WO2015043411A1

WO2015043411A1 - Cold-rolled duplex strip steel with high formability and preparation method therefor

Info

Publication number: WO2015043411A1
Application number: PCT/CN2014/086785
Authority: WO
Inventors: 朱晓东; 李伟; 薛鹏
Original assignee: 宝山钢铁股份有限公司
Priority date: 2013-09-29
Filing date: 2014-09-18
Publication date: 2015-04-02
Also published as: CN103469112A

Abstract

Provided is a cold-rolled duplex strip steel with high formability, wherein the chemical components of the strip steel in weight percentage are C 0.06-0.095%, Si ≤0.4%, Mn 2.05-2.35%, Cr 0.7-Mo-Ni/2%, Mo 0.1-0.3%, Ni 2×(Mo-0.18)%, P ≤0.015%, S ≤0.003%, N ≤0.005%, Nb 0-0.04%, Ti 0.01-0.05%, Al 0.015-0.05%, and the remainder being Fe and unavoidable impurities. A preparation method for the strip steel is also provided.

Description

High-formability cold-rolled double-phase strip steel and manufacturing method thereof

Technical field

The invention relates to a cold-rolled double-phase strip steel and a manufacturing method thereof, in particular to a high-formability cold-rolled double-phase strip steel and a manufacturing method thereof, which have low carbon equivalent and tensile strength of 980 MPa or more, for example, about 1000 MPa, and have good Weldability, elongation, hole expansion and bending properties.

Background technique

The automotive industry requires the use of higher strength steel sheets for weight reduction purposes. Among them, ultra-high-strength dual-phase steel has become the first choice for the automotive industry, because this advanced high-strength steel can effectively reduce the weight of the car body and improve safety. High-strength steel sheets require not only good elongation in the automobile manufacturing process, but also high requirements for local forming ability, that is, high requirements for hole expansion ratio and bending performance. The traditional cold-rolled dual-phase steel has a low yield ratio and has a certain drawing forming ability. However, due to insufficient local formability, it is prone to localized when manufacturing high-strength steel parts including deformation modes such as bending and reaming. Cracks, which affect the stamping effect of the entire part, leading to scrapping. Literature studies have shown that when the reaming rate and bending performance of duplex steel are low, it is often unable to adapt to more severe forming conditions, and the application field is greatly limited. High-strength dual-phase steels generally contain higher carbon and alloying elements, but higher carbon and alloying elements tend to cause segregation of components during casting, resulting in subsequent material degradation due to non-uniform composition and microstructure. , poor hole expansion and cold bendability. The band structure of the steel is distributed along the rolling direction, which is easy to become a micro crack source, further reducing the local forming ability of the steel.

The band structure of steel is mainly caused by component segregation, and the segregation occurs in the solidification process of molten steel. Firstly, the content of solidified molten steel and the content of subsequent precipitated components are different. The concentration of alloying elements in molten steel will become higher and higher, eventually resulting in The content of the first solidified portion and the post-solidified portion of the solidified structure is very different. The region where the composition is segregated is deformed and elongated during the hot rolling to finally form a band structure. The band structure usually contains high alloying elements, and it is difficult to eliminate due to the difficulty in diffusion of these alloying elements. The enrichment of the alloying elements attracts carbon in the same region, resulting in hardening of the duplex steel after banding. The brittle martensite is more harmful to local deformation performance, and has better hole-expanding performance and cold-bending performance, and is prone to cracking during forming. Lift High tissue uniformity and improved local formability of high-strength dual-phase steel are the key to obtaining balanced dual-phase steel.

