CN113061807B - 780 MPa-grade light high-strength steel and preparation method thereof - Google Patents

780 MPa-grade light high-strength steel and preparation method thereof Download PDF

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CN113061807B
CN113061807B CN202110276224.5A CN202110276224A CN113061807B CN 113061807 B CN113061807 B CN 113061807B CN 202110276224 A CN202110276224 A CN 202110276224A CN 113061807 B CN113061807 B CN 113061807B
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steel plate
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steel
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CN113061807A (en
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郭金宇
刘仁东
孟静竹
张峰
王科强
徐荣杰
孙荣生
孙建伦
陈妍
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Angang Steel Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/28—Manufacture of steel in the converter
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0081—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for slabs; for billets
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

Abstract

The invention discloses 780 MPa-grade light high-strength steel and a preparation method thereof. The steel contains C: 0.15% -0.25%, Si: 0.8% -1.5%, Mn: 1.0% -2.0%, P: 0.03-0.05%, S is less than or equal to 0.03%, Al: 3.0% -5.0%, Ti: 0.03-0.2%, Nb: 0.03 to 0.2 percent, Bi: 0.05 to 0.2 percent, and the balance of Fe and inevitable impurities, and the ratio of (13C +2Mn)/(Al +1.2Si) is more than or equal to 0.8 and less than or equal to 1.2. The heating temperature of a casting blank is 1200-1250 ℃, the initial rolling temperature is 1000-1150 ℃, the final rolling temperature is 850-930 ℃, the cooling rate is more than 20 ℃/s, and the coiling temperature is less than or equal to 240 ℃; the annealing temperature is 800-880 ℃, the annealing heat preservation time is 120-300 s, the cooling rate is 20-60 ℃/s, the aging temperature is 350-450 ℃, the aging treatment time is 300-800 s, and the cooling rate is 10-30 ℃/s to the room temperature. The requirements of high strength and high elongation of the structural member of the automobile body are met.

Description

780 MPa-grade light high-strength steel and preparation method thereof
Technical Field
The invention belongs to the field of automobile steel manufacturing, and relates to light high-strength steel and a preparation method thereof.
Background
In recent years, with the increasing requirements for energy conservation and environmental protection, the development and the mass use of high-strength and ultrahigh-strength automobile steel become the mainstream trend of the development of the automobile industry, and the effective means for realizing the light weight of automobiles is realized. With the increasing strength of steel for automobiles, it is more and more difficult to reduce the weight of automobile parts by simply increasing the strength of steel plates. Attempts have been made to manufacture automobile parts and vehicles using light materials such as Al, Mg, and carbon fibers, but the use of light materials such as Al, Mg, and carbon fibers has been limited due to high cost and insufficient workability and weldability. Therefore, the development of cold-rolled light multi-phase steel provides a good approach to solve the above problems.
Patent document CN 110983195 a discloses a low-density high-strength steel for automobiles and a preparation method thereof. The low-density high-strength steel for the automobile comprises the following components in percentage by weight: c: 0.3% -0.5%, Si: 0.2-0.5%, Mn: 1-2%, P is less than or equal to 0.01%, S is less than or equal to 0.01%, Ce: 0.020-0.040%, N is less than or equal to 0.0060%, Als: 3.50 to 4.8 percent, and the balance of Fe and inevitable impurities. The 980 MPa-grade high-strength steel is produced by adopting a cold rolling-continuous annealing production process, but the production process is complex, the elongation of the product is low, and the use requirements of complex parts of automobiles are difficult to meet.
Patent document CN 101775470a discloses a hot-rolled high-strength light dual-phase steel with tensile strength of 700 to 800MPa and a manufacturing method thereof. The main chemical components are as follows: c: 0.2-0.5%, Mn: 2.0% -6.0%, Si: 0.3-1.0%, N is less than or equal to 0.008%, P is less than or equal to 0.015%, S is less than or equal to 0.010%, Al: 4.0 to 9.0 percent of the total weight of the alloy, and also comprises at least one or more of Cr, Ti, V, Mo, Nb, Ca, Ni and Cu, wherein the ratio of (15C +0.5Mn)/(Al + Si) is more than or equal to 0.8 and less than or equal to 1.20, and the balance of Fe and inevitable impurities. The high-strength light-weight dual-phase steel with the strength level of 700-800 MPa is produced by adopting a hot rolling process, but the elongation of the product is low, and the stamping requirement of automobile parts is difficult to meet.
