A v, ti synergistically alloyed high-strength high-plasticity twip steel and a preparation method thereof

Abstract

The application provides a V and Ti synergistically alloyed high-strength and high-plasticity TWIP steel and a preparation method thereof. The TWIP steel has the following chemical components in percentage by mass: C 1.0-1.4%, V 0.2-0.6%, Ti 0.1-0.4%, Mn 15-20%, P≤0.01%, S≤0.005%, and the rest is Fe and inevitable impurities. The high-density dislocations and nanometer-sized carbide generated in the rolling deformation process are used to improve the strength of the TWIP steel. The addition of V and Ti elements can form carbides with C atoms to play the roles of precipitation strengthening and fine-grain strengthening, increase the work hardening capacity of the TWIP steel, and make the TWIP steel have more excellent mechanical properties. The hot rolling process can sharply increase the dislocation density and refine the grains, and then the cold rolling and recrystallization annealing treatment are carried out to make the high-density dislocations in the rolling process recover to restore the ability of the material to slide and deform, and finally the high-strength and high-plasticity TWIP steel is obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-strength automobile steel, and particularly relates to a V and Ti synergistically alloyed high-strength high-plasticity TWIP steel and a preparation method thereof. BACKGROUND

[0002] In recent years, the automobile industry has developed rapidly, and the number of automobiles has increased day by day, but the problems of environmental pollution and energy shortage have become increasingly serious. Energy saving and consumption reduction of the automobile industry is the main direction of its future development. Automobile lightweight design, which reduces the weight of the vehicle body under the premise of ensuring the safety of the automobile, improves the fuel economy of the automobile and reduces carbon emissions, is an effective way to solve the above problems. Although the research and application of new materials such as magnesium and aluminum alloys have developed rapidly, the strength of these materials is generally not high enough to meet the requirements of automobile crash safety, which limits their large-scale application in automobiles. Steel materials will still be the main material for automobile bodies in the future due to their low cost and good strength and toughness, so developing high-strength lightweight steel is an important way to realize automobile lightweight. The use of high-strength steel instead of low-strength automobile steel can reduce the amount of steel while ensuring the performance requirements of parts. This puts higher requirements on the strength level of automobile steel materials. The first generation of high-strength automobile steel developed by people includes dual-phase (DP) steel, transformation-induced plasticity (TRIP) steel, and martensitic steel. The development and application of these high-strength steels have to some extent solved the problems of heavy vehicle body, high fuel consumption, and high cost. However, the high-strength steel plates currently used in automobile components have a low strength and plasticity level (strength and plasticity product 15-20 GPa %), and the plasticity of the steel plate will decrease significantly after further increasing the strength, often causing difficulties in forming and processing complex-shaped components. The demand for new high-strength plasticity automobile steel plates in the automobile industry is becoming increasingly strong.

[0003] Under this background, twinning-induced plasticity (TWIP) steel emerged as the times require and has attracted widespread attention due to its superior mechanical properties (tensile strength ≥ 800 MPa, total elongation 60%~90%), becoming a strong competitor for the new generation of automobile steel. Compared with TRIP steel, DP steel, and martensitic steel, TWIP steel has high strength, plasticity, good formability, and no low-temperature brittle transition temperature, and exhibits more superior mechanical properties than the first generation of automobile steel. However, since TWIP steel has been on the market for a short time, the research on TWIP steel is still in its early stages, and the mechanical properties of TWIP steel have the potential for further improvement.

[0004] Currently, the improvement of the mechanical properties and microstructure of TWIP steel is mainly from the following aspects: first, the addition of micro-alloying elements such as Cr, Mo, Cu, etc. from the perspective of composition design, by increasing or decreasing the stacking fault energy to affect the generation of twinning structure, thereby improving the mechanical properties and microstructure of TWIP steel; second, using rolling and large deformation during the rolling process of TWIP steel to improve the mechanical properties of TWIP steel and improve the microstructure; third, using different heat treatment processes to improve the grain size, deformation structure and phase composition of TWIP steel to improve the strength.

