CN117488017A - Preparation method of cold-rolled hot-dip galvanized steel with high yield strength and high elongation - Google Patents
Preparation method of cold-rolled hot-dip galvanized steel with high yield strength and high elongation Download PDFInfo
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- 229910001335 Galvanized steel Inorganic materials 0.000 title claims abstract description 19
- 239000008397 galvanized steel Substances 0.000 title claims abstract description 19
- 238000002360 preparation method Methods 0.000 title claims abstract description 18
- 238000001816 cooling Methods 0.000 claims abstract description 105
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 72
- 239000010959 steel Substances 0.000 claims abstract description 72
- 238000000137 annealing Methods 0.000 claims abstract description 57
- 238000005098 hot rolling Methods 0.000 claims abstract description 49
- 238000005096 rolling process Methods 0.000 claims abstract description 49
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 33
- 238000010438 heat treatment Methods 0.000 claims abstract description 33
- 238000005097 cold rolling Methods 0.000 claims abstract description 32
- 238000010791 quenching Methods 0.000 claims abstract description 30
- 230000000171 quenching effect Effects 0.000 claims abstract description 30
- 238000000034 method Methods 0.000 claims abstract description 24
- 238000005242 forging Methods 0.000 claims abstract description 14
- 238000009776 industrial production Methods 0.000 claims abstract description 7
- 229910052742 iron Inorganic materials 0.000 claims abstract description 6
- 238000004519 manufacturing process Methods 0.000 claims abstract description 6
- 229910001566 austenite Inorganic materials 0.000 claims description 25
- 238000005246 galvanizing Methods 0.000 claims description 22
- 150000003839 salts Chemical class 0.000 claims description 22
- 238000004321 preservation Methods 0.000 claims description 11
- 230000002829 reductive effect Effects 0.000 claims description 10
- 229910000859 α-Fe Inorganic materials 0.000 claims description 6
- 229910001562 pearlite Inorganic materials 0.000 claims description 3
- 230000000087 stabilizing effect Effects 0.000 claims description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 abstract description 8
- 238000009826 distribution Methods 0.000 abstract description 3
- 239000002184 metal Substances 0.000 abstract description 2
- 229910052751 metal Inorganic materials 0.000 abstract description 2
- 229910000734 martensite Inorganic materials 0.000 description 20
- 230000000052 comparative effect Effects 0.000 description 18
- 229910001563 bainite Inorganic materials 0.000 description 17
- 230000000717 retained effect Effects 0.000 description 12
- 238000001878 scanning electron micrograph Methods 0.000 description 6
- 230000009466 transformation Effects 0.000 description 5
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 4
- 229910052799 carbon Inorganic materials 0.000 description 4
- 230000003247 decreasing effect Effects 0.000 description 4
- 238000000638 solvent extraction Methods 0.000 description 4
- 229910001567 cementite Inorganic materials 0.000 description 3
- 230000007547 defect Effects 0.000 description 3
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 238000005728 strengthening Methods 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 238000002441 X-ray diffraction Methods 0.000 description 2
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 238000004134 energy conservation Methods 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 239000000446 fuel Substances 0.000 description 2
- 238000011534 incubation Methods 0.000 description 2
- 238000001556 precipitation Methods 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 229910052725 zinc Inorganic materials 0.000 description 2
- 239000011701 zinc Substances 0.000 description 2
- 238000003723 Smelting Methods 0.000 description 1
- CSDREXVUYHZDNP-UHFFFAOYSA-N alumanylidynesilicon Chemical compound [Al].[Si] CSDREXVUYHZDNP-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000001887 electron backscatter diffraction Methods 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000009472 formulation Methods 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 230000036961 partial effect Effects 0.000 description 1
- 238000007747 plating Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 238000012827 research and development Methods 0.000 description 1
- 230000002441 reversible effect Effects 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 239000013585 weight reducing agent Substances 0.000 description 1
Classifications
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0236—Cold rolling
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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Abstract
The invention belongs to the technical field of metal rolling, and particularly relates to a preparation method of cold-rolled hot-dip galvanized steel with high yield strength and high elongation, wherein a traditional continuous annealing production line (industrial production) does not consider a unique quenching and distribution process during design, so that the cold-rolled hot-dip galvanized Q & P980 steel has lower yield strength-low elongation. The invention is characterized by comprising the following steps of 1: heating the forging blank, removing iron scales, and hot rolling; step 2: furnace cooling to room temperature; step 3: simulating the industrial cover annealing treatment; step 4: cold rolling; step 5: continuously annealing, and cooling to room temperature by water. Finally, the cold-rolled hot-dip galvanized Q & P980 steel with high yield strength and high elongation is produced.
Description
Technical Field
The invention belongs to the technical field of metal rolling, and particularly relates to a preparation method of cold-rolled hot-dip galvanized steel with high yield strength and high elongation.
Background
In the field of automobiles, people pay more attention to the environmental protection and safety of automobiles, and in order to reduce carbon dioxide emission and fuel consumption, the weight reduction of automobiles is one of key means. Under the premise of ensuring safety, high-strength steel, in particular advanced high-strength steel, is the most economical and effective method for lightening the automobile body at present, so that the research and development of the advanced high-strength steel has become a hot spot and a difficult point for the researches of students and various automobile companies. As one of the representative advanced high-strength steels, quenched and distributed steels (Q & P steels) are attracting attention due to their excellent high strength-plasticity, and their application to automobiles is advantageous for improving the safety of automobiles. At present, Q & P steel is widely applied by automobile enterprises to process parts with extremely high requirements on steel strength, such as automobile A column hinge plates, front and rear anti-collision beams and the like. In addition, the Q & P steel can reduce the thickness of parts, reduce fuel loss, effectively realize energy conservation and consumption reduction, and accord with the development direction of energy conservation and environmental protection steel advocated by China.