In conclusion, the existing light multi-phase automobile steel has the problems of high cost, complex process, poor product forming performance and the like, and the use requirements of automobile parts are difficult to meet.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide a 780 MPa-grade high-strength steel with high strength, high plasticity and light weight and a preparation method thereof, which meet the requirements of high strength and high elongation of automobile body structural parts.
The specific technical scheme is as follows:
the 780 MPa-grade light high-strength steel comprises the following chemical components in percentage by mass: c: 0.15% -0.25%, Si: 0.8% -1.5%, Mn: 1.0% -2.0%, P: 0.03-0.05%, S is less than or equal to 0.03%, Al: 3.0% -5.0%, Ti: 0.03% -0.2%, Nb: 0.03 to 0.2 percent, Bi: 0.05 to 0.2 percent, and the balance of Fe and inevitable impurities, wherein the elements of C, Mn, Al and Si in the steel need to meet the following relation of 0.8 to less than or equal to (13C +2Mn)/(Al +1.2Si) to less than or equal to 1.2.
The reason for the alloy design of the present invention is as follows:
c: the C element mainly plays a role in solid solution strengthening in the steel, and improves the hardness, yield strength and tensile strength of the steel plate. Meanwhile, the C element has the function of forming and stabilizing austenite, and the austenite phase of the C in the steel is enriched through the control of a heat treatment process to form a metastable austenite phase, so that the forming performance and the elongation of the steel plate are improved. In the light steel containing Al element, C element, Al and Mn are easy to form (FeMnAl) C carbide, the strength and plasticity of the steel plate are reduced, and the content of C element cannot be too high. Therefore, the content of C is controlled to be 0.15-0.25%.
Mn: the Mn element plays a role in solid solution strengthening and austenite stabilizing in steel. On one hand, the Mn element improves the strength of the steel plate through the solid solution strengthening effect, and on the other hand, the Mn element promotes the steel plate to form a residual austenite phase through the austenite stabilizing effect, thereby playing the role of improving the plasticity of the steel plate. Too high Mn content can cause the generation of banded structures in steel and reduce the toughness of the steel plate; meanwhile, austenite is too stable and is difficult to be transformed into martensite in the deformation process, so that the forming performance of the steel plate is reduced, and therefore, the content of the Mn element is controlled to be 1.0-2.0 percent.
Si: si element can inhibit cementite precipitation and promote austenite formation, thereby improving the plasticity of the steel plate; the Si element can play a role in solid solution strengthening; si can enlarge the lattice constant of the steel sheet and reduce the density of the steel sheet. The Si element content is too low, so that the effects of inhibiting cementite precipitation, improving the strength of the steel plate and reducing the weight are not achieved; too high a content of Si element may degrade the surface quality of the steel sheet. Therefore, the Si content is controlled to be 0.8-1.5% in the invention.
Al: the Al element is a light element and can play a role in reducing the density of the steel plate; al element can be dissolved in the ferrite phase of the steel plate in a solid solution mode to play a role in solid solution strengthening; the Al element can inhibit the precipitation of cementite, so that the C element can be enriched in an austenite phase and plays a role in stabilizing the austenite phase, thereby improving the plasticity of the steel plate; the Al element can enlarge the range of ferrite phase, and a certain amount of delta-ferrite phase is formed in the steel, so that a delta-ferrite and martensite dual-phase structure is formed in a welding spot area of the steel plate in the welding process, and the toughness of the welding spot is improved, thereby improving the welding performance of the steel plate. If the content of the Al element is too low, the effects of reducing the density, improving the strength and improving the plasticity and weldability are not obvious; if the content of Al element is too high, a brittle phase such as FeAl is formed in the steel, and the formability and workability of the steel sheet are deteriorated. Therefore, the Al content is controlled to be 3.0-5.0 percent in the invention.
P: the P element plays a role in strengthening in the steel on the one hand, and plays a role in inhibiting cementite precipitation on the other hand. In the invention, the content of P is controlled to be 0.03-0.05%.
S: the S element is a harmful element in steel, and the lower the content, the better. In consideration of the production cost of steel, the content of the S element is controlled below 0.03 percent.
