CN116695009A - Hot-rolled ultrahigh-strength steel plate with excellent comprehensive performance and manufacturing method thereof - Google Patents
Hot-rolled ultrahigh-strength steel plate with excellent comprehensive performance and manufacturing method thereof Download PDFInfo
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- CN116695009A CN116695009A CN202310676374.4A CN202310676374A CN116695009A CN 116695009 A CN116695009 A CN 116695009A CN 202310676374 A CN202310676374 A CN 202310676374A CN 116695009 A CN116695009 A CN 116695009A
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- 229910000797 Ultra-high-strength steel Inorganic materials 0.000 title claims abstract description 28
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 21
- 238000000034 method Methods 0.000 claims abstract description 42
- 239000000126 substance Substances 0.000 claims abstract description 14
- 238000005452 bending Methods 0.000 claims abstract description 10
- 238000005096 rolling process Methods 0.000 claims description 80
- 238000001816 cooling Methods 0.000 claims description 67
- 229910000831 Steel Inorganic materials 0.000 claims description 44
- 239000010959 steel Substances 0.000 claims description 44
- 238000004321 preservation Methods 0.000 claims description 24
- 238000010438 heat treatment Methods 0.000 claims description 22
- 239000002244 precipitate Substances 0.000 claims description 21
- 238000005266 casting Methods 0.000 claims description 18
- 238000005496 tempering Methods 0.000 claims description 13
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 13
- 229910001563 bainite Inorganic materials 0.000 claims description 10
- 230000009467 reduction Effects 0.000 claims description 8
- 239000012535 impurity Substances 0.000 claims description 4
- 229910001568 polygonal ferrite Inorganic materials 0.000 claims description 4
- 238000012797 qualification Methods 0.000 claims description 4
- 238000010079 rubber tapping Methods 0.000 claims description 4
- 238000003723 Smelting Methods 0.000 claims description 3
- 238000009749 continuous casting Methods 0.000 claims description 3
- 239000002105 nanoparticle Substances 0.000 claims 3
- 230000001186 cumulative effect Effects 0.000 claims 2
- 238000013000 roll bending Methods 0.000 claims 1
- 238000005728 strengthening Methods 0.000 abstract description 45
- 239000000463 material Substances 0.000 abstract description 33
- 230000008569 process Effects 0.000 abstract description 29
- 238000001556 precipitation Methods 0.000 abstract description 27
- 230000008859 change Effects 0.000 abstract description 13
- RMLPZKRPSQVRAB-UHFFFAOYSA-N tris(3-methylphenyl) phosphate Chemical compound CC1=CC=CC(OP(=O)(OC=2C=C(C)C=CC=2)OC=2C=C(C)C=CC=2)=C1 RMLPZKRPSQVRAB-UHFFFAOYSA-N 0.000 abstract description 6
- 229910052796 boron Inorganic materials 0.000 abstract description 3
- 229910052799 carbon Inorganic materials 0.000 abstract description 2
- 230000000052 comparative effect Effects 0.000 description 27
- 229910000859 α-Fe Inorganic materials 0.000 description 19
- 230000000694 effects Effects 0.000 description 17
- 229910001566 austenite Inorganic materials 0.000 description 16
- 239000010949 copper Substances 0.000 description 12
- 238000010587 phase diagram Methods 0.000 description 10
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 8
- 239000011159 matrix material Substances 0.000 description 8
- 238000000227 grinding Methods 0.000 description 7
- 239000000047 product Substances 0.000 description 7
- 238000012360 testing method Methods 0.000 description 7
- 238000005299 abrasion Methods 0.000 description 6
- 230000009466 transformation Effects 0.000 description 6
- 229910045601 alloy Inorganic materials 0.000 description 5
- 239000000956 alloy Substances 0.000 description 5
- 230000009286 beneficial effect Effects 0.000 description 5
- 230000006872 improvement Effects 0.000 description 5
- 229910052758 niobium Inorganic materials 0.000 description 5
- 238000010791 quenching Methods 0.000 description 5
- 230000000171 quenching effect Effects 0.000 description 5
- 229910052719 titanium Inorganic materials 0.000 description 5
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 4
- 238000003908 quality control method Methods 0.000 description 4
- 238000007670 refining Methods 0.000 description 4
- 238000011217 control strategy Methods 0.000 description 3
- 230000007547 defect Effects 0.000 description 3
- 239000007787 solid Substances 0.000 description 3
- 230000002195 synergetic effect Effects 0.000 description 3
- 239000006004 Quartz sand Substances 0.000 description 2
- 229910004283 SiO 4 Inorganic materials 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 230000006911 nucleation Effects 0.000 description 2
- 238000010899 nucleation Methods 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- 229910001562 pearlite Inorganic materials 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 238000004781 supercooling Methods 0.000 description 2
- 229910052718 tin Inorganic materials 0.000 description 2
- 229910052720 vanadium Inorganic materials 0.000 description 2
- 238000003466 welding Methods 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 229910052840 fayalite Inorganic materials 0.000 description 1
- 230000000977 initiatory effect Effects 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- 229910000734 martensite Inorganic materials 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 230000024121 nodulation Effects 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 229910052698 phosphorus Inorganic materials 0.000 description 1
- 238000005381 potential energy Methods 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 238000001953 recrystallisation Methods 0.000 description 1
- 230000002787 reinforcement Effects 0.000 description 1
- 230000003014 reinforcing effect Effects 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 238000005482 strain hardening Methods 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 238000004506 ultrasonic cleaning Methods 0.000 description 1
