CN108754307B - Method for producing economical cold-rolled DP780 steel with different yield strength grades - Google Patents
Method for producing economical cold-rolled DP780 steel with different yield strength grades Download PDFInfo
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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Abstract
The invention relates to a method for producing economic cold-rolled DP780 steel with different yield strength grades, which comprises the steps of billet heating, hot rolling, acid rolling and continuous annealing in sequence to prepare the cold-rolled DP780 steel covering three yield strength grades of 400-440 MPa, 450-490 MPa and 510-580 MPa. The invention fully considers the production organization characteristics of steel enterprises aiming at small-batch cold-rolled dual-phase steel, realizes that the cold-rolled DP780 steel products with good surface quality at three yield strength levels of 400-440 MPa, 450-490 MPa and 510-580 MPa can be produced by adopting one component system through reasonable, economic and low-cost component design and effectively controlling key process parameters of each process section, and can meet the special requirements of users on multiple parts and multiple performances of the cold-rolled dual-phase steel products.
Description
Technical Field
The invention relates to the technical field of ferrous metallurgy, in particular to a method for producing economic cold-rolled DP780 steel with different yield strength grades.
Background
In recent years, the environmental protection requirements of the automobile industry are increasingly strict, the traditional automobile is one of the main pollution sources of urban atmosphere, the automobile exhaust treatment is not slow, and the automobile technology will take safety, energy conservation, environmental protection and intelligence as the development direction in the future. The dual-phase steel in the advanced high-strength steel has the characteristics of low yield strength, high tensile strength, good plasticity and the like, and the dosage of the dual-phase steel is expected to exceed 70 percent in the advanced high-strength steel for automobiles. The production of low-cost economical dual-phase steel with stable manufacturing performance has become the pursuit target of various steel enterprises and continuously receives great attention.
In addition, each automobile main engine plant has less goods ordering amount for the cold-rolled dual-phase steel with the same grade, 20-60 tons each time, and many steel enterprises at home and abroad organize and produce 210 tons of high-strength steel with 1 furnace, 8-10 cast blanks are produced, 8-10 coils of finished products can be produced, and each coil weighs about 20-25 tons. Therefore, the production organization characteristics of steel enterprises aiming at small-batch cold-rolled dual-phase steel are fully considered, the economic cold-rolled DP780 steel with good surface quality and different yield strength grades can be produced by adopting one component system through reasonable component design and effective control of process parameters of each process section, the steel enterprises can quickly digest billet stock, the special requirements of multiple parts and multiple performances of the automobile industry can be met, and the technical problem to be solved by technical personnel in the field is urgently needed.
However, the prior art disclosed only for a cold-rolled dual-phase steel of a specific strength grade is clarified of a production method, a working method or a manufacturing method, for example, publication No. CN 105925912A, CN 102758131A, CN 104313460a or the like.
Disclosure of Invention
In order to overcome the defects, the invention aims to provide a method for producing economic cold-rolled DP780 steel with different yield strength grades, which realizes that cold-rolled DP780 steel products with three yield strength grades of 400-440 MPa, 450-490 MPa and 510-580 MPa with good surface quality can be produced by adopting one component system through reasonable, economic and low-cost component design and effectively controlling key process parameters of each process section, and can meet special requirements of users on multiple parts and multiple performances of cold-rolled dual-phase steel products.
The technical scheme adopted by the invention for solving the technical problems is as follows: a method for producing economic cold-rolled DP780 steel with different yield strength grades sequentially adopts a billet heating procedure, a hot rolling procedure, an acid rolling procedure and a continuous annealing procedure to prepare the cold-rolled DP780 steel covering three yield strength grades of 400-440 MPa, 450-490 MPa and 510-580 MPa.
Specifically, the chemical components of the steel billet comprise, by weight: 0.10-0.16%, Si is less than or equal to 0.05%, Mn: 1.80-2.10%, Alt: 0.40-0.60%, Cr: 0.20-0.40%, and limits N to be less than or equal to 0.005%, P to be less than or equal to 0.008%, S to be less than or equal to 0.005%, and the balance being Fe and other inevitable impurities.
Specifically, the thickness of the cold-rolled DP780 steel product is 0.8-2.0 mm.
