A 1000mpa grade low density medium manganese steel and a method of making the same

Abstract

This invention relates to a 1000 MPa grade low-density medium-manganese steel and its preparation method, belonging to the field of iron and steel metallurgy and metal material processing technology. The low-density medium-manganese steel is composed of the following chemical composition by mass percentage: C 0.80%~0.95%, Al 7.50%~9.30%, Mn 8.35%~12.87%, Si 0.55%~0.62%, B 0.001%~0.003%, P≤0.008%, S≤0.0012%, with the balance being Fe and unavoidable impurities. Based on Fe-Mn-Al-C series low-density medium-manganese steel, this invention optimizes the process to prepare a low-density medium-manganese steel with excellent comprehensive performance. The production cost is low, the preparation process is short, and the preparation method is simple and easy to implement. The obtained low-density medium-manganese steel not only has good elongation but also a tensile strength reaching 1000 MPa, making it suitable for the manufacture of automotive parts and further broadening its application prospects.

Description

A 1000MPa grade low-density medium-manganese steel and its preparation method Technical Field

[0001] This invention relates to a 1000 MPa grade low-density medium-manganese steel and its preparation method, belonging to the field of iron and steel metallurgy and metal material processing technology. Background Technology

[0002] With increasingly stringent global requirements for energy conservation and environmental protection, coupled with the pursuit of economic benefits, automotive lightweighting has become an urgent need and a key trend for future development in the automotive industry. The main approaches to achieving automotive lightweighting include adopting lightweight raw materials, using ultra-high-strength steel, and developing new high-strength, low-density medium-manganese steel. Common lightweight raw materials (such as aluminum alloys, magnesium alloys, engineering plastics, and carbon fiber composites) have limitations such as complex molding processes, high production costs, limited production scale, and insufficient overall performance. Therefore, developing a steel grade that integrates high strength, high elongation, and low density has become an effective way to solve these problems. Currently, new steels, represented by Fe-Mn-Al-C series high-strength, low-density medium-manganese steel, are gradually becoming ideal choices for automotive lightweighting materials due to their excellent mechanical properties and low density.

[0003] Traditional methods for preparing low-density, high-strength steel typically involve complex and multi-step smelting, processing, and heat treatment processes, while also adding expensive alloying elements (such as Mo, Ni, and Cr) to produce a steel that combines high strength, high elongation, and low density. Invention patent CN 108018494 B provides an annealing process for improving the strength and plasticity of low-density steel and a method for producing low-density steel. The alloy composition by mass percentage is: Mn 19.40~20.00%; Al 9.82~10.00%; C 0.98~1.00%; P≤0.003%; S≤0.003%, with the remainder being Fe and unavoidable impurities. After smelting, ingot casting, hot rolling, solution treatment, cold rolling, annealing (two austenitizing treatments), and aging treatment, a low-density steel with a yield strength of 920 MPa, a tensile strength of 1080 MPa, and an elongation after fracture of 48% is obtained. This process involves numerous heat treatment steps and is complex. Invention patent CN 113278896 B provides a Fe-Mn-Al-C high-strength low-density steel and its preparation method. The alloy composition by mass percentage is: C 1.0~2.0%, Mn 20~40%, Al... The alloy composition consists of 10-14% Ni+Cr≤15%. To further improve the steel's performance, the following components were added: Mo 0.10-1.00%, Si 0.20-2.00%, Cu 0.50-2.50%, B 0.001-0.005%, Nb 0.05-0.50%, Ti 0.02-0.50%, V 0.02-0.35%, RE 0.001-0.005%, Ca 0.005-0.025%, with the balance being Fe. After smelting, solidification casting, hot working (forging / rolling), and solution treatment, a low-density steel with a tensile strength of 1000 MPa was obtained. Although the above invention has a simple process, the use of various precious alloying elements (Ni, Cr, Mo, RE, Nb, etc.) in the alloy composition design significantly increases the product cost. Invention patent CN 116065081 B provides a 1000 MPa grade low-density steel plate and its preparation method. The alloy composition by mass percentage is: C 0.31%~0.34%; Mn 12.1%~12.5%; Al 8.51%~8.55%; Ni 10.0%~15.0%; P 0.005%~0.008%; S 0.001%~0.002%; H 0.0004%~0.0005%; O 0.001%~0.008%; N 0.003%~0.005%, with the remainder being Fe and unavoidable impurity elements. After smelting, casting, high-temperature homogenization, finishing, forging, solution treatment, quenching, and aging treatment, a low-density steel with a tensile strength of 1000 MPa is obtained. The above-mentioned invention process not only has many heat treatment steps and is complex, but also contains Ni, a high-cost alloying element, in its alloy composition.Therefore, it is necessary to further optimize the alloy composition and preparation process to reduce production costs and improve the overall performance of the material to meet the diverse needs of practical applications. Summary of the Invention

