CN114107806A - 450 MPa-grade hot-galvanized dual-phase steel with high work hardening rate and surface quality and production method thereof - Google Patents
450 MPa-grade hot-galvanized dual-phase steel with high work hardening rate and surface quality and production method thereof Download PDFInfo
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- 229910000885 Dual-phase steel Inorganic materials 0.000 title claims abstract description 64
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 34
- 238000005482 strain hardening Methods 0.000 title claims abstract description 22
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 58
- 239000010959 steel Substances 0.000 claims abstract description 58
- 238000001816 cooling Methods 0.000 claims abstract description 42
- 238000000034 method Methods 0.000 claims abstract description 28
- 230000008569 process Effects 0.000 claims abstract description 20
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 11
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 11
- 239000001301 oxygen Substances 0.000 claims abstract description 11
- 238000010583 slow cooling Methods 0.000 claims abstract description 9
- 238000005096 rolling process Methods 0.000 claims description 26
- 229910000859 α-Fe Inorganic materials 0.000 claims description 25
- 238000000137 annealing Methods 0.000 claims description 21
- 229910000734 martensite Inorganic materials 0.000 claims description 18
- 238000005246 galvanizing Methods 0.000 claims description 16
- 229910045601 alloy Inorganic materials 0.000 claims description 10
- 239000000956 alloy Substances 0.000 claims description 10
- 238000005097 cold rolling Methods 0.000 claims description 10
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 10
- 230000009467 reduction Effects 0.000 claims description 9
- 239000002253 acid Substances 0.000 claims description 8
- 239000000126 substance Substances 0.000 claims description 7
- 238000003723 Smelting Methods 0.000 claims description 6
- 238000005266 casting Methods 0.000 claims description 5
- 238000007670 refining Methods 0.000 claims description 5
- 229910052804 chromium Inorganic materials 0.000 claims description 4
- 229910052742 iron Inorganic materials 0.000 claims description 4
- 229910052750 molybdenum Inorganic materials 0.000 claims description 4
- 238000004321 preservation Methods 0.000 claims description 4
- 238000005406 washing Methods 0.000 claims description 4
- 238000009749 continuous casting Methods 0.000 claims description 3
- 239000012535 impurity Substances 0.000 claims description 3
- 229910052698 phosphorus Inorganic materials 0.000 claims description 3
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims 1
- 239000011574 phosphorus Substances 0.000 claims 1
- 238000013461 design Methods 0.000 abstract description 13
- 239000011572 manganese Substances 0.000 abstract description 13
- 229910052799 carbon Inorganic materials 0.000 abstract description 6
- 229910052748 manganese Inorganic materials 0.000 abstract description 6
- 229910001566 austenite Inorganic materials 0.000 description 30
- 239000011701 zinc Substances 0.000 description 18
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 17
- 229910052725 zinc Inorganic materials 0.000 description 17
- 239000000047 product Substances 0.000 description 12
- 230000001965 increasing effect Effects 0.000 description 10
- 238000010438 heat treatment Methods 0.000 description 9
- 239000007788 liquid Substances 0.000 description 9
- 229910001563 bainite Inorganic materials 0.000 description 7
- 230000000052 comparative effect Effects 0.000 description 6
- 238000005098 hot rolling Methods 0.000 description 6
- 239000000463 material Substances 0.000 description 6
- 230000009286 beneficial effect Effects 0.000 description 5
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- 238000009792 diffusion process Methods 0.000 description 3
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- 239000000203 mixture Substances 0.000 description 3
- 238000011160 research Methods 0.000 description 3
- 238000005728 strengthening Methods 0.000 description 3
- 238000009736 wetting Methods 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 2
- 125000004432 carbon atom Chemical group C* 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
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- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 229910000510 noble metal Inorganic materials 0.000 description 2
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 238000001953 recrystallisation Methods 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 230000035882 stress Effects 0.000 description 2
- 229910052717 sulfur Inorganic materials 0.000 description 2
- 230000009466 transformation Effects 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 1
- 230000032683 aging Effects 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 238000007664 blowing Methods 0.000 description 1
- 229910001567 cementite Inorganic materials 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 229910052593 corundum Inorganic materials 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
- 238000003618 dip coating Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 238000000265 homogenisation Methods 0.000 description 1
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 1
- 230000005012 migration Effects 0.000 description 1
- 238000013508 migration Methods 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 238000005554 pickling Methods 0.000 description 1
- 238000007747 plating Methods 0.000 description 1
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- 229910052814 silicon oxide Inorganic materials 0.000 description 1
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- 230000003746 surface roughness Effects 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
- 229910001845 yogo sapphire Inorganic materials 0.000 description 1
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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
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- 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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- C21D6/00—Heat treatment of ferrous alloys
- C21D6/002—Heat treatment of ferrous alloys containing Cr
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- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
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- C21D6/00—Heat treatment of ferrous alloys
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- 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
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- 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
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- 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
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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- 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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- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/14—Removing excess of molten coatings; Controlling or regulating the coating thickness
- C23C2/16—Removing excess of molten coatings; Controlling or regulating the coating thickness using fluids under pressure, e.g. air knives
- C23C2/18—Removing excess of molten coatings from elongated material
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- 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
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- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
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- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
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- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
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Abstract
The invention discloses 450 MPa-grade hot-galvanized dual-phase steel and a production method thereof, belonging to the field of steel manufacturing for galvanized automobiles, wherein the 450 MPa-grade hot-galvanized dual-phase steel is obtained by adopting a design of low-carbon and low-manganese components of trace Si, low Mo and high Cr, and through a low-temperature coiling process at 520-560 ℃, slow cooling at 640-660 ℃ and quick cooling process at more than or equal to 10 ℃, and simultaneously matching with an atmosphere with a furnace dew point of less than or equal to-40 ℃, an oxygen content of less than or equal to 5ppm and a furnace nose dew point of less than or equal to-20 ℃. The hot-dip galvanized dual-phase steel with the tensile strength of 450MPa produced by the invention has the uniform elongation of 18-23%, the work hardening rate n value of not less than 0.19 and the elongation A80 after fracture of 28-33%, and is suitable for being used as high-drawing and high-flanging complex-forming automobile parts.
