CN115772629B - Superplastic medium manganese steel for industrialization and preparation method thereof - Google Patents
Superplastic medium manganese steel for industrialization and preparation method thereof Download PDFInfo
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- 229910000617 Mangalloy Inorganic materials 0.000 title claims abstract description 77
- 238000002360 preparation method Methods 0.000 title claims abstract description 18
- 238000005096 rolling process Methods 0.000 claims abstract description 84
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 38
- 239000010959 steel Substances 0.000 claims abstract description 38
- 238000005097 cold rolling Methods 0.000 claims abstract description 32
- 238000010438 heat treatment Methods 0.000 claims abstract description 30
- 239000000126 substance Substances 0.000 claims abstract description 19
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 18
- 238000003723 Smelting Methods 0.000 claims abstract description 17
- 229910001566 austenite Inorganic materials 0.000 claims abstract description 16
- 239000011572 manganese Substances 0.000 claims abstract description 12
- 238000005242 forging Methods 0.000 claims abstract description 11
- 239000012535 impurity Substances 0.000 claims abstract description 9
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 4
- 238000000034 method Methods 0.000 claims description 13
- 238000001816 cooling Methods 0.000 claims description 12
- 230000009467 reduction Effects 0.000 claims description 9
- 238000005266 casting Methods 0.000 claims description 8
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 2
- 239000000203 mixture Substances 0.000 abstract description 8
- 239000007769 metal material Substances 0.000 abstract 1
- 230000008569 process Effects 0.000 description 8
- 239000000463 material Substances 0.000 description 7
- 238000005520 cutting process Methods 0.000 description 6
- 230000006698 induction Effects 0.000 description 6
- 238000007670 refining Methods 0.000 description 6
- 238000009864 tensile test Methods 0.000 description 6
- 230000000694 effects Effects 0.000 description 4
- 229910052748 manganese Inorganic materials 0.000 description 4
- 238000010008 shearing Methods 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- 229910052758 niobium Inorganic materials 0.000 description 3
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 238000005452 bending Methods 0.000 description 2
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- 238000011161 development Methods 0.000 description 2
- 238000004146 energy storage Methods 0.000 description 2
- 238000005098 hot rolling Methods 0.000 description 2
- 230000001965 increasing effect Effects 0.000 description 2
- 230000003993 interaction Effects 0.000 description 2
- 238000010587 phase diagram Methods 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 238000001953 recrystallisation Methods 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 230000009466 transformation Effects 0.000 description 2
- 229910052720 vanadium Inorganic materials 0.000 description 2
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- 230000006978 adaptation Effects 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
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- 238000003856 thermoforming Methods 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
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Abstract
The invention discloses industrial superplastic medium manganese steel and a preparation method thereof, and belongs to the technical field of metal material preparation. The chemical components of the superplastic medium manganese steel are respectively 0.05 to 0.3 percent of C; 3-12% of Mn; 0 to 8 percent of Al; nb is 0.05-0.3%; v is 0.05 to 0.1 percent; mo: 0.02-0.4%, and the balance of Fe and unavoidable impurities. The preparation method of the medium manganese steel mainly comprises the following steps: 1) smelting a steel ingot with a composition ratio, 2) heating and forging, 3) high differential speed ratio warm rolling, 4) high differential speed ratio cold rolling, 5) critical heat treatment, and finally obtaining the ultra-fine austenite and ferrite dual-phase medium manganese steel plate with the average grain size smaller than 200 nm. According to the designed chemical components and the preparation process, the microstructure is refined, so that the high-temperature elongation of the medium manganese steel is over 400 percent under the conditions of 500-700 ℃ and 10 ‑1s‑1～10‑3s‑1 strain rate, and the low-temperature Gao Suchao plasticity of the medium manganese steel is further realized.
Description
Technical Field
The invention relates to the technical field of preparation of medium manganese steel, in particular to industrial superplastic medium manganese steel and a preparation method thereof.
