High-strength hot-rolled medium manganese steel and preparation method thereof

Abstract

The invention belongs to the technical field of heat treatment of metal materials, and relates to high-strength hot-rolled medium manganese steel and a preparation method of the high-strength hot-rolled medium manganese steel. A matrix structure of the obtained high-strength hot-rolled medium manganese steel comprises 49-61 vol% of austenite and 39-51 vol% of martensite, a precipitated phase is a cementite and vanadium carbide double-nanometer precipitated phase, and the yield strength of the high-strength hot-rolled medium manganese steel at the room temperature is 850-920 MPa, the tensile strength is 1190-1570 MPa, and the ductility is 14.5-19.0%.

Description

Technical Field

[0001] The present invention relates to the technical field of heat treatment of metal materials, and particularly to a high-strength hot-rolled medium manganese steel and a preparation method thereof. Background Art

[0002] With the rapid development of the automotive industry, problems such as excessive energy consumption and serious environmental pollution have emerged one after another, and the lightweight of automotive steel has become extremely urgent. Medium manganese steel has the advantages of low price, good economy and excellent mechanical properties, and it is also called the new generation of high-strength steel for automobiles. The design idea of medium manganese steel is to use metastable austenite with excellent strain hardening ability and ferrite with good plasticity as the matrix structure, and improve the comprehensive mechanical properties of the material through transformation-induced plasticity (TRIP effect), twinning-induced plasticity (TWIP effect) occurring during the deformation stage of austenite, and the coordinated deformation of ferrite. Since the strength of medium manganese steel with austenite and ferrite as the sole matrix structure is limited, processes such as quenching-partitioning, quenching-partitioning-tempering, quenching-partitioning-annealing-tempering, etc. are used to regulate the microstructure of medium manganese steel, and the strength of medium manganese steel is increased by introducing pearlite and bainite, etc. into the medium manganese steel. However, long-time heat treatment not only reduces production efficiency, but also causes grain growth, coarsening of precipitated particles, reduction of dislocation density, etc., resulting in limited strength improvement.

[0003] The Chinese invention patent with the publication number CN107475618B discloses a method for regulating the microstructure of medium manganese steel by adopting a complex cycle quenching + critical annealing process. The cycle quenching temperature and critical annealing temperature of this method are as high as 900 °C and 750 °C, respectively, resulting in limited improvement in its mechanical properties. The yield strength is 545 - 601 MPa, and the tensile strength is 835 - 1030 MPa. The Chinese invention patent with the publication number CN109930078B discloses a method for regulating the microstructure of medium manganese steel by adopting a two-step quenching + low-temperature tempering process. Although the medium manganese steel prepared by this method exhibits excellent comprehensive mechanical properties (tensile strength product > 70 GPa%), its tensile strength is relatively low (< 900 MPa). In addition, the two quenching temperatures are 750 °C and 700 °C respectively, and the complex step-by-step heat treatment process increases the difficulty of industrial production. The Chinese invention patent with the publication number CN111996465B discloses a method for regulating the microstructure of medium manganese steel by adopting quenching + tempering. The yield strength of the medium manganese steel prepared by this method is 500 - 900 MPa, and the tensile strength is 1410 - 1680 MPa. However, its high strength is mainly related to the carbon content as high as 0.75 - 0.80 wt% in this medium manganese steel, and the high carbon content is not conducive to subsequent processing such as galvanizing and welding of medium manganese steel sheets for automobiles. The Chinese invention patent application with the publication number CN116904720A discloses a method for regulating the microstructure of medium manganese steel by adopting critical region annealing + isothermal treatment in the bainite region. The hot-rolled medium manganese steel is cooled to the bainite phase region temperature of 250 - 400 °C for isothermal treatment after critical annealing at 750 - 810 °C, obtaining a microstructure with 30 - 60% ferrite, 10 - 40% bainite ferrite, and 15 - 25% retained austenite. However, the low volume fraction of austenite and high volume fraction of ferrite result in its relatively low yield strength (565 - 633 MPa) and tensile strength (986 - 1075 MPa). In addition, the addition of 0.5 - 1.5 wt% silicon element also does not significantly contribute to the strength of medium manganese steel. Therefore, the prior art cannot well meet the strength requirements of hot-rolled medium manganese steel. Summary of the Invention

[0004] To solve the problems existing in the prior art, the main object of the present invention is to propose a high-strength hot-rolled medium manganese steel and a preparation method thereof.

