Preparation method of high-strength homogeneous composite steel plate with excellent impact toughness

Abstract

The invention relates to a preparation method of a high-strength homogeneous composite steel plate with excellent impact toughness. The method comprises the following steps: (1) forging a smelted martensite cast ingot into a blank with a required size; (2) cutting into equal-thickness steel sheets; (3) a rectangular tube made of plain carbon steel and a steel sheet are welded to form a packaging shell, and the steel sheet is arranged in the packaging shell; (4) forming a vacuum environment in the sealed shell, and welding and sealing; (5) the composite steel plate is heated to 1150-1200 DEG C for rolling, and the composite steel plate is rapidly cooled to the room temperature after rolling; (6) solution treatment is carried out, and then rapid quenching is carried out to obtain a martensite structure; and (7) re-heating for tempering treatment, and then air-cooling to room temperature to obtain the homogeneous composite steel plate. The high-strength homogeneous composite steel plate provided by the invention is simple in preparation process flow, excellent in obdurability matching and low in cost.

Description

Technical Field

[0001] The invention relates to a method for preparing a high-strength homogeneous composite steel plate with excellent impact toughness, and belongs to the technical field of metal composite plate production. Background Art

[0002] Steel is an important foundation for the development of the national economy and a key support for national defense construction and the development of high-end equipment. High strength and toughness are the main trends in the development of advanced steel materials, but the increase in the strength of steel materials is often accompanied by a decrease in their toughness, especially low-temperature toughness. The significant inversion of strength and toughness in steel materials seriously restricts the application of steel materials in extreme environments. It is urgent to develop an advanced steel material with both high strength and excellent impact toughness.

[0003] At present, the methods to solve the inverted relationship between strength and toughness of steel materials mainly focus on alloying design, microstructure regulation and process optimization. Through alloying design, such as adding alloying elements Ni, Co, etc., the strength and toughness of high-strength steel can be improved, and high-strength and tough steel materials represented by high-cobalt-nickel secondary hardening steel have been developed. However, due to the extremely high cost of alloys of precious metal elements such as Co and Ni, this type of material is mostly limited to the application in the field of national defense and military industry, and it is difficult to obtain large-scale application in the civilian field. In terms of organizational regulation, by designing complex preparation processes, multi-level and multi-scale microstructures can be regulated in steel materials, so that they present a variety of strengthening and toughening mechanisms, thereby obtaining excellent strength and toughness matching. However, this type of method usually has a complex process flow, and its application to mature commercial steel materials will significantly increase the manufacturing cost, and the process control is difficult, which will also pose a great challenge to the product yield rate.

[0004] Layered composite steel materials combine high-toughness and high-strength steel materials, and optimize strength and toughness by complementing each other's performance. The selection of component materials is flexible and the preparation process is simple, which provides a new idea for optimizing the strength and toughness of steel materials. For example, Chinese patent CN 116336870 A discloses a heterogeneous metal laminated composite armor and its preparation method. The method combines the advantages of high-strength metal and high-toughness metal, and realizes the combination of heterogeneous metals by selecting component layers, vacuum packaging, stack forging, rolling and other processes, forming a layered structure, and effectively improving the impact toughness of the material.

