CN115772629A - Industrial superplastic medium manganese steel and preparation method thereof - Google Patents
Industrial superplastic medium manganese steel and preparation method thereof Download PDFInfo
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- 229910000617 Mangalloy Inorganic materials 0.000 title claims abstract description 79
- 238000002360 preparation method Methods 0.000 title claims abstract description 18
- 238000005096 rolling process Methods 0.000 claims abstract description 92
- 238000010438 heat treatment Methods 0.000 claims abstract description 39
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 36
- 239000010959 steel Substances 0.000 claims abstract description 36
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 21
- 229910001566 austenite Inorganic materials 0.000 claims abstract description 19
- 239000000126 substance Substances 0.000 claims abstract description 19
- 238000003723 Smelting Methods 0.000 claims abstract description 17
- 238000005242 forging Methods 0.000 claims abstract description 17
- 239000011572 manganese Substances 0.000 claims abstract description 13
- 239000012535 impurity Substances 0.000 claims abstract description 9
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 8
- 229910052758 niobium Inorganic materials 0.000 claims abstract description 6
- 229910052720 vanadium Inorganic materials 0.000 claims abstract description 5
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 4
- 238000005097 cold rolling Methods 0.000 claims description 33
- 238000000034 method Methods 0.000 claims description 20
- 230000009467 reduction Effects 0.000 claims description 16
- 238000001816 cooling Methods 0.000 claims description 10
- 238000005266 casting Methods 0.000 claims description 8
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 5
- 239000007769 metal material Substances 0.000 abstract 1
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- 238000005520 cutting process Methods 0.000 description 6
- 230000000694 effects Effects 0.000 description 6
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- 238000009864 tensile test Methods 0.000 description 6
- 230000009286 beneficial effect Effects 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 3
- 238000004146 energy storage Methods 0.000 description 3
- 230000003993 interaction Effects 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
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- 239000002244 precipitate Substances 0.000 description 2
- 238000007670 refining Methods 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000004134 energy conservation Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
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Abstract
The invention discloses an industrial superplastic medium manganese steel and a preparation method thereof, belonging to the technical field of metal material preparation. The superplastic medium manganese steel comprises the chemical components of 0.05-0.3% of C by mass percent; 3 to 12 percent of Mn; 0 to 8 percent of Al; 0.05 to 0.3 percent of Nb; 0.05 to 0.1 percent of V; mo:0.02 to 0.4 percent, and the balance of Fe and inevitable impurities. The preparation method of the medium manganese steel mainly comprises the following steps: 1) smelting a steel ingot with a component ratio, 2) heating and forging, 3) high-differential-speed warm rolling, and 4) high-differential-speed cold rollingAnd 5) carrying out critical heat treatment to finally obtain the superfine austenite and ferrite dual-phase medium manganese steel plate with the average grain size of less than 200nm. According to the designed chemical components and preparation process, the invention leads the medium manganese steel to be refined at 500-700 ℃ and 10 ℃ through the microstructure ‑1 s ‑1 ～10 ‑3 s ‑1 The high-temperature elongation of over 400 percent is obtained under the condition of strain rate, and further the low-temperature high-speed superplasticity of the medium manganese steel is realized.
Description
Technical Field
The invention relates to the technical field of medium manganese steel preparation, in particular to industrial superplastic medium manganese steel and a preparation method thereof.
Background
The light weight of the automobile is an effective way for energy conservation and emission reduction, and is the 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 the main material for lightening the automobile at present. As a typical representative of advanced high-strength steels, medium manganese steels (3.0 to 12wt.% Mn) have an ultrafine, metastable, and multi-dimensional microstructure, and during plastic deformation, a TRIP (Transformation Induced Plasticity) effect can occur, so that they have a tensile strength of more than 1000MPa and an elongation of 30%, which has been a hot spot for material research. However, medium manganese steels face a series of technical difficulties in the forming process: (1) Due to high strength, in the cold forming process, the traditional forming equipment is seriously abraded, the process cost is increased, and the forming precision of a structural part is influenced by the rebound phenomenon; (2) In the hot forming process, or surface oxidation occurs, and the dimensional precision is difficult to control accurately; and (3) the production of high-precision complex components is difficult.
