CN-122013066-A - 980 MPa-grade high-plasticity complex-phase steel and preparation method and application thereof

CN122013066ACN 122013066 ACN122013066 ACN 122013066ACN-122013066-A

Abstract

The invention discloses 980 MPa-grade high-plasticity complex phase steel and a preparation method and application thereof, and belongs to the technical field of cold-rolled sheet strip production. The microstructure of the complex phase steel consists of 8% -15% ferrite, 70% -80% bainitic ferrite, 7% -10% retained austenite and 2% -7% martensite, and the preparation method comprises the working procedures of smelting, continuous casting, hot rolling, pickling cold rolling and continuous annealing, and the target structure is realized through process precise control. The process is suitable for the traditional acid rolling-continuous annealing production line, and has the advantages of low production cost, stable process and the like. The 980 MPa-grade complex-phase steel prepared by the process has high strength, high plasticity and high local forming performance, and is suitable for complex forming automobile structural parts.

Inventors

ZHENG HAOQING
JIN YANG
ZHOU WEI
CHANG ZHIYUAN
HU XIAO
LIU KE

Assignees

攀钢集团攀枝花钢铁研究院有限公司

Dates

Publication Date: 20260512
Application Date: 20260312

Claims (10)

1. A980 MPa grade high-plasticity complex phase steel is characterized in that the chemical components of the complex phase steel are ：C 0.15%~0.19%、Si 1.2%~1.6%、Mn 1.80%~2.10%、P≤0.008%,S≤0.005%,Als 0.020%~0.080%、Cr 0.34%~0.50%、Ti 0.040%~0.060%、Nb 0.025%~0.040%、N≤0.0045%, percent by mass of Fe and unavoidable impurities; the microstructure of the complex phase steel is composed of 8% -15% of ferrite, 70% -80% of bainitic ferrite, 7% -10% of residual austenite and 2% -7% of martensite.
2. The 980 MPa-grade high-plasticity multi-phase steel according to claim 1, wherein the yield strength of the multi-phase steel is 750-930 MPa, the tensile strength is 980-1140 MPa, the elongation after fracture A 80 is 12-15%, and the hole expansion rate is 48-51%.
3. The method for preparing 980 MPa-grade high-plasticity complex-phase steel according to claim 1 or 2, characterized by comprising the following steps of; S1, smelting, namely carrying out converter smelting on the chemical components of the multiphase steel according to claim 1, and carrying out LF refining and RH refining to obtain molten steel; S2, continuous casting, namely continuously casting the molten steel to obtain a plate blank; s3, hot rolling, namely performing dephosphorization, rough rolling, finish rolling, coiling, laminar cooling and coiling on the plate blank after heating to obtain a hot rolled coil; The tapping temperature of the heated plate blank is 1230-1280 ℃, the finish rolling temperature of finish rolling is 870-930 ℃, the intermediate temperature is 740-780 ℃, and the coiling temperature is 600-660 ℃; s4, pickling and cold rolling, namely pickling the hot rolled coil and then cold rolling to obtain cold-rolled thin strip steel; S5, continuous annealing, namely carrying out continuous annealing treatment on the cold-rolled thin strip steel to obtain 980 MPa-grade high-plasticity complex phase steel; The continuous annealing step comprises the steps of heating to 350 ℃ at the speed of 8-15 ℃ per second, heating to 870-900 ℃ at the speed of 0.5-3.0 ℃ per second, soaking and preserving heat for 260-340 s, slowly cooling to 750-780 ℃ at the speed of 0.5-3.0 ℃ per second, rapidly cooling to 350-380 ℃ at the cooling speed of 18-20 ℃ per second, performing overaging treatment, and finally cooling to room temperature.
4. A method according to claim 3, wherein in step S1 at least one of the following is satisfied: the tapping temperature of converter smelting is 1620-1660 ℃; the outbound temperature of the LF refining is 1570-1590 ℃; the outbound temperature of RH refining is 1540-1560 ℃.
5. A method according to claim 3, wherein in step S2 at least one of the following is satisfied: The continuous casting temperature is 1520-1540 ℃; The continuous casting has a pulling rate of 0.8-1.4 m/min; The thickness of the plate blank is 230-240 mm.
6. A method according to claim 3, wherein in step S3 at least one of the following is satisfied: The slab is heated specifically, the temperature of a heating section 1 is 1000-1200 ℃, the temperature of a heating section 2 is 1200-1350 ℃, the temperature of a soaking section is 1220-1300 ℃, the total furnace time is 300-450 min, and the heat preservation time of the soaking section is 40-60 min; Pre-cooling iron sheet by soft blowing water after rough rolling, fully descaling the whole length of a rolling line, wherein the descaling water pressure is more than or equal to 25MPa, and the descaling temperature of a steel billet is more than or equal to 1180 ℃; The finish rolling is specifically carried out at a finish rolling start temperature of 1020-1120 ℃, 7 finish rolling passes, a final pass reduction rate of more than or equal to 12% and lubrication rolling; the laminar cooling is specifically realized by adopting a front-section concentrated cooling mode, wherein the opening degrees of an upper header pipe and a lower header pipe are respectively 70% and 100%; the coiling method specifically comprises the steps of adopting a U-shaped coiling mode, controlling the coiling temperature of the front 30m of the belt head to be 640-700 ℃, the coiling temperature of the rear 70m of the belt tail to be 640-700 ℃ and the coiling temperature of the middle section to be 640 ℃; the thickness of the hot rolled coil is 2.0-4.5 mm.
7. A method according to claim 3, wherein in step S4 at least one of the following is satisfied: The cold rolling reduction rate is 50% -75%; the thickness of the cold-rolled thin strip steel is 1.0-2.0 mm.
8. The method of claim 7, wherein the cold rolling reduction is 60 to 70%.
9. A method according to claim 3, wherein in step S5, the overaging treatment employs three-stage temperature control: overaging 1, wherein the temperature is 360-380 ℃ and the heat preservation time is 340-412 s; overaging 2 sections, wherein the temperature is 350-370 ℃, and the heat preservation time is 340-412 s; An overaging 3 section, wherein the overaging 3 section is cooled to 230-260 ℃ at a cooling speed of 5-8 ℃ per second; The unit speed is 50-60 m/min, and the leveling elongation is 0.3-0.5%.
10. An automotive structural member, characterized in that it is made of 980 MPa-grade high-plasticity complex-phase steel according to claim 1 or 2.

