阅读说明：本技术 适用于辊压的一千兆帕级冷轧贝氏体钢板及其制备方法 (One-thousand-megapascal-grade cold-rolled bainite steel plate suitable for rolling and preparation method thereof ) 是由 许斌 贾亚飞 刘自权 何方 刘鹏 马子洋 李守华 李文进 张银普 于 2019-10-24 设计创作，主要内容包括：本发明涉及一种适用于辊压的一千兆帕级冷轧贝氏体钢板；钢板化学成分组成及其质量百分含量为：C：0.11～0.18%,Si：0.1～0.6%,Mn：1.2～2.0%,P≤0.015,S≤0.008%,Als：0.015～0.065%,Ti：0.01～0.05%,Cr：0.3～0.7%,N≤0.007%,其余为Fe及不可避免杂质。本发明还涉及一种适用于辊压的一千兆帕级冷轧贝氏体钢板的制备方法,包括冶炼、连铸、热轧、冷轧、退火、平整工序；退火工序采用连续退火,以1～3℃/s的加热速率将带钢加热至840～890℃,保温120～150s后以2～4℃/s缓冷至710～760℃,随后采用气冷快冷,随后以10～20℃/s的冷速快冷至400～450℃,过时效处理250～400s,平整延伸率为0.2～0.6%。本发明可进一步提高钢板折弯性能,满足复杂零件辊压的高折弯性能要求。(The invention relates to a cold-rolled bainite steel plate of gigapascal level suitable for rolling; the steel plate comprises the following chemical components in percentage by mass: c: 0.11 to 0.18%, Si: 0.1-0.6%, Mn: 1.2-2.0%, P is less than or equal to 0.015%, S is less than or equal to 0.008%, Als: 0.015-0.065%, Ti: 0.01-0.05%, Cr: 0.3-0.7%, N is less than or equal to 0.007%, and the balance is Fe and inevitable impurities. The invention also relates to a preparation method of the rolling bainite steel plate suitable for rolling, which comprises the working procedures of smelting, continuous casting, hot rolling, cold rolling, annealing and leveling; the annealing process adopts continuous annealing, the strip steel is heated to 840-890 ℃ at the heating rate of 1-3 ℃/s, the temperature is kept for 120-150 s, then the strip steel is slowly cooled to 710-760 ℃ at the speed of 2-4 ℃/s, then air cooling and quick cooling are adopted, then the strip steel is quickly cooled to 400-450 ℃ at the cooling speed of 10-20 ℃/s, overaging treatment is carried out for 250-400 s, and the flat elongation is 0.2-0.6%. The invention can further improve the bending property of the steel plate and meet the requirement of high bending property of rolling of complex parts.)

1. A cold rolled bainite steel plate of gigapascal level suitable for rolling is characterized in that: the steel plate comprises the following chemical components in percentage by mass: c: 0.11 to 0.18%, Si: 0.1-0.6%, Mn: 1.2-2.0%, P is less than or equal to 0.015%, S is less than or equal to 0.008%, Als: 0.015-0.065%, Ti: 0.01-0.05%, Cr: 0.3-0.7%, N is less than or equal to 0.007%, and the balance is Fe and inevitable impurities.

2. Cold rolled bainite steel sheet in the order of one gigapascal suitable for rolling according to claim 1 wherein: the steel comprises the following components in percentage by mass: c: 0.11 to 0.15%, Si: 0.2-0.6%, Mn: 1.4-2.0%, P is less than or equal to 0.015%, S is less than or equal to 0.008%, Als: 0.015-0.065%, Ti: 0.01-0.04%, Cr: 0.3-0.6% and N is less than or equal to 0.007%.

3. Cold rolled bainite steel sheet in the order of one gigapascal suitable for rolling according to claim 1 or 2, wherein: the steel plate yield strength is as follows: 800-1050 MPa, tensile strength: 1000-1150 MPa, elongation: 3-6%.

