CN115948692A - Cold-rolled bell-type annealed high-strength steel with tensile strength of 450MPa for automobile and manufacturing method thereof - Google Patents
Cold-rolled bell-type annealed high-strength steel with tensile strength of 450MPa for automobile and manufacturing method thereof Download PDFInfo
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Abstract
The invention discloses cold-rolled bell-type annealed high-strength steel for an automobile with the tensile strength of 450MPa and a manufacturing method thereof, belonging to the field of metal material smelting. The bell-type annealing high-strength steel has simple chemical components, does not need to add noble metals such as Nb, V and the like, has yield strength of more than or equal to 298MPa, tensile strength of more than or equal to 450MPa, elongation of more than or equal to 34 percent, stable mechanical property and uniform structure. The manufacturing method of the cold-rolled hood-type annealed high-strength steel comprises the process flows of smelting → continuous casting → hot rolling → acid pickling cold rolling → hood-type annealing → leveling → finished products, and the hood-type annealing is adopted, so that the problems of uneven continuous annealing product structure and poor performance stability are solved, the thickness range of the products can be produced, the manufacturing process is simple, the equipment requirement is low, the assembly is convenient, the thickness range of the products can be produced, and the method is an economical high-strength cold-rolled automobile plate manufacturing method.
Description
Technical Field
The invention belongs to the field of metal material smelting, and particularly relates to cold-rolled bell-type annealed high-strength steel for an automobile with the tensile strength of 450MPa and a manufacturing method thereof.
Background
With the development of the automobile industry, higher requirements are put forward on the collision safety, the energy-saving effect and the cost of automobile steel. The carbon-manganese high-strength steel has the characteristics of high strength, low cost, good forming performance and the like, and is one of the most widely used materials for the current automobile structural parts.
The traditional annealing mode of the high-strength carbon-manganese structural steel is continuous annealing, for example, the invention patent with the publication number of CN102839329A, namely a cold-rolled dual-phase steel plate with the tensile strength of 450MPa and a preparation method thereof, discloses cold-rolled dual-phase steel with the tensile strength of 450MPa, wherein the yield strength is 200MPa to 250MPa, the tensile strength is 440MPa to 500MPa, and the elongation is 26 percent to 32 percent; also, as the invention patent of CN103509997A, 440 MPa-grade cold-rolled high-strength automobile structural steel and a manufacturing method thereof, 440 MPa-grade cold-rolled high-strength automobile structural steel is disclosed, the yield strength is 270MPa to 370MPa, the tensile strength is 440MPa to 510MPa, the elongation is 31 percent to 38 percent, the manufacturing method comprises smelting, continuous casting, hot rolling, acid pickling and cold rolling and continuous annealing, the thickness production range of the product is less than or equal to 2.5mm, but the continuous annealing time is short, the structure of the finished product is uneven, and the performance fluctuation is large; also, for example, CN111304540A, which discloses a cold-rolled steel strip for a 280 MPa-grade automobile structure and a manufacturing method thereof, discloses a cold-rolled steel strip for a 280 MPa-grade automobile structure, the manufacturing method comprises a steel-making process, a hot rolling process, an acid continuous rolling process and a continuous annealing process, and finally the yield strength is more than or equal to 280MPa, the tensile strength is more than or equal to 440MPa, and the elongation is more than or equal to 30%. Therefore, the continuous annealing has the advantages of high production rate and high efficiency, the thickness of the produced product is 0.5-2.5 mm, but the continuous annealing also causes non-uniform annealing, so that the product has non-uniform structure and large mechanical property fluctuation, and the cracking phenomenon is easy to generate when the product is used by customers.
