CN116043120A - 1000 MPa-grade cold-rolled complex phase steel with excellent formability and preparation method thereof - Google Patents

1000 MPa-grade cold-rolled complex phase steel with excellent formability and preparation method thereof Download PDF

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CN116043120A
CN116043120A CN202310060189.2A CN202310060189A CN116043120A CN 116043120 A CN116043120 A CN 116043120A CN 202310060189 A CN202310060189 A CN 202310060189A CN 116043120 A CN116043120 A CN 116043120A
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CN116043120B (en
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顾兴利
胡智评
刘仁东
林利
郭金宇
林春青
蒋睿婷
丁庶炜
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Angang Steel Co Ltd
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
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    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite
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Abstract

The invention relates to 1000MPa grade cold-rolled complex phase steel with excellent formability and a preparation method thereof, wherein the steel comprises the following chemical components: 0.095% -0.12%, si:0.1 to 0.4 percent of Mn:2.0 to 3.0 percent, less than or equal to 0.6 percent of Cr, less than or equal to 2.5 percent and less than or equal to 3.2 percent of Mn+Cr, less than or equal to 0.4 percent of Mo, less than or equal to 1/3 and less than or equal to 2/3 of Mo/Cr, less than or equal to 0.02 percent of P, less than or equal to 0.005 percent of S, less than or equal to 0.03 percent of Ti, less than or equal to 0.03 percent of Nb, and less than or equal to Cu:0.01 to 0.3 percent of Ni:0.01 to 0.2 percent, and the balance of Fe and impurities. On the basis of no obvious improvement of alloy cost, the invention realizes the obvious improvement of the reaming performance and fatigue resistance of the steel plate only through the ingenious design of the process.

Description

1000 MPa-grade cold-rolled complex phase steel with excellent formability and preparation method thereof
Technical Field
The invention relates to the technical field of automobile steel production, in particular to 1000 MPa-level cold-rolled complex phase steel with excellent formability and a preparation method thereof.
Background
Along with the increasing demands of the automobile industry on light weight, safety and the like, the use proportion of advanced high-strength steel in new automobile types is continuously increased. In the vehicle body structure designed by the project of 'ultra-light steel vehicle body-advanced vehicle concept', the proportion of high-strength steel with the tensile strength of 1000MPa is maximum, and the proportion is about 29-30% of the weight of the vehicle body.
The high-strength steel above 1000MPa mainly comprises dual-phase steel, martensitic steel, complex phase steel, third-generation high-strength steel and the like. The complex phase steel has the characteristics of high strength and good flanging performance, and is suitable for roll forming in the automobile part forming process. The complex phase steel has higher energy absorption capacity, good mechanical property, forming property and welding property, is widely applied to the production of parts such as automobile chassis suspension parts, B columns, bumpers, seat sliding rails and the like, and has wide market prospect.
At present, the strength level of the complex phase steel produced internationally is mainly below 800MPa, and the strength of a few complex phase steels can reach 1000MPa, but other force performance indexes such as fatigue resistance, reaming performance and the like are not ideal. And fatigue resistance and reaming performance directly affect the formability and deformation energy absorbing capacity of the steel plate. Therefore, the method has important industrial production significance and value for further upgrading of the fatigue resistance and the reaming performance of 1000 MPa-level complex-phase steel.
The Chinese patent with the publication number of CN 109594020B discloses a cold-rolled complex phase steel with the tensile strength of 1000MPa and a manufacturing method thereof. The heat treatment process adopts a one-step overaging mode, the overaging temperature is 300-340 ℃, the structure is composed of ferrite, bainite and martensite, wherein the martensite is fresh martensite, and tempered martensite does not exist in the structure. After heat treatment, the yield strength of the steel plate is more than 780MPa, and the hole expansion rate is more than 50%.
Chinese patent application publication No. CN104278194a discloses a "quenched and partitioned steel sheet with high strength and high plasticity" and a method for preparing the same. The method adopts a high C and high Si/Al component system, and the element C is used for stabilizing the residual austenite except the strengthening effect; the Si/Al element is used for inhibiting carbide precipitation and indirectly acts on stabilizing the residual austenite. The content of C in the components is 0.25-0.35 wt%, the content of Si is 0.8-1.2 wt% and the content of Al is 0.5-1.0 wt%. The tensile strength of the steel plate obtained after heat treatment is greater than 980MPa, the elongation is about 20%, but the reaming performance is lower.