Background
The automobile light weight is an effective way for saving energy and reducing emission, and is a subject of development of the automobile industry. Compared with magnesium, aluminum and alloys thereof, the advanced high-strength steel can obviously reduce the weight of the automobile body on the premise of not increasing the production cost of the automobile, and becomes a main material for the light weight of the automobile at present. As a typical representation of advanced high strength steels, medium manganese steels (3.0-12 wt.% Mn) have ultra-fine, metastable and multi-sized microstructures, which can undergo TRIP (Transformation Induced Plasticity) effect during plastic deformation, making them have tensile strength greater than 1000MPa and elongation of 30%, which are hot spots for materials research. However, medium manganese steels face a series of technical challenges in the forming process: (1) Because of high strength, in the cold forming process, the traditional forming equipment is seriously worn, the process cost is increased, or rebound phenomenon occurs, and the forming precision of the structural part is affected; (2) In the thermoforming process, or surface oxidation occurs, and dimensional accuracy is difficult to control accurately; (3) high precision complex components are difficult to produce.
The research shows that the medium manganese steel has the superplastic characteristics of small deformation resistance, good fluidity, strong deformation capacity and the like under certain deformation conditions, and the method provides a thought for solving the problems of the forming rebound of the medium manganese steel and the difficult production of complex components. However, the existing superplastic manganese steel has the defects of high forming temperature and low strain rate, which is unfavorable for industrial application. Therefore, development of superplastic medium manganese steel suitable for industrial application has important significance.
Disclosure of Invention
The invention provides industrial superplastic medium manganese steel and a preparation method thereof, which aim to solve the technical problems of high forming temperature and low strain rate of the existing superplastic medium manganese steel.
The technical scheme adopted by the invention is as follows:
The superplastic medium manganese steel for industrialization is characterized by comprising the following chemical components in percentage by mass: 0.05 to 0.3 percent of C; 3-12% of Mn; 0 to 8 percent of Al; nb is 0.05-0.3%; v is 0.05 to 0.1 percent; mo: 0.02-0.4%, and the balance of Fe and unavoidable impurities.
Further, the microstructure of the medium manganese steel is duplex austenite and ferrite, and the grain size of the austenite and ferrite is below 0.2 um.
Further, the medium manganese steel is stretched at a strain rate of 10 -1s-1～10-3s-1 within a temperature range of 500-750 ℃, and the elongation of the medium manganese steel is more than 400%.
The preparation method of any industrial superplastic medium manganese steel comprises the following steps:
Step 1, smelting: proportioning, smelting and casting according to chemical components of industrial superplastic medium manganese steel to obtain a steel ingot;
Step 2, forging: heating the steel ingot to 1100-1200 ℃, preserving heat for 3-4 hours, and forging into a steel billet;
Step 3, high differential speed ratio warm rolling: heating the steel billet to 800-900 ℃, preserving heat for 2 hours, performing high differential speed ratio warm rolling for 6-7 times, wherein the rolling temperature interval is 500-700 ℃, the total rolling reduction is 60-70%, and then performing air cooling to room temperature to obtain a warm rolled plate;
step 4, high differential ratio cold rolling: cold rolling the warm-rolled plate by a cold rolling mill to obtain a cold-rolled plate, wherein the rolling reduction is 85% -95%;
step 5, critical heat treatment: and heating the cold-rolled sheet to the temperature of the two-phase region, and then water-cooling or air-cooling to room temperature to obtain the superplastic medium manganese steel with superfine, equiaxed and uniform double-phase austenite and ferrite microstructure.
By adopting the technical scheme, the shearing deformation is introduced through high-speed differential speed hot rolling, so that on one hand, the deformation-induced ferrite phase transformation is promoted, and on the other hand, the grain size of the material can be thinned through the shearing-induced fine-grain effect, so that the aim of tissue refinement is achieved. Through high-speed-difference ratio cold rolling, shear deformation can be introduced into the cold rolling process of medium manganese steel again, more slip systems can be started compared with conventional cold rolling, more dislocation slip systems are excited, the grain size of the material is broken in the rolling deformation process, more deformation energy storage can be reserved in the material, and driving force is provided for subsequent recrystallization of medium manganese steel in the critical heat treatment process. Through critical heat treatment, the experimental steel can utilize deformation energy storage in the high differential ratio cold rolling process to perform recrystallization, so as to realize grain re-refinement, and then water cooling or air cooling is performed to room temperature, so that the ultra-fine, equiaxed and uniform double-phase austenite and ferrite microstructure is obtained.
