CN113025883B - 1000MPa cold-rolled dual-phase steel with excellent local forming performance and preparation method thereof - Google Patents

Abstract

The invention discloses 1000MPa cold-rolled dual-phase steel with excellent local forming performance and a preparation method thereof, wherein the steel comprises the following chemical components in percentage by mass: c: 0.06-0.11%, Si: 0.1 to 0.3%, Mn: 1.5-2.4%, Cr: 0.2-0.6%, Mo: 0.2-0.6%, P: less than or equal to 0.010 percent, S: less than or equal to 0.006 percent, Ti: 0.01 to 0.04%, Al: 0.1-0.3%, B: 0.0001-0.005% of iron and inevitable impurities as the rest, wherein Mn + Cr + B is more than 2.1%; according to the invention, by reasonably designing chemical components, limiting the addition of the easy segregation element Mn, refining crystal grains, forming a nano precipitated phase in ferrite, strengthening a ferrite structure, obtaining balance of strength, elongation and hole expansion performance, and the product has excellent local forming performance.

Description

A 1000MPa cold-rolled dual-phase steel with excellent local formability and preparation method thereof

technical field

The invention relates to the technical field of steel preparation, in particular to a 1000 MPa cold-rolled dual-phase steel with excellent local formability and a preparation method thereof.

Background technique

With the increasingly stringent requirements of the automotive industry for lightweight, safety, and low emissions, the proportion of high-strength steel used in new car models continues to increase. A typical representative among them is the high-strength steel with a tensile strength of 1000 MPa, which accounts for the largest proportion in the body structure designed by the "Ultra Light Steel Body - Advanced Vehicle Concept" project, accounting for 29% to 30% of the car body weight. about.

The traditional dual-phase steel structure is mainly composed of a softer ferrite matrix and a high-strength martensite. This structure and properties are characterized by a lower yield ratio and excellent elongation, which are suitable for stamping and forming parts. Production. However, it is undeniable that dual-phase steel has a higher cracking rate in the forming of parts required for hole expansion and flanging, while the prior art multi-phase steel shows that the improvement of hole expansion performance plays a positive role in the improvement of edge ductility. However, In the prior art, it is common in the prior art that the addition of alloying elements leads to selective oxidation during the annealing process, which eventually results in surface defects such as poor phosphating; The development of dual-phase steel with hole expansion performance can further meet the requirements of different users.

Therefore, how to prepare a 1000MPa cold-rolled dual-phase steel with excellent local formability has become an urgent technical problem to be solved.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a 1000MPa cold-rolled dual-phase steel with excellent local formability and a preparation method thereof, which have good coating performance and good local formability.

In order to achieve the above object, the present invention provides a 1000MPa cold-rolled dual-phase steel with excellent local formability, and the chemical composition of the steel in terms of mass fraction is: C: 0.06-0.11%, Si: 0.1-0.3%, Mn : 1.5～2.4%, Cr: 0.2～0.6%, Mo: 0.2～0.6%, P: ≤0.010%, S: ≤0.006%, Ti: 0.01～0.04%, Al: 0.1～0.3%, B: 0.0001～ 0.005%, the rest are iron and inevitable impurities, wherein the mass fraction of Mn, Cr and B elements satisfies: Mn+Cr+B>2.1%.

Further, the Mn: 1.5-1.8%.

Further, the internal structure of the steel is a dual-phase structure, and the dual-phase structure contains 60-90% martensite in volume percentage, and the balance is ferrite; the martensite contains 2-90% martensite in size. 4 μm martensite islands, and the volume of the 2-4 μm martensite islands accounts for more than 80% of the total volume of the martensite.