Specifically, the thickness of the billet used in the billet heating step is 230 mm.
Specifically, in the hot rolling procedure, when the thickness of the hot rolling base stock is more than 2.00mm and less than or equal to 4.00mm, the thickness of the rough rolling outlet billet is 40mm, and when the thickness of the hot rolling base stock is more than 4.00mm and less than or equal to 6.50mm, the thickness of the rough rolling outlet billet is 50 mm.
Specifically, when the cold-rolled DP780 steel with the yield strength level of 400-440 MPa is prepared, the process parameters are as follows:
(1) a billet heating procedure: heating the steel billet, setting the temperature of a soaking section to be 1230-1270 ℃, and soaking for 30-40 min;
(2) a hot rolling procedure: and calculating the pass distribution and the reduction rate of each pass of the rough rolling mill and the finishing rolling mill by a two-stage system rough rolling set model, wherein the outlet temperature of rough rolling is 1050-1090 ℃, the finishing temperature of finish rolling is 890-920 ℃, after finish rolling, a post-rolling front-stage cooling process is adopted, the cooling speed is about 20 ℃/s, the cooling speed is 680-710 ℃, and coiling is carried out.
(3) Acid rolling process: pickling the hot rolled steel coil to remove oxides, and then carrying out cold rolling by adopting the reduction of 68.0-72.0%;
(4) continuous annealing process: and continuously annealing the acid-rolled steel strip, wherein the soaking temperature is 810-830 ℃, the slow cooling section finishing temperature is 670-690 ℃, the fast cooling section finishing temperature is 300-340 ℃, and the overaging section temperature is 280-320 ℃.
Specifically, when the cold-rolled DP780 steel with the yield strength grade of 450-490 MPa is prepared, the process parameters are as follows:
(1) a billet heating procedure: heating the steel billet, setting the temperature of a soaking section to be 1200-1240 ℃, and soaking for 30-40 min;
(2) a hot rolling procedure: the pass distribution and each pass reduction rate of the roughing mill and the finishing mill are calculated by a two-stage system roughing set model; the outlet temperature of rough rolling is 1000-1040 ℃, and the finish rolling temperature is 850-880 ℃; after finishing the finish rolling, adopting a post-rolling front-stage cooling process, cooling to 650-680 ℃ at a cooling rate of about 20 ℃/s, and coiling;
(3) acid rolling process: pickling the hot rolled steel coil to remove oxides, and then carrying out cold rolling by adopting a reduction of 63.0-66.0%;
(4) continuous annealing process: and continuously annealing the acid-rolled steel strip, wherein the soaking temperature is 780-800 ℃, the finishing temperature of a slow cooling section is 660-680 ℃, the finishing temperature of a fast cooling section is 280-330 ℃, and the temperature of an overaging section is 260-310 ℃.
Specifically, when the cold-rolled DP780 steel with the yield strength level of 510-580 MPa is prepared, the working procedure parameters are as follows:
(1) a billet heating procedure: heating the steel billet, setting the temperature of a soaking section to be 1160-1200 ℃, and soaking for less than or equal to 30 min;
(2) a hot rolling procedure: the pass distribution and each pass reduction rate of the roughing mill and the finishing mill are calculated by a two-stage system roughing set model; the outlet temperature of rough rolling is 1040-1080 ℃; the finish rolling temperature is 860-890 ℃, and the final pass reduction rate of a finish rolling rack is ensured to be more than or equal to 12%; after finishing the finish rolling, rapidly cooling to 540-570 ℃ at a cooling rate of 30-40 ℃/s by adopting a rapid cooling process of the front section after rolling, and coiling;
(3) acid rolling process: pickling the hot rolled steel coil to remove oxides, and then carrying out cold rolling by adopting the reduction of 60.0-65.0%;
(4) continuous annealing process: and continuously annealing the acid-rolled steel strip, wherein the soaking temperature is 770-790 ℃, the slow cooling section finishing temperature is 630-650 ℃, the fast cooling section finishing temperature is 230-280 ℃, and the overaging section temperature is 210-260 ℃.
The economic cold-rolled DP780 steel with different yield strength grades has the flat elongation controlled to be 0.5 +/-0.1 percent.