[0005] Chinese invention patent CN113930659A discloses a high-strength high-plasticity TWIP steel and a preparation method thereof. By sequentially performing low-temperature cold rolling, instantaneous annealing and low-temperature tempering treatment on the hot-rolled TWIP steel plate, a high-strength high-plasticity TWIP steel with a yield strength of >800 MPa and an elongation of >50% is obtained, but the preparation method is relatively complex, difficult to realize in actual production and high in cost. Chinese invention patent 103667913A discloses a production method of a high-strength high-plasticity TWIP steel. The TWIP steel improves the mechanical properties of the TWIP steel by controlling the harmful elements in the steelmaking process, selecting appropriate composition of the protective slag in the continuous casting process, and using cold rolling pre-deformation, near-recrystallization temperature annealing and other processes, and the yield strength of the TWIP steel is more than 1000 MPa, but the uniform elongation is only 10%.

[0006] According to the research results of Gwon et al., the addition of V and Ti can reduce the grain size of TWIP steel, improve the yield strength of the steel, and also affect the activity of twinning. In TWIP steel, carbides are often formed with carbon elements, and when the size of the precipitates is small and the number is large and uniformly distributed in the grain interior, the effect of precipitation strengthening is produced to improve the strength of the steel, but the size of the precipitates is too large, which will deteriorate the plasticity of the material. Selecting appropriate annealing temperature to control the size of the precipitates plays an important role in improving the strength and plasticity matching of TWIP steel. Further improving the strength-plasticity product of TWIP steel can make TWIP steel have better stamping formability, and at the same time make the parts made of TWIP steel have higher energy absorption and resistance to collision deformation, meet the demand of automobile industry for high-strength automobile steel, and is conducive to promoting the wide application of TWIP steel in automobile industry. SUMMARY

[0007] The present application provides a new type of TWIP steel with high carbon content and the addition of V and Ti alloying elements. The addition of C element plays a solid solution strengthening effect, which can improve the strength of TWIP steel; and forms precipitates with V and Ti elements to play a precipitation strengthening effect. However, the size of the precipitates is too large, which will damage the plasticity of the steel, so selecting appropriate annealing temperature plays an important role in improving the strength and plasticity of TWIP steel.

[0008] The application also provides a preparation method of the TWIP steel, which adopts a hot rolling, cold rolling and recrystallization annealing process to prepare a finished steel plate with austenite grains of different sizes. In the tensile test process, the high-density dislocations in the new TWIP steel generate dynamic recovery, which improves the strength of the steel and maintains good plasticity, and improves the work hardening capacity of the TWIP steel. The emergence of delayed plastic instability enables the new TWIP steel to have higher strength and better plasticity, with a tensile strength of more than 1061 MPa and a plastic elongation of more than 70%.

[0009] To achieve the above object, the technical scheme of the application is as follows:

[0010] The application provides a V and Ti synergistically alloyed high-strength and high-plasticity TWIP steel, which has the following chemical components: C 1.0-1.4%, V 0.2-0.6%, Ti 0.1-0.4%, Mn 15-20%, P≤0.01%, S≤0.005%, and the rest is Fe and inevitable impurities. C is easy to form carbides with V and Ti elements to play a precipitation strengthening role, but at the same time, it will reduce the C content dissolved in the austenite matrix, weaken the solid solution strengthening effect of C, and lead to a decrease in the work hardening capacity of the TWIP steel. Therefore, the addition amount of C elements is increased in the application to ensure that sufficient C is retained in the TWIP steel matrix to play a better solid solution strengthening role.

[0011] The TWIP steel has a tensile strength of ≥1061 MPa, a total elongation of up to 76.5%, and a strength-plasticity product of ≥74 GPa %.

