CN115558844A - 1180 MPa-grade steel, galvanized steel, preparation method of galvanized steel and automobile accessory - Google Patents
1180 MPa-grade steel, galvanized steel, preparation method of galvanized steel and automobile accessory Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 125
- 239000010959 steel Substances 0.000 title claims abstract description 125
- 229910001335 Galvanized steel Inorganic materials 0.000 title claims abstract description 32
- 239000008397 galvanized steel Substances 0.000 title claims abstract description 32
- 238000002360 preparation method Methods 0.000 title claims abstract description 13
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- 239000012535 impurity Substances 0.000 claims abstract description 8
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- 229910052717 sulfur Inorganic materials 0.000 claims abstract description 7
- 229910001566 austenite Inorganic materials 0.000 claims description 37
- 238000010438 heat treatment Methods 0.000 claims description 37
- 238000001816 cooling Methods 0.000 claims description 34
- 238000000034 method Methods 0.000 claims description 31
- 229910000859 α-Fe Inorganic materials 0.000 claims description 24
- 229910000734 martensite Inorganic materials 0.000 claims description 23
- 238000005246 galvanizing Methods 0.000 claims description 21
- 230000008569 process Effects 0.000 claims description 20
- 239000011159 matrix material Substances 0.000 claims description 16
- 230000000717 retained effect Effects 0.000 claims description 15
- 238000000137 annealing Methods 0.000 claims description 13
- 229910001563 bainite Inorganic materials 0.000 claims description 13
- 230000003647 oxidation Effects 0.000 claims description 12
- 238000007254 oxidation reaction Methods 0.000 claims description 12
- 238000009749 continuous casting Methods 0.000 claims description 11
- 239000000463 material Substances 0.000 claims description 10
- 238000005096 rolling process Methods 0.000 claims description 10
- 238000010583 slow cooling Methods 0.000 claims description 10
- 238000002791 soaking Methods 0.000 claims description 10
- 239000000126 substance Substances 0.000 claims description 8
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- 238000005097 cold rolling Methods 0.000 claims description 5
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- 230000000052 comparative effect Effects 0.000 description 15
- 229910000797 Ultra-high-strength steel Inorganic materials 0.000 description 12
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Images
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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
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D63/00—Motor vehicles or trailers not otherwise provided for
- B62D63/02—Motor vehicles
- B62D63/04—Component parts or accessories
-
- 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
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- 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
- C21D6/002—Heat treatment of ferrous alloys containing Cr
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- 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
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- 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
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- 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
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- 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
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- 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
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- 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
- C21D8/0273—Final recrystallisation annealing
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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
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
- C23C2/06—Zinc or cadmium or alloys based thereon
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
- C23C2/36—Elongated material
- C23C2/40—Plates; Strips
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- 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
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- 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
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- 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
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- 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
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- 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
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Abstract
The invention provides 1180 MPa-grade steel, galvanized steel, a preparation method of the galvanized steel and automobile accessories, and belongs to the technical field of steel preparation, wherein the 1180 MPa-grade steel comprises the following components: C. si, mn, cr, nb, P, S, N, fe and impurities from the preparation of the 1180 MPa-grade steel; in 1180 MPa-grade steel, the content of Si is as follows by mass fraction: 0.5 to 1 percent; the content of the Cr is as follows: 0.3 to 0.8 percent; the content of Nb is as follows: 0.015 to 0.03 percent. The application provides a 1180MPa level steel, under guaranteeing 1180MPa level tensile strength, has the characteristic of high yield strength and high elongation simultaneously, can satisfy current auto-parts like user demand such as high elongation, high yield, bendability, reaming nature.
Description
Technical Field
The application relates to the technical field of steel preparation, in particular to 1180 MPa-grade steel, galvanized steel, a preparation method of the galvanized steel and automobile accessories.
Background
With the development of automobiles in the direction of energy conservation, environmental protection, safety and comfort, the requirements on corrosion resistance and impact resistance are higher and higher while the automobile body is developed in the direction of light weight. The steel sheet for automobile is forced to develop a high strength by coating treatment by adding a competitive pressure from materials such as aluminum, magnesium, plastics, etc. With the increasing use of coated ultra-high strength steel sheets, the requirements for formability, such as high elongation, high yield, bendability, hole expansibility, etc., are also increasing.
At present, dual-phase steel mainly comprising ferrite and martensite is most widely applied, but the steel has extremely low yield strength, and the ultrahigh-strength steel cannot have high yield strength and high elongation at the same time under the condition of ensuring 1180MPa tensile strength.