Further, the thickness of the warm rolled plate obtained in the step 3 is not more than 16mm and not less than 12mm. The proper thickness is favorable for the precipitation of micro-alloy precipitates so as to facilitate the interaction with dislocation in the rolling process, thereby achieving the aim of further tissue refinement.
In the step 3, the rolling speed ratio of the upper roller and the lower roller which are rolled at high differential speed ratio is more than or equal to 4. In this step, in order to alleviate plate bending due to different rolling speeds of upper and lower rolls, plate reversing reciprocating rolling operation is adopted in the rolling process.
In the step 4, the rolling speed ratio of the upper and lower rolls of the high differential speed ratio cold rolling is more than or equal to 3. In this step, in order to alleviate plate bending due to different rolling speeds of upper and lower rolls, plate reversing reciprocating rolling operation is adopted in the rolling process.
Further, in step 5, the cold-rolled sheet is heated to the temperature of the two-phase region and then is kept for 3 to 5 minutes, and then is cooled or air-cooled to room temperature, so that the superfine equiaxed duplex austenitic and ferritic microstructure with smaller grain size can be obtained.
The invention has the beneficial effects that:
(1) Aiming at the difficult problems of high superplastic deformation temperature and low strain rate of the prior medium manganese steel, the invention adopts the thought of microstructure refinement to prepare the medium manganese steel microstructure, because grain refinement can lead the grain boundary sliding of the superplastic material to be easy to start, and low-temperature and high-speed superplasticity can be easily carried out, however, common grain refinement methods, such as equal channel angular extrusion (Equal Channel Angular Pressing, ECAP), accumulated lap welding (Accumulative Roll Bonding, ARB) and the like, have certain limitations and are specifically embodied in: (1) high production cost; (2) The obtained sample size is usually small, which is not beneficial for industrial application. According to the invention, the chemical components of the medium manganese steel are optimized, and the high differential ratio rolling technology is adopted to roll the medium manganese steel by shearing force, so that the refining of the microstructure of the medium manganese steel is realized, the aim of low-temperature high-speed superplasticity of the medium manganese steel is fulfilled, and the method has the characteristics of small equipment dependence, short flow, capability of preparing large-size medium manganese steel plates and suitability for industrial application.
(2) Unlike available medium manganese steel composition design, the present invention adopts Nb, mo and V composite microalloying, in which Nb and Mo may be separated out in high temperature area, and this has important effect in regulating the microstructure of medium manganese steel in high temperature area, and the V separating out temperature is relatively less to play a role in low temperature area.
(3) Unlike available microstructure refining process, the present invention has three steps of refining medium manganese steel microstructure, including the first step of refining the medium manganese steel microstructure through inducing ferrite core to refine crystal grain in high differential speed ratio hot rolling, the second step of refining the medium manganese steel grain through the interaction of microalloy precipitate and dislocation and high shearing force in high differential speed ratio cold rolling, and the third step of re-crystallizing the medium manganese steel and refining the microstructure of material in critical heat treatment. Through the comprehensive effect of the design, the superfine medium manganese steel microstructure is obtained, and the industrial application of the medium manganese steel superplasticity is realized.
Drawings
FIG. 1 is a diagram of the medium manganese steel after high differential temperature rolling in example 1 of the present invention.
FIG. 2 is a golden phase diagram of medium manganese steel after high differential cold rolling in example 1 of the present invention.
FIG. 3 is a golden phase diagram of medium manganese steel after critical heat treatment in example 1 of the present invention.
