CN113549821A - 800 MPa-grade hot-rolled and pickled multiphase steel with low yield ratio and high hole expansion rate and production method thereof - Google Patents
800 MPa-grade hot-rolled and pickled multiphase steel with low yield ratio and high hole expansion rate and production method thereof Download PDFInfo
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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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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
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- C21D2211/002—Bainite
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Abstract
The invention relates to hot-rolled complex phase steel, in particular to 800 MPa-grade hot-rolled acid-pickled complex phase steel with low yield ratio and high hole expansion rate and a production method thereof. The complex phase steel comprises the following components in percentage by weight: 0.010 to 0.042 percent of V, 0.030 to 0.132 percent of Ti, 0.0020 to 0.0050 percent of B, 0.010 to 0.050 percent of rare earth elements La and Ce, less than or equal to 0.020 percent of P and less than or equal to 0.007 percent of S. The production method comprises the following steps of: 1) heating a continuous casting slab with the thickness of between 80 and 300mm to the temperature of between 1,130 and 1,270 ℃, and preserving the heat for 5 to 6 hours; 2) performing rough rolling, wherein the initial rolling temperature is not higher than 1,080 ℃, the thickness of an intermediate slab is between 25 and 50mm, the final rolling temperature is between 840 and 900 ℃, the thickness of a finished product is between 1.8 and 5.3mm, and the total reduction rate is more than or equal to 85 percent; 3) performing rapid continuous laminar cooling on the front section after final rolling, and coiling; 4) slowly cooling a slow cooling cover, and performing air cooling to room temperature; and 5) pickling. The complex phase steel has high strength and high formability, is suitable for manufacturing automobile structural members, reinforcing members and safety members, and has excellent fatigue resistance, welding performance and cold forming performance.
Description
Technical Field
The invention relates to hot-rolled complex phase steel, in particular to 800 MPa-grade hot-rolled pickled complex phase steel with low yield ratio and high hole expansibility and a production method thereof.
Background
The new generation of automobiles has the development trend of energy conservation, consumption reduction, environmental protection and safety. Advanced high-strength steel is widely used in the automobile manufacturing industry to achieve the goal of light weight thereof. The research and development and application of advanced high-strength and ultrahigh-strength steel are the leading direction of the future material technology development. The advanced high-strength steel mainly comprises five major types, namely low-alloy high-strength steel, dual-phase steel, complex-phase steel, transformation induced plasticity steel, martensitic steel and the like, has the strength range of 500-1600 MPa, has high strength and good formability, and has the advantages of high weight reduction potential, high collision absorption energy, high formability and the like in automobile manufacturing application.
The common structure in the complex phase steel is ferrite, bainite, martensite and a certain content of residual austenite and fine precipitates. The complex phase steel is suitable for manufacturing structural members, reinforcing members, safety members and other members, such as bumpers, B-pillar reinforcing members and the like.
The existing hot-rolled complex phase steel has low yield strength, low tensile strength, low elongation and high yield ratio which do not meet the requirements of high-strength formed automobile structural parts; and the fatigue resistance, the welding performance and the cold forming performance are not ideal.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides the 800 MPa-grade hot-rolled pickled complex-phase steel with low yield ratio and high hole expansion rate and the production method thereof, which have high strength and good formability and are suitable for manufacturing automobile structural parts, reinforcements and safety parts; and has excellent fatigue resistance, welding performance and cold forming performance.
In order to achieve the purpose, the invention adopts the following technical scheme:
the hot-rolled and pickled multiphase steel with low yield ratio and high hole expansion rate of 800MPa comprises the following chemical components in percentage by weight:
c: 0.075-0.132%, Si: 0.08-0.40%, Mn: 1.15% -2.02%, Al: 0.10% -0.30%, Mo: 0.08 to 0.35 percent of Ti, 0.010 to 0.042 percent of V, 0.030 to 0.132 percent of Ti, 0.0020 to 0.0050 percent of B, 0.010 to 0.050 percent of rare earth element La + Ce, less than or equal to 0.020 percent of P, less than or equal to 0.007 percent of S and the balance of Fe and inevitable impurities.