[0005] To solve the above technical problems, according to one aspect of the present invention, the following technical solutions are provided:

[0006] A preparation method of a high-strength hot-rolled medium manganese steel, comprising the following steps:

[0007] S1. Homogenization annealing: The medium manganese steel ingot is subjected to homogenization annealing to obtain an annealed ingot;

[0008] S2. Hot rolling: The annealed ingot is hot-rolled and water-cooled to room temperature to obtain a hot-rolled plate;

[0009] S3. Continuous heat treatment: The hot-rolled sheet is subjected to high-temperature annealing in the dual-phase region + tempering in the martensite phase region:

[0010] S31. High-temperature annealing in the dual-phase region: The hot-rolled sheet is heat-insulated in the way of entering the furnace when reaching the temperature, and then rapidly cooled to the temperature of the martensite phase region;

[0011] S32. Tempering in the martensite phase region: Heat-insulate at the temperature of the martensite phase region, and then air-cool to room temperature; High-strength hot-rolled medium manganese steel is obtained.

[0012] As a preferred embodiment of the preparation method of the high-strength hot-rolled medium manganese steel described in the present invention, wherein: the high-strength hot-rolled medium manganese steel, by mass percentage, includes: C: 0.35 - 0.50%, Mn: 9.5 - 11.0%, Al: 2.0 - 3.0%, V: 0.5 - 0.7%, and the balance is Fe and inevitable impurities.

[0013] As a preferred embodiment of the preparation method of the high-strength hot-rolled medium manganese steel described in the present invention, wherein: before the step S1, there is also included S0. Melting the medium manganese steel ingot: Prepare the ingredients according to the composition of the medium manganese steel, and add them to the furnace cavity of the vacuum induction melting furnace in turn according to the order of the melting points of each element from low to high. The melting temperature is 1400 - 1500°C. After melting, cast into an ingot in a mold and air-cool to room temperature.

[0014] As a preferred embodiment of the preparation method of the high-strength hot-rolled medium manganese steel described in the present invention, wherein: in the step S1, the annealing temperature is 1100 - 1150°C, the annealing time is 2 - 4 h, and the cooling method is air cooling.

[0015] As a preferred embodiment of the preparation method of the high-strength hot-rolled medium manganese steel described in the present invention, wherein: in the step S2, the starting rolling temperature is 1000 - 1050°C, the final rolling temperature is 950 - 1000°C; The hot rolling is divided into 3 - 4 passes, and the total deformation amount of the hot rolling is 65 - 75%.

[0016] As a preferred embodiment of the preparation method of the high-strength hot-rolled medium manganese steel described in the present invention, wherein: in the step S31, the heat-insulating temperature is 700 - 750°C, the heat-insulating time is 10 - 50 min; The cooling rate is not less than 30°C / s.

[0017] As a preferred embodiment of the preparation method of the high-strength hot-rolled medium manganese steel described in the present invention, wherein: in the step S32, the heat-insulating temperature is 180 - 240°C, the heat-insulating time is 30 - 120 min.

[0018] To solve the above technical problems, according to another aspect of the present invention, the present invention provides the following technical solutions:

[0019] A high-strength hot-rolled medium manganese steel is prepared by using the preparation method of the above-mentioned high-strength hot-rolled medium manganese steel.

[0020] As a preferred embodiment of the high-strength hot-rolled medium manganese steel described in the present invention, wherein: the yield strength of the hot-rolled medium manganese steel at room temperature is 850-920 MPa, the tensile strength is 1190-1570 MPa, and the elongation is 14.5-19.0%.

[0021] As a preferred embodiment of the high-strength hot-rolled medium manganese steel described in the present invention, wherein: the matrix structure of the high-strength hot-rolled medium manganese steel includes 49-61 vol% austenite and 39-51 vol% martensite, and the precipitation phases are cementite and vanadium carbide double-nano precipitation phases.

