CN111363902B - Method for promoting formation of residual austenite of hot-rolled medium manganese steel plate - Google Patents
Method for promoting formation of residual austenite of hot-rolled medium manganese steel plate Download PDFInfo
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- C—CHEMISTRY; METALLURGY
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Abstract
The invention discloses a method for promoting the formation of residual austenite of a hot-rolled medium manganese steel plate, which comprises the working procedures of heating, hot rolling, coiling and heat treatment; the heat treatment process adopts a twice-distribution process after annealing, a sample is placed in a muffle furnace for heat preservation for 5-15 min at the heating temperature of 650-780 ℃, then placed in molten salt at the temperature of 100-150 ℃ for isothermal heat preservation for 1-5 min, and then moved to the muffle furnace for heat preservation at the temperature of 450-500 ℃ for 3-5 min for first carbon and manganese element distribution; and then placing the sample in molten salt at the temperature of 100-120 ℃ for medium-temperature heat preservation for 1-3 min, then moving the sample to a muffle furnace at the temperature of 400-450 ℃ for heat preservation for 5-10 min for secondary carbon and manganese element distribution, and then taking out the sample and air-cooling the sample to room temperature. The invention combines the two-time distribution process after annealing based on component design, remarkably promotes the formation and the stability of the residual austenite of the hot-rolled medium manganese steel plate under the room temperature condition, the volume fraction of the residual austenite is more than or equal to 23 percent, the product of strength and elongation after uniaxial tension test is more than 31GPa percent, and the requirement of the third-generation automobile steel performance is completely met.
Description
Technical Field
The invention belongs to the technical field of metallurgy, and particularly relates to a method for promoting formation of residual austenite of a hot-rolled medium manganese steel plate.
Background
In order to balance the comprehensive requirements of light weight and collision safety of automobiles, development of novel automobile steel with strength and toughness matching becomes a hot point of research. The medium manganese steel is used as the third-generation automobile steel, a proper amount of manganese element is adopted, and a certain content of silicon and aluminum are added to inhibit the performance of cementite in the steel. The medium manganese steel has wide application prospect as third generation automobile steel, and has essentially different cost and production feasibility compared with second generation high manganese TWIP steel.
The mechanical properties of the medium manganese steel, such as strength, plasticity and the like, are closely related to the content of residual austenite and the stability thereof. The residual austenite content in the steel depends on its chemical composition and heat treatment schedule. The medium manganese steel has high content of alloy elements, an alloy addition system and temperature drop control are difficult in the smelting process, columnar crystals are developed due to low heat conductivity coefficient in the casting blank solidification process, cracks and blank breaking risks exist in the high-temperature thermoplastic poor bending straightening of the casting blank, the macrosegregation of elements in the casting blank is serious, and the above links form serious challenges for the smelting process. Furthermore, it is most critical to obtain a suitable residual austenite content. The content of the retained austenite depends on a heat treatment system, and the aggregation degree, dislocation density and the like of carbon and manganese in steel during heat treatment influence the content and stability of the retained austenite. The difference of atomic diffusion capacity caused by the difference of carbon and manganese atomic radius in steel is important to design a reasonable heat treatment system by combining the components of steel grades.
By improving the stability of austenite and matching with a specific heat treatment process, the proper content of the residual austenite is obtained under the room temperature condition, and when instantaneous strong strain is generated in the automobile collision process, the residual austenite in the medium manganese steel generates martensite transformation, so that the strength of an automobile body can be improved and the expansion of cracks can be inhibited.
