Carbon-free high-modulus low-density light structural steel plate and preparation method thereof

Abstract

The invention provides a carbon-free high-modulus low-density light structural steel plate and a preparation method thereof. The light steel comprises the following components in percentage by weight: 10.0 to 16.0 percent of Mn, 1.5 to 4.0 percent of A1, 0.0 to 3.0 percent of Cr, 1.8 to 5.0 percent of Ti, 1.0 to 2.1 percent of B, 0.0 to 0.2 percent of Nb and the balance of Fe and impurities. Wherein Ti and B elements are added in an intermediate alloy mode, the weight content of Ti in Fe-Ti is 40%, the weight content of B in Fe-B is 19%, the steel plate is novel low-density steel, the low density of 6.88-7.45 g / cm < 3 > is achieved, meanwhile, the high Young modulus of 220-250 GPa is kept, and therefore the high specific modulus is generated. Compared with traditional Fe-TiB2 steel, the yield strength of the novel steel is improved by nearly 30-100% in the aspect of mechanical performance, meanwhile, good ductility is kept, and the development requirement of light-weight steel and iron materials is met.

Description

Technical Field

[0001] The present invention relates to the metallurgy and technical fields of metal materials, and in particular to a carbon-free high-modulus low-density light structural steel plate and a preparation method thereof. Background Art

[0002] The research and development of automotive steel with the design concept of improving strength and plasticity has become the mainstream solution for thinning components. However, the continuous thinning of steel plates will significantly reduce the stiffness of components, that is, the ability to resist elastic deformation, leading to risks such as instability. It is urgent to further increase the Young's modulus E of the material or reduce the density ρ (increase the specific modulus E / ρ). Although alloying with lightweight elements such as aluminum and magnesium can reduce density, it also sacrifices Young's modulus, resulting in a deterioration in component stiffness and collision safety. Therefore, the development of automotive steel has excessively pursued high strength and plasticity and ignored the significance of specific modulus, limiting its lightweight potential in structural parts such as chassis and suspension. How to have both low density and high Young's modulus while ensuring high strength and plasticity is a hot and difficult issue facing the development needs of lightweight steel materials.

[0003] At present, adding sufficient lightweight high modulus ceramic particles to steel is an effective way to improve the specific modulus. A new type of Fe-TiB2 high modulus steel based on in-situ self-generation (hereinafter referred to as in-situ high modulus steel) is proposed: using the eutectic reaction of the Fe-Ti-B system, ferrite matrix and TiB2 particles are generated in situ during the cooling process of the molten steel. The latter has an extremely high Young's modulus (565GPa) and a lower density (4.5g / cm 3 ), significantly improving the specific modulus of steel. However, the plasticity and formability of this new type of in-situ high modulus steel will drop sharply with the increase of ceramic content. Therefore, how to maintain high plasticity under the premise of sufficient ceramic content is the core prerequisite for the practical application of in-situ high modulus steel. Summary of the invention

[0004] A technical problem to be solved by the present invention is: how to maintain high plasticity under the premise of sufficient ceramic content.

[0005] In order to solve the above technical problems, the embodiment of the present disclosure provides a carbon-free high modulus low density light structural steel plate, characterized in that: the components of the light steel are as follows by weight: Mn: 10.0-16.0%, A1: 1.5-4.0%, Cr: 0.0-3.0%, Ti: 1.8-5.0%, B: 1.0-2.1%, Nb: 0.0-0.2%, and the balance is Fe and impurities;

[0006] The Ti and B elements are added in the form of intermediate alloys, and the weight content of Ti in Fe-Ti is 40%, and the weight content of B in Fe-B is 19%.

[0007] In some embodiments, the aforementioned carbon-free high modulus low density light structural steel plate, wherein the light steel has a Young's modulus of 220 to 250 GPa and a density of 6.88 to 7.45 g / cm 3 , the yield strength is 300-700MPa, the tensile strength is 600-865MPa, and the total elongation is 10-32%.

[0008] In some embodiments, in the aforementioned carbon-free high modulus low density lightweight structural steel plate, the lightweight steel in-situ generated reinforcement phase is TiB2 particles and / or M2B particles, and the volume fraction of the in-situ generated reinforcement phase is 3.3-17%.

[0009] In some embodiments, in the aforementioned carbon-free high modulus low density lightweight structural steel plate, the in-situ generated reinforcement phase is TiB2 particles, and the volume fraction of the TiB2 particles is 1.2-13%; or

[0010] The in-situ generated reinforcement phase is M2B particles, and the volume fraction of M2B particles is 2-8%; or

[0011] The in-situ generated reinforcement phases are TiB2 and M2B particles, and the volume fraction of TiB2 and M2B particles is 5-17%.

