CN115125442B - Low-density high-strength steel with low crack rate and preparation method thereof - Google Patents

Low-density high-strength steel with low crack rate and preparation method thereof Download PDF

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CN115125442B
CN115125442B CN202210684337.3A CN202210684337A CN115125442B CN 115125442 B CN115125442 B CN 115125442B CN 202210684337 A CN202210684337 A CN 202210684337A CN 115125442 B CN115125442 B CN 115125442B
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steel
cooling
low
strength steel
temperature
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CN115125442A (en
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姜英花
谢春乾
刘华赛
邱木生
阳锋
王海全
邹英
滕华湘
韩赟
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Shougang Group 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
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold 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
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0242—Flattening; Dressing; Flexing
    • 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
    • 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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • 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
    • C21D2211/005—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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

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  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)

Abstract

The application relates to the field of steel smelting, in particular to low-density high-strength steel with low crack rate and a preparation method thereof; the high-strength steel comprises the following chemical components in percentage by mass: c, si, mn, alt, P, S, N, the balance being Fe and unavoidable impurities; wherein the C, mn, and Alt satisfy: x=28 [ Alt ] -56[ C ] -6[ Mn ] is less than or equal to 35; the method comprises the following steps: obtaining molten steel after smelting; continuously casting the molten steel to obtain a casting blank; firstly heating a casting blank, and then performing rough rolling and finish rolling to obtain a hot rolled plate; carrying out laminar cooling on the hot rolled plate, and then coiling to obtain a hot rolled coil; cold rolling the hot rolled coil, and then continuously annealing to obtain strip steel; flattening the strip steel, and curling to obtain low-density high-strength steel with low crack rate; by limiting the content relation between C, mn and Al, the content stability of delta ferrite and kappa-carbide can be effectively controlled by controlling the content relation between the delta ferrite and the Al, and the low crack rate of the steel plate is ensured.

Description

Low-density high-strength steel with low crack rate and preparation method thereof
Technical Field
The application relates to the field of steel smelting, in particular to low-density high-strength steel with low crack rate and a preparation method thereof.
Background
With the rapid development of the automobile industry, as the automobile mostly consumes non-renewable resources such as fuel oil, the continuously developed automobile industry brings about the problems of energy consumption pressure and tail gas emission pollution, and the automobile weight reduction is one of the most effective measures for improving the fuel oil economic benefit and reducing the automobile tail gas emission; at present, the light weight of automobiles is mainly realized through light weight materials, advanced processes and structural optimization, wherein the light weight materials are mainly adopted.
The existing lightweight materials including high-strength steel, aluminum alloy, magnesium alloy, engineering plastics, composite materials and the like are the lightweight materials which are common and have more application at present; in recent years, the application growth speed of lightweight materials in various fields is rapid, the lightweight development progress of steel materials is directly threatened, the lightweight of the steel materials is limited by simply realizing the lightweight by a high-ductility high-strength steel plate, and a new method for realizing the lightweight of the steel materials is further required to be searched.
The novel advanced steel developed by combining the concepts of light materials and high-strength steel is one of the research directions for realizing the light weight of the automobile steel materials. The novel advanced steel is prepared by adding a certain amount of light element Al into the chemical components of the original advanced high-strength steel, and then performing heat treatment to obtain the low-density high-strength steel with high strength and high toughness for the automobile; however, as the amount of Al added increases, a certain proportion remains in the delta ferrite up to the normal temperature state below the freezing point, and at the same time, the residual delta ferrite forms brittle kappa-carbide ((Fe, mn) 3 AlC), and at the time of hot rolling, the delta ferrite and the kappa-carbide form specific regions, which cause cracks at the edge of the hot rolled sheet, which cause cracking problems during the subsequent cold rolling.
Therefore, how to reduce the crack rate of low-density high-strength steel under the condition of high Al content is a technical problem to be solved urgently.
Disclosure of Invention
The application provides low-density high-strength steel with low crack rate and a preparation method thereof, which are used for solving the technical problem that the low-density high-strength steel is difficult to reduce under the condition of high Al content in the prior art.