The invention has the following beneficial effects: the invention fully considers the production organization characteristics of steel enterprises aiming at small-batch cold-rolled dual-phase steel, realizes that a cold-rolled DP780 steel product with three yield strength grades of 400-440 MPa, 450-490 MPa and 510-580 MPa with good surface quality can be produced by adopting a component system through reasonable, economic and low-cost component design and effectively controlling key process parameters of each process section, and can meet the special requirements of users on multiple parts and multiple performances of the cold-rolled dual-phase steel product; the cold-rolled DP780 steel with the yield strength level of 400-440 MPa is particularly suitable for deep-processing forming and automobile structural parts and partial inner and outer plates with high geometric precision requirements; the cold-rolled DP780 steel with the yield strength level of 450-490 MPa is particularly suitable for automobile structural parts and reinforcing parts with high cold-working forming requirements; the cold-rolled DP780 steel with the yield strength level of 510-580 MPa is particularly suitable for automobile structural parts and reinforcing parts with the requirements of reaming and flanging.
Drawings
FIG. 1 is a microstructure diagram of a 400-440 MPa yield strength grade DP780 steel prepared by the process 1-II in the embodiment 1 of the invention.
FIG. 2 is a microstructure diagram of a 450-490 MPa yield strength grade DP780 steel prepared by the process 1-III in the embodiment 1 of the invention.
FIG. 3 is a microstructure diagram of a DP780 steel with yield strength grade of 510-580 MPa prepared by the process 1-VI in the embodiment 1 of the invention.
Detailed Description
In the embodiment of the invention, the microstructure and the mechanical property of the sample are tested by adopting the following method:
cutting a metallographic sample from a cold-rolled and annealed finished steel coil, grinding and polishing the metallographic sample, and then adopting a 4% nital solution and a Lepera reagent (1% Na)2S2O5The volume ratio of the water solution to picric acid alcohol solution with the mass fraction of 4% is 1: 1 mixing) to carry out corrosion, wherein a white structure in the structure can be distinguished as martensite by a Lepera reagent corrosion method, and a gray structure is distinguished as ferrite; and measuring and calculating the volume fraction of martensite by using Leica image analysis software.
Sampling from a cold-rolled and annealed finished steel coil, manufacturing a tensile sample according to the GB/T228 standard, testing the mechanical property on an SANA universal tester, wherein the effective gauge length is 80 multiplied by 20 mm.
Sampling from a cold-rolled and annealed finished steel coil, preparing a tensile sample according to the standard GB/T228, wherein the effective gauge length is 80 multiplied by 20mm, and the baking hardening value (BH) is provided by the standard GB/T241742) The measuring method of (2) is used for testing and calculating; the samples were taken according to standard GB/T15825.4 for the reaming test and the reaming ratio was calculated.
The present invention will now be described in further detail with reference to the accompanying drawings.
Example 1
In the embodiment, the molten steel for steel tapping of the steel billet comprises the following chemical components in percentage by weight: 0.13%, Si: 0.05%, Mn: 1.80%, Alt: 0.40%, Cr: 0.35%, N: 0.003%, P: 0.008%, S: 0.003%, and the balance of Fe and other inevitable impurities, and the thickness of the billet is 230 mm.
In the embodiment, the thickness of the rough rolling outlet billet with the thickness of the hot rolling base material being more than 2.00mm and less than or equal to 4.00mm is 40 mm; the thickness of the rough rolling outlet billet is more than 4.00mm and less than or equal to 6.50mm, and the thickness of the rough rolling outlet billet is 50 mm.
