A 30GPa%-level vanadium microalloyed lightweight steel, its preparation and its composition design method

Abstract

The present invention discloses a 30GPa%-level vanadium microalloyed lightweight steel, its preparation method and its composition design method. The mass percentages of the vanadium microalloyed lightweight steel are as follows: C: 0.15 - 0.25%, Mn: 4.5 - 5.5%, Si: 0.2 - 0.5%, Al: 1.5 - 2.5%, V: 0.05 - 0.20%, and the balance is Fe and inevitable impurities. The direct quenching temperature of the cold-rolled sheet is 730°C and the holding time is 3 minutes. The present invention innovatively formulates a reasonable criterion based on the hot rolling and heat treatment processes through high-throughput calculation of the integrated material thermodynamics and thermophysical properties, and optimally designs the composition of the lightweight steel, solving the technical problem of how to scientifically and reasonably design the composition of the lightweight steel so that it can achieve both a tensile strength of not less than 980 MPa, an elongation of not less than 30%, and a density of not higher than 7.65 g / cm 3 ³ under the condition of direct quenching. The present invention improves the comprehensive mechanical properties of the lightweight steel on the premise of ensuring a low alloying level, and realizes the integrated computational composition design of a new type of high-performance lightweight steel.

Description

Technical Field

[0001] The present invention relates to a vanadium microalloyed lightweight steel at the 30 GPa% level, its composition design and preparation method, and is applied to the technical field of high-strength and high-toughness, low-density special steel. Background Art

[0002] With the intensification of the global energy crisis and environmental pollution problems, the design direction of the automotive industry is turning to lightweight to meet the practical requirements of energy conservation, emission reduction, environmental protection and safety. Against this background, the research significance and value of lightweight high-strength steel for automobiles are becoming increasingly prominent. Taking a Class A car as an example, the weight of its body-in-white is about 350 kg. If the weight reduction of the body structure reaches 10%, 6% - 8% of fuel can be saved and 5% - 6% of exhaust emissions can be reduced. Research shows that compared with traditional advanced high-strength steel for automobiles, when the aluminum content in the steel reaches 5 - 6 wt% (mass percentage), the weight of automotive parts can be reduced by 8 - 10%. Due to the addition of a large amount of aluminum elements, the density of the steel is significantly reduced, and this kind of steel is called lightweight steel.

[0003] Patent document CN104674109A discloses a third-generation cold-rolled automotive steel sheet of the Fe-Mn-Al-C system with high strength and toughness and low density, and its preparation method. A steel sheet with a strength-ductility product reaching 40 GPa% is prepared. Its deficiency is that a large amount of Mn elements and Al elements are added to the steel, which is likely to cause smelting problems, not only bringing difficulties to mass production, but also increasing the production cost of the steel sheet, thus limiting its application. Patent document CN106498307B discloses a 780 MPa grade high-strength and high-toughness cold-rolled lightweight steel and its manufacturing method. Its deficiency is that the tensile strength can only reach the 780 MPa grade, which cannot meet the requirements of automobile manufacturers for the ultra-high strength of cold-rolled lightweight high-strength steel. Patent document CN111020367A discloses a 980 MPa grade cold-rolled high-strength lightweight high-strength steel and its manufacturing method. Its deficiency is that the elongation after fracture is less than 20%, which cannot meet the requirements of automobile manufacturers for the formability of cold-rolled lightweight high-strength steel. Therefore, there is an urgent need to develop a low-alloyed lightweight steel with both high strength and high elongation rate to facilitate industrial production and promote the development of high-strength steel for automobiles. Summary of the Invention

[0004] In order to solve the problems of the existing technology, the purpose of the present invention is to overcome the deficiencies of the existing technology and provide a vanadium microalloyed lightweight steel at the 30 GPa% level, its preparation and its composition design method, and solve how to scientifically and reasonably prepare vanadium microalloyed lightweight steel and design the composition of lightweight steel so that it can achieve both a tensile strength of not less than 980 MPa, an elongation rate of not less than 30% and a density of not more than 7.65 g / cm 3Technical problems. Under the premise of ensuring a low alloying level, the present invention improves the comprehensive mechanical properties of lightweight steel and realizes the integrated computational composition design of a new type of high-performance lightweight steel.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A 30 GPa%-level vanadium microalloyed lightweight steel, the elemental mass percentage composition of which is:

[0007] C: 0.15 - 0.25%, Mn: 4.5 - 5.5%, Si: 0.2 - 0.5%, Al: 1.5 - 2.5%, V: 0.05 - 0.20%, and the balance is Fe and unavoidable impurities.