[0012] In some embodiments, in the aforementioned carbon-free, high modulus, low-density lightweight structural steel plate, the in-situ generated reinforcing phase is TiB2 particles, and the chemical composition of the lightweight steel is as follows in weight percentage: Mn: 15.0-16.0%, A1: 3.9-4.0%, Ti: 4.8-5.0%, B: 1.9-2.1%, and the remainder is Fe and impurities.

[0013] In some embodiments, in the aforementioned carbon-free, high modulus, low-density, lightweight structural steel plate, when the in-situ generated reinforcing phase is TiB2 and M2B particles, the high modulus lightweight steel composition is as follows in weight percentage: Mn: 15.0-16.0%, A1: 1.5-3.7%, Cr: 0.0-3%, Ti: 1.8-3.5%, B: 1.0-2.1%, Nb: 0.0-0.2%, and the remainder is Fe and some unavoidable impurity elements.

[0014] The second aspect of the present application provides a method for preparing a carbon-free high modulus low density lightweight structural steel plate, comprising the following steps:

[0015] S1. Proportioning the light steel components and smelting and casting to obtain a steel ingot, heating the steel ingot to 1080-1180° C., keeping the temperature for 2 hours, and forging the steel ingot into a steel billet with a thickness of 20-30 mm;

[0016] S2, heating the steel billet in S1 to 1080-1180°C, keeping the temperature for 2 hours, hot rolling it into a thin plate with a thickness of 3-5 mm through 6 passes, and cooling it to room temperature;

[0017] Among them, the initial rolling temperature is 1050-1130°C, the final rolling temperature is not less than 800°C, and then air-cooled to room temperature;

[0018] S3, pre-annealing the thin plate in S2, keeping the thin plate at 650°C to 950°C for 0.05h to 4h, and air-cooling to room temperature to obtain experimental steel;

[0019] S4, pickling the experimental steel in S3 with a hydrochloric acid and alcohol solution with a volume fraction of 1:1;

[0020] S51, cold-rolling the experimental steel pickled in S4 to a thickness of 1 to 1.5 mm using liquid nitrogen to obtain a first cold-rolled steel;

[0021] S6. Heat-treating the first cold-rolled steel in S51 at 1000° C. for 3 minutes and air-cooling to room temperature to obtain light steel.

[0022] S52, cold rolling the experimental steel pickled in S4 to a thickness of 1 to 1.5 mm to obtain a second cold rolled steel;

[0023] S7. The second cold-rolled steel in S52 is heat treated, firstly at 950°C for full austenitization for 0.8 to 5 minutes, then kept in the two-phase temperature range of 600 to 630°C for 1 to 4 hours, and air-cooled to room temperature to obtain light steel.

[0024] In some embodiments, in the aforementioned method for preparing a carbon-free high modulus low density lightweight structural steel plate, the volume fraction of austenite in the steel in S2, S51 and S7 is 65-80%.

[0025] Through the above technical solution, the Al content in a carbon-free high modulus low-density light structural steel plate of the present invention is less than 4wt.%, and the production method uses a traditional cost-effective steel manufacturing route, and this light steel is a hot-rolled heterogeneous microstructure, characterized by a fully equiaxed austenite matrix embedded with slender delta ferrite bands and micron-sized TiB2 particles. In terms of physical properties, this light steel is a new type of low-density steel that achieves 6.88g / cm 3 The new steel has a low density while maintaining a high Young's modulus of 225GPa, resulting in a high specific modulus. Mechanically, the new steel has a yield strength that is nearly 100% higher than conventional Fe-TiB2 steel while maintaining good ductility, meeting the development needs of lightweight steel materials.

[0026] At the same time, the present invention optimizes the composition, reduces the Ti content from 5wt.% to 3.5wt.%, or adds a certain amount of Cr, and in situ self-generates two B-containing ceramic reinforcement phases (TiB2+M2B) in the light steel of the present invention. During the solidification process, the two phases compete for the B element, thereby achieving the refinement of the ceramic reinforcement phase particles, and during the solidification of the molten steel during processing, M2B effectively inhibits the floating of low-density TiB2 and the agglomeration phenomenon. When the specific modulus of this light steel is consistent with that of 5Ti wt.% high modulus low-density steel, the mechanical properties are greatly improved.