Classifications
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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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0242—Flattening; Dressing; Flexing
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/004—Dispersions; Precipitations
-
- 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
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Abstract
The invention discloses a hot-rolled ultra-high strength steel plate with excellent comprehensive performance and a manufacturing method thereof, wherein the chemical components of the hot-rolled ultra-high strength steel plate comprise C, si, mn, B, ti, nb, cu, als, fe, and the chemical components simultaneously meet the following requirements: ti-3.42 x N-3*S-B is more than or equal to 0.13% and less than or equal to 0.18%; the heat-treatment-free TMCP process is adopted, the strengthening mode is precipitation strengthening, phase change strengthening and fine grain strengthening, the tensile strength of the material is more than or equal to 1200MPa, the wear resistance reaches NM360 level, the cold bending performance reaches 180 degrees, D=2a is qualified, the unevenness of a plate is controlled to be less than or equal to 5mm/m, the plate shape percent of pass is more than or equal to 95%, and the material has the advantages of high surface, high plate shape, high strength, high wear resistance, easy forming, low production cost and the like, and can be applied to manufacturing high-strength wear-resistant parts such as special vehicles, engineering machinery and the like.
Description
Technical Field
The invention belongs to the technical field of wear-resistant steel, and particularly relates to a hot-rolled ultrahigh-strength steel plate with excellent comprehensive performance and a manufacturing method thereof.
Background
With the increasingly obvious development trend of light weight in industries such as special vehicles, engineering machinery and the like, 700 MPa-level high-strength steel cannot meet the light weight technical requirement of downstream industries, the market demand of hot-rolled high-strength steel with the pressure of more than or equal to 1000MPa is increased sharply, preliminary statistics is carried out, the market demand of thin-specification hot-rolled high-strength steel with the pressure of Rm of more than or equal to 1000MPa in China is about 80-100 ten thousand tons/year, and the market demand is huge.
Regarding hot rolled high-strength steel with the grade of more than or equal to 1000MPa, the main flow production process at present is quenching and tempering heat treatment, and a quenching and tempering heat treatment product has the advantages of high strength, high wear resistance, stable plate shape and the like, but has long process flow and high production cost, and the product has limited forming performance, the cold bending performance can only ensure 90 degrees, and D=6a is qualified.
The other process is TMCP (controlled rolling and controlled cooling), and has no heat treatment process, and is divided into two processes of phase change strengthening and precipitation strengthening according to a material strengthening mode. Adopts a phase transformation strengthening mode, such as the patent published by the publication number CN103233161A, CN104532126A, CN108411203A, CN110760752A, CN111334720A and the like, the tensile strength of the product is more than or equal to 1000MPa, the structure type is martensite and ferrite, and the product has the advantages of high strength, high wear resistance, easy forming and the like. The phase change strengthening mode can well solve the problem that the material strength is high and the forming is difficult to achieve, but on one hand, the shape control difficulty of the phase change strengthening type hot rolled high-strength steel is high and the industry is always difficult due to the influences of thin product specification, high ultra-fast cooling strength, narrow cooling process window, low-temperature coiling and the like; on the other hand, si with higher content is often added in the chemical components, so that the surface red rust is serious, and the surface quality control is not facilitated. On one hand, the precipitation strengthening mode is adopted, such as the patent disclosed in the publication No. CN105734423A, CN106119700A, on the other hand, precious microalloy elements Nb and V with higher content are added into chemical components, and the alloy cost is higher; on the other hand, the chemical components are added with Si with higher content, so that the surface red rust is serious, and the surface quality control is not facilitated; on the other hand, the chemical components are added with higher content of Al, so that the Al is easy to be combined with the important component SiO in the casting powder 2 The reaction is carried out, so that the nozzle of the crystallizer is easy to generate nodulation and blockage, and the pouring property of molten steel is poor.
The chemical components of the ultra-high strength precipitation-strengthened steel disclosed by the publication No. CN113215500A adopt medium C, high Mn, high Ti, high Sn and Cr, si and Sn with a certain content, and the corrosion resistance can be improved, but on one hand, the chemical components are added with Sn with higher content and the alloy cost is higher; on the other hand, sn has low melting point, oxidation potential energy lower than that of iron, is easy to gather at grain boundary, is easy to form a low-melting-point enrichment phase on the surface of a slab, causes surface net-shaped cracks on the surface of hot-rolled strip steel, and is unfavorable for the surface quality control of casting blanks and hot-rolled strip steel.