4. The preparation method of the cold rolled bainite steel plate of the gigapascal level suitable for rolling comprises the working procedures of smelting, continuous casting, hot rolling, cold rolling, annealing and leveling; the method is characterized in that:

in the continuous casting process, molten steel after smelting is continuously cast to obtain a continuous casting billet, and the continuous casting billet comprises the following chemical components in percentage by mass: c: 0.11 to 0.18%, Si: 0.1-0.6%, Mn: 1.2-2.0%, P is less than or equal to 0.015%, S is less than or equal to 0.008%, Als: 0.015-0.065%, Ti: 0.01-0.05%, Cr: 0.3-0.7%, N is less than or equal to 0.007%, and the balance is Fe and inevitable impurities.

5. A method of producing cold rolled bainite steel sheet in the class of one gigapascal suitable for rolling as claimed in claim 4 wherein: the continuous casting billet comprises the following chemical components in percentage by mass: c: 0.11-0.15%; si: 0.2-0.6%; mn: 1.4-2.0%; p is less than or equal to 0.015 percent, S is less than or equal to 0.008 percent, Als: 0.015-0.065%, Ti: 0.01-0.04%; cr: 0.3-0.6%; n is less than or equal to 0.007 percent, and the balance of Fe and inevitable impurities.

6. A method of producing cold rolled bainite steel sheet in the class of one gigapascal suitable for rolling as claimed in claim 4 wherein: the annealing process adopts continuous annealing, the strip steel is heated to 840-890 ℃ at the heating rate of 1-3 ℃/s, the temperature is kept for 120-150 s, then the strip steel is slowly cooled to 710-760 ℃ at the speed of 2-4 ℃/s, then air cooling and rapid cooling are adopted, then the strip steel is rapidly cooled to 400-450 ℃ at the cooling speed of 10-20 ℃/s, overaging treatment is carried out for 250-400 s, and the flat elongation is 0.2-0.6%.

7. A method of producing cold rolled bainite steel sheet in the class of one gigapascal suitable for rolling as claimed in claim 4 wherein: in the hot rolling process, the plate blank is heated to 1220-1290 ℃, the final rolling temperature is controlled to 870-930 ℃, and the plate blank is cooled to 610-680 ℃ through a laminar cooling system after being rolled and coiled;

in the cold rolling process, the cold rolling reduction is controlled to be 45-60%.

Technical Field

The invention belongs to the technical field of metallurgy, and particularly relates to a one-thousand-megapascal-level cold-rolled bainite steel plate suitable for rolling and a preparation method thereof.

Background

With the rapid development of the automobile industry and the urgent need of the global environment, the light weight of the automobile industry becomes the focus of future development, and the research and development requirements of the high-strength thin plate are also generated. The thin ultrahigh-strength automobile plate can effectively reduce the dead weight of the automobile, reduce the fuel consumption, reduce the exhaust emission, improve the safety and reduce the environmental pollution.

The roll forming process is to process the open flat strip steel into a desired shape by adopting a continuous bending mode. The forming mode can form steel grades with different mechanical property levels and structures, can form parts with smaller bending radius according to the thickness and the mechanical property of the steel, and can reduce forming procedures compared with the traditional stamping forming. Roll-formed articles are widely used in the automotive manufacturing field. Common steel types for roll forming include dual-phase steel, martensitic steel, formed part pipe parts, anti-collision beams, threshold parts and the like. The requirements of the safety parts on strength are higher and higher, and the shapes of formed parts are increasingly complex, so that a high-strength steel plate suitable for roll forming is urgently needed to be developed, the roll forming is ensured, and the strength of the parts is improved.

The cold rolled bainite steel plate suitable for rolling is a steel type mainly based on phase change strengthening, the microstructure of the cold rolled bainite steel plate mainly comprises a bainite phase, softer ferrite and hard martensite, the cold rolled bainite steel plate can be obtained by low-carbon steel through a critical zone heat treatment and controlled rolling process, and the cold rolled bainite steel plate has good strong plasticity and cold bending performance through reasonable proportion of matrix phase content.

The material adopted by the existing rolling technology is mostly martensitic steel, for example, patent application with publication number CN102534373A discloses "an ultrahigh strength cold rolled steel strip suitable for roll forming and a manufacturing method thereof", which adopts a martensitic steel process to carry out roll forming, but with the complicated type and shape of rolled parts, the requirement for bending performance is further improved, and the martensitic steel can not meet the requirement of higher formability, and the problem of part cracking is easy to occur.