The existing cold-rolled duplex steels involving continuous annealing production with a strength close to 1000 MPa are as follows:

Chinese Patent Application No. CN201010034472.0 discloses a C-Si-Mn-Ti series of cold-rolled dual-phase steel having a chemical composition of 0.03-0.2% C, 0.2-0.8% Si, 1.2-2.0% Mn, Ti: 0.03-0.15%, ≤0.02% P, S≤0.015, 0.02-0.15% Al, the others are composed of Fe and unavoidable impurities. After hot rolling and cold rolling, in the critical zone annealing, when the cooling rate is less than 50 ° C / s, a cold rolled dual phase steel of 980 MPa or more is obtained. The design of the steel is based on a lower continuous cooling rate, so a higher C, Mn content is used. In addition, the only difference between this application and a common invention or commercial product is the replacement of Nb with Ti.

Japanese Patent Laid-Open No. Hei 11-350038 discloses a steel of 980 MPa having good ductility and formability, and its composition is designed to be C: 0.1-0.15%, Si: 0.8-1.5%, Mn: 1.5-2.0%, P: 0.01. -0.05%, S≤0.005%, Sol Al: 0.01-0.07%, N: ≤0.01%, and Nb: 0.001-0.02%, V: 0.001-0.02%, Ti: 0.001-0.02% one or more . Carbon equivalent = (C + Mn / 6 + Si / 24) = 0.4 - 0.52, hot rolling above Ar3, coiling at 500-650 ° C, holding between Ac1-AC3, cooling to 580-720 ° C, fast cooling to After room temperature, it is over-aged at 230-300 °C. The steel has a higher carbon content and a higher carbon equivalent.

Chinese Patent No. 200810119823.0 discloses a method for producing 980 MPa duplex steel, C: 0.14-0.21%, Si: 0.4-0.9%, Mn: 1.5-2.1%, P: ≤ 0.02%, S ≤ 0.01%, Nb: 0.001-0.05%, V: 0.001-0.02%, after hot rolling cold rolling, heat preservation at 760-820 ° C, cooling rate 40-50 ° C / s, over 180-300 s over 180-300 s. The steel has a higher carbon equivalent design.

The above patents relate to tensile strength 1000Mpa dual-phase steel, which adopts high carbon and high Si design, which is not only bad for weldability, surface quality and phosphating performance. Other inventions have adopted a low carbon, high Si design, but the strength level is much lower, and the composition of the tensile strength of 1000 MPa is relatively poor in comparability, elongation and hole reproducibility. In addition, these designs use a low-carbon design. Although the weldability is favorable, the reduction of carbon is not conducive to the effect of high Si on promoting ductility, and there is also a certain design irrationality. Therefore, the above design has certain advantages, and there are also obvious disadvantages.

Summary of the invention

The object of the invention is a high-formability cold-rolled double-phase strip steel and a manufacturing method thereof, and a cold-rolled dual-phase steel having a tensile strength of 980 MPa or more, for example, about 1000 MPa, is obtained by rational component design and process design. In terms of mechanical properties, it has good elongation, hole expansion and cold bending properties; at the same time, the difference in strength and plasticity between 0 and 90 degrees is small. In terms of organization, the matrix structure of the steel is fine and uniform, and the martensite island is also finely and evenly distributed on the substrate, and the banded structure is slight.

In order to achieve the above object, the technical solution of the present invention is:

In a first aspect of the invention, there is provided a high formability cold rolled duplex steel strip having a chemical composition weight percentage of:

C 0.06～0.095%

Si ≤ 0.4%

Mn 2.05～2.35%

Cr 0.7-Mo-Ni/2%

Mo 0.1-0.3%

Ni 2×(Mo-0.18)%

P ≤0.015%

S ≤0.003%

N ≤0.005%

Nb 0～0.04%

Ti 0.01 to 0.05%

Al 0.015～0.05%

The rest are Fe and inevitable impurities. In a preferred embodiment, when the weight percentage of Mo is 0.1% ≤ Mo < 0.2%, the content of Ni is 0%; when the weight percentage of Mo is 0.2-0.3%, the content of Ni is 2 × (Mo -0.18)%. In a preferred embodiment, the Si content is from 0.02 to 0.4%.