Disclosure of Invention
The embodiment of the application provides 1180 MPa-grade steel, galvanized steel, a preparation method of the galvanized steel and automobile accessories, and aims to solve the technical problem that the conventional 1180 MPa-grade ultrahigh-strength steel cannot have both high yield strength and high elongation.
In a first aspect, an embodiment of the present application provides a 1180 MPa-grade steel, where the 1180 MPa-grade steel includes the following components: C. si, mn, cr, nb, P, S, N, fe and impurities from the preparation of the 1180 MPa-grade steel;
in 1180 MPa-grade steel, the content of Si is as follows by mass fraction: 0.5 to 1 percent; the content of the Cr is as follows: 0.3 to 0.8 percent; the content of Nb is as follows: 0.015 to 0.03 percent.
Further, the 1180 MPa-grade steel comprises the following components in percentage by mass:
c:0.19 to 0.22 percent, si:0.5% -1%, mn: 1.8-2.5%, cr:0.3% -0.8%, nb: 0.015-0.03%, P is less than or equal to 0.01%, S is less than or equal to 0.01%, N is less than or equal to 0.004%, and the balance of Fe and impurities from 1180 MPa-grade steel.
Further, the metallographic structure of 1180 MPa-grade steel comprises, by volume fraction: 65-80% of hard martensite bainite phase matrix; 5 to 10 percent of retained austenite; 10 to 30 percent of ferrite.
Further, the grain size of the hard martensite bainite phase matrix is 0.5-1 μm; the grain size of the retained austenite is 0.2-0.5 μm; the grain size of the ferrite is 1.5-2.5 μm.
Further, the yield strength of the 1180 MPa-grade steel is more than 850MPa, and the A50 elongation is more than 15%.
In a second aspect, embodiments of the present application provide a galvanized steel including a steel body substrate and a galvanized layer attached to a surface of the steel body substrate,
the steel body base material is 1180 MPa-grade steel material in the first aspect.
In a third aspect, embodiments of the present application provide a method for preparing a galvanized steel according to the second aspect, where the method includes:
obtaining a continuous casting slab containing the same chemical components of 1180 MPa-grade steel in the first aspect;
heating, rough rolling and finish rolling the continuous casting plate blank to obtain a hot rolled plate;
cooling the hot rolled plate, and then coiling to obtain a hot rolled coil;
cold rolling the hot rolled coil to obtain a cold hard coil;
continuously annealing the cold hard coil to obtain annealed strip steel;
and carrying out hot galvanizing on the annealed strip steel to obtain galvanized steel.
Further, the continuous annealing comprises a preheating section, an oxidation section, a heating section, a soaking section, a slow cooling section and a quick cooling section;
the preheating section comprises: heating the mixture to 210-230 ℃ from room temperature at the speed of 8-12 ℃/s;
the oxidation section comprises: heating to 640-660 ℃ from 210-230 ℃ at the speed of 3-8 ℃/s;
the heating section includes: heating to 850-990 ℃ from 640-660 ℃ at the rate of 1-3 ℃/s;
the soaking section comprises: keeping the temperature at 850-990 ℃ and keeping the temperature for 60-150 s;
the slow cooling section comprises: cooling from 850-990 ℃ to 760-840 ℃ at the speed of 2-6 ℃/s;
the rapid cooling section comprises: cooling from 760 ℃ to 840 ℃ at the rate of 20 ℃/s to 40 ℃/s to 250 ℃ to 350 ℃, and keeping the temperature for 60s to 120s.
Further, the hot galvanizing process parameters comprise: the hot galvanizing temperature is 450-460 ℃, the temperature is cooled to 420-430 ℃ after the galvanizing is finished, and then the temperature is cooled to 250-300 ℃ from 420-430 ℃ at the speed of 6-9 ℃/s.
In a fourth aspect, embodiments of the present application provide an automobile part made of the 1180MPa grade steel of the first aspect, and/or the galvanized steel of the third aspect.
Compared with the prior art, the technical scheme provided by the embodiment of the application has the following advantages:
the embodiment provides 1180 MPa-grade steel, which is 1180 MPa-grade ultrahigh-strength steel, and the ultrahigh-strength steel has the characteristics of high yield strength and high elongation by controlling the dosage of Si, cr and Nb in the 1180 MPa-grade steel. The main principle is as follows: controlling the content of Si as follows: 0.5% -1%, can forbid the cementite to separate out, make the carbon enrich in the austenite, obtain the austenite of certain content, raise the elongation; meanwhile, the soft phase strength is improved, the hardness difference between the hard phase and the soft phase is reduced, and the low-temperature hard phase group is refined; controlling the content of Cr as follows: 0.3 to 0.8 percent, ensures the content of the introduced required hard phase, refines the low-temperature hard phase structure and improves the yield strength; controlling the content of Nb as follows: 0.015-0.03%, can refine the microstructure and improve the yield strength.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description, serve to explain the principles of the invention.