Ti: ti element reacts with C, N element to generate TiC, TiN, TiCN and other compounds, which play the role of limiting the growth of crystal grains and disperse and separate out to improve the strength of the steel plate. The high content of Ti element will increase the cost, the high strength of the steel plate and the plasticity decrease, therefore, the Ti element content is determined to be 0.03-0.2%.
Nb: the Nb element mainly forms carbide or nitride to play a role in refining grains and improving the strength of the steel plate, and can improve the recrystallization temperature of the steel plate and refine ferrite grains. The plasticity of the steel sheet is reduced due to the excessively high Nb content, and therefore, the Nb element content is determined to be 0.03-0.2% in the invention.
Bi: the Bi element is mainly distributed at crystal grains and crystal boundaries to inhibit C, O element from diffusing on the crystal boundaries, so that the effects of reducing and inhibiting decarburization and oxidation, reducing steel plate rolling cracks and improving the surface quality and mechanical properties of the steel plate are achieved. The excessively high Bi content results in the weakening of the grain boundary bonding force and the reduction of the plasticity of the steel plate. Therefore, the invention controls the Bi content to be 0.05-0.2%.
In the invention, the elements of C, Mn, Al and Si are required to meet the following relation of 0.8-1.2 Si of (13C +2Mn)/(Al +1.2 Si). Therefore, the steel plate can be ensured to form a certain amount of delta-ferrite + alpha-ferrite + bainite + residual austenite + martensite structures, and the steel plate has good mechanical properties, forming properties, welding properties, low density and other good effects. C. Mn, Al and Si elements are required to meet the requirement that (13C +2Mn)/(Al +1.2Si) is more than or equal to 0.8, and 30-50% of bainite structure and 10-25% of austenite structure can be formed in steel, so that the strength and the forming performance of the steel plate are ensured; C. the Mn, Al and Si elements can ensure that the steel plate can form 30 to 50 percent delta-ferrite and alpha-ferrite according to the requirement that (13C +2Mn)/(Al +1.2Si) is less than or equal to 1.2, thereby ensuring the low density, high forming performance, low yield strength and good welding performance of the steel plate.
A preparation method of high-strength lightweight steel comprises the following steps: converter smelting, continuous casting, hot rolling, acid washing and continuous annealing.
The preparation process comprises the following specific steps:
smelting by adopting a converter smelting method, wherein the molten steel comprises the following chemical components in percentage by mass: c: 0.15% -0.25%, Si: 0.8-1.5%, Mn: 1.0% -2.0%, P: 0.03-0.05%, S is less than or equal to 0.03%, Al: 3.0% -5.0%, Ti: 0.03% -0.2%, Nb: 0.03 to 0.2 percent, Bi: 0.05 to 0.2 percent, the balance being Fe and inevitable impurities, and the elements of C, Mn, Al and Si in the steel are required to meet the following relation of 0.8 to (13C +2Mn)/(Al +1.2Si) to 1.2
And in the continuous casting process, a conventional continuous casting machine is adopted for continuous casting to obtain a continuous casting billet.
The hot rolling process comprises the following steps: the heating temperature is 1200-1250 ℃, the initial rolling temperature is 1000-1150 ℃, the final rolling temperature is 850-930 ℃, the cooling mode adopts a laminar cooling mode, the cooling rate is more than 20 ℃/s, and the coiling temperature is below 240 ℃. The thickness of the hot-rolled plate is less than 2.5 mm.
The pickling process comprises the following steps: the main purpose of the conventional pickling process is to remove oxides from the surface of the hot rolled steel sheet.
A continuous annealing process: the annealing temperature is 800-880 ℃, the annealing heat preservation time is 120-300 s, the cooling rate is 20-60 ℃/s, the temperature is cooled to 350-450 ℃, the aging treatment is carried out, the aging treatment time is 300-800 s, and finally the steel plate is cooled to the room temperature at the cooling rate of 10-30 ℃/s.
The tensile strength is greater than 780MPa, the elongation is greater than 28%, and the density is lower than 7.5g/cm 3 The cold-rolled high-strength light steel.