The Q & P steel process first heats the steel to full or partial austenitization, then quenches to a point between the Ms and Mf points (forming part of the martensite, denoted as initial martensite), then performs partitioning (partitioning of carbon in the initial martensite into unconverted austenite) at or above the quenching temperature, and finally performs quenching. Since carbon in the initial martensite is distributed into the unconverted austenite during the distribution process, the unconverted austenite is more stable, part of the austenite can be reserved to room temperature and is marked as residual austenite, and the residual austenite improves the plasticity through transformation induced plasticity (TRIP effect) during the service process.
The hot dip galvanizing Q & P steel technology under laboratory conditions calculates the optimal quenching temperature according to the components of Q & P through a thermodynamic theoretical model (CCE model), wherein the optimal quenching temperature is generally about 200 ℃. The quenching temperature in the hot dip galvanizing Q & P steel process is critical, and determines the content of initial martensite, the distribution of carbon, the stability of residual austenite, the content of each phase in a final structure and the final mechanical property. However, the conventional continuous annealing production line (industrial production) is not designed with a unique quenching and partitioning process in mind. The traditional continuous annealing line design has the following defects: (1) The reverse heating capacity of the high-frequency induction heater is limited (the limit heating capacity is about 150 ℃), and the hot galvanizing Q & P steel production process needs to meet the temperature condition of 460 ℃ of hot galvanizing, so that the hot galvanizing Q & P steel has higher quenching temperature (the quenching temperature is 300-350 ℃), and the initial martensite content in a final-state structure is less under the higher quenching temperature condition; (2) The partitioning (incubation at 460 ℃) is short (incubation time 20s-90 s) resulting in less carbon content in the unconverted austenite and thus less bainite content in the final structure. The initial martensite and bainite contents in the final structure are low, so that the secondary martensite content in the final structure is high, the obtained residual austenite is unstable, and the cold-rolled hot-dip galvanized Q & P980 steel has low yield strength and low elongation.
At present, the Q & P980 steel produced in China is bare sheet cold-rolled Q & P980 steel (cold-rolled: CR), and the bare sheet cold-rolled Q & P980 steel is easy to corrode and oxidize; the other type is cold-rolled hot-dip galvanized Q & P980 steel, and the aluminum-silicon coating or the nano zinc coating on the surface of the cold-rolled hot-dip galvanized Q & P980 steel is used for solving the problem that the surface is easy to oxidize and corrode, but the current cold-rolled hot-dip galvanized Q & P980 steel products in the market have the following defects: (1) The product with low yield strength and high elongation rate Q & P980 has the brand CR550/980QP, the yield strength of 550MPa-750MPa, the elongation rate A50 of 18.0% or more and the tensile strength of 980MPa or more; (2) The product with high yield strength and low elongation rate Q & P980 has the brand CR650/980QP, the yield strength of 650MPa-850MPa, the elongation rate A50 of 15.0% or more and the tensile strength of 980MPa or more. Therefore, in the market, the hot dip galvanized Q & P980 product is difficult to achieve both high yield strength and high elongation, namely, the yield strength is 650MPa-850MPa, and the elongation A50 is not less than 18.0%. In the automotive industry, however, the need for an advanced high strength steel with excellent formability and a high resistance to deformation during service is becoming more and more intense, so that the production of a cold-rolled hot-dip Q & P980 steel product with high yield strength-high elongation is a hot spot of research.
Disclosure of Invention
Aiming at the problem of low yield strength and low elongation of cold-rolled hot-dip galvanized Q & P980 steel under the condition of high quenching temperature, the invention provides a preparation method of cold-rolled hot-dip galvanized steel with high yield strength and high elongation.
A preparation method of cold-rolled hot-dip galvanized steel with high yield strength and high elongation comprises the following steps:
step 1: heating and preserving heat of the forging blank in a heating furnace, removing iron scales, and performing hot rolling to obtain a hot rolled plate;
step 2: after the hot rolling is finished, performing primary furnace cooling on the hot rolled plate, and performing secondary furnace cooling to room temperature after cooling to obtain a hot rolled steel plate;
step 3: the hot rolled steel plate after furnace cooling is put into an atmosphere furnace for heating, and the industrial covering and annealing treatment is simulated;
step 4: cold rolling the hot-rolled steel plate for 6-8 passes to obtain a cold-rolled plate;
step 5: continuous annealing: the cold-rolled sheet is put into an atmosphere furnace for heating and preserving heat for a certain time, then is put into a salt bath furnace for simulating industrial quenching and preserving heat for a certain time, then is put into the salt bath furnace for simulating industrial hot galvanizing and preserving heat for a certain time, and finally is cooled to room temperature.
The steel comprises the following components in percentage by mass: c:0.15% -0.30%, mn:1.00% -2.50%, si:1.00% -2.00%, al:0.01% -0.10%, ti:0.01% -0.03%, cr:0.01% -0.30% and the balance of Fe.
