example 1 1965 1893 11.0 Example 2 1944 1874 11.5 Example 3 1917 1856 12.5 Example 4 1923 1861 11.5 Comparative Example 1 1882 1856 8.0 Comparative Example 2 1810 1742 10.0 Comparative Example 3 1783 1701 10.0

[0118] The results of Example 1 show that the bimodal heterogeneous structure maraging steel obtained by the present application has an average effective grain size of 2.1μm in the coarse grain region and an average effective grain size of 236nm in the fine grain region, wherein the volume ratio of the fine grain region is 86%. As shown in Figs. Figure 1 and Figure 2 The bimodal heterogeneous structure maraging steel not only has high strength, but also has good plasticity.

[0119] Preferably, the bimodal heterogeneous structure maraging steel has a yield strength at room temperature of not less than 1850MPa, a tensile strength of not less than 1900MPa, and an elongation of not less than 10%.

[0120] Compared with Example 1, the ball milling speed in Example 2 is reduced from 120r / min to 90r / min. The reduction of the ball milling speed reduces the volume ratio of the fine grain region in the surface layer of the original particles and increases the volume ratio of the coarse grain region in the core. As shown in Figs. Figure 3As shown in the microstructure of the bimodal heterogeneous structure maraging steel prepared in Example 2, the proportion of white coarse grain zone in the microstructure increased, and the coarse grain zone and fine grain zone presented a layered alternating distribution after rolling. At this time, the proportion of fine grain zone decreased from 86% to 70%. Since the hardness of coarse grain zone is lower than that of fine grain zone, the increase of soft phase zone reduces the strength of the material, but improves the plasticity. As can be seen from Table 1, the yield strength and tensile strength decreased from 1893 MPa and 1965 MPa to 1874 MPa and 1944 MPa, respectively, and the elongation increased from 11.0% to 11.5%.

[0121] Compared with Example 1, the rotation speed of Example 3 was reduced from 120 r / min to 60 r / min. As shown in the microstructure of the bimodal heterogeneous structure maraging steel prepared in Example 3, Figure 4 As shown in the microstructure of the bimodal heterogeneous structure maraging steel prepared in Example 3, due to the further reduction of the rotation speed, the proportion of white coarse grain zone in the material further increased, and after rolling, the coarse grain zone and fine grain zone still presented a layered alternating distribution. At this time, the volume proportion of fine grain zone decreased to 54%, and the size of white coarse grain zone increased significantly, and the coarse grain layer became wider. Compared with Example 1, the soft phase zone further increased, so that the yield strength of the material decreased from 1893 MPa to 1856 MPa, the tensile strength decreased from 1965 MPa to 1944 MPa, but the elongation increased from 11.0% to 12.5%.

[0122] Compared with Example 2, the ball-to-powder ratio of Example 4 was reduced from 6:1 to 4:1. The reduction of the ball-to-powder ratio led to a decrease in the probability of collision between the grinding balls and the powder, thereby reducing the proportion of fine grain zone in the surface layer of the powder. As shown in the microstructure of the bimodal heterogeneous structure maraging steel prepared in Example 4, Figure 5 As shown in the microstructure of the bimodal heterogeneous structure maraging steel prepared in Example 3, due to the further reduction of the rotation speed, the proportion of white coarse grain zone in the material further increased, and after rolling, the coarse grain zone and fine grain zone still presented a layered alternating distribution. At this time, the volume proportion of fine grain zone decreased to 54%, and the size of white coarse grain zone increased significantly, and the coarse grain layer became wider. Compared with Example 1, the soft phase zone further increased, so that the yield strength of the material decreased from 1893 MPa to 1856 MPa, the tensile strength decreased from 1965 MPa to 1944 MPa, but the elongation increased from 11.0% to 12.5%.

[0123] Compared with Example 1, the same ball milling speed and ball milling time were used in Comparative Example 1, but no Y powder was added during ball milling, and no oxide was formed to pin the grain boundary, so that a coarse grain structure was presented after heat curing, forming, forging, rolling and heat treatment. As shown in the microstructure of the bimodal heterogeneous structure maraging steel prepared in Comparative Example 1, Figure 6As shown in the microstructure of the maraging steel prepared in Comparative Example 1, the material lacks a bimodal structure characterized by coarse-grained and fine-grained regions. Instead, all primary particles contain coarse-grained, lath-shaped martensite. The yield strength and tensile strength drop to 1856 MPa and 1882 MPa, respectively, while the elongation is 8%.

[0124] Comparative Example 2 was prepared by conventional smelting method compared with Example 1. Figure 7 As shown in the metallographic structure of the maraging steel prepared in Comparative Example 1, the material produced by the smelting method lacks primary grain boundaries. After solution treatment and aging, the original austenite grains are equiaxed with an average grain size of 25 μm, and the grains are composed entirely of martensitic laths. Its yield strength is 1742 MPa, tensile strength is 1810 MPa, and elongation is 10.0%. Compared to maraging steel with a bimodal heterogeneous structure, its strength is approximately 100 MPa lower, and its elongation is also slightly lower.