Disclosure of Invention
The invention provides 1000MPa grade cold rolled complex phase steel with excellent formability and a preparation method thereof, and on the basis of no obvious improvement of alloy cost, the steel plate reaming performance and fatigue resistance performance are obviously improved only through ingenious design of a process.
In order to achieve the above purpose, the invention is realized by adopting the following technical scheme:
1000MPa grade cold-rolled complex phase steel with excellent formability comprises the following chemical components in percentage by mass: 0.095% -0.12%, si:0.1 to 0.4 percent of Mn:2.0 to 3.0 percent, less than or equal to 0.6 percent of Cr, less than or equal to 2.5 percent and less than or equal to 3.2 percent of Mn+Cr, less than or equal to 0.4 percent of Mo, less than or equal to 1/3 and less than or equal to 2/3 of Mo/Cr, less than or equal to 0.02 percent of P, less than or equal to 0.005 percent of S, less than or equal to 0.03 percent of Ti, less than or equal to 0.03 percent of Nb, and less than or equal to Cu:0.01 to 0.3 percent of Ni:0.01% -0.2%, and the balance of Fe and unavoidable impurities; the finished steel plate structure comprises ferrite, bainite, tempered martensite, fresh martensite and carbide precipitation; the ferrite content is less than 40% and contains 0, the bainite content is less than 20%, the tempered martensite content is 40-90%, and the fresh martensite content is less than 20% as counted by a plane area method.
Further, the ferrite contains a quantity of 1×10 6 Individual/mm 2 Precipitates having a size of 30nm or less; tempered martensite containing 1×10 in unit area 7 Individual/mm 2 Precipitates having a size of 100nm or less.
Further, the ratio of the bainite content to the fresh martensite content is greater than 2; the ratio of the hardness of bainite to the hardness of fresh martensite is greater than 0.7; the ratio of the hardness of bainite to the hardness of tempered martensite is 0.8 to 1.2; the ratio of the hardness of bainite to the hardness of ferrite is less than 2.
Further, the tensile strength of the finished steel plate is more than 1000MPa, the yield strength is 820-950 MPa, the elongation is more than or equal to 11%, and the reaming ratio is more than or equal to 70%; the high cycle fatigue limit strength is more than or equal to 470mpa, and 160-DEG bending does not crack.
A preparation method of 1000MPa grade cold-rolled complex phase steel with excellent formability comprises the working procedures of smelting, hot rolling, acid washing, cold rolling, continuous annealing and finishing, and the specific procedures are as follows:
1) Smelting;
2) Hot rolling; the heating temperature is controlled between 1200 and 1280 ℃; the initial rolling temperature is controlled to 1100-1150 ℃ and the final rolling temperature is controlled to be more than 900 ℃; the coiling temperature is controlled at 600-700 ℃;
3) Acid washing;
4) Cold rolling; the cold rolling reduction rate is 50-58%;
5) Continuous annealing;
(1) the isothermal temperature is controlled between 820 and 880 ℃, and the isothermal time is controlled between 80 and 150 seconds; the slow cooling temperature is 700-750 ℃, and the slow cooling speed is controlled to be 0.5-5 ℃/s;
(2) after slow cooling, cooling to 250-360 ℃ at a cooling speed of more than 25 ℃/s, heating to 350-420 ℃ at a heating speed of more than 10 ℃/s, keeping the isothermal time at 300-650 s, and finally cooling to room temperature at a cooling speed of more than 2 ℃/s;
6) Finishing; the finishing elongation is controlled to be 0.1% -0.5%.
Further, in the hot rolling process, the thickness of the hot rolled steel sheet is 2.8 to 4.0mm.
Compared with the prior art, the invention has the beneficial effects that:
(1) The chemical components of the steel plate take C, mn as main elements, have no noble alloy such as V and the like, have the C content lower than 0.12 percent, and are favorable for adopting laser welding and resistance spot welding in the production and application processes;
(2) According to the invention, a quenching-distribution heat treatment process is adopted, a tempered martensite structure is introduced into the original ferrite, bainite and fresh martensite structure of the complex phase steel, so that the structure distribution is more uniform, the hardness difference of each phase in the structure is effectively reduced, and the fatigue resistance and the reaming performance of the steel plate are effectively improved;
(3) The invention realizes the good plasticity, the formability and the fatigue resistance of the steel plate through the low-cost alloy design and the ingenious process design.