In a second aspect of the invention, there is provided a high formability cold rolled duplex steel strip having a chemical composition weight percentage of:

C 0.06～0.095%

Si 0.02-0.6%

Mn 2.05～2.35%

Cr 0.7-Mo-Ni/2%

Mo 0.1-0.3%

Ni 2×(Mo-0.18)%

P ≤0.015%

S ≤0.003%

N ≤0.005%

Ti 0.01 to 0.05%

Al 0.015～0.05%

The rest are Fe and inevitable impurities; wherein when the weight percentage of Mo is 0.1% ≤ Mo < 0.2%, the content of Ni is 0%; when the weight percentage of Mo is 0.2-0.3%, the content of Ni is 2 × ( Mo-0.18)%. In a preferred embodiment, the Si content is from 0.02 to 0.4%. In another preferred embodiment, the high formability cold rolled duplex steel further comprises Nb in the chemical composition, and the weight percentage thereof is 0 < Nb ≤ 0.04%.

In a third aspect of the invention, there is provided a high formability cold rolled duplex steel strip having a chemical composition weight percentage of:

C 0.06～0.095%

Si 0.02-0.6%

Mn 2.05～2.35%

Cr 0.7-Mo-Ni/2%

Mo 0.1-0.3%

Ni 2×(Mo-0.18)%

P ≤0.015%

S ≤0.003%

N ≤0.005%

Nb 0<Nb≤0.04%

Al 0.015～0.05%

The rest are Fe and inevitable impurities; wherein when the weight percentage of Mo is 0.1% ≤ Mo < 0.2%, the content of Ni is 0%; when the weight percentage of Mo is 0.2-0.3%, the content of Ni is 2 × ( Mo-0.18)%. In a preferred embodiment, the Si content is from 0.02 to 0.4%.

In the composition design of the steel of the invention:

C: affects the hardness of martensite, affects the content of martensite, and has a great influence on the strength. The increase in carbon content is unfavorable for weldability. Therefore, the carbon content is selected to be between 0.06 and 0.95 wt%, and if it is less than 0.06%, the strength is insufficient; if it is higher than 0.095%, the weldability is lowered, and casting defects are increased. For example, the carbon content may be ≥0.065%, or ≥0.07%, or ≥0.075%, or ≥0.08%, or ≤0.09%, or ≤0.085%. In the present invention, the content of carbon may be a numerical range formed by arbitrarily combining the above respective end values.

Si: acts as a solid solution strengthening in duplex steel, and Si suppresses the precipitation of carbides and promotes the formation of retained austenite, which is advantageous for plasticity. However, Si promotes the segregation of C in the Mn-rich region, which is not conducive to the uniformity of the structure. In addition, Si promotes the generation of surface defects and is unfavorable for the phosphating performance. Therefore, the upper limit of the Si content is controlled, and the content is required to be ≤0.6 wt%. Or ≤0.5wt%, or ≤0.4wt%, or ≤0.35wt%, or ≤0.3wt%, or ≤0.25wt%, or ≤0.2wt%; in addition, it is also necessary to control the lower limit, requiring Si content >0 weight, or ≥0.005 wt%, or ≥0.01 wt%, or ≥0.02 wt%, or ≥0.05 wt%, or ≥0.08 wt%, or ≥0.010 wt%, or ≥0.02 wt%. In the present invention, the content of Si may be a numerical range formed by arbitrarily combining the above respective end values.

Mn: It can improve the hardenability of steel and effectively increase the strength of steel, but it is not good for welding. Mn segregates in steel and is easily rolled into a band-shaped Mn-rich region during hot rolling to form a band-like structure, which is not conducive to the uniformity of the microstructure of the duplex steel. Therefore, the content of Mn is selected to be 2.05-2.35 wt%, the hardenability of steel below 2.05% is insufficient, and the strength is insufficient; above 2.35%, the band structure is intensified, and the uniformity of the structure is deteriorated. For example, the manganese content may be ≥2.08%, or ≥2.10%, or ≥2.13%, or ≥2.15%, or ≥2.20%; or ≤2.30%, or ≤2.25%, or ≤2.20%. In the present invention, the content of Mn may be a numerical range formed by arbitrarily combining the above respective end values.

