CN110669913B

CN110669913B - Hot-rolled and acid-washed dual-phase steel for high-strength automobile wheels and production method thereof

Info

Publication number: CN110669913B
Application number: CN201910942496.7A
Authority: CN
Inventors: 董毅; 时晓光; 王进臣; 景鹤; 孙成钱; 张宇; 张建军; 刘仁东; 韩楚菲; 王俊雄
Original assignee: Angang Steel Co Ltd
Current assignee: Angang Steel Co Ltd
Priority date: 2019-09-30
Filing date: 2019-09-30
Publication date: 2021-05-28
Anticipated expiration: 2039-09-30
Also published as: CN110669913A

Abstract

The invention discloses a hot-rolled and acid-washed dual-phase steel for high-strength automobile wheels and a production method thereof. The steel contains C: 0.060% to 0.090%, Si: 0.010% -0.090%, Mn: 1.10% -1.49%, P: 0.020-0.040%, S is less than or equal to 0.003%, Als: 0.41-0.59%, rare earth element La + Ce: 0.020-0.040%, and the balance of Fe and inevitable impurities. Heating the casting blank to 1180-1200 ℃, and preserving heat for 1-2 hours; the reduction rate of a finish rolling area is more than 92%, the finish rolling temperature is 760-820 ℃, and the constant rolling speed is 3.5-4.5 m/s; carrying out ultra-fast cooling after the laminar cooling speed is 8-10 ℃/s and the temperature is 640-660 ℃, wherein the ultra-fast cooling speed is more than 100 ℃/s, cooling the steel plate to be less than or equal to 150 ℃, coiling and air-cooling to room temperature; the steel plate is cooled to room temperature and then pickled. The tensile strength of the steel plate is 690-730 MPa, the yield ratio is 0.55-0.59, and the elongation is more than or equal to 27.0%.

Description

Hot-rolled and acid-washed dual-phase steel for high-strength automobile wheels and production method thereof

Technical Field

The invention belongs to the technical field of steel rolling, and particularly relates to a hot-rolled pickled dual-phase steel plate for a high-strength automobile wheel and a production method thereof. The hot-rolled pickled dual-phase steel plate is mainly suitable for manufacturing high-strength automobile wheels with complex shapes and higher surface quality requirements.

Background

With the development of the automobile industry, the manufacturing method and process of automobile parts are greatly improved, and the requirements on steel materials are more strict. As an important component of an automobile, the production process of the automobile wheel is greatly improved, and the automobile wheel is promoted to provide more individual requirements for used steel materials, such as wheel products with high technical content, such as high-ventilation-hole wheels, and the like, the steel is required to have good mechanical property indexes and forming property indexes, and the steel is also required to have good surface quality, good mechanical property stability and the like so as to meet the requirements of forming procedures, electrophoresis procedures, appearance and the like. The hot-rolled dual-phase steel consisting of a large amount of ferrite and a small amount of martensite has the advantages of good strong plasticity proportion, excellent cold forming performance and the like, and is widely applied to the production of automobile wheels, while the traditional hot-rolled dual-phase steel plate used in the market at present can not meet the rigorous requirements proposed by the technical development in the field of wheel manufacturing. Therefore, it is necessary to develop a high-strength hot-rolled pickled dual-phase steel sheet having excellent overall properties and satisfying the requirements of high-end automobile wheels.

The patent with the publication number of CN107746931A provides a hot-rolled dual-phase steel plate for automobile wheels and a manufacturing method thereof, wherein a C-Si-Mn-Cr-P component system is adopted, wherein the Si content is 0.1-0.25%, the Cr content is 0.50-0.60%, and the P content is 0.035-0.070%, and a three-section cooling mode is adopted after the steel plate is finally rolled, so that the hot-rolled dual-phase steel plate with good comprehensive performance of 600MPa grade can be obtained. The steel plate has high cost due to the fact that the Si content in the steel plate is high, the surface quality of the steel plate does not meet the requirement of steel for high-end wheels, and the steel plate contains high Cr content, and meanwhile, the finished steel plate is a hot-rolled product instead of a hot-rolled pickled product.