Chinese patent with publication number CN107354376B discloses 'a cold-rolled steel sheet with yield strength of 550MPa for roll forming and a production method', the yield strength of the annealed steel sheet is more than or equal to 550MPa, the tensile strength is more than or equal to 620MPa, and the steel sheet has low strength level. With the increasing strength and light weight requirements of rolled parts, the use of high-strength grade steel grades is increasingly demanded.

Disclosure of Invention

The invention aims to solve the technical problem of providing a one-thousand-MPa cold-rolled bainite steel plate suitable for rolling and a preparation method thereof.

In order to solve the technical problems, the invention adopts the technical scheme that:

the cold-rolled bainite steel plate is suitable for rolling and comprises the following chemical components in percentage by mass: c: 0.11 to 0.18%, Si: 0.1-0.6%, Mn: 1.2-2.0%, P is less than or equal to 0.015%, S is less than or equal to 0.008%, Als: 0.015-0.065%, Ti: 0.01-0.05%, Cr: 0.3-0.7%, N is less than or equal to 0.007%, and the balance is Fe and inevitable impurities.

Preferably, the steel comprises the following components in percentage by mass: c: 0.11 to 0.15%, Si: 0.2-0.6%, Mn: 1.4-2.0%, P is less than or equal to 0.015%, S is less than or equal to 0.008%, Als: 0.015-0.065%, Ti: 0.01-0.04%, Cr: 0.3-0.6%, N is less than or equal to 0.007%,

the steel plate has the following yield strength: 800-1050 MPa, tensile strength: 1000-1150 MPa, elongation: 3-6%.

A preparation method of a rolling bainite steel plate suitable for rolling comprises the working procedures of smelting, continuous casting, hot rolling, cold rolling, annealing and leveling;

in the continuous casting process, molten steel after smelting is continuously cast to obtain a continuous casting billet, and the continuous casting billet comprises the following chemical components in percentage by mass: c: 0.11 to 0.18%, preferably 0.11 to 0.15%; si: 0.1 to 0.6%, preferably 0.2 to 0.6%; mn: 1.2-2.0%, preferably 1.4-2.0%; p is less than or equal to 0.015 percent, S is less than or equal to 0.008 percent, Als: 0.015-0.065%, Ti: 0.01 to 0.05%, preferably 0.01 to 0.04%; cr: 0.3 to 0.7%, preferably 0.3 to 0.6%; n is less than or equal to 0.007 percent, and the balance of Fe and inevitable impurities.

According to the preparation method of the rolling once gigapascal grade cold-rolled bainite steel plate, continuous annealing is adopted in the annealing process, the strip steel is heated to 840-890 ℃ at the heating rate of 1-3 ℃/s, the temperature is kept for 120-150 s, then the strip steel is slowly cooled to 710-760 ℃ at 2-4 ℃/s, then air cooling and rapid cooling are adopted, then the strip steel is rapidly cooled to 400-450 ℃ at the cooling rate of 10-20 ℃/s, overaging treatment is carried out for 250-400 s, and the flat elongation is 0.2-0.6%.

The smelting process adopts converter smelting and an LF + RH duplex process.

In the hot rolling process, the slab is heated to 1220-1290 ℃, the final rolling temperature is controlled to 870-930 ℃, and the slab is cooled to 610-680 ℃ through a laminar cooling system after rolling and is coiled. In the cold rolling process, the cold rolling reduction is controlled to be 45-60%.

The invention has the following contents and functions of the elements:

c: carbon is an effective strengthening element and can greatly improve the strength of the steel. However, too high carbon content deteriorates the weldability of steel, and the solid solution strengthening causes an increase in strength and a decrease in plasticity. According to the invention, the C content is selected to be 0.11-0.18 wt%, and the steel plate strength cannot be ensured if the C content is too low.