[0008] Preferably, for the 30 GPa%-level vanadium microalloyed lightweight steel of the present invention, the elemental mass percentage composition is: C: 0.18 - 0.22%, Mn: 5.11 - 5.43%, Si: 0.26 - 0.44%, Al: 1.93 - 2.19%, V: 0.09 - 0.14%, and the balance is Fe and unavoidable impurities.

[0009] Preferably, for the 30 GPa%-level vanadium microalloyed lightweight steel of the present invention, its tensile strength is not less than 980 MPa, the elongation is not less than 30%, the product of strength and plasticity is not less than 30 GPa%, and the density is not higher than 7.65 g / cm 3 .

[0010] Further preferably, for the 30 GPa%-level vanadium microalloyed lightweight steel of the present invention, its tensile strength is not less than 980 MPa, the yield strength is not less than 742 MPa, the elongation is not less than 31.2%, the product of strength and plasticity is not less than 31 GPa%, and the density is not higher than 7.647 g / cm 3 .

[0011] Preferably, the 30 GPa%-level vanadium microalloyed lightweight steel of the present invention is characterized in that its structure is ferrite and retained austenite structure, accompanied by nano-scale precipitation of carbides.

[0012] A preparation method for the 30 GPa%-level vanadium microalloyed lightweight steel of the present invention, the steps are as follows:

[0013] (1) Alloy melting and casting:

[0014] Weigh the raw materials according to the composition ratio of the target-prepared vanadium microalloyed lightweight steel, smelt them in a vacuum induction furnace, protect them with argon gas during the smelting process, and then carry out ingot casting;

[0015] (2) Primary forming processing:

[0016] After demoulding, the ingot is heated to not less than 1200°C, kept warm for at least 1 hour, and then hot rolled. The initial rolling temperature of hot rolling is controlled at 1050-1150°C, and the final rolling temperature is controlled at 900-1000°C. After hot rolling to a thickness of not more than 3mm, it is air-cooled to room temperature.

[0017] (3) Deep processing and molding:

[0018] In order to reduce the cold rolling resistance and avoid cracking, the hot rolled steel sheet is annealed before cold rolling at a temperature of 750-800°C for at least 3 hours; the annealed steel sheet is pickled to remove the oxide scale, and then cold rolled to obtain a cold rolled steel sheet with a thickness not exceeding 1.5 mm;

[0019] (4) Post-processing:

[0020] The cold-rolled steel sheet is directly quenched, the quenching temperature is controlled, the cold-rolled steel sheet is heated to not less than 730°C, kept warm for at least 3 minutes, and then water-quenched to room temperature to obtain the vanadium microalloyed lightweight steel sheet. Thus, the vanadium microalloyed lightweight steel with a strength-ductility product greater than 30 GPa% is obtained.

[0021] A composition design method for 30 GPa% vanadium microalloyed lightweight steel of the present invention optimizes the chemical composition of vanadium microalloyed lightweight steel by integrating high-throughput calculation of thermodynamic and thermophysical properties of materials, and the steps are as follows:

[0022] 1) According to the low alloying target of lightweight steel, the composition ranges of C, Mn, Si, Al and V are initially proposed to be 0.10-0.25wt%, 2.0-5.5wt%, 0.1-0.5wt%, 1.0-3.0wt% and 0.05-0.20wt%, respectively, and the balance is Fe;

[0023] 2) According to the hot rolling process, vanadium microalloying and density requirements, formulate the composition optimization criteria:

[0024] Criterion 1: Within the hot rolling temperature range of 900-1150℃, lightweight steel is located in a single austenite phase region to ensure hot rolling quality, that is, Vf γ =100%;

[0025] Criterion 2: At the direct quenching temperature of 730°C, the volume fraction of vanadium carbide is not less than 0.1% to ensure the precipitation of vanadium carbide, that is, Vf VC ≥0.1%;

[0026] Criterion 3: After quenching and cooling to room temperature, the density of lightweight steel is not higher than 7.65g / cm 3 , to meet the weight reduction requirements, that is, ρ≤7.65. In addition, under the premise of meeting the three major criteria, try to ensure low alloying;

[0027] 3) According to the above criteria, Thermo-Calc calculation software and MATLAB interface are used to compile a program file that can be used to optimize the composition of vanadium microalloyed lightweight steel. Thermodynamics and density calculations are performed using the iron-based database TCFE9 provided by the Thermo-Calc software. The components are screened based on a given composition range and step size, and the composition ratio that meets the criteria and is low-alloyed is preferably obtained to prepare the target vanadium microalloyed lightweight steel.