In summary, for the disclosed patent of hot rolled high-strength steel with the pressure of more than or equal to 1000MPa, the quenching and tempering heat treatment method has the defects of long process flow, high production cost, limited material forming performance and the like. The heat-treatment-free TMCP method and the material strengthening mode are phase change strengthening, so that the problem of difficult plate shape control exists. The heat-treatment-free TMCP method is adopted, the material strengthening mode is precipitation strengthening, and the problems of high alloy cost, poor molten steel castability, serious red rust on the surface of the strip steel, easy occurrence of surface net cracks on the surface of the strip steel and the like exist.
Disclosure of Invention
Aiming at the problems of high production cost, poor surface quality, difficult plate shape control, easy cracking in forming and the like in the existing hot-rolled high-strength steel with the pressure of more than or equal to 1000MPa, the invention provides a hot-rolled ultra-high-strength steel plate with excellent comprehensive performance and a manufacturing method thereof, wherein a heat-treatment-free TMCP process is adopted, the strengthening mode is precipitation strengthening, phase change strengthening and fine grain strengthening, the tensile strength of the material is more than or equal to 1200MPa, the wear resistance reaches NM360 level, the cold bending performance reaches 180 degrees, D=2a is qualified, the plate opening unevenness is controlled to be less than or equal to 5mm/m, the plate shape qualification rate is more than or equal to 95%, and the material has the advantages of high surface, high plate shape, high strength, high wear resistance, easy forming, low production cost and the like, and can be applied to manufacturing of high-strength wear-resistant parts such as special vehicles, engineering machinery and the like.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
a hot rolled ultra-high strength steel plate with excellent comprehensive performance comprises the following chemical components in percentage by weight: c: 0.09-0.15%; si:0.10 to 0.20 percent; mn:1.80 to 3.00 percent; ti:0.14 to 0.22 percent; nb:0.015 to 0.030 percent; b:0.0010 to 0.0030 percent; cu:0.10 to 0.40 percent; als: 0.020-050%; p: less than or equal to 0.012%; s: less than or equal to 0.005%; n: less than or equal to 0.0050%; o: less than or equal to 0.0030 percent, and the balance of Fe and unavoidable impurities, and simultaneously meets the following requirements: ti-3.42 x N-3*S-B is less than or equal to 0.13% and less than or equal to 0.18%.
The metallographic structure of the hot-rolled ultra-high strength steel plate is lath bainite+polygonal ferrite, the volume fraction of lath bainite is 86-90%, the equivalent grain size of lath bainite is 10-20 mu m, and the average grain size of polygonal ferrite is 2.1-4.5 mu m.
The hot rolled ultra-high strength steel plate contains submicron-level precipitates and nano-level precipitates, wherein the size of the submicron-level precipitates is 100-300 nm, the size of the nano-level precipitates is 8-30nm, and the proportion of submicron-level and nano-level precipitates is 0.30-0.45%.
The submicron-level precipitate is TiC and NbC submicron-level precipitate; the nano-scale precipitates are TiC and NbC nano-scale precipitates.
The yield strength of the hot-rolled ultrahigh-strength steel plate is more than or equal to 900MPa, the tensile strength is more than or equal to 1200MPa, the wear resistance reaches NM360 level, the cold bending performance reaches 180 degrees, D=2a is qualified, the open plate unevenness is controlled to be less than or equal to 5mm/m, and the plate shape qualification rate is more than or equal to 95%.
The invention provides a manufacturing method of a hot-rolled ultra-high strength steel plate with excellent comprehensive performance, which comprises the following steps: smelting, continuous casting, heating, rolling, cooling, coiling, flattening and flattening.
In the heating step, the tapping temperature of the casting blank is 1230-1280 ℃, the temperature of the head part of the casting blank in the length direction is 20-30 ℃ lower than the temperature of the tail part of the casting blank, and the heat preservation time of the casting blank temperature is controlled to be more than or equal to 1230 ℃ for 30-50 min.
In the rolling step, rolling is carried out by adopting a 2-frame rough rolling mill and 7-frame finish rolling hot continuous rolling mill, primary high-pressure water descaling, rough rolling inter-pass descaling, secondary high-pressure water descaling before a finishing mill group and descaling water among the frames of finish rolling F1-F3 are opened.
In the rolling step, the rough rolling finishing temperature is 1080-1130 ℃, the rough rolling accumulated rolling reduction is more than or equal to 80%, the finish rolling accumulated rolling reduction is more than or equal to 85%, and the convexity C of the F7 stand 40 Is 10-30 mu m, wedge-shaped W 40 The finish rolling temperature FDT is 850-900 ℃ and the finish rolling speed of the F7 stand is more than or equal to 7m/s.
In the cooling and coiling steps, the strip steel is cooled to 620-680 ℃ at a cooling speed of more than or equal to 100 ℃/s after rolling, is cooled to 460-520 ℃ at a cooling speed of more than or equal to 50 ℃/s after air cooling for 8-15 s, is coiled, is covered with a heat preservation cover for on-line tempering treatment after coiling and coil unloading, is removed from the heat preservation cover after heat preservation for 60-90 min, and is cooled to room temperature.
In the cooling and coiling step, the strip steel is cooled to 620-680 ℃ at a cooling speed of 100-115 ℃/s after rolling, is cooled to 460-520 ℃ at a cooling speed of 50-80 ℃/s for coiling after air cooling for 8-15 s, is covered with a heat preservation cover for on-line tempering treatment after coiling and coil unloading, and is removed from the heat preservation cover after heat preservation for 60-90 min and is cooled to room temperature.