Description
Technical Field
The invention belongs to the field of steel manufacturing for galvanized automobiles, and particularly relates to 450 MPa-grade hot-galvanized dual-phase steel and a production method thereof. The production method is suitable for continuous hot dip coating of pure zinc coated steel plates for automobiles.
Background
Compared with cold-rolled dual-phase steel, the hot-galvanized dual-phase steel is beneficial to forming, ensures the dent resistance and improves the absorption capacity of collision energy, well solves the contradiction between high strength and formability, and is considered to be an ideal material for the continuous lightweight design of automobiles in the future because the surface zinc layer has good corrosion resistance. However, the galvanizing production line and the continuous annealing production line are greatly different, such as the cooling rate is low, the overaging section is not available to eliminate the internal stress homogenization structure, and the like, and products with good coating adhesion and mechanical properties are a pair of contradiction aggregates, so that great challenges are provided for the chemical composition design and the controlled rolling and controlled cooling technology of steel matrixes. The tensile strength grade of most of hot dip galvanized dual-phase steel applied at present is 450-980 MPa. The mainstream research mainly focuses on hot galvanizing dual-phase steel of 500-800 MPa level. The hot-dip galvanized dual-phase steel of 450MPa level has less related research, because the C content is lower, and the common characteristic that the cooling speed of the existing galvanized wire is lower than that of a continuous annealing line, martensite is more difficult to form, more precious alloy elements such as Cr, Mo and the like are added to delay the transformation of pearlite and bainite in order to ensure the performance, an ideal martensite + ferrite dual-phase structure is obtained, and the requirements on components and process design are higher than that of the hot-dip galvanized dual-phase steel of high strength level. But the yield strength is lower and is not more than 300MPa generally, so that the alloy has high plastic deformation capability, has the advantages of good dent resistance, bake-hardening performance, no aging and the like, and is expected to replace the traditional phosphorus-reinforced low-alloy high-strength steel to become a new-generation automobile outer covering material. In addition, alloying elements in the steel and annealing processes have a great influence on the surface quality of the finished product. Therefore, the problems of difficult production, high cost and the like exist, and the hot problem of the current hot galvanizing industry research is how to balance the surface quality and the performance and save the alloy cost as much as possible.
The initial work hardening rate (n value) is a quite important performance index for hot-dip galvanized dual-phase steel, determines the maximum stress when the material begins to neck down, and also determines the maximum uniform deformation amount which can be generated, which is very critical for parts needing flanging and bulging, and the higher the value is, the easier the flanging and bulging are. The high work hardening rate also resists local non-uniform deformation or fracture due to excessive plastic deformation, and provides reliable guarantee for safe use of the material. The technology for improving the n value of the 450 MPa-grade hot-galvanized dual-phase steel is reported. The stability control of the surface quality is closely related to the chemical composition design and the continuous annealing process of the material, and no relevant report is found for the dual-phase steel of the grade.
Through search, the invention name of Chinese patent CN105369135A is a 450MPa class galvanized dual-phase steel for cars and a production method thereof. The components do not contain Si design, the coiling temperature is high, uniform and refined austenite grains are not easy to obtain, the reduction of the ductility performance of a banded structure is easy to occur, the work hardening rate of the prepared dual-phase steel is relatively low, the local necking phenomenon is easy to generate during forming, and the dual-phase steel is not high-hardening rate dual-phase steel.
The patent publication number is CN103938097A, and the invention name is a cold-rolled hot-galvanized dual-phase steel and a preparation method thereof. However, in the above production method, high-temperature coiling and high-temperature slow cooling are adopted, so that a band-shaped structure is easily generated, the structure of a final product is not uniform, the elongation is reduced, and press cracking is easily caused.