In view of this, there has also been studied the production of steel for automobile structures by the bell annealing. For example, the invention patent with publication number CN104498822A, steel for automobile structure and a production method thereof, discloses steel for automobile structure and a production method thereof, and by reasonably controlling components and optimizing the processes of hot rolling, cold rolling, cover annealing and the like, the produced cover-type annealed steel plate has the tensile strength of more than or equal to 539MPa, the yield strength of more than or equal to 330MPa and the elongation of more than or equal to 23.2 percent, but the metal Nb is added, so the cost is higher; also, as disclosed in "a low-cost manufacturing method of 700 MPa-grade cold-rolled high-strength steel and thin steel strip based on hood-type annealing treatment" of publication No. CN103866182A, a low-cost manufacturing method of 700 MPa-grade cold-rolled high-strength steel and thin steel strip based on hood-type annealing treatment is disclosed, which includes hot rolling, primary cold rolling, hood-type annealing, and secondary cold rolling, to obtain a steel strip with tensile strength of above 700MPa, elongation of above 8%, and good formability, but with addition of metal element V, the cost is high.
Therefore, a cover annealing process needs to be developed for production, the production process is not limited by product specifications, processes and the like, the assembly is convenient, the manufacturing cost is low, the structure of a finished product is uniform, and the mechanical property is stable.
Disclosure of Invention
1. Objects of the invention
The invention aims to provide cold-rolled cover-type annealed high-strength steel for an automobile with the tensile strength of 450MPa and a manufacturing method thereof, solves the problems of uneven product structure and poor performance stability of products produced by a continuous annealing process, and simultaneously does not add elements such as metal Nb, metal V and the like, obviously reduces the cost and enlarges the range of producible thickness.
2. Technical scheme
In order to solve the problems, the technical scheme adopted by the invention is as follows:
the invention provides cold-rolled bell-type annealed high-strength steel with tensile strength of 450MPa for an automobile, which comprises the following main chemical components in percentage by mass: c:0.05 to 0.20%, si: less than or equal to 0.50 percent, mn:1.0 to 2.0%, als: 0.015-0.060%, P is less than or equal to 0.022%, S is less than or equal to 0.015%, and the balance is Fe and inevitable impurities; the invention realizes the stable production of 450MPa high-strength steel by adding C and Mn elements, and the invention has lower cost because no elements with high cost such as Nb, mo, cr and the like are added, and the addition of the elements is not sensitive to the fluctuation of the hot rolling and annealing process, thereby realizing the stability of the product performance. Wherein:
c: the most effective strengthening element is the most economic and strongest strengthening element, and when the content of C is lower, the formability and the welding performance are better; but the content of C is too low, the required strength is difficult to obtain, and meanwhile, the supersaturation degree of C is too low, the carbide element is difficult to form and precipitate, so that the anti-aging property is poor; in order to obtain the required strength and good anti-aging performance, the lower limit of the C content is controlled to be 0.05 percent; the C content is too high, so that the extensibility and the welding performance of the steel are reduced, and therefore, the upper limit of the C content is controlled to be 0.20 percent;
si: the steel has stronger strengthening effect, but Si is easy to form oxides, is not beneficial to forming oxidation color on the surface after acid cleaning and annealing, and also reduces the coating property of the steel plate, so that the invention adds a small amount of Si or does not add Si, and the upper limit of the invention is controlled to be 0.50%;
mn: the Mn dissolved in the steel has a solid solution strengthening effect, so that lattice distortion is caused, the lattice distortion increases the resistance of dislocation movement, and slippage is difficult to perform, the strength and the hardness of the alloy steel are increased, and the yield ratio (toughness and plasticity) of the steel is reduced; in addition, the steel can act with S in the steel to prevent the hot brittleness of the steel; in the patent, mn mainly acts with S to prevent hot brittleness of steel and simultaneously plays a role in solid solution strengthening, and the upper limit of Mn is controlled to be 2.0%;
al: the alloy mainly plays a role in deoxidation in steel, and Al can form AlN precipitation to play a role in refining grains to a certain extent; the ductility of the steel can be improved on the premise of ensuring the strength performance due to the existence of a small amount of Al; however, the Al content is too high, the crystallizer is easy to block, and meanwhile, the casting blank is easy to generate defects such as cracks and the like, and the cost is also increased; therefore, the Al content of the invention is controlled between 0.015 percent and 0.060 percent;
p: the S content is controlled to be 0.022% at the upper limit in the invention because the P content in the steel is strictly controlled because the S content is inevitable harmful impurities in the steel and has adverse effects on the stamping performance, cold brittleness, secondary processing brittleness and the like of the steel;
s: the S content in the steel is strictly controlled to increase the smelting cost of the steel, so the upper limit of the S content is controlled to be 0.015 percent.