Description

980 MPa-grade high-plasticity complex-phase steel and preparation method and application thereof Technical Field The invention belongs to the technical field of cold-rolled sheet strip production, and particularly relates to 980 MPa-grade high-plasticity complex phase steel, and a preparation method and application thereof. Background In the wave trend of the automobile industry for lightening and electric transformation, 980MPa grade or more complex phase steel is a core material for realizing dual purposes of safety performance, energy conservation and emission reduction of a high-end train enterprise by virtue of high strength and excellent formability. The microstructure of the complex phase steel is usually ferrite or bainite matrix with a small amount of martensite and a small amount of residual austenite distributed thereon, and the hardness difference between the phases is small, so that the phenomenon of 'inter-phase debonding' is not easy to occur, and therefore, the complex phase steel has good local forming performance, such as flange extension and reaming capability. However, although the traditional 980 MPa-level complex-phase steel has good reaming and flanging performances, the elongation rate is generally low, usually only about 7%, and the application of the complex-phase steel on complex automobile structural members is limited. How to realize fine regulation and control of tissue proportion by process precise control on a conventional continuous annealing production line, so as to obtain complex-phase steel with good ductility and local forming capability, and the complex-phase steel becomes a hot problem to be solved urgently in the industry. In addition, the conventional continuous annealing production line is limited by equipment capacity and quenching capacity, and the overaging section generally does not have an induction heating function, so that advanced processes such as quenching and re-allocation are difficult to implement, which further limits development of cold-rolled ultra-high-strength steel, and makes it difficult to obtain balanced strength-plasticity-reaming performance. The prior art has been searched for the above problems. For example, CN 112251668A discloses a forming reinforced composite steel and a preparation method thereof, wherein the Si content is designed to be 0.2% -0.7%, and the heat preservation is carried out for 800s in an overaging section of a continuous annealing process. When the Si content is at the middle lower limit, carbide precipitation is difficult to effectively inhibit, the formation of the carbide can obviously reduce the stability of the residual austenite, a large amount of fresh martensite is generated in the final cooling stage, and the martensite content in the structure is as high as 25% -45%. The high content of martensite seriously impairs the toughness and the local formability of the material, making it difficult to obtain the desired plasticity index. For another example, CN 118497615A discloses a 980MPa grade multi-phase steel plate which is multipurpose and a production method thereof, wherein the C content is 0.08% -0.1% and the Si content is 0.4% -0.5%. The C content is low, meanwhile, the surface quality of a coating is considered, the low Si content is added, so that more ferrite exists in a tissue obtained by cold-rolling the complex phase steel, the residual austenite content is only 3% -6%, the elongation of the cold-rolling complex phase steel produced by continuous annealing is low, the elongation after A50 breaking is about 10%, the complex part forming is not facilitated, and the application scene is severely limited. In conclusion, how to obtain 980MPa grade complex phase steel with high strength, high plasticity and excellent reaming performance through reasonable component design and process regulation and control within the capability range of a conventional continuous annealing production line so as to meet the severe requirements of the automobile industry on steel for complex structural members is still a problem to be solved in the current technical development. Disclosure of Invention The invention aims to solve the technical problem of how to solve the problem that the existing 980 MPa-grade complex phase steel is difficult to achieve high strength, high plasticity and high local forming performance within the capacity range of a conventional continuous annealing production line. In order to achieve the purposes of the application, the technical scheme adopted by the application is as follows. According to the first aspect, the 980MPa grade high-plasticity complex phase steel comprises, by mass, ：C 0.15%~0.19%、Si 1.2%~1.6%、Mn 1.80%~2.10%、P≤0.008%,S≤0.005%,Als 0.020%~0.080%、Cr0.34%~0.50%、Ti 0.040%~0.060%、Nb 0.025%~0.040%、N≤0.0045%, parts of Fe and unavoidable impurities as the rest elements, and has a microstructure composed of 8% -15% of ferrite, 70% -80% of bainitic ferrite, 7% -10% of retained austenite an