In the leveling step, the rolling force of the leveling machine is 500-700 t, the bending force is 80-100 t, and the leveling speed is 40-100 m/min.
In the hot rolled ultra-high strength steel plate with excellent comprehensive performance, the functions and the control of each component are as follows:
c:0.09% -0.15%, C is a basic element in steel, plays a very important role in improving the strength and hardness of the steel, and in order to obtain higher strength and hardness, the content of C must be ensured to be more than 0.09%, but the content of C cannot be high, and when the content of C is more than or equal to 0.17%, on one hand, a hollow cooling section is easy to produce pearlite structure in the cooling process, so that the tensile strength of the material is only about 800MPa, and the strength is lower; on the other hand, in the cooling process, a certain proportion of ferrite is difficult to form in the hollow cold section, and the plasticity of the material is affected.
Si:0.10 to 0.20 percent, si has the function of solid solution strengthening, can improve the strength of the material, but the content of Si is too high, the red rust on the surface of the strip steel is serious and difficult to remove, and the control of the surface quality is not facilitated. Meanwhile, when the Si content is more than or equal to 0.10%, the copper embrittlement defect can be improved.
Mn:1.80 to 3.00 percent of Mn is taken as a reinforcing element of steel, the hardenability of the steel can be obviously improved, the strength of the steel is improved, in order to ensure that the tensile strength of the material is more than or equal to 1200MPa, the Mn content is controlled to be more than 1.8 percent, but the Mn content cannot be more than 3.0 percent, on one hand, the center segregation of a casting blank is easy to cause, and the welding performance and the forming performance of the material are not facilitated; on the other hand, mn as an original for improving the stability of austenite increases the content of retained austenite, and conversely decreases the strength and hardness of the material.
Ti:0.14 to 0.22 percent, ti is used as an important element of the invention, and the purpose of adding higher content is to increase the grain refining effect of the prior austenite by the synergistic effect of the Ti and Nb element in the heating process; on the other hand, ti which is dissolved in the matrix in the heating process can separate out a large amount of nano TiC after cooling and air-cooling sections and coiling and heat preservation, thereby playing the role of precipitation strengthening and improving the strength and hardness of the material. The Ti which is not dissolved in the matrix in the heating process is refined into submicron TiC in the subsequent rolling and cooling process, and the submicron TiC has high hardness, so that the wear resistance of the material can be obviously improved; in addition, ti can fix excessive B, so that the quantity of FeB and the like precipitated in a grain boundary can be reduced, and the FeB is dispersed and distributed on a ferrite matrix, thereby being beneficial to improving the strength, the hardness and the wear resistance of the material. In order to fully exert the precipitation strengthening effect of Ti, ti-3.42 x N-3*S-B is not less than 0.13%, when the content of Ti-3.42 x N-3*S-B is more than 0.18% according to the analysis of a solid solubility product formula, the total solid solution temperature of TiC is more than 1285 ℃, a large amount of hard micron-sized TiC is formed after rolling and cooling in the heating process, and the micron-sized TiC becomes a crack initiation source, which is unfavorable for the plasticity and toughness of materials and cold bending forming performance.
Nb:0.015% -0.030%, the effect of refining austenite grains in the heating and rolling processes of Nb and Ti is more remarkable than that of adding Nb or adding Ti alone, and Nb achieves the effect of refining ferrite and bainite grains finally mainly by dragging strong solute on austenite grain boundaries through the synergistic effect of Nb and Ti in the heating process and improving the recrystallization temperature in the rolling process.
B:0.0010% -0.0030%, B is used as another important element of the invention, can be used for improving the austenite stability, and can avoid forming pearlite structure in the cooling air cooling section on the one hand; on the other hand, the transformation from austenite to ferrite can be delayed, and the problems of formation of a large amount of soft-phase ferrite structure, material strength and hardness reduction caused by the increase of TiC precipitation quantity and the increase of precipitation strengthening effect in the cooling air cooling section and the need of prolonging air cooling time are avoided. The addition of a certain amount of B can properly prolong the air cooling time, inhibit ferrite formation, increase the quantity and proportion of TiC precipitates and improve the precipitation strengthening effect.
Cu:0.10% -0.40%, the solid solubility of Cu in austenite is relatively large, the solid solubility of Cu in ferrite is relatively small, after rolling, the austenite phase is converted into ferrite phase after cooling, a large amount of fine Cu-containing precipitate particles can be separated out from the ferrite matrix, and the strength of the ferrite matrix is enhanced. Therefore, adding Cu with a certain content can improve the precipitation strengthening effect, the material strength, the hardness and the wear resistance. However, the Cu content is not high, the problem of Cu embrittlement is easily formed in the rolling process when Cu is more than or equal to 0.50%, and the Cu content is preferably less than or equal to 0.40% based on the comprehensive consideration of the precipitation strengthening and the problem of Cu embrittlement.
Als:0.020 to 0.050 percent, wherein Als is mainly used as a deoxidizer and can react with N to generate AlN pinning grain boundary to play a role of refining grains.
