CN107829027B - thin 780 MPa-grade dual-phase steel and processing method thereof - Google Patents

thin 780 MPa-grade dual-phase steel and processing method thereof Download PDF

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CN107829027B
CN107829027B CN201710978892.6A CN201710978892A CN107829027B CN 107829027 B CN107829027 B CN 107829027B CN 201710978892 A CN201710978892 A CN 201710978892A CN 107829027 B CN107829027 B CN 107829027B
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steel
rolling
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CN107829027A (en
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刘斌
毛新平
徐进桥
刘永前
汪水泽
朱万军
王成
彭浩
韩荣东
魏星
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Wuhan Iron and Steel Co Ltd
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    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/02Ferrous alloys, e.g. steel alloys containing silicon
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226Hot rolling
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/04Ferrous alloys, e.g. steel alloys containing manganese
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/06Ferrous alloys, e.g. steel alloys containing aluminium
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00Microstructure comprising significant phases
    • C21D2211/005Ferrite
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00Microstructure comprising significant phases
    • C21D2211/008Martensite

Abstract

The invention discloses thin 780 MPa-grade dual-phase steels and a processing method thereof, belonging to the technical field of steel rolling, wherein the dual-phase steels comprise, by mass, 0.05-0.08% of C, 0.60-1.00% of Si, 1.40-1.80% of Mn, less than or equal to 0.015% of P, less than or equal to 0.004% of S, 0.30-0.70% of Cr, 0.020-0.060% of Als, and the balance Fe and inevitable impurities.

Description

thin 780 MPa-grade dual-phase steel and processing method thereof
Technical Field
The invention relates to the technical field of steel rolling, in particular to thin 780 MPa-grade dual-phase steels and a processing method thereof.
Background
In order to deal with the environmental protection pressure, the nation issues series compendial documents in succession, and clearly points out the transition pace that the manufacturing industry of China needs to accelerate green manufacturing and ecological development.
At present, the dual-phase steel for the automobile body structure mostly contains precious alloy elements such as Mo, Nb, Cu and the like from the aspect of composition, and has high alloy cost, and from the aspect of production process, the production flow energy consumption of a cold rolling product is high, the cost is high, while the thickness of a strip steel produced by a hot rolling process is only 1.5mm at the thinnest, and the use requirement of the ultra-thin dual-phase steel with the thickness of less than 1.5mm cannot be met, therefore, how to develop the novel automobile advanced high-strength steel with greenness, low cost and thin specification becomes a brand new topic of in the steel industry.
Disclosure of Invention
The invention aims to provide thin 780 MPa-grade dual-phase steels, which do not contain precious alloy elements such as Mo, Nb, Cu and the like, reduce the alloy cost and meet the use requirements of high-strength steel for automobiles.
Another purpose of the invention is to provide a processing method of thin 780 MPa-grade dual-phase steels, which adopts the thin slab continuous casting and rolling process to produce the thin dual-phase steels with the thickness of 1.0-3.0mm to replace cold-rolled products, thereby reducing the production cost and having excellent comprehensive mechanical properties.
In order to achieve the purpose, the invention provides thin 780 MPa-grade dual-phase steels, which comprise, by mass, 0.05-0.08% of C, 0.60-1.00% of Si, 1.40-1.80% of Mn, less than or equal to 0.015% of P, less than or equal to 0.004% of S, 0.30-0.70% of Cr, 0.020-0.060% of Als, and the balance Fe and inevitable impurities.
, the internal microstructure of the dual phase steel is ferrite + martensite.
, the internal microstructure of the dual-phase steel is composed of ferrite with volume fraction of 60% -70% and martensite with volume fraction of 30% -40%.
The invention also provides processing methods of the thin 780 MPa-grade dual-phase steel, which are based on the thin slab continuous casting and rolling process and comprise the following steps:
smelting molten iron;
refining the smelted molten iron to obtain alloyed molten steel;
carrying out sheet billet continuous casting and rolling on the molten steel to obtain a steel coil; wherein the heating temperature of the continuous casting and rolling is 1150-1230 ℃, the constant-speed rolling is adopted, and the rolling speed is 5.0-10.0 m/s;
cooling and coiling the steel coil, wherein the cooling adopts a sectional cooling mode of water cooling, air cooling and water cooling, the water cooling speed of the th section is 40-120 ℃/s, the steel coil is cooled to 640-710 ℃, then the steel coil is air cooled for 3.0-10.0 s, the water cooling speed of the second section is 120-200 ℃/s, and the steel coil is cooled to be less than or equal to 200 ℃ for coiling;
and (4) carrying out leveling treatment on the coiled steel coil, wherein the leveling force is controlled to be 80-220 tons, and obtaining a finished steel plate with the thickness of 1.0-3.0 mm.