And C is an element for stabilizing austenite in the cold-rolled hot-dip galvanized steel.
In the step 1, the forging blank is heated to 1150-1200 ℃ in a heating furnace and is kept for 1-2 h, the hot rolling start temperature is 1100-1200 ℃, the hot rolling pass is 6-8 passes, the final rolling temperature is 880-950 ℃, and the thickness of a hot rolled plate is 1.5-2.6 mm.
In the step 2, the first furnace cooling rate is 5 ℃/s-30 ℃/s, and the temperature is reduced to 500 ℃ -700 ℃; the second furnace cooling rate is 20 ℃/s, and the furnace is cooled to room temperature.
In the step 2, the microstructure of the hot rolled steel sheet is ferrite and lamellar pearlite.
In the step 3, the temperature range of the cover annealing is as follows: the cover-removing time is 3h-10h at 500-700 ℃, and then air cooling is carried out to room temperature.
In the step 4, the thickness of the cold-rolled sheet is 0.8mm-1.6mm.
In the step 5, the temperature is heated to 840-860 ℃ and the heat preservation time is 66-110 s after heating.
In the step 5, the quenching temperature is 300-350 ℃, the cooling rate is 30-50 ℃/s, and the heat preservation time after quenching is 32-52 s.
In the step 5, the hot galvanizing temperature is 460 ℃, and the heat preservation time after hot galvanizing is 27s-34s.
In the step 5, in actual industrial production, the heat preservation time of each specific stage is determined by the continuous annealing line belt speed, and the belt speed of the general industrial production is 60m/min-100m/min.
The principle of the invention is as follows:
a too high C content deteriorates the weldability, and therefore cold-rolled hot dip galvanizing Q&The content of C in the P980 steel is 0.15-0.30%; mn is added to reduce Ms point and improve stability of austenite, but when Mn content is high, component segregation is liable to occur, so cold-rolled hot dip zinc Q&Mn content in P980 steel is 1.00% -2.50%; si is a non-carbide forming element and can strongly inhibit Fe 3 C is formed, but higher Si content deteriorates hot rolling property and surface plating property of steel, more surface defects and the like are generated, so Si content is 1.00% -2.00%; al is mainly used for deoxidizing, so that 0.01 to 0.10 percent of aluminum is added for removing oxides in molten steel; the main roles of Ti in steel are fine-grain strengthening and precipitation strengthening,the mass percentage of Ti is 0.01-0.03%; the main function of Cr in the steel is precipitation strengthening, and the mass percentage of Cr is 0.01-0.30%.
Compared with the prior art, the preparation method of the cold-rolled hot-dip galvanized steel with high yield strength and high elongation has the following beneficial effects:
under the condition of high quenching temperature (quenching temperature range: 300-350 ℃), the shape (spheroidization and coarsening) of cementite in an initial structure is regulated and controlled through a covering and annealing process, so that the bainite content in a final structure is remarkably improved, the secondary martensite content is reduced, the bainite content in the final structure of the cold-rolled hot-dip galvanized Q & P980 steel is improved from 18.0% to 30.0-45.0%, and the secondary martensite content is reduced from 30.0-10.0%.
The problems of low yield strength and low elongation of hot dip galvanized Q & P980 steel under the conditions of high quenching temperature and short formulation time are solved by a covering and annealing process, the yield strength is improved from 458MPa which is not covered to 650MPa-850MPa, the elongation A50 is improved from 18.2% which is not covered to 20.0% -22.0%, the tensile strength is 980MPa-1080MPa, and the mechanical properties of the hot dip galvanized Q & P980 steel are compatible with those of national standard marks CR550/980QP and CR650/980QP products.
The preparation method has low requirements on equipment of a continuous annealing production line, and the annealing temperature is less than or equal to 860 ℃ and is 840-860 ℃; the quenching temperature is not less than 300 ℃ and is 300 ℃ to 350 ℃.
Drawings
FIG. 1 is a process flow diagram of hot dip galvanizing Q & P980;
FIG. 2 is an SEM image of the initial structure of comparative example 1;
FIG. 3 is an SEM image of the final structure of comparative example 1;
FIG. 4 is an XRD pattern of the final structure of comparative example 1;
FIG. 5 is an SEM image of the initial structure of example 1;
FIG. 6 is an SEM image of the final structure of example 1;
FIG. 7 is an XRD pattern for the final structure of example 1;
FIG. 8 is an SEM image of the final structure of example 2;
FIG. 9 is an SEM image of the final structure of example 3.
Detailed Description
In the embodiment of the invention, an Ultra55 field emission scanning electron microscope of Zeiss company is adopted for representing microstructure, rigaku D/Max2400 equipment is adopted for representing residual austenite, a SANSCT-30000 stretcher is adopted for a stretcher, and the steps of industrial production are simulated: smelting, casting, forging, hot rolling, furnace cooling, simulated industrial cover annealing treatment, cold rolling and continuous annealing, and the process flow is shown in figure 1.