[0028] Principle of the present invention:

[0029] The composition design method of vanadium microalloyed lightweight steel of the present invention integrates high-throughput calculation of thermodynamic and thermophysical properties of materials, formulates reasonable criteria based on hot working technology, and screens the composition of lightweight steel, thereby obtaining a tensile strength of not less than 980MPa, an elongation of not less than 30% and a density of not more than 7.65g / cm 3 New vanadium microalloyed lightweight steel.

[0030] The alloy system of lightweight steel is mainly concentrated in Fe-Mn-Al-C. The addition of Al can reduce the density, but the formation of high-temperature ferrite can easily cause the mechanical properties to decrease. Usually, more Mn and C are added to ensure the mechanical properties, which in turn causes a series of production problems such as smelting and hot processing. Therefore, Mn and C should be added in appropriate amounts. The addition of Si can improve the fluidity of molten steel, and the addition of V can play a role in grain refinement and precipitation strengthening through the precipitation of carbides, but V and Al will increase the stability of ferrite and affect hot rolling. Therefore, the Al and V contents need to be strictly controlled. On this basis, in order to ensure the quality of hot rolling, it is necessary to ensure that the structure of lightweight steel is a single austenite within the hot rolling temperature range, that is, criterion 1. In order to achieve the effects of grain refinement and precipitation strengthening, it is necessary to ensure the precipitation of vanadium carbide during direct quenching treatment, that is, criterion 2. In addition, according to the density requirements of vanadium microalloyed lightweight steel, criterion 3 is set to achieve the purpose of weight reduction. Based on the three major criteria, the composition of lightweight steel is optimized and the alloying elements are kept at a low alloying level as much as possible, ultimately obtaining the ideal composition of vanadium micro-alloyed lightweight steel.

[0031] Through the above-mentioned composition design method, the traditional material R & D mode of "experimental guidance based on experience" is abandoned, and a new R & D mode of "theoretical prediction and scientific design" is realized, which greatly improves the R & D speed of new materials and reduces the R & D cost. The innovation of the present invention lies in the hot rolling and heat treatment processes of lightweight steel. By integrating high-throughput calculations of the thermodynamics and thermophysical properties of materials, the composition design of new lightweight steel is realized. After direct quenching treatment, a ferrite and retained austenite structure is obtained, accompanied by nano-scale precipitation of carbides. Under the action of an external load, the austenite undergoes a transformation-induced plasticity (TRIP) effect, effectively improving the strength and elongation, and obtaining a lightweight high-strength steel with a tensile strength higher than 980 MPa, an elongation higher than 30%, and a density lower than 7.65 g / cm 3 3.

[0032] Compared with the prior art, the present invention has the following obvious outstanding substantial features and remarkable advantages:

[0033] 1. The present invention designs and prepares a high-strength, tough and low-density special steel with a tensile strength of not less than 980 MPa, an elongation of not less than 30%, and a density of not more than 7.65 g / cm 3 3;

[0034] 2. On the premise of ensuring a low alloying level, the present invention improves the comprehensive mechanical properties of lightweight steel and realizes the integrated computational composition design of new high-performance lightweight steel;

[0035] 3. The 30 GPa%-level vanadium microalloyed lightweight steel of the present invention can meet the requirements of cold-rolled automotive steel sheets, has outstanding strength performance, is easy to process and form, and is easy to realize industrial production, which has important value for promoting the development of high-strength steel for automobiles. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is the calculation result of composition screening according to criterion 1 in the preferred embodiment of the present invention.

[0037] Figure 2 It is the calculation result of composition screening according to criterion 2 and criterion 3 in the preferred embodiment of the present invention.