Cr: can improve the hardenability of steel, adding Cr can supplement the role of Mn, Cr and Mo, Ni used together, Cr content = 0.7-Mo-Ni/2.

Mo: It can improve the hardenability of steel, effectively increase the strength of steel, and Mo can improve the distribution of carbides. Mo and Cr together promote the hardenability, and the amount of Mo added is controlled at a level of 0.1-0.3. For example, the Mo content may be ≥0.15%, or ≥0.18%, or ≥0.19%, or ≥0.2%, or ≥0.22%, or ≤0.25%, or ≤0.24%. In the present invention, Mo The content may be a range of values formed by arbitrarily combining the above respective end values.

Ni: It has a small promoting effect on the hardenability of steel, and is also beneficial to plasticity and toughness, and is advantageous for the delayed cracking performance of ultra-high strength steel. The amount of addition of Ni is related to Mo. When Mo is greater than or equal to 0.1% and less than 0.2%, no Ni is added. When Mo is greater than or equal to 0.2% to less than or equal to 0.3%, the amount of Ni added is controlled at 2*. (Mo-0.18).

P: an impurity element in steel, requiring ≤ 0.015 wt%. For example, the content of P may be ≥0.006%, or ≥0.0065%, or ≥0.0066%, or ≥0.008; or ≤0.012%, or ≤0.010%. In the present invention, the content of P may be a numerical range formed by arbitrarily combining the above respective end values.

S: It is an impurity element in steel and requires ≤0.003 wt%. For example, the content of S may be ≥ 0.0005%, or ≥ 0.001%, or ≥ 0.0015%, or ≤ 0.0025%, or ≤ 0.002%. In the present invention, the content of S may be a numerical range formed by arbitrarily combining the above respective end values.

Al: plays a role in deoxidation and grain refinement in steel, and requires Al: 0.015-0.05 wt%. For example, the content of Al may be ≥0.020%, or ≥0.025%, or ≥0.030%, or ≥0.035%, or ≤0.045%, or ≤0.040%. In the present invention, the content of Al may be a numerical range formed by arbitrarily combining the above respective end values.

N: an impurity element in steel, requiring ≤0.005 wt%. For example, the content of N can be ≥ 0.0015%, or ≥ 0.0020%, or ≥ 0.0025%, or ≤ 0.0045%, or ≤ 0.0040%, or ≤ 0.0035%, or ≤ 0.0030%. In the present invention, the content of N may be a numerical range formed by arbitrarily combining the above respective end values.

Nb and Ti: are precipitation strengthening elements, which function to refine grains, and may be added separately or in combination, that is, any one of these two elements may be added, or both elements may be added at the same time. These two elements are added in an amount of Nb: 0-0.04% by weight and Ti: 0.01-0.05% by weight. Preferably, the content of Nb is 0 wt% < Nb ≤ 0.04%, or Nb content ≥ 0.01%, or ≥ 0.015%, or ≥ 0.02%, or Nb ≤ 0.035%, or ≤ 0.03%, or ≤ 0.025%; in the present invention The content of Nb may be a numerical range formed by arbitrarily combining the above respective end values. The content of Ti may be ≥0.020%, or ≥0.025%, or ≤0.040%, or ≤0.035%, or ≤0.030%. In the present invention, the content of Ti may be a numerical range formed by arbitrarily combining the above respective end values.

In the present invention, the various percentages used in defining the chemical composition of the duplex steel strip are by weight based on the total weight of the strip.