Comparative example 1
Cold-rolled hot-dip galvanized Q & P980 steel with low yield strength and low elongation comprises the following components in percentage by mass: c:0.18%, mn:1.90%, si:1.50%, al:0.03%, ti:0.02%, cr:0.02% of Fe and the balance of Fe;
the preparation method comprises the following steps:
step 1: heating the forged blank with the components to 1200 ℃ along with a furnace, preserving heat for 2 hours, removing surface iron scales, carrying out hot rolling for 6 times at a hot rolling start temperature of 1180 ℃, and carrying out hot rolling for each pass at rolling reduction rates of 36.0%, 38.0%, 37.8%, 35.0%, 29.0% and 23.5%, wherein a final rolling temperature of 890 ℃ to obtain a hot rolled plate with the thickness of 2.6 mm;
step 2: cooling to 580 ℃ at a cooling rate of 30 ℃/s after hot rolling, then placing the hot rolled steel plate into a pit type heating furnace for furnace cooling, wherein the furnace cooling rate is 20 ℃/h, and cooling to room temperature to obtain a hot rolled steel plate, and the structure of the hot rolled steel plate is shown in figure 2: lamellar cementite and ferrite;
step 3: cold rolling: cold rolling the hot rolled steel plate, wherein the cold rolling passes are 6 passes, the total reduction is 61.5%, the reduction rate of each pass is 20.0%, 10.0% and 7.0%, and the final thickness of the final rolled plate is 1mm;
step 4: continuous annealing treatment: the cold-rolled sheet with the thickness of 1mm is placed into an atmosphere furnace to be heated to 855 ℃ and kept for 82.5 seconds, then placed into a salt bath furnace with the temperature of 310 ℃ to simulate industrial quenching, cooled to 310 ℃ at the cooling speed of 40 ℃/s and kept for 39 seconds, then placed into the salt bath furnace with the temperature of 460 ℃ to simulate industrial hot galvanizing, kept for 34 seconds, and finally cooled to the room temperature by water.
The final structure obtained is shown in fig. 3, and the structure is as follows: ferrite, primary martensite, bainite, secondary martensite, and retained austenite. The primary martensite content was found to be 10.0%, the bainite content was 18.0%, the secondary martensite content was found to be 30.0%, and the retained austenite content was found to be 24.0% by XRD (fig. 4), the mechanical properties were: yield strength 458MPa, tensile strength 986MPa and elongation 18.3%.
Example 1
Cold-rolled hot-dip galvanized Q & P980 steel with 650MPa yield strength and high elongation, and the steel comprises the following components in percentage by mass: c:0.18%, mn:1.90%, si:1.50%, al:0.03%, ti:0.02%, cr:0.02% of Fe and the balance of Fe;
the preparation method comprises the following steps:
step 1: rolling and cooling control treatment: heating the forging blank of the components to 1200 ℃ along with a furnace and preserving heat for 2 hours; removing furnace iron scale, and performing 6-pass hot rolling, wherein the reduction rate of each pass of hot rolling is 36.0%, 38.0%, 37.8%, 35.0%, 29.0% and 23.5%, and the hot rolling start temperature and the hot rolling finish temperature are 1180 ℃ and 890 ℃ respectively, so as to roll into a hot rolled plate with the thickness of 2.6 mm;
step 2: cooling to 580 ℃ at a cooling rate of 30 ℃/s after hot rolling, and then carrying out furnace-following cooling, wherein the furnace cooling rate is 20 ℃/h, and cooling to room temperature to obtain a hot-rolled steel plate;
step 3: simulating industrial cover annealing: the hot rolled steel plate after furnace cooling is covered and withdrawn for 5 hours in an atmosphere heating furnace, the covering and withdrawing temperature is 580 ℃, and then air cooling is carried out to room temperature, and the structure is shown in fig. 5: spheroidized cementite and ferrite were spheroidized and coarsened in lamellar pearlite as compared to comparative example 1;
step 4: cold rolling: cold rolling the hot rolled plate subjected to the cover withdrawal, wherein the cold rolling passes are 6 passes, the total reduction is 61.5%, the reduction rate of each pass is 20.0%, 10.0% and 7.0%, and the final thickness of the final rolled plate is 1mm and the final rolled plate is subjected to continuous withdrawal;
step 5: continuous annealing treatment: the cold-rolled sheet is put into an atmosphere furnace to be heated to 855 ℃ and kept for 82.5 seconds, then is put into a salt bath furnace at 310 ℃ to simulate industrial quenching, the cooling speed is 40 ℃/s, the temperature is kept for 39 seconds, then is put into the salt bath furnace at 460 ℃ to simulate industrial hot galvanizing, the temperature is kept for 34 seconds, and finally the water cooling is carried out to room temperature.
Example 1 differs from comparative example 1: example 1 a shield annealing process was performed before cold rolling, the shield annealing process being at 580 ℃ for 5 hours. The final structure is shown in FIG. 6, and is organized as: ferrite, primary martensite, bainite, secondary martensite and retained austenite, the secondary martensite content was found to be reduced (about 20.0%) by the phase transformation statistics, the bainite content was more (about 35.0%), the bainite content was increased by the cage back, the secondary martensite content was reduced, and the retained austenite content was found to be reduced to 17.0% by XRD (fig. 7), but the size of the retained austenite was thinned by the EBSD found cage back process, compared to comparative example 1. The stretching result shows that the mechanical property can be improved by the cover annealing process. The yield strength is increased from 458MPa to 659MPa of comparative example 1, the tensile strength is increased from 986MPa to 1055MPa, and the elongation is increased from 18.3% to 20.8%.