The present invention also provides a method for preparing the 1000MPa cold-rolled dual-phase steel with excellent local formability, the method comprising:

Use the chemical composition of the 1000MPa cold-rolled dual-phase steel with excellent local formability to carry out smelting and forging to obtain a steel billet;

subjecting the steel billet to pre-rolling heating, rough rolling, finishing rolling and coiling to obtain a hot-rolled sheet;

cold-rolling the hot-rolled sheet to obtain chilled strip;

The chilled steel strip is annealed to obtain an annealed steel sheet; the annealing includes a heating section, a soaking section, a slow cooling section and a fast cooling section, and the heating section is a temperature of 0.9°C/s to 21°C/s from room temperature The heating rate is heated to 780℃～835℃; the atmosphere of the soaking section adopts _N2 - _H2 mixed gas, the _H2 content is 5%～15%, the soaking temperature is 780℃～835℃, and the soaking temperature is 780℃～835℃. The time is 28s～210s, the dew point is -45℃～-41℃, and the oxygen content is 2ppm～5ppm; the slow cooling section is from the soaking temperature to 600℃～700℃; 600℃～700℃ cooled to 250℃～330℃ at a rate of ≥30℃/s;

The annealed steel sheet is subjected to a levelling treatment to obtain the 1000 MPa cold-rolled dual-phase steel with excellent local formability.

Further, in the heating before rolling, the temperature of the heating before rolling is controlled to be 1150°C to 1300°C, the soaking time is 130min to 250min, and the furnace is released after soaking, and the temperature of the furnace is controlled to be 1120°C to 1230°C.

Further, the outlet temperature of the rough rolling is 910°C to 1030°C, and the rough rolling passes are 6 to 10 passes.

Further, the finishing rolling temperature of the finishing rolling is 880°C to 940°C; the coiling temperature is 540°C to 660°C.

Further, the cold rolling reduction ratio is 45% to 60%.

Further, in the annealing process, the speed of the strip passing through the heating section, the soaking section, the slow cooling section, and the fast cooling section is all controlled at 120 m/min to 170 m/min.

Further, during the flattening treatment, the flattening elongation is 0.1%-0.2%.

One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

The invention provides a 1000MPa cold-rolled dual-phase steel with excellent local formability and a preparation method thereof. By rationally designing the chemical composition, the addition amount of Mn, a segregation-prone element, is limited, and Mn+Cr+B>2.1% is controlled; The steel source inhibits the formation of the band-like structure of the final product, and at the same time, it is matched to add a certain microalloying element Ti without adding expensive Nb, which saves costs on the one hand, and further refines the grains on the other hand. Nano-precipitate phase strengthens the ferrite structure and obtains the balance of strength, elongation and hole expansion performance. At the same time, the special continuous annealing process in the present invention is used to temper the martensite structure to reduce the amount of martensite and ferrite. The purpose of the hardness difference between the two phases of the body; the final product yield strength ≥ 600MPa, tensile strength ≥ 1000MPa, elongation ≥ 12%, hole expansion rate ≥ 60%, 180° bending radius along the rolling direction 0.5T without cracking, showing Excellent local formability.

Description of drawings

In order to illustrate the technical solutions in the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings used in the description of the embodiments. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained from these drawings without any creative effort.

1 is a metallographic structure diagram of a 1000MPa cold-rolled dual-phase steel with excellent local formability prepared in Example 1 of the present invention;

Fig. 2 is the EPMA analysis result of Cr and Mn of the 1000MPa cold-rolled dual-phase steel with excellent local formability prepared in Example 1 of the present invention; wherein (A) is the EPMA analysis result of Cr; (B) is the EPMA analysis result of Mn Analysis results

Detailed ways

The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly presented therefrom. It should be understood by those skilled in the art that these specific embodiments and examples are used to illustrate the present invention, but not to limit the present invention.

Throughout the specification, unless specifically stated otherwise, terms used herein are to be understood as commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification takes precedence.

Unless otherwise specified, all kinds of raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or can be obtained by existing methods.

The technical solutions of the embodiments of the present application are to solve the above-mentioned technical problems, and the general idea is as follows:

According to a typical embodiment of the embodiment of the present invention, a 1000MPa cold-rolled dual-phase steel with excellent local formability is provided, and the chemical composition of the steel in terms of mass fraction is: C: 0.06-0.11%, Si: 0.1 ～0.3%, Mn: 1.5～2.4%, Cr: 0.2～0.6%, Mo: 0.2～0.6%, P: ≤0.010%, S: ≤0.006%, Ti: 0.01～0.04%, Al: 0.1～0.3% , B: 0.0001-0.005%, and the rest are iron and inevitable impurities, wherein the mass fractions of Mn, Cr and B elements satisfy: Mn+Cr+B>2.1%.