Preferably, the cold-rolled bell-type annealed high-strength steel comprises the following main chemical components in percentage by mass: c:0.09%, si:0.40%, mn:1.46%, al:0.038%, P:0.001%, S:0.003% and the balance of Fe and inevitable impurities.
Preferably, the cold-rolled bell-type annealed high-strength steel comprises the following main chemical components in percentage by mass: c:0.10%, si:0.39%, mn:1.48%, al:0.047%, P:0.015%, S:0.004%, and the balance of Fe and inevitable impurities.
Preferably, the cold-rolled bell-type annealed high-strength steel comprises the following main chemical components in percentage by mass: c:0.11%, si:0.41%, mn:1.46%, al:0.042%, P:0.015%, S:0.002%, and the balance of Fe and inevitable impurities.
Preferably, the yield strength of the cold-rolled bell-type annealed high-strength steel is more than or equal to 298MPa, the tensile strength is more than or equal to 450MPa, the elongation is more than or equal to 34 percent, and the yield ratio is less than or equal to 0.68.
The invention also provides a manufacturing method of the cold-rolled cover-type annealed high-strength steel, which comprises the following steps: smelting → continuous casting → hot rolling → acid pickling cold rolling → cover annealing → leveling process flow.
Preferably, the process flow is as follows:
(1) Smelting and continuous casting: the method is suitable for smelting in a converter, an electric furnace and an induction furnace to obtain target molten steel; continuous casting is adopted to produce a casting blank, and molten steel is formed and rapidly solidified and crystallized under the action of a crystallizer to form a plate blank;
(2) Hot continuous rolling of a casting blank: heating the plate blank to 1200-1240 ℃, carrying out dephosphorization and rough rolling for 6 passes, carrying out finish rolling for 7 passes, and carrying out hot rolling on the plate blank to the target thickness of the raw material required by cold rolling, wherein the final rolling temperature is as follows: 860 to 890 ℃, and the coiling temperature is 500 to 580 ℃; after finish rolling, a higher cooling rate is adopted, so that N is not precipitated in the hot rolling process, and carbides are fine and uniformly distributed, thereby being beneficial to obtaining fine grains and improving the plasticity and stamping performance of steel;
(3) Acid pickling and cold rolling: sufficiently removing iron oxide scales on the surface of the strip steel by adopting an acid washing process, then cold-rolling to the required thickness specification of a finished product, and controlling the cold-rolling reduction rate at 50-75%;
(4) Cover annealing: controlling the annealing target temperature of the steel plate processed in the pickling and cold rolling step to be 600-660 ℃, and performing furnace-following segmented heating and cooling, wherein the segmented heating process is as follows: 400 +/-40 ℃,1 +/-0.1h, 450 +/-45 ℃,1 +/-0.1h, 500 +/-50 ℃,1 +/-0.1h, 550 +/-10 ℃,1 +/-0.1 h and a target temperature of 8 +/-0.1 h.
(5) Leveling: the flattening elongation is controlled to be 1.0-2.0%, the fluctuation range of the upper and lower yield points of the flattened strip steel is reduced, the yield elongation can be basically eliminated, the tensile strength is slightly increased, the elongation is slightly reduced, the amplitude is not large, the flattening rate is too small (the flattening rate is not more than 1.0%), the influence on the performance of the strip steel is small or not, and the flattening rate is too large (the flattening rate is not more than 2.0%), obvious work hardening occurs, and the comprehensive performance of the strip steel is greatly deteriorated.