Si is a non-carbide forming element, can enlarge α + gamma region in Fe-C phase diagram, raise austenite-ferrite transformation temperature and promote ferrite precipitation, and the Si content is 0.1-0.6 wt%, and the Si content is too high, so that it can easily result in surface quality problem.

Mn: manganese is an austenite stabilizing element, has an obvious inhibiting effect on the recrystallization process of austenite, can fully utilize unrecrystallized control to roll refined grains by properly increasing the content of Mn, has a certain solid solution strengthening effect, and can improve the ductility and toughness. The Mn content is selected to be 1.2-2.0 wt%.

Ti: the addition of Ti in sufficient amount can effectively refine grains and fix nitrogen elements. The Ti content is selected to be 0.01-0.05 wt%.

Cr: adding enough Cr to improve hardenability, wherein the Cr content is 0.3-0.7 wt%.

P: the impurity elements in the steel are required to be less than or equal to 0.015 percent.

S: the impurity elements in the steel are required to be less than or equal to 0.008 percent.

And Als: the alloy plays roles in deoxidizing and refining grains in steel, and the content of ALs is required to be 0.015-0.065%.

N: the impurity elements in the steel are required to be less than or equal to 0.007 percent.

Aiming at the characteristics of roll forming, the bainite high-strength steel with excellent welding and cold bending properties and high cold bending properties is obtained through proper component design and process design. The specific measures are that a relatively high carbon content interval is adopted, a relatively low Si content is matched, meanwhile, the Mn content is properly increased, the austenite stability is improved, the strength is optimized, a uniform tissue is favorably obtained, and the mechanical uniformity of coiling is improved. The Ti and Cr elements are added to refine grains, improve hardenability, ensure that the strip steel has enough strength and refine grain structure. The surface quality problem caused by overhigh Si content can be effectively avoided by selecting lower Si content. The smelting and hot rolling process adopts a conventional production process. And obtaining the finished product structure of the steel through matching annealing and hot rolling processes. During annealing, the annealing heat preservation temperature higher than that of the conventional process is adopted, so that the uniformity of austenite grains and the structure transformation are ensured. And then slowly cooling to 710-760 ℃, then quickly cooling by air cooling to 400-450 ℃ at a high speed, effectively obtaining a uniformly refined bainite structure, and then carrying out aging treatment and small amount of flattening. The final product has excellent performance and good bending performance, and meets the increasingly complex requirements of roll forming.

Adopt the produced beneficial effect of above-mentioned technical scheme to lie in:

according to the invention, through low-carbon and Cr and Ti microalloying component design and matching with reasonable rolling and bainite annealing process design, the high cold-bending bainite high-strength steel with excellent welding and cold-bending properties is obtained, the tensile strength reaches over 1000MPa, the structure is uniform, the roll forming property can be effectively improved, and the part is good in roll forming.

Drawings

FIG. 1 is a metallographic structure drawing (1000X) of a cold-rolled bainite steel plate produced in example 1;

FIG. 2 is a metallographic structure drawing (1000X) of a cold-rolled bainite steel plate produced in example 2;

FIG. 3 is a metallographic structure drawing (1000X) of a cold-rolled bainite steel plate produced in example 3;

FIG. 4 is a metallographic structure drawing (1000X) of a cold-rolled bainite steel plate produced in example 4;

FIG. 5 is a metallographic structure drawing (1000X) of a cold-rolled bainite steel plate produced in example 5;

FIG. 6 is a metallographic structure drawing (1000X) of a cold-rolled bainite steel plate produced in example 6;

FIG. 7 is a metallographic structure drawing (1000X) of a cold-rolled bainite steel plate produced in example 7;

FIG. 8 is a metallographic structure drawing (1000X) of a cold-rolled bainite steel plate produced in example 8;

FIG. 9 is a metallographic structure drawing (1000X) of a cold-rolled bainite steel plate produced in example 9;

FIG. 10 is a metallographic structure drawing (1000X) of a cold-rolled bainite steel plate produced in example 10.

Detailed Description

The present invention is described in detail with reference to specific examples 1 to 10, and the method for manufacturing the cold rolled bainite steel sheet of gigapascal class suitable for rolling will be described in detail below.