CN112410681A - High-strength-ductility medium manganese steel and preparation method thereof - Google Patents
High-strength-ductility medium manganese steel and preparation method thereof Download PDFInfo
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Abstract
The invention provides high-strength-ductility medium manganese steel and a preparation method thereof, belonging to the field of automobile steel. The medium manganese steel comprises the following chemical components in percentage by weight: c: 0.1-0.3%, Mn: 4-12% of Fe and the balance of Fe; the preparation method comprises the following steps: smelting molten steel from chemical components of medium manganese steel according to weight percentage, casting the molten steel into an ingot, forging the ingot into a plate blank, cooling the plate blank to room temperature in air, and cutting the plate blank to obtain a plate; carrying out multi-pass warm rolling treatment on the plate to obtain a warm rolled plate; critical region annealing treatment is carried out between two adjacent passes; annealing and insulating the warm-rolled plate at 780-810 ℃ in a critical region for 20-40 min, and cooling in air to room temperature. The invention prepares the ultrafine grain medium manganese steel structure with coarse grain austenite and fine grain austenite structures by the circulating warm rolling and critical annealing process, so that the material obtains ultrahigh product of strength and elongation, and is beneficial to improving the strength and toughness of the steel for automobiles.
Description
Technical Field
The invention relates to the field of automobile steel, in particular to high-strength-plastic-product medium manganese steel and a preparation method thereof.
Background
Since the development of the automobile, medium manganese steel plate used for the automobile is reformed to third generation advanced automobile steel, third generation automobile steel with high product of strength and elongation (30 Gpa. cndot.) because the automobile steel is developed toward the standard of light weight and high safety.
From the aspect of macroscopic mechanical properties, the product of strength and elongation of the traditional third generation advanced automotive steel is 30Gpa · percent, and how to obtain the medium manganese steel plate with higher product of strength and elongation performance becomes a current research trend. Meanwhile, in terms of microstructure, because austenite generates martensite structure due to deformation in the cold rolling process of the medium manganese steel, the deformation resistance of the medium manganese steel in the cold rolling process is larger, and meanwhile, because the medium manganese steel obtained by single-pass cold rolling and reverse phase change annealing process has uneven structure, the medium manganese steel has poor mechanical property and lower product of strength and elongation. How to improve the product of strength and elongation of medium manganese steel is a technical problem to be solved urgently at present.
The austenite reverse phase transformation process principle is as follows: by heating the martensite structure to a temperature above the austenite transformation starting temperature for a period of time, the austenite transformation of the structure will occur, and the austenite phase is stabilized by further C, Mn element partition, so that a higher content of austenite structure is retained at room temperature. The metastable austenite phase can undergo the TRIP effect during deformation, resulting in a sustained work hardening rate, thereby achieving a good combination of high strength and high plasticity.
Disclosure of Invention
The invention aims to provide high-strength-ductility medium manganese steel and a preparation method thereof, wherein a superfine-grain medium manganese steel structure with coarse-grain austenite and fine-grain austenite structures is prepared through a circulating warm rolling and critical annealing process, so that the material obtains ultrahigh strength-ductility product, and the strength and toughness of the automobile steel are improved.
In order to achieve the above purpose of the present invention, the following technical solutions are adopted:
a preparation method of high-strength-ductility medium manganese steel comprises the following chemical components in percentage by weight: c: 0.1-0.3%, Mn: 4-12% of Fe and the balance of Fe;
the preparation method comprises the following steps:
according to the weight percentage, smelting molten steel from chemical components of the medium manganese steel, casting into an ingot, forging the ingot into a plate blank, cooling in air to room temperature, and cutting to obtain a plate;
carrying out multi-pass warm rolling treatment on the plate, wherein the warm rolling temperature is 300-400 ℃, and the warm rolling reduction rate is 50-60%, so as to obtain a warm-rolled plate; annealing treatment is carried out in a critical area between two adjacent passes, the annealing temperature is 780-810 ℃, the annealing time is 5-15 min, and then air cooling is carried out until the temperature reaches 300-400 ℃ to carry out warm rolling of the next pass;
and annealing and preserving the temperature of the warm-rolled plate for 20-40 min at the temperature of 780-810 ℃ in a critical region, and cooling the warm-rolled plate to room temperature in the air.