Preferably, the high cooling rate after the final rolling in the hot rolling is 12 to 20 ℃/S. Further, the cooling rate was 16 ℃ 1S.
3. Advantageous effects
Compared with the prior art, the invention has the beneficial effects that:
(1) The cold-rolled hood-type annealed high-strength steel for the automobile with the tensile strength of 450MPa and the manufacturing method thereof adopt hood-type annealing, the hood-type annealing time is long, the tissue grows sufficiently and uniformly, the obvious strengthening elements of the invention are C and Mn, and microalloy elements such as Nb, mo, cr and the like which are sensitive to the process are not added, so that the problems of nonuniform tissue and poor performance stability of a continuous annealing product are solved, the producible thickness range of the product is expanded, the preparation process is simple, the equipment requirement is low, the assembly is convenient, the producible thickness range is large, and the method is an economical high-strength cold-rolled automobile plate preparation method.
(2) The cold-rolled bell-type annealed high-strength steel for the automobile with the tensile strength of 450MPa and the manufacturing method thereof have the advantages that the chemical components are simple, noble metals such as Nb and V are not required to be added, the manufacturing cost is saved, the yield strength of the produced finished product is more than or equal to 298MPa, the tensile strength is more than or equal to 450MPa, the elongation is more than or equal to 34%, the yield ratio is less than or equal to 0.66, the mechanical property is stable, the structure is uniform, the yield ratio is low, the plastic property is good, the steel is stably stamped at a client, and the problem of cracking is not easily caused.
Drawings
FIG. 1 is a metallographic structure photograph of a cold-rolled cap-annealed high-strength steel of example 1;
FIG. 2 is a metallographic structure photograph of a cold rolled hood annealed high strength steel of example 2;
FIG. 3 is a metallographic structure photograph of a cold rolled hood annealed high strength steel of example 3;
fig. 4 is a metallographic structure picture of a conventional process.
Detailed Description
The invention is further described with reference to specific examples.
It is to be noted that, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs; as used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
The examples, in which specific conditions are not specified, were carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
Example 1
The embodiment provides cold-rolled hood-annealed high-strength steel for an automobile with the tensile strength of 450MPa and a manufacturing method thereof, wherein the hood-annealed high-strength steel comprises the following chemical components in percentage by mass: c:0.09%, mn:1.46%, si:0.40%, P:0.001%, S:0.003%, al:0.038%, the balance being Fe and unavoidable impurities.
The production method of the bell-type annealed high-strength steel comprises the following process flows: smelting → continuous casting → hot rolling → acid pickling cold rolling → cover annealing → leveling → finished product, the specific technological parameters are as follows: performing converter smelting according to the components, continuously casting the components into a plate blank with the thickness of 230mm, heating the plate blank to 1230 ℃ for hot rolling, performing acid pickling and cold rolling, wherein the hot rolling finishing temperature is 880 ℃, the final rolling is performed at a cooling rate of 16 ℃/S, the coiling temperature is 560 ℃, the hot rolling coil thickness is 3.2mm, the cold rolling reduction rate is 69%, the cold rolling is performed until the target thickness is 1.0mm, the cover annealing temperature is 650 ℃, furnace-following segmented heating and furnace-following cooling are adopted, and the segmented heating process is set as follows: 400 ℃,1h,450 ℃,1h,500 ℃,1h,550 ℃,1h,650 ℃,8h and the leveling elongation is 1.3 percent.
The structure of the obtained cover annealing high-strength steel is shown in figure 1, and the yield strength is 298MPa, the tensile strength is 468MPa, the elongation is 34 percent, and the yield ratio is 0.64.
Example 2
The embodiment provides cold-rolled hood-type annealed high-strength steel for an automobile with the tensile strength of 450MPa and a manufacturing method thereof, wherein the hood-type annealed high-strength steel comprises the following chemical components in percentage by mass: c:0.10%, mn:1.48%, si:0.39%, P:0.015%, S:0.004%, al:0.047%, and the balance of Fe and inevitable impurities.