[0027] Therefore, this type of lightweight steel can maintain high plasticity while having sufficient ceramic content and a higher specific modulus, which can meet the needs of different usage scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a stress-strain curve diagram of a carbon-free high modulus low-density lightweight structural steel plate disclosed in Example 1 of the present disclosure;

[0029] Figure 2 This is a SEM image of the microstructure of a hot-rolled slab of a carbon-free, high modulus, low-density, lightweight structural steel plate disclosed in Example 1 of the present disclosure;

[0030] Figure 3 is a stress-strain curve diagram of a carbon-free high modulus low-density lightweight structural steel plate disclosed in Example 2 of the present disclosure;

[0031] Figure 4 is a SEM image of the as-cast microstructure of a carbon-free, high modulus, low-density lightweight structural steel plate disclosed in Example 2 of the present disclosure;

[0032] Figure 5 This is a SEM image of the microstructure of a hot-rolled slab of a carbon-free, high modulus, low-density lightweight structural steel plate disclosed in Example 2 of the present disclosure;

[0033] Figure 6 is a stress-strain curve diagram of a carbon-free high modulus low-density lightweight structural steel plate disclosed in Example 3 of the present disclosure;

[0034] Figure 7 is a stress-strain curve diagram of a carbon-free high modulus low-density lightweight structural steel plate disclosed in Example 4 of the present disclosure;

[0035] Figure 8 is a stress-strain curve diagram of a carbon-free high modulus low-density lightweight structural steel plate disclosed in Example 5 of the present disclosure;

[0036] Fig. 9 is a stress-strain curve diagram of a carbon-free high modulus low density lightweight structural steel plate disclosed in Example 6 of the present disclosure;

[0037] Fig.10 is a SEM image of the as-cast microstructure of a carbon-free high modulus low-density lightweight structural steel plate disclosed in Example 6 of the present disclosure;

[0038] Fig.11 This is a SEM image of the microstructure of a hot-rolled slab of a carbon-free, high modulus, low-density, lightweight structural steel plate disclosed in Example 6 of the present disclosure;

[0039] Fig.12 It is a heat treatment process curve diagram of a carbon-free high modulus low density light structural steel plate disclosed in Example 1 of the present disclosure;

[0040] Fig.13 is a heat treatment process curve diagram of a carbon-free, high modulus, low-density, lightweight structural steel plate disclosed in Example 5 of the present disclosure;

[0041] Fig.14 is a heat treatment process curve diagram of a carbon-free high modulus low density light structural steel plate disclosed in Example 4 of the present disclosure;

[0042] Fig.15 It is a heat treatment process curve diagram of a carbon-free high modulus low density lightweight structural steel plate disclosed in the present invention. DETAILED DESCRIPTION

[0043] Example 1

[0044] The components and weight percentages of the light steel in this embodiment are: Mn: 15.50%, Al: 3.95%, Ti: 5.00%, B: 2.15%, and the balance is Fe and impurities. The specific preparation method is as follows:

[0045] S1 is melted at 1650°C according to the alloy composition ratio of light steel and forged into a steel billet with a thickness of 30 mm;

[0046] S2 heats the steel billet to 1180°C and keeps it warm for 2h; the initial rolling temperature is 1130°C, the final rolling temperature is not less than 950°C, and the steel billet is hot-rolled into a 5mm thick sheet through 6 passes, and the hot-rolled sheet is air-cooled to room temperature;

[0047] like Figure 1 and Figure 2 As shown, the carbon-free high modulus low-density lightweight structural steel plate produced in this embodiment produces a hot-rolled heterogeneous microstructure through only the traditional steel manufacturing route, in which the fully equiaxed austenite matrix is ​​embedded with slender delta ferrite bands and micron-sized TiB2 particles, and the final matrix organization is an equiaxed austenite + high-temperature ferrite two-phase organization. Specifically, the Young's modulus is 225GPa and the density is 6.88g / cm 3 The yield strength is 503MPa, the tensile strength is 671MPa, and the total elongation is 15%.

[0048] Example 2

[0049] The components and weight percentages of the light steel in this embodiment are: Mn: 15.50%, Al: 3.7%, Ti: 3.50%, B: 2.15%, Nb: 0.2% and the remainder is Fe and impurities. The specific preparation method is as follows:

[0050] The difference compared with Example 1 is:

[0051] The thickness of the steel billet in S1 is 20 mm;

[0052] The heating temperature of the steel billet in S2 is 1100°C, wherein the initial rolling temperature is 1080°C, the final rolling temperature is not less than 900°C, and after 5 passes of hot rolling, the steel sheet is rolled into a 4mm thick sheet, and the hot-rolled steel sheet is air-cooled to room temperature.