The patent publication No. CN102732791A discloses a production method of cold-rolled dual-phase steel with tensile strength of 450MPa, the component C content is high, Si design is not contained, the addition amount of Cr and Mo noble metals is high, the coiling temperature is high, uniform and refined austenite grains are not easy to obtain, the processing performance of an actual product is poor, and the method is not suitable for producing hot-galvanized 450MPa dual-phase steel.
The patent publication No. CN109321825A discloses a 450 MPa-grade automobile lightweight cold-rolled dual-phase steel and a production method thereof, the content of the component C is high, the control of coiling temperature is not mentioned, and the steel is not suitable for producing hot-galvanized 450 MPa-grade dual-phase steel.
Disclosure of Invention
1. Problems to be solved
Aiming at the problem of low work hardening rate of the existing 450MPa grade hot galvanizing dual-phase steel, the invention provides 450MPa grade hot galvanizing dual-phase steel which has higher work hardening rate and meets the use requirement.
The invention also aims to provide a production method of the 450 MPa-grade hot-dip galvanized dual-phase steel, which has the advantages that the steps are connected in order, and the work hardening rate of the hot-dip galvanized dual-phase steel is further improved by matching with a process on the basis of the improvement of the components.
2. Technical scheme
In order to solve the problems, the technical scheme adopted by the invention is as follows:
the 450 MPa-grade hot-galvanized dual-phase steel comprises the following chemical components in percentage by weight: 0.045-0.06% of C, 0.1-0.2% of Si, 1.25-1.35% of Mn, 0.03-0.06% of Al, 0.36-0.41% of Cr, 0.1-0.14% of Mo, less than or equal to 0.015% of P, less than or equal to 0.006% of S, less than or equal to 0.004% of N, and the balance of Fe and inevitable impurities, and is subjected to low-temperature coiling at 520-560 ℃, slow cooling at 640-660 ℃ and fast cooling at the temperature of more than or equal to 10 ℃, and simultaneously matched with the atmosphere with the furnace dew point of less than or equal to-40 ℃, the oxygen content of less than or equal to 5ppm, and the furnace nose dew point of less than or equal to-20 ℃ to obtain the 450MPa grade hot galvanized dual-phase steel.
Further, in the 450 MPa-grade hot-dip galvanized dual-phase steel, the weight percentages of Cr and Mo are Cr: mo is more than or equal to 3: 1.
Further, the thickness of the hot-dip galvanized dual-phase steel is 0.6-2.5 mm; the homogeneous elongation of the dual-phase steel is 18-23%, the work hardening rate n value is not less than 0.19, and the elongation A80 after fracture is as high as 28-33%.
The yield strength of the hot-dip galvanized dual-phase steel in actual production is 270-320 MPa, and the tensile strength is 470-520 MPa.
Further, the metallographic structure of the hot-dip galvanized dual-phase steel is ferrite and martensite, and the average grain size is 9-10.5; wherein, the volume percentages of ferrite and martensite are respectively 80-87% and 13-20%, and in order to ensure that the tensile strength of the product can reach 450MPa, the volume percentage of the martensite can not be less than 13%; and the martensite percentage can not exceed 20%, if the martensite percentage exceeds 20%, the corresponding ferrite content is reduced, the elongation and the value are reduced, the yield strength is high, and the deep drawing and flanging performances are not facilitated.
The reasons for controlling the effects and the content of the chemical components of the 450 MPa-grade hot-dip galvanized dual-phase steel are as follows:
c: is the most basic strengthening element in steel, has the lowest price and is easy to obtain, and plays a key role in the formation of austenite stable martensite. The content of C is increased, and the plasticity and the welding performance of the dual-phase steel are sharply reduced; the C content is reduced, the hardenability of austenite is reduced, and the cooling process is easy to decompose, so that the tensile strength is insufficient. The content of C in the invention is 0.045-0.06% by combining the control level of a production line C.
Si: the economic and effective solid solution strengthening elements can not only improve the continuity of the ferrite matrix of the dual-phase steel and avoid forming a continuous martensite chain to reduce the product plasticity, but also improve the activity of carbon atoms in the ferrite to enable the carbon atoms to be more easily diffused to austenite from the ferrite, thereby not only playing the role of removing and purifying ferrite solid solution carbon, but also playing the role of stabilizing the austenite. The continuous ferrite grains provide a channel for the rapid migration of dislocation in the process of processing deformation, thereby improving the strain hardening rate and the ductility. The content of Si is increased, and SiO is easily generated by enrichment on the surface2Particularly, the wetting property of the steel strip and the zinc liquid is not facilitated, surface defects such as plating leakage and the like are caused by improper process control,the need to match a suitable furnace atmosphere can avoid this drawback. The control difficulty of the performance and the surface quality is comprehensively considered, and the Si content in the invention is 0.1-0.2%.