In order to more clearly illustrate the embodiments or technical solutions in the prior art of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious for those skilled in the art to obtain other drawings without inventive labor.
FIG. 1 is a schematic flow chart of a method for preparing a galvanized steel according to an embodiment of the present application;
FIG. 2 is a metallographic structure diagram of 1180MPa grade galvanized high-strength steel manufactured in example 1 of the present invention.
Detailed Description
The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that these specific embodiments and examples are for the purpose of illustrating the invention and are not to be construed as limiting the invention.
Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. If there is a conflict, the present specification will control.
Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.
With the development of automobiles in the direction of energy conservation, environmental protection, safety and comfort, the requirements on corrosion resistance and impact resistance are higher and higher while the automobile body is developed in the direction of light weight. The steel sheet for automobile is forced to develop a high strength by coating treatment by adding a competitive pressure from materials such as aluminum, magnesium, plastics, etc. With the increasing use of coated ultra-high strength steel sheets, the requirements for formability, such as high elongation, high yield, bendability, hole expansibility, etc., are also increasing.
At present, dual-phase steel mainly comprising ferrite and martensite is most widely applied, but the steel has extremely low yield strength, the yield strength is difficult to reach more than 850MPa under the condition of ensuring 1180MPa tensile strength, and the high rigidity in a use state is difficult to reach. Although the yield strength is improved by flattening the pre-yield, the intrinsic structure is unchanged, and the material is easy to crack in the subsequent forming process. The introduction of the secondary hard phase or precipitates can increase the yield strength, but at the same time, a certain elongation is lost, and it is difficult to achieve both high yield strength and high elongation in the ultrahigh-strength steel.
Therefore, how to prepare 1180MPa grade galvanized high-strength steel, which has ultrahigh-strength steel and high yield strength and elongation rate, is a technical problem to be solved urgently.
In order to solve the technical problems, the embodiment of the invention provides the following general ideas:
in a first aspect, an embodiment of the present application provides a 1180 MPa-grade steel, where the 1180 MPa-grade steel includes the following components: C. si, mn, cr, nb, P, S, N, fe and impurities from the preparation of the 1180 MPa-grade steel;
in 1180 MPa-grade steel, the content of Si is as follows by mass fraction: 0.5 to 1 percent; the content of the Cr is as follows: 0.3 to 0.8 percent; the content of Nb is as follows: 0.015 to 0.03 percent.
The embodiment provides 1180 MPa-grade steel, which is 1180 MPa-grade ultrahigh-strength steel, and the ultrahigh-strength steel has the characteristics of high yield strength and high elongation rate at the same time by controlling the dosage of Si, cr and Nb in the 1180 MPa-grade steel. The main principle is as follows: controlling the content of Si as follows: 0.5% -1%, can forbid the cementite to separate out, make carbon enrich in austenite, obtain austenite of certain content, raise the elongation; meanwhile, the soft phase strength is improved, the hardness difference between the hard phase and the soft phase is reduced, and the low-temperature hard phase group is refined; controlling the content of Cr as follows: 0.3 to 0.8 percent, ensures the content of the introduced required hard phase, refines the low-temperature hard phase structure and improves the yield strength; controlling the content of Nb as follows: 0.015-0.03%, can refine the microstructure and improve the yield strength.
As an implementation manner of the embodiment of the present application, the 1180 MPa-grade steel includes the following components by mass fraction:
c:0.19 to 0.22 percent, si:0.5% -1%, mn: 1.8-2.5%, cr:0.3% -0.8%, nb:0.015 to 0.03 percent, less than or equal to 0.01 percent of P, less than or equal to 0.01 percent of S, less than or equal to 0.004 percent of N, and the balance of Fe and impurities from 1180 MPa-grade steel.
The control principle in the design of each chemical component in the application is as follows:
c:0.19 to 0.22 percent, and C is the most effective solid solution strengthening element and the most important element for ensuring the content of the hard phase of the steel, so the weight percentage content of C needs to be controlled within 0.19 to 0.22 percent, and if the weight percentage content is too small, the content of the hard phase cannot be ensured, the required strength is difficult to achieve, and if the weight percentage content is too large, the weldability is deteriorated.
Si:0.5 to 1 percent of Si is an important element for inhibiting the precipitation of cementite, so the weight percentage of Si needs to be controlled between 0.5 and 1 percent, and the precipitation of cementite is difficult to inhibit when the content is too small, thereby generating a small amount of retained austenite, influencing the ductility of steel and greatly deteriorating the galvanizability.