A production method of 800 MPa-grade hot-rolled pickled complex phase steel with low yield ratio and high hole expansibility comprises the following steps:
1) putting a continuous casting plate blank with the thickness of 80-300 mm into a stepping heating furnace, heating to 1130-1270 ℃, and preserving heat for 5-6 hours;
2) the rolling control means is adopted, the initial rolling temperature of rough rolling is not higher than 1080 ℃, the thickness of an intermediate blank is 25-50mm, the final rolling temperature is 840-900 ℃, the thickness of a finished product is 1.8-5.3mm, and the total rolling reduction rate is more than or equal to 85%;
3) after finishing rolling, adopting front-stage rapid continuous laminar cooling and coiling, wherein the cooling rate is more than 120 ℃/s, and the coiling temperature is 580-650 ℃;
4) after the steel plate is coiled, the steel plate immediately enters a slow cooling cover to be slowly cooled to below 130 ℃, the slow cooling speed is not more than 14 ℃/h, the steel coil is taken out, and the steel coil is cooled to room temperature in an air cooling mode;
5) then pickling, wherein before pickling, the steel plate is subjected to straightening and withdrawal with the straightening and withdrawal elongation rate of 0.2-1.6%, and sequentially passes through 3 pickling tanks, the steel plate passing speed is 60-120 m/min, and the steel plate is pickled with tension in the pickling process, wherein the tension is 20-50 kN; the pickling solution of 3 pickling tanks for pickling is hydrochloric acid, the concentration of free acid in the tank No. 1 is 80-120 g/l, and the temperature of the pickling solution is 80.0-86.0 ℃; the concentration of free acid in the No. 2 tank is 120-150 g/l, and the temperature of the acid pickling liquid is 75.0-80.0 ℃; the concentration of free acid in the No. 3 tank is 150-185 g/l, and the temperature of the pickling solution is 68.0-75.0 ℃.
Compared with the prior art, the invention has the beneficial effects that:
1) according to the invention, by adding alloy elements such as V, Ti, Mo and B and combining a corresponding rolling schedule and a cooling schedule, the production of the hot-rolled and pickled complex-phase steel with fine-grain strengthening, precipitation strengthening and phase-change strengthening is realized.
The vanadium in a solid solution state can inhibit static and dynamic recrystallization in the thermal deformation process, increase the strain accumulation of a rear part of a stand in the continuous rolling process, promote the transformation from austenite to ferrite, refine ferrite grains and realize fine grain strengthening. Vanadium, carbon and nitrogen are combined to form a tiny carbonitride pinning crystal boundary, recrystallization is delayed, austenite grains are prevented from growing, and an obvious precipitation strengthening effect is achieved. Ti can also exist in the form of second phase particles in steel, plays a role in precipitation strengthening, molybdenum delays pearlite transformation, a bainite forming window is expanded, a bainite hard phase is formed in a wider process range, ferrite and proper amount of bainite and martensite are promoted to form, phase transformation strengthening is realized, boron can obviously improve the hardenability of the steel, and the strength of a steel plate is improved.
2) According to the invention, 0.010% -0.050% of rare earth element La + Ce is added, the rare earth has strong deoxidizing and desulfurizing capacities, the appearance of sulfide inclusions can be changed, the plasticity of the steel plate can be improved, the anisotropy of the steel plate is reduced, the fatigue performance of the steel plate can be improved, the welding performance of the steel plate can be improved, and the cold forming performance of the steel plate can be improved.
3) The invention does not need sectional cooling control through chemical components, corresponding rolling system and front-section rapid continuous laminar cooling system control, and the control means is simple and easy to operate. The produced hot-rolled pickled steel plate has a ferrite, bainite and martensite multiphase structure, wherein the bainite structure accounts for 70-80 percent by volume percent, the yield strength is more than or equal to 540MPa, the tensile strength is more than or equal to 800MPa, and the elongation A is80More than or equal to 20 percent, the yield ratio is less than or equal to 0.70, and the hole expansion ratio is more than or equal to 90 percent.