[0012] The application provides a preparation method of the V and Ti synergistically alloyed high-strength and high-plasticity TWIP steel, which specifically comprises the following steps:

[0013] 1) Fe, Mn, C, V and Ti powders with a purity of ≥99.9% are selected as alloy raw materials, the alloy raw materials are placed in an electromagnetic induction furnace, vacuum melting is performed under argon protection to obtain molten steel, and then the molten steel is cast to obtain an ingot;

[0014] Preferably, the chemical components of the ingot are as follows: C 1.0-1.4%, V 0.2-0.6%, Ti 0.1-0.4%, Mn 15-20%, P≤0.01%, S≤0.005%, and the rest is Fe and inevitable impurities.

[0015] 2) The ingot is subjected to homogenization treatment, and then hot-forged into a billet, and then air-cooled to room temperature;

[0016] Preferably, the homogenization treatment is that the ingot is heated to 1150±30℃ and kept for 4 h.

[0017] Preferably, the billet is a square billet with a cross-sectional size of 45 mm x 35 mm.

[0018] Preferably, the hot forging temperature is 850-1150 ℃.

[0019] 3) after reheating the billet, hot rolling is performed, and then air cooling is performed to room temperature to obtain a hot-rolled steel plate;

[0020] Preferably, the billet is reheated to 1200±30 ℃ for 0.5 h, and then 5 passes of rolling are performed by using a rolling mill to obtain a hot-rolled steel plate with a thickness of 4-8 mm.

[0021] Preferably, the hot-rolling open rolling temperature is 1150±20 ℃, and the finish rolling temperature is higher than 900 ℃.

[0022] 4) after pickling the hot-rolled steel plate, cold rolling is performed to obtain a cold-rolled steel plate;

[0023] Preferably, after pickling the hot-rolled steel plate, 10 passes of rolling and 1 pass of flat rolling are performed by using a four-high cold rolling mill to obtain a cold-rolled steel plate with a thickness of 1-2 mm, and the rolling reduction is 75%.

[0024] 5) after performing recrystallization annealing treatment on the cold-rolled steel plate, water quenching is performed after annealing to room temperature to obtain the TWIP steel, which is a finished steel plate with austenite grains of different sizes.

[0025] Preferably, the annealing temperature is 800-1050 ℃, and the holding time is 15-25 min. Further reducing the annealing temperature will cause a large amount of V and Ti carbides, especially large blocky TiC, to precipitate, and the steel material is prone to brittle fracture, resulting in simultaneous reduction of the strength and plasticity of the material.

[0026] The TWIP steel produced by the present application has the following beneficial effects:

[0027] The chemical composition of the TWIP steel disclosed by the present application increases the content of C and adds V and Ti elements. VC and TiC precipitates formed by V and Ti and C elements can refine the grains and simultaneously play a role of precipitation strengthening, thereby improving the strength of the TWIP steel. The mechanical properties of the TWIP steel produced by the present application meet the following requirements: tensile strength ≥ 1061 MPa, total elongation is up to 76.5%, and strength-plasticity product ≥ 74 GPa % or more, the strength-plasticity matching is excellent, and the TWIP steel has better formability and collision energy absorption capacity than general automobile steel.

[0028] The TWIP steel is prepared by a process of hot rolling, cold rolling and recrystallization annealing, and has simple and economical preparation method, and can be mass produced on the basis of existing production line. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort.

[0030] Figure 1 Fig. 1 is a metallographic structure picture of the TWIP steel of Example 1 in the present application, which is cold-rolled and recrystallized annealed at 800 DEG C;

[0031] Figure 2 Fig. 2 is a metallographic structure picture of the TWIP steel of Example 2 in the present application, which is cold-rolled and recrystallized annealed at 900 DEG C;

[0032] Figure 3 Fig. 3 is a metallographic structure picture of the TWIP steel of Example 3 in the present application, which is cold-rolled and recrystallized annealed at 1000 DEG C;