The present application forms a 1000MPa cold-rolled dual-phase steel with excellent local formability of the above chemical composition by optimizing the composition elements, introducing an intermediate layer-nickel plating layer, and is based on the following principles:

C: 0.06～0.11%, C element is the most important solid solution strengthening element and element to improve austenite hardenability in cold-rolled dual-phase steel. To avoid excessive C content from deteriorating welding performance, the C content should be controlled at 0.06-0.11%.

Si: 0.1-0.3%, Si element is also an important solid solution strengthening element. At the same time, Si can effectively promote the enrichment of C element to austenite, improve the hardenability of austenite, and purify the ferrite phase and improve the elongation. However, the disadvantage of Si is that its too high content (>0.3%) will enrich the surface during the continuous retreat process and affect the subsequent coating, so the Si content needs to be controlled at 0.1-0.3%.

Mn: 1.5-2.4%, Mn element is also an important element for solid solution strengthening and stabilizing austenite, and plays an important role in strengthening, but too high Mn content can easily cause microstructure segregation, easily lead to forming cracking, and deteriorate the overall performance of the steel. It will also be enriched to the surface during the annealing process, so the Mn content should not be too high and should be controlled at 1.5-2.4%. In order to avoid the segregation of the structure, the stress concentration caused by the segregation of the structure causes the early cracking of the segregation, which further deteriorates the hole expansion and bending performance, and the preferred Mn is less than or equal to 1.8%.

P: ≤ 0.010%, P element can inhibit the formation of carbides, so it is considered beneficial to contain a very small amount of P element, but segregation at the grain boundary will lead to a decrease in grain boundary strength and deteriorate the mechanical properties of the material, and it is equivalent to carbon. Contributing significant elements, the content of P element in the present invention is controlled below 0.010%.

S: ≤0.006%, as a harmful element, S element mainly prevents the combination with Mn to generate MnS to deteriorate the material properties, and contributes significantly to the carbon equivalent. The content of S element in the present invention is controlled below 0.006%.

Cr: 0.2-0.6%, Cr element can improve the hardenability of austenite, so as to obtain a sufficient amount of martensite to ensure the strength, and adding a certain content of Cr to obtain the strength ensures that the manufacturing cost of the alloy is low enough; but at the same time, the Cr element is The ferrite area expands the element. Too much Cr element will lead to the shrinking of the two-phase area and hinder the bainite transformation. Therefore, the addition of Cr is limited to ensure the acquisition of a certain amount of bainite. Therefore, the Cr content needs to be controlled at 0.2-0.6% .

Mo: 0.2-0.6%, Mo element can also improve the hardenability of austenite, so as to obtain a sufficient amount of martensite to ensure the strength, but too much Mo element is easy to segregate in the ferrite and deteriorate the ductility. The element cost is high, so the Mo content needs to be controlled within an appropriate range. Therefore, the Mo content needs to be controlled at 0.2 to 0.6%.

Ti: 0.01-0.04%, as a micro-alloying element, Ti element can combine with C to form nano-precipitation phase, which plays the role of grain refinement and precipitation strengthening, and has a significant effect on improving the microstructure and yield strength, but the content If it is too high, it will adversely affect the elongation. Adding a certain amount of Ti can obtain the balance of strength, elongation and hole expansion performance. At the same time, adding Ti microalloy can also inhibit the formation of MnS harmful impurities, which is beneficial to reduce the nucleation point of microcracks during local forming, so its content should be controlled at 0.01-0.04%.

B: 0.0001-0.005%, adding a small amount of B can significantly improve the hardenability of steel, and has no obvious effect on other properties while improving the strength of the material, but too high content of B will cause brittleness, so its content should be controlled within 0.0001- 0.0005%.

Al: 0.1-0.3%. As the main deoxidizer in steelmaking, Al has a thermodynamic effect similar to that of Si, which can inhibit the formation of carbides and indirectly stabilize austenite. The aluminum content of the present invention needs to be controlled at Al: 0.1-0.3%.

In order to ensure that sufficient martensite can still be obtained to guarantee the tensile strength after continuous withdrawal, the content of hardenability-improving elements such as Mn, Cr, and B needs to be further limited. The present invention stipulates that Mn+Cr+B>2.1%.

As a preferred embodiment, the Mn: 1.5-1.8%. Further obtain sufficient martensite to guarantee tensile strength.