[0005] At present, most layered composite steel materials are made of heterogeneous materials, that is, a combination of high-strength and low-toughness steel (high-strength component) and high-toughness and low-strength steel (high-toughness component). Although this method has improved the strength and toughness of steel materials to a certain extent, it also has some bottleneck problems. First, heterogeneous layered composite steel materials will significantly increase the alloy cost. For example, compared with Q235 carbon steel, although the Q235 / 316L stainless steel composite plate has better impact toughness, the introduction of 316L stainless steel in the composite plate will greatly increase the alloy cost of the material. Secondly, although heterogeneous layered composite steel materials can improve the strength-toughness matching, they often improve toughness by losing the strength of the high-strength component. For example, although the C300 martensitic steel / 316L stainless steel composite plate has good strength and toughness, the strength of the composite plate is significantly lower than that of the C300 martensitic steel. The above problems limit the widespread application of heterogeneous composite steel materials. Therefore, there is an urgent need to innovate the design of traditional layered composite materials and develop new layered composite steel materials that have both high strength and toughness and low alloy cost. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing a high-strength homogeneous composite steel plate with excellent impact toughness in view of the deficiencies in the current technology. The present invention proposes a homogeneous composite process for steel materials, which uses only one high-strength martensitic steel as a component material, and achieves high-strength metallurgical bonding at the interface between homogeneous components through assembly, packaging, hot rolling and subsequent heat treatment to form a homogeneous composite steel material. Different from heterogeneous composite steel materials containing multiple components, the present invention only uses one high-strength martensitic steel as a component to prepare a layered homogeneous composite steel material. While ensuring the high strength of the original components, the innovative design of the assembly method and rolling process simplifies the preparation process of traditional layered composite steels, thereby improving the preparation efficiency and yield rate. At the same time, the above-mentioned multi-layer composite process can construct multiple interlayer interfaces inside the composite steel, which can realize stress-strain redistribution of the material during deformation, reduce stress concentration, and inhibit crack initiation. The extended cracks will also undergo crack passivation and crack deflection when propagating to the interface, releasing the energy at the crack tip and greatly improving the impact toughness of the material. In addition, due to the use of homogeneous materials for composite, this method also avoids the problem of increased material costs caused by traditional heterogeneous materials composite. The high-strength homogeneous composite steel plate proposed by the present invention has a simple preparation process, excellent strength-toughness matching, and low cost, providing a new idea for the development of high-strength and tough steel materials.

[0007] The technical solution of the present invention is: A method for preparing a high-strength homogeneous composite steel plate with excellent impact toughness, the method comprising the following steps: (1) Smelting martensitic steel ingots; The composition and content of the martensitic steel are as follows: C: 0.25-0.31 wt.%, Si: 0.18-0.35 wt.%, Mn: 0.35-0.55 wt.%, Cr: 1.80-2.30 wt.%, Mo: 0.25-0.35 wt.%, Ni≤ 0.50 wt.%, Cu≤0.30 wt.%, P<0.015 wt.%, S<0.01 wt.%, and the balance is Fe and unavoidable impurities; (2) The smelted ingot is heated to 1150-1200°C, kept at this temperature for 2-3 hours, and then forged into a billet of the required size; (3) Cut the forged billet into steel sheets of equal thickness, grind the surface roughness to Ra1.6~3.2μm, and the difference in surface roughness between each steel sheet should not exceed Ra1.0μm, then clean and wipe; Among them, the thickness of each steel sheet is 2 ~ 10mm; (4) According to the size of the steel sheet, a rectangular tube of plain carbon steel and a steel sheet are welded to form a packaging shell. The thickness of the carbon steel used is 7% to 12% of the total thickness of the assembled steel sheet. The cleaned martensitic steel sheets are stacked in the thickness direction and then placed in the shell and welded to make it sealed; The number of steel sheets is 5~30; (5) Drill holes and weld a vacuum tube outside the sealed shell, and use a diffusion pump to evacuate the air inside the shell to form a vacuum degree of not less than 10 ﹣3 Pa vacuum environment, then heat the vacuum tube and pressurize and weld it with hydraulic pliers to seal it; (6) After the heating furnace is heated to 1150~1200℃, the sealed shell is placed in and kept warm for 1~2 hours. The rolling temperature is 1050~1100℃, the rolling passes are 5~8 passes, the total rolling reduction is controlled at 80%~90%, and the rolling reduction of the first pass is 10~15%. After rolling, it is cooled to room temperature by water cooling; (7) The rolled plate is heated to 850-900°C and kept at this temperature for 0.5-1 hour for solution treatment to completely austenitize the structure, and then quickly cooled to room temperature with water to obtain a martensitic structure; (8) The quenched steel plate is heated again to 550°C to 600°C, kept at this temperature for 30 to 60 minutes, and then air-cooled to room temperature. After the tempering treatment is completed, the plate is cut and polished to remove the package shell and burrs, thereby obtaining a homogeneous composite steel plate; The essential features of the present invention are: The following problems exist in the current heterogeneous composite plate technology: (1) Heterogeneous layered composite materials often obtain moderate strength and toughness by combining high-strength and low-toughness components with high-toughness and low-strength components, but their strength is much lower than that of the original high-strength components, which is equivalent to losing strength to gain toughness. (2) There is a large difference in the alloy cost between the two components in the heterogeneous composite material. Compared with the low-cost component, the cost of the composite plate must increase significantly. For example, Q235 steel and 316 stainless steel are composited. Although the composite plate has higher toughness than Q235 alone, due to the composite of the expensive 316 stainless steel layer, the cost of the composite plate will inevitably increase compared to Q235 steel.