In a first aspect, the present application provides a low-density high-strength steel with a low crack rate, comprising the following chemical components in mass fraction: 0.3 to 0.5 percent of C, 0.2 to 0.5 percent of Si, mn:5% -15%, alt:3 to 5 percent, P is less than or equal to 0.01 percent, S is less than or equal to 0.01 percent, N is less than or equal to 0.004 percent, and the balance is Fe and unavoidable impurities;
wherein the C, mn, and Alt satisfy:
X＝28[Alt]-56[C]-6[Mn]≤35；
wherein [ C ] is the mass fraction of C, [ Mn ] is the mass fraction of Mn, and [ Alt ] is the mass fraction of Alt.
Optionally, the microstructure of the high-strength steel includes, in volume fractions:
retained austenite: 20% -30%, ferrite: 15% -20% of martensite: 50% -65%.
In a second aspect, the present application provides a method of preparing the high strength steel of the first aspect, the method comprising:
obtaining molten steel after smelting;
continuously casting the molten steel to obtain a casting blank;
firstly heating the casting blank, and then performing rough rolling and finish rolling to obtain a hot rolled plate;
performing laminar cooling on the hot rolled plate, and then coiling to obtain a hot rolled coil;
cold rolling the hot rolled coil, and then continuously annealing to obtain strip steel;
and flattening the strip steel, and curling to obtain the low-density high-strength steel with low crack rate.
Optionally, the continuous annealing includes preheating, second heating, first holding, first cooling, aging, and second cooling.
Optionally, the preheating end point temperature is 210-230 ℃, and the preheating heating speed is 8-12 ℃/s;
the end temperature of the second heating is 750-830 ℃, and the heating rate of the second heating is 1.5-4 ℃/s.
Optionally, the first heat preservation time is 60 s-100 s.
Optionally, the end temperature of the first cooling is 650-700 ℃, the cooling speed of the first cooling is 8-12 ℃/s, the end temperature of the second cooling is 150-170 ℃, and the cooling speed of the second cooling is 2-4 ℃/s.
Optionally, the aging treatment comprises a third cooling and a second heat preservation, wherein the end temperature of the third cooling is 300-400 ℃, and the time of the second heat preservation is 300-400 s.
Optionally, the end point temperature of the first heating is 1200 ℃ to 1250 ℃, the finish rolling temperature of the finish rolling is 900 ℃ to 1000 ℃, and the coiling temperature is 550 ℃ to 600 ℃.
Optionally, the reduction rate of the cold rolling is 50% -60%.
Compared with the prior art, the technical scheme provided by the embodiment of the application has the following advantages:
according to the low-density high-strength steel with low crack rate, the contents of C, si, mn and Al are respectively limited, the contents of harmful elements P and S are also limited, and the content relation between C, mn and Al is limited, so that the content stability of delta ferrite and kappa-carbide can be effectively controlled by controlling the content relation between the delta ferrite and the kappa-carbide, a special area is prevented from being formed between the delta ferrite and the kappa-carbide, cracks at the edge of the steel are avoided, the content of C, mn is controlled, residual austenite can be obtained, the microstructure of the steel is improved, the generation of cracks on the surface of the steel is further avoided, and the low crack rate of the steel plate is further ensured.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the application and together with the description, serve to explain the principles of the application.
In order to more clearly illustrate the embodiments of the application or the technical solutions of the prior art, the drawings which are used in the description of the embodiments or the prior art will be briefly described, and it will be obvious to a person skilled in the art that other drawings can be obtained from these drawings without inventive effort.
Fig. 1 is a schematic flow chart of a method according to an embodiment of the present application.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present application more apparent, the technical solutions of the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application, and it is apparent that the described embodiments are some embodiments of the present application, but not all embodiments of the present application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
In one embodiment of the application, a low-density high-strength steel with low crack rate is provided, and the chemical components of the high-strength steel comprise in mass fraction: 0.3 to 0.5 percent of C, 0.2 to 0.5 percent of Si, mn:5% -15%, alt:3 to 5 percent, P is less than or equal to 0.01 percent, S is less than or equal to 0.01 percent, N is less than or equal to 0.004 percent, and the balance is Fe and unavoidable impurities;
wherein the C, mn, and Alt satisfy:
X＝28[Alt]-56[C]-6[Mn]≤35；
wherein [ C ] is the mass fraction of C, [ Mn ] is the mass fraction of Mn, and [ Alt ] is the mass fraction of Alt.