Drawings
FIG. 1 is a photograph of a typical SME structure of a finished steel sheet of example 1 of the present invention.
Detailed Description
The 1000MPa grade cold-rolled complex phase steel with excellent formability comprises the following chemical components in percentage by mass: 0.095% -0.12%, si:0.1 to 0.4 percent of Mn:2.0 to 3.0 percent, less than or equal to 0.6 percent of Cr, less than or equal to 2.5 percent and less than or equal to 3.2 percent of Mn+Cr, less than or equal to 0.4 percent of Mo, less than or equal to 1/3 and less than or equal to 2/3 of Mo/Cr, less than or equal to 0.02 percent of P, less than or equal to 0.005 percent of S, less than or equal to 0.03 percent of Ti, less than or equal to 0.03 percent of Nb, and less than or equal to Cu:0.01 to 0.3 percent of Ni:0.01% -0.2%, and the balance of Fe and unavoidable impurities; the finished steel plate structure comprises ferrite, bainite, tempered martensite, fresh martensite and carbide precipitation; the ferrite content is less than 40% and contains 0, the bainite content is less than 20%, the tempered martensite content is 40-90%, and the fresh martensite content is less than 20% as counted by a plane area method.
Further, the ferrite contains a quantity of 1×10 6 Individual/mm 2 Precipitates having a size of 30nm or less; tempered martensite containing 1×10 in unit area 7 Individual/mm 2 Precipitates having a size of 100nm or less.
Further, the ratio of the bainite content to the fresh martensite content is greater than 2; the ratio of the hardness of bainite to the hardness of fresh martensite is greater than 0.7; the ratio of the hardness of bainite to the hardness of tempered martensite is 0.8 to 1.2; the ratio of the hardness of bainite to the hardness of ferrite is less than 2.
Further, the tensile strength of the finished steel plate is more than 1000MPa, the yield strength is 820-950 MPa, the elongation is more than or equal to 11%, and the reaming ratio is more than or equal to 70%; the high cycle fatigue limit strength is more than or equal to 470mpa, and 160-DEG bending does not crack.
The invention relates to a preparation method of 1000 MPa-grade cold-rolled complex phase steel with excellent formability, which comprises the following steps of smelting, hot rolling, pickling, cold rolling, continuous annealing and finishing:
1) Smelting;
2) Hot rolling; the heating temperature is controlled between 1200 and 1280 ℃; the initial rolling temperature is controlled to 1100-1150 ℃ and the final rolling temperature is controlled to be more than 900 ℃; the coiling temperature is controlled at 600-700 ℃;
3) Acid washing;
4) Cold rolling; the cold rolling reduction rate is 50-58%;
5) Continuous annealing;
(1) the isothermal temperature is controlled between 820 and 880 ℃, and the isothermal time is controlled between 80 and 150 seconds; the slow cooling temperature is 700-750 ℃, and the slow cooling speed is controlled to be 0.5-5 ℃/s;
(2) after slow cooling, cooling to 250-360 ℃ at a cooling speed of more than 25 ℃/s, heating to 350-420 ℃ at a heating speed of more than 10 ℃/s, keeping the isothermal time at 300-650 s, and finally cooling to room temperature at a cooling speed of more than 2 ℃/s;
6) Finishing; the finishing elongation is controlled to be 0.1% -0.5%.
Further, in the hot rolling process, the thickness of the hot rolled steel sheet is 2.8 to 4.0mm.
The chemical composition design reason of the 1000MPa grade cold-rolled complex phase steel with excellent formability is as follows:
c: the C element is a traditional and economic strengthening element of low-carbon steel; the excessive content of the element C can inhibit bainite transformation, increase hardness difference of each phase in a steel plate structure, reduce reaming performance of the steel plate, and cause difficulty in smelting and welding; if the content of the C element is too low, the strength of the steel plate is difficult to reach 1000MPa; therefore, the content of C element is controlled to be 0.095-0.12%.
Si: si mainly plays a role in strengthening ferrite, but excessive Si content can inhibit cementite precipitation in an overaging stage, so that retained austenite or high-hardness martensite is formed, and the reaming performance of the steel plate is not facilitated. Therefore, the content of Si element is controlled to be 0.1-0.4%.