The production method of the bell-type annealed high-strength steel comprises the following process flows: smelting → continuous casting → hot rolling → acid pickling cold rolling → cover annealing → flattening → finished product, the specific technological parameters are: performing converter smelting according to the components, continuously casting the components into a 230mm thick plate blank, heating the plate blank to 1200 ℃ for hot rolling, wherein the hot rolling finishing temperature is 860 ℃, the cooling rate of 12 ℃/S is adopted after finishing rolling, the coiling temperature is 500 ℃, the thickness of a hot rolled coil is 2.6mm, then performing acid pickling and cold rolling, the cold rolling reduction rate is 69%, the cold rolling is performed until the target thickness is 0.8mm, the cover annealing temperature is 600 ℃, furnace-following segmented heating and furnace-following cooling are adopted, and the segmented heating process is set as follows: 400 ℃,1h,450 ℃,1h,500 ℃,1h,550 ℃,1h,600 ℃,8h and the leveling elongation is 1.0 percent.
The structure of the obtained cover annealing high-strength steel is shown in figure 2, and the yield strength is 302MPa, the tensile strength is 465MPa, the elongation is 35 percent, and the yield ratio is 0.65.
Example 3
The embodiment provides cold-rolled hood-type annealed high-strength steel for an automobile with the tensile strength of 450MPa and a manufacturing method thereof, wherein the hood-type annealed high-strength steel comprises the following chemical components in percentage by mass: c:0.11%, mn:1.46%, si:0.41%, P:0.015%, S:0.002%, al:0.042%, and the balance of Fe and inevitable impurities.
The production method of the bell-type annealed high-strength steel comprises the following process flows: smelting → continuous casting → hot rolling → acid pickling cold rolling → cover annealing → flattening → finished product, the specific technological parameters are: performing converter smelting according to the components, continuously casting the components into a 230mm thick plate blank, heating the plate blank to 1240 ℃ for hot rolling, wherein the hot rolling finishing temperature is 890 ℃, the coiling temperature is 580 ℃, the hot rolling coil thickness is 6.0mm, then performing acid pickling and cold rolling, the cold rolling reduction rate is 50%, the cold rolling is performed until the target thickness is 3.0mm, the cover annealing temperature is 660 ℃, furnace-following sectional heating and furnace-following cooling are adopted, and the sectional heating process is set as follows: 400 ℃,1h,450 ℃,1h,500 ℃,1h,550 ℃,1h,600 ℃,8h and the leveling elongation is 2.0%.
The structure of the obtained bell-annealed high-strength steel is shown in FIG. 3, and the yield strength is 305MPa, the tensile strength is 474MPa, the elongation is 35 percent, and the yield ratio is 0.64.
Comparative example
The chemical components (mass percent) of the comparative example are as follows: c:0.10%, mn:1.21%, si:0.025%, P:0.012%, S:0.004%, al:0.041 percent, and the balance of Fe and inevitable impurities.
The production method of the product comprises the following process flows: smelting → continuous casting → hot rolling → acid pickling cold rolling → continuous annealing → leveling → finished product, the specific technological parameters are as follows: the components are smelted in a converter, continuously cast into a 230mm thick plate blank, then the plate blank is heated to 1200 ℃ for hot rolling, the hot rolling finishing temperature is 880 ℃, the cooling rate of 12 ℃/S is adopted after finishing rolling, the coiling temperature is 600 ℃, the thickness of a hot rolled coil is 2.6mm, then acid pickling and cold rolling are carried out, the cold rolling reduction rate is 69%, the cold rolling is carried out until the target thickness is 0.8mm, the annealing temperature is 790 ℃, and the leveling elongation is 1.2%.
The resulting structure is shown in FIG. 4, and has a yield strength of 323MPa, a tensile strength of 448MPa, an elongation of 33%, and a yield ratio of 0.72.