The invention also provides a method for manufacturing the above cold-rolled high-strength dual-phase strip steel, comprising the following steps Step:

1) Smelting, continuous casting

According to the above composition smelting, continuous casting, continuous heating of molten steel is less than or equal to 40 ° C, using a uniform pulling speed of 0.5 ~ 1.2 m / min;

2) Hot rolling

Reheating temperature is not lower than 1200 ° C, holding time is not less than 20 minutes; after hot rolling above Ar3 temperature, rapid cooling after rolling, coiling temperature of 480 ~ 620 ° C;

3) Cold rolling

Cold rolling reduction rate of 35 to 80%;

4) Annealing

The holding temperature is 770-850 ° C, rapid cooling to 720-580 ° C, cooling to below 300 ° C at a speed of not less than 50 ° C / s, after tempering at 220 ~ 350 ° C for 100 ~ 300s, then 0 ~ 0.4% smooth.

Preferably, the superheat of the molten steel during continuous casting is less than or equal to 40 ° C, and a uniform pulling speed of 0.6 to 1.0 m / min is employed. Using a uniform two-cold water process, the latter third of the cooling strength (spray water) is not less than 0.75 L water / kg billet.

Further, the hot rolling reheating temperature is not lower than 1200 ° C, and the holding time is not less than 25 minutes. After hot rolling at Ar3 or higher temperature, it is rapidly cooled after rolling, and the coiling temperature is 480-620 °C; the cold rolling reduction rate is 40-65%; during annealing, the holding temperature is 780-840 °C, and the rapid cooling is between 700-600 °C. It is cooled to below 300 °C at a speed of not less than 60 ° C / s, after tempering at 220-320 ° C for 150-300 s, and then 0 to 0.3% leveling.

In terms of weldability, the steel of the present invention is designed by a low carbon equivalent component to facilitate the improvement of weldability, and a welded cross-stretch button-like fracture can be obtained.

In terms of composition design, the low carbon design is beneficial to the good plasticity of ferrite in duplex steel, which is beneficial to the overall plasticity of duplex steel. The design of Si, under the premise of low-carbon design, the use of Si can promote the reduction of carbon content in ferrite, the appropriate addition of Si, and in consideration of low carbon, high Si contributes less to formability. Instead, it affects the surface quality and therefore uses a low Si design. The composite addition of alloying elements Mn, Mo and Ni is beneficial to obtain refined structure and improve the band structure in steel. At the same time, Mo, Ti and Ni play a role in improving the local deformation ability of steel. Good, and ultimately improve the steel's hole expansion rate and cold bending performance.

In terms of technology, for the organization of high-strength advanced high-strength steel, a series of measures are taken to obtain uniform structure and minimize the band structure. The measures include: controlling the casting process under the premise of low carbon design, thereby reducing the microsegregation tendency in the solidification process, and obtaining the as-cast microstructure of the uniform carbide distributed on the ferrite matrix. In the hot rolling process, low temperature finish rolling and low temperature coiling are used to refine the grains.

In terms of organization, the structure of the steel of the present invention consists of fine uniform ferrite and finely dispersed martensite islands, and does not deliberately obtain residual austenite and bainite, but does not exclude the inclusion of a very small amount of retained austenite and Bainite. body. From the physical examination score, the content of martensite is about 30-60%, and most of the rest is ferrite. The ferrite has a grain size of not more than 8 μm, and there are dispersed fine micro-alloy carbide precipitated particles in the ferrite matrix.

With the above design, the weldability and surface quality of the steel can be improved, and the rapid cooling and reasonable alloying element addition can be used to obtain a strength of 980 MPa or more, for example, about 1000 MPa, and at the same time, the structure is uniform and fine, plasticity, hole expansion ratio and cold bending property. All are good. At a strength of 980 MPa or more, the hole expansion ratio can reach 30% or more, and the 180 degree bending can reach a bending diameter/plate thickness ≤3.