Disclosure of Invention
The invention aims to provide a method for promoting the formation of residual austenite of a hot-rolled manganese steel plate. According to the invention, the formation of the retained austenite is promoted by twice distribution after annealing, the formation of the retained austenite is promoted by twice distribution of elements such as carbon, manganese and the like at different temperatures after annealing, and the mechanical performance indexes such as the toughness, the product of strength and elongation and the like of the obtained medium manganese steel are obviously improved.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows: a method for promoting the formation of residual austenite of a hot-rolled medium manganese steel plate comprises the following steps of heating, hot rolling, coiling and heat treatment:
(1) a heating procedure: completely burning a medium manganese steel casting blank in a heating furnace at 1150-1200 ℃;
(2) a hot rolling procedure: the initial rolling temperature of hot rolling and rough rolling is more than or equal to 1000 ℃, the initial rolling temperature of finish rolling is 900-950 ℃, the finish rolling temperature of finish rolling is 760-830 ℃, and the outlet temperature of laminar cooling is 700-740 ℃;
(3) a coiling step: the coiling temperature is controlled to be 660-700 ℃;
(4) a heat treatment process: adopting a twice-distribution process after annealing, placing a sample in a muffle furnace for heating at 650-780 ℃ for 5-15 min, then placing the sample in molten salt at 100-150 ℃ for isothermal heat preservation for 1-5 min, and then moving the sample to the muffle furnace for heat preservation at 450-500 ℃ for 3-5 min for first carbon and manganese element distribution; and then placing the sample in molten salt at the temperature of 100-120 ℃ for medium-temperature heat preservation for 1-3 min, then moving the sample to a muffle furnace at the temperature of 400-450 ℃ for heat preservation for 5-10 min for secondary carbon and manganese element distribution, and then taking out the sample for air cooling to room temperature.
The medium manganese steel plate comprises the following chemical components in percentage by mass: c: 0.10 to 0.25%, Mn: 4.95-7.02%, Si: 1.31-1.65%, Als: 0.013-0.035%, P is less than or equal to 0.015%, S is less than or equal to 0.010%, and the balance of Fe and inevitable impurity elements.
The thickness specification of the medium manganese steel plate is 2.0-5.0 mm.
The medium manganese steel plate of the invention: the tensile strength is 941-1083 MPa, the yield strength is 693-862 MPa, and the elongation after fracture is 23-43%.
The medium manganese steel plate has a product of strength and elongation of more than or equal to 31GPa and a volume fraction of retained austenite of more than or equal to 23%.
The design idea of the invention is as follows:
the medium manganese steel hot-rolled steel plate with the thickness of 2.0-5.0 mm is produced based on component design and by combining the forming technology of distributing twice to promote the residual austenite after annealing. Through reasonable design of austenite forming elements such as carbon, manganese, silicon, aluminum and the like, the stability of the austenite at room temperature is improved, and a foundation is laid for promoting the formation of residual austenite at room temperature after heat treatment is completed. In the two-step distribution process after annealing, carbon, manganese and the like are diffused and enriched to grain boundaries from carbon-rich martensite (bainite) to promote the formation of the retained austenite, and meanwhile, the element enrichment leads to the increase of the stability of the retained austenite, and the retained austenite can stably exist at room temperature.
Adopting a twice-distribution process after annealing, placing a sample in a muffle furnace for heating at 650-780 ℃ for 5-15 min, then placing the sample in molten salt at 100-150 ℃ for isothermal heat preservation for 1-5 min, and then moving the sample to the muffle furnace for heat preservation at 450-500 ℃ for 3-5 min for first carbon and manganese element distribution; and then placing the sample in molten salt at the temperature of 100-120 ℃ for medium-temperature heat preservation for 1-3 min, then moving the sample to a muffle furnace at the temperature of 400-450 ℃ for heat preservation for 5-10 min for secondary carbon and manganese element distribution, and then taking out the sample for air cooling to room temperature. The volume fraction of the retained austenite of the hot-rolled steel plate after heat treatment is more than or equal to 23 percent through detection, and the product of strength and elongation of the steel plate after heat treatment is more than 31GPa percent through a uniaxial tensile experiment, thereby completely meeting the performance requirements of third-generation automobile steel.