In the embodiment of the application, the positive effect that the mass fraction of C is 0.3-0.5% is that in the mass fraction range, because the C element is the most important solid solution strengthening element in the steel and the element for ensuring the hardenability of austenite, proper C content can ensure that the steel obtains enough martensite in the cooling process so as to ensure the strength of the steel, and meanwhile, C and Mn can mutually influence so as to obtain a certain amount of residual austenite, improve the microstructure of the steel and further avoid the generation of cracks on the surface of the steel; when the value of the mass fraction is smaller than the minimum value of the end point of the range, the content of C is too low, enough martensite and a certain amount of residual austenite cannot be obtained, the strength of the steel cannot be ensured, and meanwhile, the edge of the steel is easy to crack.
The positive effect of the Si with the mass fraction of 0.2-0.5% is that in the mass fraction range, because Si is a solid solution strengthening element of the steel, the austenite hardenability can be improved, meanwhile, the ferrite phase can be purified, and the elongation of the steel can be improved, so that the good mechanical property of the edge of the steel can be ensured, and the probability of cracking of the steel can be reduced; when the value of the mass fraction is smaller than the minimum value of the end point of the range, the Si content is too low, the austenite hardenability cannot be improved, the elongation of the steel is too low, and the steel is easy to be brittle.
The mass fraction of Mn is 5% -15%, and in the mass fraction range, because Mn is an important element for solid solution strengthening and stabilizing austenite, the Mn plays an important role in strengthening the mechanical properties of steel, and enough Mn forms a certain amount of residual austenite with C; when the mass fraction is smaller than the minimum value of the end point of the range, the Mn content is insufficient, the effects of solid solution strengthening and austenite stabilizing cannot be effectively achieved, and meanwhile, sufficient residual austenite cannot be obtained.
The Al has the positive effects that the Al has a deoxidization effect within the mass fraction range, and ensures the cold forming performance of the steel, thereby promoting the steel plate to be completely formed and avoiding the cracking of the steel plate; when the value of the mass fraction is smaller than the minimum value of the end point of the range, the deoxidization in the steel cannot be ensured to be clean due to insufficient content of Al, so that the cold forming performance of the steel is affected.
The positive effect of P being less than or equal to 0.01 percent is that in the mass fraction range, the P can inhibit the formation of carbide, and the carbon equivalent of the whole steel can be ensured to be in a proper range; when the mass fraction is larger than the end point maximum value of the range, carbide is caused to be biased at the grain boundary, the grain boundary strength is reduced, the mechanical properties of the material are deteriorated, and the risk of cracking of the steel is increased.
The positive effect of S being less than or equal to 0.01 percent is that in the mass fraction range, S is a harmful element and can be combined with Mn to generate MnS, so that the mechanical property of the steel is deteriorated and the risk of cracking the steel is increased; when the mass fraction is larger than the maximum value of the end point of the range, the S content is excessive, on one hand, the use amount of Al is increased, and on the other hand, the mechanical properties of the steel are weaker, and the risk of cracking of the steel is increased.
In the range of the mass fraction, N forms a precipitated phase and is easy to enrich in a crystal boundary, so that the strength of the crystal boundary is reduced to deteriorate the mechanical property of the material, and the risk of cracking of steel is increased; when the mass fraction is larger than the end point maximum value of the range, the N content is excessive, the educts are increased, the performance of the steel is affected, and the cracking risk of the steel is increased.
The positive effects of 28 Alt-56C-6 Mn-35 are that in the range of the mass fraction relation, the content stability of delta ferrite and kappa-carbide can be effectively controlled by controlling the content relation among the three, thereby preventing the delta ferrite and kappa-carbide from forming a special area and avoiding the edge of steel from cracking; when the relation value of the mass fraction ranges is larger than the end value of the range, the delta ferrite and kappa-carbide content can not be effectively controlled to be stable, so that the edge quality of the steel is affected.
In some alternative embodiments, the microstructure of the high strength steel comprises, in volume fractions:
retained austenite: 20% -30%, ferrite: 15% -20% of martensite: 50% -65%.
In the embodiment of the application, the volume fraction of the residual austenite is 20-30%, and the positive effect is that the toughness of the steel can be improved to a certain extent within the volume fraction range, so that the excellent mechanical property of the steel is ensured, and the edge cracking of the steel is avoided; when the volume fraction is larger than the end value of the range, the strength of the steel is deteriorated and the service life of the steel is affected.
