CN111411299A

CN111411299A - 1000 MPa-grade cold-rolled high-elongation Q & P steel plate and preparation method thereof

Info

Publication number: CN111411299A
Application number: CN202010306288.0A
Authority: CN
Inventors: 贾亚飞; 何方; 刘自权; 李俊生; 于晓飞; 刘鹏; 马子洋
Original assignee: Handan Iron and Steel Group Co Ltd; HBIS Group Hansteel Co
Current assignee: Handan Iron and Steel Group Co Ltd; HBIS Group Hansteel Co
Priority date: 2020-04-17
Filing date: 2020-04-17
Publication date: 2020-07-14

Abstract

The invention relates to a 1000 MPa-grade cold-rolled high-elongation Q & P steel plate which comprises the following chemical components in percentage by mass: c: 0.17-0.24%; si: 1.1-1.7%; mn: 2.0-2.5%; p is less than or equal to 0.015 percent; s is less than or equal to 0.008 percent; and Als: 0.02-0.08%; nb: 0.01 to 0.025%; ti: 0.01 to 0.025%; n: 0.003 to 0.007 percent; the balance of Fe and inevitable impurities; the preparation method of the 1000 MPa-grade cold-rolled high-elongation Q & P steel plate comprises the steps of heating a strip steel to 780-820 ℃ at a heating rate of 1-3 ℃/s in an annealing process, keeping the temperature for 120-150 s, then slowly cooling the strip steel to 680-700 ℃ at 2-4 ℃/s, then quickly cooling the strip steel to 200-250 ℃ at a cooling speed of 10-20 ℃/s in an air cooling mode, heating the strip steel to 380-450 ℃ at a heating rate of 20-30 ℃/s in an air cooling mode, carrying out overaging treatment for 250-400 s, and enabling the flat elongation to be 0.2-0.6%. The tensile strength of the steel plate produced by the method reaches more than 1000MPa, the elongation is 19-25%, the structure is uniform, the processing formability is effectively improved, and the requirements of increasingly complex parts of an automobile on the strength and the elongation performance of the material are met.

Description

1000 MPa-grade cold-rolled high-elongation Q & P steel plate and preparation method thereof

Technical Field

The invention belongs to the technical field of production methods of automobile steel, and particularly relates to a 1000 MPa-grade cold-rolled high-elongation Q & P steel plate and a preparation method thereof.

Background

The Q & P steel is a third-generation automobile steel with high strength and high plasticity. And the microstructure is regulated and controlled from the aspects of multi-phase transformation, metastable transformation and the like, so that excellent mechanical properties are obtained. With the gradual improvement of light weight, the performance of Q & P steel is widely accepted by users, but the types of automobile parts are various and the deformation is complex, so that the forming capability of the traditional 1000MPa grade Q & P steel is difficult to meet the forming requirement. Therefore, the development of Q & P steel with higher extension grade of 1000MPa is urgently needed.

The patent application with the publication number of CN108193138A discloses a 980 MPa-grade cold-rolled high-strength Q & P steel for automobiles and a production method thereof, wherein the process adopts a Q & P one-step process, namely the initial quenching temperature is consistent with the carbon distribution temperature, the Q & P steel produced by the method has low plasticity and elongation although the strength meets the use requirement, and the forming capability of complex automobile parts in the processing process mainly depends on the plasticity.

Disclosure of Invention

The invention aims to solve the technical problem of providing a 1000 MPa-grade cold-rolled high-elongation Q & P steel plate and a preparation method thereof.

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

the 1000 MPa-grade cold-rolled high-elongation Q & P steel plate comprises the following chemical components in percentage by mass: c: 0.17-0.24%; si: 1.1-1.7%; mn: 2.0-2.5%; p is less than or equal to 0.015 percent; s is less than or equal to 0.008 percent; and Als: 0.02-0.08%; nb: 0.01 to 0.025%; ti: 0.01 to 0.025%; n: 0.003 to 0.007 percent; the balance of Fe and inevitable impurities.

Preferably, the steel plate comprises the following components in percentage by mass: c: 0.17-0.23%, Si: 1.1-1.6%, Mn: 2.0-2.4%, P is less than or equal to 0.015%, S is less than or equal to 0.008%, Als: 0.025-0.075%, Nb: 0.01 to 0.025%, Ti: 0.01 to 0.025%, N: 0.003-0.007%.