Researches find that the medium manganese steel has the superplastic characteristics of small deformation resistance, good fluidity, strong deformability and the like under a certain deformation condition, and an idea is provided for solving the problems of medium manganese steel forming resilience and complex member production difficulty. However, the existing superplastic manganese steel has the defects of high forming temperature and low strain rate, which is not favorable for industrial application. Therefore, the development of the superplastic medium manganese steel suitable for industrial application has important significance.
Disclosure of Invention
The invention provides an industrial superplastic medium manganese steel and a preparation method thereof, aiming at solving 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 to 12 percent of Mn; 0 to 8 percent of Al; 0.05 to 0.3 percent of Nb; 0.05 to 0.1 percent of V; mo: 0.02-0.4%, and the balance of Fe and inevitable impurities.
Furthermore, the microstructure of the medium manganese steel is dual-phase austenite and ferrite, and the grain size of the austenite and the ferrite is below 0.2 um.
Further, the medium manganese steel is 10 ℃ within the temperature range of 500-750 DEG C -1 s -1 ～10 -3 s -1 And stretching at a strain rate, wherein the elongation is more than 400%.
The preparation method of any one of the industrial superplastic medium manganese steels 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 h, and forging into a steel billet;
step 3, high differential speed ratio warm rolling: heating a steel billet to 800-900 ℃, preserving heat for 2h, carrying out 6-7-pass differential speed ratio warm rolling, wherein the rolling temperature interval is 500-700 ℃, the total reduction rate is 60-70%, and then carrying out air cooling to the intermediate room temperature to obtain a warm rolling plate;
step 4, cold rolling with high differential ratio: cold rolling the warm-rolled plate by a cold rolling mill with the reduction rate of 85-95% to obtain a cold-rolled plate;
and 5, critical heat treatment: and heating the cold-rolled sheet to the temperature of a two-phase region, and then cooling the cold-rolled sheet to room temperature by water or air to obtain the superplastic medium manganese steel with superfine, equiaxial and uniform duplex austenite and ferrite microstructures.
By adopting the technical scheme, through high differential speed ratio warm rolling and introduction of shear deformation, on one hand, deformation induced ferrite phase change is promoted, on the other hand, the grain size of the material can be refined through a shear induced fine grain effect, and therefore the purpose of tissue refinement is achieved. Through high differential ratio cold rolling, the shearing deformation can be introduced into the cold rolling process of the medium manganese steel again, compared with the conventional cold rolling, more sliding systems can be started, more dislocation sliding is excited, the grain size of the material is crushed in the rolling deformation process, in addition, more deformation energy storage can be stored in the material, and a driving force is provided for the subsequent recrystallization of the 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 recrystallize, so that grains are refined again, and then the experimental steel is cooled by water or air to room temperature, so as to obtain superfine, equiaxial and uniform duplex austenite and ferrite microstructures.
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 beneficial to the precipitation of microalloy precipitates so as to be convenient for interaction with dislocation in the rolling process, thereby achieving the aim of further structure refinement.
Furthermore, in the step 3, the rolling speed ratio of the upper and lower rollers of the high differential speed ratio warm rolling is more than or equal to 4. In this step, in order to reduce the bending of the plate shape caused by the difference of the rolling speed of the upper and lower rolls, the plate reverse reciprocating rolling operation is adopted in the rolling process.
Further, in the step 4, the rolling speed ratio of the upper and lower rollers of the high differential ratio cold rolling is more than or equal to 3. In the step, in order to reduce the bending of the plate shape caused by the difference of the rolling speed of the upper rolling and the lower rolling, the plate reversing reciprocating rolling operation is adopted in the rolling process.
Further, in the step 5, the cold-rolled sheet is heated to the temperature of the two-phase region, then is subjected to heat preservation for 3min to 5min, and then is cooled by water or air to the room temperature, so that superfine and equiaxial duplex austenite and ferrite microstructures with smaller grain size can be obtained.