The temperature of the hot rolling furnace is selected to be 1200-1250 ℃, and homogenization treatment is carried out. The initial rolling temperature of hot rolling is 1000-1150 ℃, the final rolling temperature is 880-950 ℃, and the steel plate is in a temperature range of a double phase region by controlling the rolling temperature, so that the content of delta-ferrite in the steel plate is ensured to be between 20% and 50%. And the delta-ferrite in the steel is in a lath shape through controlled rolling and controlled cooling, the temperature is kept to be room temperature, and the steel is still in a layered lath shape in the subsequent continuous annealing process, so that the plasticity and the forming performance of the steel plate are improved. The finishing rolling temperature is controlled to be 880-950 ℃, so that grains are refined, and excessive growth of austenite grains is inhibited.
The cooling rate is more than 20 ℃/s, and the cooling rate of more than 20 ℃/s is required to be below 240 ℃ after hot rolling, so that the austenite in the steel is converted into a martensite structure, and the nucleation point of the austenite is increased in the subsequent continuous annealing process, so as to refine austenite grains.
The coiling temperature adopts a low-temperature coiling mode, the coiling temperature is less than 240 ℃, preferably less than 200 ℃, austenite in the steel is completely transformed into martensite, a fine martensite lath structure is formed, and more nucleation points are provided for austenite formation in the next continuous annealing process. If the coiling temperature is too high, sufficient martensite may not be formed in the steel.
And (3) continuous annealing process: the annealing temperature is 800-880 ℃, the annealing time is 120-300 s, and the annealing temperature and the annealing time are controlled in the interval, so that the delta-ferrite, the alpha-ferrite and a proper amount of austenite structures with proper proportions can be obtained in the final structure of the steel plate. Too high annealing temperature or too long annealing time can cause too low alpha-ferrite content, too high austenite content and too large grains, and reduce the strength and elongation of the steel plate; too low annealing temperature or too short annealing time may result in incomplete recrystallization of ferrite, incomplete transformation of martensite into austenite, and deterioration of strength and elongation of the steel sheet.
The cooling rate is between 20 and 60 ℃/s, a small amount of alpha-ferrite structure is formed in the steel plate cooling process, the cooling rate is controlled to be between 20 and 60 ℃/s, if the cooling rate is too low, a pearlite structure appears in the steel, and the austenite content of the final steel plate is too low, so that the performance of the steel plate is deteriorated.
The cooling temperature is 350-450 ℃, so that austenite in the steel is transformed into martensite, bainite and residual austenite structures, the strength and plasticity of the steel plate are poor due to overhigh temperature, the austenite content in the steel is too low due to overlow temperature, and the elongation of the steel plate is reduced.
Aging time: the aging treatment time is 300-800 s, the stability of austenite in steel can be reduced due to short aging time, the austenite structure can be decomposed due to too long aging time, and the elongation of the steel plate can be reduced.
And finally cooling to room temperature at a cooling rate of 10-30 ℃/s to convert a small amount of unstable austenite in the steel into a martensite structure.
The final structure of the steel plate is a delta-ferrite, alpha-ferrite, bainite, austenite and martensite multiphase structure, and the delta-ferrite and alpha-ferrite content is 30-50%, the bainite content is 30-50%, the austenite content is 10-25% and the martensite content is less than 5% in percentage by volume.
Has the advantages that:
compared with the prior art, the invention has the following beneficial effects:
(1) the tensile strength of the steel for the automobile prepared by the invention is more than 780MPa, the yield strength is more than 400MPa, the elongation is more than 28%, and the density is less than 7.5g/cm 3 The automobile bumper has the characteristics of high strength, high plasticity and light weight, and meets the requirements of energy conservation, weight reduction and safety improvement in the automobile industry.
(2) The invention obtains the multi-phase steel containing the delta-ferrite laminated structure by adding Al element and combining the control of hot rolling and annealing process, and the plasticity and welding performance of the steel plate can be improved by the delta-ferrite with the specific laminated structure.
(3) According to the invention, through C, Si, Mn, Al and other alloy elements, the control of hot rolling and annealing process is combined, the multiphase structure of delta-ferrite, alpha-ferrite, bainite, austenite and a small amount of martensite is obtained, wherein the austenite content is between 10% and 25%.
(4) The invention is implemented on the existing production line, no new equipment is added, and the invention has good popularization prospect.
Drawings
FIG. 1 shows the metallographic structure of the steel sheet of example 1.
Detailed Description
The present invention is described in more detail by way of examples, which are merely illustrative of the best mode of carrying out the invention and are not intended to limit the scope of the invention in any way.