Mn:1.8 to 2.5 percent of Mn, which is an important element for stabilizing austenite while being a solid solution strengthening element, so that the weight percentage of Mn is controlled to be 1.8 to 2.5 percent, and if the Mn is too small, the hard phase of steel is difficult to ensure, and the high strength is difficult to achieve, and the processability and the weldability are greatly deteriorated.
Cr: 0.3-0.8%, and Cr is a solid solution strengthening element to improve hardenability and steel plate strength. The invention controls the weight percentage content of Cr to be 0.3-0.8%, and if the weight percentage content is too small, the hard phase of steel is difficult to ensure, the high strength is difficult to achieve, and the processability is greatly deteriorated.
Nb:0.015% -0.03%, nb can refine the grain effectively and improve the steel structure homogeneity, therefore the invention controls Nb content at 0.015% -0.03%, too small plays no role in grain refinement, too big worsens ductility.
P: phosphorus tends to significantly reduce the plasticity and toughness of steel, so the content is required to be as low as possible, and the content of P by weight needs to be controlled to be less than 0.01%.
S: s is a harmful impurity element in steel, causes hot brittleness of steel, reduces ductility and toughness of steel, and causes cracks in forging and rolling. Therefore, the weight percentage of S is controlled to be below 0.01 percent.
N is less than or equal to 0.004 percent, and nitrogen is a solid solution element like carbon. The stamping processability of the steel is deteriorated along with the increase of the content of N in the steel, and meanwhile, the solid solution of N is a main reason for aging of a finished galvanized sheet, particularly the influence of nitrogen on the strain aging effect after flattening is large, so that the N is required to be as low as possible. For the tin plate of the present invention, the N content in the steel should be controlled to be 0.004% or less.
As an implementation manner of the embodiment of the present application, the metallographic structure of 1180 MPa-grade steel includes, by volume fraction: 65-80% of hard martensite bainite phase matrix; 5 to 10 percent of retained austenite; 10 to 30 percent of ferrite.
In the present application, the metallographic structure of the steel includes 65% to 80% of a matrix of a hard bainite martensite phase, which can provide strength, 5% to 10% of retained austenite and 10% to 30% of ferrite provide ductility of the steel, and a uniform structure composition provides high yield strength. If the hard bainite martensite phase matrix is less than 65% and has insufficient strength, and if it is more than 80%, residual austenite and ferrite are insufficient, which may result in poor ductility of the steel.
In the present application, austenite is a phase of iron, another common phase is martensite, supercooled austenite means austenite that does not undergo martensitic transformation at a certain supercooling degree, and retained austenite means austenite that does not undergo martensitic transformation and remains in a certain amount. The hard martensite bainite phase matrix refers to a combination of bainite and martensite.
As an embodiment of the embodiments of the present application, the hard martensite bainite phase matrix has a grain size of 0.5 μm to 1 μm; the grain size of the residual austenite is 0.2-0.5 mu m; the grain size of the ferrite is 1.5-2.5 μm.
In the application, the metallographic structure of 1180 MPa-grade steel is a uniform structure with a refined hard phase structure as a matrix. The hard bainitic ferrite phase matrix is different from general ferrite, and bainitic ferrite is lath-shaped ferrite with high dislocation density and improves the strength like martensite. In addition, fine film-like retained austenite is easily formed between grain boundaries of lathy bainitic ferrite, and extremely excellent workability can be obtained. The second phase of the steel is fine film-like retained austenite between lath hard phases, and when the second phase structure is coarse block-like retained austenite, it is easily transformed into coarse martensite phase under stress load. Such martensite has a hardness difference from other structures, and voids are likely to be generated at the interface of the hardness difference. When the generated voids are connected to each other, they are likely to be broken, which results in a decrease in workability. Further, when coarse bulk martensite exists in the vicinity of the grain boundary, martensite itself may become a starting point of fracture. The hard phase matrix in the structure provides strength, the retained austenite and ferrite provide ductility of the steel, and the uniform structure provides high yield strength.
As an implementation mode of the embodiment of the application, the yield strength of 1180 MPa-grade steel is more than 850MPa, and the A50 elongation is more than 15%.
The 1180MPa ultrahigh-strength steel provided by the embodiment of the application has the characteristics of high yield strength and high elongation, and can meet the use requirements of the existing automobile parts such as high elongation, high yield, bendability, hole expansibility and the like.