Mn/Cr: mn and Cr are austenite stabilizing elements, have obvious solid solution strengthening effect on high-strength steel, can obviously improve the hardenability of the steel, have the effects of solid solution strengthening and refining ferrite grains, can obviously delay pearlite and bainite transformation, improve the strength of the steel, and are main strengthening elements except C. In combination with the content of C, the content of Mn+Cr is controlled to be 2.5-3.2 percent in order to ensure that the strength of the steel plate reaches more than 1000 MPa. Too low a Mn+Cr content tends to cause insufficient strength of the steel sheet, and too high a Mn+Cr content tends to lower hole-enlarging performance.
Mo: the Mo and Cr composite additive has better effect, and the Mo content in the invention is 1/3-2/3 of the Cr content.
Cu is a solid solution strengthening element, and firstly plays a role in improving strength, and secondly, cu can be separated out in a simple substance or compound form in the heat treatment process, so that the strength and fatigue resistance of the steel plate are improved.
Ni: ni is an austenite stabilizing element and a solid solution strengthening element, the hardenability of the steel plate can be improved, and the composite addition of Ni and Cu can improve the deformation resistance and fatigue resistance of the steel plate and reduce rolling cracking.
Ti: ti can capture free N atoms in steel and plays a role in fixing N. Meanwhile, tiN can be separated out in the solidification process to play a role in pinning a grain boundary, and Ti (C, N) is separated out in the hot rolling stage to play a role in pinning a prior austenite grain boundary and refining the prior austenite grain. Meanwhile, a small amount of Ti is precipitated in the continuous annealing stage to play a role in strengthening ferrite and bainite; however, adding too much Ti has limited effects and increases costs. Therefore, the Ti element content is controlled to be less than 0.03%.
Nb can form Nb precipitation with C, N and other elements, can prevent ferrite grains from growing so as to refine the grains, and can accelerate bainite transformation, thereby being beneficial to improving the formability of the steel plate; the present invention thus controls the content of Nb element within a suitable range.
P: the P element is a harmful element in steel, and the lower the content is, the better. In view of cost, the invention controls the content of P element below 0.02%.
S: the S element is a harmful element in steel, and the lower the content is, the better. In view of cost, the invention controls the S element content below 0.005%.
The preparation method of the 1000 MPa-level complex-phase steel plate with excellent formability comprises a series of procedures of smelting, hot rolling, pickling, cold rolling, continuous annealing, finishing and the like, and comprises the following specific procedures:
1. smelting: smelting by a converter to obtain alloy components in accordance with the design range.
2. And (3) hot rolling:
(1) the heating temperature is controlled between 1230 and 1280 ℃, the precipitation behavior of Ti atoms is ensured, a good N fixing effect is achieved on the steel plate, and the precipitation of Ti (C, N) is ensured to play the roles of pinning the prior austenite grain boundary and refining the prior austenite grain.
(2) The initial rolling temperature is controlled between 1100 ℃ and 1150 ℃, the final rolling temperature is controlled above 900 ℃, the rolling temperature of a recrystallization zone is ensured, the dynamic recrystallization behavior of prior austenite grains in the hot rolling stage is promoted, and the grains are refined.
(3) The coiling temperature is controlled between 660 and 700 ℃, so that the difficulty of cold rolling is prevented from being increased due to the excessively low coiling temperature. The thickness of the hot rolled steel plate is controlled between 2.8 and 4.0mm.
3. Acid washing: and (5) removing the oxidized iron scales generated on the hot-rolled surface and ensuring the surface quality of the cold-rolled steel plate.
4. Cold rolling: the cold rolling reduction rate is 50% -58%, and the reduction rate of more than 50% is ensured so as to promote tissue fibrosis in cold rolling configuration; the reduction ratio of not more than 58% is to prevent excessive deformation resistance due to excessive cold rolling reduction ratio, and it is difficult to roll to a target thickness.
5. Continuous annealing:
(1) the isothermal temperature is controlled between 820 and 880 ℃, and the isothermal time is controlled between 80 and 150 seconds; the slow cooling temperature is 700-750 ℃, and the slow cooling speed is controlled to be 0.5-5 ℃/s;
(2) after slow cooling, cooling to 250-360 ℃ at a cooling speed of more than 25 ℃/s, heating to 350-420 ℃ at a heating speed of more than 10 ℃/s, keeping the isothermal time at 300-650 s, and finally cooling to room temperature at a cooling speed of more than 2 ℃/s;
6. and (3) finishing: the steel plate enters a finishing machine for plate shape adjustment, and the finishing elongation is controlled to be 0.1% -0.5%.