Mn: beneficial and economic solid solution strengthening elements in steel are easy to form high-melting-point MnS with S elements remained in molten steel, so that the brittle failure problem in the hot rolling process is reduced; because of high atomic activity, the austenite is easy to diffuse into austenite, thereby improving the hardenability of the austenite. Too high Mn content easily causes the reduction of ductility of the strip structure, affects the weldability of the steel sheet, and increases the cost. Therefore, the Mn content in the present invention is 1.25% to 1.35%.
Al: al is a common deoxidizer in steel, the content of Al is too low, and coarse Mn and Si oxides are increased, so that the purity of the steel is reduced; the Al content is too high, the aluminum oxide impurities are increased, the plasticity of steel is damaged, and the difficulty of smelting and casting is increased. Meanwhile, Al can inhibit cementite from precipitating out and promote carbon to enrich and stabilize austenite to austenite, and AlN particles formed by combining with N can pin-roll grain boundaries to play a certain role in refining grains. The Al content in the invention is 0.03-0.06%.
Cr: the hardenability of the steel is effectively improved, the temperature of a ferrite-austenite two-phase region is reduced by adding Cr, and austenitizing is easier to carry out. And the dissolution temperature of carbide is increased, the band-shaped structure can be obviously improved, the ductility can be improved, the decomposition speed of austenite can be slowed down, and the obtained martensite with fine and uniform size can be used together with other alloy elements to improve the comprehensive performance of steel. The Cr content in the invention is 0.36-0.41%.
Mo: the element which can improve the hardenability of the steel more strongly is combined with C, so that dispersed and fine Mo carbide can be precipitated at low temperature, the tendency that the carbide forms a continuous net on a crystal boundary is avoided, crystal grains are refined, ferrite can be strengthened, the strength of the steel is improved, and meanwhile, the plasticity of the steel is not reduced too much. Meanwhile, the transformation of bainite is strongly delayed in the continuous annealing and cooling process, the method is more effective than Cr, and oxides are basically not formed on the surface along with the change of the atmosphere in the furnace in the continuous annealing process to influence the wettability of a steel strip and a zinc liquid, so that the method is very suitable for producing hot-dip galvanized dual-phase steel. However, the high content of Mo leads to higher yield strength and greatly increases the production cost. Therefore, the Mo content in the invention is 0.1-0.15%.
P, S, N: p is easy to segregate at grain boundaries to increase the cold brittleness of steel, S can cause hot brittleness, N can obviously improve the strength of steel, and the P and the N are elements which obviously reduce the plasticity and the toughness of the steel and need to strictly control the content of P, S, N in the steel. The content of P is less than or equal to 0.015 percent, the content of S is less than or equal to 0.006 percent, and the content of N is less than or equal to 0.004 percent.
The production method of 450 MPa-grade hot-galvanized dual-phase steel comprises the following steps:
(1) pouring a slab: smelting and casting into a plate blank according to a process route of molten iron pretreatment → converter smelting → alloy fine adjustment → LF furnace refining → continuous casting;
(2) dephosphorization, fine rolling and rough rolling: heating the plate blank to 1210-1250 ℃, carrying out dephosphorization and rough rolling for 6 passes, carrying out finish rolling for 7 passes, wherein the finish rolling starting temperature is 1000-1080 ℃, the outlet temperature is 860-900 ℃, and laminar cooling is carried out to 520-560 ℃ to obtain a hot rolled plate, and then coiling and naturally cooling in the air;
(3) acid washing and cold rolling: carrying out acid washing in three sections of acid liquor tanks to remove surface iron scales, wherein the temperature of the acid liquor is ensured to be within the range of 85 +/-5 ℃, the concentration of HCL is 20-60 g/L, 100-140 g/L and 150-190 g/L in sequence, and then carrying out cold rolling, wherein the cold rolling reduction rate is 55-80%;
(4) continuous annealing and hot galvanizing: and carrying out continuous annealing and hot galvanizing, heating the steel coil to 770-790 ℃, keeping the dew point in the furnace to be less than or equal to minus 40 ℃, keeping the oxygen content to be less than or equal to 5ppm, slowly cooling the steel coil after heat preservation, cooling the steel coil to 640-660 ℃ at a cooling rate of 3-6 ℃/s, then cooling the steel coil to 470-490 ℃ at a cooling rate of 10-15 ℃/s, then carrying out hot galvanizing in a zinc pot at 460 +/-5 ℃, blowing off redundant zinc liquid by using an air knife, then cooling the steel coil to the room temperature by using a variable frequency fan, wherein the dew point of the furnace nose is controlled to be less than or equal to minus 20 ℃, carrying out finishing after the steel coil is cooled to the room temperature, and the finishing elongation is 0.3-0.6%.