[0033] Figure 4 Fig. 4 is a metallographic structure picture of the TWIP steel of Example 4 in the present application, which is cold-rolled and recrystallized annealed at 1050 DEG C;

[0034] Figure 5 Fig. 5 is a metallographic structure picture of the TWIP steel of Comparative Example 2 in the present application, which is cold-rolled and recrystallized annealed at 750 DEG C;

[0035] Figure 6 Fig. 6 is an engineering stress-strain curve of the TWIP steel of the present application under room temperature and unidirectional stretching, wherein 1- is the tensile data of the product of Example 1, 2- is the tensile data of the product of Example 2, 3- is the tensile data of the product of Example 3, 4- is the tensile data of the product of Example 4, 5- is the tensile data of the product of Comparative Example 1, and 6- is the tensile data of the product of Comparative Example 2. DETAILED DESCRIPTION

[0036] In order to make the purposes, technical solutions and beneficial technical effects of the present application clearer, the present application will be described in detail in combination with specific embodiments. It should be understood that the embodiments described in the present specification are only for explaining the present application, and are not intended to limit the present application.

[0037] Example 1

[0038] Fe, Mn, C, V, Ti powders with purity ≥99.9% are selected as alloy raw materials, the alloy raw materials are placed in an electromagnetic induction furnace, vacuum melting is carried out under the protection of argon, and then the molten steel is cast into an ingot. The chemical composition of the ingot is as follows: C 1.0%, V 0.3%, Ti 0.1%, Mn 20%, P ≤0.01%, S ≤0.005%, and the rest is Fe and inevitable impurities. The ingot is heated to 1150±30 ℃ and kept for 4 h for homogenization treatment, and then hot forging is carried out to form a square billet with a cross-sectional size of 45 mm×35 mm, and the forging temperature is 1150-850 ℃. The forged billet is reheated to 1200±30 ℃ and kept for 0.5 h, and then 5 passes of rolling are carried out by using a rolling mill to obtain a hot-rolled steel plate with a thickness of 8 mm, the opening rolling temperature is 1150±20 ℃, the final rolling temperature is higher than 900 ℃, and the hot-rolled steel plate is air-cooled to room temperature after hot rolling. The hot-rolled steel plate is pickled, and then 10 passes of rolling and 1 pass of flat rolling are carried out by using a four-roll cold rolling mill to obtain a cold-rolled steel plate with a thickness of 2 mm, and the rolling reduction is 75%. The cold-rolled steel plate is subjected to recrystallization annealing treatment, the annealing temperature is 800 ℃, the holding time is 25 min, and the structure is completely recrystallized austenitic structure after rapid quenching in water to room temperature, as shown in Figure 1 .

[0039] The tensile properties of the TWIP steel prepared in this embodiment are tested. According to GBT228-2002, “Metal Material Room Temperature Tensile Test Method”, the steel plate after heat treatment is processed into a standard tensile specimen, and the tensile rate is 0.05 mm / s. The tensile properties of the TWIP steel prepared in this embodiment measured in this way are shown in Table 1 below, and the engineering stress-strain curve is shown as curve 1 in Figure 6 . It can be seen that the TWIP steel after 800 ℃ recrystallization annealing obtains a completely recrystallized structure, the grain size is 3.8 μm, the tensile strength reaches 1279 MPa, the total elongation is 59.7%, and the strength-plasticity product reaches 76.95 GPa.