The invention has the beneficial effects that:
(1) Aiming at the problems of high superplastic deformation temperature and low strain rate of the traditional medium manganese steel, the invention adopts the idea of microstructure refinement to prepare the medium manganese steel microstructure, because the grain refinement can enable the grain boundary of the superplastic material to slide and start easily, and the superplasticity at low temperature and high speed is easy to carry out, however, common grain refinement methods, such as Equal Channel Angular Pressing (ECAP), accumulative Roll Bonding (ARB) and the like, have certain limitations, and the specific embodiment is as follows: (1) the production cost is high; (2) The size of the obtained sample is usually small, which is not beneficial to industrial application. According to the invention, through optimizing the chemical components of the medium manganese steel and adopting a high differential ratio rolling technology, the medium manganese steel is subjected to shear force rolling, and the microstructure of the medium manganese steel is refined, so that the purpose of low-temperature high-speed superplasticity of the medium manganese steel is achieved, 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) Different from the existing medium manganese steel component design, the invention adopts Nb, mo and V composite microalloying, wherein Nb and Mo can be compositely separated out in a high temperature region, which has an important effect on the control of the microstructure of the medium manganese steel in the high temperature region, and V separation temperature is relatively low, which is beneficial to playing a role in a low temperature region, so that the microstructure of the medium manganese steel can be synergistically controlled with the high differential ratio rolling actual process in the invention on the one hand, and the microstructure of the medium manganese steel can be finally refined through the interaction of pinning effect and the unique high differential ratio rolling dislocation multiplication effect on the other hand.
(3) The method is different from the conventional common microstructure refining process, and comprises the steps of refining the microstructure of the medium manganese steel in three steps, wherein in the first step, the crystal grains are refined by inducing ferrite nucleation through unique shear deformation in the high differential ratio warm rolling process, in the second step, the crystal grains of the medium manganese steel are refined through the interaction of microalloy precipitates and dislocation and strong shear force in the high differential ratio cold rolling process, and in the third step, the method fully utilizes high deformation energy storage in the high differential ratio cold rolling process in the critical heat treatment process, and is matched with short-time critical heat treatment to recrystallize the medium manganese steel and refine the microstructure of the material again. By the comprehensive effect of the design, the superfine medium manganese steel microstructure is obtained, and the industrial application of medium manganese steel superplasticity is facilitated.
Drawings
FIG. 1 is a metallographic picture of a medium manganese steel after warm rolling at a high differential speed ratio according to example 1 of the present invention.
FIG. 2 is a metallographic graph of a medium manganese steel sheet after cold rolling at a high differential ratio according to example 1 of the present invention.
FIG. 3 is a gold phase diagram of the medium manganese steel after critical heat treatment according to example 1 of the present invention.
Detailed Description
The invention is further described below with reference to specific examples to facilitate understanding of the invention, but the invention is not limited 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, 0.02wt.% Mo, and 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 by smelting and casting according to the chemical component proportion of the medium manganese steel.
Step 2, forging: heating the steel ingot to 1100 ℃, preserving heat for 3 hours, and forging into a steel billet with the sectional area of 100mm multiplied by 40 mm.
Step 3, high differential speed ratio warm rolling: heating the billet to 800 ℃, preserving heat for 2h, carrying out 6-pass differential speed ratio warm rolling, wherein the rolling speed ratio of an upper rolling mill and a lower rolling mill is 4, the rolling temperature interval is 500-700 ℃, then carrying out air cooling to room temperature to obtain a warm rolling plate with the thickness of 16mm, and the microstructure of the obtained warm rolling plate is shown in figure 1.
Step 4, cold rolling with high differential ratio: and (3) cold rolling the high differential speed specific temperature rolled sheet by a cold rolling mill at a reduction rate of 85%, wherein the rolling speed ratio of an upper rolling mill to a lower rolling mill is 3, so as to obtain the cold rolled sheet, and the microstructure of the obtained cold rolled sheet is shown in figure 2.
And 5, critical heat treatment: and heating the cold-rolled sheet to 500 ℃, and preserving heat for 3min to obtain the superplastic medium manganese steel with superfine, equiaxed and uniform double-phase austenite and ferrite microstructures, wherein the average grain size of the austenite and the ferrite is 160nm, and the microstructure of the obtained superplastic medium manganese steel is shown in figure 3.