[0053] The carbon-free high modulus low density light structural steel plate prepared in this embodiment has a Ti content reduced by 1.5wt.% compared with the composition of Example 1. Figure 4 As shown, M2B in the as-cast structure presents a fishbone-like eutectic structure; Figure 5 As shown, a hot rolled heterogeneous microstructure (high temperature ferrite + austenite + TiB2 + M2B) with a Young's modulus of 224 GPa and a density of 6.99 g / cm3 was produced through a conventional cost-effective steel manufacturing route. Figure 3 As shown, according to the engineering stress-strain curve of the slab, the yield strength is 442 MPa, the tensile strength is 695 MPa, and the total elongation is 18.3%.

[0054] Example 3

[0055] The components and weight percentages of the light steel in this embodiment are: Mn: 15.50%, Al: 3.7%, Ti: 3.50%, B: 2.15%, Nb: 0.2% and the remainder is Fe and impurities. The specific preparation method is as follows:

[0056] The difference compared with Example 1 is:

[0057] The thickness of the steel billet in S1 is 20 mm;

[0058] In S2, the heating temperature of the steel billet is 1100°C, wherein the initial rolling temperature is 1080°C, the final rolling temperature is not less than 900°C, and the steel billet is hot-rolled into a 4mm thick sheet through 5 passes, and the hot-rolled steel sheet is air-cooled to room temperature;

[0059] S3 puts the hot-rolled plate in S2 into a tubular resistance furnace at a temperature of 950°C for heat treatment, keeps the temperature for 5 minutes, and then air-cools to room temperature, finally obtaining a carbon-free high modulus lightweight hot-rolled annealed steel plate.

[0060] like Figure 6 As shown, the carbon-free high modulus low density light structural steel plate prepared in this embodiment has a yield strength of 389 MPa, a tensile strength of 691 MPa, and a total elongation of 26.6% according to the engineering stress-strain curve of the slab.

[0061] Example 4

[0062] The components and weight percentages of the light steel in this embodiment are: Mn: 15.50%, Al: 3.7%, Ti: 3.50%, B: 2.15%, Nb: 0.2% and the remainder is Fe and impurities. The specific preparation method is as follows:

[0063] The difference compared with Example 1 is:

[0064] The thickness of the steel billet in S1 is 20 mm;

[0065] In S2, the heating temperature of the steel billet is 1100°C, wherein the initial rolling temperature is 1080°C, the final rolling temperature is not less than 900°C, and the steel billet is hot-rolled into a 4mm thick sheet through 5 passes, and the hot-rolled steel sheet is air-cooled to room temperature;

[0066] S3: The hot-rolled plate in S2 is kept at 650°C for 4 hours, and then air-cooled to room temperature to obtain experimental steel;

[0067] S4 pickles the experimental steel in S3 with a hydrochloric acid and alcohol solution with a volume fraction of 1:1;

[0068] S5 uses a cold rolling mill to repeatedly roll the pickled experimental steel in S4 into a cold rolled steel plate with a thickness of 1.5 mm through multiple passes. The reduction amount of each pass in the rolling process is adjusted according to the rolling force of the rolling mill. During the rolling process, the rolling force on both sides of DS and OS is ensured not to exceed 400 kN, and the rolling speed is 3 mm / s;

[0069] S6 high temperature heat treatment for full austenitization: the cold rolled plate is placed in a tubular resistance furnace at a temperature of 950°C for heat treatment, kept warm for 5 minutes, and then air cooled to room temperature; followed by two-phase zone annealing treatment: the steel plate is placed in a tubular resistance furnace at a temperature of 600°C for heat treatment, kept warm for 1 hour, and then air cooled to room temperature, finally obtaining a carbon-free, high modulus, low-density, lightweight structural steel plate.