Detailed Description
The invention will be further described with reference to specific examples to facilitate an understanding of the invention, but are not intended to limit the invention thereto.
Example 1
The superplastic medium manganese steel for industrialization comprises the following chemical components in percentage by mass:
0.05% C, 3.0% Mn, 0.05% Nb, 0.05% V, 0.02% Mo, the balance Fe and unavoidable impurities.
The preparation method of the medium manganese steel comprises the following steps:
step 1, smelting: in a vacuum induction furnace, steel ingots are obtained according to the chemical composition ratio of medium manganese steel by smelting and casting.
Step 2, forging: the steel ingot is heated to 1100 ℃, kept for 3 hours, and forged into a steel billet with the cross section of 100mm multiplied by 40 mm.
Step 3, high differential speed ratio warm rolling: the billet is heated to 800 ℃, kept for 2 hours, subjected to 6-pass high differential speed ratio warm rolling, the rolling speed ratio of an upper rolling mill roller and a lower rolling mill roller is 4, the rolling temperature interval is 500-700 ℃, and then air-cooled to room temperature, so as to obtain a 16mm thick warm rolled plate, and the microstructure of the obtained warm rolled plate is shown in figure 1.
Step 4, high differential ratio cold rolling: and (3) cold rolling the Gao Chasu-ratio warm-rolled sheet by a cold rolling mill, wherein the rolling speed ratio of the upper rolling mill roller to the lower rolling mill roller is 3, and obtaining a cold-rolled sheet, and the microstructure of the obtained cold-rolled sheet is shown in figure 2.
Step 5, critical heat treatment: the cold-rolled sheet was heated to 500 c and kept for 3min to obtain a superplastic medium manganese steel having a "ultra-fine, equiaxed, uniform" duplex austenitic and ferritic microstructure, the average grain size of the austenitic and ferritic being 160nm, the microstructure of the resulting superplastic medium manganese steel being as shown in fig. 3.
The critically heat treated samples were then subjected to a high temperature tensile test in which the tensile samples were processed by wire cutting according to American standard (ASTM-E8-E8M). The tensile results are shown in Table 1, and the test steels obtained an elongation of over 400% at a strain rate of 10 -1s-1～10- 3s-1 at 500℃to 750 ℃.
TABLE 1
| Deformation temperature | Strain rate | High temperature elongation |
| 500℃ | 10-1s-1 | 412％ |
| 500℃ | 10-3s-1 | 942％ |
| 600℃ | 10-1s-1 | 689％ |
| 600℃ | 10-3s-1 | 1052％ |
| 750℃ | 10-1s-1 | 1125％ |
| 750℃ | 10-3s-1 | 1236％ |
Example 2
The superplastic medium manganese steel for industrialization comprises the following chemical components in percentage by mass:
0.3% of C, 12.0% of Mn, 8.0% of Al, 0.3% of Nb, 0.1% of V, 0.4% of Mo, and the balance of Fe and unavoidable impurities.
The preparation method of the medium manganese steel comprises the following steps:
Step1, smelting: in a vacuum induction furnace, steel ingots are obtained according to the chemical composition ratio of medium manganese steel by smelting and casting.
Step 2, forging: the steel ingot is heated to 1200 ℃, kept for 4 hours, and forged into a steel billet with the cross section of 100mm multiplied by 40 mm.
Step 3, high differential speed ratio warm rolling: heating the billet to 900 ℃, preserving heat for 2 hours, performing 7-pass high differential speed ratio warm rolling, wherein the rolling speed ratio of the upper rolling mill and the lower rolling mill is 5, the rolling temperature interval is 500-700 ℃, the rolling reduction is 70%, and then performing air cooling to room temperature to obtain a warm rolled plate with the thickness of 12 mm.
Step 4, high differential ratio cold rolling: and (3) cold rolling the warm-rolled sheet by a cold rolling mill, wherein the rolling ratio of the upper rolling mill to the lower rolling mill is 3.5, and the cold-rolled sheet is obtained.