Preferably, the heating temperature of the thin slab continuous casting and rolling is 1190-1230 ℃, the rolling speed is 5.5-10.0 m/s, and/or the water cooling speed of the th section is 60-120 ℃/s, the thin slab continuous casting and rolling is cooled to 670-690 ℃, then the thin slab continuous casting and rolling is carried out by air cooling for 3.2-8.0 s, the water cooling speed of the second section is 120-150 ℃/s, the thin slab continuous casting and rolling is carried out when the temperature is less than or equal to 180 ℃, and/or the leveling force is 150-220 tons.
More preferably, the heating temperature of the dual-phase steel with the thickness of less than 1.5mm is controlled to be 1200-1230 ℃, the rolling speed is 8.0-10.0 m/s, the water cooling speed of the th section after rolling is controlled to be 90-120 ℃/s, and the leveling force is controlled to be 160-220 tons.
Preferably, the thickness of a casting blank in the continuous casting and rolling is 50-150 mm, and the continuous casting and pulling speed is controlled to be 3.0-8.0 m/min.
More preferably, the thickness of the casting blank is 50-70 mm, and the continuous casting pulling speed is controlled to be 4.0-5.0 m/min.
Preferably, the finishing temperature of the continuous casting and rolling is 800-880 ℃.
Preferably, the internal microstructure of the dual-phase steel is ferrite + martensite, and/or the tensile strength is more than or equal to 780MPa, and/or the yield strength is more than or equal to 420 MPa.
or more technical solutions in the embodiment of the present application have at least the following technical effects or advantages:
1. the thin 780 MPa-grade dual-phase steel provided by the embodiment of the application adopts simple alloy components of a C-Mn-Cr system, and elements such as Si, Al and the like are added; the carbon content affects the volume fraction of martensite, the tensile strength of the steel can be improved, the Mn can improve the strength and the toughness, the Cr can obstruct the diffusion of carbon atoms, the Si can purify a ferrite structure, the mechanical property and the cold forming property of the final material are ensured under the combined action of all elements, and the thin 780 MPa-grade dual-phase steel is obtained.
2. The processing method of the 780 MPa-grade thin-gauge dual-phase steel provided by the embodiment of the application adopts a thin slab continuous casting and rolling process, controls the heating temperature, the constant-speed rolling process and the cooling mode in the production process, enables the steel plate to obtain ferrite and martensite structures with reasonable proportion, realizes the stable batch manufacturing of the thin-gauge dual-phase steel with the thickness of 1.0-3.0mm, shortens the manufacturing process, reduces the production cost, has excellent comprehensive mechanical properties, can replace cold-rolled products, and can meet the use requirements of high-strength steel for automobiles.
Drawings
FIG. 1 is a flow chart of a processing method of thin 780MPa grade dual-phase steel in an embodiment of the application;
FIG. 2 is a photograph of the metallographic structure of the dual phase steel obtained in example 1 of the present application.
Detailed Description
The embodiment of the application provides thin 780 MPa-grade dual-phase steels and a processing method thereof, and the thin dual-phase steels with the thickness of 1.0-3.0mm are produced by adopting a thin slab continuous casting and rolling process, so that the production cost is reduced, and the steel has excellent comprehensive mechanical properties.
The technical solutions of the present application are described in detail below with reference to the drawings and specific embodiments, and it should be understood that the specific features in the embodiments and examples of the present application are described in detail in the technical solutions of the present application, but not limited to the technical solutions of the present application, and the technical features in the embodiments and examples of the present application may be combined with each other without conflict.
The term "and/or" herein, which is only , describes the association relationship of the associated objects, indicates that there may be three relationships, for example, a and/or B, and may indicate that there are three cases of a alone, a and B together, and B alone.
In order to achieve the purpose, the embodiment of the application provides thin 780 MPa-grade dual-phase steels, and the chemical compositions of the dual-phase steels comprise, by mass, 0.05-0.08% of C, 0.60-1.00% of Si, 1.40-1.80% of Mn, less than or equal to 0.015% of P, less than or equal to 0.004% of S, 0.30-0.70% of Cr, 0.020-0.060% of Als, and the balance Fe and inevitable impurities, preferably, the content of C in the dual-phase steels is 0.06-0.07%, the content of Si is 0.85-1.00%, the content of Mn is 1.60-1.70%, and the content of Cr is 0.43-0.60%.