Adopt the produced beneficial effect of above-mentioned technical scheme to lie in: 1. the hot-rolled medium manganese steel plate with the specification of 2.0-5.0 mm is produced by combining the component design with the twice distribution process after annealing, the formation and the stability of residual austenite under the room temperature condition are obviously promoted, and the mechanical properties such as toughness, product of strength and elongation and the like of the hot-rolled medium manganese steel plate are improved. 2. After the hot-rolled manganese steel plate is subjected to heat treatment, the volume fraction of the retained austenite is more than or equal to 23%, the product of strength and elongation after uniaxial tensile test is more than 31GPa%, the tensile strength is 941-1083 MPa, the yield strength is 693-862 MPa, and the elongation after fracture is 23-43%, so that the requirements of third-generation automobile steel performance are completely met. 3. The method has the characteristics of stable process, excellent product performance and the like.
Drawings
Fig. 1 is a schematic diagram of a heat treatment process.
Detailed Description
The invention is described in further detail below with reference to the figures and specific examples.
Example 1
The thickness of the manganese steel plate in the hot rolling of the embodiment is 2.0mm, and the chemical composition and the mass percentage are shown in table 1.
The method for promoting the formation of the residual austenite of the manganese steel plate in the hot rolling comprises the following steps of heating, hot rolling, coiling and heat treatment, and the specific process steps are as follows:
(1) a heating procedure: the medium manganese steel casting blank is completely burnt through in a heating furnace, and the heating temperature is 1173 ℃;
(2) a hot rolling procedure: the starting temperature of hot rolling and rough rolling is 1051 ℃, the starting temperature of finish rolling is 936 ℃, the finishing temperature of finish rolling is 791 ℃, and the outlet temperature of laminar cooling is 720 ℃;
(3) a coiling step: the coiling temperature is controlled at 673 ℃;
(4) a heat treatment process: adopting a twice-distribution process after annealing, placing a sample in a muffle furnace for heating at 650 ℃ for 5min, then placing the sample in 130 ℃ molten salt for carrying out moderate temperature heat preservation for 3min, and then moving the sample to a muffle furnace for carrying out heat preservation at 473 ℃ for 3min to carry out first carbon and manganese element distribution; then placing the mixture in 108 ℃ molten salt, preserving heat for 2min at medium temperature, and then transferring the mixture to 436 ℃ and preserving heat for 8min to carry out secondary carbon and manganese element distribution; promoting the formation of residual austenite and then air-cooling to room temperature.
Hot-rolled medium manganese steel sheet of this example: the tensile strength is 941MPa, the yield strength is 709MPa, the elongation after fracture is 23%, the product of strength and elongation is 31GPa%, and the volume fraction of the retained austenite is 23%.
Example 2
The thickness of the manganese steel plate in the hot rolling of the embodiment is 3.0mm, and the chemical composition and the mass percentage are shown in table 1.
The method for promoting the formation of the residual austenite of the manganese steel plate in the hot rolling comprises the following steps of heating, hot rolling, coiling and heat treatment, and the specific process steps are as follows:
(1) a heating procedure: the medium manganese steel casting blank is completely burnt in a heating furnace at the heating temperature of 1150 ℃;
(2) a hot rolling procedure: the hot rolling and rough rolling start temperature is 1037 ℃, the finish rolling start temperature is 903 ℃, the finish rolling temperature is 809 ℃, and the outlet temperature of laminar cooling is 719 ℃;
(3) a coiling step: the coiling temperature is controlled to 676 ℃;
(4) a heat treatment process: adopting a twice-distribution process after annealing, placing a sample in a muffle furnace for heating at 780 ℃ for 5min, then placing the sample in 150 ℃ molten salt for carrying out moderate temperature heat preservation for 5min, and then moving the sample to the muffle furnace for carrying out heat preservation at 450 ℃ for 3min for carrying out first carbon and manganese element distribution; then placing the mixture in 100 ℃ molten salt for isothermal heat preservation for 1min, and then moving to 400 ℃ for heat preservation for 5min for secondary carbon and manganese element distribution; promoting the formation of residual austenite and then air-cooling to room temperature.