Further, in a preferred embodiment of the invention, the chemical composition of the medium manganese steel further comprises one or more of the following elements in percentage by weight: al: 0 to 4 percent; si: 0-2%; cr: 0.2-3.0%; ni: 0.1-3.0%; v: 0 to 2.0 percent; mo: 0 to 0.7 percent; nb: 0 to 0.3 percent; cu: 0.5 to 2.0 percent.
Further, in a preferred embodiment of the present invention, the step of forging the ingot comprises heating the ingot to 1100-1300 ℃ and keeping the temperature for 1.5-2.5 hours.
Further, in a preferred embodiment of the present invention, the thickness of the forged plate is 2 to 4 mm; the thickness of the warm-rolled plate is 1-2 mm.
Further, in a preferred embodiment of the present invention, the number of times of the warm rolling in the multi-pass warm rolling process is 3 times, and the number of times of the annealing process in the critical region is 2 times.
Further, in a preferred embodiment of the present invention, the chemical composition of the medium manganese steel comprises, by weight: c: 0.26%, Mn: 10.02%, Al: 2.86%, Si: 1.86 percent and the balance of Fe.
The high-strength-ductility medium manganese steel comprises the following chemical components in percentage by weight: c: 0.1-0.3%, Mn: 4-12% of Fe and the balance of Fe; it is prepared by the preparation method.
Further, in a preferred embodiment of the present invention, the chemical composition of the medium manganese steel comprises, by weight: c: 0.26%, Mn: 10.02%, Al: 2.86%, Si: 1.86 percent and the balance of Fe.
It is prepared by the preparation method as described above.
The invention has the following effects:
the principle of the preparation method of the invention is as follows: after forging, air cooling treatment is carried out, so that the medium manganese steel plate contains a high austenite and ferrite dual-phase structure, the residual stress is released, and warm rolling treatment is facilitated. Meanwhile, the medium manganese steel plate is warm-rolled at 300-400 ℃, so that the medium manganese steel plate has low rolling deformation resistance and good flatness of the surface of the plate can be ensured. And carrying out annealing treatment in a critical area between adjacent warm rolling processes, so that a martensite structure generated by deformation in the warm rolling process is converted into a fine-grained austenite structure through reverse phase transformation, and the fine-grained austenite structure coexists with a coarse-grained austenite structure stored in air cooling after original forging, so that the medium manganese steel is a coexisting structure of coarse-grained austenite, fine-grained austenite and ferrite. By controlling the temperature annealing and the heat preservation time of the critical zone, the coarse grain austenite and the fine grain austenite of the medium manganese steel plate are kept in a proper proportion, and the austenite phase and the ferrite phase are kept in a proper proportion, so that the medium manganese steel material can generate a coexistence mechanism of a TWIP effect and a TRIP effect, and the medium manganese steel plate with ultrahigh strength-elongation product and warm rolling is prepared.
Compared with the traditional cold rolling process, the invention has the following technical characteristics:
1. the invention can ensure that the microstructure of the medium manganese steel is uniformly distributed to generate an austenite phase and ferrite phase dual-phase structure, wherein austenite generates coarse austenite grains and fine austenite grains generated by critical annealing treatment, and the ferrite phase are uniformly distributed, so that the coarse austenite is firstly subjected to martensite phase transformation to generate plasticizing behavior (namely TRIP effect) in the deformation process, and the fine austenite starts to be subjected to phase transformation along with the increase of the deformation, so that the plasticizing behavior of the medium manganese steel is represented by continuous and stable TRIP effect and TWIP effect, and further the product of strength and elongation of the medium manganese steel is improved.
2. Warm rolling is a rolling process performed in a temperature range of not lower than the recovery temperature but lower than the crystallization temperature. The warm-rolling process can reduce the deformation resistance in the rolling process of the steel, ensure the surface quality of the steel, has small deformation resistance, smooth surface, high production efficiency and energy conservation, and has the characteristics of high plastic shape and large allowable deformation amount during thermal deformation. The phenomena of thick oxide skin, pit and the like after hot rolling do not exist. Meanwhile, the grain size can be ensured to be refined by warm rolling.
3. The method adopting the warm rolling and critical region annealing process can ensure that the deformation resistance of the medium manganese steel is reduced in the rolling process, the reverse phase transformation of the deformed martensite after critical annealing is ensured to generate a fine grain austenite structure, and the coexistence structure of coarse grain austenite and fine grain austenite is ensured to appear on the medium manganese steel plate, so that the medium manganese steel plate with the ultrahigh product of strength and elongation is prepared.