In this example, the internal microstructure of the dual phase steel was ferrite + martensite.
Preferably, the internal microstructure of the dual phase steel consists of ferrite with a volume fraction of 60% to 70% and martensite with a volume fraction of 30% to 40%. The proportion of the structure type can ensure that the tensile strength of the dual-phase steel is more than or equal to 780MPa, and simultaneously has better cold forming performance.
In the embodiment, the thickness of the dual-phase steel is 1.0-3.0 mm.
The application optimizes alloy elements to form the dual-phase steel with the chemical components, and is based on the following principles:
according to the application range of the steel grade, the steel grade is mainly used for processing parts such as automobile body structural parts and the like, and needs to be subjected to stamping deformation processing to a greater extent, so that the material is required to have good cold forming performance while meeting the strength requirement, if the carbon content is less than 0.05%, the hardness of the martensite can be reduced, under the condition of components, the tensile strength of the material cannot meet the standard requirement, if the carbon content is more than 0.08%, the good forming performance of the material cannot be met, and meanwhile peritectic reaction of molten steel in the casting process can be caused, and the risk of continuous casting steel leakage is increased, so the carbon content is limited to be in the range of 0.05-0.08%.
The content range of Si element is controlled to be 0.60% -1.00%, silicon accelerates the segregation of carbon to austenite in dual-phase steel, ferrite is further purified , gap solid solution strengthening is avoided, coarse carbide can be avoided from being generated during cooling, meanwhile, the interaction of dislocation can be influenced by the silicon dissolved in the ferrite, the work hardening rate and the uniform extension under a given strength level are increased, if the content of the silicon is more than 1.00%, the difficulty in removing iron oxide scales on the surface of the material is increased, the surface quality is influenced, and if the content of the silicon is less than 0.60%, the strengthening effect cannot be met, so the content of the silicon is limited to be 0.60% -1.00%.
According to the embodiment of the application, the content range of Mn element is controlled to be 1.40% -1.80%, Mn is the most effective element for improving the strength and the toughness, and the pearlite transformation can be effectively delayed in the dual-phase steel. If the content is less than 1.40%, the strength requirement of the material cannot be met; however, addition of an excessive amount of manganese inhibits precipitation of ferrite in the dual phase steel, and is limited to 1.80% in view of this. Therefore, the manganese content is limited to 1.40 to 1.80%.
In the embodiment of the application, the content of the P element is controlled to be less than or equal to 0.015 percent, P is a harmful element, and the content of the P element is controlled to be less than 0.015 percent in order to avoid the deterioration of the welding performance, the stamping forming performance, the toughness and the secondary processing performance of the material.
The content of the S element is controlled to be less than or equal to 0.004%, sulfur in steel often exists in a manganese sulfide form, and sulfide inclusions are very unfavorable for the impact toughness of the steel and cause performance anisotropy, so that the lower the content of the sulfur in the steel is, the better the content is.
The content range of the Cr element is controlled to be 0.30-0.70%, the chromium is a carbide forming element, the affinity with carbon is strong, the diffusion of carbon atoms can be hindered, and the comprehensive effect of manganese is added, so that the transformation of pearlite and bainite is remarkably delayed, and the method is favorable for producing dual-phase steel. When the chromium content is less than 0.30%, the effect cannot be exerted; chromium contents greater than 0.70% have met the operating requirements and continued addition can raise costs. Therefore, the chromium content is controlled to be 0.30-0.70%.
In the examples of the present application, the content of Al element is controlled to be in the range of 0.020% to 0.060%, aluminum is added for deoxidation, and when the content of Als is less than 0.020%, the effect is not exhibited, and in , an excessive amount of aluminum is added to easily form alumina agglomerates, so that the upper limit of Als is defined to be 0.060%.
The dual phase steel according to the embodiment of the present application is composed of the above chemical components, and noble alloying elements such as Nb, Ti, Cu, Ni, and Mo are not added from the viewpoint of improving the formability of the material and the economy.
According to the content, the steel plate has good weldability by adopting simple alloy components of a C-Mn-Cr system, meanwhile, elements such as Si are added to improve the performance stability, the mechanical property and the cold forming property of the final material are ensured under the combined action of the elements, and the alloy cost is greatly reduced; by adopting the component design, the thin steel plate with the thickness of 1.0-3.0mm can be obtained. The tensile strength of the dual-phase steel is more than or equal to 780MPa, the yield strength is more than or equal to 420MPa, and the elongation percentage A50The yield ratio is not more than 16 percent, the yield ratio is not more than 0.60, and the bending core diameter D is qualified to be 1.5a in a 180-degree transverse bending test.