The mechanism of the technical process is as follows: firstly, annealing in a two-phase region to obtain ferrite and prior austenite with proper proportions; the cooling to 250-360 ℃ aims at obtaining a large amount of martensite, and the martensite formed in the stage is tempered in the subsequent overaging stage, so that the hardness of the martensite is reduced, and the hardness difference of the whole structure is reduced. Secondly, compared with bainite, the tempered martensite can obviously improve the yield strength of the steel plate and reduce the work hardening capacity of the steel plate in the subsequent continuous deformation process; meanwhile, tempered martensite can increase nucleation points of subsequent bainite, a low-Si component system is combined to promote bainite formation, fresh martensite is reduced to be formed in the final quenching stage, the hardness difference of the whole structure is reduced, and the reaming performance of the steel plate is improved. In addition, a large amount of tempered martensite precipitates fine carbides in the tempering stage, and the fatigue resistance of the steel sheet can be improved.
The structure of the final steel plate is as follows: ferrite (< 40%) +tempered martensite (40% -90%) +bainite (< 20%) +fresh martensite (< 20%). Therefore, the novel multi-phase steel is produced by adopting the quenching-distribution process, a proper amount of tempered martensite is introduced on the basis of the traditional multi-phase steel, and the low Si component is adopted to promote the bainite transformation and carbide precipitation, so that the difference of the hardness of the final structure is small, the structure is more uniform, and the fatigue resistance and the reaming performance of the steel plate are facilitated.
The cold-rolled steel plate obtained by the method has the tensile strength of more than 1000MPa, the yield strength of 820-950 MPa, the elongation of more than 11%, the hole expansion rate of more than 70%, the high cycle fatigue limit strength of more than or equal to 470MPa and no cracking after 160-DEG bending, and realizes the good strong plasticity, the formability and the fatigue resistance of the steel plate.
The following examples are given by way of illustration of detailed embodiments and specific procedures based on the technical scheme of the present invention, but the scope of the present invention is not limited to the following examples.
[ example ]
The chemical composition of the steels in examples 1 to 8 are shown in Table 1, the continuous casting and hot rolling process parameters of the steels in examples 1 to 8 are shown in Table 2, the continuous annealing process parameters of the steels in examples 1 to 8 are shown in Table 3, and the mechanical properties of the steels in examples 1 to 8 are shown in Table 4. A photograph of a typical SME structure of the finished steel sheet of example 1 is shown in fig. 1.
Table 1 chemical composition of steel, wt%
Examples C Mn Cr Mn+Cr Mo Mo/Cr Si Ti Nb Cu Ni P S
1 0.11 2.2 0.5 2.7 0.3 3/5 0.3 0.02 0 0.2 0.1 0.010 0.005
2 0.10 2.3 0.4 2.7 0.2 1/2 0.2 0.02 0 0.3 0.1 0.009 0.005
3 0.10 2.0 0.6 2.6 0.3 2/3 0.4 0.015 0 0.1 0.1 0.010 0.003
4 0.095 2.3 0.4 2.7 0.2 1/2 0.4 0.02 0.02 0.2 0.1 0.005 0.005
5 0.095 2.6 0 2.6 0 1/3 0.4 0.02 0.02 0.2 0.1 0.009 0.003
6 0.095 2.5 0.3 2.8 0.1 1/3 0.2 0.015 0 0.1 0.2 0.008 0.005
7 0.095 2.4 0.3 2.7 0.2 2/3 0.4 0 0.02 0.2 0.1 0.01 0.005
8 0.10 2.3 0.5 2.8 0.2 2/5 0.2 0.015 0 0.3 0.2 0.02 0.004
Table 2 continuous casting and hot rolling process parameters of steel
Figure BDA0004061116390000071
Table 3 parameters of continuous annealing process for steels
Figure BDA0004061116390000072
Figure BDA0004061116390000081
Table 4 mechanical properties of steels
Figure BDA0004061116390000082
In table 4, rp0.2 is the yield strength, rm is the tensile strength, a50 is the elongation, and λ is the hole expansion ratio.