4. The annealing temperature adopted by the invention is obtained by simulating Thermo-calc thermodynamic calculation software, and the temperature (Ac) of completely transforming ferrite into austenite is obtained by calculation3) And the temperature is about 800 ℃, and the intermediate annealing temperature of the warm rolling circulation process is 780-810 ℃ according to the temperature, so that the martensite generated in the deformation process can be fully converted into an austenite structure.
5. The medium manganese steel provided by the invention adopts element components in special proportion, and is beneficial to improving the product of strength and elongation of the medium manganese steel. Among them, carbon can improve the stability of austenite in the medium manganese steel, and generally, the mass fraction of carbon is increased by 1%, and the transformation temperature Ms of martensite is decreased by 423 ℃. However, the C content is 0.1 to 0.3% in the invention because the C content is too high and the weldability of the medium manganese steel is poor. The Mn element can widen an austenite phase region, strengthen a matrix and improve the stability of austenite, but the Mn element can generate segregation when the Mn content is too high, so that the homogenization of the structure components is difficult to realize by diffusion annealing, and therefore, the Mn content of the medium manganese steel is 4-12%. The Si element can promote the formation of austenite and increase the content of residual austenite at room temperature. The Al element has similar action with the Si element, and meanwhile, the Al element can remarkably reduce the density of the medium manganese steel, so that the quality of the automobile steel is reduced, the formation of austenite mainly depends on the stacking fault energy, the Al element can increase the stacking fault energy of the austenite, but the excessive Al element can cause the water gap to be blocked in the continuous casting process and influence the production, so that the Al content is not more than 3 percent, and the Si content is not more than 2 percent.
6. The manganese steel in the ultrahigh-strength plastic-product warm rolling has the advantages of excellent performance, good wear resistance, strong deformation bearing capacity, low material density and wide application range, and can meet the performance indexes of different parts of an automobile and the requirements of light weight and high safety of the automobile.
Drawings
FIG. 1 is a drawing size of a micro-tensile sample according to the present invention;
FIG. 2 is a process curve of different annealing temperatures of 750 ℃ to 850 ℃ in example 1 of the present invention;
FIG. 3 is a graph of the process at 750 ℃ for different annealing times in example 2 of the present invention;
FIG. 4 is EBSD analysis of austenite of medium manganese steel after warm rolling annealing in example 1 of the present invention;
FIG. 5 is a grain size analysis of austenite of a medium manganese steel after warm rolling annealing in example 1 of the present invention;
FIG. 6 is the change in the austenite volume fraction before and after the sample is stretched after warm rolling annealing in example 1 of the present invention;
FIG. 7 is an engineering stress-strain curve at different annealing temperatures for example 1 of the present invention;
FIG. 8 is a graph of engineering stress-strain curves at 750 ℃ for various time periods in example 2 of the present invention;
FIG. 9 is a simulated phase diagram of Thermo-calc thermodynamic calculation software of the present invention;
FIG. 10 is a (SEM) microstructure of different annealing temperatures (750 ℃, 800 ℃, 850 ℃) in example 1 of the present invention;
FIG. 11 is the engineering stress-strain curve of single-pass warm rolling of medium manganese steel in the range of 800-30 min in comparative example 1 of the present invention.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
The equipment for carrying out the room temperature tensile test in the embodiment of the invention is carried out on an INSTRON 8801 hydraulic servo fatigue testing machine from the forging laboratory of Yanshan university.
The apparatus for the microscopic characterization technique in the examples of the present invention was a ZEISS Sigma500 scanning electron microscope equipped with an electron back-scattered diffraction analysis System (EBSD).
The device for measuring the volume fraction of retained austenite in the embodiment of the invention is a D/MAX-2500/PCX-ray diffractometer.
The heat treatment furnace adopted in the embodiment of the invention is a high-temperature furnace.
In the embodiment of the invention, the warm-rolled ultrahigh-strength-product medium manganese steel is processed into the tensile sample with the size shown in figure 1, sand paper with the granularity of 1000 is adopted for polishing and brightening, and then a tensile experiment is carried out, wherein the deformation rate is 3mm/min until the tensile sample is broken.
In the examples of the present invention, experimental hot-setting was performed on a 30mm diameter disk, which was then ground with sandpaper and mechanically polished. And then, corroding by using a copper chloride corrosive liquid for 1min, cleaning by using alcohol after the corrosion is finished, and observing by using XRD, OM and SEM after the corrosion is finished.