[0008] The present invention compounds homogeneous high-strength martensitic steel. Since each layer is made of the same material, the strength of the composite material does not change. However, the interlayer interface is introduced through layered composite, and the failure mode of the material when subjected to impact load is changed. The existence of the interlayer interface can effectively hinder the propagation of cracks, thereby greatly improving the toughness, and ultimately achieving the goal of improving the toughness while maintaining the original high strength.

[0009] The beneficial effects of the present invention are: The present invention aims at the characteristics of homogeneous composite steel and determines the best preparation process suitable for this type of composite material through systematic experiments. Compared with the traditional heterogeneous composite steel preparation technology, the present invention omits the commonly used hot pressing process and makes specific designs in the packaging, hot rolling and heat treatment processes to be suitable for the homogeneous composite steel of the present invention. The beneficial effects produced are: (1) The layered structure formed by hot rolling gives the homogeneous composite steel plate extremely excellent impact toughness. The examples show that under the same rolling and heat treatment conditions, the tensile properties of the homogeneous composite steel plate are basically the same as those of the martensitic steel component. However, compared with the martensitic steel component, the impact toughness of the homogeneous composite steel plate in a wide temperature range (-40 ~ 25 ℃) is significantly improved, with the room temperature impact absorption energy increased from about 70J to more than 110J, and the low temperature impact absorption energy of -40℃ increased from less than 40J to more than 110J. The impact toughness of the homogeneous composite steel plate has low temperature sensitivity, achieving the effect of significantly improving the impact toughness while maintaining the material strength unchanged.

[0010] (2) Compared with traditional heterogeneous composite steel plates, the homogeneous composite plates proposed in this patent are composited from the same type of high-strength martensitic steel, so they will not lead to an increase in alloy costs. Ultimately, while maintaining the original alloy cost, the strength and toughness of the original steel material is significantly improved through layered structure construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1The microstructure of the 20-layer 2.5mm martensitic steel homogeneous composite plate obtained in Example 1; Figure 2 Comparison of tensile properties between the 20-layer 2.5mm martensitic steel homogeneous composite plate obtained in Example 1 and the martensitic steel component; Figure 3 Comparison of the impact properties of the 20-layer 2.5mm martensitic homogeneous composite plate obtained in Example 1 and the martensitic steel component; Figure 4 The microstructure of the 25-layer 2mm martensitic steel homogeneous composite plate obtained in Example 2; Figure 5 Comparison of tensile properties between the 25-layer 2mm martensitic steel homogeneous composite plate obtained in Example 2 and the martensitic steel component; Figure 6 Comparison of the impact properties of the 25-layer 2mm martensitic homogeneous composite plate obtained in Example 2 and the martensitic steel component; DETAILED DESCRIPTION

[0012] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, but should not be construed as limiting the present application.

[0013] The production method described in the present application is described in detail below in conjunction with the embodiments.

[0014] The material used in the example is martensitic steel, and the chemical elements and their contents are: C: 0.25~0.31 wt.%, Si: 0.18~0.35 wt.%, Mn: 0.35~0.55 wt.%, Cr: 1.80~2.30 wt.%, Mo: 0.25~0.35wt.%, Ni≤ 0.50wt.%, Cu≤0.30 wt.%, P<0.015 wt.%, S<0.01 wt.%, and the balance is Fe and unavoidable impurities.