[0040] Example 2

[0041] Fe, Mn, C, V, Ti powders with purity ≥99.9% are selected as alloy raw materials, the alloy raw materials are placed in an electromagnetic induction furnace, vacuum melting is carried out under the protection of argon, and then the molten steel is cast into an ingot. The chemical composition of the ingot is as follows: C 1.1%, V 0.2%, Ti 0.3%, Mn 18%, P ≤0.01%, S ≤0.005%, and the rest is Fe and inevitable impurities. The ingot is heated to 1150±30 ℃ and kept for 4 h for homogenization treatment, and then hot forging is carried out to form a square billet with a cross-sectional size of 45 mm×35 mm, and the forging temperature is 1150-850 ℃. The forged billet is reheated to 1200±30 ℃ and kept for 0.5 h, and then 5 passes of rolling are carried out by using a rolling mill to obtain a hot-rolled steel plate with a thickness of 6 mm, the open rolling temperature is 1150±20 ℃, the final rolling temperature is higher than 900 ℃, and the hot-rolled steel plate is air-cooled to room temperature after hot rolling. The hot-rolled steel plate is pickled, and then 10 passes of rolling and 1 pass of flat rolling are carried out by using a four-roll cold rolling mill to obtain a cold-rolled steel plate with a thickness of 1.5 mm, and the rolling reduction is 75%. The cold-rolled steel plate is subjected to recrystallization annealing treatment, the annealing temperature is 900 ℃, the holding time is 20 min, and the structure is completely recrystallized austenitic structure, as shown in Figure 2 .

[0042] The tensile properties of the TWIP steel prepared in this embodiment are tested. According to GBT228-2002, “Metal Material Room Temperature Tensile Test Method”, the steel plate after heat treatment is processed into a standard tensile specimen, and the tensile rate is 0.05 mm / s. The tensile properties of the TWIP steel prepared in this embodiment measured in this way are shown in Table 1 below, and the engineering stress-strain curve is shown as curve 2 in Figure 6 . It can be seen that the cold-rolled TWIP steel after 900 ℃ recrystallization annealing obtains a completely austenitic structure, the grain size is 4.5 μm, the tensile strength reaches 1212 MPa, the total elongation is 72.9%, and the strength-plasticity product reaches 88.35 GPa%.

[0043] Example 3

[0044] Fe, Mn, C, V, Ti powders with purity ≥99.9% are selected as alloy raw materials, the alloy raw materials are placed in an electromagnetic induction furnace, vacuum melting is carried out under the protection of argon, and then the molten steel is cast into an ingot. The chemical composition of the ingot is as follows: C 1.3%, V 0.5%, Ti 0.4%, Mn 16%, P ≤0.01%, S ≤0.005%, and the rest is Fe and inevitable impurities. The ingot is heated to 1150±30 ℃ and kept for 4 h for homogenization treatment, and then hot forging is carried out to form a square billet with a cross-sectional size of 45 mm×35 mm, and the forging temperature is 1150-850 ℃. The forged billet is reheated to 1200±30 ℃ and kept for 0.5 h, and then 5 passes of rolling are carried out by using a rolling mill to obtain a hot-rolled steel plate with a thickness of 4 mm, the open rolling temperature is 1150±20 ℃, the final rolling temperature is higher than 900 ℃, and the hot-rolled steel plate is air-cooled to room temperature after hot rolling. The hot-rolled steel plate is pickled, and then 10 passes of rolling and 1 pass of flat rolling are carried out by using a four-roll cold rolling mill to obtain a cold-rolled steel plate with a thickness of 1 mm, and the rolling reduction is 75%. The cold-rolled steel plate is subjected to recrystallization annealing treatment, the annealing temperature is 1000 ℃, the holding time is 18 min, and the steel plate is rapidly quenched into water after annealing to cool to room temperature, and the microstructure is a completely recrystallized austenitic structure, as shown in Figure 3

[0045] The tensile properties of the TWIP steel prepared in this embodiment are tested. According to GBT228-2002, “Metal Material Room Temperature Tensile Test Method”, the steel plate after heat treatment is processed into a standard tensile specimen, and the tensile rate is 0.05 mm / s. The tensile properties of the TWIP steel prepared in this embodiment measured in this way are shown in Table 1 below, and the engineering stress-strain curve is shown as curve 3 in Figure 6 It can be seen that the cold-rolled TWIP steel obtains a completely austenitic structure after recrystallization annealing at 900 ℃, the grain size is 11.2 μm, the tensile strength reaches 1107 MPa, the total elongation is 76.5%, and the strength-plasticity product reaches 84.68 GPa %.