As a preferred embodiment, the internal structure of the steel is a dual-phase structure, and the dual-phase structure contains 60-90% martensite by volume percentage, and the balance is ferrite; the martensite It contains martensite islands with a size of 2-4 μm, and the volume of the 2-4 μm martensite islands accounts for more than 80% of the total volume of the martensite.

The formation of nano-precipitated phases in the ferrite can strengthen the ferrite structure and obtain the balance of strength, elongation and hole expansion performance; at the same time, the martensitic structure is tempered in the aging section of the continuous annealing process, so that the 2-4 μm martensite structure is tempered. The volume of the ingot island accounts for more than 80% of the total volume of the martensite, so as to achieve the purpose of reducing the hardness difference between the two phases of martensite and ferrite. A nano-precipitate phase is formed in the ferrite, and the volume of the nano-precipitate phase accounts for less than 1% of the volume fraction in the ferrite; The existence of shale will induce the risk of cracking along the phase interface, which will have an adverse effect on the improvement of local formability;

According to another typical embodiment of the present invention, a preparation method of the 1000MPa cold-rolled dual-phase steel with excellent local formability is provided, and the preparation method includes:

Use the chemical composition of the 1000MPa cold-rolled dual-phase steel with excellent local formability to carry out smelting and forging to obtain a steel billet;

subjecting the steel billet to pre-rolling heating, rough rolling, finishing rolling and coiling to obtain a hot-rolled sheet;

cold-rolling the hot-rolled sheet to obtain chilled strip;

The chilled steel strip is annealed to obtain an annealed steel sheet; the annealing includes a heating section, a soaking section, a slow cooling section and a fast cooling section, and the heating section is a temperature of 0.9°C/s to 21°C/s from room temperature The heating rate is heated to 780℃～835℃; the atmosphere of the soaking section adopts _N2 - _H2 mixed gas, the _H2 content is 5%～15%, the soaking temperature is 780℃～835℃, and the soaking temperature is 780℃～835℃. The time is 28s～210s, the dew point is -45℃～-41℃, and the oxygen content is 2ppm～5ppm; the slow cooling section is from the soaking temperature to 600℃～700℃; 600℃～700℃ cooled to 250℃～330℃ at a rate of ≥30℃/s;

The annealed steel sheet is subjected to a levelling treatment to obtain the 1000 MPa cold-rolled dual-phase steel with excellent local formability.

The special continuous annealing process in the present invention (annealing includes heating section, soaking section, slow cooling section and rapid cooling section) tempers the martensite structure, so as to reduce the hardness difference between the two phases of martensite and ferrite. Purpose: The final product yield strength ≥ 600MPa, tensile strength ≥ 1000MPa, elongation ≥ 12%, hole expansion rate ≥ 60%, 180° bending radius 0.5T along the rolling direction without cracking, showing excellent local formability.

As an optional embodiment, in the pre-rolling heating, the temperature of the pre-rolling heating is controlled to be 1150°C to 1300°C, the soaking time is 130min to 250min, and the furnace is released after soaking, and the temperature of the furnace is controlled to be 1120℃～1230℃.

As an optional embodiment, the outlet temperature of the rough rolling is 910°C to 1030°C, and the rough rolling passes are 6 to 10 passes.

As an optional embodiment, the finishing rolling temperature of the finishing rolling is 880°C to 940°C; the coiling temperature is 540°C to 660°C.

As an optional embodiment, the cold rolling reduction ratio is 45% to 60%.

As an optional embodiment, in the annealing process, the speed of the strip passing through the heating section, soaking section, slow cooling section, and rapid cooling section is controlled at 120 m/min to 170 m/min. Controlling the speed within the stated speed is beneficial to control the time of the strip steel in the furnace zone within a certain range, which has an important influence on the regulation and control organization.

As an optional embodiment, during the flattening treatment, the flattening elongation is 0.1% to 0.2%. It is beneficial to obtain better surface quality and further adjust the yield strength.

A 1000MPa cold-rolled dual-phase steel with excellent local formability and a preparation method thereof of the present application will be described in detail below with reference to the examples, comparative examples and experimental data.

(1) The molten steel is smelted in a converter, and the continuous casting billet is obtained by continuous casting; the actual chemical composition is shown in Table 1.