[0038] Figure 3 It is the SEM micrograph of the 30 GPa%-level vanadium microalloyed lightweight steel in the first preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0039] The above scheme will be further described below in conjunction with specific implementation examples. The preferred embodiments of the present invention are described in detail as follows:

[0040] The present invention relates to a 30GPa%-level vanadium microalloyed lightweight steel, whose mass percentage composition is as follows: C 0.15 - 0.25%, Mn 4.5 - 5.5%, Si 0.2 - 0.5%, Al 1.5 - 2.5%, V 0.05 - 0.20%, and the balance is Fe and inevitable impurities;

[0041] The steel billet of the above components is smelted in a vacuum induction furnace, and argon gas is filled for protection during the smelting process, and then ingot casting is carried out; after demoulding, the ingot is heated to 1200 °C, held for 1 hour and then hot-rolled. The initial rolling temperature of the hot rolling is controlled at 1050 - 1150 °C, and the final rolling temperature is controlled at 900 - 1000 °C. After hot-rolling to 3 mm, it is air-cooled to room temperature; the hot-rolled steel plate is annealed at 780 °C for 3 h. After the annealed steel plate is pickled to remove the scale, it is cold-rolled to 1.5 mm, and the cold-rolled plate is directly quenched. The quenching temperature is controlled at 730 °C, held for 3 min, and water-quenched to room temperature to obtain the vanadium microalloyed lightweight steel with a strength-ductility product greater than 30GPa%.

[0042] Combined with specific embodiments, the 30GPa%-level vanadium microalloyed lightweight steel and its composition design and preparation method are further described. Based on the hot rolling and direct quenching treatment processes of the vanadium microalloyed lightweight steel, the high-throughput calculation of the material thermodynamics and thermophysical properties is innovatively integrated, and three criteria are established: Vf γ = 100%, Vf VC ≥ 0.1%, ρ ≤ 7.65. Using the thermodynamic calculation software Thermo-Calc and the MATLAB interface, and using the program for optimizing the composition of the vanadium microalloyed lightweight steel, the ideal composition ratio is optimized. Combined with the preparation method, a lightweight high-strength steel with a tensile strength higher than 980 MPa, an elongation higher than 30% and a density lower than 7.65 g / cm 3 is obtained. Specifically as follows:

[0043] 1) Initially determine the composition range of the experimental steel plate: According to the low-alloying goal of the lightweight steel, the composition ranges of C, Mn, Si, Al, and V are initially determined to be 0.10 - 0.25 wt%, 2.0 - 5.5 wt%, 0.1 - 0.5 wt%, 1.0 - 3.0 wt%, 0.05 - 0.20 wt% respectively, and the balance is Fe;

[0044] 2) Establish the composition optimization criteria for the experimental steel plate: According to the requirements of hot rolling process, vanadium microalloying, density, etc., three composition optimization criteria are established:

[0045] Criterion 1: Within the range of hot rolling temperature of 900 - 1150 °C, the lightweight steel is located in the single austenite phase region, that is, Vf γ = 100%, to ensure the quality of hot rolling;

[0046] Criterion 2: At the direct quenching temperature of 730°C, the volume fraction of vanadium carbide is not less than 0.1%, that is, Vf VC ≥0.1%, to ensure the precipitation of vanadium carbide;

[0047] Criterion 3: After quenching and cooling to room temperature, the density of lightweight steel is less than 7.65g / cm 3 , i.e. ρ≤7.65, to meet the requirements of weight reduction; on this basis, the components with the lowest alloying level are selected;

[0048] 3) Using a high-throughput computational screening program that integrates three criteria: Based on the above criteria, the Thermo-Calc calculation software and MATLAB interface are used to compile and analyze Vf under different composition and temperature conditions. γ 、Vf VC , ρ, and use loop statements and conditional statements to set three major criteria to achieve the screening of component ratios that meet the three major criteria;

[0049] 4) Design calculation conditions and run the calculation program to achieve component optimization:

[0050] The composition range determined in step 1) is divided into certain steps, as shown in Table 1. The total number of all composition ratios is 4×8×5×21×4=13440. Combined with the hot rolling temperature range and the direct quenching temperature, based on the above-mentioned high-throughput calculation and screening program, combined with the iron-based database TCFE9 provided by the Thermo-Calc software, all composition ratios are calculated, and the composition ratios that meet the three criteria are screened out. The calculation results are as follows: Figure 1 and Figure 2 As shown; According to criterion 1, that is, light steel is located in a single austenite phase region within the hot rolling temperature range of 900-1150℃, 1887 component ratios that meet the conditions can be screened out, such as Figure 1 As shown by the arrows; according to criteria 2 and 3, 17 components were further screened out, such as Figure 2 As shown; according to the requirement of low alloying level, the first five components with lower alloying degree are selected, as shown in Table 2.