[0004] To address the aforementioned problems in existing technologies, this invention provides a 1000 MPa grade low-density medium-manganese steel and its preparation method. Based on Fe-Mn-Al-C series low-density medium-manganese steel, this invention selects economical alloying elements B and Si. By adjusting the alloy composition, processing technology, and quenching parameters, a high-strength, high-elongation, and low-density medium-manganese steel is prepared. This method features low production cost, a short preparation process, and simple and easy implementation, making it particularly suitable for the manufacture of automotive parts, demonstrating good economic viability and application prospects.

[0005] A 1000 MPa grade low-density medium-manganese steel is composed of the following chemical composition by mass percentage: C 0.80%~0.95%, Al 7.50%~9.30%, Mn 8.35%~12.87%, Si 0.55%~0.62%, B 0.001%~0.003%, P≤0.008%, S≤0.0012%, with the balance being Fe and unavoidable impurities.

[0006] Furthermore, the microstructure of the low-density medium-manganese steel is a three-dimensional interpenetrating network structure composed of ferrite and austenite, wherein the mass percentage of austenite is 60%~75% and the mass percentage of ferrite is 20%~30%.

[0007] Furthermore, the low-density medium-manganese steel has a yield strength of 810~864 MPa, a tensile strength of 1000~1038 MPa, an elongation after fracture of 25%~33%, and a density of 6.62~6.96 g / cm³. 3 .

[0008] The main functions of each chemical component in the 1000 MPa grade low-density medium-manganese steel described in this invention are as follows:

[0009] C: C added to low-density steel is one of the most important alloying elements in steel. It mainly improves the strength of steel through solid solution strengthening. The appropriate addition of C helps to increase the hardenability of steel and improve the strengthening effect during heat treatment.

[0010] Mn: The addition of Mn can improve the strength of steel through solid solution strengthening, promote the stability of the austenite phase, help achieve excellent ductility and plasticity, and also promote the high-temperature oxidation resistance and thermal stability of steel.

[0011] Al: As a low-density element, Al is a key alloying element for achieving lightweight steel. Its addition not only helps to significantly reduce the density of the material, but also effectively increases the stacking fault energy of austenite, thereby inhibiting the martensitic phase transformation. This allows the steel to maintain a stable austenitic structure even after being cooled to room temperature relatively quickly, thus improving the plasticity of the material. In addition, Al helps to enhance the stability of the high-temperature structure, inhibit carbide precipitation, improve corrosion resistance, and to a certain extent, has a positive effect on grain refinement, while also increasing the strength of the steel.

[0012] Si: Si can promote the formation of ferrite in low-density medium-manganese steel, enhance the steel's oxidation resistance, and improve the steel's thermal stability. An appropriate amount of Si can accelerate the formation kinetics of κ-carbides and increase the C distribution coefficient, promoting the enrichment of C into κ-carbides, resulting in local dislocation slip and dynamic strain aging phenomena during deformation, thereby enhancing the strengthening effect and improving the steel's wear resistance and high-temperature resistance.

[0013] B: Trace amounts of boron (B) can significantly improve the hardenability of steel and optimize its heat treatment properties. B can inhibit the growth of initial austenite grains through grain boundary segregation and the precipitation of boron carbides, refine the microstructure, and improve the stability of austenite, thereby improving the strength and hardness of steel. The addition of B can regulate the distribution of κ-carbides, thereby reducing the tendency for edge cracking during hot rolling. In addition, B promotes the distribution of carbon from martensite to austenite and ferrite during heat treatment, improves the uniformity of microstructure, and reduces stress concentration, thereby improving fracture toughness.

[0014] P and S: P and S are harmful impurity elements in steel, which can seriously affect the strength, toughness and corrosion resistance of steel. Their content must be strictly controlled during the smelting process to minimize it. Therefore, this invention controls the content of P to below 0.008% and the content of S to below 0.0012%.