[0022] The beneficial effects of the present invention are as follows:

[0023] The present invention provides a high-strength hot-rolled medium manganese steel and a preparation method thereof. By adopting a continuous heat treatment process of homogenization annealing, hot rolling, high-temperature annealing in the two-phase region + tempering in the martensite phase region, through reasonable chemical composition and process design, the matrix structure of the obtained high-strength hot-rolled medium manganese steel includes 49-61 vol% austenite and 39-51 vol% martensite, and the precipitation phases are cementite and vanadium carbide double-nano precipitation phases. The high-strength hot-rolled medium manganese steel has a yield strength of 850-920 MPa, a tensile strength of 1190-1570 MPa, and an elongation of 14.5-19.0% at room temperature. Brief Description of the Drawings

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0025] Figure 1 SEM diagram of the hot-rolled medium manganese steel of Embodiment 1 of the present invention;

[0026] Figure 2 SEM diagram of the hot-rolled medium manganese steel of Embodiment 2 of the present invention;

[0027] Figure 3 SEM and TEM diagrams of the hot-rolled medium manganese steel of Embodiment 3 of the present invention.

[0028] The realization, functional characteristics and advantages of the object of the present invention will be further described in conjunction with the embodiments and with reference to the drawings. Detailed Embodiments

[0029] The technical solutions in the embodiments will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0030] According to one aspect of the present invention, the present invention provides the following technical solutions:

[0031] A preparation method of a high-strength hot-rolled medium manganese steel, comprising the following steps:

[0032] S1. Homogenization annealing: The medium manganese steel ingot is subjected to homogenization annealing to obtain an annealed ingot;

[0033] S2. Hot rolling: The annealed ingot is hot-rolled and water-cooled to room temperature to obtain a hot-rolled plate;

[0034] S3. Continuous heat treatment: The hot-rolled plate is subjected to high-temperature annealing in the dual-phase region + tempering in the martensite phase region:

[0035] S31. High-temperature annealing in the dual-phase region: The hot-rolled plate is heat-insulated in a way of being put into the furnace when reaching the temperature, and then rapidly cooled to the temperature of the martensite phase region;

[0036] S32. Tempering in the martensite phase region: Heat-insulation is carried out at the temperature of the martensite phase region, and then air-cooled to room temperature; the high-strength hot-rolled medium manganese steel is obtained.

[0037] Preferably, the high-strength hot-rolled medium manganese steel, by mass percentage, comprises: C: 0.35-0.50%, Mn: 9.5-11.0%, Al: 2.0-3.0%, V: 0.5-0.7%, and the balance is Fe and unavoidable impurities.

[0038] Preferably, before the step S1, it further includes S0. Melting the medium manganese steel ingot: Prepare the ingredients according to the composition of the medium manganese steel, and add them to the furnace cavity of the vacuum induction melting furnace in the order of increasing melting points of each element. The melting temperature is 1400-1500°C. After melting, it is cast into an ingot in a mold and air-cooled to room temperature. Specifically, the melting temperature can be any one or the range between any two of, for example, 1400°C, 1420°C, 1440°C, 1460°C, 1480°C, 1500°C.

[0039] Preferably, in the step S1, the annealing temperature is 1100-1150 °C, the annealing time is 2-4 h, and the cooling method is air cooling. Specifically, the annealing temperature can be, for example, any one of 1100 °C, 1110 °C, 1120 °C, 1130 °C, 1140 °C, 1150 °C or the range between any two of them; the annealing time can be, for example, any one of 2 h, 3 h, 4 h or the range between any two of them.

[0040] Preferably, in the step S2, the starting rolling temperature is 1000-1050 °C, and the finishing rolling temperature is 950-1000 °C; the hot rolling is divided into 3-4 passes, the total deformation amount of the hot rolling is 65-75%, and the thickness of the hot rolled plate is 5-7 mm. Specifically, the total deformation amount of the hot rolling can be, for example, any one of 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75% or the range between any two of them; the starting rolling temperature can be, for example, any one of 1000 °C, 1010 °C, 1020 °C, 1030 °C, 1040 °C, 1050 °C or the range between any two of them; the finishing rolling temperature can be, for example, any one of 950 °C, 960 °C, 970 °C, 980 °C, 990 °C, 1000 °C or the range between any two of them; the thickness of the hot rolled plate can be, for example, any one of 5 mm, 5.5 mm, 6 mm, 6.5 mm, 7 mm or the range between any two of them.