[0051] Table 1. Composition (wt%) and temperature (°C) conditions of vanadium microalloyed lightweight steel

[0052] Condition C Mn Si Al V Lower limit 0.10 2.0 0.1 1.0 0.05 Upper limit 0.25 5.5 0.5 3.0 0.20 Step size 0.05 0.5 0.1 0.1 0.05

[0053] 5) Select five steel grades with the lowest alloying level according to the ingredient ratios that meet the three major criteria; prepare experimental steels based on the steel grades: smelt using a vacuum induction furnace, protect with argon gas during the smelting process, and then perform ingot casting; after demolding, heat the ingot to 1200 °C, hold for 1 hour and then perform hot rolling. Control the initial rolling temperature of hot rolling at 1050 - 1150 °C and the final rolling temperature at 900 - 1000 °C. After hot rolling to 3 mm, air cool to room temperature; anneal the hot-rolled steel plate at 780 °C for 3 h, and after pickling to remove the scale, cold roll it to 1.5 mm; the measured composition is shown in Table 2;

[0054] Table 2 Composition of the experimental steel plate in this example (wt%)

[0055] Example C Mn Si Al V 1 Preferred composition 0.20 5.0 0.3 2.0 0.10 Measured composition 0.18 5.14 0.26 2.19 0.13 2 Preferred composition 0.20 5.5 0.4 2.0 0.10 Measured composition 0.20 5.32 0.33 2.11 0.09 3 Preferred composition 0.20 5.5 0.4 2.0 0.15 Measured composition 0.19 5.11 0.29 1.93 0.12 4 Preferred composition 0.20 5.5 0.5 2.0 0.10 Measured composition 0.22 5.43 0.44 2.11 0.09 5 Preferred composition 0.20 5.5 0.5 2.0 0.15 Measured composition 0.21 5.40 0.41 1.98 0.14

[0056] The parameter control of the preparation process for preparing vanadium microalloyed lightweight steel is shown in Table 3.

[0057] Table 3 Parameters of the preparation process for the experimental steel plate in this example

[0058]

[0059] Among them, directly quench the cold-rolled plate, control the quenching temperature at 730 °C, hold for 3 min, and water quench to room temperature to obtain a ferrite and retained austenite structure, accompanied by nano-scale precipitation of carbides, as Figure 3 shown, to achieve the requirements of a tensile strength higher than 980 MPa, an elongation higher than 30%, and a density lower than 7.65 g / cm 3 . The specific density and mechanical properties of each component steel grade are shown in Table 4. It can be seen that the tensile strength of the experimental steels prepared with the optimized components in this example all reach 980 MPa, the elongation is higher than 30%, and the density is lower than 7.65 g / cm 3 .

[0060] Table 4 Direct quenching temperature and mechanical properties of the experimental steel plate in this example

[0061]

[0062]

[0063] The mechanical properties of the embodiments of the present invention were compared with those of high-strength steel for automobiles reported in the literature, as shown in Table 5. In Comparative Examples 1 and 2, a continuous annealing treatment process was adopted. By adding Al, the density was reduced, and by increasing the C content, the strength was enhanced. Therefore, the carbon content in Comparative Examples 1 and 2 was relatively high, reaching more than 0.3 wt%, and the aluminum content was also higher than 3 wt%. The tensile strength could reach 980 MPa, but the elongation was much lower than 30%. In Comparative Example 3, both the strength and plasticity could meet the performance indicators of the present invention, but its Mn content was relatively high, reaching 10.02%, far exceeding the requirements of low alloying. Through comparison, it can be found that the vanadium microalloyed lightweight steel designed and prepared by the method of the present invention not only has a relatively low alloy content and a simple heat treatment process, but also can meet the index requirements of both strength and plasticity, and has excellent comprehensive mechanical properties.

[0064] Table 5 Comparison of the mechanical properties of the steel for automobiles in this example and those reported in the literature

[0065] Steel grade Yield strength (MPa) Tensile strength (MPa) Elongation rate (%) Product of strength and plasticity (MPa%) 1 468 997 12 11964 2 468 1023 19 19437 3 570.32 1105.62 76.87 84.99 Example 1 750 980 34.0 33320 Example 2 758 992 31.7 31446 Example 3 742 985 33.8 33293 Example 4 767 1001 31.2 31231 Example 5 753 987 33.5 33065