In the embodiment, the process parameters of each process section of the DP780 steel with the yield strength level of 400-440 MPa are controlled according to the following method:
(1) a heating procedure: heating the steel billet, setting the temperature of a soaking section to be 1230-1250 ℃, and soaking for 40 min;
(2) a hot rolling procedure: the pass distribution and each pass reduction rate of the roughing mill and the finishing mill are calculated by a two-stage system roughing set model; the outlet temperature of rough rolling is 1082-1090 ℃, and the finish rolling temperature is 917-920 ℃; after finishing the finish rolling, adopting a post-rolling front-stage cooling process, cooling to 706-710 ℃ at a cooling rate of about 20 ℃/s, and coiling;
(3) acid rolling process: pickling the hot rolled steel coil to remove oxides, and then carrying out cold rolling by adopting the reduction of 68.0-69.2%;
(4) continuous annealing process: continuously annealing the acid-rolled steel strip, wherein the soaking temperature is 810-820 ℃, the slow cooling section finishing temperature is 670-675 ℃, the fast cooling section finishing temperature is 310-320 ℃, and the overaging section temperature is 280-290 ℃;
(5) leveling: the flattening elongation is controlled to be 0.5 +/-0.1 percent.
In the embodiment, the 450-490 MPa yield strength DP780 steel in each process section is subjected to process parameter control according to the following method:
(1) a heating procedure: heating the steel billet, setting the temperature of a soaking section to be 1220-1240 ℃, and soaking for 40 min;
(2) a hot rolling procedure: the pass distribution and each pass reduction rate of the roughing mill and the finishing mill are calculated by a two-stage system roughing set model; the outlet temperature of rough rolling is 1000-1006 ℃, and the finish rolling temperature of finish rolling is 850-854 ℃; after finishing the finish rolling, adopting a post-rolling front-stage cooling process, cooling to 650-652 ℃ at a cooling rate of about 20 ℃/s, and coiling;
(3) acid rolling process: pickling the hot rolled steel coil to remove oxides, and then carrying out cold rolling by adopting a reduction of 63.1-66.0%;
(4) continuous annealing process: continuously annealing the acid-rolled steel strip, wherein the soaking temperature is 790-800 ℃, the slow cooling section finishing temperature is 675-680 ℃, the fast cooling section finishing temperature is 320-330 ℃, and the overaging section temperature is 300-310 ℃;
(5) leveling: the flattening elongation is controlled to be 0.5 +/-0.1 percent.
In the embodiment, the DP780 steel with the yield strength level of 510-580 MPa is subjected to control on the process parameters of each process section according to the following method:
(1) a heating procedure: heating the steel billet, setting the temperature of a soaking section to 1180-1200 ℃, and soaking for 30 min;
(2) a hot rolling procedure: the pass distribution and each pass reduction rate of the roughing mill and the finishing mill are calculated by a two-stage system roughing set model; the outlet temperature of rough rolling is 1073-1080 ℃; the finish rolling temperature is 884-890 ℃, and the final pass reduction rate of the finish rolling stand is ensured to be more than or equal to 12%; after finishing the finish rolling, rapidly cooling to 567-570 ℃ at a cooling rate of about 40 ℃/s by adopting a rapid cooling process of a front section after rolling, and coiling;
(3) acid rolling process: pickling the hot rolled steel coil to remove oxides, and then performing cold rolling by adopting 60.0% of reduction;
(4) continuous annealing process: continuously annealing the acid-rolled steel strip, wherein the soaking temperature is 780-790 ℃, the slow cooling section finishing temperature is 635-650 ℃, the fast cooling section finishing temperature is 270-280 ℃, and the overaging section temperature is 250-260 ℃;
(5) leveling: the flattening elongation is controlled to be 0.5 +/-0.1 percent.
The main process control parameters in this example are shown in table 1.
Table 1 main process control parameters in example 1
FIG. 1 is a microstructure diagram of 400-440 MPa yield strength grade DP780 steel prepared by the process 1-II in the embodiment 1 of the invention; FIG. 2 is a microstructure diagram of 450-490 MPa yield strength grade DP780 steel prepared by the process 1-III in the example 1 of the invention; fig. 3 is a microstructure diagram of DP780 steel with yield strength level of 510-580 MPa prepared by processes 1-vi in example 1 of the present invention, and it can be known from microstructure analysis and calculation results of volume fraction test of each phase that the economical cold-rolled DP780 steel with different yield strength levels prepared in the example of the present invention is composed of ferrite and martensite.
Example 2
In the embodiment, the molten steel for steel tapping of the steel billet comprises the following chemical components in percentage by weight: 0.16%, Si: 0.003%, Mn: 2.10%, Alt: 0.46%, Cr: 0.20%, N: 0.005%, P: 0.004%, S: 0.005%, and the balance Fe and other inevitable impurities, and the thickness of the billet is 230 mm.