The critically heat treated specimens were then subjected to a high temperature tensile test in which the tensile specimens were processed using wire cutting according to the American Standard (ASTM-E8-E8M). The tensile results are shown in Table 1, and the tensile results are shown in the experimental steels at 10 ℃ within 500 ℃ to 750 ℃ -1 s -1 ～10 - 3 s -1 Elongation in excess of 400% was obtained at strain rate.
TABLE 1
| Temperature of deformation | Rate of strain | Elongation at high temperature |
| 500℃ | 10 -1 s -1 | 412％ |
| 500℃ | 10 -3 s -1 | 942％ |
| 600℃ | 10 -1 s -1 | 689％ |
| 600℃ | 10 -3 s -1 | 1052％ |
| 750℃ | 10 -1 s -1 | 1125％ |
| 750℃ | 10 -3 s -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 Fe and inevitable 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 by smelting and casting according to the chemical component proportion of the medium manganese steel.
Step 2, forging: heating the steel ingot to 1200 ℃, preserving heat for 4 hours, and forging into a billet with the sectional area of 100mm multiplied by 40 mm.
Step 3, high differential speed ratio warm rolling: heating the billet to 900 ℃, preserving heat for 2h, carrying out 7-pass differential speed ratio warm rolling, wherein the rolling speed ratio of an upper rolling mill and a lower rolling mill is 5, the rolling temperature interval is 500-700 ℃, the reduction rate is 70%, and then carrying out air cooling to room temperature to obtain a warm-rolled plate with the thickness of 12mm.
Step 4, cold rolling with high differential ratio: and (3) cold rolling the warm-rolled plate by a cold rolling mill at a reduction rate of 95%, wherein the rolling speed ratio of an upper rolling mill to a lower rolling mill is 3.5, so as to obtain the cold-rolled plate.
And 5, critical heat treatment: heating the cold-rolled sheet to 800 ℃, and preserving heat for 5min to obtain the superplastic medium manganese steel with superfine, equiaxial and uniform dual-phase austenite and ferrite microstructures, wherein the average grain size of austenite and ferrite is 200nm.
The critically heat treated samples were then subjected to high temperature tensile testing, wherein the tensile samples were processed using wire cutting according to American Standard (ASTM-E8-E8M). The tensile results are shown in Table 2, and the test steels are 10 ℃ in the range of 500 ℃ to 750 ℃ -1 s -1 ～10 -3 s -1 Elongation of over 400% was obtained at strain rate.
TABLE 2
| Temperature of deformation | Rate of strain | Elongation at high temperature |
| 500℃ | 10 -1 s -1 | 408％ |
| 500℃ | 10 -3 s -1 | 789％ |
| 750℃ | 10 -1 s -1 | 658％ |
| 750℃ | 10 -3 s -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 inevitable 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 by smelting and casting according to the chemical component proportion of the medium manganese steel.
Step 2, forging: heating the steel ingot to 1100 ℃, preserving heat for 4h, and forging into a steel billet with the sectional area of 100mm multiplied by 40 mm.
Step 3, high differential speed ratio warm rolling: heating the billet to 850 ℃, preserving heat for 2h, carrying out 7-pass differential speed ratio warm rolling, wherein the rolling speed ratio of an upper rolling mill and a lower rolling mill is 4.5, the rolling temperature range is 500-700 ℃, the reduction rate is 60%, and then carrying out air cooling to room temperature to obtain a warm rolling plate with the thickness of 16 mm.
Step 4, cold rolling with high differential ratio: and (3) cold rolling the warm-rolled plate by a cold rolling mill at a reduction rate of 95%, wherein the rolling speed ratio of an upper rolling mill to a lower rolling mill is 4, so as to obtain the cold-rolled plate.
And 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 superfine, equiaxial and uniform dual-phase austenite and ferrite microstructures, wherein the average grain size of austenite and ferrite is 186nm.