Claims (9)
1. The cold-rolled hood-type annealed high-strength steel for the automobile with the tensile strength of 450MPa is characterized by comprising the following main chemical components in percentage by mass: c:0.05 to 0.20%, si: less than or equal to 0.50%, mn:1.0 to 2.0%, als: 0.015-0.060%, P is less than or equal to 0.022%, S is less than or equal to 0.015%, and the balance is Fe and inevitable impurities.
2. The cold-rolled hood-type annealed high-strength steel for the automobile with the tensile strength of 450MPa according to claim 1, which is characterized by comprising the following main chemical components in percentage by mass: c:0.09%, si:0.40%, mn:1.46%, al:0.038%, P:0.001%, S:0.003% and the balance of Fe and inevitable impurities.
3. The cold-rolled hood-annealed high-strength steel for the automobile with the tensile strength of 450MPa according to claim 1 is characterized by comprising the following main chemical components in percentage by mass: c:0.10%, si:0.39%, mn:1.48%, al:0.047%, P:0.015%, S:0.004%, and the balance of Fe and inevitable impurities.
4. The cold-rolled hood-type annealed high-strength steel for the automobile with the tensile strength of 450MPa according to claim 1, which is characterized by comprising the following main chemical components in percentage by mass: c:0.11%, si:0.41%, mn:1.46%, al:0.042%, P:0.015%, S:0.002%, and the balance of Fe and inevitable impurities.
5. The cold-rolled bell-type annealed high-strength steel for the automobile with the tensile strength of 450MPa according to any one of claims 1 to 4, characterized in that the yield strength of the cold-rolled bell-type annealed high-strength steel is more than or equal to 298MPa, the tensile strength of the cold-rolled bell-type annealed high-strength steel is more than or equal to 450MPa, and the elongation of the cold-rolled bell-type annealed high-strength steel is more than or equal to 34%.
6. The method for preparing the cold-rolled hood annealed high-strength steel for the automobile with the tensile strength of 450MPa according to any one of claims 1 to 5, which is characterized by comprising the process flows of smelting → continuous casting → hot rolling → acid pickling cold rolling → hood annealing → flattening → finished product.
7. The method for preparing the cold-rolled hood-type annealed high-strength steel for the automobile with the tensile strength of 450MPa according to claim 6, wherein the method is characterized in that
Smelting: the method is suitable for smelting of a converter, an electric furnace and an induction furnace to obtain target molten steel;
continuous casting: continuous casting is adopted to produce a casting blank, and molten steel is formed, rapidly solidified and crystallized under the action of a crystallizer to form a plate blank;
hot rolling: adopting a conventional hot rolling process to hot-roll the plate blank to a target thickness of raw materials required by cold rolling, wherein the final rolling temperature is as follows: 860 to 890 ℃, and the coiling temperature is 500 to 580 ℃; a higher cooling rate is adopted after finish rolling;
acid pickling and cold rolling: adopting a conventional pickling process, then cold-rolling to the required thickness specification of a finished product, and controlling the cold-rolling reduction rate to be 50-75%;
cover annealing: controlling the annealing temperature of the steel plate treated in the pickling and cold rolling step to be 600-660 ℃, and adopting furnace heating and furnace cooling;
leveling: the leveling elongation is controlled to be 1.0-2.0%.
8. The preparation method of the cold-rolled hood annealed high-strength steel for the automobile with the tensile strength of 450MPa according to claim 7, characterized in that a furnace-segmented heating process in the hood annealing is set as follows: 400 +/-40 ℃,1 +/-0.1h, 450 +/-45 ℃,1 +/-0.1h, 500 +/-50 ℃,1 +/-0.1h, 550 +/-10 ℃,1 +/-0.1 h and 8 +/-0.1 h of annealing temperature.
9. The preparation method of the cold-rolled hood annealed high-strength steel for the automobile with the tensile strength of 450MPa according to claim 7 or 8, characterized in that a higher cooling rate of 12-20 ℃ and 1S is adopted after finish rolling in hot rolling.
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Citations (6)
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