In the embodiment, the thickness of the rough rolling outlet billet with the thickness of the hot rolling base material being more than 2.00mm and less than or equal to 4.00mm is 40 mm; the thickness of the rough rolling outlet billet is more than 4.00mm and less than or equal to 5.50mm, and the thickness of the rough rolling outlet billet is 50 mm.
In the embodiment, the process parameters of each process section of the DP780 steel with the yield strength level of 400-440 MPa are controlled according to the following method:
(1) a heating procedure: heating the steel billet, setting the temperature of a soaking section at 1250-1270 ℃, and soaking for 30 min;
(2) a hot rolling procedure: the pass distribution and each pass reduction rate of the roughing mill and the finishing mill are calculated by a two-stage system roughing set model; the outlet temperature of rough rolling is 1043-1050 ℃, and the finish rolling temperature is 884-890 ℃; after finishing the finish rolling, adopting a post-rolling front-stage cooling process, cooling to 680-684 ℃ at a cooling rate of about 20 ℃/s, and coiling;
(3) acid rolling process: pickling the hot rolled steel coil to remove oxides, and then carrying out cold rolling by adopting 70.5-71.9% of reduction;
(4) continuous annealing process: continuously annealing the acid-rolled steel strip, wherein the soaking temperature is 820 ℃, the slow cooling section finishing temperature is 680-690 ℃, the fast cooling section finishing temperature is 330-340 ℃, and the overaging section temperature is 310 ℃;
(5) leveling: the flattening elongation is controlled to be 0.5 +/-0.1 percent.
In the embodiment, the 450-490 MPa yield strength DP780 steel in each process section is subjected to process parameter control according to the following method:
(1) a heating procedure: heating the steel billet, setting the temperature of a soaking section to be 1210-1230 ℃, and soaking for 30 min;
(2) a hot rolling procedure: the pass distribution and each pass reduction rate of the roughing mill and the finishing mill are calculated by a two-stage system roughing set model; the outlet temperature of rough rolling is 1035-1040 ℃, and the finish rolling temperature is 877-880 ℃; after finishing the finish rolling, adopting a post-rolling front-stage cooling process, cooling to 675-680 ℃ at a cooling rate of about 20 ℃/s, and coiling;
(3) acid rolling process: pickling the hot rolled steel coil to remove oxides, and then carrying out cold rolling by adopting a reduction of 63.6-64.3%;
(4) continuous annealing process: continuously annealing the acid-rolled steel strip, wherein the soaking temperature is 800 ℃, the finishing temperature of a slow cooling section is 660-670 ℃, the finishing temperature of a fast cooling section is 280-290 ℃, and the temperature of an overaging section is 260 ℃;
(5) leveling: the flattening elongation is controlled to be 0.5 +/-0.1 percent.
In the embodiment, the DP780 steel with the yield strength level of 510-580 MPa is subjected to control on the process parameters of each process section according to the following method:
(1) a heating procedure: heating the steel billet, setting the temperature of a soaking section to be 1160-1180 ℃, and soaking for 20 min;
(2) a hot rolling procedure: the pass distribution and each pass reduction rate of the roughing mill and the finishing mill are calculated by a two-stage system roughing set model; the outlet temperature of the rough rolling is 1040-1042 ℃; the finish rolling temperature is 860-862 ℃, and the final pass reduction rate of the finish rolling stand is ensured to be more than or equal to 12%; after finishing the finish rolling, rapidly cooling to 540-543 ℃ at a cooling rate of about 30 ℃/s by adopting a post-rolling front-section rapid cooling process, and coiling;
(3) acid rolling process: pickling the hot rolled steel coil to remove oxides, and then carrying out cold rolling by adopting a reduction of 63.6-65.0%;
(4) continuous annealing process: continuously annealing the acid-rolled steel strip, wherein the soaking temperature is 770-790 ℃, the slow cooling section finishing temperature is 640-650 ℃, the fast cooling section finishing temperature is 230-260 ℃, and the overaging section temperature is 210-240 ℃;
(5) leveling: the flattening elongation is controlled to be 0.5 +/-0.1 percent.