The critically heat treated samples were then subjected to high temperature tensile testing, wherein the tensile samples were processed using wire cutting according to American Standard (ASTM-E8-E8M). The tensile results are shown in Table 3, and the test steels were 10 ℃ at 500 ℃ to 750 ℃ -1 s -1 ～10 -3 s -1 Elongation in excess of 400% was obtained at strain rate.
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 inevitable 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 by smelting and casting according to the chemical component proportion of the medium manganese steel.
Step 2, forging: heating the steel ingot to 1100 ℃, preserving heat for 3 hours, and forging into a billet with the sectional area of 100mm multiplied by 40 mm.
Step 3, high differential speed ratio warm rolling: heating the billet to 850 ℃, preserving heat for 2h, carrying out 7-pass differential speed ratio warm rolling, wherein the rolling speed ratio of an upper rolling mill and a lower rolling mill is 4.5, the rolling temperature range is 500-700 ℃, the reduction rate is 60%, and then carrying out air cooling to room temperature to obtain the warm rolling plate with the thickness of 16 mm.
Step 4, cold rolling with high differential ratio: and (3) cold rolling the warm-rolled plate by a cold rolling mill at a reduction rate of 95%, wherein the rolling speed ratio of an upper rolling mill to a lower rolling mill is 4, so as to obtain the cold-rolled plate.
And 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 superfine, equiaxial and uniform dual-phase austenite and ferrite microstructures, wherein the average grain size of austenite and ferrite is 176nm.
The critically heat treated samples were then subjected to high temperature tensile testing, wherein the tensile samples were processed using wire cutting according to American Standard (ASTM-E8-E8M). The tensile results are shown in Table 4, where the test steels are 10 ℃ at a temperature ranging from 500 ℃ to 750 ℃ - 1 s -1 ～10 -3 s -1 Elongation of over 400% was obtained at strain rate.
TABLE 4
| Temperature of deformation | Rate of strain | Elongation at high temperature |
| 500℃ | 10 -1 s -1 | 542％ |
| 500℃ | 10 -3 s -1 | 724％ |
| 750℃ | 10 -1 s -1 | 682％ |
| 750℃ | 10 -3 s -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 Fe and inevitable 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 by smelting and casting according to the chemical component proportion of manganese steel.
Step 2, forging: heating the steel ingot to 1100 ℃, preserving heat for 3 hours, and forging into a billet with the sectional area of 100mm multiplied by 40 mm.
Step 3, high differential speed ratio warm rolling: heating the billet to 850 ℃, preserving heat for 2h, carrying out 7-pass differential speed ratio warm rolling, wherein the rolling speed ratio of an upper rolling mill and a lower rolling mill is 4.5, the rolling temperature interval is 500-700 ℃, the reduction rate is 60%, and then carrying out air cooling to room temperature to obtain the warm rolling plate with the thickness of 16 mm.
Step 4, cold rolling with high differential ratio: and (3) cold rolling the warm-rolled plate by a cold rolling mill at a reduction rate of 95%, wherein the rolling speed ratio of an upper rolling mill to a lower rolling mill is 4, so as to obtain the cold-rolled plate.
And 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 superfine, equiaxial and uniform dual-phase austenite and ferrite microstructures.
The critically heat treated specimens were then subjected to a high temperature tensile test in which the tensile specimens were processed using wire cutting according to the American Standard (ASTM-E8-E8M). The stretching results are shown in table 5. The temperature of the experimental steel is within the range of 500-600 ℃ and is 10 DEG C -1 s -1 ～10 -3 s -1 Rate of strainElongation of more than 400% was obtained in all cases.
TABLE 5
| Temperature of deformation | Rate of strain | Elongation at high temperature |
| 500℃ | 10 -1 s -1 | 436％ |
| 500℃ | 10 -3 s -1 | 823％ |
| 600℃ | 10 -1 s -1 | 643％ |
| 600℃ | 10 -3 s -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 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 by smelting and casting according to the chemical component proportion of the medium manganese steel.
Step 2, forging: heating the steel ingot to 1200 ℃, preserving heat for 4 hours, and forging into a billet with the sectional area of 100mm multiplied by 40 mm.