Hot-rolled medium manganese steel sheet of this example: the tensile strength is 983MPa, the yield strength is 753MPa, the elongation after fracture is 36 percent, the product of strength and elongation is 35.4 GPa%, and the volume fraction of retained austenite is 26 percent.
Example 3
The thickness of the manganese steel plate in the hot rolling of this example was 4.0mm, and the chemical composition and mass percentage thereof are shown in table 1.
The method for promoting the formation of the residual austenite of the manganese steel plate in the hot rolling comprises the following steps of heating, hot rolling, coiling and heat treatment, and the specific process steps are as follows:
(1) a heating procedure: the medium manganese steel casting blank is completely burnt through in a heating furnace, and the heating temperature is 1200 ℃;
(2) a hot rolling procedure: the hot rolling and rough rolling start temperature is 1022 ℃, the finish rolling start temperature is 900 ℃, the finish rolling temperature is 830 ℃, and the outlet temperature of laminar cooling is 740 ℃;
(3) a coiling step: the coiling temperature is controlled at 700 ℃;
(4) a heat treatment process: adopting a twice-distribution process after annealing, placing a sample in a muffle furnace for heating at 660 ℃ for 15min, then placing the sample in 110 ℃ molten salt for carrying out moderate temperature heat preservation for 5min, and then moving the sample to a muffle furnace for carrying out heat preservation at 450 ℃ for 3min for carrying out first carbon and manganese element distribution; then placing the mixture in 100 ℃ molten salt for isothermal heat preservation for 1min, and then moving to 430 ℃ for heat preservation for 10min for secondary carbon and manganese element distribution; promoting the formation of residual austenite and then air-cooling to room temperature.
Hot-rolled medium manganese steel sheet of this example: the tensile strength is 1083MPa, the yield strength is 862MPa, the elongation after fracture is 43 percent, the product of strength and elongation is 46.6 GPa%, and the volume fraction of the retained austenite is 29 percent.
Example 4
The thickness of the manganese steel plate in the hot rolling of this example was 5.0mm, and the chemical composition and mass% thereof are shown in table 1.
The method for promoting the formation of the residual austenite of the manganese steel plate in the hot rolling comprises the following steps of heating, hot rolling, coiling and heat treatment, and the specific process steps are as follows:
(1) a heating procedure: the medium manganese steel casting blank is completely burnt in a heating furnace, and the heating temperature is 1160 ℃;
(2) a hot rolling procedure: the hot rolling and rough rolling start temperature is 1000 ℃, the finish rolling start temperature is 925 ℃, the finish rolling temperature is 760 ℃, and the outlet temperature of laminar cooling is 700 ℃;
(3) a coiling step: the coiling temperature is controlled at 660 ℃;
(4) a heat treatment process: adopting a twice distribution process after annealing, placing a sample in a muffle furnace for heating at 719 ℃ for 7min, then placing the sample in 150 ℃ molten salt for isothermal heat preservation for 4min, and then moving the sample to the muffle furnace for heat preservation at 481 ℃ for 4min for first carbon and manganese element distribution; then placing the mixture in molten salt at 109 ℃ for medium-temperature heat preservation for 2min, and then moving to 429 ℃ for heat preservation for 6min for secondary carbon and manganese element distribution; promoting the formation of residual austenite and then air-cooling to room temperature.
Hot-rolled medium manganese steel sheet of this example: the tensile strength is 1007MPa, the yield strength is 779MPa, the elongation after fracture is 41%, the product of strength and elongation is 41.3 GPa%, and the volume fraction of retained austenite is 27%.
Example 5
The thickness of the manganese steel plate in the hot rolling of the embodiment is 3.5mm, and the chemical composition and the mass percentage are shown in table 1.