[0125] Compared with Comparative Example 2, Comparative Example 3 increases the solution temperature, and its effective grain size increases, resulting in a further decrease in strength.

[0126] Implementation results demonstrate that the bimodal heterogeneous maraging steel obtained by this invention exhibits a mixed distribution of ultrafine and micron-sized grains. During plastic deformation, the higher-hardness fine-grained regions and the lower-hardness coarse-grained regions deform to different degrees, resulting in a plastic deformation strain gradient. Numerous geometric dislocations accumulate within the heterogeneous structure, simultaneously enhancing the overall strength and plasticity of the material.

[0127] The above embodiments are only for illustrating the technical concept and features of the present invention and are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made based on the spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for producing a bimodal heterogeneous structured maraging steel, characterized in that, The alloying composition of the maraging steel is as follows in percentage by weight: 18.0%<Ni≤21.0%, Mo: 2.5~3.5%, Ti: 1.0~1.8%, 0.01≤Y≤0.2, C≤0.01%, Si≤0.10%, Mn≤0.10%, S≤0.008%, P≤0.008%, and Fe balance; The preparation method of the bimodal heterogeneous structure maraging steel comprises the following steps: (1) master alloy smelting; (2) gas atomization powder spraying; (3) low-energy ball milling, the ball milling time is 10~50h, and the rotating speed is 40~180r / min; (4) packaging and air extraction; (5) hot isostatic pressing solidification forming; (6) forging and rolling; (7) solid solution + aging heat treatment; In the low-energy ball milling process, pure Y powder is added, the rotating speed and the ball milling time are controlled, and the powder particles form a bimodal grain size core-shell structure with a fine crystal zone on the surface wrapping a coarse crystal zone in the center. The microstructure of the maraging steel has a bimodal grain size, the center of the original particle is a coarse crystal zone with an average grain size of 2~10μm, and the edge of the original particle is a fine crystal zone with an average grain size of ≤250nm; wherein the volume fraction of the fine crystal zone is 30%~90%. The maraging steel has a room temperature yield strength of ≥1850MPa, a tensile strength of ≥1900MPa, and an elongation of ≥10%.

2. The method of manufacturing a bimodal heterogeneous structure maraging steel according to claim 1, characterized in that, In steps (1) and (2), the composition obtained by smelting the master alloy is 18.0%<Ni≤21.0%, Mo: 2.5~3.5%, Ti: 1.0~1.8%, C≤0.01%, Si≤0.10%, Mn≤0.10%, S≤0.008%, P≤0.008%, and Fe balance; the master alloy is subjected to gas atomization powder spraying, the powder particle size is <75μm, the atomization gas pressure is ≥3.5MPa, the superheat degree is ≥200℃, and the protective atmosphere is argon with a volume purity of more than 99.99%.

3. The method of producing a bimodal heterogeneous structure maraging steel according to claim 1, characterized in that, In step (3), the Y powder with a particle size of <45μm is subjected to low-energy ball milling with the master alloy atomized powder in percentage by weight of 0.01≤Y≤0.2, and the process parameters of the low-energy ball milling are controlled as follows: the ball milling atmosphere is argon with a volume purity of more than 99.99%, and the ball-to-material mass ratio is (3~8):

1.

4. The method of producing a bimodal heterogeneous structure maraging steel according to claim 1, characterized in that, In step (4), in order to remove the gas adsorbed on the surface of the powder particles and reduce the porosity, the powder particles in the package are <200 μm; the vacuum pumping parameters of the package are as follows: the vacuum air pressure is ≤10 -2 Pa, the temperature is 150-450 °C, and the time is 3-8 h.

5. The method of producing a bimodal heterogeneous structure maraging steel according to claim 1, characterized in that, In step (5), the hot isostatic pressing solidification forming process of the package is as follows: the pressure is 100~180MPa, the temperature is 1000~1200℃, and the holding time is 3~8h.

6. The method of producing a bimodal heterogeneous structure maraging steel according to claim 1, characterized in that, In step (6), in order to further improve the density and mechanical properties of the maraging steel after solidification forming, the forging process is as follows: the open forging temperature is 1100~1200℃, and the final forging temperature is 850~950℃; and then the hot rolling process of the forged blank is as follows: the open rolling temperature is 1100~1200℃, the final rolling temperature is 900~950℃, the rolling pass is 3~10 times, the deformation amount of each pass is 10~30%, and the total deformation amount is 50~70%.

7. The method of producing a bimodal heterogeneous structure maraging steel according to claim 1, characterized in that, In step (7), the heat treatment process is as follows: the solid solution process parameters are 800-950 ℃ for 60-90 min, and then water cooling; the aging process parameters are 450-550 ℃ for 3-6 h, and then air cooling.

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