The embodiment of the application also provides a processing method of thin 780 MPa-grade dual-phase steels, which comprises the processes of smelting → refining → thin slab continuous casting and rolling → cooling → coiling → flattening, and as shown in figure 1, the specific steps are as follows:
step S110: smelting molten iron; preferably, the molten iron is subjected to desulfurization treatment before smelting;
step S120: refining the smelted molten iron to obtain alloyed molten steel;
specifically, molten iron smelted by a converter enters an LF furnace or an RH furnace for refining treatment, and the molten steel after alloying treatment in the refining process comprises the following chemical components: c: 0.05-0.08%, Si: 0.60% -1.00%, Mn: 1.40-1.80%, P is less than or equal to 0.015%, S is less than or equal to 0.004%, Cr: 0.30% -0.70%, Als: 0.020% to 0.060% and the balance of Fe and inevitable impurities.
Step S130: carrying out sheet billet continuous casting and rolling on the molten steel to obtain a steel coil;
specifically, the molten steel is produced by continuous casting and rolling of a thin slab: the thickness of the cast steel billet is 50-150 mm, and the continuous casting speed is 3.0-8.0 m/min; heating the casting blank in a soaking furnace, wherein the heating temperature is controlled to be 1150-1230 ℃; rolling in a 7-stand finishing mill, and rolling at a constant speed according to the thickness specification, wherein the rolling speed is controlled to be 5.0-10.0 m/s, the final rolling temperature is controlled to be 800-880 ℃, and the rolling thickness is 1.0-3.0 mm. The continuous casting drawing speed is controlled to be 3.0-8.0 m/min, and the purpose is to increase the temperature of the billet entering the soaking pit furnace, so that the energy consumption of the soaking pit furnace is reduced, and the cost is reduced; the rolling speed of the steel coil is controlled to be 5.0-10.0 m/s according to the thickness of a final finished product, so that enough time is provided for ferrite transformation in the subsequent sectional cooling process, and a ferrite structure with a proper proportion is obtained.
Preferably, the thickness of the cast steel billet is 50-70 mm, the continuous casting drawing speed is 4.0-5.0 m/min, the heating temperature of a soaking furnace is 1190-1230 ℃, the rolling speed is 5.5-10.0 m/s, and the final rolling temperature is 800-840 ℃.
Step S140: cooling and coiling the steel coil;
specifically, a rolled steel coil is cooled to 640-710 ℃ in a 'water cooling + air cooling + water cooling' sectional cooling mode, wherein the water cooling speed of the th section is 40-120 ℃/s, the steel coil is cooled to 640-710 ℃, then air cooling is carried out, the air cooling time is 3.0-10.0 s, the water cooling speed of the second section is 120-200 ℃/s, the steel coil is cooled to be less than or equal to 200 ℃ for coiling, the water temperature of cooling water is controlled to be less than or equal to 30 ℃, the 'water cooling + air cooling + water cooling' sectional cooling process is adopted, the front end of the th section of water cooling process is rapidly cooled to 640-710 ℃ according to the cooling speed of 40-120 ℃/s, the steel coil is cooled to be less than or equal to 200 ℃ in time when steel grains do not start to grow, generation of coarse grains is avoided, the material obtains a fine austenite grain structure, the air cooling speed is 3.0-10.0 s, part of the austenite structure is converted to ferrite, the second section is cooled to be less than or equal to 200 ℃ in the second section, and the steel coil is cooled to be less than or equal to be controlled to be a martensite cooling water temperature when the steel grains are not started to be.
Preferably, the water cooling speed of the th section is 60-120 ℃/s, the cooling is carried out to 670-690 ℃, then air cooling is carried out, the air cooling time is 3.2-8.0 s, the water cooling speed of the second section is 120-150 ℃/s, the cooling is carried out to the temperature of less than or equal to 180 ℃, the coiling is carried out, and the water temperature of the cooling water is controlled to be less than or equal to 25 ℃.
Step S150: and flattening the coiled steel coil to obtain a finished steel plate with the thickness of 1.0-3.0 mm.