P, S as an impurity element adversely affects the properties of steel such as plasticity, forming, welding, etc., and the lower the content thereof, the better the production cost factor is considered, and P is controlled in actual production: less than or equal to 0.012 percent, S: less than or equal to 0.005 percent.
O, N as a harmful gas element, since Ti is extremely active, it preferentially reacts with O, N to precipitate, which affects the yield of Ti, the precipitation amount of TiC and the precipitation strengthening effect, and N: less than or equal to 0.0050%; o: less than or equal to 0.0030 percent. .
In the manufacturing method of the hot rolled ultrahigh-strength steel plate with excellent comprehensive performance, high-temperature heating and gradient heating are adopted in the heating process, and the heat preservation time of a high-temperature section is emphasized to be prolonged instead of the total time of a furnace. The purposes of high-temperature heating and the tapping temperature of the casting blank is 1230-1280 ℃, on one hand, the method aims at improving the atomic proportion of Ti dissolved in a matrix and creating conditions for precipitating a large amount of TiC precipitates in the cooling and coiling process; on the other hand, the temperature of the slab is controlled during the descaling with high-pressure water before rough rolling>1173℃Ensure fayalite Fe 2 SiO 4 Is in a molten state and is easy to remove, and prevent Fe 2 SiO 4 The nail is rolled on the surface of the steel plate matrix, and is difficult to remove. The heat preservation time of the casting blank temperature of more than or equal to 1230 ℃ is controlled to be 30-50 min, so that Ti atoms can be fully dissolved into a matrix for enough time, and meanwhile, the defects that the strength is not improved due to too thick austenite grains and the surface quality is not controlled due to too thick scale. The temperature of the head part of the casting blank in the length direction is 20-30 ℃ lower than the temperature of the tail part, and the casting blank is mainly used for constant-speed rolling.
In the rolling process, the primary high-pressure water descaling, the rough rolling inter-pass descaling, the secondary high-pressure water descaling before the finishing mill group and the descaling water among the frames of finish rolling F1-F3 are all opened to remove oxidized iron scales on the surface of the strip steel as much as possible, so that the surface quality is improved. The rough rolling stage gives full play to the characteristics of high temperature and large deformation, so that austenite is fully recrystallized. The method improves the accumulated deformation of the non-recrystallized region in the finish rolling stage and combines with lower finish rolling temperature, is favorable for generating larger accumulated strain energy, increases nucleation positions, refines the austenite grain size and the grain size of converting austenite into ferrite or bainite, and improves the fine grain strengthening effect. The improvement of the finish rolling speed is mainly to reduce the precipitation of submicron TiC in austenite as much as possible and improve the precipitation quantity of nanometer TiC in the cooling air cooling section and the coiling process. Meanwhile, in order to control the quality of the finish rolling outlet plate shape, a control strategy of small convexity, small wedge shape and constant speed rolling is adopted.
According to the invention, on the cooling process, a control strategy of sectional cooling and online tempering after coiling is adopted, so that the synergistic effect of three strengthening modes of fine grain strengthening, precipitation strengthening and phase change strengthening is fully exerted, and the problem that precipitation strengthening (high coiling temperature requirement) and phase change strengthening (low coiling temperature requirement) cannot be achieved by adopting a one-stage continuous cooling process after rolling is avoided. The cooling speed after rolling is more than or equal to 100 ℃ per second, mainly aims to improve the transformation supercooling degree and increase the nucleation position, refines the ferrite grain size formed by austenite transformation and the bainite grain size formed by residual austenite transformation, and is beneficial to improving the material strength and the cold roll forming performance. The main purpose of rapid cooling to 620-680 ℃ is that the temperature range is near the temperature of the nose tip of the PTT curve, and on the premise that the proportion of ferrite of the B element is stably controlled in a certain range, nano TiC precipitates with more proportion can be rapidly formed, thereby fully playing the precipitation strengthening effect and the improving effect of hard TiC on the wear resistance of the material. The air cooling time is controlled between 8 and 15 seconds, if the air cooling time is less than 8 seconds, the quantity of TiC precipitation is small, and if the air cooling time is more than 15 seconds, the ferrite proportion is gradually increased, the grain size is increased, the TiC precipitation proportion is large, but the quantity of precipitation strengthening on the increase of the material strength is smaller than the quantity of reduction of the ferrite proportion on the transformation strengthening, on the contrary, the improvement of the material strength, the hardness and the wear resistance is not facilitated, and the laminar cooling line length is limited, and the condition of long-time air cooling is not provided. The air cooling starting temperature is controlled between 620 ℃ and 680 ℃, if the air cooling temperature is more than 700 ℃, the supercooling degree is small, the phase change driving force is low, the ferrite tissue proportion is small, the ferrite grain size growth speed is high, the ferrite grain size is large, meanwhile, the temperature is not in the optimal precipitation temperature range of TiC precipitates at more than 700 ℃, the quantity of TiC precipitates is small, the size is large, and the improvement of the material strength, the hardness and the wear resistance is not facilitated. If the air cooling temperature is too low, especially <620 ℃, the bainitic structure and the phase change strengthening effect are better, but the quantity of TiC precipitates and the precipitation strengthening effect are reduced at the same time, which is unfavorable for improving the strength and the wear resistance of the final material. After air cooling, the steel plate is rapidly cooled to 460-520 ℃ at a speed of more than or equal to 50 ℃/s, and medium-temperature coiling is adopted, so that on one hand, lath bainite with higher strength can be obtained, and the effect of phase change reinforcement on material strength improvement is fully exerted; on the other hand, compared with low-temperature coiling (less than or equal to 300 ℃), the medium-temperature coiling has obvious advantages in the aspect of controlling the shape of the thin high-strength hot rolled strip steel. Meanwhile, on-line tempering is carried out by matching with a coiling and heat-preserving process, on one hand, tiC which is not precipitated in a cooling air cooling section can be continuously precipitated, and the precipitation strengthening effect is further improved; on the other hand, the uniformity control of the length, the width direction temperature, the mechanical property and the residual stress of the hot coil is facilitated, the plate shape quality is further facilitated, and the plate shape flatness is improved.