[0015] Embodiment 1: Component material smelting: Martensitic steel ingot meeting the above chemical composition requirements is obtained by smelting, with specific composition and content as follows: C: 0.30 wt.%, Si: 0.25 wt.%, Mn: 0.40 wt.%, Cr: 2.0 wt.%, Mo: 0.30 wt.%, Ni: 0.30 wt.%, Cu: 0.20 wt.%, P<0.015 wt.%, S<0.01 wt.%, and the balance being Fe and unavoidable impurities.

[0016] Assembly: Heat the ingot to 1150℃, keep it warm for 2h, forge it into a square ingot with a size of 85mm×65mm, cut 20 steel sheets along the thickness direction, each with a thickness of 2.5mm, grind the surface and side of the steel sheet until the roughness Ra is 2μm, the surface roughness difference between each steel sheet is about Ra0.5μm, and the surface of the steel sheet is smooth and burr-free. Using Q235 rectangular tubes and plates with a wall thickness of 5mm, a square cup-shaped shell with an internal size of 85mm×65mm×50mm is prepared by tungsten inert gas welding (TIG) method, and a circular hole with a diameter of 10mm is opened on the shell wall. After cleaning the dirt with alcohol, the 20 polished martensitic steel sheets are stacked and wrapped with insulation cloth and placed in the cup-shaped shell so that the billet does not shake in the shell, and another Q235 square sheet is welded to seal the shell. Take a stainless steel tube with a diameter of 10 mm and weld it to the previously opened circular hole as a vacuum tube. Finally, check whether the package shell has any defects such as welding leakage and sand holes. After confirming that it is correct, use a three-cylinder diffusion pump to connect the vacuum tube to evacuate air to form a vacuum environment. The vacuum degree is 1.7 × 10 ﹣3 Pa; finally, after heating the vacuum tube with a flame spray gun, the vacuum tube is closed with hydraulic clamps to maintain a vacuum-tight environment inside the shell.

[0017] Rolling and heat treatment: The total thickness of the billet is 60mm. It is placed in a heating furnace and kept at 1200℃ for 1h before rolling. The rolling temperature is about 1150℃. The pass setting is that the roll gap is set to 51mm in the first pass, 41mm in the second pass, 31mm in the third pass, 21mm in the fourth pass, and 13mm in the fifth pass. Ensure that the rolling temperature is above 950℃. After 5 passes, a hot-rolled composite plate with a thickness of 13mm is obtained, which is then cooled to room temperature by water cooling. The hot-rolled plate is reheated to 850℃ and kept warm for 0.5h for solution treatment, and cooled to room temperature by water cooling; the hot-rolled plate after solution treatment is heated to 560℃ again, kept warm for 0.5h for tempering, and air-cooled to room temperature. Finally, the obtained composite plate is cut and polished to remove the packaging shell and burrs, and the homogeneous composite steel plate in this example can be obtained.

[0018] Metallographic samples were cut from the prepared homogeneous composite steel plate, and after grinding and polishing, the microstructure was observed using a TESCANGAIA3Ga ion dual-beam scanning electron microscope. The results are shown in the figure. Figure 1 As shown, the left picture is the interlayer interface bonding morphology of the homogeneous composite steel plate. There are no obvious inclusions and oxides at the interlayer interface, and the bonding is good. It can be observed that the martensite structure has penetrated the interlayer interface, indicating that the interface has achieved metallurgical bonding. The right picture is the microstructure morphology of the homogeneous composite steel plate at low magnification. It can be seen that the microstructure is mainly composed of lath martensite, and there are no defects at the interface.