The patent with the publication number of CN108467996A provides ferrite/martensite hot-rolled dual-phase steel for wheel spokes and a manufacturing method thereof, the steel plate adopts a C-Si-Mn-Cr-Mo component system, wherein the content of Si is 0.4-0.6%, the content of Cr is 0.30-0.40%, and the content of Mo is 0.1-0.2%, a continuous casting billet is heated and then is rolled, cooled, pickled and oiled, and finally the 600 MPa-level hot-rolled pickled dual-phase steel plate is obtained.

In view of the above problems, it is a current trend to develop hot rolled pickled dual phase steel sheet for high end automobile wheels having good surface quality and excellent overall properties.

Disclosure of Invention

The invention aims to provide a high-strength hot-rolled pickled dual-phase steel plate with good surface quality and excellent comprehensive performance and a production method thereof aiming at the development requirements in the field of automobile wheel manufacturing.

The specific technical scheme is as follows:

the hot-rolled pickled dual-phase steel plate for the high-strength automobile wheel comprises the following chemical components in percentage by mass: 0.060% to 0.090%, Si: 0.010% -0.090%, Mn: 1.10% -1.49%, P: 0.020-0.040%, S is less than or equal to 0.003%, Als: 0.41-0.59%, rare earth (La + Ce): 0.020-0.040%, and the balance of Fe and inevitable impurities.

The steel plate of the invention mainly comprises the following components:

c: carbon is mainly responsible for the formation of the desired amount of martensite and for ensuring the strength of the steel. The welding performance of the steel plate is affected by the content of C which is too high, the martensite structure is not obtained by too low C, and the optimal range of C in the invention is 0.060-0.090%.

Si: silicon can enlarge the alpha + gamma region of the Fe-C phase diagram, is favorable for promoting the transformation from austenite to ferrite, is a main element for ensuring the percentage content of the ferrite in the dual-phase steel, and the Si content in the traditional production process is generally more than 0.50 percent. However, the steel plate surface has a large amount of iron scales due to the over-high Si content, and the steel plate surface after pickling has the defects of oxidation stripes, color difference and the like, so that the manufacturing requirement of the wheel under the new process condition is not met. The steel plate provided by the invention adopts a low-Si component system, and the Si content is 0.010-0.090%.

Mn: manganese is a typical austenite stabilizing element, remarkably improves the hardenability of steel, plays a role in solid solution strengthening and ferrite grain refinement, and can remarkably delay pearlite transformation and bainite transformation. However, when the Mn content is too high, pearlite transformation is delayed and precipitation of ferrite is delayed, and the steel sheet tends to have a band structure. Therefore, the Mn content is selected to be 1.10-1.49%.

P: phosphorus can promote the diffusion of carbon, postpone the generation of cementite and increase the stability of austenite; meanwhile, phosphorus enables the form of the martensite island to be obviously changed, so that the size of the martensite island is thinned and uniformly distributed. The phosphorus content in the patent is 0.020-0.040%.

S: since sulfur forms sulfide inclusions such as MnS and becomes a starting point of cracks to deteriorate workability, the smaller the content, the better the content, and the upper limit of the content is 0.003%.

Al: the effect of aluminium is similar with Si in this patent, has Al to take the place of Si and is favorable to guaranteeing ferrite content in the steel sheet to improve steel sheet surface quality, add Al simultaneously and impel the martensite to be island-like distribution, and play certain refined crystalline grain effect. The range of Als in the invention is 0.41-0.59%.

La + Ce: la + Ce is a rare earth element which has strong deoxidizing and desulfurizing capacities, can change the appearance of sulfide inclusions, can improve the plasticity of the steel plate and reduce the anisotropy; the rare earth can improve the fatigue property of the steel plate, improve the welding property of the steel plate and simultaneously improve the cold forming property of the steel plate. Therefore, the content of the rare earth (La + Ce) is controlled to be 0.020-0.040%.