Table 1-Chemical composition of 1000MPa cold-rolled dual-phase steel (wt%)

group C Si Mn P S Cr Alt Ti Mo B Example 1 0.07 0.2 1.7 0.007 0.003 0.45 0.15 0.03 0.2 0.003 Example 2 0.10 0.15 1.7 0.008 0.004 0.42 0.11 0.02 0.22 0.002 Example 3 0.08 0.25 1.65 0.007 0.003 0.48 0.12 0.01 0.24 0.0023 Example 4 0.08 0.25 2.4 0.007 0.003 0.4 0.14 0.01 0.24 0.0023 Example 5 0.10 0.15 1.6 0.007 0.003 0.4 0.12 0.01 0.24 0.0023 Comparative Example 1 0.07 0.2 1.3 0.007 0.003 0.45 0.15 0.03 0.2 0.003 Comparative Example 2 0.07 0.2 1.7 0.007 0.003 0.45 0.15 0.03 0.2 0.003

(2) The above-mentioned continuous casting billet is subjected to hot rolling to obtain a hot-rolled sheet, the continuous casting billet is heated to 1150-1300 ℃, and the temperature is kept warm, the final rolling temperature is 880-940 ℃, and the coiling temperature is 540-660 ℃. The cold hard strip is obtained by rolling, and the cold rolling deformation amount is 45-60%, as shown in Table 2.

Table 2-1000MPa cold-rolled dual-phase steel hot rolling process and product thickness

(3) The above-mentioned chilled strip steel is subjected to a continuous annealing process to obtain a finished product. The continuous annealing process is shown in Table 3.

Table 3 Continuous annealing process of 1000MPa cold-rolled dual-phase steel

The mechanical properties of the finished product samples were tested, and the results are shown in Table 4.

Table 4-Mechanical properties of 1000MPa cold-rolled dual-phase steel

group Rm/MPa Rp0.2/MPa A80/% Hole expansion ratio/% Example 1 1022 674 13 66 Example 2 1011 682 13 65 Example 3 1024 708 12 64 Example 4 1043 742 12 44 Example 5 972 666 13 62 Comparative Example 1 852 528 18 45 Comparative Example 2 1110 682 1- 28

It can be seen from the data in Table 4 that:

The hole expansion rate is used to measure the hole turning ability of the steel plate during stamping. The higher the hole expansion rate, the better the local deformation resistance of the material;

In Comparative Example 1, Mn+Cr+B<2.1%, the rest of the steps are the same as in Example 1, and the strength is low;

In Comparative Example 2, the annealing process of the present invention was not adopted, and the remaining steps were the same as those in Example 1, with high strength, poor plasticity, and low hole expansion performance;

The final product in Examples 1-5 has a yield strength of ≥600MPa, a tensile strength of ≥1000MPa, an elongation rate of ≥12%, a hole expansion rate of ≥60%, and no cracking along the rolling direction with a 180° bending radius of 0.5T;

Detailed description of accompanying drawing 1:

Figure 1 shows a typical microstructure photo of the cold-rolled dual-phase steel sample of Example 1. It can be seen from FIG. 1 that the structure includes ferrite and martensite, and nano-precipitated phases are formed in the ferrite; the martensite includes martensite islands with a size of 2-4 μm, and the size of the 2-4 μm is The volume of martensite islands accounts for more than 80% of the total volume of the martensite.

It can be seen from Figure 2 that the distribution of Cr and Mn elements is very uniform, which further illustrates the homogeneity of the composition within the strip, eliminates the band-like defects caused by the segregation of the composition, and further improves the localized forming of the strain inside each phase. uniformity.

Finally, it should also be noted that the terms "comprising", "comprising" or any other variation thereof are intended to encompass a non-exclusive inclusion such that a process, method, article or device comprising a series of elements includes not only those elements, but also Also included are other elements not expressly listed or inherent to such a process, method, article or apparatus.