[0015] Another object of the present invention is to provide a method for preparing the above-mentioned 1000 MPa grade low-density medium-manganese steel, including batching, vacuum smelting and casting, controlled rolling and cooling, and quenching treatment processes. The controlled rolling and cooling process includes heat treatment, rough rolling, finish rolling and cooling steps. The quenching treatment process involves treating the rolled steel billet at 780~820℃ for 20 min and then rapidly water cooling it to room temperature.

[0016] In the above technical solution, the vacuum smelting and casting process involves heating and melting the prepared raw materials to obtain liquid metal, which is then poured into a casting mold and cooled to obtain an ingot with a thickness of 120~180 mm.

[0017] In the above technical solution, the heat treatment step in the controlled rolling and cooling process involves heating the ingot in a homogenizing furnace at a heating rate of 10℃ / min, holding it in the furnace for 0.5 min / mm, and tapping the steel at a temperature of 1100~1150℃.

[0018] In the above technical solution, the rough rolling step in the controlled rolling and cooling process involves rough rolling the heat-treated ingot using a large reduction method. The initial rolling temperature is 1050~1100℃, and the rolling is performed in 5 passes. The reduction rate of the last 3 passes is ≥20%, and the cumulative compression ratio is 60%.

[0019] Furthermore, the thickness of the ingot obtained after rough rolling is 50~70 mm.

[0020] In the above technical solution, the finishing rolling step in the controlled rolling and cooling process involves finishing rolling the ingot obtained after rough rolling. The initial rolling temperature is 880~950℃, the final rolling temperature is 780~810℃, and it is rolled in 12 passes with a reduction rate of 11%~20% per pass, resulting in a cumulative reduction rate of 85%~91%. The initial cooling temperature after finishing rolling is 750~810℃.

[0021] In the above technical solution, the cooling step in the controlled rolling and cooling process involves cooling the ingot obtained after precision rolling to room temperature using laminar flow cooling to obtain a rolled steel billet with a thickness of 5~10 mm.

[0022] The 1000 MPa grade low-density medium-manganese steel designed in this invention avoids the use of high-cost precious metal elements by rationally optimizing the alloy composition design, and selects economical alloying elements B and Si. Combined with simplified production processes (smelting and casting, controlled rolling and cooling, and quenching treatment), it effectively reduces production costs and process complexity while ensuring excellent comprehensive performance of material strength, plasticity and density, showing good economic benefits and application prospects.

[0023] The beneficial effects of this invention are:

[0024] In terms of alloy composition design, this invention is based on Fe-Mn-Al-C system low-density medium-manganese steel. It uses the basic design concept of low-cost alloying elements such as B and Si, and prepares low-density medium-manganese steel with excellent comprehensive performance through smelting and casting, controlled rolling and cooling and one quenching treatment. This invention has low production cost, short preparation process and simple and easy preparation method. The resulting low-density medium-manganese steel can achieve a tensile strength of 1000 MPa while ensuring good elongation, and has the advantages of high strength and good toughness.

[0025] This invention successfully prepared a dual-phase lightweight steel with a gradient strengthening phase distribution through a specific process. After quenching, the steel forms a three-dimensional interpenetrating network structure with recrystallized austenite as the continuous matrix and multi-scale ferrite as the reinforcing phase. δ-ferrite bands oriented along the rolling direction improve load distribution efficiency through interfacial stress transfer mechanisms; granular α-ferrite dispersed at the austenite grain boundaries inhibits grain coarsening through the Zener pinning effect; and a large number of small-sized κ-carbides precipitate uniformly, forming high-density strengthening phase particles. This synergistic effect of the multi-scale microstructure achieves superimposed enhancement through fine-grain strengthening and precipitation strengthening, enabling the medium-manganese steel material obtained by this invention to maintain high strength while retaining elongation.

[0026] The alloying elements used in this invention have low cost and simple preparation process, resulting in products with stable performance and good potential for industrial production, making them easy to apply and promote. Attached Figure Description

[0027] Figure 1 is a flowchart of the preparation process of the low-density medium-manganese steel obtained by the present invention.

[0028] Figure 2 is a stress-strain curve of the steel in Embodiment 4 of the present invention.

[0029] Figure 3 is a microstructure diagram of the steel in Example 4 of the present invention. Detailed Implementation

[0030] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way.