The invention carries out the leveling process after coiling, mainly based on the consideration of improving the strip steel shape and the uniformity of the width direction performance, and under the condition of ensuring the strip steel shape, the control strategy of small leveling force and large bending roller force is preferentially adopted, and the main purpose is to avoid the aggravation of the strip steel work hardening degree and not to be beneficial to the uniformity of the strip steel width direction performance. Meanwhile, in order to control the strip shape stability in the flattening process, the strip flattening speed is not too high.
Compared with the prior art, the invention has the following beneficial effects:
1) The invention adopts the low-C low-Si high-Mn high-Ti and Nb, B and Cu alloying design in the chemical composition design, does not add Mo, V, ni, sn and other noble alloy elements, has lower alloy cost and lower Si element, and is beneficial to surface quality control;
2) The invention adopts TMCP process, has no quenching and tempering heat treatment process, short process flow and lower process cost by 1000-1200 yuan/t compared with the quenching and tempering heat treatment process.
3) The invention adopts a sectional cooling process, can fully exert the effect of two strengthening modes of precipitation strengthening and phase change strengthening on the improvement of the material strength, solves the problem that the traditional one-section continuous cooling process is difficult to obtain the effect of high precipitation strengthening and high phase change strengthening at the same time, and the hot rolled steel plate produced by the invention has the tensile strength of more than or equal to 1200MPa, the hardness of more than or equal to 360HB, the cold bending performance of 180 degrees, D=2a is qualified, better solves the difficult problems of coordinated control of high strength, high hardness and easy forming, and is suitable for manufacturing high-strength and high-wear-resistant structural members such as engineering machinery, special vehicles and the like.
4) The unevenness of the hot rolled steel plate produced by the invention after transverse cutting and leveling is controlled to be less than or equal to 5mm/m, preferably to be 0mm/m, the qualification rate of the plate shape is more than or equal to 95%, and the plate shape can better meet the use requirements of downstream users.
Drawings
FIG. 1 is a typical golden phase diagram of a hot rolled ultra high strength steel sheet in example 1;
FIG. 2 is a typical golden phase diagram of the hot rolled ultra high strength steel sheet in example 2;
FIG. 3 is a typical golden phase diagram of the hot rolled ultra high strength steel sheet in example 3;
FIG. 4 is a typical golden phase diagram of the hot rolled ultra high strength steel sheet in example 4;
FIG. 5 is a typical golden phase diagram of a hot rolled steel sheet in comparative example 1;
FIG. 6 is a typical golden phase diagram of a hot rolled steel sheet in comparative example 2;
FIG. 7 is a typical golden phase diagram of a hot rolled steel sheet in comparative example 3;
FIG. 8 is a typical golden phase diagram of a hot rolled steel sheet in comparative example 4;
FIG. 9 is a typical golden phase diagram of a hot rolled steel sheet in comparative example 5;
FIG. 10 is a typical golden phase diagram of a hot rolled steel sheet in comparative example 6.
Detailed Description
The invention provides a hot-rolled ultrahigh-strength steel plate with excellent comprehensive performance, which comprises the following chemical components in percentage by weight: c: 0.09-0.15%; si:0.10 to 0.20 percent; mn:1.80 to 3.00 percent; ti:0.14 to 0.22 percent; nb:0.015 to 0.030 percent; b:0.0010 to 0.0030 percent; cu:0.10 to 0.40 percent; als: 0.020-050%; p: less than or equal to 0.012%; s: less than or equal to 0.005%; n: less than or equal to 0.0050%; o: less than or equal to 0.0030 percent, and the balance of Fe and unavoidable impurities, and simultaneously meets the following requirements: ti-3.42 x N-3*S-B is less than or equal to 0.13% and less than or equal to 0.18%.
The manufacturing method of the hot rolled ultrahigh-strength steel plate with excellent comprehensive performance comprises the following steps: smelting, continuous casting, heating, rolling, cooling, coiling, flattening and flattening.