[0070] like Figure 7 and Fig.14As shown, the carbon-free high modulus lightweight cold-rolled steel plate obtained in this embodiment has a yield strength of 440 MPa, a tensile strength of 720 MPa, and a total elongation of 24% according to the engineering stress-strain curve of the slab. The specific process includes pre-annealing before cold rolling → cold rolling → short-time austenitization → critical zone annealing, wherein the pre-annealing temperature before cold rolling is between Ac1 and Ac3, and the purpose of annealing is to achieve the first pass of Mn element distribution, and the matrix structure is a three-phase structure of high-temperature ferrite + room-temperature ferrite + austenite to reduce the difficulty of rolling; wherein the short-time austenitization temperature is higher than Ac3, and the austenitization is air-cooled to room temperature, and the Mn element is partially recovered during the austenitization process; then the critical zone annealing temperature is between Ac1 and Ac3, and the air cooling is performed to room temperature. In this stage, the second pass of Mn element distribution is achieved, and it is enriched in the austenite, and finally the matrix is ​​obtained as an equiaxed austenite + high-temperature ferrite two-phase structure.

[0071] It can be understood that the cold rolling preparation method is more convenient to operate, the required reaction conditions are easy to achieve, and it is conducive to the efficient production of light steel.

[0072] Example 5

[0073] The components and weight percentages of the light steel in this embodiment are: Mn: 15.50%, Al: 3.7%, Ti: 3.50%, B: 2.15%, Nb: 0.2% and the remainder is Fe and impurities. The specific preparation method is as follows:

[0074] The difference compared with Example 1 is:

[0075] The thickness of the steel billet in S1 is 20 mm;

[0076] In S2, the heating temperature of the steel billet is 1100°C, wherein the initial rolling temperature is 1080°C, the final rolling temperature is not less than 900°C, and the steel billet is hot-rolled for 5 passes into a 4mm thick sheet; and the hot-rolled steel sheet is air-cooled to room temperature;

[0077] S3: The hot-rolled plate in S2 is kept at 950°C for 10 min, and then air-cooled to room temperature to obtain experimental steel;

[0078] S4 pickles the experimental steel in S3 with a hydrochloric acid and alcohol solution with a volume fraction of 1:1;

[0079] S5 uses liquid nitrogen cold rolling to repeatedly roll the steel plate into a cold-rolled steel plate with a thickness of 1.5 mm after multiple passes of the experimental steel plate after pickling in S4. The reduction amount of each pass in the rolling process is adjusted according to the rolling force of the rolling mill. During the rolling process, the rolling force on both sides of DS and OS is ensured not to exceed 400 kN, and the rolling speed is 3 mm / s;

[0080] S6 high temperature heat treatment for full austenitization: the cold rolled plate is placed in a tubular resistance furnace at a temperature of 1000°C for heat treatment, kept warm for 3 minutes, and then air-cooled to room temperature; finally, a carbon-free, high modulus, low-density, lightweight structural steel plate is obtained.

[0081] like Figure 8 and Fig.13 As shown, the carbon-free high modulus lightweight cold-rolled steel plate obtained in this embodiment has a yield strength of 349 MPa, a tensile strength of 682 MPa, and a total elongation of 32.7% according to the engineering stress-strain curve of the slab. The specific process includes pre-annealing before liquid nitrogen cold rolling → deep cold rolling → short-time austenitization, wherein the pre-annealing before liquid nitrogen cold rolling is higher than Ac3 to reduce the difficulty of rolling; after short-time austenitization, it is air-cooled to room temperature, and the Mn element is partially recovered during the austenitization process, and finally the matrix is ​​obtained as an equiaxed austenite + high-temperature ferrite two-phase structure.

[0082] It is understandable that light steel produced by liquid nitrogen cold rolling has better yield strength and tensile strength. The steel is softer and will not break easily when used in low temperature scenarios, ensuring the normal use of the steel.

[0083] Example 6

[0084] The components and weight percentages of the light steel in this embodiment are: Mn: 15.50%, Al: 3.4%, Cr: 3.4wt.%, Ti: 3.50%, B: 2.15%, Nb: 0.2%, and the balance is Fe and impurities. The specific preparation method is as follows:

[0085] The difference compared with Example 1 is:

[0086] The thickness of the steel billet in S1 is 20 mm;

[0087] In S2, the heating temperature of the steel billet is 1100°C, wherein the initial rolling temperature is 1080°C, the final rolling temperature is not less than 900°C, and the steel billet is hot-rolled into a 4.5 mm thick sheet through 5 passes, and the hot-rolled steel sheet is air-cooled to room temperature;

[0088] like Fig. 9 , Fig.10 and Fig.11 As shown, the carbon-free high modulus low density light structural steel plate prepared in this embodiment introduces 3wt.% Cr content and the M2B in the as-cast structure presents a fishbone eutectic structure. Specifically, the Young's modulus is 234 GPa and the density is 6.92 g / cm 3 The yield strength is 496MPa, the tensile strength is 753MPa, and the total elongation is 17%.