[0041] Preferably, in the step S31, the heat preservation temperature is 700-750 °C, the heat preservation time is 10-50 min; the cooling rate is not less than 30 °C / s. Specifically, the heat preservation temperature can be, for example, any one of 700 °C, 710 °C, 720 °C, 730 °C, 740 °C, 750 °C or the range between any two of them; the heat preservation time can be, for example, any one of 10 min, 20 min, 30 min, 40 min, 50 min or the range between any two of them;

[0042] Preferably, in the step S32, the heat preservation temperature is 180-240 °C, and the heat preservation time is 30-120 min. Specifically, the heat preservation temperature can be, for example, any one of 180 °C, 190 °C, 200 °C, 210 °C, 220 °C, 230 °C, 240 °C or the range between any two of them; the heat preservation time can be, for example, any one of 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min or the range between any two of them.

[0043] According to another aspect of the present invention, the present invention provides the following technical solutions:

[0044] A high-strength hot-rolled medium manganese steel is prepared by using the preparation method of the above high-strength hot-rolled medium manganese steel. The yield strength of the hot-rolled medium manganese steel at room temperature is 850-920 MPa, the tensile strength is 1190-1570 MPa, and the elongation is 14.5-19.0%.

[0045] Preferably, the matrix structure of the high-strength hot-rolled medium manganese steel includes 49-61 vol% austenite and 39-51 vol% martensite, and the precipitation phases are cementite and vanadium carbide double nano-precipitation phases. Specifically, the volume percentage of the austenite can be, for example, any one of 49 vol%, 50 vol%, 51 vol%, 52 vol%, 53 vol%, 54 vol%, 55 vol%, 56 vol%, 57 vol%, 58 vol%, 59 vol%, 60 vol%, 61 vol% or the range between any two of them; the volume percentage of the martensite can be, for example, any one of 39 vol%, 40 vol%, 41 vol%, 42 vol%, 43 vol%, 44 vol%, 45 vol%, 46 vol%, 47 vol%, 48 vol%, 49 vol%, 50 vol%, 51 vol% or the range between any two of them.

[0046] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0047] The medium manganese steel used in the comparative examples of each embodiment is prepared by the following method: Prepare the ingredients according to the composition of the medium manganese steel, and add them to the furnace cavity of a vacuum induction melting furnace in the order of increasing melting point of each element. The melting temperature is 1400-1500 °C. After melting, it is cast into an ingot in a mold and air-cooled to room temperature.

[0048] The chemical composition of the medium manganese steel ingot is shown in Table 1.

[0049] Table 1 Chemical composition of the medium manganese steel ingots in each embodiment (mass percentage)

[0050] element Mn Al C V Fe and inevitable impurities content 10.2 2.2 0.41 0.60 balance

[0051] Example 1

[0052] A preparation method of a high-strength hot-rolled medium manganese steel includes the following steps:

[0053] S1. Homogenization annealing: The medium manganese steel ingot is subjected to homogenization annealing to obtain an annealed ingot; the annealing temperature is 1130 °C, the annealing time is 3 h, and the cooling method is air cooling;

[0054] S2. Hot rolling: The annealed ingot is hot rolled and cooled to room temperature by water cooling to obtain a hot rolled plate with a thickness of 6 mm. The starting rolling temperature is 1020 °C, and the final rolling temperature is 980 °C. The hot rolling is divided into 3 passes, and the total deformation amount of hot rolling is 70%.

[0055] S3. Continuous heat treatment: The hot rolled plate is subjected to high temperature annealing in the dual-phase region + tempering in the martensite phase region:

[0056] S31. High temperature annealing in the dual-phase region: The hot rolled plate is heat-preserved by the method of entering the furnace when reaching the temperature, and then quickly cooled to the martensite phase region temperature. The heat preservation temperature is 700 °C, and the heat preservation time is 30 min. The cooling rate is not less than 30 °C / s.

[0057] S32. Tempering in the martensite phase region: Heat preservation is carried out at the martensite phase region temperature. The heat preservation temperature is 200 °C, and the heat preservation time is 120 min. Then it is air-cooled to room temperature to obtain high-strength hot rolled medium manganese steel.

[0058] The SEM diagram of the hot rolled medium manganese steel prepared in this example is as Figure 1 shown. Its matrix structure includes 39 vol% martensite, 61 vol% austenite, and high-density double nano-precipitation (cementite and vanadium carbide) particles. The yield strength of the hot rolled medium manganese steel prepared in this example is 850 MPa, the tensile strength is 1190 MPa, and the elongation after fracture is 18.6%.