Step 5, critical heat treatment: and heating the cold-rolled sheet to 800 ℃, and preserving heat for 5min to obtain the superplastic medium manganese steel with the microstructure of ultra-fine, equiaxed and uniform duplex austenite and ferrite, wherein the average grain size of the austenite and the ferrite is 200nm.
The critically heat treated samples were then subjected to a high temperature tensile test in which the tensile samples were processed by wire cutting according to American standard (ASTM-E8-E8M). The tensile results are shown in Table 2, and the test steels obtained elongation exceeding 400% at 10 -1s-1～10-3s-1 strain rates in the range of 500℃to 750 ℃.
TABLE 2
| Deformation temperature | Strain rate | High temperature elongation |
| 500℃ | 10-1s-1 | 408％ |
| 500℃ | 10-3s-1 | 789％ |
| 750℃ | 10-1s-1 | 658％ |
| 750℃ | 10-3s-1 | 1102％ |
Example 3
The superplastic medium manganese steel for industrialization comprises the following chemical components in percentage by mass:
0.2% of C, 7.0% of Mn, 3.0% of Al, 0.1% of Nb, 0.1% of V, 0.2% of Mo, and the balance of Fe and unavoidable impurities.
The preparation method of the medium manganese steel comprises the following steps:
Step1, smelting: in a vacuum induction furnace, steel ingots are obtained according to the chemical composition ratio of medium manganese steel by smelting and casting.
Step 2, forging: the steel ingot is heated to 1100 ℃, kept for 4 hours, and forged into a steel billet with the cross section of 100mm multiplied by 40 mm.
Step 3, high differential speed ratio warm rolling: heating the billet to 850 ℃, preserving heat for 2 hours, performing 7-pass high differential speed ratio warm rolling, wherein the rolling speed ratio of the upper rolling mill roller and the lower rolling mill roller is 4.5, the rolling temperature interval is 500-700 ℃, the rolling reduction is 60%, and then performing air cooling to room temperature to obtain a warm rolled plate with the thickness of 16 mm.
Step 4, high differential ratio cold rolling: and (3) cold rolling the warm-rolled sheet by a cold rolling mill, wherein the rolling ratio of the upper rolling mill to the lower rolling mill is 4, and the cold-rolled sheet is obtained.
Step 5, critical heat treatment: and heating the cold-rolled sheet to 700 ℃, and preserving heat for 5min to obtain the superplastic medium manganese steel with the microstructure of ultra-fine, equiaxed and uniform duplex austenite and ferrite, wherein the average grain size of the austenite and ferrite is 186nm.
The critically heat treated samples were then subjected to a high temperature tensile test in which the tensile samples were processed by wire cutting according to American standard (ASTM-E8-E8M). The tensile results are shown in Table 3, and the test steels obtained elongation exceeding 400% at 10 -1s-1～10-3s-1 strain rate at 500℃to 750 ℃.
TABLE 3 Table 3
Example 4
The superplastic medium manganese steel for industrialization comprises the following chemical components in percentage by mass:
0.1% of C, 5.0% of Mn, 2.0% of Al, 0.1% of Nb, 0.1% of V, 0.2% of Mo, and the balance of Fe and unavoidable impurities.
The preparation method of the medium manganese steel comprises the following steps:
Step1, smelting: in a vacuum induction furnace, steel ingots are obtained according to the chemical composition ratio of medium manganese steel by smelting and casting.
Step 2, forging: the steel ingot is heated to 1100 ℃, kept for 3 hours, and forged into a steel billet with the cross section of 100mm multiplied by 40 mm.
Step 3, high differential speed ratio warm rolling: heating the billet to 850 ℃, preserving heat for 2 hours, performing high differential speed ratio warm rolling for 7 times, wherein the rolling speed ratio of the upper rolling mill roller and the lower rolling mill roller is 4.5, the rolling temperature interval is 500-700 ℃, the rolling reduction is 60%, and then performing air cooling to room temperature to obtain a warm rolled plate with the thickness of 16 mm.