In a second aspect, embodiments of the present application provide a galvanized steel including a steel body substrate and a galvanized layer attached to a surface of the steel body substrate,
the steel body base material is 1180 MPa-grade steel material in the first aspect.
The galvanized steel provided by the embodiment of the application adopts the 1180 MPa-grade steel as the steel body base material, ensures the 1180 MPa-grade tensile strength, has the characteristics of high yield strength and high elongation, and can meet the use requirements of the existing automobile parts such as high elongation, high yield, bendability, hole expansibility and the like.
In a third aspect, embodiments of the present application provide a method for preparing a galvanized steel according to the second aspect, where the method includes:
obtaining a continuous casting slab containing the same chemical components of 1180 MPa-grade steel in the first aspect;
heating, rough rolling and finish rolling the continuous casting plate blank to obtain a hot rolled plate;
cooling the hot rolled plate, and then coiling to obtain a hot rolled coil;
cold rolling the hot rolled coil to obtain a cold hard coil;
continuously annealing the cold hard coil to obtain annealed strip steel;
and carrying out hot galvanizing on the annealed strip steel to obtain galvanized steel.
In this application, the method for obtaining a continuous casting slab containing the same chemical components as those of the 1180 MPa-grade steel material according to the first aspect may include: smelting the molten steel with chemical components of 1180MPa grade galvanized high-strength steel to obtain a continuous casting plate blank. In some specific embodiments, in the smelting process, the target temperature of the end point of the converter is 1650-1670 ℃, slag is added in the tapping process, the slag is added before the tapping amount reaches 1/5, and the slag is 700-900 kg of small-particle lime and 100-300 kg of fluorite per furnace; wherein the slag discharging amount of tapping is less than or equal to 80mm, and the tapping time is more than or equal to 4min.
In some embodiments, the heating temperature of the continuous casting slab is 1220-1280 ℃, and the finishing temperature of the finish rolling is 870-920 ℃.
In some embodiments, the coiling temperature is 670 ℃ to 720 ℃.
In some embodiments, the cold rolling reduction is controlled to be 50% to 60%.
In some embodiments, the annealed strip steel is hot-galvanized and then leveled, and the leveling elongation is controlled to be 0.3% -0.5%.
As an implementation manner of the embodiment of the present application, the continuous annealing includes a preheating section, an oxidation section, a heating section, a soaking section, a slow cooling section, and a fast cooling section;
the preheating section comprises: heating the mixture to 210-230 ℃ from room temperature at the speed of 8-12 ℃/s;
the oxidation section comprises: heating from 210 ℃ to 230 ℃ to 640 ℃ to 660 ℃ at the rate of 3 ℃/s to 8 ℃/s;
the heating section includes: heating to 850-990 ℃ from 640-660 ℃ at the rate of 1-3 ℃/s;
the soaking section comprises: keeping the temperature at 850-990 ℃ and keeping the temperature for 60-150 s;
the slow cooling section comprises: cooling from 850-990 ℃ to 760-840 ℃ at the speed of 2-6 ℃/s;
the rapid cooling section comprises: cooling from 760 ℃ to 840 ℃ at the rate of 20 ℃/s to 40 ℃/s to 250 ℃ to 350 ℃, and keeping the temperature for 60s to 120s.
In this application, continuous annealing is as the preparation galvanized steel's key step, and continuous annealing includes preheating section, oxidation section, heating section, soaking section, slow cooling section and fast cooling section, and the concrete principle is as follows:
a preheating section: firstly heating the chilled coil to 210-230 ℃ to realize preheating to obtain strip steel, wherein the heating speed is 8-12 ℃/s; in this process, the cold-deformed ferrite recovers.
An oxidation section: heating the preheated steel strip to 640-660 ℃ to realize oxidation to obtain the strip steel, wherein the heating speed is 3-8 ℃/s; in the process, pre-oxidation is realized, wherein, in mass fraction, O 2 ≧0.1％、H 2 O is not less than 1%.
A heating section: further heating the preheated strip steel to 850-950 ℃, wherein the heating speed is 1-3 ℃/s; this process effects recrystallization of the cold rolled ferrite structure, and pearlite is first transformed into austenite and grows toward ferrite.
A soaking section: and preserving the heat of the strip steel after further heating for 60-150 s within the temperature range of 850-950 ℃, and realizing full or partial austenitization in the process to obtain more austenite. At the same time, in terms of mass fraction, at O 2 <0.1％、H 2 O is not less than 1 percent.
A slow cooling section: cooling the heat-preserved strip steel to 760-840 ℃ at a cooling speed of 2-6 ℃/s; this process results in partial transformation of austenite to ferrite, with elements C, mn, etc., concentrated into austenite.