In the heating step, the tapping temperature of the casting blank is 1230-1280 ℃, the temperature of the head part of the casting blank in the length direction is 20-30 ℃ lower than the temperature of the tail part of the casting blank, and the heat preservation time of the casting blank temperature is controlled to be more than or equal to 1230 ℃ for 30-50 min.
In the rolling step, rolling is carried out by adopting a 2-frame rough rolling mill and 7-frame finish rolling hot continuous rolling mill, primary high-pressure water descaling, rough rolling inter-pass descaling, secondary high-pressure water descaling before a finishing mill group and descaling water among the frames of finish rolling F1-F3 are opened.
In the rolling step, the rough rolling finishing temperature is 1080-1130 ℃, the rough rolling accumulated rolling reduction is more than or equal to 80%, the finish rolling accumulated rolling reduction is more than or equal to 85%, and the convexity C of the F7 stand 40 Is 10-30 mu m, wedge-shaped W 40 Is-10 mu m, the final rolling temperature FDT is 850-900 ℃, and the constant-speed rolling and the F7 frame final rolling speed are adopted≥7m/s。
In the cooling and coiling steps, the strip steel is cooled to 620-680 ℃ at a cooling speed of more than or equal to 100 ℃/s after rolling, is cooled to 460-520 ℃ at a cooling speed of more than or equal to 50 ℃/s after air cooling for 8-15 s, is coiled, is covered with a heat preservation cover for on-line tempering treatment after coiling and coil unloading, is removed from the heat preservation cover after heat preservation for 60-90 min, and is cooled to room temperature.
In the cooling and coiling step, the strip steel is cooled to 620-680 ℃ at a cooling speed of 100-115 ℃/s after rolling, is cooled to 460-520 ℃ at a cooling speed of 50-80 ℃/s for coiling after air cooling for 8-15 s, is covered with a heat preservation cover for on-line tempering treatment after coiling and coil unloading, and is removed from the heat preservation cover after heat preservation for 60-90 min and is cooled to room temperature.
In the leveling step, the rolling force of the leveling machine is 500-700 t, the bending force is 80-100 t, and the leveling speed is 40-100 m/min.
The present invention will be described in detail with reference to examples.
The chemical compositions of the examples and the comparative examples are shown in Table 1, the rolling process parameters are shown in Table 2, the cooling process parameters are shown in Table 3, the leveling process parameters are shown in Table 4, the structure types are shown in Table 5, the mechanical properties are shown in Table 6, the plate shape percent of pass of the plate opening plate is shown in Table 7, and the abrasion loss weight and the relative abrasion resistance are shown in Table 8.
Table 1 chemical Components (weight percent, wt%) of examples and comparative examples
Table 2 rolling process parameters of examples and comparative examples
Table 3 cooling process parameters for examples and comparative examples
Table 4 example and comparative example planarization process parameters
TABLE 5 tissue types for examples and comparative examples
Table 6 mechanical properties of examples and comparative examples
Table 7 plate shape yield of examples and comparative examples
Remarks: the unevenness of the open plate is less than or equal to 8mm/m, and the plate shape percent of pass is equal to the weight of the open plate qualified product/the weight of the hot coil.
Table 8 grinding loss weight and relative abrasion resistance of examples and comparative examples
| Numbering device | The loss weight delta m (g) of the mill | Relative wear resistance |
| Example 1 | 1.5516 | 1.54 |
| Example 2 | 1.5623 | 1.53 |
| Example 3 | 1.5501 | 1.55 |
| Example 4 | 1.5454 | 1.55 |
| Comparative example 1 | 2.0399 | 1.17 |
| Comparative example 2 | 1.9318 | 1.24 |
| Comparative example 3 | 2.0863 | 1.15 |
| Comparative example 4 | 2.3026 | 1.04 |
| Comparative example 5 | 2.2408 | 1.07 |
| Comparative example 6 | 2.3954 | 1.00 |
| Comparative example 7 | 1.7314 | 1.38 |
| Comparative example 8 | 1.4339 | 1.64 |
| Comparative example 9 | 1.5561 | 1.53 |
Note that: the abrasive wear test was performed on an MLS-225 wet rubber wheel tester, and the sample size of the abrasive wear test was: 57mm (length). Times.25.5 mm (width). Times.2.5 mm (thickness), wherein the 57 mm.times.25.5 mm face is a wear face, the wear face is polished. The test parameters were as follows: the hardness of the rubber wheel is 60HS, the rotating speed of the rubber wheel is 240r/min, the abrasive is a solution formed by mixing quartz sand and water according to the proportion of 1:1, the particle size of the quartz sand is 20-40 meshes, and the load is 170N. Firstly, the abrasion surface of a sample is subjected to 1000r pre-grinding, the weight m1 of the sample after the pre-grinding is recorded, then the sample is subjected to 60min fine grinding, the weight m2 of the sample after the fine grinding is recorded, the sample after the pre-grinding and the sample after the fine grinding are subjected to ultrasonic cleaning, and the weight is measured by adopting an electronic balance (the precision is 0.1 mg). The wear loss weight Deltam (m 1-m 2) is taken as a main parameter for evaluating the wear resistance of the material, and the smaller the wear loss weight is, the better the wear resistance of the material is. 3 pieces of each test material were respectively selected under the same test conditions for the abrasive wear test, and the average value of the abrasion loss weights of 3 pieces of the test materials was taken as the final abrasion loss weight.