The volume fraction of the martensite is 50% -65%, and the positive effects are that in the range of the volume fraction, the strength of the steel can be ensured to be in a proper range, meanwhile, the steel is ensured to have certain toughness, and the edge of the steel is ensured not to crack; when the volume fraction is larger or smaller than the end value of the range, the whole strength of the steel is unstable, so that the stability of the mechanical property of the steel cannot be ensured.
In one embodiment of the present application, as shown in fig. 1, there is provided a method for preparing a low-density high-strength steel with a low crack rate, the method comprising:
s1, obtaining molten steel after smelting;
s2, continuously casting the molten steel to obtain a casting blank;
s3, performing first heating on the casting blank, and performing rough rolling and finish rolling to obtain a hot rolled plate;
s4, carrying out laminar cooling on the hot rolled plate, and then coiling to obtain a hot rolled coil;
s5, cold rolling the hot rolled coil, and then continuously annealing to obtain strip steel;
s6, flattening the strip steel, and then curling to obtain the low-density high-strength steel with low crack rate.
In some alternative embodiments, the continuous annealing includes preheating, second heating, first holding, first cooling, aging, and second cooling.
In some alternative embodiments, the end temperature of the preheating is 210 ℃ to 230 ℃, and the heating rate of the preheating is 8 ℃/s to 12 ℃/s;
the end temperature of the second heating is 750-830 ℃, and the heating rate of the second heating is 1.5-4 ℃/s.
In the embodiment of the application, the preheating terminal temperature is 210-230 ℃, and the positive effects are that in the temperature range, the recovery of cold deformed ferrite in the hot rolled coil after cold rolling can be ensured, and the subsequent phase change is padded; when the temperature is higher or lower than the end value of the range, the cold deformed ferrite cannot be recovered, and the subsequent phase change is affected.
The preheating temperature rising speed is 8 ℃/s-12 ℃/s, and the positive effects are that in the temperature rising speed range, the cold deformed ferrite recovery speed of the hot rolled coil after cold rolling is ensured to be in a proper range, and the stability of the subsequent phase change is ensured; when the temperature rising speed is greater than or less than the end value of the range, ferrite recovery is insufficient, so that the stability of the subsequent phase change cannot be ensured.
The end temperature of the second heating is 750-830 ℃, and the positive effects are that in the temperature range, the recrystallization of the cold-rolled ferrite can be ensured, and meanwhile, the pearlite is firstly transformed into austenite and the length of the pearlite is large; when the temperature is higher than the end maximum value of the range, the adverse effect is that the austenite fraction is too high due to the high temperature, so that the stability of the retained austenite is difficult to be ensured, and when the temperature is lower than the end minimum value of the range, the adverse effect is that the temperature is too low, the ferrite lacks recrystallization, and the ductility is not sufficiently ensured.
The heating rate of the second heating is 1.5 ℃/s to 4 ℃/s, and the positive effects are that in the temperature range, the stable operation in the process of the recrystallization of the cold-rolled ferrite can be ensured, meanwhile, the stable rate of the pearlite firstly converted into austenite and growing to the ferrite can be ensured, and the mechanical property of the steel is further ensured, so that the crack rate of the steel is reduced; when the temperature rise rate is greater than or less than the end value of the range, the recrystallization process is not stably performed, and the rate at which austenite reaches ferrite is not stable.
In some alternative embodiments, the first incubation time is between 60s and 100s.
In the embodiment of the application, the positive effect that the time of the first heat preservation is 60-100 s is that in the time range, C, mn element in ferrite can be ensured to be transferred into austenite and homogenized in the austenite, so that partial austenitization is realized; when the time value of the first heat preservation is larger or smaller than the end value of the range, the austenitizing process cannot be fully performed, incomplete conversion in the steel is caused, and the strength of the steel is affected.
In some alternative embodiments, the end temperature of the first cooling is 650 ℃ to 700 ℃, the cooling rate of the first cooling is 8 ℃/s to 12 ℃/s, the end temperature of the second cooling is 150 ℃ to 170 ℃, and the cooling rate of the second cooling is 2 ℃/s to 4 ℃/s.