The method for promoting the formation of the residual austenite of the manganese steel plate in the hot rolling comprises the following steps of heating, hot rolling, coiling and heat treatment, and the specific process steps are as follows:
(1) a heating procedure: the medium manganese steel casting blank is completely burnt through in a heating furnace, and the heating temperature is 1181 ℃;
(2) a hot rolling procedure: the hot rolling and rough rolling start temperature is 1037 ℃, the finish rolling start temperature is 941 ℃, the finish rolling temperature is 793 ℃, and the outlet temperature of laminar cooling is 724 ℃;
(3) a coiling step: the coiling temperature is controlled at 683 ℃;
(4) a heat treatment process: by adopting a twice distribution process after annealing, a sample is placed in a muffle furnace to be heated at 749 ℃ for heat preservation for 8min, then placed in 141 ℃ molten salt to be subjected to isothermal heat preservation for 3min, and then moved to the muffle furnace to be subjected to heat preservation for 3min at 477 ℃ to carry out first carbon and manganese element distribution; then placing the mixture in 112 ℃ molten salt for isothermal heat preservation for 3min, and then moving to 443 ℃ for heat preservation for 7min for secondary carbon and manganese element distribution; promoting the formation of residual austenite and then air-cooling to room temperature.
Hot-rolled medium manganese steel sheet of this example: the tensile strength is 967MPa, the yield strength is 712MPa, the elongation after fracture is 35 percent, the product of strength and elongation is 33.8 GPa%, and the volume fraction of the retained austenite is 25 percent.
Example 6
The thickness of the manganese steel plate in the hot rolling of the embodiment is 2.6mm, and the chemical composition and the mass percentage are shown in table 1.
The method for promoting the formation of the residual austenite of the manganese steel plate in the hot rolling comprises the following steps of heating, hot rolling, coiling and heat treatment, and the specific process steps are as follows:
(1) a heating procedure: the medium manganese steel casting blank is completely burnt in a heating furnace at the heating temperature of 1192 ℃;
(2) a hot rolling procedure: the hot rolling and rough rolling start temperature is 1025 ℃, the finish rolling start temperature is 916 ℃, the finish rolling temperature is 775 ℃, and the outlet temperature of laminar cooling is 732 ℃;
(3) a coiling step: the coiling temperature is controlled at 694 ℃;
(4) a heat treatment process: adopting a twice-distribution process after annealing, placing a sample in a muffle furnace for heating at 682 ℃ for 11min, then placing the sample in 122 ℃ molten salt for moderate temperature for 2min, and then transferring to the muffle furnace for heat preservation at 495 ℃ for 4.5min for first carbon and manganese element distribution; then placing the mixture in 115 ℃ molten salt for isothermal heat preservation for 3min, and then moving the mixture to 418 ℃ for heat preservation for 9min to carry out secondary carbon and manganese element distribution; promoting the formation of residual austenite and then air-cooling to room temperature.
Hot-rolled medium manganese steel sheet of this example: the tensile strength is 953MPa, the yield strength is 707MPa, the elongation after fracture is 36 percent, the product of strength and elongation is 34.3GPa percent, and the volume fraction of the retained austenite is 26 percent.
Example 7
The thickness of the manganese steel plate in the hot rolling of the embodiment is 4.2mm, and the chemical composition and the mass percentage are shown in table 1.
The method for promoting the formation of the residual austenite of the manganese steel plate in the hot rolling comprises the following steps of heating, hot rolling, coiling and heat treatment, and the specific process steps are as follows:
(1) a heating procedure: the medium manganese steel casting blank is completely burnt in a heating furnace, and the heating temperature is 1156 ℃;
(2) a hot rolling procedure: the hot rolling and rough rolling start temperature is 1015 ℃, the finish rolling start temperature is 910 ℃, the finish rolling temperature is 786 ℃, and the outlet temperature of laminar cooling is 708 ℃;
(3) a coiling step: the coiling temperature is controlled to be 664 ℃;
(4) a heat treatment process: by adopting the twice distribution process after annealing, a sample is placed in a muffle furnace to be heated at 725 ℃ for 10min, then placed in 136 ℃ molten salt to be subjected to medium temperature heat preservation for 2min, and then moved to the muffle furnace to be subjected to heat preservation at 478 ℃ for 3.5min to carry out first carbon and manganese element distribution; then placing the mixture in 105 ℃ molten salt, preserving heat for 2.5min at medium temperature, moving to 405 ℃ and preserving heat for 7.5min to carry out secondary carbon and manganese element distribution; promoting the formation of residual austenite and then air-cooling to room temperature.