Example 1
The embodiment provides high-strength-ductility medium manganese steel, and a preparation method thereof comprises the following steps:
1. smelting molten steel according to set components, and then casting into 20kg of cast ingot; the molten steel comprises the following components in percentage by mass: c: 0.26%, Mn: 10.02%, Al: 2.86%, Si: 1.86% and the balance of Fe and inevitable impurities.
2. Heating the cast ingot to 1200 ℃, preserving heat for 2 hours, forging the cast ingot into a plate blank, and cooling the plate blank to room temperature in air; and performing linear cutting treatment on the plate blank by adopting a linear cutting technology, and cutting a steel plate with the plate thickness of 3 mm.
3. Heating the steel plate to 400 ℃, preserving heat for 1h, then carrying out three-pass warm rolling, rolling the steel plate from 3mm to 1.5mm, wherein the rolling reduction rate of the warm rolling is 50%, and manufacturing a warm rolled plate and air cooling the plate to room temperature; and performing intermediate annealing between the warm rolling processes of two adjacent passes, wherein the annealing temperature is 800 ℃, the annealing time is 10min, and then cooling to 400 ℃ to perform the next warm rolling process again.
4. And then, respectively keeping the same warm-rolled plates at 750 ℃, 800 ℃ and 850 ℃ for 30min, performing heat treatment process as shown in figure 2, and then performing air cooling to room temperature to prepare three groups of warm-rolled medium manganese steel plates.
The performance test of the three groups of prepared manganese steel plates is shown in table 1:
TABLE 1 Performance test results of medium manganese steel sheet
| Temperature of the sheet | Tensile strength | Elongation after fracture | Product of strength and | Yield strength | |
| 750℃ | 1012.24MPa | 68.31％ | 69.15GPa·％ | 735.98 |
|
| 800℃ | 1105.62MPa | 76.87％ | 84.99GPa·％ | 570.32 |
|
| 850℃ | 1154.77MPa | 37.76％ | 43.60GPa·％ | 484.13MPa |
As can be seen from Table 1, after the multi-pass warm rolling and annealing process is carried out, the obtained warm-rolled plate is kept at 800 ℃ for 30min, the product of post-fracture elongation and strength and elongation of the obtained medium manganese steel plate is remarkably increased, and meanwhile, the good tensile strength and yield strength can be kept.
The EBSD observation result is shown in figure 4, the grain size analysis is shown in figure 5, and the microstructure analysis shows that after the manganese steel plate is annealed at 800 ℃ for 30min in warm rolling, the red ferrite structure is uniformly distributed on the blue austenite structure, the austenite grains have fine crystal austenite below 5um, and the coarse crystal austenite above 10 um. Therefore, the good mechanical property of the manganese steel plate in warm rolling comes from the mixed crystal structure of coarse crystal austenite and fine crystal austenite, and because of the austeniteThe crystal grain sizes of the cementite are different, and the cementite has the formula Ms of 545-432C-30.4Mn-60.5Vγ -1/3C, Mn represents the volume fraction of the elements in the experimental steel, VγThe austenite grain size in the experimental steel is represented, and the smaller the austenite grain size is, the lower the Ms (the starting temperature of martensite transformation) is, and the higher the austenite stability is, because the austenite in the mixed crystal structure contains coarse austenite and fine crystal austenite, the stability of the coarse crystal austenite is poorer, the martensite phase transformation firstly occurs, the stability of the fine crystal austenite is higher, the martensite phase transformation occurs again along with the increase of deformation, and then the continuous work hardening behavior is generated, thereby ensuring that the experimental steel has good mechanical property.