[0031] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0032] One of the specific implementation methods:

[0033] A method for preparing 1000 MPa grade low-density medium-manganese steel specifically includes the following steps:

[0034] (1) Ingredients: Weigh the raw materials according to the following mass percentages: C 0.80%~0.95%, Al 7.50%~9.30%, Mn 8.35%~12.87%, Si 0.55%~0.62%, B 0.001%~0.003%, P≤0.008%, S≤0.0012%, with the balance being Fe and unavoidable impurities;

[0035] (2) Vacuum smelting and casting: The raw materials prepared in step (1) are placed into a vacuum smelting furnace for heating and melting. The molten metal obtained by smelting is poured into a casting mold and cooled to obtain a low-density medium manganese steel ingot with a thickness of 120~180 mm.

[0036] (3) Controlled rolling and cooling: The ingot obtained in step (2) is heated in a soaking furnace at a heating rate of 10℃ / min and a holding time of 0.5 min / mm. The tapping temperature is 1100~1150℃. Then, a two-stage rolling process of roughing and finishing is adopted. The roughing rolling start temperature is 1050~1100℃. After 5 passes, the reduction rate of the last three passes is ≥20%. Large reduction rolling is adopted. The cumulative reduction of roughing is 58~63%. The finishing rolling start temperature is 880~950℃ and the finishing rolling temperature is 780~810℃. After 12 passes, the reduction rate of each pass is 11%~20%, and the cumulative reduction rate is 85~91%. The initial cooling temperature after finishing is 750~810℃. After rolling, laminar flow cooling is adopted to cool to room temperature to obtain a rolled steel billet with a thickness of 5~10 mm.

[0037] (4) Quenching treatment: The rolled steel billet is heated in a high-temperature furnace at a temperature of 780~820℃ for 20 min, and then rapidly water-cooled to room temperature to obtain a 1000 MPa grade low-density medium manganese steel product with a thickness of 5~10 mm.

[0038] In the method of the present invention, in step (3), the thickness of the ingot obtained after rough rolling is 50~70 mm.

[0039] In the method described in this invention, the yield strength of the 1000 MPa grade low-density medium-manganese steel product is 810~864 MPa, the tensile strength is 1000~1038 MPa, the elongation after fracture is 25%~33%, and the density is 6.62~6.96 g / cm³. 3 .

[0040] Example 1

[0041] A method for preparing 1000 MPa grade low-density medium-manganese steel with a thickness of 5 mm specifically includes the following steps:

[0042] (1) Ingredients: Ingredients were prepared according to the chemical composition of Example 1 given in Table 1;

[0043] (2) Smelting and casting: The prepared materials are placed in a vacuum smelting furnace for heating and melting. The molten metal obtained from smelting is poured into a casting mold and cooled to obtain a low-density medium-manganese steel ingot with a thickness of 120 mm.

[0044] (3) Controlled rolling and cooling: The 120 mm thick ingot obtained above is heated in a soaking furnace for 60 min and the tapping temperature is 1100℃. Then rough rolling and finish rolling are carried out. The initial rolling temperature of the rough rolling stage is 1050℃. After 5 passes of rolling, the cumulative reduction ratio of the rough rolling is 58%, and the thickness of the intermediate billet is 50.4 mm. The initial rolling temperature of the finish rolling stage is 880℃. After 12 passes of rolling, the final rolling temperature is 780℃ and the cumulative reduction rate of the finish rolling is 90.1%. The initial cooling temperature after the finish rolling is 750℃~780℃. After rolling, laminar flow cooling is used to cool to room temperature to obtain a rolled steel billet with a thickness of 5 mm.

[0045] (4) Quenching treatment: The rolled steel billet with a thickness of 5 mm obtained above is heated in a high-temperature furnace at a temperature of 780°C for 20 min, and then rapidly water-cooled to room temperature to obtain a 1000 MPa grade low-density medium manganese steel with a thickness of 5 mm.

[0046] Examples 2-5

[0047] The difference between Examples 2-5 and Example 1 is that the mass percentage of chemical components in step (1) and the process parameters in steps (2)-(4) are different. The specific mass percentage is shown in Table 1 and the process parameters are shown in Table 2.

[0048] Examples 6-7

[0049] A method for preparing 1000 MPa grade low-density medium-manganese steel with thicknesses of 8 mm and 10 mm specifically includes the following steps:

[0050] (1) Ingredients: Ingredients were prepared according to the chemical composition of Examples 6 and 7 given in Table 1;

[0051] (2) Smelting and casting: The prepared materials are placed into a vacuum smelting furnace for heating and melting. The molten metal obtained from smelting is poured into casting molds. After cooling, low-density medium-manganese steel ingots with thicknesses of 160 mm and 180 mm are obtained.