[0046] Example 4

[0047] ​Fe, Mn, C, V, Ti powders with purity ≥ 99.9% are selected as alloy raw materials, the alloy raw materials are placed in an electromagnetic induction furnace, vacuum melting is carried out under argon protection, and then the molten steel is cast into an ingot, the chemical composition of the ingot is as follows: C 1.4%, V 0.6%, Ti 0.2%, Mn 15%, P ≤ 0.01%, S ≤ 0.005%, and the rest is Fe and inevitable impurities; the ingot is heated to 1150±30 ℃ and held for 4 h for homogenization treatment, and then hot forging is carried out to form a square billet with a cross-sectional size of 45 mm×35 mm, and the forging temperature is 1150-850 ℃; the forged billet is reheated to 1200±30 ℃ and held for 0.5 h, 5 passes of rolling are carried out by using a rolling mill, a hot-rolled steel plate with a thickness of 6 mm is obtained, the opening rolling temperature is 1150±20 ℃, the final rolling temperature is higher than 900 ℃, and the hot-rolled steel plate is air-cooled to room temperature after hot rolling; the hot-rolled steel plate is pickled, and then 10 passes of rolling and 1 pass of flat rolling are carried out by using a four-roll cold rolling mill to obtain a cold-rolled steel plate with a thickness of 1.5 mm, and the rolling reduction is 75%; the cold-rolled steel plate is subjected to recrystallization annealing treatment, the annealing temperature is 1050 ℃, the holding time is 15 min, and the steel plate is rapidly quenched into water after annealing to cool to room temperature, and the microstructure is a completely recrystallized austenitic structure, as shown in Figure 4 .

[0048] The tensile properties of the TWIP steel prepared in this example are tested. According to GBT228-2002, “Metal Material Room Temperature Tensile Test Method”, the steel plate after heat treatment is processed into a standard tensile specimen, and the tensile rate is 0.05 mm / s. The tensile properties of the TWIP steel prepared in this example measured in this way are shown in Table 1 below, and the engineering stress-strain curve is shown by curve 4 in Figure 6 . It can be seen that the cold-rolled TWIP steel after recrystallization annealing at 1050 ℃ obtains a completely austenitic structure, the grain size is 15.6 μm, the tensile strength reaches 1061 MPa, the total elongation is 70.6%, and the strength-plasticity product reaches 74.91 GPa%.

[0049] Comparative Example 1

[0050] The chemical composition of the Mn, V, Ti main alloy elements of the steel material in Comparative Example 1 is the same as that in Example 2, and the only difference is that the content of the C element in the steel material of Comparative Example 1 is 0.61, and the reduced element content is supplemented with Fe. The same preparation method as in Example 2 is adopted.

[0051] The TWIP steel prepared in the present comparative example was subjected to tensile property test. The steel plate after heat treatment was processed into standard tensile sample according to GBT228-2002, "Metallic materials-tensile testing at ambient temperature", and the tensile rate was 0.05 mm / s. The tensile property of the TWIP steel prepared in the present example was measured and shown in Table 1 below, and the engineering stress-strain curve was shown in the curve marked 5 in Figure 6 Due to the decrease of carbon content, the solid solution strengthening and work hardening capacity of the material were reduced, so that the strength of the steel was reduced, the tensile strength reached 986 MPa, the total elongation was 70.8%, and the strength-plasticity product was 69.81 GPa%.

[0052] Comparative Example 2

[0053] The chemical composition of the steel in Comparative Example 2 was the same as that in Example 2, and the same preparation method as in Example 2 was adopted, the only difference being that the annealing temperature of Comparative Example 2 was 750°C, and the annealing structure was partially recrystallized austenite and contained a large amount of blocky precipitates, as shown in Figure 5 .