[0089] The contents explained in the above embodiments should be understood as these embodiments are only used to more clearly illustrate the present invention, and are not used to limit the scope of the present invention. Various equivalent modifications of the present invention by those skilled in the art fall within the scope defined by the claims attached to this application.

Claims

1. A carbon-free high modulus low density lightweight structural steel plate, characterized in that: The components of the light steel are as follows by weight: Mn: 10.0-16.0%, A1: 1.5-4.0%, Cr: 0.0-3.0%, Ti: 1.8-5.0%, B: 1.0-2.1%, Nb: 0.0-0.2%, and the balance is Fe and impurities; The Ti and B elements are added in the form of intermediate alloys, and the weight content of Ti in Fe-Ti is 40%, and the weight content of B in Fe-B is 19%.

2. The carbon-free high modulus low density lightweight structural steel plate according to claim 1, characterized in that: The Young's modulus of the light steel is 220-250 GPa, and the density is 6.88-7.45 g / cm 3 , the yield strength is 300-700MPa, the tensile strength is 600-865MPa, and the total elongation is 10-32%.

3. The carbon-free high modulus low density lightweight structural steel plate according to claim 1, characterized in that: The in-situ generated reinforcement phase of the light steel is TiB2 particles and / or M2B particles, and the volume fraction of the in-situ generated reinforcement phase is 3.3-17%.

4. The carbon-free high modulus low density lightweight structural steel plate according to claim 1, characterized in that: The in-situ generated reinforcement phase is TiB2 particles, and the volume fraction of the TiB2 particles is 1.2-13%; or The in-situ generated reinforcement phase is M2B particles, and the volume fraction of the M2B particles is 2-8%; or The in-situ generated reinforcement phase is TiB2 and M2B particles, and the volume fraction of the TiB2 particles and the M2B particles is 5-17%.

5. The carbon-free high modulus low density light structural steel plate according to claim 3, characterized in that: When the in-situ generated reinforcing phase is TiB2 particles, the chemical composition of the light steel is as follows in terms of weight percentage: Mn: 15.0-16.0%, A1: 3.9-4.0%, Ti: 4.8-5.0%, B: 1.9-2.1%, and the remainder is Fe and impurities.

6. The carbon-free high modulus low density light structural steel plate according to claim 3, characterized in that: When the in-situ generated reinforcing phase is TiB2 and M2B particles, the high modulus lightweight steel composition is as follows in weight percentage: Mn: 15.0-16.0%, A1: 1.5-3.7%, Cr: 0.0-3%, Ti: 1.8-3.5%, B: 1.0-2.1%, Nb: 0.0-0.2%, and the remainder is Fe and some inevitable impurity elements.

7. A method for preparing the light steel according to any one of claims 1 to 6, characterized in that: The steps include: S1. The light steel components are proportioned and smelted and cast to obtain a steel ingot, the steel ingot is heated to 1080-1180°C, kept warm for 2 hours, and the steel ingot is forged into a steel billet with a thickness of 20-30 mm; S2, heating the steel billet in S1 to 1080-1180°C, keeping the temperature for 2 hours, hot rolling it into a thin plate with a thickness of 3-5 mm through 6 passes, and cooling it to room temperature; Among them, the initial rolling temperature is 1050-1130°C, the final rolling temperature is not less than 800°C, and then air-cooled to room temperature; S3, pre-annealing the thin plate in S2, keeping the thin plate at 650° C. to 950° C. for 0.05 h to 4 h, and air-cooling to room temperature to obtain experimental steel; S4, pickling the experimental steel in S3 with a hydrochloric acid and alcohol solution with a volume fraction of 1:1; S51, cold-rolling the experimental steel pickled in S4 with liquid nitrogen to a thickness of 1 to 1.5 mm to obtain a first cold-rolled steel; S6. Heat-treating the first cold-rolled steel in S51 at 1000° C. for 3 minutes, and air-cooling to room temperature to obtain the light steel. S52, cold rolling the experimental steel pickled in S4 to a thickness of 1 to 1.5 mm to obtain a second cold-rolled steel; S7, heat-treating the second cold-rolled steel in S52, firstly performing full austenitizing heat treatment at 950°C for 0.8 to 5 minutes, then keeping the heat within the two-phase temperature range of 600 to 630°C for 1 to 4 hours, and air-cooling to room temperature to obtain the light steel.

8. The method according to claim 7, characterized in that In S2, S51 and S7, the volume fraction of austenite in the steel is 65-80%.

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