The production method of hot rolling comprises the following steps: in the production method of 450 MPa-grade hot-dip galvanized dual-phase steel with low cost, high work hardening rate and surface quality and easy production, during hot rolling, slab heating is the first step of hot rolling, and the heating temperature of 1210-1250 ℃ is adopted to eliminate the defects of a casting blank and reduce the deformation resistance of the steel. A rolling system of 6 rough rolling passes and 7 finish rolling passes is adopted, so that rolling load is reasonably distributed to realize controlled rolling. The method adopts a finish rolling start temperature of 1000-1080 ℃ and a finish rolling temperature of 860-900 ℃ to control the recrystallization behavior of austenite and refine grains by controlling temperature. The coiling temperature of 520-560 ℃ is adopted, so that a hot rolled coil with a structure of ferrite, pearlite and bainite is obtained through controlled cooling, hot rolled structure grains are refined, subsequent deformation energy storage is increased, short-distance diffusion of alloy elements such as C, Mn in the subsequent continuous annealing period is facilitated, the content of solid solution C in the ferrite is reduced, uniform, fine and stable austenite is obtained, uniform and dispersedly distributed martensite island-shaped structures are formed in the subsequent cooling process and embedded on ferrite grain boundaries to achieve the required tensile strength, the yield ratio is reduced, and the work hardening rate and the elongation are improved.
The production method of acid rolling comprises the following steps: during acid pickling cold continuous rolling, the cold rolling reduction rate is less than or equal to 80 percent from the perspective of the capacity of a rolling mill; from the viewpoint of increasing deformation energy storage and refining grains, the cold rolling reduction rate is more than or equal to 58 percent. Therefore, a cold rolling reduction of 58% to 80% is used.
The production method of continuous annealing and hot galvanizing comprises the following steps: when continuous annealing and hot galvanizing are carried out, the heating temperature is 770-790 ℃, so that austenite grains are fine and contain enough C content while recrystallization is fully carried out, and the proportion of ferrite and austenite is controlled to ensure the stability of austenite; heating the steel strip from normal temperature to 780 ℃ at a heating speed of 3-6 ℃/s, setting the dew point in an annealing furnace to be less than or equal to 40 ℃ below zero, and setting the oxygen content to be less than or equal to 5ppm, so as to inhibit oxides of Si and Mn from being precipitated on the outermost surface and obtain a pure and active strip steel surface. After heat preservation, slowly cooling to 640-660 ℃ at a cooling rate of 3-6 ℃/s so as to convert part of austenite into oriented periphytic ferrite, enrich C into unconverted austenite and increase the stability of unconverted austenite; and rapidly cooling to 470-490 ℃ at a cooling rate of 10-15 ℃/s so as to avoid pearlite and bainite regions and enable the untransformed austenite to be fully transformed into martensite after the steel strip is taken out of a zinc pot. And a dew point of less than or equal to 20 ℃ below zero is adopted in a furnace nose area where the steel strip enters the zinc pot to avoid excessive aluminum oxide films generated on the surface of zinc liquid from being adhered to the surface of the steel strip to deteriorate the surface quality, and meanwhile, the temperature of the steel strip entering the zinc pot is kept to be less than or equal to 470 ℃ to avoid the excessively severe Fe-Zn reaction to deteriorate the coating quality. The finishing elongation of 0.3-0.6% is adopted to control the plate shape and the surface roughness, and the number and the density of dislocation are adjusted, so that the yield strength is adjusted to the required range.
The invention adopts the design of low-carbon and low-manganese components of trace Si, low Mo and high Cr and the processes of low-temperature coiling, low-temperature slow cooling and high-speed quick cooling, thereby producing the tensile strength 450 MPa-grade hot-dip galvanized dual-phase steel with the uniform elongation of 18-23%, the work hardening rate n value not less than 0.19 and the elongation A80 after fracture up to 28-33%, and being suitable for being used as high-drawing and high-flanging complex-forming automobile parts. Meanwhile, in order to further improve the surface quality of the product, the wettability of a steel matrix and zinc liquid is enhanced by adopting a production process of low annealing furnace dew point, low oxygen content and low furnace nose dew point, so that the product with the surface quality meeting the requirements of an automobile outer covering part is obtained.
The trace amount of Si and low Mn combined with a dew point of-40 deg.C or less and an oxygen content of 5ppm or less is to avoid the formation of thick, network-like distribution of difficult-to-reduce SiO before the strip is annealed and cooled into the zinc bath2The MnO oxide film causes the increase of the wetting difficulty of the strip steel and the zinc liquid; the atmosphere with the furnace nose dew point less than or equal to minus 20 ℃ is used for avoiding the reaction of excessive humidified gas of the furnace nose and Al in the molten zinc liquid at the temperature of about 460 ℃, namely 2Al +3H2O＝3H2+Al2O3Excessive Al generation2O3The film is adhered to the surface of the strip steel to prevent the wetting of the zinc liquid and the steel matrix, thereby improving the surface quality; on one hand, the low Mo design is that the low Mo works together with Cr to obtain uniform and fine ferrite grains, and refine carbide particles so as to be easier to diffuse into austenite with low carbon content through grain boundaries to stabilize austenite, thereby obtaining an ideal ferrite + dispersion distribution martensite structure in the cooling processThe density of movable dislocation is enhanced in ferrite in the process of forming fine martensite islands, so that the aim of enhancing the work hardening rate of a product is achieved, and on the other hand, the production cost is reduced; the high Cr design and the low temperature coiling ensure that the hot coiled strip-shaped structure is reduced and the important elements of the work hardening rate are improved, and the low C content is combined to stabilize austenite in the annealing and cooling process, improve the hardenability and ensure the yield strength and the tensile strength of the product to meet the requirements.