[0019] In this example, tensile specimens were prepared according to GB / T 228.1-2010 standard. The tensile specimens were sampled parallel to the rolling direction and tested by an electronic universal testing machine DNS300. Figure 2 The engineering stress-strain curves of the homogeneous composite martensitic steel and its component martensitic steel obtained under the same preparation process are given. It can be seen from the figure that under the same sample processing method and test standard, the strength and elongation of the homogeneous composite steel plate are basically consistent with those of the martensitic component. The impact specimens were prepared according to GB / T 229-2020 standard, with a size of 55mm×10mm×10mm, a V-notch, and tested using a fully automatic pendulum impact tester (PTM2302-C) at room temperature and -40°C. Figure 3 The impact absorption energy comparison between the homogeneous composite martensitic steel and its component martensitic steel under the same preparation process is given. Under room temperature test conditions, the impact absorption energy of the martensitic component is 76J, while the impact energy of the homogeneous composite martensitic steel reaches 115J, and the impact toughness is significantly improved. Under the -40℃ low temperature impact test, the impact absorption energy of the martensitic component is 34J, while the impact energy of the homogeneous composite martensitic steel reaches 112J, and the impact toughness is improved by about 3 times. In addition, it can be found that as the test temperature decreases, the impact toughness of the martensitic component decreases significantly, while the impact toughness of the homogeneous composite martensitic steel remains basically unchanged, indicating that the homogeneous composite martensitic steel has lower temperature sensitivity and lower ductile-brittle transition temperature.

[0020] Embodiment 2: Component material smelting: Martensitic steel ingot meeting the above chemical composition requirements is obtained by smelting, with specific composition and content as follows: C: 0.30 wt.%, Si: 0.25 wt.%, Mn: 0.40 wt.%, Cr: 2.0 wt.%, Mo: 0.30 wt.%, Ni: 0.30 wt.%, Cu: 0.20 wt.%, P<0.015 wt.%, S<0.01 wt.%, and the balance being Fe and unavoidable impurities.

[0021] Assembly: Heat the ingot to 1150℃, keep it warm for 2h, forge it into a square ingot with a size of 85mm×65mm, cut 25 steel sheets with a thickness of 2mm each along the thickness direction, grind the surface and side of the steel sheet until the roughness Ra is 2μm, the surface roughness difference between each steel sheet is about Ra0.5μm, and the surface of the steel sheet is smooth and burr-free. Using Q235 rectangular tubes and plates with a wall thickness of 5mm, a square cup-shaped shell with an internal size of 85mm×65mm×50mm is prepared by tungsten inert gas welding (TIG) method, and a circular hole with a diameter of 10mm is opened on the shell wall. Wash the 25 polished martensitic steel sheets with alcohol to remove dirt, stack them in sequence, wrap them with insulation cloth and put them into the cup-shaped shell so that the billet does not shake in the shell, and take another Q235 square sheet to weld and seal the shell. Take a 10mm diameter stainless steel tube and weld it to the previously opened circular hole as a vacuum tube. Finally, check whether the package shell has any defects such as welding leakage and sand holes. After confirming that it is correct, use a three-cylinder diffusion pump to connect the vacuum tube to pump air to form a vacuum environment. The vacuum degree is 1.5×10 ﹣3 Pa; finally, after heating the vacuum tube with a flame spray gun, the vacuum tube is closed with hydraulic clamps to maintain a vacuum-tight environment inside the shell.

[0022] Rolling and heat treatment: The total thickness of the billet is 60mm. It is placed in a heating furnace and kept at 1200℃ for 1h before rolling. The rolling temperature is about 1150℃. The pass setting is that the roll gap is set to 51mm in the first pass, 41mm in the second pass, 31mm in the third pass, 21mm in the fourth pass, and 13mm in the fifth pass. Ensure that the rolling temperature is above 950℃. After 5 passes, a hot-rolled composite plate with a thickness of 13mm is obtained, which is then cooled to room temperature by water cooling. The cooled hot-rolled plate is reheated to 850℃ and kept for 0.5h for solution treatment, and cooled to room temperature by water cooling; the hot-rolled plate after solution treatment is heated to 560℃ again, kept for 0.5h for tempering, and air-cooled to room temperature. Finally, the obtained composite plate is cut and polished to remove the packaging shell and burrs, and the homogeneous composite steel plate in this example can be obtained.