The beneficial effects of the invention:

The steel of the invention has fine ferrite structure, uniform distribution of martensite islands and slight band structure; according to the invention, high-strength dual-phase steel with a strength of 980 MPa or more, for example about 1000 MPa, can be produced, and has good elongation ( ≥13%), hole expansion ratio (≥30%) and cold bending performance (180 degree bending can reach bending diameter/plate thickness ≤3), good mechanical properties uniformity, small difference between longitudinal and transverse mechanical properties, up to 50MPa It is beneficial to the stamping forming of duplex steel; the carbon equivalent is low, the weldability is good, and the cross-stretching in the welding current range is a button-like fracture. The steel of the invention has better painting characteristics, and the surface phosphating film is fine and compact (phosphorus crystal diameter ≤ 20 μm) with high coverage, and meets the painting performance of the automobile board. It is fully in line with the requirements for the use of high-strength dual-phase steel in the field of automobile manufacturing, and is superior to the existing similar products.

Compared with the prior patents mentioned in the background section, the present invention has the following features:

First, the present invention is significantly different from Comparative Document 1 (Chinese Patent Application No. CN201010034472.0), which discloses a steel having a chemical composition of 0.03-0.2% C, 0.2-0.8% Si, and 1.2-2.0% Mn. , Ti: 0.03-0.15%, P ≤ 0.02%, S ≤ 0.015, 0.02-0.15% Al, but it is stated that the cooling rate is less than 50 ° C / s, and the carbon content of the embodiment is much higher than 0.1%, if the carbon content is less than 0.1%, then under slow cooling conditions, It is impossible to achieve an intensity of 980 MPa. Therefore, the portion whose carbon content is less than 0.1% cannot reach the target strength level of the invention.

The present invention adopts a low carbon design and adopts a higher rapid cooling technique than the above-mentioned reference 1, and the total amount of alloying elements such as Mn, Cr, Mo, etc. is higher than the above patent, which is proof. From the viewpoint of mechanical properties, the above reference 1 is only a basic requirement for a duplex steel having a strength of 980 MPa, and the weldability, surface quality, and hole expanding performance are far less than that of the present invention.

The steel composition disclosed in Comparative Document 2 (Japanese Patent Laid-Open No. Hei 11-350038) is designed to have C: 0.1-0.15%, Si: 0.8-1.5%, Mn: 1.5-2.0%, P: 0.01-0.05%, S ≤ 0.005%, Sol Al: 0.01-0.07%, N: ≤ 0.01%, Nb: 0.001-0.02%, V: 0.001-0.02%, Ti: 0.001-0.02% one or more. It is a high carbon, high Si design, which is essentially similar to Comparative Document 1. The invention has the advantages of good weldability, good surface quality, high steel purity and good band structure. The hole expansion ratio is superior to that of Comparative Document 2, and the advantage of Comparative Document 2 is that the elongation rate is slightly higher.

The steel composition disclosed in Comparative Document 3 (Chinese Patent No. 200810119823.0) is designed to be C: 0.14 - 0.21%, Si: 0.4 - 0.9%, Mn: 1.5 - 2.1%, P ≤ 0.02%, S ≤ 0.01%, Nb: 0.001-0.05%, V: 0.001-0.02%. The steel has a high carbon content and a low Si content. The steel is a moderately versatile steel grade, and has no advantages in weldability, elongation, hole expansion ratio, surface quality, and comparison of the present invention.

DRAWINGS

1 is a microstructure of a dual phase steel of the present invention - a ferrite matrix and a diffusely distributed martensite island;

2 is a broken joint of a resistance spot welding cross-stretch button of a dual-phase steel according to the present invention;

Figure 3 is a topography of a phosphate film of the present invention.

detailed description

The invention is further illustrated by the following examples and the accompanying drawings.

1 is the chemical composition of the steel of the embodiment of the present invention, A1-A9 is the steel serial number of the embodiment of the present invention, and the process of the steel of the present invention is shown in Table 2. The steel of the present invention is smelted, hot rolled, cold rolled, annealed and flattened. The strength obtained after is shown in Table 3.

As can be seen from Table 3, according to the present invention, a tensile strength of 980 MPa or more can be produced. High-strength dual-phase steel has good elongation, high hole expansion ratio and relatively small anisotropy of mechanical properties.

Figure 1 shows the structure of the steel of the present invention, from which it can be seen that the tissue is fine and the banded structure is relatively slight.