3. Advantageous effects
Compared with the prior art, the invention has the beneficial effects that:
(1) the method adopts the design of low-carbon-low-manganese components of trace Si, low Mo and high Cr, the fine uniform banded structure is obtained by coiling at the low temperature of 520-560 ℃, the ferrite and martensite island structures with the grain size of 9-10.5 are obtained by slow cooling at the temperature of 640-660 ℃ and fast cooling at the temperature of not less than 10 ℃, and a hot-dip galvanized dual-phase steel product with excellent surface coating quality is obtained by matching the atmosphere with the furnace internal dew point of not more than-40 ℃, the oxygen content of not more than 5ppm and the furnace nose dew point of not more than-20 ℃; on the premise that the strength meets the requirement of basic performance of 450MPa hot-dip galvanized dual-phase steel in GBT/2518-2008, the strength and the plasticity of the product are obviously improved, the uniform elongation is 18-23%, the work hardening rate n value is not lower than 0.19, and the elongation A80 after fracture is up to 28-33%;
(2) the invention adopts the design of adding trace Si to reduce the generation of excessive SiO due to the oxidation of the trace oxygen in the annealing process of the Si2The surface is enriched to hinder the wettability of strip steel and zinc liquid, the ferrite strength is increased, the rapid diffusion of C to austenite grains in the continuous annealing process is promoted to stabilize austenite, the problem that the austenite is unstable and is easily decomposed into bainite due to the lower cooling speed of a galvanizing line is solved, and the initial work hardening rate n of the dual-phase steel is improved;
(3) the invention adopts the technology of low-temperature slow cooling and high-speed quick cooling, increases the generation amount of the oriented periphytic ferrite, reduces the yield strength of the product, and simultaneously avoids the situation that the austenite is prematurely decomposed into bainite on the way of finishing the quick cooling to the zinc discharging pot, which is not beneficial to the improvement of the n value;
(4) the method adopts a low-temperature coiling technology to obtain a hot-rolled coil with a structure of ferrite, pearlite and bainite, refines grains, increases subsequent deformation energy storage, and is beneficial to obtaining a uniform and fine microstructure, so that short-range diffusion of C and alloy elements to austenite grains in a subsequent continuous annealing process is realized, a martensite island is formed on a ferrite grain boundary after cooling, and the basic performance requirement that the required yield strength is 250-340 MPa and the tensile strength is more than or equal to 450MPa is realized;
(5) on one hand, the invention utilizes the low C + Mn + Cr + Mo component design to control the noble metal Mo at a lower level and control the Cr: mo is more than or equal to 3:1, the reduction of banded structures is realized, the performance of the prepared material has low yield strength and high work hardening rate, and the production cost is reduced.
Drawings
The technical solutions of the present invention will be described in further detail below with reference to the accompanying drawings and examples, but it should be understood that these drawings are designed for illustrative purposes only and thus do not limit the scope of the present invention. Furthermore, unless otherwise indicated, the drawings are intended to be illustrative of the structural configurations described herein and are not necessarily drawn to scale.
FIG. 1 is a schematic view of a metallographic structure (x 500) of a 450MPa hot-dip galvanized dual-phase steel according to the present invention;
FIG. 2 is a schematic view of a high power electron microscopic structure (x 2000) of a 450MPa hot-dip galvanized dual-phase steel according to the present invention;
FIG. 3 shows the surface quality of 450MPa hot dip galvanized dual phase steel.
Detailed Description
The following detailed description of exemplary embodiments of the invention refers to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration exemplary embodiments in which the invention may be practiced. Although these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be realized and that various changes to the invention may be made without departing from the spirit and scope of the present invention. The following more detailed description of the embodiments of the invention is not intended to limit the scope of the invention, as claimed, but is presented for purposes of illustration only and not limitation to describe the features and characteristics of the invention, to set forth the best mode of carrying out the invention, and to sufficiently enable one skilled in the art to practice the invention. Accordingly, the scope of the invention is to be limited only by the following claims.
The detailed description and exemplary embodiments of the invention will be better understood when read in conjunction with the appended drawings, where the elements and features of the invention are identified by reference numerals.