[0023] Metallographic samples were cut from the prepared homogeneous composite steel plate, and after grinding and polishing, the microstructure was observed using a TESCANGAIA3Ga ion dual-beam scanning electron microscope. The results are shown in the figure. Figure 4 As shown, the left figure is a morphology diagram of the interlayer interface bonding of the homogeneous composite steel plate. Similar to Example 1, it can be observed that the martensite structure has penetrated the interlayer interface, indicating that the interface has achieved metallurgical bonding, and there are no obvious inclusions and oxides at the interlayer interface; the right figure is a microstructure diagram of the homogeneous composite steel plate, and the microstructure is mainly composed of lath martensite.

[0024] In this example, tensile specimens were prepared according to GB / T 228.1-2010 standard. The tensile specimens were sampled parallel to the rolling direction and tested by an electronic universal testing machine DNS300. Figure 5 The tensile performance curves of the homogeneous composite martensitic steel and its component martensitic steel obtained under the same preparation process are given. It can be seen from the figure that under the same sample processing method and test standard, the strength and elongation of the homogeneous composite steel plate are basically consistent with those of the martensitic component. The impact specimens were prepared according to GB / T 229-2020 standard, with a size of 55mm×10mm×10mm, a V-notch, and tested using a fully automatic pendulum impact tester (PTM2302-C) at room temperature and -40°C. Figure 6 The impact absorption energy comparison between the homogeneous composite martensitic steel and its component martensitic steel under the same preparation process is given. Under room temperature test conditions, the impact absorption energy of the martensitic component is 76J, while the impact energy of the homogeneous composite martensitic steel reaches 132J, and the impact toughness is significantly improved. Under the -40℃ low temperature impact test, the impact absorption energy of the martensitic component is 34J, while the impact energy of the homogeneous composite martensitic steel reaches 111J. In addition, it can be found that as the test temperature decreases, the impact toughness of the martensitic component decreases, while the impact toughness of the homogeneous composite martensitic steel remains basically unchanged, indicating that the homogeneous composite martensitic steel has lower temperature sensitivity and lower ductile-brittle transition temperature.

[0025] It can be seen from the above embodiments that, compared with the preparation process of traditional heterogeneous layered composite steel materials, the commonly used hot pressing link is omitted in the present invention, the preparation process is simplified, and high-quality homogeneous composite steel materials are also obtained through the innovative design of the assembly and rolling process. In the assembly process step, different from the neglect of surface roughness in the assembly process of heterogeneous layered composite materials, the present invention requires that the surface roughness of each assembly steel sheet should be between Ra1.6 and 3.2μm, and the difference in surface roughness between each other should be less than Ra1.0μm, so as to ensure that there will be no obvious displacement between the steel sheets during the rolling process; in the packaging process step, according to the total thickness of the assembly steel sheet, the present invention has determined through a large number of trial and error experiments that the optimal wall thickness of the carbon steel used for the packaging shell should be 7% to 12% of the thickness of the assembly, so as to ensure that the shell will not crack during the rolling process; in the hot rolling process step, different from the large deformation strategy of the first pass commonly used in conventional rolling, the present invention controls the rolling reduction of the first pass to 10 to 15%, effectively preventing the cracking of the packaging shell during the rolling process, and making the components The local temperature of the interface can be increased through intense friction, which can promote dynamic recrystallization of the contact grains at the interface, form new grains across the interface, and obtain a metallurgical bonding interface; in the post-rolling heat treatment process, this patent adds additional post-rolling heat treatment (solution treatment + tempering treatment) to further enhance the element diffusion at the internal interface of the composite plate, further increase the interface bonding strength, and at the same time make the deformed structure after hot rolling completely recrystallize, eliminate the residual stress inside the material after rolling, and improve the performance stability; different from the high-temperature solution treatment commonly used for steel (above 1100°C), this patent adopts a low-temperature solution treatment method (850~900°C), which can effectively inhibit grain coarsening while ensuring complete austenitization of the structure, and then obtain fine martensite in the subsequent quenching process, further ensuring the high strength of the composite plate.