[0059] Example 2

[0060] A preparation method of high-strength hot rolled medium manganese steel, comprising the following steps:

[0061] S1. Homogenization annealing: The medium manganese steel ingot is subjected to homogenization annealing to obtain an annealed ingot. The annealing temperature is 1130 °C, the annealing time is 3 h, and the cooling method is air cooling.

[0062] S2. Hot rolling: The annealed ingot is hot rolled and cooled to room temperature by water cooling to obtain a hot rolled plate with a thickness of 6 mm. The starting rolling temperature is 1020 °C, and the final rolling temperature is 980 °C. The hot rolling is divided into 3 passes, and the total deformation amount of hot rolling is 70%.

[0063] S3. Continuous heat treatment: The hot rolled plate is subjected to high temperature annealing in the dual-phase region + tempering in the martensite phase region:

[0064] S31. High temperature annealing in the dual-phase region: The hot rolled plate is heat-preserved by the method of entering the furnace when reaching the temperature, and then quickly cooled to the martensite phase region temperature. The heat preservation temperature is 725 °C, and the heat preservation time is 30 min. The cooling rate is not less than 30 °C / s.

[0065] S32. Tempering in the martensite phase region: Heat preservation is carried out at the martensite phase region temperature. The heat preservation temperature is 200 °C, and the heat preservation time is 120 min. Then it is air-cooled to room temperature to obtain high-strength hot rolled medium manganese steel.

[0066] The SEM image of the hot-rolled medium manganese steel prepared in this example is as Figure 2 shown. Its matrix structure includes 45 vol% martensite, 55 vol% austenite, and high-density double-nano precipitates (cementite and vanadium carbide) particles. The yield strength of the hot-rolled medium manganese steel prepared in this example is 895 MPa, the tensile strength is 1390 MPa, and the elongation after fracture is 16.6%.

[0067] Example 3

[0068] A preparation method of high-strength hot-rolled medium manganese steel includes the following steps:

[0069] S1. Homogenization annealing: The medium manganese steel ingot is subjected to homogenization annealing to obtain an annealed ingot; the annealing temperature is 1130 °C, the annealing time is 3 h, and the cooling method is air cooling;

[0070] S2. Hot rolling: The annealed ingot is hot-rolled and water-cooled to room temperature to obtain a hot-rolled plate with a thickness of 6 mm; the starting rolling temperature is 1020 °C, and the final rolling temperature is 980 °C; the hot rolling is divided into 3 passes, and the total deformation amount of the hot rolling is 70%;

[0071] S3. Continuous heat treatment: The hot-rolled plate is subjected to high-temperature annealing in the dual-phase region + tempering in the martensite phase region:

[0072] S31. High-temperature annealing in the dual-phase region: The hot-rolled plate is heat-insulated in the way of entering the furnace when reaching the temperature, and then quickly cooled to the martensite phase region temperature; the heat-insulation temperature is 750 °C, and the heat-insulation time is 30 min; the cooling rate is not less than 30 °C / s;

[0073] S32. Tempering in the martensite phase region: Heat-insulation is carried out at the martensite phase region temperature, the heat-insulation temperature is 200 °C, and the heat-insulation time is 120 min; then air-cooled to room temperature; high-strength hot-rolled medium manganese steel is obtained.

[0074] The SEM and TEM images of the hot-rolled medium manganese steel prepared in this example are as Figure 3 shown ( Figure 3 the left image in the middle is the SEM image, Figure 3 the right image in the middle is the TEM image), its matrix structure includes 51 vol% martensite, 49 vol% austenite, and high-density double-nano precipitates (cementite and vanadium carbide) particles. The yield strength of the hot-rolled medium manganese steel prepared in this example is 920 MPa, the tensile strength is 1570 MPa, and the elongation after fracture is 14.5%.

[0075] Comparative Example 1

[0076] The difference from Example 1 is that step S3 is not carried out.

[0077] The matrix structure of the medium manganese steel prepared in this comparative example includes 19 vol% martensite / ferrite and 81 vol% austenite. The yield strength of the hot-rolled medium manganese steel prepared in this example is 740 MPa, the tensile strength is 869 MPa, and the elongation after fracture is 11%.

[0078] Comparative Example 2

[0079] The difference from Example 1 is that step S32 is not carried out.