[0066] In summary, the above embodiments innovatively developed a vanadium microalloyed lightweight steel at the 30 GPa% level, its composition design and preparation method. On the premise of ensuring a low alloying level, based on the high-throughput calculation of the integrated thermodynamics and thermophysical properties of materials for composition design, combined with a direct quenching treatment process, a new type of vanadium microalloyed lightweight steel was obtained. The above embodiments of the present invention, the vanadium microalloyed lightweight steel at the 30 GPa% level, its composition design and preparation method, innovatively formulated a reasonable criterion based on hot rolling and heat treatment processes through the high-throughput calculation of the integrated thermodynamics and thermophysical properties of materials, and optimized the design of the composition of the lightweight steel, solving the technical problem of how to scientifically and reasonably design the composition of the lightweight steel so that it can achieve a tensile strength of not less than 980 MPa, an elongation of not less than 30%, and a density of not higher than 7.65 g / cm 3 under the condition of direct quenching. The present invention improves the comprehensive mechanical properties of the lightweight steel on the premise of ensuring a low alloying level, and realizes the integrated computational composition design of a new type of high-performance lightweight steel.

[0067] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made according to the purpose of the invention of the present invention. Any changes, modifications, substitutions, combinations, or simplifications made based on the spirit and principle of the technical solution of the present invention shall be equivalent replacement methods, as long as they meet the purpose of the invention of the present invention and do not depart from the technical principle and inventive concept of the present invention, they all fall within the protection scope of the present invention.

Claims

1. A composition design method for a 30GPa%-level vanadium microalloyed lightweight steel, characterized in that, Optimize the chemical composition of vanadium microalloyed lightweight steel through high-throughput calculation of the thermodynamics and thermophysical properties of the integrated materials, and the steps are as follows: 1) According to the low-alloying target of lightweight steel, preliminarily determine the composition ranges of C, Mn, Si, Al, and V to be 0.10 - 0.25 wt%, 2.0 - 5.5 wt%, 0.1 - 0.5 wt%, 1.0 - 3.0 wt%, and 0.05 - 0.20 wt% respectively, with the balance being Fe; 2) Develop composition optimization criteria according to the hot rolling process, vanadium microalloying, and density requirements: Criterion 1: Within the hot rolling temperature range of 900 - 1150 °C, the lightweight steel is located in a single austenite phase region to ensure the hot rolling quality, i.e., Vf γ = 100%; Criterion 2: At the direct quenching temperature of 730 °C, the volume fraction of vanadium carbide shall not be less than 0.1% to ensure the precipitation effect of vanadium carbide, i.e., Vf VC ≥ 0.1%; Criterion 3: After quenching and cooling to room temperature, the density of the lightweight steel is not higher than 7.65 g / cm 3 , to meet the weight reduction requirement, i.e., ρ ≤ 7.65; In addition, on the premise of meeting the three criteria, try to ensure low alloying; 3) According to the above criteria, use the Thermo-Calc calculation software and the MATLAB interface, and utilize the program file that can carry out the composition optimization of vanadium microalloyed lightweight steel. For thermodynamics and density calculations, use the built-in iron-based database TCFE9 of the Thermo-Calc software, and screen the composition based on the given composition range and step size. Optimally obtain the composition ratio that meets the criteria and low alloying, and use it to prepare the target 30GPa% level vanadium microalloyed lightweight steel, and its elemental mass percentage composition is: C: 0.15 - 0.25%, Mn: 4.5 - 5.5%, Si: 0.2 - 0.5%, Al: 1.5 - 2.5%, V: 0.05 - 0.20%, with the balance being Fe and unavoidable impurities.

2. The composition design method of the 30GPa%-level vanadium microalloyed lightweight steel according to claim 1, characterized in that Its elemental mass percentage composition is: C: 0.18 - 0.22%, Mn: 5.11 - 5.43%, Si: 0.26 - 0.44%, Al: 1.93 - 2.19%, V: 0.09 - 0.14%, with the balance being Fe and unavoidable impurities.

3. The composition design method of 30GPa%-level vanadium microalloyed lightweight steel according to claim 1, characterized in that: Its tensile strength is not less than 980 MPa, elongation is not less than 30%, the product of strength and plasticity is not less than 30 GPa%, and the density is not higher than 7.65 g / cm 3 .

4. The composition design method of the 30GPa%-level vanadium microalloyed lightweight steel according to claim 3, characterized in that: Its tensile strength is not less than 980 MPa, yield strength is not less than 742 MPa, elongation is not less than 31.2%, the product of strength and plasticity is not less than 31 GPa%, and the density is not higher than 7.647 g / cm 3 .

5. The composition design method of the 30GPa%-level vanadium microalloyed lightweight steel according to claim 1, wherein: Its microstructure is ferrite and retained austenite microstructure, accompanied by nano-scale precipitation of carbides.

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