Although preferred embodiments of the present invention have been described, additional changes and modifications to these embodiments may occur to those skilled in the art once the basic inventive concepts are known. Therefore, the appended claims are intended to be construed to include the preferred embodiment and all changes and modifications that fall within the scope of the present invention.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention. Thus, provided that these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims (9)

1. A 1000MPa cold-rolled dual-phase steel with excellent local formability, characterized in that the chemical composition of the steel in terms of mass fraction is: C: 0.06-0.11%, Si: 0.1-0.3%, Mn: 1.5 ～2.4%, Cr: 0.2～0.6%, Mo: 0.2～0.6%, P: ≤0.010%, S: ≤0.006%, Ti: 0.01～0.04%, Al: 0.1～0.3%, B: 0.0001～0.005% , and the rest are iron and inevitable impurities, wherein the mass fractions of Mn, Cr and B elements satisfy: Mn+Cr+B>2.1%, the internal structure of the steel is a dual-phase structure, and the dual-phase structure is volumetric The percentage meter contains 60-90% martensite, and the balance is ferrite; nano-precipitated phases are formed in the ferrite, and the volume of the nano-precipitated phases accounts for less than 1% of the volume fraction in the ferrite; The martensite contains martensite islands with a size of 2-4 μm, and the volume of the 2-4 μm martensite islands accounts for more than 80% of the total volume of the martensite, and the yield of the cold-rolled dual-phase steel is Strength ≥ 600MPa, tensile strength ≥ 1000MPa, elongation ≥ 12%, hole expansion rate ≥ 60%, 180° bending radius along the rolling direction 0.5T without cracking. 2 . The 1000MPa cold-rolled dual-phase steel with excellent local formability according to claim 1 , wherein the Mn is 1.5-1.8%. 3 . 3. A preparation method of 1000MPa cold-rolled dual-phase steel with excellent local formability according to any one of claims 1-2, characterized in that the method comprises: The chemical composition of the 1000MPa cold-rolled dual-phase steel with excellent local formability described in any one of claims 1-2 is used for smelting and forging to obtain a billet; subjecting the steel billet to pre-rolling heating, rough rolling, finishing rolling and coiling to obtain a hot-rolled sheet; cold-rolling the hot-rolled sheet to obtain chilled strip; The chilled steel strip is annealed to obtain an annealed steel sheet; the annealing includes a heating section, a soaking section, a slow cooling section and a fast cooling section, and the heating section is a temperature of 0.9°C/s to 21°C/s from room temperature The heating rate is heated to 780℃～835℃; the atmosphere of the soaking section adopts _N2 - _H2 mixed gas, the _H2 content is 5%～15%, the soaking temperature is 780℃～835℃, and the soaking temperature is 780℃～835℃. The time is 28s～210s, the dew point is -45℃～-41℃, and the oxygen content is 2ppm～5ppm; the slow cooling section is from the soaking temperature to 600℃～700℃; 600℃～700℃ cooled to 250℃～330℃ at a rate of ≥30℃/s; The annealed steel sheet is subjected to a levelling treatment to obtain the 1000 MPa cold-rolled dual-phase steel with excellent local formability. 4 . The method for preparing 1000MPa cold-rolled dual-phase steel with excellent local formability according to claim 3 , wherein, in the pre-rolling heating, the temperature of the pre-rolling heating is controlled to be 1150° C. to 1300° C. 4 . , the soaking time is 130min～250min, and the furnace is released after soaking, and the temperature of the furnace is controlled to be 1120℃～1230℃. 5 . The method for preparing 1000MPa cold-rolled dual-phase steel with excellent local formability according to claim 3 , wherein the rough rolling outlet temperature is 910°C to 1030°C, and the rough rolling passes 6 to 10 lanes. 6 . The method for preparing a 1000 MPa cold-rolled dual-phase steel with excellent local formability according to claim 3 , wherein the finishing temperature of the finishing rolling is 880° C. to 940° C.; the coiling The temperature is 540℃～660℃. 7 . The method for preparing 1000 MPa cold-rolled dual-phase steel with excellent local formability according to claim 3 , wherein the cold-rolling reduction ratio is 45% to 60%. 8 . 8. The method for preparing a 1000MPa cold-rolled dual-phase steel with excellent local formability according to claim 3, wherein in the annealing process, the strip passes through the heating section, soaking section, slow cooling The speed of the section and the fast cooling section are controlled at 120m/min ~ 170m/min. 9 . The method for preparing a 1000MPa cold-rolled dual-phase steel with excellent local formability according to claim 3 , wherein, during the leveling treatment, the leveling elongation is 0.1% to 0.2%. 10 .

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