The volume fraction change curve of austenite before and after stretching is shown in fig. 6, the plate is obtained by heat preservation treatment at 800 ℃, the volume fraction of austenite before stretching is 60%, the volume fraction of austenite after stretching is 26%, and the austenite transformation amount of a manganese steel plate micro-stretching sample in warm rolling in the stretching deformation process is 34%; the transformation amount of austenite in the stretching deformation process of the plate obtained by heat preservation treatment at 750 ℃ is 20 percent; the sheet obtained after the heat-insulating treatment at 850 ℃ had an austenite transformation amount during the tensile deformation of 36%. Therefore, the obvious TRIP effect occurs in the experimental steel, a large amount of austenite is transformed into a martensite structure, the transformation amount of the austenite is small at 750 ℃, and further, the engineering stress-strain curve of the experimental steel is caused, and as shown in FIG. 7, no obvious inflection point is generated, so that the elongation is low. The austenite transformation amount at 850 ℃ is enough, but the engineering stress-strain curve of the test steel is too obvious in curve rise as shown in FIG. 7, which shows that the austenite stability is too low at 850 ℃, the TRIP effect is too fast in the deformation process, and the continuous work hardening effect cannot be generated. At 800 ℃, the austenite transformation amount is 34% which is similar to the austenite transformation amount 36% at 850 ℃, but from the experimental steel engineering stress-strain curve, as shown in fig. 7, the mechanical property is excellent, which is related to the moderate austenite stability and the continuous TRIP effect generated in the deformation process.
The stress-strain curve is shown in FIG. 7, FIG. 7 is the engineering stress-strain curve of the warm-rolled medium manganese steel at different annealing temperatures, the experimental steel is annealed at 750 ℃, the yield strength is 735.98MPa, the tensile strength is 1012.24MPa, the elongation is 68.31%, and the product of strength and elongation is 69.15 GPa%. Annealing at 800 ℃, wherein the yield strength is 570.32MPa, the tensile strength is 1105.62MPa, the elongation is 76.87 percent, and the product of strength and elongation is 84.99 GPa. Annealing at 850 ℃, wherein the yield strength is 484.13MPa, the tensile strength is 1154.77MPa, the elongation is 37.76 percent, and the product of strength and elongation is 43.60 GPa. Therefore, the experimental steel has the optimal annealing mechanical property at 800 ℃, and the product of strength and elongation can reach 84.99 GPa.
Fig. 9 is a phase diagram simulated by Thermo-calc thermodynamic calculation software, and it can be seen from the phase diagram that Ac3 (ferrite full-austenite temperature) of the experimental steel is about 800 ℃, which shows that above 800 ℃, ferrite full-austenite structure is transformed, i.e. ferrite structure can generate sufficient transformation reaction to generate austenite structure at 800 ℃.
The microstructure diagrams of different annealing temperatures are shown in fig. 10, and metallographic structure pictures of different annealing temperatures show that at 750 ℃, the annealing temperature is lower and the ferrite turns into a small austenite structure. At 800 c, the amount of transformation of austenite increases as the annealing temperature increases, and the size of the austenite structure begins to increase. At 850 ℃, due to the excessively high annealing temperature, the austenite structure is excessively large in size, and the austenite stability is reduced.
Example 2
The embodiment provides a high-strength-product medium manganese steel, and the preparation method is basically the same as that of embodiment 1, except that:
and (3) respectively keeping the warm rolled plates obtained after the three warm rolling and annealing processes in the step (3) at 800 ℃ for 15min, 30min and 60min, performing a heat treatment process as shown in the figure 3, and then performing air cooling to room temperature to prepare three groups of medium manganese steel plates with high strength-elongation product.
The performance test of the three groups of prepared manganese steel plates is carried out, and the results are shown in table 2:
TABLE 2 Performance test results of medium manganese steel sheet
| Heat preservation time of sheet material | Tensile strength | Elongation after fracture | Product of strength and elongation | Yield strength |
| 15min | 1112.12MPa | 76.75％ | 85.36GPa·％ | 625.19MPa |
| 30min | 1105.62MPa | 76.87％ | 84.99GPa·％ | 570.32MPa |
| 60min | 1103.10MPa | 75.63％ | 83.43GPa·％ | 556.53MPa |
As can be seen from table 2, after the multi-pass warm rolling and annealing process is performed, the obtained warm rolled plate is kept at 800 ℃ for 15min, 30min and 60min, and the mechanical properties of the obtained medium manganese steel plate are excellent, which indicates that the medium manganese steel plate is annealed at 800 ℃ in warm rolling, the influence of the heat preservation time on the medium manganese steel plate is small, and meanwhile, the experimental steel can ensure the excellent mechanical properties in a short time (for example, 15 min).
As shown in FIG. 8, the yield strength of the experimental steel is slightly reduced from 625.19MPa to 556.53MPa as the annealing time is prolonged. The change of the tensile strength and the elongation is not obvious, which indicates that the experimental steel can keep good mechanical property after annealing for 15-60 min.