The main process control parameters in this example are shown in table 2.
Table 2 main process control parameters in example 2
The prepared cold-rolled DP780 samples with different yield strength grades are subjected to microstructure analysis and mechanical property test, and the test and analysis results are shown in Table 3.
Table 3 mechanical properties and volume fraction of martensite in microstructure of example 2
Example 3
In the embodiment, the molten steel for steel tapping of the steel billet comprises the following chemical components in percentage by weight: 0.10%, Si: 0.01%, Mn: 1.95%, Alt: 0.60%, Cr: 0.40%, N: 0.005%, P: 0.007%, S: 0.005%, and the balance Fe and other inevitable impurities, and the thickness of the billet is 230 mm.
In the production method of the cold rolling DP780 of different yield strength levels in this example, the process parameters of each process section were controlled according to the method described in example 2, and the specific process control parameters are shown in table 4.
Table 4 main process control parameters in example 3
The prepared cold-rolled DP780 samples with different yield strength grades are subjected to microstructure analysis and mechanical property test, and the test and analysis results are shown in Table 5.
TABLE 5 mechanical Properties and volume fraction of martensite in microstructure of example 3
The present invention is not limited to the above embodiments, and any structural changes made under the teaching of the present invention shall fall within the protection scope of the present invention, which is similar or similar to the technical solutions of the present invention.
The techniques, shapes, and configurations not described in detail in the present invention are all known techniques.
Claims (3)
1. A method of producing economical cold rolled DP780 steel of different yield strength grades, characterized by: the method sequentially adopts a billet heating procedure, a hot rolling procedure, an acid rolling procedure and a continuous annealing procedure, wherein the billet comprises the following chemical components in percentage by weight: 0.10-0.16%, Si is less than or equal to 0.05%, Mn: 1.80-2.10%, Alt: 0.40-0.60%, Cr: 0.20-0.40%, and limits N to be less than or equal to 0.005%, P to be less than or equal to 0.008%, S to be less than or equal to 0.005%, and the balance being Fe and other inevitable impurities; the thickness of the prepared cold-rolled DP780 steel product is 0.8-2.0 mm;
when the cold-rolled DP780 steel with the yield strength grade of 400-440 MPa is prepared, the working procedure parameters are as follows:
(1) a billet heating procedure: heating the steel billet, setting the temperature of a soaking section to be 1230-1270 ℃, and soaking for 30-40 min; the thickness of the billet adopted in the billet heating process is 230 mm;
(2) a hot rolling procedure: the pass distribution and the reduction rate of each pass of the rough rolling mill and the finishing rolling mill are calculated by a two-stage system rough rolling set model, wherein the outlet temperature of rough rolling is 1050-1090 ℃, the finishing temperature of finish rolling is 890-920 ℃, a post-rolling front-section cooling process is adopted after finish rolling, the cooling speed is 20 ℃/s to 680-710 ℃, and coiling is carried out; in the hot rolling procedure, when the thickness of the hot rolling base stock is more than 2.00mm and less than or equal to 4.00mm, the thickness of the rough rolling outlet billet is 40mm, and when the thickness of the hot rolling base stock is more than 4.00mm and less than or equal to 6.50mm, the thickness of the rough rolling outlet billet is 50 mm;
(3) acid rolling process: pickling the hot rolled steel coil to remove oxides, and then carrying out cold rolling by adopting the reduction of 68.0-72.0%;
(4) continuous annealing process: and continuously annealing the acid-rolled steel strip, wherein the soaking temperature is 810-830 ℃, the slow cooling section finishing temperature is 670-690 ℃, the fast cooling section finishing temperature is 300-340 ℃, and the overaging section temperature is 280-320 ℃.