[0052] (3) Controlled rolling and cooling: 160 mm and 180 mm thick ingots were heated in a soaking furnace for 60 min and 90 min respectively, and the tapping temperatures were 1138℃ and 1150℃ respectively. Then rough rolling and finish rolling were carried out. The starting rolling temperature in the rough rolling stage was 1085℃ and 1100℃ respectively. After 5 passes of rolling, the cumulative reduction rates were 61.5% and 62.1% respectively, and the thicknesses of the intermediate billets were 61.6 mm and 68.6 mm respectively. The starting rolling temperature in the finish rolling stage was 900℃ and 950℃. After 12 passes of rolling, the cumulative reduction rates were 87% and 85.4% respectively, and the final rolling temperatures were 790℃ and 810℃ respectively. The initial cooling temperatures after finish rolling were 780℃ and 810℃ respectively. After rolling, laminar flow cooling was used to cool to room temperature to obtain rolled steel billets with thicknesses of 8 mm and 10 mm respectively.

[0053] (4) Quenching treatment: Rolled steel billets with thicknesses of 8 mm and 10 mm are heated in a high-temperature furnace at temperatures of 800℃ and 820℃ respectively, and the heat treatment time is 20 min for each. Then they are rapidly water-cooled to room temperature to obtain 1000 MPa grade low-density medium manganese steel with thicknesses of 8 mm and 10 mm respectively.

[0054] Comparative Example 1

[0055] The main difference between this comparative example and Example 1 is that the quenching temperature in this comparative example is 750°C.

[0056] Comparative Example 2

[0057] The main difference between this comparative example and Example 1 is that the quenching temperature in this comparative example is 850°C.

[0058] Comparative Example 3

[0059] The main difference between this comparative example and Example 1 is that the content of the alloying element Si in this comparative example is 0.30%.

[0060] Comparative Example 4

[0061] The main difference between this comparative example and Example 1 is that the content of alloying element C in this comparative example is 0.50%.

[0062] The chemical composition of the steels obtained in Examples 1-7 and Comparative Examples 1-4 of this invention is shown in Table 1, the main process parameters are shown in Table 2, and the performance tests are conducted in accordance with GB / T 228.1-2021. The yield strength, tensile strength, and elongation after fracture of the steels obtained above are tested, and the mechanical property results are shown in Table 3.

[0063] Table 1 Chemical composition (mass percentage) of the examples and comparative examples

[0064]

[0065] Table 2. Process parameters for the examples and comparative examples

[0066]

[0067] Table 3 Performance parameters of manganese steel obtained from the examples and comparative examples

[0068]

[0069] Figure 2 is a stress-strain curve of the steel in Example 4 of the present invention. It can be seen that the steel obtained in Example 4 has a good strength and toughness match. Its yield strength is 855 MPa, its tensile strength is 1027 MPa, and its elongation after fracture is 25.2%. This shows that the material has a certain plasticity while maintaining high strength, and exhibits excellent comprehensive mechanical properties.

[0070] Figure 3 shows the microstructure of the steel in Example 4 of this invention. It can be seen that the microstructure of the steel obtained in Example 4 mainly consists of a continuous matrix of recrystallized austenite, with multi-scale ferrite distributed within the phase, forming an interpenetrating network structure. Specifically, banded δ-ferrite is oriented along the rolling direction, enhancing the anisotropic strengthening characteristics of the microstructure; granular α-ferrite is dispersed at the austenite grain boundaries, effectively pinning austenite grains, inhibiting the growth of recrystallized grains, and improving the stability of the microstructure. Furthermore, a large number of fine κ-carbides precipitate uniformly in the austenite matrix, forming high-density strengthening particles, significantly improving the overall strength level of the material.

[0071] This multiphase microstructure system, composed of recrystallized austenite, δ / α-ferrite, and κ-carbide, achieves synergistic control of grain refinement, uniform distribution of strengthening phases, and stress-coordinated deformation, ensuring high strength while also maintaining good ductility.

[0072] The comparison between Example 1 and Comparative Examples 1 and 2 shows that the proper control of quenching temperature has a decisive influence on the mechanical properties of the experimental steel. When the quenching temperature is too high, the austenite grains grow significantly, the number of grain boundaries decreases, and the proportion of large-angle grain boundaries increases. Although this can improve the elongation of the material to a certain extent, the yield strength and tensile strength caused by grain coarsening decrease significantly, resulting in a deterioration of the overall mechanical properties. Conversely, when the quenching temperature is too low, austenitization is insufficient, leading to a high content of residual ferrite in the matrix and a large amount of undissolved carbides. The synergistic effect of these two factors will cause a double reduction in the strength and plasticity of the material, which is not conducive to performance optimization.