[0026] Compared with traditional homogeneous martensitic steel materials, when the homogeneous composite steel plate proposed in the present invention is subjected to rapid impact load, the stress and strain inside the material will be redistributed at the interface, reducing local stress concentration and inhibiting crack initiation. At the same time, the initiated and propagated cracks will also undergo crack blunting and crack deflection when propagating to the interface, greatly releasing the energy at the crack tip, so that the homogeneous composite steel has excellent impact toughness.

[0027] Therefore, it can be concluded that the present invention provides a method for preparing a high-strength homogeneous composite steel plate with excellent impact toughness. Through the layered structure design, while ensuring the original high strength of the component materials, the impact resistance of the steel material in normal and low temperature environments is greatly improved, meeting the service requirements of steel materials in harsh environments such as severe cold. At the same time, the present invention also simplifies the preparation process, reduces costs, and is conducive to the promotion and application of high-performance composite steel plates.

[0028] The above is a detailed description of the preferred experimental method of the present invention. It can be understood that the above embodiments are exemplary and cannot be construed as limitations of the present invention. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present invention.

[0029] Matters not covered by the present invention are known technologies.

Claims

1. A method for preparing a high-strength homogeneous composite steel plate with excellent impact toughness, characterized in that the method comprises the following steps: (1) The smelted martensitic steel ingot is heated to 1150-1200°C, kept at this temperature for 2-3 hours, and then forged into a billet of the required size; (2) Cut the forged billet into steel sheets of equal thickness. The surface roughness needs to be polished to Ra1.6~3.2μm, and the surface roughness difference between each steel sheet should not exceed Ra1.0μm, and then clean and wipe; (3) According to the size of the steel sheet, a rectangular tube of plain carbon steel and a steel sheet are welded to form a packaging shell. The thickness of the carbon steel used is 7% to 12% of the total thickness of the assembled steel sheet. The cleaned martensitic steel sheets are stacked in the thickness direction and then placed in the shell and welded to make it sealed; (4) Drill holes outside the sealed shell and weld a vacuum tube. Use a diffusion pump to evacuate the air inside the shell to form a vacuum environment with a vacuum degree of not less than 10-3 Pa. Then heat the vacuum tube and pressurize and weld it with hydraulic pliers to seal it. (5) After the heating furnace is heated to 1150~1200℃, the sealed shell is placed in and kept warm for 1~2 hours. The rolling temperature is 1050~1100℃, the rolling passes are 5~8 passes, the total rolling reduction is controlled at 80%~90%, and the rolling reduction of the first pass is 10~15%. After rolling, it is cooled to room temperature by water cooling; (6) The rolled plate is heated to 850-900°C and kept at this temperature for 0.5-1 hour for solution treatment to completely austenitize the structure, and then quickly cooled to room temperature with water to obtain a martensitic structure; (7) The quenched steel plate is heated again to 550°C~600°C, kept at this temperature for 30~60 min, and then air-cooled to room temperature. After the tempering treatment is completed, a homogeneous composite steel plate can be obtained.

2. The method for preparing a high-strength homogeneous composite steel plate with excellent impact toughness as described in claim 1 is characterized in that the composition and content of the martensitic steel are: C: 0.25~0.31 wt.%, Si: 0.18~0.35 wt.%, Mn: 0.35~0.55 wt.%, Cr: 1.80~2.30 wt.%, Mo: 0.25~0.35wt.%, Ni≤ 0.50 wt.%, Cu≤0.30 wt.%, P<0.015 wt.%, S<0.01 wt.%, and the balance is Fe and unavoidable impurities.

3. The method for preparing a high-strength homogeneous composite steel plate with excellent impact toughness as claimed in claim 1, characterized in that In the step (2), the thickness of each steel sheet is 2 to 10 mm.

4. The method for preparing a high-strength homogeneous composite steel plate with excellent impact toughness according to claim 1, characterized in that In the step (3), the number of stacked steel sheets is 5 to 30 sheets.

5. The method for preparing a high-strength homogeneous composite steel plate with excellent impact toughness according to claim 1, characterized in that In the above step (7), after the tempering treatment, the plate is also cut and polished to remove the packaging shell and burrs.

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