Comparative example
The comparative example provides a medium manganese steel, and the preparation method comprises the following steps:
1. smelting molten steel according to set components, and then casting into 20kg of cast ingot; the molten steel comprises the following components in percentage by mass: c: 0.26%, Mn: 10.02%, Al: 2.86%, Si: 1.86% and the balance of Fe and inevitable impurities.
2. Heating the cast ingot to 1200 ℃, preserving heat for 2 hours, forging the cast ingot into a plate blank, and cooling the plate blank to room temperature in air; and (3) performing line cutting on the plate blank by adopting a line cutting technology, and cutting off a steel plate with the plate thickness of 3 mm.
3. Heating the steel plate to 400 ℃, preserving heat for 1h, then carrying out single-pass warm rolling, wherein the intermediate critical zone annealing process of 800 ℃ is not adopted in the middle of the warm rolling, the warm rolling deformation is 50%, and air cooling to room temperature.
4. And then, preserving the heat of the obtained warm rolling plate at 800 ℃ for 30min, and then air-cooling the warm rolling plate to room temperature to manufacture the grouped rolled medium manganese steel plate.
The micro-tensile test piece of the obtained medium manganese steel plate is cut, the engineering stress-strain curve of the material is shown in fig. 11, the tensile strength is 1177.17MPa, the elongation after fracture is 54.38%, and the product of strength and elongation is 64.01 GPa%.
The above-mentioned embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements made to the technical solution of the present invention by those skilled in the art without departing from the spirit of the present invention shall fall within the protection scope defined by the claims of the present invention.
Claims (8)
1. The preparation method of the medium manganese steel with high strength-elongation product is characterized in that the medium manganese steel comprises the following chemical components in percentage by weight: c: 0.1-0.3%, Mn: 4-12% of Fe and the balance of Fe;
the preparation method comprises the following steps:
according to the weight percentage, smelting molten steel from chemical components of the medium manganese steel, casting into an ingot, forging the ingot into a plate blank, cooling in air to room temperature, and cutting to obtain a plate;
carrying out multi-pass warm rolling treatment on the plate, wherein the warm rolling temperature is 300-400 ℃, and the warm rolling reduction rate is 50-60%, so as to obtain a warm-rolled plate; annealing treatment is carried out in a critical area between two adjacent passes, the annealing temperature is 780-810 ℃, the annealing time is 5-15 min, and then air cooling is carried out until the temperature reaches 300-400 ℃ to carry out warm rolling of the next pass;
and annealing and preserving the temperature of the warm-rolled plate for 20-40 min at the temperature of 780-810 ℃ in a critical region, and cooling the warm-rolled plate to room temperature in the air.
2. The method for preparing the high-strength-product medium manganese steel according to claim 1, wherein the chemical composition of the medium manganese steel further comprises one or more of the following elements in percentage by weight: al: 0 to 4 percent; si: 0-2%; cr: 0.2-3.0%; ni: 0.1-3.0%; v: 0 to 2.0 percent; mo: 0 to 0.7 percent; nb: 0 to 0.3 percent; cu: 0.5 to 2.0 percent.
3. The method for preparing the high-strength-product medium manganese steel according to claim 1, wherein the step of forging the ingot comprises heating the ingot to 1100-1300 ℃ and keeping the temperature for 1.5-2.5 hours.
4. The method for preparing the high-strength-product medium manganese steel according to claim 1, wherein the thickness of the forged plate is 2-4 mm; the thickness of the warm-rolled plate is 1-2 mm.
5. The method for preparing the high-strength-ductility medium manganese steel according to claim 1, wherein the number of times of warm rolling in the multi-pass warm rolling treatment is 3, and the number of times of annealing treatment in the critical region is 2.
6. The method for preparing the high-strength-product medium manganese steel according to claim 1, wherein the medium manganese steel comprises the following chemical components in percentage by weight: c: 0.26%, Mn: 10.02%, Al: 2.86%, Si: 1.86 percent and the balance of Fe.
7. The high-strength-ductility medium manganese steel is characterized by comprising the following chemical components in percentage by weight: c: 0.1-0.3%, Mn: 4-12% of Fe and the balance of Fe; which is prepared by the preparation method as claimed in any one of claims 1 to 5.
8. The high-strength-product medium manganese steel according to claim 7, characterized in that the chemical composition of the medium manganese steel comprises, in weight percent: c: 0.26%, Mn: 10.02%, Al: 2.86%, Si: 1.86 percent and the balance of Fe.
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