Example 1
The technical scheme of the invention comprises the following implementation steps:
(1) smelting and casting into a plate blank according to a process route of molten iron pretreatment → converter smelting → alloy fine adjustment → LF furnace refining → continuous casting;
(2) heating the plate blank to 1210-1250 ℃, carrying out dephosphorization and rough rolling for 6 passes, carrying out finish rolling for 7 passes, wherein the finish rolling starting temperature is 1000-1080 ℃, the outlet temperature is 860-900 ℃, and laminar cooling is carried out to 520-560 ℃ to obtain a hot rolled plate, and then coiling and naturally cooling in the air;
(3) cold rolling is carried out after normal acid washing, and the cold rolling reduction rate is 55-80%;
(4) and carrying out continuous annealing and hot galvanizing, heating the steel coil to 770-790 ℃, enabling the dew point in the furnace to be less than or equal to minus 40 ℃, enabling the oxygen content to be less than or equal to 5ppm, carrying out slow cooling after heat preservation, cooling to 640-660 ℃ at a cooling rate of 3-6 ℃/s, then cooling to 470-490 ℃ at a cooling rate of 10-15 ℃/s, and then carrying out conventional hot galvanizing and air cooling, wherein the dew point of the nose of the furnace is controlled to be less than or equal to minus 20 ℃, and carrying out finishing after the steel coil is cooled to the room temperature, wherein the finishing elongation is 0.3-0.6%.
The method specifically comprises the following steps:
the chemical components of the hot-dip galvanized dual-phase steel of the examples 1 to 3 are shown in table 1, the hot rolling process parameters of the examples 1 to 3 are shown in table 2, the continuous annealing and galvanizing parameters of the examples 1 to 3 are shown in table 3, and the mechanical properties of the steel plates prepared in the examples 1 to 3 are shown in table 4.
TABLE 1 chemical composition of the examples (wt%)
| C | Si | Mn | P | S | Al | Cr | Mo | N | |
| Example 1 | 0.047 | 0.10 | 1.32 | 0.008 | 0.0029 | 0.039 | 0.37 | 0.12 | 0.0026 |
| Example 2 | 0.054 | 0.15 | 1.31 | 0.0098 | 0.0018 | 0.045 | 0.38 | 0.12 | 0.0026 |
| Example 3 | 0.057 | 0.20 | 1.3 | 0.011 | 0.0039 | 0.048 | 0.37 | 0.13 | 0.0025 |
| Comparative example 1 | 0.077 | 0.007 | 1.2 | 0.005 | 0.005 | 0.03 | 0.40 | 0.10 | 0.0048 |
| Comparative example 2 | 0.046 | 0.17 | 1.27 | 0.01 | 0.004 | 0.056 | 0.62 | / | / |
TABLE 2 Hot and Cold Rolling Process parameters for examples 1-3
TABLE 3 continuous annealing + galvanization parameters for examples 1-3
TABLE 4 mechanical Properties of the steel sheets obtained in examples 1 to 3
Note: the method for measuring the mechanical properties (yield strength, tensile strength and elongation after fracture) adopts the national standard GB/T228.1-2010, the type number of the sample is P6, and the direction of the sample is longitudinal. FD is the surface quality of the strip steel, wherein one surface of the surface quality of the strip steel meets the surface quality grade required by an automobile outer covering part, the other surface of the surface quality of the strip steel meets the surface quality grade of FC, the FC is the surface quality of the strip steel, one surface of the surface quality of the strip steel meets the harsher quality requirement but is not higher than the requirement of the outer covering part, and the other surface of the surface quality of the strip steel meets the requirement of automobile inner parts.
The results show that the technical scheme of the invention has good adaptability, and the uniform elongation rate of the three embodiments reaches 19-22% on the premise that the strength meets the national standard requirement. The post-fracture elongation of the comparative example 1 and the comparative example 2 is not high, the work hardening rate caused by the excessively high C content of the comparative example 1 is obviously low, the forming requirements of high-drawing and high-flanging parts cannot be met, the slow cooling temperature of the comparative example 2 is high, the tensile strength is low, the yield ratio is excessively high, the improvement of uniform elongation is not facilitated, and the risk of stamping and fracture resistance is increased.
The above description is only a specific exemplary description of the method for producing 450MPa grade hot-dip galvanized dual-phase steel with low cost, high work hardening rate and surface quality, and it should be noted that the specific implementation of the present invention is not limited by the above manner, and it is within the scope of the present invention to apply the technical concept and technical solution of the present invention to other occasions without any substantial improvement or without any improvement.
Claims (10)
1. The 450 MPa-grade hot-galvanized dual-phase steel is characterized by comprising the following chemical components in percentage by weight: 0.045-0.06% of C, 0.1-0.2% of Si, 1.25-1.35% of Mn, 0.03-0.06% of Al, 0.36-0.41% of Cr, 0.1-0.14% of Mo, less than or equal to 0.015% of P, less than or equal to 0.006% of S, less than or equal to 0.004% of N, and the balance of Fe and inevitable impurities, and is subjected to low-temperature coiling at 520-560 ℃, slow cooling at 640-660 ℃ and fast cooling at the temperature of more than or equal to 10 ℃, and simultaneously matched with the atmosphere with the furnace dew point of less than or equal to-40 ℃, the oxygen content of less than or equal to 5ppm, and the furnace nose dew point of less than or equal to-20 ℃ to obtain the 450MPa grade hot galvanized dual-phase steel.