The yield strength of the 1000 MPa-grade cold-rolled high-elongation Q & P steel plate is as follows: 600-850 MPa, tensile strength: 1000-1150 MPa, elongation: 19 to 25 percent.

The invention also provides a preparation method of the 1000 MPa-grade cold-rolled high-elongation Q & P steel plate, which comprises the working procedures of converter smelting, L F + RH duplex refining, continuous casting, hot rolling, cold rolling, annealing and leveling, wherein in the continuous casting working procedure, molten steel is continuously cast after smelting to obtain a continuous casting blank, and the chemical components and the mass percentage of the continuous casting blank are 0.17-0.24% of C, 1.1-1.7% of Si, 2.0-2.5% of Mn, less than or equal to 0.015% of P, less than or equal to 0.008% of S, 0.02-0.08% of Als, 0.01-0.025% of Nb, 0.01-0.025% of Ti, 0.003-0.007% of N, and the balance of Fe and inevitable impurity.

The preparation method of the 1000 MPa-grade cold-rolled high-elongation Q & P steel plate comprises the annealing process of continuous annealing, wherein the strip steel is heated to 780-820 ℃ at the heating rate of 1-3 ℃/s, is slowly cooled to 680-700 ℃ at the temperature of 2-4 ℃/s after being kept warm for 120-150 s, is quickly cooled to 200-250 ℃ at the cooling speed of 10-20 ℃/s by air cooling, is heated to 380-450 ℃ at the heating rate of 20-30 ℃/s for overaging treatment for 250-400 s, and the flat elongation is 0.2-0.6%.

According to the preparation method of the 1000 MPa-grade cold-rolled high-elongation Q & P steel plate, 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%.

In the preparation method of the 1000MPa grade cold-rolled high-elongation Q & P steel plate, the carbon contents of the steel plate at different stages of the continuous annealing process are respectively as follows: the C content of austenite at the trifurcate grain boundary before quenching is 0.35-0.38 wt%, the C content of internal flaky austenite before quenching is 0.18-0.22 wt%, the C content of austenite at the trifurcate grain boundary after partitioning is stabilized to 0.36-0.39 wt%, and the C content of internal flaky austenite after partitioning is 0.68-0.71 wt%.

According to the invention, Nb and Ti are added to form Nb/Ti (C, N) with a certain size in a matrix structure, and the phase plays a pinning role in a soaking stage of a continuous annealing process, so that the growth of austenite is inhibited, and the formation of a refined austenite phase is promoted. In addition, the phase ratio of austenite to ferrite is relatively stable in the soaking stage, and the precise control of the phase ratio can be realized in the process of forming flaky austenite and ferrite through reasonably matching three elements of soaking temperature, soaking time and C/Nb/Ti in the continuous annealing process, wherein the ratio of austenite to ferrite reaches 80% to 20%. In this process, carbon-rich austenite is easily formed at the trifurcated grain boundaries of the lamellar austenite, while the internal lamellar austenite is carbon-poor.

And (3) with the continuous annealing entering the slow cooling stage, carbon is further discharged into austenite in the ferrite forming process, the austenite is further enriched with carbon, and the stability of the austenite is improved. In the quenching stage (gas cooling is adopted for rapid cooling, the temperature is rapidly cooled to 200-250 ℃ at the cooling speed of 10-20 ℃/s), and part of the poor-stability carbon-poor austenite is converted into martensite; after entering a reheating and partitioning stage (heating to 380-450 ℃ at a heating rate of 2-4 ℃/s for overaging treatment for 250-400 s), residual austenite is not decomposed, stable carbon-rich austenite is formed through carbon partitioning, the content of the residual austenite of a finished product is improved, and good comprehensive mechanical properties are obtained.

Compared with a one-step method, the two-step method has the advantages that the initial quenching temperature is lower than the carbon partitioning temperature, the partitioning time is shortened, the precipitation of carbides is relatively less, the content of the retained austenite is relatively more, the stable carbides can be precipitated from the martensite matrix in the partitioning process by C, and the retained austenite plays a role in improving the plasticity and the toughness, so that the elongation of the product is improved.