And (3) a rapid cooling section: the strip steel cooled to 760-840 ℃ is quickly cooled to the aging temperature of 250-350 ℃ by air blowing, and the temperature is kept for 60-120 s within the temperature range, so as to obtain the annealed strip steel; in the process, bainite martensite and untransformed austenite in a certain proportion are obtained, and elements such as C, mn are further gathered into the austenite by heat preservation.
As an implementation manner of the embodiment of the present application, the process parameters of the hot dip galvanizing include: the hot galvanizing temperature is 450-460 ℃, the temperature is cooled to 420-430 ℃ after the galvanizing is finished, and then the temperature is cooled to 250-300 ℃ from 420-430 ℃ at the speed of 6-9 ℃/s.
In the application, the hot galvanizing of the annealed strip steel comprises a hot galvanizing stage and a cooling stage:
heating the annealed strip steel to the galvanizing temperature of 450-460 ℃ through induction heating, and cooling to 420-430 ℃ through air knife blowing after the galvanizing is finished; in the process, the stay time of the strip steel in the equalizing section, the furnace nose and the zinc pot is reduced as much as possible through rapid induction heating, and partial austenite decomposition at high temperature is avoided.
Air cooling the front end of the air knife between the air knife and the top roller, matching the air cooling the rear end of the air knife with the air cooling, and finally cooling the air knife to 250-300 ℃ at a cooling speed of 6-9 ℃/s; during this process, a portion of the minor austenite phase transforms into the martensite phase.
In a fourth aspect, embodiments of the present application provide an automobile part made of the 1180MPa grade steel of the first aspect, and/or the galvanized steel of the third aspect.
The embodiment of the application provides an automobile part, which is made of 1180 MPa-grade steel in the first aspect and/or galvanized steel in the third aspect, has the characteristics of ultrahigh strength (tensile strength is greater than 1180 MPa), high yield strength (yield strength is greater than 850 MPa) and high elongation (A50 elongation is greater than 15%), and has wide practical application value.
In the present application, the automobile parts include a body, a door, and the like.
The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. The experimental methods without specifying specific conditions in the following examples were generally determined according to national standards. If there is no corresponding national standard, it is carried out according to the usual international standards, to the conventional conditions or to the conditions recommended by the manufacturer.
Examples 1 to 5 and comparative examples 1 to 3 provide a galvanized steel, the manufacturing method of which is shown in fig. 1, comprising:
s1, smelting by using molten steel containing the same chemical components as 1180 MPa-grade steel to obtain a continuous casting plate blank; examples 1 to 5 and comparative examples 1 to 3 were respectively smelted using the chemical compositions shown in table 1 to obtain molten steels;
s2, heating, rough rolling and finish rolling the continuous casting plate blank to obtain a hot rolled plate;
s3, cooling the hot rolled plate and then coiling to obtain a hot rolled coil;
s4, cold rolling the hot rolled coil to obtain a cold-hard coil;
s5, continuously annealing the cold hard coil to obtain annealed strip steel; the continuous annealing comprises a preheating section, an oxidation section, a heating section, a soaking section, a slow cooling section and a quick cooling section; the preheating section is heated to 210-230 ℃ from room temperature at the rate of 8-12 ℃/s, the oxidation section is heated to 640-660 ℃ from 210-230 ℃ at the rate of 3-8 ℃/s, wherein O 2 ≧0.1％、H 2 Pre-oxidizing in an atmosphere with O being equal to or larger than 1%, wherein the heating section is used for heating from 640-660 ℃ to 850-950 ℃ at the rate of 1-3 ℃/s, the soaking section is kept at 850-950 ℃ and is kept at the temperature for 60-150 s, and O is 2 <0.1％、H 2 Reducing in an atmosphere with O being equal to or larger than 1 percent, wherein the slow cooling section is cooled to 760-840 ℃ from 850-990 ℃ at the rate of 2-6 ℃/s, and the fast cooling section is cooled to 250-350 ℃ from 760-840 ℃ at the rate of 20-40 ℃/s and is kept for 60-120 s isothermally; the continuous annealing parameters described in examples 1 to 5 and comparative examples 1 to 3 are shown in table 2;
s6, carrying out hot galvanizing on the annealed strip steel, wherein the hot galvanizing temperature is 450-460 ℃, cooling to 420-430 ℃ after the galvanizing is finished, and then cooling to 250-300 ℃ from 420-430 ℃ at the speed of 6-9 ℃/S to obtain the hot galvanized strip steel; the hot dip galvanizing parameters of the examples 1 to 5 and the comparative examples 1 to 3 are shown in the table 2;
s7, leveling the hot-dip galvanized strip steel to obtain 1180 MPa-grade galvanized high-strength steel; the flat elongation in examples 1 to 5 and comparative examples 1 to 3 is shown in Table 2.