In the embodiment of the application, the end temperature of the first cooling is 650-700 ℃, and the positive effects are that in the temperature range, the austenite part is ensured to be transferred into ferrite, elements such as C, mn are further gathered into austenite, so that the mechanical property of the steel can be ensured, and the low crack rate of the steel is further ensured; when the temperature is higher or lower than the end point value of the range, the process of converting austenite into ferrite is influenced, the mechanical property of the steel cannot be ensured, and the low crack rate of the steel cannot be ensured.
The positive effect of the cooling speed of the first cooling is 8-12 ℃/s, in the cooling speed range, the proper speed of austenite to ferrite transformation can be ensured, so that the amount of the final residual austenite is ensured, the mechanical property of the steel is ensured, and the low crack rate of the steel is ensured; when the temperature rising speed is larger or smaller than the end value of the range, the transformation speed from austenite to ferrite is unstable, the amount of the final residual austenite is insufficient, and the mechanical property of the steel is affected.
The end temperature of the second cooling is 150-170 ℃, and the positive effect is that in the temperature range, a part of unstable austenite can be ensured to be converted into martensite, so that the strength of the steel can be improved, and the risk of cracking of the steel is reduced; when the temperature is higher or lower than the end point value of the range, unstable austenite cannot be converted into martensite, so that the strength of the steel cannot be improved, and the risk of cracking of the steel cannot be reduced.
The positive effect of the cooling speed of the second cooling is 2 ℃/s-4 ℃/s, and in the range of the cooling speed, the process of converting partial unstable austenite into martensite can be ensured to be more stable, so that the strength of the steel can be effectively improved, and the risk of cracking of the steel is reduced; when the temperature rising speed is greater than or less than the end value of the range, the unstable phase of converting partial unstable austenite into martensite is caused, and the generation of martensite is influenced, so that the strength of the steel cannot be effectively improved, and the risk of cracking of the steel cannot be reduced.
In some alternative embodiments, the aging treatment includes a third cool down having an end temperature of 300 ℃ to 400 ℃ and a second hold down for a period of 300s to 400s.
In the embodiment of the application, the end temperature of the third cooling is 300-400 ℃, and the positive effect is that in the temperature range, the aging treatment can be ensured under the condition of low temperature, so that a hard phase with a certain content can be obtained, the stability of the strength of the steel is ensured, and the risk of cracking of the steel is further reduced.
The positive effect of the second heat preservation time of 300-400 s is that the inclusions can be effectively converted into a hard phase within the time range, so that the strength of the steel is improved; when the time is greater or less than the end of the range, the overall time consumption increases, and the formation of the hard phase cannot be ensured.
In some alternative embodiments, the end temperature of the first heating is 1200 ℃ to 1250 ℃, the finish rolling temperature of the finish rolling is 900 ℃ to 1000 ℃, and the coiling temperature is 550 ℃ to 600 ℃.
In the embodiment of the application, the end temperature of the first heating is 1200-1250 ℃, and the positive effect is that in the temperature range, the casting blank can be ensured to perform phase change in the temperature range, thereby facilitating the subsequent rough rolling and finish rolling and ensuring the mechanical property of the subsequent steel plate; when the temperature is higher or lower than the end value of the range, the phase change of the casting blank is insufficient, and the follow-up rough rolling and finish rolling are affected.
The finish rolling temperature of the finish rolling is 900-1000 ℃, and the positive effect is that in the temperature range, the thermal deformation resistance and extensibility of the steel plate can be ensured to be in a proper range, thereby ensuring the smooth rolling; when the temperature is higher or lower than the end of the range, the heat distortion resistance increases, precipitation of kappa-carbide occurs, and the ductility of the steel sheet decreases, which makes rolling difficult.
The coiling temperature is 550-600 ℃, and the positive effect is that in the temperature range, the kappa-carbide content can be ensured to be in a proper range, so that the good mechanical property of the coiled steel is ensured, and the smooth proceeding of the subsequent cold rolling stage is ensured; when the temperature is higher or lower than the end value of the range, precipitation of kappa-carbide is caused, and the steel remains in cold rolling, and the ductility of the steel in the cold rolling stage is adversely affected.
In some alternative embodiments, the cold rolling reduction is 50% to 60%.