The welding property of the invention is good, and all of the welding current ranges are button-shaped fractures, as shown in FIG. 2 .

In addition, the phosphating property is better, fully meet the automotive panel coating requirements, as shown in Figure 3.

Therefore, the present invention differs from the prior invention or is superior to the prior art in various aspects, such as composition design and process design, and finally obtained results.

Table 1 Chemical composition (wt%) of steel according to an embodiment of the present invention

Table 2 Process parameters and mechanical properties of the examples of the present invention

table 3

Claims

A high formability cold rolled duplex steel strip having a chemical composition weight percentage of:

C 0.06～0.095%

Si ≤ 0.4%

Mn 2.05～2.35%

Cr 0.7-Mo-Ni/2%

Mo 0.1-0.3%

Ni 2×(Mo-0.18)%

P ≤0.015%

S ≤0.003%

N ≤0.005%

Nb 0～0.04%

Ti 0.01 to 0.05%

Al 0.015～0.05%

The rest are Fe and inevitable impurities.
A method of manufacturing a high-formability cold-rolled duplex steel strip according to claim 1, comprising the steps of:

1) Smelting, continuous casting

According to the above composition smelting, continuous casting, continuous heating of molten steel is less than or equal to 40 ° C, using a uniform pulling speed of 0.5 ~ 1.2 m / min;

2) Hot rolling

Reheating temperature is not lower than 1200 ° C, holding time is not less than 20 minutes; after hot rolling above Ar3 temperature, rapid cooling after rolling, coiling temperature of 480 ~ 620 ° C;

3) Cold rolling

Cold rolling reduction rate of 35 to 80%;

4) Annealing

The holding temperature is 770-850 ° C, rapid cooling to 720-580 ° C, cooling to below 300 ° C at a speed of not less than 50 ° C / s, after tempering at 220 ~ 350 ° C for 100 ~ 300s, then 0 ~ 0.4% smooth.
A method of producing a high-formability cold-rolled duplex steel strip according to claim 2, characterized in that Yes, the superheat of molten steel during continuous casting is less than or equal to 40 ° C, and a uniform pulling speed of 0.6 to 1.0 m / min is used.
The method of producing a high-formability cold-rolled duplex steel according to claim 2, wherein the hot rolling reheating temperature is not lower than 1200 ° C, and the heat retention time is not less than 25 minutes. After hot rolling at Ar3 or higher temperature, it is rapidly cooled after rolling, and the coiling temperature is 480-620 °C; the cold rolling reduction rate is 40-65%; during annealing, the holding temperature is 780-840 °C, and the rapid cooling is 700-600 °C. During the period, the temperature is cooled to not more than 300 ° C / s to below 300 ° C, after tempering at 220 ~ 320 ° C for 150 ~ 300s, and then 0 ~ 0.3% leveling.
The high-formability cold-rolled duplex steel strip according to claim 1, wherein when the weight percentage of Mo is 0.1% ≤ Mo < 0.2%, the content of Ni is 0%; and when the weight percentage of Mo is 0.2. When -0.3%, the content of Ni is 2 × (Mo - 0.18)%.
A high formability cold rolled duplex steel strip having a chemical composition weight percentage of:

C 0.06～0.095%

Si 0.02-0.6%

Mn 2.05～2.35%

Cr 0.7-Mo-Ni/2%

Mo 0.1-0.3%

Ni 2×(Mo-0.18)%

P ≤0.015%

S ≤0.003%

N ≤0.005%

Ti 0.01 to 0.05%

Al 0.015～0.05%

The rest are Fe and inevitable impurities; wherein when the weight percentage of Mo is 0.1% ≤ Mo < 0.2%, the content of Ni is 0%; when the weight percentage of Mo is 0.2-0.3%, the content of Ni is 2 × ( Mo-0.18)%.
The high-formability cold-rolled duplex steel according to claim 6, wherein the chemical composition of the high-formability cold-rolled duplex steel further contains Nb in a weight percentage of 0 < Nb ≤ 0.04%.
A high formability cold rolled duplex steel strip having a chemical composition weight percentage of:

C 0.06～0.095%

Si 0.02-0.6%

Mn 2.05～2.35%

Cr 0.7-Mo-Ni/2%

Mo 0.1-0.3%

Ni 2×(Mo-0.18)%

P ≤0.015%

S ≤0.003%

N ≤0.005%

Nb 0<Nb≤0.04%

Al 0.015～0.05%

The rest are Fe and inevitable impurities; wherein when the weight percentage of Mo is 0.1% ≤ Mo < 0.2%, the content of Ni is 0%; when the weight percentage of Mo is 0.2-0.3%, the content of Ni is 2 × ( Mo-0.18)%.
The high-formability cold-rolled duplex steel according to any one of claims 1 and 6 to 8, wherein the weight percentage of Si is 0.02 to 0.4%.
The high-formability cold-rolled duplex steel strip according to any one of claims 1 and 6 to 9, wherein the strip steel structure is composed of fine uniform ferrite and finely dispersed martensite islands; The content of martensite is 30-60% with respect to the volume percentage of the total volume of the high-formity cold-rolled duplex steel strip, and the rest is ferrite; the grain size of the ferrite is not more than 8 μm, ferrite There are dispersed fine micro-alloy carbide precipitated particles in the body matrix.
The high-formability cold-rolled duplex steel strip according to claim 10, wherein the strip structure further contains a very small amount of retained austenite and bainite.
The high-formability cold-rolled duplex steel strip according to claim 10 or 11, wherein the high-formability cold-rolled duplex steel strip has a tensile strength ≥ 980 MPa, an elongation ≥ 13%, and a hole expansion ratio. ≥ 30%, 180 degree bending diameter / thickness ≤ 3, longitudinal and transverse strength difference ≤ 50MPa.
The high-formability cold-rolled duplex steel strip according to claim 12, wherein the high-formity cold-rolled duplex steel strip has a cross-stretching in a welding current range as a button-like fracture and surface phosphating crystallization. Diameter ≤ 20μm.
A method of producing a high-formability cold-rolled duplex steel strip according to any one of claims 6 to 13, comprising the steps of:

1) Smelting, continuous casting

The smelting and continuous casting of the high-formability cold-rolled double-phase strip steel according to any one of claims 6-13, wherein the superheat of the molten steel is less than or equal to 40 ° C during continuous casting, and a uniform pulling speed of 0.5 to 1.2 is adopted. m/min;

2) Hot rolling

Reheating temperature is not lower than 1200 ° C, holding time is not less than 20 minutes; after hot rolling above Ar3 temperature, rapid cooling after rolling, coiling temperature of 480 ~ 620 ° C;

3) Cold rolling

Cold rolling reduction rate of 35 to 80%;

4) Annealing

The holding temperature is 770-850 ° C, rapid cooling to 720-580 ° C, cooling to below 300 ° C at a speed of not less than 50 ° C / s, after tempering at 220 ~ 350 ° C for 100 ~ 300s, then 0 ~ 0.4% smooth.
The method of producing a high-formability cold-rolled duplex steel according to claim 14, wherein the molten steel has a superheat degree of 40 ° C or less and a uniform drawing speed of 0.6 to 1.0 m / min.
A method of producing a high-formability cold-rolled duplex steel strip according to claim 14, wherein the hot rolling reheating temperature is not lower than 1200 ° C and the holding time is not less than 25 minutes. After hot rolling at Ar3 or higher temperature, it is rapidly cooled after rolling, and the coiling temperature is 480-620 °C; the cold rolling reduction rate is 40-65%; during annealing, the holding temperature is 780-840 °C, and the rapid cooling is 700-600 °C. During the period, the temperature is cooled to not more than 300 ° C / s to below 300 ° C, after tempering at 220 ~ 320 ° C for 150 ~ 300s, and then 0 ~ 0.3% leveling.