2. A method of producing economical cold rolled DP780 steel of different yield strength grades, characterized by: the method sequentially adopts a billet heating procedure, a hot rolling procedure, an acid rolling procedure and a continuous annealing procedure, wherein the billet comprises the following chemical components in percentage by weight: 0.10-0.16%, Si is less than or equal to 0.05%, Mn: 1.80-2.10%, Alt: 0.40-0.60%, Cr: 0.20-0.40%, and limits N to be less than or equal to 0.005%, P to be less than or equal to 0.008%, S to be less than or equal to 0.005%, and the balance being Fe and other inevitable impurities; the thickness of the prepared cold-rolled DP780 steel product is 0.8-2.0 mm;
when the cold-rolled DP780 steel with the yield strength grade of 450-490 MPa is prepared, the working procedure parameters are as follows:
(1) a billet heating procedure: heating the steel billet, setting the temperature of a soaking section to be 1200-1240 ℃, and soaking for 30-40 min; the thickness of the billet adopted in the billet heating process is 230 mm;
(2) a hot rolling procedure: the pass distribution and each pass reduction rate of the roughing mill and the finishing mill are calculated by a two-stage system roughing set model; the outlet temperature of rough rolling is 1000-1040 ℃, and the finish rolling temperature is 850-880 ℃; after finishing the finish rolling, adopting a post-rolling front-stage cooling process, cooling to 650-680 ℃ at a cooling rate of 20 ℃/s, and coiling; in the hot rolling procedure, when the thickness of the hot rolling base stock is more than 2.00mm and less than or equal to 4.00mm, the thickness of the rough rolling outlet billet is 40mm, and when the thickness of the hot rolling base stock is more than 4.00mm and less than or equal to 6.50mm, the thickness of the rough rolling outlet billet is 50 mm;
(3) acid rolling process: pickling the hot rolled steel coil to remove oxides, and then carrying out cold rolling by adopting a reduction of 63.0-66.0%;
(4) continuous annealing process: and continuously annealing the acid-rolled steel strip, wherein the soaking temperature is 780-800 ℃, the finishing temperature of a slow cooling section is 660-680 ℃, the finishing temperature of a fast cooling section is 280-330 ℃, and the temperature of an overaging section is 260-310 ℃.
3. A method of producing economical cold rolled DP780 steel of different yield strength grades, characterized by: the method sequentially adopts a billet heating procedure, a hot rolling procedure, an acid rolling procedure and a continuous annealing procedure, wherein the billet comprises the following chemical components in percentage by weight: 0.10-0.16%, Si is less than or equal to 0.05%, Mn: 1.80-2.10%, Alt: 0.40-0.60%, Cr: 0.20-0.40%, and limits N to be less than or equal to 0.005%, P to be less than or equal to 0.008%, S to be less than or equal to 0.005%, and the balance being Fe and other inevitable impurities; the thickness of the prepared cold-rolled DP780 steel product is 0.8-2.0 mm;
when the cold-rolled DP780 steel with the yield strength grade of 510-580 MPa is prepared, the working procedure parameters are as follows:
(1) a billet heating procedure: heating the steel billet, setting the temperature of a soaking section to be 1160-1200 ℃, and soaking for less than or equal to 30 min; the thickness of the billet adopted in the billet heating process is 230 mm;
(2) a hot rolling procedure: the pass distribution and each pass reduction rate of the roughing mill and the finishing mill are calculated by a two-stage system roughing set model; the outlet temperature of rough rolling is 1040-1080 ℃; the finish rolling temperature is 860-890 ℃, and the final pass reduction rate of a finish rolling rack is ensured to be more than or equal to 12%; after finishing the finish rolling, rapidly cooling to 540-570 ℃ at a cooling rate of 30-40 ℃/s by adopting a rapid cooling process of the front section after rolling, and coiling; in the hot rolling procedure, when the thickness of the hot rolling base stock is more than 2.00mm and less than or equal to 4.00mm, the thickness of the rough rolling outlet billet is 40mm, and when the thickness of the hot rolling base stock is more than 4.00mm and less than or equal to 6.50mm, the thickness of the rough rolling outlet billet is 50 mm;
(3) acid rolling process: pickling the hot rolled steel coil to remove oxides, and then carrying out cold rolling by adopting the reduction of 60.0-65.0%;
(4) continuous annealing process: and continuously annealing the acid-rolled steel strip, wherein the soaking temperature is 770-790 ℃, the slow cooling section finishing temperature is 630-650 ℃, the fast cooling section finishing temperature is 230-280 ℃, and the overaging section temperature is 210-260 ℃.
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