Relative wear resistance = wear loss weight of example or comparative example/loss weight of comparative example 6, with reference to loss weight of comparative example 6.
The above detailed description of a hot rolled ultra high strength steel sheet having excellent combination properties and a method for manufacturing the same with reference to the examples is illustrative and not restrictive, and several examples can be enumerated according to the restricted scope, so that variations and modifications may be considered within the scope of the present invention without departing from the general inventive concept.
Claims (11)
1. The hot rolled ultrahigh-strength steel plate with excellent comprehensive performance is characterized by comprising the following chemical components in percentage by weight: c: 0.09-0.15%; si:0.10 to 0.20 percent; mn:1.80 to 3.00 percent; ti:0.14 to 0.22 percent; nb:0.015 to 0.030 percent; b:0.0010 to 0.0030 percent; cu:0.10 to 0.40 percent;
als: 0.020-050%; p: less than or equal to 0.012%; s: less than or equal to 0.005%; n: less than or equal to 0.0050%; o: less than or equal to 0.0030 percent, and the balance of Fe and unavoidable impurities, and simultaneously meets the following requirements: ti-3.42 x N-3*S-B is less than or equal to 0.13% and less than or equal to 0.18%.
2. The hot-rolled ultra-high strength steel sheet having excellent combination properties according to claim 1, wherein the metallographic structure of the hot-rolled ultra-high strength steel sheet is lath bainite+polygonal ferrite, the volume fraction of lath bainite is 86 to 90%, the equivalent grain size of lath bainite is 10 to 20 μm, and the average grain size of polygonal ferrite is 2.1 to 4.5 μm.
3. The hot-rolled ultra-high strength steel sheet having excellent combination properties according to claim 1, wherein the hot-rolled ultra-high strength steel sheet contains submicron-sized precipitates and nano-sized precipitates, wherein the submicron-sized precipitates are 100 to 300nm in size, the nano-sized precipitates are 8 to 30nm in size, and the proportion of submicron + nano-sized precipitates is 0.30 to 0.45%.
4. The hot-rolled ultra-high strength steel sheet with excellent comprehensive properties according to claim 1, wherein the yield strength of the hot-rolled ultra-high strength steel sheet is more than or equal to 900MPa, the tensile strength is more than or equal to 1200MPa, the wear resistance reaches NM360 level, the cold bending performance reaches 180 °, d=2a is qualified, the open plate unevenness is controlled to be less than or equal to 5mm/m, and the plate shape qualification rate is more than or equal to 95%.
5. The method for manufacturing a hot rolled ultra high strength steel sheet having excellent combination properties as claimed in any one of claims 1 to 4, comprising the steps of: smelting, continuous casting, heating, rolling, cooling, coiling, flattening and flattening.
6. The method according to claim 5, wherein in the heating step, the tapping temperature of the casting blank is 1230-1280 ℃, the head temperature of the casting blank in the length direction is 20-30 ℃ lower than the tail temperature, and the heat preservation time of the casting blank temperature is controlled to be greater than or equal to 1230 ℃ for 30-50 min.
7. The method according to claim 5, wherein in the rolling step, rolling is performed by using a hot tandem rolling mill set of 2-stand rough rolling and 7-stand finish rolling, and the primary high-pressure water descaling, the descaling between rough rolling passes, the secondary high-pressure water descaling before the finishing mill set, and the descaling between the stands of finish rolling F1 to F3 are all opened.
8. The method according to claim 5, wherein in the rolling step, the rough rolling finishing temperature is 1080 to 1130 ℃, the rough rolling cumulative rolling reduction is 80% or more, the finish rolling cumulative rolling reduction is 85% or more, and the F7 stand convexity C 40 Is 10-30 mu m, wedge-shaped W 40 The finish rolling temperature FDT is 850-900 ℃ and the finish rolling speed of the F7 stand is more than or equal to 7m/s.
9. The method according to claim 5, wherein in the cooling and coiling steps, the strip steel is cooled to 620-680 ℃ at a cooling rate of not less than 100 ℃/s after rolling, is cooled to 460-520 ℃ at a cooling rate of not less than 50 ℃/s after air cooling for 8-15 s, is coiled, is covered with a heat preservation cover for on-line tempering after coiling and uncoiling, is removed from the heat preservation cover after heat preservation for 60-90 min, and is cooled to room temperature.
10. The method according to claim 5, wherein in the cooling and coiling steps, the strip steel is cooled to 620-680 ℃ at a cooling rate of 100-115 ℃/s after rolling, is cooled to 460-520 ℃ at a cooling rate of 50-80 ℃/s after air cooling for 8-15 s, is coiled, is covered with a heat preservation cover for on-line tempering after coiling and coil stripping, is removed from the heat preservation cover after heat preservation for 60-90 min, and is cooled to room temperature.
11. The method according to claim 5, wherein in the flattening step, the flattening machine has a rolling force of 500 to 700t, a roll bending force of 80 to 100t, and a flattening rate of 40 to 100m/min.
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