Example 2
Cold-rolled hot-dip galvanized Q & P980 steel with 650MPa yield strength and high elongation, and the steel comprises the following components in percentage by mass: c:0.18%, mn:1.90%, si:1.50%, al:0.03%, ti:0.02%, cr:0.02% of Fe and the balance of Fe;
the preparation method comprises the following steps:
step 1: rolling and cooling control treatment: heating the forging blank of the components to 1200 ℃ along with a furnace and preserving heat for 1h; descaling, removing scale, and rolling into a hot rolled plate with the thickness of 2.6mm by 6 times of hot rolling, wherein the reduction rate of each time of hot rolling is 36.0%, 38.0%, 37.8%, 35.0%, 29.0% and 23.5%, and the hot rolling start rolling temperature and the hot rolling finish rolling temperature are 1180 ℃ and 880 ℃ respectively;
step 2: cooling to 580 ℃ at a cooling rate of 30 ℃/s after hot rolling, cooling along with a furnace at a furnace cooling rate of 20 ℃/h, and cooling to room temperature;
step 3: simulating industrial cover annealing: covering and annealing the hot rolled plate after furnace cooling in an atmosphere heating furnace for 3 hours, wherein the covering and annealing temperature is 700 ℃, and then air cooling to room temperature;
step 4: cold rolling: cold rolling the hot rolled sheet after the cover is removed: the cold rolling passes are 6 passes, the total rolling reduction is 61.5%, the rolling reduction of each pass is 20.0%, 10.0% and 7.0%, and the final thickness of the final rolled plate is 1mm for continuous annealing;
step 5: continuous annealing treatment: the cold-rolled sheet is put into an atmosphere furnace to be heated to 860 ℃ and kept for 82.5 seconds, then is put into a salt bath furnace with the temperature of 300 ℃ to simulate industrial quenching, the cooling speed is 40 ℃/s, the temperature is kept for 39 seconds, then is put into a salt bath furnace with the temperature of 460 ℃ to simulate industrial hot galvanizing, the temperature is kept for 34 seconds, and finally the water cooling is carried out to the room temperature.
The final structure was characterized by SEM, and as shown in fig. 8, the final structure was found to have a higher bainite content than that of comparative example 1, the bainite content was found to be increased from 18.0% to 45.0% by calculation with a phase transformation machine, the secondary martensite content was found to be decreased from 30.0% to 10.0%, and the retained austenite content was found to be decreased from 24.0% to 17.0% by XRD. Compared with comparative example 1, the yield strength of the steel is improved from the uncovered back 458MPa to 652MPa, the tensile strength is improved from 986MPa to 1056MPa, and the elongation is improved from 18.3% to 20.6%.
Example 3
Cold-rolled hot-dip galvanized Q & P980 steel with 650MPa yield strength and high elongation, and the steel comprises the following components in percentage by mass: c:0.18%, mn:1.90%, si:1.50%, al:0.03%, ti:0.02%, cr:0.02% of Fe and the balance of Fe;
the preparation method comprises the following steps:
step 1: rolling and cooling control treatment: heating the forging blank of the components to 1200 ℃ along with a furnace and preserving heat for 1h; descaling, removing scale, and rolling into a hot rolled plate with the thickness of 2.6mm by 6 times of hot rolling, wherein the reduction rate of each time of hot rolling is 36.0%, 38.0%, 37.8%, 35.0%, 29.0% and 23.5%, and the hot rolling start rolling temperature and the hot rolling finish rolling temperature are 1100 ℃ and 880 ℃ respectively;
step 2: cooling to 500 ℃ at a cooling rate of 5 ℃/s after hot rolling, cooling along with a furnace at a furnace cooling rate of 20 ℃/h, and cooling to room temperature;
step 3: simulating industrial cover annealing: covering and annealing the hot rolled plate after furnace cooling in an atmosphere heating furnace for 10 hours at the covering and annealing temperature of 580 ℃, and then air-cooling to room temperature;
step 4: cold rolling: cold rolling the hot rolled sheet after the cover is removed: the cold rolling passes are 6 passes, the total rolling reduction is 61.5%, the rolling reduction of each pass is 20.0%, 10.0% and 7.0%, and the final thickness of the final rolled plate is 1mm for continuous annealing;
step 5: continuous annealing treatment: the cold-rolled sheet is put into an atmosphere furnace to be heated to 840 ℃ and kept for 82.5s, then is put into a salt bath furnace at 310 ℃ to simulate industrial quenching, the cooling speed is 40 ℃/s, the temperature is kept for 39s, then is put into a salt bath furnace at 460 ℃ to simulate industrial hot galvanizing, the temperature is kept for 34s, and finally the water cooling is carried out to room temperature.
The final structure is shown in FIG. 9, and the final structure of example 3 has a bainite content of 35.0%, a secondary martensite content of 19.0% and a retained austenite content of 18.0%, which are substantially identical to those of example 1. In addition, the yield strength is increased from 458MPa to 653MPa, the tensile strength is increased from 986MPa to 1050MPa, and the elongation is increased from 18.3% to 20.0%.