TABLE 1
| C％ | Si％ | Mn％ | Cr％ | Nb％ | P％ | S％ | N％ | |
| Example 1 | 0.19 | 1 | 2.2 | 0.6 | 0.02 | 0.005 | 0.003 | 0.0022 |
| Example 2 | 0.20 | 0.8 | 2.1 | 0.7 | 0.015 | 0.006 | 0.004 | 0.0024 |
| Example 3 | 0.21 | 0.7 | 2.5 | 0.5 | 0.017 | 0.004 | 0.0027 | 0.0021 |
| Example 4 | 0.19 | 0.6 | 2.3 | 0.8 | 0.025 | 0.007 | 0.005 | 0.0028 |
| Example 5 | 0.22 | 0.5 | 1.8 | 0.5 | 0.03 | 0.008 | 0.007 | 0.003 |
| Comparative example 1 | 0.15 | 0.9 | 2.5 | 0.5 | 0.03 | 0.005 | 0.005 | 0.0026 |
| Comparative example 2 | 0.25 | 0.9 | 2.3 | 0.6 | 0.02 | 0.004 | 0.003 | 0.0027 |
| Comparative example 3 | 0.19 | 1 | 2.4 | 0.6 | 0.01 | 0.005 | 0.003 | 0.0022 |
TABLE 2
Test example
In this example, the performance of the galvanized steels provided in examples 1 to 5 and comparative examples 1 to 3 was tested and characterized, and the results are shown in tables 3 and 4, and the metallographic structure of 1180MPa grade galvanized high-strength steel produced in example 1 of the present invention is shown in fig. 2.
TABLE 3 metallographic structure (in volume fraction) of each of the galvanized steels obtained in examples
| Numbering | Hard phase matrix | Retained austenite | Ferrite |
| Example 1 | 65％ | 7％ | 28％ |
| Example 2 | 72％ | 8％ | 20％ |
| Example 3 | 65％ | 5％ | 30％ |
| Example 4 | 75％ | 9％ | 16％ |
| Example 5 | 80％ | 10％ | 10％ |
| Comparative example 1 | 38％ | 6％ | 56％ |
| Comparative example 2 | 55％ | 3％ | 42％ |
| Comparative example 3 | 45％ | 5％ | 50％ |
TABLE 4
As can be seen from the data in tables 3 to 4:
the element C of comparative example 1 reaches 0.15% and is not in the range of 0.19% to 0.22% of the present invention, and the contents of other components and process parameters are substantially the same as those of example 1, and a certain content of hard phase cannot be secured, resulting in relatively low strength.
The comparative example 2 in which the content of C element was 0.25% was out of the range of 0.19% to 0.22% of the present invention, and the contents of other components and process parameters were substantially the same as those of example 1, a certain content of residual austenite phase could not be secured, resulting in relatively low elongation.
In comparative example 3, the heating section in the continuous annealing was heated to 850 ℃ at 5 ℃/s, the rapid cooling section was rapidly cooled to 400 ℃ and the temperature was maintained for 60s, the contents of other components and process parameters were substantially the same as those in example 1, and a certain content of retained austenite was hardly secured due to too high rapid cooling temperature, resulting in low elongation.
The 1180 MPa-grade galvanized high-strength steel finally prepared in the embodiments 1-5 of the invention has the tensile strength of more than 1180MPa, the yield strength of more than 850MPa and the A50 elongation of more than 15%.
Detailed description of the drawings fig. 2:
FIG. 2 is a metallographic structure diagram of 1180MPa grade galvanized high-strength steel manufactured in example 1 of the present invention; as can be seen from FIG. 2, the metallurgical structure of 1180MPa grade galvanized high-strength steel of the invention is calculated by volume fraction: 65-80% of hard bainite Ma Xiang matrix, 5-10% of residual austenite and 10-30% of ferrite.
In conclusion, the invention provides 1180 MPa-grade steel, galvanized steel, a preparation method thereof and automobile parts, wherein the galvanized steel adopts a continuous annealing and hot galvanizing process, a high-temperature heating and low-temperature rapid cooling aging mode is utilized to obtain a lath hard bainite martensite phase matrix, retained austenite and ferrite between lath hard phases, the hard phase matrix in the structure provides strength, the retained austenite and ferrite provide ductility of the steel, and the uniform structure provides high yield strength, so that the ultrahigh-strength steel has high yield strength and high elongation, the tensile strength is greater than 1180MPa, the yield strength is greater than 850MPa, and the A50 elongation is greater than 15%.