Step 3, high differential speed ratio warm rolling: heating the billet to 900 ℃, preserving heat for 2h, carrying out 7-pass differential speed ratio warm rolling, wherein the rolling speed ratio of an upper rolling mill and a lower rolling mill is 5, the rolling temperature interval is 500-700 ℃, the reduction rate is 70%, and then carrying out air cooling to room temperature to obtain a warm rolling plate with the thickness of 12mm.
Step 4, cold rolling with high differential ratio: and (3) cold rolling the warm-rolled plate by a cold rolling mill at a reduction rate of 95%, wherein the rolling speed ratio of an upper rolling mill to a lower rolling mill is 3.5, so as to obtain the cold-rolled plate.
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 a superfine, equiaxial and uniform double-phase austenite and ferrite microstructure.
The critically heat treated specimens were then subjected to a high temperature tensile test in which the tensile specimens were processed using wire cutting according to the American Standard (ASTM-E8-E8M). The stretching results are shown in table 6. The experimental steel is within the range of 500-750 ℃ and 10 DEG C -1 s -1 ～10 -3 s -1 Elongation in excess of 400% was obtained at strain rate.
TABLE 6
| Temperature of deformation | Rate of strain | Elongation at high temperature |
| 500℃ | 10 -1 s -1 | 425％ |
| 500℃ | 10 -3 s -1 | 684％ |
| 750℃ | 10 -1 s -1 | 725％ |
| 750℃ | 10 -3 s -1 | 1225％ |
The foregoing is only a preferred embodiment of the present invention, and it should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and the improvements and modifications are also within the protection scope of the present invention.
Claims (8)
1. The industrial superplastic medium manganese steel is characterized by comprising the following chemical components in percentage by mass: 0.05 to 0.3 percent of C; 3 to 12 percent of Mn; 0 to 8 percent of Al; 0.05 to 0.3 percent of Nb; 0.05 to 0.1 percent of V; mo:0.02 to 0.4 percent, and the balance of Fe and inevitable impurities.
2. The industrial superplastic medium manganese steel of claim 1, wherein 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.
3. The industrial superplastic medium manganese steel as claimed in claim 2, wherein said medium manganese steel is at a temperature of 500-750 ℃In the range of 10 -1 s -1 ～10 -3 s -1 And stretching at a strain rate, wherein the elongation is more than 400%.
4. The method for preparing the industrial superplastic medium manganese steel according to any one of claims 1 to 3, characterized in that it comprises the following steps:
step 1, smelting: proportioning, smelting and casting according to chemical components of the 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 h, and forging into a steel billet;
step 3, high differential speed ratio warm rolling: heating a steel billet to 800-900 ℃, preserving heat for 2h, carrying out 6-7-pass differential speed ratio warm rolling, wherein the rolling temperature interval is 500-700 ℃, the total reduction rate is 60-70%, and then carrying out air cooling to the intermediate room temperature to obtain a warm rolling plate;
step 4, cold rolling with high differential ratio: cold rolling the warm-rolled plate by a cold rolling mill with the reduction rate of 85-95% to obtain a cold-rolled plate;
and 5, critical heat treatment: and heating the cold-rolled sheet to the temperature of a two-phase region, 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 duplex austenite and ferrite microstructures.
5. The method for preparing the industrial superplastic medium manganese steel according to claim 4, wherein the thickness of the warm-rolled plate obtained in step 3 is not more than 16mm and not less than 12mm.
6. The preparation method of the industrial superplastic medium manganese steel according to claim 4, wherein in step 3, the rolling speed ratio of the upper and lower rolls of the high-differential speed ratio warm rolling is not less than 4.
7. The method for preparing the industrial superplastic medium manganese steel according to claim 4, wherein in the step 4, the rolling speed ratio of the upper and lower rolls for the high differential ratio cold rolling is not less than 3.
8. The preparation method of the industrial superplastic medium manganese steel of claim 4, wherein in the step 5, the cold-rolled sheet is heated to the temperature of the two-phase region, then the temperature is kept for 3min to 5min, and then the cold-rolled sheet is cooled by water or air to the room temperature.
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