Hot-rolled medium manganese steel sheet of this example: the tensile strength is 942MPa, the yield strength is 693MPa, the elongation after fracture is 34 percent, the product of strength and elongation is 32 GPa%, and the volume fraction of the retained austenite is 25 percent.
Example 8
The thickness of the manganese steel plate in the hot rolling of the embodiment is 3.4mm, and the chemical composition and the mass percentage of the manganese steel plate are shown in Table 1.
The method for promoting the formation of the residual austenite of the manganese steel plate in the hot rolling comprises the following steps of heating, hot rolling, coiling and heat treatment, and the specific process steps are as follows:
(1) a heating procedure: the medium manganese steel casting blank is completely burnt through in a heating furnace, and the heating temperature is 1164 ℃;
(2) a hot rolling procedure: the hot rolling and rough rolling start temperature is 1042 ℃, the finish rolling start temperature is 950 ℃, the finish rolling temperature is 815 ℃, and the outlet temperature of laminar cooling is 712 ℃;
(3) a coiling step: the coiling temperature is controlled to be 688 ℃;
(4) a heat treatment process: adopting a twice-distribution process after annealing, placing a sample in a muffle furnace for heating at 755 ℃ for 13min, then placing the sample in 100 ℃ molten salt for moderate temperature and heat preservation for 1min, and then moving to the muffle furnace for heat preservation at 500 ℃ for 5min for first carbon and manganese element distribution; then placing the mixture in 120 ℃ molten salt, preserving heat for 1.5min at medium temperature, moving to 450 ℃ and preserving heat for 9.5min to carry out secondary carbon and manganese element distribution; promoting the formation of residual austenite and then air-cooling to room temperature.
Hot-rolled medium manganese steel sheet of this example: the tensile strength is 1007MPa, the yield strength is 754MPa, the elongation after fracture is 40%, the product of strength and elongation is 40.3 GPa%, and the volume fraction of the retained austenite is 28%.
Comparative example 1
The thickness specification of the manganese steel plate in the hot rolling of the comparative example is 5.0mm, and the chemical composition and the mass percentage content are shown in table 1.
The method for promoting the formation of the residual austenite of the hot-rolled manganese steel plate in the comparative example comprises the working procedures of heating, hot rolling and coiling, and the specific process steps are as follows:
(1) a heating procedure: the medium manganese steel casting blank is completely burnt through in a heating furnace, and the heating temperature is 1181 ℃;
(2) a hot rolling procedure: the hot rolling and rough rolling start temperature is 1037 ℃, the finish rolling start temperature is 941 ℃, the finish rolling temperature is 793 ℃, and the outlet temperature of laminar cooling is 724 ℃;
(3) a coiling step: the coiling temperature was controlled at 683 ℃.
The hot-rolled medium manganese steel sheet of this comparative example: the tensile strength is 1031MPa, the yield strength is 875MPa, the elongation after fracture is 21 percent, the product of strength and elongation is 21.6GPa percent, and the volume fraction of the retained austenite is 15 percent.
Comparative example 2
The thickness specification of the manganese steel plate in the hot rolling of the comparative example is 5.0mm, and the chemical composition and the mass percentage content are shown in table 1.
The method for promoting the formation of the residual austenite of the hot-rolled manganese steel plate in the comparative example comprises the working procedures of heating, hot rolling and coiling, and the specific process steps are as follows:
(1) a heating procedure: the medium manganese steel casting blank is completely burnt through in a heating furnace, and the heating temperature is 1181 ℃;
(2) a hot rolling procedure: the hot rolling and rough rolling start temperature is 1037 ℃, the finish rolling start temperature is 941 ℃, the finish rolling temperature is 793 ℃, and the outlet temperature of laminar cooling is 724 ℃;
(3) a coiling step: the coiling temperature was controlled at 683 ℃.