It should be understood that the endpoints of the ranges and any values disclosed herein are not limited to the precise range or value and that such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
It is noted that, in this document, relational terms such as "first" and "second," and the like, may be 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. Also, 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. In addition, the term "and/or" appearing herein is only one type of association that describes an associated object, meaning that three relationships may exist, e.g., a and/or B, may represent: a exists alone, A and B exist simultaneously, and B exists alone.
The above description is merely illustrative of particular embodiments of the invention that enable those skilled in the art to understand or practice the invention. 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 invention. Thus, the present invention 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 (10)
1. A1180 MPa-grade steel is characterized by comprising the following components in parts by weight: C. si, mn, cr, nb, P, S, N, fe and impurities from the preparation of the 1180 MPa-grade steel;
in 1180 MPa-grade steel, the content of Si is as follows by mass fraction: 0.5 to 1 percent; the content of the Cr is as follows: 0.3 to 0.8 percent; the content of Nb is as follows: 0.015 to 0.03 percent.
2. The 1180MPa grade steel product according to claim 1, wherein the 1180MPa grade steel product comprises the following components in mass fraction:
c: 0.19-0.22%, si: 0.5-1%, mn: 1.8-2.5%, cr:0.3% -0.8%, nb: 0.015-0.03%, P is less than or equal to 0.01%, S is less than or equal to 0.01%, N is less than or equal to 0.004%, and the balance of Fe and impurities from 1180 MPa-grade steel.
3. The 1180MPa grade steel product according to claim 1, wherein the metallographic structure of 1180MPa grade steel product comprises, in volume fraction: 65-80% of hard martensite bainite phase matrix; 5 to 10 percent of retained austenite; 10 to 30 percent of ferrite.
4. The 1180MPa grade steel of claim 3, wherein the hard martensitic bainite phase matrix has a grain size of 0.5 to 1 μm; the grain size of the residual austenite is 0.2-0.5 mu m; the grain size of the ferrite is 1.5-2.5 mu m.
5. The 1180MPa grade steel product according to any one of claims 1 to 4, wherein the 1180MPa grade steel product has a yield strength of greater than 850MPa and an A50 elongation of greater than 15%.
6. A galvanized steel, characterized in that the galvanized steel comprises a steel body substrate and a galvanized layer attached to the surface of the steel body substrate,
the steel body substrate is the 1180 MPa-grade steel product according to any one of claims 1 to 5.
7. The method for producing a galvanized steel according to claim 6, characterized in that the production method comprises:
obtaining a continuous casting slab containing the same chemical components as those of the 1180 MPa-grade steel material of any one of claims 1 to 5;
heating, rough rolling and finish rolling the continuous casting plate blank to obtain a hot rolled plate;
cooling the hot rolled plate, and then coiling to obtain a hot rolled coil;
cold rolling the hot rolled coil to obtain a cold-hard coil;
continuously annealing the cold hard coil to obtain annealed strip steel;
and carrying out hot galvanizing on the annealed strip steel to obtain galvanized steel.
8. The method for preparing galvanized steel according to claim 7, wherein the continuous annealing includes a preheating section, an oxidation section, a heating section, a soaking section, a slow cooling section, and a fast cooling section;
the preheating section comprises: heating the mixture to 210-230 ℃ from room temperature at the speed of 8-12 ℃/s;
the oxidation section comprises: heating from 210 ℃ to 230 ℃ to 640 ℃ to 660 ℃ at the rate of 3 ℃/s to 8 ℃/s;
the heating section includes: heating to 850-990 ℃ from 640-660 ℃ at the rate of 1-3 ℃/s;
the soaking section comprises: keeping the temperature at 850-990 ℃ and keeping the temperature for 60-150 s;
the slow cooling section comprises: cooling from 850-990 ℃ to 760-840 ℃ at the speed of 2-6 ℃/s;
the rapid cooling section comprises: cooling from 760 ℃ to 840 ℃ at the rate of 20 ℃/s to 40 ℃/s to 250 ℃ to 350 ℃, and keeping the temperature for 60s to 120s.
9. The method for preparing galvanized steel according to claim 7, wherein the hot galvanizing process parameters comprise: the hot galvanizing temperature is 450-460 ℃, the temperature is cooled to 420-430 ℃ after the galvanizing is finished, and then the temperature is cooled to 250-300 ℃ from 420-430 ℃ at the speed of 6-9 ℃/s.
10. An automobile part, characterized in that it is made of 1180MPa grade steel according to any one of claims 1 to 5 and/or galvanized steel according to claim 6.
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