Step 4, high differential ratio cold rolling: and (3) cold rolling the warm-rolled sheet by a cold rolling mill, wherein the rolling ratio of the upper rolling mill to the lower rolling mill is 4, and the cold-rolled sheet is obtained.
Step 5, critical heat treatment: and heating the cold-rolled sheet to 700 ℃, and preserving heat for 5min to obtain the superplastic medium manganese steel with the microstructure of ultra-fine, equiaxed and uniform duplex austenite and ferrite, wherein the average grain size of the austenite and the ferrite is 176nm.
The critically heat treated samples were then subjected to a high temperature tensile test in which the tensile samples were processed by wire cutting according to American standard (ASTM-E8-E8M). The tensile results are shown in Table 4, and the test steels obtained elongation exceeding 400% at 10 - 1s-1～10-3s-1 strain rate at a temperature ranging from 500℃to 750 ℃.
TABLE 4 Table 4
| Deformation temperature | Strain rate | High temperature elongation |
| 500℃ | 10-1s-1 | 542％ |
| 500℃ | 10-3s-1 | 724％ |
| 750℃ | 10-1s-1 | 682％ |
| 750℃ | 10-3s-1 | 1101％ |
Example 5
The superplastic medium manganese steel for industrialization comprises the following chemical components in percentage by mass:
0.1% of C, 7.0% of Mn, 3.0% of Al, 0.05% of Nb, 0.1% of V, 0.4% of Mo, and the balance of Fe and unavoidable impurities.
The preparation method of the medium manganese steel comprises the following steps:
step 1, smelting: in a vacuum induction furnace, steel ingots are obtained according to the chemical composition ratio of manganese steel by smelting and casting.
Step 2, forging: the steel ingot is heated to 1100 ℃, kept for 3 hours, and forged into a steel billet with the cross section of 100mm multiplied by 40 mm.
Step 3, high differential speed ratio warm rolling: heating the billet to 850 ℃, preserving heat for 2 hours, performing high differential speed ratio warm rolling for 7 times, wherein the rolling speed ratio of the upper rolling mill roller and the lower rolling mill roller is 4.5, the rolling temperature interval is 500-700 ℃, the rolling reduction is 60%, and then performing air cooling to room temperature to obtain a warm rolled plate with the thickness of 16 mm.
Step 4, high differential ratio cold rolling: and (3) cold rolling the warm-rolled sheet by a cold rolling mill, wherein the rolling ratio of the upper rolling mill to the lower rolling mill is 4, and the cold-rolled sheet is obtained.
Step 5, critical heat treatment: and heating the cold-rolled sheet to 700 ℃, and preserving heat for 5min to obtain the superplastic medium manganese steel with the microstructure of ultra-fine, equiaxed and uniform duplex austenite and ferrite.
The critically heat treated samples were then subjected to a high temperature tensile test in which the tensile samples were processed by wire cutting according to American standard (ASTM-E8-E8M). The stretching results are shown in Table 5. The elongation of the experimental steel is over 400% at 10 -1s-1～10-3s-1 strain rate in the range of 500-600 ℃.
TABLE 5
| Deformation temperature | Strain rate | High temperature elongation |
| 500℃ | 10-1s-1 | 436％ |
| 500℃ | 10-3s-1 | 823％ |
| 600℃ | 10-1s-1 | 643％ |
| 600℃ | 10-3s-1 | 984％ |
Example 6
The superplastic medium manganese steel for industrialization comprises the following chemical components in percentage by mass:
0.2% of C, 4.0% of Mn, 2.0% of Al, 0.1% of Nb, 0.1% of V, 0.3% of Mo, and the balance of Fe and unavoidable impurities.
The preparation method of the medium manganese steel comprises the following steps:
Step1, smelting: in a vacuum induction furnace, steel ingots are obtained according to the chemical composition ratio of medium manganese steel by smelting and casting.
Step 2, forging: the steel ingot is heated to 1200 ℃, kept for 4 hours, and forged into a steel billet with the cross section of 100mm multiplied by 40 mm.