The manufacturing method of the hot-rolled pickled dual-phase steel plate for the high-end automobile wheel comprises the following steps of: the method comprises the following steps of slab continuous casting, heating, rolling, cooling and pickling:

(1) slab continuous casting: in the continuous casting process, a soft reduction and electromagnetic stirring process is put into the continuous casting process, so that the defects of casting blank center segregation, looseness and the like are prevented, and the occurrence of steel plate banded structure defects is reduced;

(2) a heating process: heating a casting blank with the thickness of 170-230 mm to 1180-1200 ℃, and preserving heat for 1-2 hours. The proper heating temperature and heat preservation time can ensure that the components of the casting blank are sufficiently uniform and the original austenite grains are fine;

(3) and (3) rolling and cooling processes: the reduction rate of a steel plate finish rolling area is more than 92%, the finish rolling temperature is 760-820 ℃, constant-speed rolling is adopted, and the steel throwing speed of the steel plate is 3.5-4.5 m/s; and after finishing rolling, adopting a cooling mode of laminar cooling and ultra-fast cooling, wherein the cooling speed of the laminar cooling is 8-10 ℃/s, carrying out ultra-fast cooling after cooling to 640-660 ℃, the cooling speed of the ultra-fast cooling is more than 100 ℃/s, cooling the steel plate to be less than or equal to 150 ℃, coiling and air cooling to room temperature.

(4) Acid washing process: and (2) cooling the steel plate to room temperature, then carrying out acid pickling, before acid pickling, carrying out pull-straightening on the steel plate, wherein the pull-straightening elongation rate is 0.2-0.5%, the acid pickling solution is hydrochloric acid, the concentration is 150-200 g/l, the steel plate penetrating speed is 20-40 m/min, acid pickling is carried out under tension in the acid pickling process, the tension is 5-10 KN, and the thickness of a steel plate finished product is 3.0-6.0 mm.

According to the invention, the steel plate adopts a low-temperature high-pressure process, so that the steel plate structure is favorably refined, the percentage content of ferrite in the steel plate structure is increased, and the influence of the reduction of the content of Si on the steel plate structure and the mechanical property is reduced; the constant-speed rolling is adopted instead of the traditional accelerated rolling method, so that the control precision of the rolling parameters of the steel plate is improved, and the uniformity and the stability of the structure, the mechanical property and the coil passing performance of the steel plate are improved; the steel plate generates a large amount of fine ferrite in the process of layer cooling, and then is rapidly cooled to a low-temperature area so that the residual austenite is completely converted into martensite, the phenomenon of martensite self-tempering caused by high-temperature coiling is avoided, and the structure and mechanical property characteristics of the steel plate are ensured; the small withdrawal and straightening elongation rate is beneficial to ensuring that the steel plate keeps a small yield ratio on the premise of ensuring the pickling effect; the pickling effect can be effectively improved by adopting higher pickling concentration, belt tension pickling and other methods.

The finished steel plate structure consists of ferrite and martensite, wherein the volume fraction of the ferrite is 85-90%, and the volume fraction of the martensite is 10-15%; the tensile strength of the steel plate is 690-730 MPa, the yield ratio is 0.55-0.59, and the elongation is more than or equal to 27.0%; the grain size of the steel plate is more than or equal to 11 grades, the band-shaped structure is less than or equal to 1.0 grade, and the grade of the non-metallic inclusion is less than or equal to 1.0 grade; the finished steel plate has an acid-washed surface, good surface quality, no iron scale stripes, color difference, cracks and other defects, and the surface roughness Ra of the steel plate is 0.8-1.0 mu m.

Has the advantages that:

compared with the prior art, the invention has the following beneficial effects:

(1) the low-Si component design is adopted, the Si content is 0.01-0.09%, the percentage content is far lower than the percentage content of more than 0.5% in the traditional process, a high-surface-quality steel plate without the defects of iron scale stripes, color difference, cracks and the like can be obtained, the surface roughness Ra of the steel plate after acid cleaning is 0.8-1.0 mu m, and the steel plate is suitable for the production requirement of automobile wheels under the existing process conditions;

(2) the steel plate has fine microstructure and good performance stability by adopting the manufacturing methods of low-temperature large-pressure rolling, constant-speed rolling, low-temperature coiling and the like, the grain size of the steel plate is more than 11 grades, and the tensile strength fluctuation of the steel plates of different batches can be controlled within 40 MPa;

(3) through reasonable component design and matching of smelting, hot rolling and pickling process parameters, the steel plate provided by the patent has the tensile strength higher than 690MPa, the yield ratio lower than 0.60, the band-shaped structure less than or equal to 1.0 grade, the non-metallic inclusion grade less than or equal to 1.0 grade and good forming performance.