Specifically, the steel coil is subjected to flattening treatment with the flattening force of 80-220 tons, and finally the dual-phase steel with the thickness of 1.0-3.0mm and the ferrite and martensite as the internal microstructure is obtained. Wherein, the flattening treatment is to improve the shape of the hot-rolled strip steel so as to meet the requirements of cold-rolled products; meanwhile, the dual-phase steel has higher initial work hardening rate, and the leveling force needs to be limited, so that the leveling force is controlled to be 80-220 tons according to the thickness of a finished steel coil. Preferably, the leveling force is 150-220 tons.
, preferably, for the ultra-thin dual-phase steel with the thickness of less than 1.5mm, the heating temperature is controlled to be 1200-1230 ℃, the load in the rolling process can be effectively reduced, the rolling speed is 8.0-10.0 m/s, and simultaneously, the water cooling speed of th section after rolling is controlled to be 90-120 ℃/s, so that the stable ferrite transformation time of the strip steel in the cooling process can be kept, the performance stability of the material is improved, and the flexible leveling is adopted, and the leveling force is 160-220 tons.
According to the content, the processing method of the dual-phase steel provided by the application is based on the thin slab continuous casting and rolling process, and the stable ferrite transformation time of the steel strip is kept in the cooling process by controlling the heating temperature, the constant-speed rolling process and the cooling mode in the production process, so that the performance stability of the material is improved, and the ferrite + martensite structure with a reasonable proportion is finally obtained. The method can be used for producing the steel plate with the thickness of 1.0-3.0mm, and the dual-phase steel produced according to the embodiment has the following properties: tensile strength is greater than or equal to 780MPa, yield strength is greater than or equal to 420MPa, and elongation A50mmNot less than 16 percent and the yield ratio not more than 0.60; the structure of the material is a ferrite and martensite dual-phase structure. The product has the characteristics of low cost, thin or extremely thin thickness, low yield ratio and the like, and can be used for manufacturing the body structural member of the passenger vehicle instead of cold-rolled dual-phase steel.
The present application is described in more detail by way of examples below. These examples are merely illustrative of the best mode of carrying out the invention and do not limit the scope of the invention in any way.
Molten iron is smelted in a converter and then enters an LF furnace or an RH furnace for refining treatment, and the chemical components of the molten steel after alloying treatment in the refining process are shown in Table 1.
TABLE 1 example dual phase steel composition (mass fraction%, balance Fe and unavoidable impurities)
Figure BDA0001438861270000091
The molten steel with different compositions shown in the table 1 is subjected to thin slab continuous casting and rolling production, laminar cooling, coiling and leveling treatment, and the main process parameters are shown in the table 2.
Table 2 example main process parameter list
Figure BDA0001438861270000101
The properties of the dual phase steel of the examples of the present application are shown in table 3.
Table 3 example main performance tabulation
Figure BDA0001438861270000102
As can be seen from Table 3, the dual phase steels having thickness specifications of 1.0 to 3.0mm obtained in examples 1 to 8 all satisfy the yield strength RP0.2Not less than 420MPa, tensile strength RmNot less than 780MPa, elongation A50Not less than 16 percent and the yield ratio not more than 0.60. Fig. 2 is a metallographic structure diagram of a dual phase steel obtained in examples of the present application, and it can be seen from fig. 2 that: the structure of the strip steel is ferrite + martensite, and the grain size of the ferrite is 12 grades. The comparative example had a high yield strength, and had a problem of large springback when punching cold-formed parts, and the cold-formability was not good.
The above results show that the dual-phase steel with the thickness specification of 1.0-3.0mm and the tensile strength of 780MPa grade can be obtained by adopting the component design and the process control in the embodiment of the application.
or more technical solutions in the embodiment of the present application have at least the following technical effects or advantages:
1., the embodiment of the application adopts simple alloy components of C-Mn-Cr series to realize the production of 780MPa dual-phase steel, so that the alloy cost is greatly reduced, , the embodiment of the application adopts a thin slab continuous casting and rolling process to produce the advanced high-strength steel for the automobile, so that the manufacturing process is shortened, and the production process cost can be greatly reduced.
2. The production process is green. According to the embodiment of the application, the thin slab continuous casting and rolling process is adopted to produce the advanced high-strength steel for the automobile to replace the traditional cold-rolled product, so that the complex cold-rolling process is omitted, the manufacturing process is greatly shortened, the energy consumption and water consumption and the discharge of various wastes are reduced, the comprehensive energy consumption per ton of steel can be reduced by more than 70%, and the equivalent CO is equivalent2The discharge amount can be reduced by about 30%, and green manufacturing is realized.