2. The 450MPa grade hot-dip galvanized dual-phase steel according to claim 1, characterized in that the weight percentages of Cr and Mo in the hot-dip galvanized dual-phase steel are Cr: mo is more than or equal to 3: 1.
3. The 450MPa grade hot-dip galvanized dual-phase steel according to claim 1, characterized in that the 450MPa grade hot-dip galvanized dual-phase steel has a thickness of 0.6-2.5 mm, a uniform elongation of 18-23%, a work hardening rate n of not less than 0.19, a post-fracture elongation A80 of 28-33%, a yield strength of 270-320 MPa, and a tensile strength of 470-520 MPa.
4. The 450 MPa-grade hot-dip galvanized dual-phase steel according to claim 1, wherein a metallographic structure of the hot-dip galvanized dual-phase steel is ferrite and martensite, an average grain size is 9-10, a volume percentage of the ferrite is 80-87%, and a volume percentage of the martensite is 13-20%.
5. A production method for a 450MPa grade hot galvanized dual-phase steel according to any one of claims 1 to 4, characterized by comprising the following steps:
s1, casting a slab;
s2, removing phosphorus, fine rolling and rough rolling;
s3, acid washing and cold rolling;
s4, continuous annealing and hot galvanizing;
s5, finishing: and (5) cooling the steel coil to room temperature and then finishing.
6. The production method of 450MPa grade hot galvanized dual-phase steel according to claim 5, characterized in that the cast slab in the step S1 is smelted and cast into the slab according to the process route of molten iron pretreatment → converter smelting → alloy fine adjustment → LF furnace refining → continuous casting.
7. The production method of 450 MPa-grade hot-dip galvanized dual-phase steel according to claim 5, characterized in that in step S2, the slab is heated to 1210-1250 ℃, and subjected to dephosphorization and 6-pass rough rolling, 7-pass finish rolling is carried out, the finish rolling start rolling temperature is 1000-1080 ℃, the exit temperature is 860-900 ℃, and laminar cooling is carried out to 520-560 ℃ to obtain a hot rolled plate, and then the hot rolled plate is coiled and naturally cooled in air.
8. The method for producing 450MPa grade hot dip galvanized dual phase steel according to claim 5, characterized in that in step S3, the cold rolling reduction is 55% -80%.
9. The method for producing 450MPa grade hot-dip galvanized dual-phase steel according to claim 5, characterized in that in step S4, the steel coil is heated to 770-790 ℃, the dew point in the furnace is less than or equal to-40 ℃, the oxygen content is less than or equal to 5ppm, the steel coil is slowly cooled after heat preservation, the steel coil is cooled to 640-660 ℃ at a cooling rate of 3-6 ℃/S, then the steel coil is cooled to 470-490 ℃ at a cooling rate of 10-15 ℃/S, and then hot-dip galvanizing and air cooling are carried out, wherein the furnace nose dew point is controlled to be less than or equal to-20 ℃.
10. The method for producing 450MPa grade hot dip galvanized dual phase steel according to claim 5, characterized in that, in step S5, the finishing elongation is 0.3% -0.6%.
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| CN114535810A (en) * | 2022-04-07 | 2022-05-27 | 攀钢集团攀枝花钢铁研究院有限公司 | 980 MPa-grade cold-rolled dual-phase steel with low yield ratio and welding method of acid rolling process thereof |
| CN114535806A (en) * | 2022-04-07 | 2022-05-27 | 攀钢集团攀枝花钢铁研究院有限公司 | 450 MPa-grade cold-rolled dual-phase steel and welding method for acid rolling process thereof |
| CN114535808A (en) * | 2022-04-07 | 2022-05-27 | 攀钢集团攀枝花钢铁研究院有限公司 | 590 MPa-grade high-forming cold-rolled dual-phase steel and welding method thereof in acid rolling process |
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| CN115074623A (en) * | 2022-06-16 | 2022-09-20 | 唐山钢铁集团高强汽车板有限公司 | Hydrogen-induced cracking resistant galvanized hot stamping steel and production method thereof |
| CN115074623B (en) * | 2022-06-16 | 2023-08-25 | 唐山钢铁集团高强汽车板有限公司 | Zinc-plated hot stamping steel resistant to hydrogen induced cracking and production method thereof |
| CN115612934A (en) * | 2022-10-19 | 2023-01-17 | 鞍钢蒂森克虏伯汽车钢有限公司 | 590 MPa-level high-formability hot-dip galvanized dual-phase steel plate and preparation method thereof |
| CN115992333A (en) * | 2022-10-19 | 2023-04-21 | 鞍钢蒂森克虏伯汽车钢有限公司 | Low-cost 590 MPa-level high-formability alloyed hot-dip galvanized dual-phase steel plate and manufacturing method thereof |
| CN115612934B (en) * | 2022-10-19 | 2024-02-02 | 鞍钢蒂森克虏伯汽车钢有限公司 | 590 MPa-level high-formability hot dip galvanized dual-phase steel plate and preparation method thereof |
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