[0073] A comparison of Example 1 and Comparative Example 3 shows that a decrease in Si content also has an adverse effect on microstructure evolution and properties. As a typical ferrite-forming element, a decrease in Si content will inhibit ferrite formation, thereby weakening the thermal stability of the experimental steel. Simultaneously, a decrease in Si will also affect the precipitation behavior of κ-carbides, slowing down their precipitation kinetics and causing carbides to coarsen during high-temperature residence, thus hindering the refinement of precipitation strengthening effects and ultimately negatively impacting mechanical properties.

[0074] A comparison of Example 1 and Comparative Example 4 shows that, as a strong austenite stabilizing element, a decrease in C content weakens the thermal stability of austenite, leading to a decrease in austenite content and an increase in the proportion of δ-ferrite, thereby reducing the material's plasticity. Simultaneously, a decrease in C also inhibits the precipitation of κ-carbides, weakening the precipitation strengthening mechanism and resulting in a decrease in material strength. Furthermore, a lower C content is also detrimental to the deformation-induced martensitic transformation (TRIP effect), reducing strain hardening capacity and ductility.

Claims

1. A 1000 MPa grade low-density medium-manganese steel, characterized in that: The low-density medium-manganese steel is composed of the following chemical composition by mass percentage: C 0.80%~0.95%, Al 7.50%~9.30%, Mn 8.35%~12.87%, Si 0.55%~0.62%, B 0.001%~0.003%, P≤0.008%, S≤0.0012%, with the balance being Fe and unavoidable impurities. The microstructure of the low-density medium-manganese steel is a three-dimensional interpenetrating network structure composed of ferrite and austenite, and a multiphase microstructure system composed of κ-carbides, wherein the mass percentage of austenite is 60%~75%, and the mass percentage of ferrite is 20%~30%. The yield strength of the low-density medium-manganese steel is 810~864 MPa, the tensile strength is 1000~1038 MPa, the elongation after fracture is 25%~33%, and the density is 6.62~6.96 g / cm³. 3 The preparation method of the low-density medium-manganese steel includes batching, vacuum smelting and casting, controlled rolling and cooling, and quenching processes. The controlled rolling and cooling process includes heat treatment, rough rolling, finish rolling and cooling steps. The quenching process involves treating the rolled steel billet at 780~820℃ for 20 min and then rapidly water cooling it to room temperature.

2. The 1000 MPa grade low-density medium-manganese steel according to claim 1, characterized in that: The vacuum smelting and casting process involves heating and melting the prepared raw materials to obtain molten metal, which is then poured into a casting mold and cooled to obtain an ingot with a thickness of 120-180 mm.

3. The 1000 MPa grade low-density medium-manganese steel according to claim 1, characterized in that: In the heat treatment step of the controlled rolling and cooling process, the ingot is heated in a soaking furnace at a heating rate of 10℃ / min, the holding time in the furnace is 0.5min / mm, and the tapping temperature is 1100~1150℃.

4. The 1000 MPa grade low-density medium-manganese steel according to claim 1, characterized in that: In the controlled rolling and cooling process, the rough rolling step involves rough rolling the heat-treated ingot using a large reduction method. The initial rolling temperature is 1050~1100℃, and the rolling is performed in 5 passes. The reduction rate of the last 3 passes is ≥20%, and the cumulative compression ratio is 60%.

5. The 1000 MPa grade low-density medium-manganese steel according to claim 1, characterized in that: The thickness of the ingot obtained after rough rolling is 50~70 mm.

6. The 1000 MPa grade low-density medium-manganese steel according to claim 1, characterized in that: In the controlled rolling and cooling process, the ingot obtained after rough rolling is subjected to finish rolling. The initial rolling temperature is 880~950℃, the final rolling temperature is 780~810℃, and it is rolled in 12 passes with a reduction rate of 11%~20% per pass, resulting in a cumulative reduction rate of 85%~91%. The initial cooling temperature after finish rolling is 750~810℃.

7. The 1000 MPa grade low-density medium-manganese steel according to claim 1, characterized in that: In the controlled rolling and controlled cooling process, the ingot obtained after precision rolling is cooled to room temperature using laminar flow cooling to obtain a rolled steel billet with a thickness of 5~10 mm.

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