[0080] The matrix structure of the medium manganese steel prepared in this comparative example includes 27 vol% martensite / ferrite and 73 vol% austenite. The yield strength of the hot-rolled medium manganese steel prepared in this example is 730 MPa, the tensile strength is 1020 MPa, and the elongation after fracture is 17%.

[0081] It can be seen from the examples and comparative examples of the present invention that the present invention adopts a continuous heat treatment process of homogenization annealing, hot rolling, annealing in the dual-phase region at high temperature + tempering in the martensite phase region. Through reasonable chemical composition and process design, the matrix structure of the high-strength hot-rolled medium manganese steel obtained includes 49-61 vol% austenite and 39-51 vol% martensite, and the precipitation phases are double-nanometer precipitation phases of cementite and vanadium carbide. The yield strength of the high-strength hot-rolled medium manganese steel at room temperature is 850-920 MPa, the tensile strength is 1190-1570 MPa, and the elongation is 14.5-19.0%.

[0082] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention. Any equivalent structural transformation made by using the content of the specification of the present invention under the inventive concept of the present invention, or direct / indirect application in other related technical fields is included in the patent protection scope of the present invention.

Claims

1. A method for preparing high-strength hot-rolled medium manganese steel, characterized in that: The steps include: S1. Homogenization annealing: the medium manganese steel ingot is subjected to homogenization annealing to obtain an annealed ingot; S2. Hot rolling: hot rolling the annealed ingot, and then cooling it to room temperature to obtain a hot-rolled plate; S3, continuous heat treatment: hot rolled plate undergoes dual phase high temperature annealing + martensite phase tempering: S31, dual phase high temperature annealing: the hot rolled plate is kept warm by entering the furnace at the temperature reached, and then rapidly cooled to the martensitic phase temperature; the holding temperature is 700-750°C, and the cooling rate is not less than 30°C / s; S32, martensite phase tempering: keep warm at the martensite phase temperature, the holding temperature is 180 ~ 240 ℃, and then air cool to room temperature; Obtain high-strength hot-rolled medium manganese steel; The high-strength hot-rolled medium manganese steel comprises, by mass percentage: C: 0.35~0.50%, Mn: 9.5~11.0%, Al: 2.0~3.0%, V: 0.5~0.7%, and the balance is Fe and inevitable impurities.

2. The method for preparing high-strength hot-rolled medium manganese steel according to claim 1, characterized in that: Before step S1, the method further includes: S0, smelting medium manganese steel ingot: preparing ingredients according to the composition of medium manganese steel, adding the ingredients into the furnace chamber of vacuum induction melting furnace in the order of melting points of the elements from low to high, the smelting temperature is 1400-1500° C., and after the smelting is completed, casting the ingot into a mold and air cooling it to room temperature.

3. The method for preparing high-strength hot-rolled medium manganese steel according to claim 1, characterized in that: In the step S1, the annealing temperature is 1100-1150° C., the annealing time is 2-4 hours, and the cooling method is air cooling.

4. The method for preparing high-strength hot-rolled medium manganese steel according to claim 1, characterized in that: In step S2, the initial rolling temperature is 1000-1050°C, and the final rolling temperature is 950-1000°C; the hot rolling is divided into 3-4 passes, and the total deformation of the hot rolling is 65-75%.

5. The method for preparing high-strength hot-rolled medium manganese steel according to claim 1, characterized in that: In the step S31, the heat preservation time is 10 to 50 minutes.

6. The method for preparing high-strength hot-rolled medium manganese steel according to claim 1, characterized in that: In step S32, the insulation time is 30 to 120 minutes.

7. A high-strength hot-rolled medium manganese steel, characterized in that: The steel is prepared by the method for preparing high-strength hot-rolled medium manganese steel according to any one of claims 1 to 6.

8. The high-strength hot-rolled medium manganese steel according to claim 7, characterized in that: The yield strength of hot-rolled medium manganese steel at room temperature is 850-920 MPa, the tensile strength is 1190-1570 MPa, and the elongation is 14.5-19.0%.

9. The high-strength hot-rolled medium manganese steel according to claim 7, characterized in that: The matrix structure of the high-strength hot-rolled medium manganese steel comprises 49-61 vol% austenite and 39-51 vol% martensite, and the precipitation phase is cementite and vanadium carbide double nano-precipitation phase.

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