Step 3, high differential speed ratio warm rolling: heating the billet to 900 ℃, preserving heat for 2 hours, performing high differential speed ratio warm rolling for 7 times, wherein the rolling speed ratio of the upper rolling mill and the lower rolling mill is 5, the rolling temperature interval is 500-700 ℃, the rolling reduction is 70%, and then performing air cooling to room temperature to obtain a warm rolled plate with the thickness of 12 mm.
Step 4, high differential ratio cold rolling: and (3) cold rolling the warm-rolled sheet by a cold rolling mill, wherein the rolling ratio of the upper rolling mill to the lower rolling mill is 3.5, and the cold-rolled sheet is obtained.
Step 5, critical heat treatment: and heating the cold-rolled sheet to 800 ℃, and preserving heat for 5min to obtain the superplastic medium manganese steel with the microstructure of ultra-fine, equiaxed and uniform duplex austenite and ferrite.
The critically heat treated samples were then subjected to a high temperature tensile test in which the tensile samples were processed by wire cutting according to American standard (ASTM-E8-E8M). The stretching results are shown in Table 6. The elongation of the experimental steel is over 400% at 10 -1s-1～10-3s-1 strain rate in the range of 500-750 ℃.
TABLE 6
| Deformation temperature | Strain rate | High temperature elongation |
| 500℃ | 10-1s-1 | 425％ |
| 500℃ | 10-3s-1 | 684％ |
| 750℃ | 10-1s-1 | 725％ |
| 750℃ | 10-3s-1 | 1225％ |
The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention and remain within the scope of the invention.
Claims (4)
1. The preparation method of the superplastic medium manganese steel for industrialization is characterized by comprising the following chemical components in percentage by mass: 0.05 to 0.3 percent of C; 3-12% of Mn; 0 to 8 percent of Al; nb is 0.05-0.3%; v is 0.05 to 0.1 percent; mo: 0.02-0.4%, and the balance of Fe and unavoidable impurities;
the preparation method of the medium manganese steel comprises the following steps:
Step 1, smelting: proportioning, smelting and casting according to chemical components of industrial superplastic medium manganese steel to obtain a steel ingot;
Step 2, forging: heating the steel ingot to 1100-1200 ℃, preserving heat for 3-4 hours, and forging into a steel billet;
step 3, high differential speed ratio warm rolling: heating the steel billet to 800-900 ℃, preserving heat for 2 hours, performing high differential speed ratio warm rolling for 6-7 times, wherein the rolling temperature interval is 500-700 ℃, the total rolling reduction is 60-70%, and then performing air cooling to room temperature to obtain a warm rolled plate; the rolling speed ratio of the upper roller and the lower roller is more than or equal to 4;
step 4, high differential ratio cold rolling: cold rolling the warm-rolled plate by a cold rolling mill to obtain a cold-rolled plate, wherein the rolling reduction is 85% -95%; the rolling speed ratio of the upper roller and the lower roller is more than or equal to 3;
step 5, critical heat treatment: and heating the cold-rolled sheet to the temperature of the two-phase region, preserving heat for 3-5 min, and then cooling the cold-rolled sheet to room temperature by water or air to obtain the superplastic medium manganese steel with superfine, equiaxed and uniform double-phase austenite and ferrite microstructure.
2. The method for producing superplastic medium manganese steel for industrialization according to claim 1, wherein the microstructure of the medium manganese steel is two-phase austenite and ferrite, and the grain size of the austenite and ferrite is 0.2um or less.
3. The method for preparing industrial superplastic medium manganese steel according to claim 1, wherein the medium manganese steel is stretched at a strain rate of 10 -1s-1～10-3s-1 at a temperature of 500-750 ℃ and has an elongation of more than 400%.
4. The method for preparing industrial superplastic medium manganese steel according to claim 1, wherein the thickness of the warm rolled plate obtained in the step 3 is not more than 16mm and not less than 12mm.
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