Example 4
Cold-rolled hot-dip galvanized Q & P980 steel with yield strength of 800MPa and high elongation, and the steel comprises the following components in percentage by mass: c:0.30%, mn:2.50%, si:1.00%, al:0.03%, ti:0.02%, cr:0.02% of Fe and the balance of Fe;
the preparation method comprises the following steps:
step 1: rolling and cooling control treatment: heating the forging blank of the components to 1150 ℃ along with a furnace and preserving heat for 2 hours; removing furnace iron scale, and performing 8-pass hot rolling to obtain a hot rolled plate with the thickness of 2.1mm, wherein the rolling reduction rate of each pass of hot rolling is respectively 20.0%, 20%, 38.0%, 37.8%, 35.0%, 29.0% and 23.5%, and the initial rolling temperature and the final rolling temperature of 20.0% are respectively 1100 ℃ and 950 ℃;
step 2: cooling to 700 ℃ at a cooling rate of 30 ℃/s after hot rolling, cooling along with a furnace at a furnace cooling rate of 20 ℃/h, and cooling to room temperature;
step 3: simulating industrial cover annealing: covering and annealing the hot rolled plate after furnace cooling in an atmosphere heating furnace for 10 hours at the covering and annealing temperature of 500 ℃, and then air-cooling to room temperature;
step 4: cold rolling: cold rolling the hot rolled sheet after the cover is removed: the cold rolling passes are 7 passes, the total rolling reduction is 69%, the rolling reduction of each pass is 20.0%, 10.0%, 7.0% and 20.0%, and the final thickness of the cold-rolled sheet is 0.8mm, and the cold-rolled sheet is continuously annealed;
step 5: continuous annealing treatment: the cold-rolled sheet is put into an atmosphere furnace to be heated to 855 ℃ and kept for 82.5 seconds, then is put into a salt bath furnace at 310 ℃ to simulate industrial quenching, the cooling speed is 40 ℃/s, the temperature is kept for 39 seconds, then is put into the salt bath furnace at 460 ℃ to simulate industrial hot galvanizing, the temperature is kept for 34 seconds, and finally the water cooling is carried out to room temperature.
The results of phase transformation and XRD revealed that the bainite content in the final structure of example 4 was increased from 18.0% to 35.0%, the retained austenite content was decreased from 24.0% to 19.0%, and that the yield strength was increased from 458MPa to 836MPa, the tensile strength was increased from 986MPa to 1033MPa, and the elongation was increased from 18.3% to 21.6% in comparison with comparative example 1.
Example 5
Cold-rolled hot-dip galvanized Q & P980 steel with 650MPa yield strength and high elongation, and the steel comprises the following components in percentage by mass: c:0.15%, mn:2.50%, si:1.00%, al:0.10%, ti:0.02%, cr:0.02% of Fe and the balance of Fe;
the preparation method comprises the following steps:
step 1: rolling and cooling control treatment: heating the forging blank of the components to 1150 ℃ along with a furnace and preserving heat for 2 hours; descaling, removing scale, and rolling into a hot rolled plate with the thickness of 2.1mm by 8 times of hot rolling, wherein the reduction rate of each time of hot rolling is respectively 20.0%, 20%, 38.0%, 37.8%, 35.0%, 29.0%, 23.5%, and the initial rolling temperature and the final rolling temperature of 20.0% of hot rolling are respectively 1100 ℃ and 880 ℃;
step 2: cooling to 500 ℃ at a cooling rate of 30 ℃/s after hot rolling, cooling along with a furnace at a furnace cooling rate of 20 ℃/h, and cooling to room temperature;
step 3: simulating industrial cover annealing: covering and annealing the hot rolled plate after furnace cooling in an atmosphere heating furnace for 8 hours, wherein the covering and annealing temperature is 500 ℃, and then air cooling to room temperature;
step 4: cold rolling: cold rolling the hot rolled sheet after the cover is removed: the cold rolling passes are 7 passes, the total rolling reduction is 69%, the rolling reduction of each pass is 20.0%, 10.0%, 7.0% and 20.0%, and the final thickness of the cold-rolled sheet is 0.8mm, and the cold-rolled sheet is continuously annealed;
step 5: continuous annealing treatment: the cold-rolled sheet is put into an atmosphere furnace to be heated to 840 ℃ and kept for 110 seconds, then is put into a salt bath furnace at 350 ℃ to simulate industrial quenching, the cooling speed is 40 ℃/s and kept for 52 seconds, then is put into a salt bath furnace at 460 ℃ to simulate industrial hot galvanizing, and is kept for 45 seconds, and finally is cooled to room temperature.
The results of phase transformation and XRD revealed that the bainite content in the final structure of example 5 was increased from 18.0% to 33.0%, the retained austenite content was decreased from 24.0% to 17.0%, and that the yield strength was increased from 458MPa to 676MPa, the tensile strength was increased from 986MPa to 1067MPa, and the elongation was increased from 18.3% to 21.0% in comparison with comparative example 1.