(4) A heat treatment process: the method adopts a twice distribution process after annealing, the heating temperature is 749 ℃, the heat preservation time is 8min, then the temperature is cooled to 141 ℃, the heat preservation time is 3min, the temperature is increased to 477 ℃, the heat preservation time is 3min, the first carbon and manganese element distribution is carried out to promote the formation of residual austenite, and then the air cooling is carried out to the room temperature.
(4) A heat treatment process: by adopting the twice distribution process after annealing, a sample is placed in a muffle furnace to be heated at the temperature of 749 ℃ for heat preservation for 8min, then placed in 141 ℃ molten salt to be subjected to isothermal heat preservation for 3min, then moved to the muffle furnace at the temperature of 477 ℃ for heat preservation for 3min to carry out first carbon and manganese element distribution to promote the formation of residual austenite, and then air-cooled to the room temperature.
The hot-rolled medium manganese steel sheet of this comparative example: the tensile strength is 993MPa, the yield strength is 847MPa, the elongation after fracture is 27%, the product of strength and elongation is 26.8 GPa%, and the volume fraction of retained austenite is 18%.
Table 1 examples 1 to 8 chemical composition of manganese steel sheet in hot rolling and mass% thereof
The balance of the ingredients in table 1 are Fe and inevitable impurity elements.
Although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that: modifications and equivalents may be made thereto without departing from the spirit and scope of the invention and it is intended to cover in the claims the invention as defined in the appended claims.
Claims (2)
1. The method for promoting the formation of the residual austenite of the hot-rolled medium manganese steel plate is characterized by comprising the working procedures of heating, hot rolling, coiling and heat treatment, and comprises the following specific process steps:
(1) a heating procedure: completely burning a medium manganese steel casting blank in a heating furnace at 1150-1200 ℃;
(2) a hot rolling procedure: the starting temperature of hot rolling and rough rolling is more than or equal to 1000 ℃, the starting temperature of finish rolling is 900-950 ℃, the finishing temperature of finish rolling is 760-830 ℃, and the outlet temperature of laminar cooling is 700-740 ℃;
(3) a coiling procedure: the coiling temperature is controlled to be 660-700 ℃;
(4) a heat treatment process: adopting a twice-distribution process after annealing, placing a sample in a muffle furnace for heating at 650-780 ℃ for 5-15 min, then placing the sample in molten salt at 100-150 ℃ for isothermal heat preservation for 1-5 min, and then moving the sample to the muffle furnace for heat preservation at 450-500 ℃ for 3-5 min for first carbon and manganese element distribution; then placing the sample in molten salt at the temperature of 100-120 ℃ for medium-temperature heat preservation for 1-3 min, then moving the sample to a muffle furnace at the temperature of 400-450 ℃ for heat preservation for 5-10 min for secondary carbon and manganese element distribution, and then taking out the sample and cooling the sample to room temperature;
the medium manganese steel plate comprises the following chemical components in percentage by mass: c: 0.10 to 0.25%, Mn: 4.95-7.02%, Si: 1.31-1.65%, Als: 0.013-0.035%, P is less than or equal to 0.015%, S is less than or equal to 0.010%, and the balance of Fe and inevitable impurity elements;
the thickness specification of the medium manganese steel plate is 2.0-5.0 mm;
the product of strength and elongation of the medium manganese steel plate is more than or equal to 31GPa, and the volume fraction of the residual austenite is more than or equal to 23%.
2. The method of promoting the formation of retained austenite in a hot rolled medium manganese steel sheet of claim 1, wherein said medium manganese steel sheet: the tensile strength is 941-1083 MPa, the yield strength is 693-862 MPa, and the elongation after fracture is 23-43%.
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