In the embodiment of the application, the rolling reduction of the cold rolling is 50-60%, and the rolling reduction is within the range of the rolling reduction, so that the cold rolling process is facilitated, the microstructure rolling uniformity in the cold rolling stage is ensured, the excellent mechanical property of the steel is ensured, and the crack rate of the steel is reduced; when the reduction ratio is larger or smaller than the end value of the range, the microstructure rolling in the cold rolling stage is uneven, and the mechanical property of the steel is affected.
The chemical compositions of the high-strength steels of each example and comparative example are shown in table 1:
table 1 table of chemical component contents of the respective high-strength steel products
The process parameters conditions for each example and comparative example are shown in Table 2
TABLE 2 Condition tables of various production process parameters
The performance parameters of the steel products obtained in each of the examples and comparative examples are shown in Table 3:
TABLE 3 mechanical properties parameters and cracking conditions of high-strength steel products
Group of Tensile strength (MPa) Yield strength (MPa) Elongation A50 (%) Whether or not to crack
Example 1 1186 815 27.6 Whether or not
Example 2 1140 775 25 Whether or not
Example 3 1019 715 35 Whether or not
Example 4 995 685 32 Whether or not
Comparative example 1 1085 727 20.1 Is that
Comparative example 1 1120 769 23.2 Is that
Specific analysis of table 3:
the yield strength refers to the yield limit of the prepared steel plate when the yield phenomenon occurs, namely the stress resisting micro plastic deformation, and the higher the yield strength, the higher the yield limit of the steel plate.
The tensile strength refers to the maximum stress value which can be born by the prepared steel plate before the steel plate is broken, and the larger the tensile strength is, the larger the maximum stress value which can be born by the steel plate before the steel plate is broken.
The elongation after breaking refers to the percentage of the elongation of the gauge length of the steel plate after breaking to the original gauge length, and the higher the elongation after breaking, the better the toughness of the steel plate.
From the data of examples 1-4, it can be seen that:
by adopting the method, the contents of C, si, mn and Al are respectively limited, the contents of harmful elements P and S are also limited, and the content relation between C, mn and Al is limited, so that the content stability of delta ferrite and kappa-carbide can be effectively controlled by controlling the content relation between the three, and the low crack rate of the steel plate is ensured.
From the data of comparative example 1-N, it can be seen that:
if the content relation between C, mn and Al defined by the application is not adopted, cracking of the steel during rolling is caused.
One or more technical solutions in the embodiments of the present application at least further have the following technical effects or advantages:
(1) According to the high-strength steel provided by the embodiment of the application, the contents of C, si, mn and Al are respectively limited, the contents of harmful elements P and S are also limited, and the content relation between C, mn and Al is limited, so that the content stability of delta ferrite and kappa-carbide can be effectively controlled by controlling the content relation between the three, and the low crack rate of the steel plate is ensured.
(2) The high-strength steel provided by the embodiment of the application can reach tensile strength of 980MPa, yield strength of 680MPa and elongation of more than 25%, and can ensure that cracking does not occur in rolling and product forming stages.
(3) The density of the high-strength steel provided by the embodiment of the application is higher than that of the traditional steel (7.81 g/cm 3 ) The weight of the automobile is reduced by 5 to 7 percent, so the automobile can be applied to the automobile, and the weight of the automobile is reduced substantially.
(4) According to the method provided by the embodiment of the application, the process parameters of the rolling, cooling and continuous annealing stages of the steel are sequentially limited, so that the full progress of each stage can be ensured, and the performance of the steel plate can be ensured to reach the expectations.
It should be noted that in this document, relational terms such as "first" and "second" and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
The endpoints and any values of the ranges disclosed herein are not limited to the precise range or value, and are understood to encompass values approaching those ranges or values. For numerical ranges, one or more new numerical ranges may be found between the endpoints of each range, between the endpoint of each range and the individual point value, and between the individual point value, in combination with each other, and are to be considered as specifically disclosed herein.