As can be seen from the above examples, the cold rolled steel plate prepared by the invention has tensile strength of more than 1000MPa, yield strength of 820-950 MPa, elongation of more than 11% and hole expansion rate of more than 70% through low-cost alloy design and ingenious process design; meanwhile, the high cycle fatigue limit strength is more than or equal to 470mpa, 160-DEG bending is not cracked, and the good plasticity, the formability and the fatigue resistance of the steel plate are realized.
The foregoing is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art, who is within the scope of the present invention, should make equivalent substitutions or modifications according to the technical scheme of the present invention and the inventive concept thereof, and should be covered by the scope of the present invention.

Claims (6)

1. The 1000MPa grade cold-rolled complex phase steel with excellent formability is characterized in that the steel comprises the following chemical components in percentage by mass: 0.095% -0.12%, si:0.1 to 0.4 percent of Mn:2.0 to 3.0 percent, less than or equal to 0.6 percent of Cr, less than or equal to 2.5 percent and less than or equal to 3.2 percent of Mn+Cr, less than or equal to 0.4 percent of Mo, less than or equal to 1/3 and less than or equal to 2/3 of Mo/Cr, less than or equal to 0.02 percent of P, less than or equal to 0.005 percent of S, less than or equal to 0.03 percent of Ti, less than or equal to 0.03 percent of Nb, and less than or equal to Cu:0.01 to 0.3 percent of Ni:0.01% -0.2%, and the balance of Fe and unavoidable impurities; the finished steel plate structure comprises ferrite, bainite, tempered martensite, fresh martensite and carbide precipitation; the ferrite content is less than 40% and contains 0, the bainite content is less than 20%, the tempered martensite content is 40-90%, and the fresh martensite content is less than 20% as counted by a plane area method.
2. The 1000 MPa-grade cold-rolled complex phase steel excellent in formability of claim 1, wherein the ferrite contains 1×10 amount 6 Individual/mm 2 Precipitates having a size of 30nm or less; tempered martensite containing 1×10 in unit area 7 Individual/mm 2 Precipitates having a size of 100nm or less.
3. The 1000MPa grade cold rolled complex phase steel excellent in formability of claim 1, wherein the ratio of the bainite content to the fresh martensite content is more than 2; the ratio of the hardness of bainite to the hardness of fresh martensite is greater than 0.7; the ratio of the hardness of bainite to the hardness of tempered martensite is 0.8 to 1.2; the ratio of the hardness of bainite to the hardness of ferrite is less than 2.
4. The 1000MPa grade cold-rolled complex phase steel with excellent formability of claim 1, wherein the tensile strength of the finished steel plate is more than 1000MPa, the yield strength is 820-950 MPa, the elongation is more than or equal to 11%, and the hole expansion rate is more than or equal to 70%; the high cycle fatigue limit strength is more than or equal to 470mpa, and 160-DEG bending does not crack.
5. The method for preparing 1000 MPa-grade cold-rolled complex phase steel with excellent formability according to any one of claims 1 to 4, comprising the steps of smelting, hot rolling, pickling, cold rolling, continuous annealing and finishing, comprising the following steps:
1) Smelting;
2) Hot rolling; the heating temperature is controlled between 1200 and 1280 ℃; the initial rolling temperature is controlled to 1100-1150 ℃ and the final rolling temperature is controlled to be more than 900 ℃; the coiling temperature is controlled at 600-700 ℃;
3) Acid washing;
4) Cold rolling; the cold rolling reduction rate is 50-58%;
5) Continuous annealing;
(1) the isothermal temperature is controlled between 820 and 880 ℃, and the isothermal time is controlled between 80 and 150 seconds; the slow cooling temperature is 700-750 ℃, and the slow cooling speed is controlled to be 0.5-5 ℃/s;
(2) after slow cooling, cooling to 250-360 ℃ at a cooling speed of more than 25 ℃/s, heating to 350-420 ℃ at a heating speed of more than 10 ℃/s, keeping the isothermal time at 300-650 s, and finally cooling to room temperature at a cooling speed of more than 2 ℃/s;
6) Finishing; the finishing elongation is controlled to be 0.1% -0.5%.
6. The method for producing 1000 MPa-grade cold-rolled complex phase steel excellent in formability according to claim 5, wherein the thickness of the hot-rolled steel sheet in the hot rolling process is 2.8 to 4.0mm.
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