The chemical composition of the example steels is listed in table 1, the hot rolling process parameters of the example steels are listed in table 2, the continuous annealing process parameters of the example steels are listed in table 3, the structure of the example steels is listed in table 4, and the mechanical properties of the example steels are listed in table 5.
Table 1 chemical composition of the example steels, wt.%
Examples C Mn Si Al P S Ti Nb Bi (13C+2Mn)/(Al+1.2Si)
1 0.15 1.82 0.92 4.83 0.04 0.002 0.07 0.14 0.051 0.94
2 0.24 1.27 1.48 3.21 0.05 0.002 0.04 0.07 0.067 1.14
3 0.16 1.54 0.81 3.52 0.042 0.003 0.13 0.06 0.13 1.15
4 0.17 1.63 1.12 3.65 0.038 0.006 0.06 0.12 0.15 1.10
5 0.18 1.72 1.23 3.82 0.045 0.005 0.15 0.03 0.24 1.09
6 0.21 1.48 1.33 4.23 0.032 0.007 0.08 0.05 0.27 0.98
7 0.22 1.15 1.42 4.48 0.038 0.009 0.09 0.18 0.31 0.83
8 0.23 1.33 0.85 4.63 0.041 0.008 0.13 0.06 0.38 1.00
TABLE 2 Hot Rolling Process of the steels of the examples
Figure BDA0002976745220000081
Table 3 continuous annealing process of steel of examples
Figure BDA0002976745220000091
TABLE 4 Structure of the steels of the examples
Examples Delta-ferrite + alpha-ferrite/%) Bai shiVolume/%) Austenite/% Martensite/% of
1 35.7 48.6 12.3 3.4
2 42.8 40.2 14.2 2.8
3 36.9 49.2 9.7 4.2
4 32.4 53.8 11.2 2.6
5 47.8 36.8 13.6 1.8
6 46.5 37.2 14.9 1.4
7 39.9 48.9 11.2 0
8 34.5 49.3 11.4 4.8
TABLE 5 mechanical properties of the steels of the examples
Figure BDA0002976745220000092
As can be seen from the above examples, the automobile steel prepared by adopting the component design, rolling and annealing process of the invention has tensile strength of more than 780MPa, yield strength of more than 400MPa, elongation of more than 28 percent and density of less than 7.5g/cm 3 And the requirements of high strength and high elongation of the automobile body structural part are met.

Claims (2)

1. A780 MPa-grade light high-strength steel plate is characterized in that the steel contains the following chemical components in percentage by mass: c: 0.15% -0.25%, Si: 1.12% -1.5%, Mn: 1.0% -1.82%, P: 0.03-0.045%, S is less than or equal to 0.03%, and Al: 3.0% -5.0%, Ti: 0.03% -0.2%, Nb: 0.03% -0.2%, Bi: 0.05-0.2 percent, and the balance of Fe and inevitable impurities, wherein the ratio of (13C +2Mn)/(Al +1.2Si) is more than or equal to 0.8 and less than or equal to 1.2; the steel plate structure contains delta-ferrite, alpha-ferrite, bainite, austenite and martensite multiphase structures, and the sum of the contents of the delta-ferrite and the alpha-ferrite is 30-50%, the content of the bainite is 30-50%, the content of the austenite is 10-25% and the content of the martensite is less than 5% in percentage by volume;the thickness of the steel plate is less than 2.5 mm; the tensile strength of the steel plate is more than or equal to 780MPa, the elongation is more than or equal to 28 percent, and the density is less than 7.5g/cm 3 (ii) a The production process of the steel plate comprises the following steps: smelting, continuous casting, hot rolling, acid washing and continuous annealing; and (3) continuous annealing process: the annealing temperature is 800-880 ℃, the annealing heat preservation time is 120-300 s, the cooling rate is 20-60 ℃/s, the aging treatment is carried out when the temperature is cooled to 350-450 ℃, the aging treatment time is 300-800 s, and finally the temperature is cooled to the room temperature at the cooling rate of 10-30 ℃/s.
2. The 780 MPa-grade light-weight high-strength steel plate as claimed in claim 1, wherein in the hot rolling process, the heating temperature of a casting blank is 1200-1250 ℃, the initial rolling temperature is 1000-1150 ℃, the final rolling temperature is 850-930 ℃, and the cooling mode adopts laminar cooling, the cooling rate is more than 20 ℃/s, and the coiling temperature is less than or equal to 240 ℃.
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