The distribution treatment in the Q & P process adopts high-temperature distribution, the distribution time is greatly shortened, stable carbide is precipitated on a martensite matrix in the distribution process of C, the production time is shortened, the production efficiency is improved, and meanwhile, the performance stability of the steel is also greatly improved.

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

according to the invention, through the component design of high carbon, Nb and Ti microalloying and the matching of reasonable rolling and QP continuous annealing processes, more residual austenite is obtained, so that the plasticity and toughness of the steel plate are improved, the high-strength steel with excellent comprehensive mechanical properties is obtained, the tensile strength reaches more than 1000MPa, and the elongation is as follows: 19-25%, the structure is uniform, the processing formability can be effectively improved, and the requirements of increasingly complex parts of automobiles on the strength and the extensibility of materials are met.

Drawings

FIG. 1 is a metallographic structure diagram (1000 ×) of a Q & P steel sheet produced in example 1;

FIG. 2 is a metallographic structure diagram (1000 ×) of a Q & P steel sheet produced in example 2;

FIG. 3 is a metallographic representation (1000 ×) of the Q & P steel sheet produced in example 3;

FIG. 4 is a metallographic structure diagram (1000 ×) of a Q & P steel sheet produced in example 4;

FIG. 5 is a metallographic structure diagram (1000 ×) of the Q & P steel sheet produced in example 5;

FIG. 6 is a metallographic structure diagram (1000 ×) of a Q & P steel sheet produced in example 6;

FIG. 7 is a metallographic structure diagram (1000 ×) of a Q & P steel sheet produced in example 7;

FIG. 8 is a metallographic structure diagram (1000 ×) of a Q & P steel sheet produced in example 8;

FIG. 9 is a metallographic structure diagram (1000 ×) of a Q & P steel sheet produced in example 9;

FIG. 10 is a metallographic structure diagram (1000 ×) of a Q & P steel sheet produced in example 10;

FIG. 11 shows an austenite grain boundary structure diagram (2000 ×).

Detailed Description

The present invention will be described in further detail with reference to specific examples 1 to 10.

In the embodiment 1-10, a 260-ton converter is adopted for smelting, the main tasks of converter procedures are decarburization, dephosphorization and temperature control, L F + RH duplex refining is mainly for desulfurization, degassing, alloy fine adjustment, inclusion removal and the like, continuous casting adopts protective pouring to prevent nitrogen increase and secondary oxidation, constant-pulling-speed pouring is adopted, the process control is stable, the fluctuation of the liquid level is controlled within +/-3 mm, the section of a plate blank is 1500 x 241mm, a hot rolling unit with the thickness of 2250mm is adopted for hot rolling, the heating temperature is 1220-1290 ℃, the final rolling temperature is 870-930 ℃, the steel plate is cooled to 610-680 ℃ through a laminar cooling system after rolling, the coiling reduction rate is controlled to 45-60%, the specification of a cold-hardened steel plate is 1.3 x 1350mm, continuous annealing is adopted in an annealing mode, the steel plate is heated to 780-820 ℃ at the heating rate of 1-3 ℃/s, heat preservation is carried out for 120-150 s, then slow cooling to 680-700 ℃ at the temperature of 2-4 ℃/s, air cooling is carried out, then, the steel plate is quickly cooled to 200-250 ℃ at the cooling rate, and the temperature is carried out for flattening at the heating rate of 10-20 ℃/s, and the temperature is carried out for flattening, and the annealing process.

Table 1 shows the chemical compositions (wt%) of the cold rolled high elongation Q & P steel sheets of 1000MPa grade prepared in examples 1-10:

TABLE 1 niobium-titanium composite 1000MPa cold-rolled high-elongation Q & P steel plate chemical composition and mass percentage content

The balance of the ingredients in table 1 were Fe and unavoidable impurities.