[0054] The TWIP steel prepared in the present comparative example was subjected to tensile property test. The steel plate after heat treatment was processed into standard tensile sample according to GBT228-2002, "Metallic materials-tensile testing at ambient temperature", and the tensile rate was 0.05 mm / s. The tensile property of the TWIP steel prepared in the present example was measured and shown in Table 1 below, and the engineering stress-strain curve was shown in the curve marked 6 in Figure 6 Due to the decrease of annealing temperature, a large amount of blocky precipitates were contained in the annealing structure of the steel plate, so that the elongation of the steel was greatly reduced, the tensile strength reached 1322 MPa, the total elongation was only 37.2%, and the strength-plasticity product was 49.17 GPa. The scanning energy spectrum analysis showed that the blocky precipitates were TiC.

[0055] Table 1 Average grain size and mechanical property data of the products obtained in each example and comparative example

[0056]

[0057] The above merely illustrates the specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any modification or replacement within the technical range disclosed by the present application can be easily thought by those skilled in the art, and these modifications or replacements shall be covered in the protection scope of the present application. Therefore, the protection scope of the present application shall be determined by the protection scope of the claims.

Claims

1. A V, Ti synergistically alloyed high-strength and high-plasticity TWIP steel, characterized in that: Its chemical composition by mass percentage is: C1.1-1.4%, V 0.2-0.6%, Ti 0.1-0.4%, Mn 15-20%, P≤0.01%, S≤0.005%, and the rest is Fe and inevitable impurities; and its tensile strength is ≥1061MPa, the maximum total elongation is 76.5%, and the strength-ductility product is ≥74 GPa %; The preparation method of the V and Ti synergistically alloyed high-strength and high-plasticity TWIP steel comprises: Alloy raw material smelting, ingot casting, homogenization treatment, hot forging, hot rolling, cold rolling and recrystallization annealing; wherein the annealing temperature is 800-1050 ° C and the holding time is 15-25 minutes.

2. The method for preparing V and Ti synergistically alloyed high-strength and high-plasticity TWIP steel according to claim 1, characterized in that: The following steps are involved: 1) Fe, Mn, C, V, and Ti powders with a purity of ≥99.9% are selected as alloy raw materials, the alloy raw materials are placed in an electromagnetic induction furnace, and vacuum smelted under argon protection to obtain molten steel, which is then cast to obtain ingots; 2) homogenizing the ingot, then hot forging it into a billet, and then air cooling it to room temperature; the hot forging temperature is 850-1150° C.; 3) reheating the steel billet and then hot rolling it, and then air cooling it to room temperature to obtain a hot-rolled steel plate; 4) pickling the hot-rolled steel sheet and then cold-rolling it to obtain a cold-rolled steel sheet; 5) performing recrystallization annealing on the cold-rolled steel sheet, and then cooling the cold-rolled steel sheet to room temperature by water quenching to obtain the TWIP steel.

3. The method according to claim 2, characterized in that In step 2), the homogenization treatment is as follows: heating the ingot to 1150±30° C. and keeping the temperature for 4 h.

4. The method according to claim 2, characterized in that In step 2), the steel billet is a square steel billet with a cross-sectional size of 45 mm×35 mm.

5. The method according to claim 2, characterized in that In step 3), the steel billet is reheated to 1200±30° C. and kept at this temperature for 0.5 h, and then rolled by a rolling mill for 5 passes to obtain a hot-rolled steel plate with a thickness of 4-8 mm.

6. The method according to claim 2, characterized in that In step 3), the hot rolling start temperature is 1150±20°C, and the final rolling temperature is higher than 900°C.

7. The method according to claim 2, characterized in that In step 4), the hot-rolled steel plate is pickled and then subjected to 10 passes of rolling and 1 pass of temper rolling using a four-roll cold rolling mill to obtain a cold-rolled steel plate with a thickness of 1-2 mm and a rolling reduction of 75%.

8. The method according to claim 2, characterized in that In step 5), the annealing temperature is 800-1050° C., and the holding time is 15-25 min.

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