The foregoing is only a specific embodiment of the application to enable those skilled in the art to understand or practice the application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (2)

1. A low-density high-strength steel with a low crack rate, characterized in that the chemical components of the high-strength steel include, in mass fraction: 0.3 to 0.5 percent of C, 0.2 to 0.5 percent of Si, mn:5% -15%, alt:3 to 5 percent, P is less than or equal to 0.01 percent, S is less than or equal to 0.01 percent, N is less than or equal to 0.004 percent, and the balance is Fe and unavoidable impurities;
wherein C, mn and Alt satisfy the following content relationship: x=28 [ Alt ] -56[ C ] -6[ Mn ] is less than or equal to 35;
the microstructure of the high-strength steel comprises, in volume fraction:
retained austenite: 20% -30%, ferrite: 15% -20% of martensite: 50% -65%;
the method for preparing the high-strength steel comprises the following steps:
obtaining molten steel after smelting;
continuously casting the molten steel to obtain a casting blank;
firstly heating the casting blank, and then performing rough rolling and finish rolling to obtain a hot rolled plate;
performing laminar cooling on the hot rolled plate, and then coiling to obtain a hot rolled coil;
cold rolling the hot rolled coil, and then continuously annealing to obtain strip steel;
flattening the strip steel, and curling to obtain low-density high-strength steel with low crack rate;
the continuous annealing comprises preheating, second heating, first heat preservation, first cooling, aging treatment and second cooling;
the end temperature of the preheating is 210-230 ℃, and the heating rate of the preheating is 8-12 ℃/s;
the end temperature of the second heating is 750-830 ℃, and the heating rate of the second heating is 1.5-4 ℃/s;
the first heat preservation time is 60-100 s;
the end temperature of the first cooling is 650-700 ℃, the cooling speed of the first cooling is 8-12 ℃/s, the end temperature of the second cooling is 150-170 ℃, and the cooling speed of the second cooling is 2-4 ℃/s;
the aging treatment comprises third cooling and second heat preservation, wherein the end temperature of the third cooling is 300-400 ℃, and the time of the second heat preservation is 300-400 s;
the final temperature of the first heating is 1200-1250 ℃, the final rolling temperature of the finish rolling is 900-1000 ℃, and the coiling temperature is 550-600 ℃.
2. The high-strength steel according to claim 1, wherein the cold rolling reduction is 50% to 60%.
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CN104928456A (en) * 2015-06-30 2015-09-23 宝山钢铁股份有限公司 Manufacturing method for improving extensibility of commonly-cooled ferrite lightweight steel
CN104928568A (en) * 2015-06-30 2015-09-23 宝山钢铁股份有限公司 Ferrite low-density high-strength steel and manufacturing method thereof
KR101816439B1 (en) * 2016-09-13 2018-01-08 현대자동차주식회사 High strength low carbon light-weight steel and method of manufacturing the same
CN108950392A (en) * 2018-07-19 2018-12-07 首钢集团有限公司 A kind of superelevation ductility low density steel and preparation method thereof
CN109136761A (en) * 2018-09-26 2019-01-04 首钢集团有限公司 A kind of 980MPa grades high ductility low-density automobile austenitic steel and preparation method thereof
CN109554621A (en) * 2018-12-03 2019-04-02 东北大学 A kind of low-density Fe-Mn-Al-C hot rolling Q&P steel and its manufacturing method
KR102245227B1 (en) * 2019-11-25 2021-04-28 주식회사 포스코 Clad steel sheet having excellent strength, formability and galvanizability, and method for manufacturing thereof

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104928456A (en) * 2015-06-30 2015-09-23 宝山钢铁股份有限公司 Manufacturing method for improving extensibility of commonly-cooled ferrite lightweight steel
CN104928568A (en) * 2015-06-30 2015-09-23 宝山钢铁股份有限公司 Ferrite low-density high-strength steel and manufacturing method thereof
KR101816439B1 (en) * 2016-09-13 2018-01-08 현대자동차주식회사 High strength low carbon light-weight steel and method of manufacturing the same
CN108950392A (en) * 2018-07-19 2018-12-07 首钢集团有限公司 A kind of superelevation ductility low density steel and preparation method thereof
CN109136761A (en) * 2018-09-26 2019-01-04 首钢集团有限公司 A kind of 980MPa grades high ductility low-density automobile austenitic steel and preparation method thereof
CN109554621A (en) * 2018-12-03 2019-04-02 东北大学 A kind of low-density Fe-Mn-Al-C hot rolling Q&P steel and its manufacturing method
KR102245227B1 (en) * 2019-11-25 2021-04-28 주식회사 포스코 Clad steel sheet having excellent strength, formability and galvanizability, and method for manufacturing thereof

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