Table 2 shows the hot rolling process parameters used in examples 1 to 10:

TABLE 2 Hot Rolling Process parameters

Table 3 lists the parameters of the cold rolling and annealing processes of examples 1-10:

TABLE 3 Cold Rolling and annealing Process parameters

Table 4 shows the carbon content percentages of niobium-titanium composite 1000MPa cold-rolled high-elongation Q & P steel plate finished products prepared in examples 1-10 before and after distribution:

TABLE 4 carbon content percentages before and after the distribution of niobium-titanium composite 1000MPa grade cold rolled high elongation Q & P steel plate finished products

Table 5 shows the mechanical properties of finished niobium-titanium composite 1000MPa cold-rolled high-elongation Q & P steel plates prepared in examples 1-10:

TABLE 5 mechanical properties of Nb-Ti compounded 1000MPa grade cold-rolled high-elongation Q & P steel plate

From the table 5, the niobium-titanium composite 1000 MPa-level cold-rolled high-elongation Q & P steel plate has excellent mechanical properties and tensile strength of more than 1000 MPa.

Fig. 1 to 10 show metallographic structures of niobium-titanium composite 1000MPa grade cold-rolled high-elongation Q & P steel plates (1000 ×) produced in examples 1 to 10, wherein the metallographic structures mainly comprise ferrite, martensite and retained austenite, and the mechanical properties of the steel plates are ensured by reasonable mixture ratio of three matrix phases.

FIG. 11 shows the structure of the trifurcated grain boundary, which is an austenite grain boundary.

Claims

1.1000 MPa-grade cold-rolled high-elongation Q & P steel plate, which is characterized in that: the steel plate comprises the following chemical components in percentage by mass: c: 0.17-0.24%; si: 1.1-1.7%; mn: 2.0-2.5%; p is less than or equal to 0.015 percent; s is less than or equal to 0.008 percent; and Als: 0.02-0.08%; nb: 0.01 to 0.025%; ti: 0.01 to 0.025%; n: 0.003 to 0.007 percent; the balance of Fe and inevitable impurities.

2. The 1000MPa grade cold rolled high elongation Q & P steel sheet according to claim 1, wherein: the steel plate comprises the following chemical components in percentage by mass: c: 0.17-0.23%, Si: 1.1-1.6%, Mn: 2.0-2.4%, P is less than or equal to 0.015%, S is less than or equal to 0.008%, Als: 0.025-0.075%, Nb: 0.01 to 0.025%, Ti: 0.01 to 0.025%, N: 0.003 to 0.007 percent;

steel plate yield strength: 600-850 MPa, tensile strength: 1000-1150 MPa, elongation: 19 to 25 percent.

The preparation method of the 3.1000 MPa-grade cold-rolled high-elongation Q & P steel plate comprises the working procedures of converter smelting, L F + RH duplex refining, continuous casting, hot rolling, cold rolling, annealing and leveling, and is characterized in that in the continuous casting working procedure, the chemical components of the continuous casting billet comprise, by mass, 0.17-0.24% of C, 1.1-1.7% of Si, 2.0-2.5% of Mn, less than or equal to 0.015% of P, less than or equal to 0.008% of S, 0.02-0.08% of Als, 0.01-0.025% of Nb, 0.01-0.025% of Ti, 0.003-0.007% of N, and the balance Fe and inevitable impurity.

4. The method for manufacturing a 1000MPa grade cold rolled high elongation Q & P steel sheet according to claim 3, wherein: the annealing process is continuous annealing, the strip steel is heated to 780-820 ℃ at the heating rate of 1-3 ℃/s, the strip steel is slowly cooled to 680-700 ℃ at the speed of 2-4 ℃/s after being kept warm for 120-150 s, then the strip steel is quickly cooled to 200-250 ℃ at the cooling speed of 10-20 ℃/s by adopting air cooling, then the strip steel is heated to 380-450 ℃ at the heating rate of 20-30 ℃/s for overaging treatment for 250-400 s, and the flat elongation is 0.2-0.6%.

5. The method for manufacturing a 1000MPa grade cold rolled high elongation Q & P steel sheet according to claim 3, 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%.

6. The method for manufacturing a 1000MPa grade cold rolled high elongation Q & P steel sheet according to claim 3, wherein: the carbon content of the steel plate at different stages of the annealing process is respectively as follows: the C content of austenite at the trifurcate grain boundary before quenching is 0.35-0.38 wt%, the C content of internal flaky austenite before quenching is 0.18-0.22 wt%, the C content of austenite at the trifurcate grain boundary after partitioning is stabilized to 0.36-0.39 wt%, and the C content of internal flaky austenite after partitioning is 0.68-0.71 wt%.