3. Realizing the production of the ultra-thin dual-phase steel with the thickness of less than 1.5 mm. The thin-slab continuous casting and rolling process is adopted to produce the ultra-thin dual-phase steel, and when the thickness of the strip steel is reduced from 1.5mm to 1.0mm, the difficulties of high rolling load, unstable ferrite transformation, large plate shape fluctuation and the like exist. The embodiment of the application adopts the technology of high-temperature heating, constant-speed rolling, rapid cooling and flexible leveling, can effectively reduce the rolling load of the strip steel below 1.5mm, stabilize the ferrite transformation time, improve the shape of the thin dual-phase steel plate and realize the batch stable manufacture of the ultra-thin dual-phase steel below 1.5mm in thickness.
Finally, it should be noted that the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the present invention has been described in detail with reference to examples, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, which should be covered by the claims of the present invention.

Claims (6)

  1. The thin 780 MPa-grade dual-phase steel is characterized by comprising, by mass, 0.05% -0.08% of C, 0.60% -1.00% of Si, 1.40% -1.80% of Mn, less than or equal to 0.015% of P, less than or equal to 0.004% of S, 0.30% -0.70% of Cr, 0.020% -0.060% of Als, and the balance Fe and inevitable impurities, wherein an internal microstructure of the dual-phase steel consists of 60% -70% of ferrite and 30% -40% of martensite in volume fraction, the tensile strength is greater than or equal to 780MPa, and the yield strength is greater than or equal to 420 MPa;
    the processing method of the dual-phase steel comprises the following steps:
    smelting molten iron;
    refining the smelted molten iron to obtain alloyed molten steel;
    performing continuous casting and rolling on the molten steel to obtain a steel coil, wherein the heating temperature of the continuous casting and rolling is 1190-1230 ℃, the constant-speed rolling is adopted, the rolling speed is 5.5-10.0 m/s, the steel coil is cooled and coiled, the cooling adopts a sectional cooling mode of water cooling, air cooling and water cooling, the water cooling speed of the th section is 60-120 ℃/s, the cooling is carried out to 670-690 ℃, then the air cooling is carried out for 3.2-8.0 s, the water cooling speed of the second section is 120-150 ℃/s, and the cooling is carried out to be less than or equal to 180 ℃ for coiling;
    and (4) carrying out leveling treatment on the coiled steel coil, wherein the leveling force is controlled to be 150-220 tons, and obtaining a finished steel plate with the thickness of 1.0-3.0 mm.
  2. 2. The method for processing the thin gauge 780MPa grade dual phase steel according to claim 1, wherein the method is based on a thin slab continuous casting and rolling process, and comprises the following steps:
    smelting molten iron;
    refining the smelted molten iron to obtain alloyed molten steel;
    performing continuous casting and rolling on the molten steel to obtain a steel coil, wherein the heating temperature of the continuous casting and rolling is 1190-1230 ℃, the constant-speed rolling is adopted, the rolling speed is 5.5-10.0 m/s, the steel coil is cooled and coiled, the cooling adopts a sectional cooling mode of water cooling, air cooling and water cooling, the water cooling speed of the th section is 60-120 ℃/s, the cooling is carried out to 670-690 ℃, then the air cooling is carried out for 3.2-8.0 s, the water cooling speed of the second section is 120-150 ℃/s, and the cooling is carried out to be less than or equal to 180 ℃ for coiling;
    and (4) carrying out leveling treatment on the coiled steel coil, wherein the leveling force is controlled to be 150-220 tons, and obtaining a finished steel plate with the thickness of 1.0-3.0 mm.
  3. 3. The method of claim 2, wherein the heating temperature of the dual-phase steel with a thickness of 1.5mm or less is controlled to 1200 to 1230 ℃, the rolling speed is controlled to 8.0 to 10.0m/s, the water cooling speed at th stage after rolling is controlled to 90 to 120 ℃/s, and the temper rolling is controlled to 160 to 220 tons.
  4. 4. The method for processing the 780MPa grade thin dual-phase steel as claimed in of claims 2-3, wherein the thickness of the cast slab in the continuous casting and rolling is 50-150 mm, and the continuous casting speed is controlled to be 3.0-8.0 m/min.
  5. 5. The method for processing the thin 780MPa grade dual phase steel according to claim 4, wherein the thickness of the casting blank is 50-70 mm, and the continuous casting drawing speed is controlled to be 4.0-5.0 m/min.
  6. 6. The method for processing the 780MPa grade thin gauge dual phase steel of of claims 2-3, wherein the finishing temperature of the continuous casting and rolling is 800-880 ℃.
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