Example 6
Cold-rolled hot-dip galvanized Q & P980 steel with 650MPa yield strength and high elongation, and the steel comprises the following components in percentage by mass: c:0.15%, mn:1.00%, si:2.00%, al:0.03%, ti:0.02%, cr:0.30% of Fe and the balance of Fe;
the preparation method comprises the following steps:
step 1: rolling and cooling control treatment: heating the forging blank of the components to 1200 ℃ along with a furnace and preserving heat for 2 hours; descaling, removing furnace scale, and rolling into a hot rolled plate with the thickness of 2.6mm by 6 times of hot rolling, wherein the reduction rate of each time of hot rolling is 36%, 38.0%, 37.8%, 35.0%, 29.0% and 23.5% respectively, and the initial rolling temperature and the final rolling temperature of the hot rolling are 1100 ℃ and 880 ℃ respectively;
step 2: cooling to 580 ℃ at a cooling rate of 30 ℃/s after hot rolling, cooling along with a furnace at a furnace cooling rate of 20 ℃/h, and cooling to room temperature;
step 3: simulating industrial cover annealing: covering and annealing the hot rolled plate after furnace cooling in an atmosphere heating furnace for 5 hours at the covering and annealing temperature of 580 ℃, and then air-cooling to room temperature;
step 4: cold rolling: cold rolling the hot rolled sheet after the cover is removed: the cold rolling passes are 7 passes, the total rolling reduction is 69%, the rolling reduction of each pass is 20.0%, 10.0%, 7.0% and 20.0%, and the final thickness of the cold-rolled sheet is 0.8mm, and the cold-rolled sheet is continuously annealed;
step 5: continuous annealing treatment: the cold-rolled sheet is put into an atmosphere furnace to be heated to 840 ℃ and kept for 82.5s, then is put into a salt bath furnace with the temperature of 300 ℃ to simulate industrial quenching, the cooling speed is 40 ℃/s, the temperature is kept for 39s, then is put into a salt bath furnace with the temperature of 460 ℃ to simulate industrial hot galvanizing, the temperature is kept for 34s, and finally the water cooling is carried out to the room temperature.
Compared with comparative example 1, the bainite content in the final structure of example 6 is improved from 18.0% to 32.0%, the retained austenite content is reduced from 24.0% to 18.0%, and the mechanical properties of the composition are compared with those of comparative example 1: the yield strength is improved from 458MPa to 666MPa, the tensile strength is improved from 986MPa to 1067MPa, and the elongation is improved from 18.3% to 22.0%.
Example 7
Cold-rolled hot-dip galvanized Q & P980 steel with 650MPa yield strength and high elongation, and the steel comprises the following components in percentage by mass: c:0.25%, mn:1.00%, si:1.50%, al:0.03%, ti:0.02%, cr:0.02% of Fe and the balance of Fe;
the preparation method comprises the following steps:
step 1: rolling and cooling control treatment: heating the forging blank of the components to 1200 ℃ along with a furnace and preserving heat for 2 hours; descaling, removing furnace scale, and rolling into a hot rolled plate with the thickness of 2.6mm by 6 times of hot rolling, wherein the reduction rate of each time of hot rolling is 36%, 38.0%, 37.8%, 35.0%, 29.0% and 23.5% respectively, and the initial rolling temperature and the final rolling temperature of the hot rolling are 1100 ℃ and 880 ℃ respectively;
step 2: cooling to 580 ℃ at a cooling rate of 30 ℃/s after hot rolling, cooling along with a furnace at a furnace cooling rate of 20 ℃/h, and cooling to room temperature;
step 3: simulating industrial cover annealing: covering and annealing the hot rolled plate after furnace cooling in an atmosphere heating furnace for 5 hours, wherein the covering and annealing temperature is 580 ℃, and then air cooling to room temperature;
step 4: cold rolling: cold rolling the hot rolled sheet after the cover is removed: the cold rolling passes are 6 passes, the total rolling reduction is 53.9%, the rolling reduction of each pass is 20.0%, 10.0%, 8.0% and 4.0%, and the final thickness of the cold-rolled sheet is 1.2mm for continuous annealing;
step 5: continuous annealing treatment: the cold-rolled sheet is put into an atmosphere furnace to be heated to 860 ℃ and kept for 82.5 seconds, then is put into a salt bath furnace with the temperature of 300 ℃ to simulate industrial quenching, the cooling speed is 40 ℃/s, the temperature is kept for 39 seconds, then is put into a salt bath furnace with the temperature of 460 ℃ to simulate industrial hot galvanizing, the temperature is kept for 34 seconds, and finally the water cooling is carried out to the room temperature.
Compared with comparative example 1, the bainite content in the final structure of example 7 was increased from 18.0% to 35.0%, and the retained austenite content was reduced from 24.0% to 17.0%, as compared with comparative example 1, and the mechanical properties thereof were found: the yield strength is improved from 458MPa to 656MPa, the tensile strength is improved from 986MPa to 1047MPa, and the elongation is improved from 18.3% to 21.0%.
Example 8
Cold-rolled hot-dip galvanized Q & P980 steel with yield strength of 800MPa and high elongation, and the steel comprises the following components in percentage by mass: c:0.25%, mn:2.50%, si:1.50%, al:0.10%, ti:0.02%, cr:0.02% of Fe and the balance of Fe;
the preparation method comprises the following steps:
step 1: rolling and cooling control treatment: heating the forging blank of the components to 1200 ℃ along with a furnace and preserving heat for 2 hours; descaling, removing furnace scale, and rolling into a hot rolled plate with the thickness of 2.6mm by 6 times of hot rolling, wherein the reduction rate of each time of hot rolling is 36%, 38.0%, 37.8%, 35.0%, 29.0% and 23.5% respectively, and the initial rolling temperature and the final rolling temperature of the hot rolling are 1100 ℃ and 880 ℃ respectively;
step 2: cooling to 580 ℃ at a cooling rate of 30 ℃/s after hot rolling, cooling along with a furnace at a furnace cooling rate of 20 ℃/h, and cooling to room temperature;
step 3: simulating industrial cover annealing: covering and annealing the hot rolled plate after furnace cooling in an atmosphere heating furnace for 5 hours, wherein the covering and annealing temperature is 580 ℃, and then air cooling to room temperature;
step 4: cold rolling: cold rolling the hot rolled sheet after the cover is removed: the cold rolling passes are 6 passes, the total rolling reduction is 53.8%, the rolling reduction of each pass is respectively 10.0%, 8.0% and 9.0%, the final thickness of the cold-rolled sheet is 1.6mm, and the cold-rolled sheet is subjected to continuous annealing;
step 5: continuous annealing treatment: the cold-rolled sheet is put into an atmosphere furnace to be heated to 860 ℃ and kept for 66 seconds, then is put into a salt bath furnace at 350 ℃ to simulate industrial quenching, the cooling speed is 40 ℃/s, the temperature is kept for 32 seconds, then is put into the salt bath furnace at 460 ℃ to simulate industrial hot galvanizing, the temperature is kept for 27 seconds, and finally the temperature is cooled to the room temperature.