Drawings

FIG. 1 shows the microstructure of a steel sheet according to example 2 of the present invention.

Detailed Description

The following examples are intended to illustrate the invention in detail, and are intended to be a general description of the invention, and not to limit the invention.

Table 1 shows the chemical composition of the steels of the examples of the present invention; table 2 shows the rolling method of the steel of the examples of the present invention; table 3 shows the cooling schedule of the steels of the examples of the present invention; table 4 shows the pickling schedule of the steel of the examples of the present invention; table 5 shows the mechanical properties of the steels of the examples of the invention; table 6 shows the grain size, band structure, inclusion grade and roughness of the steels of examples of the present invention.

TABLE 1 chemical composition wt% of steel sheet of inventive example

Examples	C	Si	Mn	P	S	Als	La+Ce
								1	0.061	0.089	1.48	0.039	0.003	0.58	0.039
2	0.075	0.072	1.45	0.032	0.002	0.52	0.036
								3	0.068	0.068	1.38	0.030	0.002	0.50	0.031
4	0.082	0.054	1.34	0.028	0.003	0.48	0.027
								5	0.080	0.027	1.22	0.025	0.002	0.44	0.024
6	0.089	0.012	1.10	0.021	0.001	0.42	0.021

TABLE 2 Rolling schedule of examples of the present invention

TABLE 3 Cooling regimes for examples of the invention

TABLE 4 acid pickling System for examples of the present invention

TABLE 5 organization and mechanical Property parameters of the examples of the invention

TABLE 6 grain size, band-like texture, inclusion grade and roughness of examples of the present invention

Examples	Grain size	Strip tissue	Non-metallic inclusions	Roughness of
					1	11	0.5	0.5	0.8
2	13	0.5	1.0	0.9
					3	12	1.0	1.0	0.8
4	11	1.0	0.5	0.8
					5	12	0.5	0.5	0.9
6	12	0.5	1.0	1.0

Claims

1. A production method of hot-rolled acid-washed dual-phase steel for high-strength automobile wheels is characterized in that the steel comprises the following chemical components in percentage by mass: c: 0.060% to 0.090%, Si: 0.010% -0.090%, Mn: 1.10% -1.49%, P: 0.020-0.040%, S is less than or equal to 0.003%, Als: 0.41-0.59%, rare earth element La + Ce: 0.020-0.040 percent, the balance of Fe and inevitable impurities, the tensile strength of the steel plate is 690-730 MPa, the yield ratio is 0.55-0.59, and the elongation is more than or equal to 27.0 percent;

the production process of the steel plate comprises the following steps: slab continuous casting-heating-rolling-cooling-pickling, wherein,

(1) slab continuous casting: putting a soft reduction and electromagnetic stirring process in the continuous casting process, wherein the thickness of a casting blank is 170-230 mm;

(2) a heating process: heating the casting blank to 1180-1200 ℃, and preserving heat for 1-2 hours;

(3) and (3) rolling and cooling processes: the reduction rate of a finish rolling area is more than 92%, the finish rolling temperature is 760-820 ℃, constant-speed rolling is adopted, and the steel throwing speed of a steel plate is 3.5-4.5 m/s; after finishing rolling, adopting a cooling mode of laminar cooling and ultra-fast cooling, wherein the cooling speed of the laminar cooling is 8-10 ℃/s, carrying out ultra-fast cooling after cooling to 640-660 ℃, the cooling speed of the ultra-fast cooling is more than 100 ℃/s, cooling the steel plate to be less than or equal to 150 ℃, coiling and air-cooling to room temperature;

(4) acid washing process: and (3) pickling the steel plate after cooling to room temperature, straightening the steel plate before pickling, wherein the straightening elongation is 0.2-0.5%, the running speed of the steel plate during pickling is 20-40 m/min, and the steel plate is pickled with tension in the pickling process, wherein the tension is 5-10 KN.

2. The method for producing a hot-rolled pickled dual-phase steel for high-strength automobile wheels as claimed in claim 1, wherein the pickling solution is hydrochloric acid with a concentration of 150-200 g/l in the pickling process.