Compared with comparative example 1, the bainite content in the final structure of example 8 is improved from 18.0% to 38.0%, the retained austenite content is reduced from 24.0% to 18.0%, and the mechanical properties of the composition are compared with those of comparative example 1: the yield strength is improved from 458MPa to 816MPa, the tensile strength is improved from 986MPa to 1040MPa, and the elongation is improved from 18.3% to 20.0%.
Claims (10)
1. The preparation method of the cold-rolled hot-dip galvanized steel with high yield strength and high elongation is characterized by comprising the following steps:
step 1: heating and preserving heat of the forging blank in a heating furnace, removing iron scales, and performing hot rolling to obtain a hot rolled plate;
step 2: after the hot rolling is finished, performing primary furnace cooling on the hot rolled plate, and performing secondary furnace cooling to room temperature after cooling to obtain a hot rolled steel plate;
step 3: the hot rolled steel plate after furnace cooling is put into an atmosphere furnace for heating, and the industrial covering and annealing treatment is simulated;
step 4: cold rolling the hot-rolled steel plate for 6-8 passes to obtain a cold-rolled plate;
step 5: continuous annealing: and (3) placing the cold-rolled sheet into an atmosphere furnace for heating and heat preservation, then placing the cold-rolled sheet into a salt bath furnace for simulating industrial quenching and heat preservation, then placing the cold-rolled sheet into the salt bath furnace for simulating industrial hot galvanizing and heat preservation, and finally cooling the cold-rolled sheet to room temperature.
2. The method for preparing the cold-rolled hot-dip galvanized steel with high yield strength and high elongation according to claim 1, wherein the steel comprises the following components in percentage by mass: c:0.15% -0.30%, mn:1.00% -2.50%, si 1.00% -2.00%, al:0.01% -0.10%, ti:0.01% -0.03%, cr:0.01% -0.30%, and the balance of Fe; and C is an element for stabilizing austenite in the cold-rolled hot-dip galvanized steel.
3. The method for preparing the cold-rolled hot-dip galvanized steel with high yield strength and high elongation according to claim 1, wherein in the step 1, the forging blank is heated to 1150-1200 ℃ and kept for 1-2 h in a heating furnace, the hot rolling start temperature is 1100-1200 ℃, the hot rolling pass is 6-8 passes, the final rolling temperature is 880-950 ℃, and the thickness of a hot-rolled plate is 1.5-2.6 mm.
4. The method for preparing cold-rolled hot-dip galvanized steel with high yield strength and high elongation according to claim 1, wherein in the step 2, the first furnace cooling rate is 5 ℃/s-30 ℃/s, and the temperature is reduced to 500 ℃ -700 ℃; the second furnace cooling rate is 20 ℃/s, the furnace cooling is carried out to room temperature, and the microstructure of the hot rolled steel plate is ferrite and lamellar pearlite.
5. The method for preparing cold-rolled hot-dip galvanized steel with high yield strength and high elongation according to claim 1, wherein in the step 3, the temperature range of the shield annealing is as follows: the cover-removing time is 3h-10h at 500-700 ℃, and then air cooling is carried out to room temperature.
6. The method for producing a cold-rolled hot-dip galvanized steel with high yield strength and high elongation according to claim 1, wherein the thickness of the cold-rolled sheet in step 4 is 0.8mm to 1.6mm.
7. The method for preparing cold-rolled hot-dip galvanized steel with high yield strength and high elongation according to claim 1, wherein in the step 5, the steel is heated to 840-860 ℃ and the heat preservation time after heating is 66-110 s.
8. The method for preparing the cold-rolled hot-dip galvanized steel with high yield strength and high elongation according to claim 1, wherein in the step 5, the quenching temperature is 300-350 ℃, the cooling speed is 30-50 ℃/s, and the heat preservation time after quenching is 32-52 s.
9. The method for preparing the cold-rolled hot-dip galvanized steel with high yield strength and high elongation according to claim 1, wherein in the step 5, the hot-dip galvanizing temperature is 460 ℃, and the heat preservation time after hot-dip galvanizing is 27s-34s.
10. The method for preparing cold-rolled hot-dip galvanized steel with high yield strength and high elongation according to claim 1, wherein in step 5, the specific heat preservation time of each stage is determined by continuous annealing line belt speed in actual industrial production, and the belt speed of the general industrial production is 60m/min-100m/min.
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