4) The invention obtains ferrite, bainite and martensite multiphase structure through reasonable matching of chemical components, corresponding rolling system and cooling system, wherein the bainite structure is 70-80% by volume percentage, the yield strength is more than or equal to 540MPa, the tensile strength is more than or equal to 800MPa, the elongation A80 is more than or equal to 20%, the yield ratio is less than or equal to 0.70, the hole expansion ratio is more than or equal to 90%, and the formability is good. Steel grades not only have high strength but also have good formability.
5) And taking out the steel coil, air-cooling to room temperature, and then carrying out acid cleaning to improve the surface quality of the steel plate so that the roughness of the steel plate is 0.80-1.86 mu m.
Drawings
FIG. 1 is a metallographic structure diagram of example 1 of the present invention.
Detailed Description
The invention discloses a hot-rolled and pickled multiphase steel with low yield ratio and high hole expansion rate of 800MPa and a production method thereof. Those skilled in the art can modify the process parameters appropriately to achieve the desired results with reference to the disclosure herein. It is expressly intended that all such similar substitutes and modifications which would be obvious to one skilled in the art are deemed to be included in the invention. While the methods and applications of this invention have been described in terms of preferred embodiments, it will be apparent to those of ordinary skill in the art that variations and modifications in the methods and applications described herein, as well as other suitable variations and combinations, may be made to implement and use the techniques of this invention without departing from the spirit and scope of the invention.
The hot-rolled and pickled multiphase steel with low yield ratio and high hole expansion rate of 800MPa comprises the following chemical components in percentage by weight:
c: 0.075-0.132%, Si: : 0.08-0.40%, Mn: 1.15% -2.02%, Al: 0.10% -0.30%, Mo: 0.08 to 0.35 percent of Ti, 0.010 to 0.042 percent of V, 0.030 to 0.132 percent of Ti, 0.0020 to 0.0050 percent of B, 0.010 to 0.050 percent of rare earth element La + Ce, less than or equal to 0.020 percent of P, less than or equal to 0.007 percent of S and the balance of Fe and inevitable impurities.
C: the proper carbon content can ensure sufficient strength of the steel sheet. The carbon content is too low, so that proeutectoid ferrite is easy to appear, and the complex phase structure of bainite and martensite with high strength is not easy to obtain. On the other hand, if the carbon content is too high, the pearlite structure is easily formed, and the formation of the bainite structure is inhibited. Therefore, the carbon content range of the invention is 0.075-0.132%.
Si: a ferrite forming element which is dissolved in ferrite to play a role of solid solution strengthening, but the surface of a steel plate after rolling can be red iron scale due to the excessively high content of silicon, thus deteriorating the surface quality. Therefore, the silicon content of the invention is 0.08-0.40%.
Mn: the steel can stabilize an austenite structure, and the existence of the steel can shift the C curve of the steel to the right, so that the hardenability is increased strongly, the critical cooling rate for forming bainite and martensite is reduced, and the bainite or martensite structure is favorably obtained. Therefore, the content range of manganese in the invention is 1.15-2.02%.
Al: a small amount of Al is added into the steel, which is a commonly used deoxidizer in the steel, can form AlN precipitation to play a role in refining grains, and the Al also has oxidation resistance and corrosion resistance, so that the combination of the Al, Cr and Si can obviously improve the high-temperature non-peeling performance of the steel and improve the surface quality of a steel plate. Therefore, the aluminum content range of the invention is 0.10-0.30%.
Mo: postponing pearlite transformation, enlarging bainite formation window and forming bainite hard phase in wider process range. Therefore, molybdenum is selected as a hardenability element in the component design, ferrite and proper amount of bainite and martensite are promoted to form, and the adverse effect of the formation of excessive hard phase structure on the elongation is avoided, so that the content range of the molybdenum is 0.08-0.35%.
V: the vanadium in a solid solution state can inhibit static and dynamic recrystallization in the thermal deformation process, increase the strain accumulation of a rear part of a stand in the continuous rolling process, promote the transformation from austenite to ferrite and refine ferrite grains. Vanadium combines with carbon and nitrogen to form tiny carbonitride pinning crystal boundary, delays recrystallization, prevents austenite crystal grains from growing and has obvious precipitation strengthening effect. Therefore, the content range of the vanadium is 0.010-0.042%.
Ti: the strong carbide forming element, and adds a small amount of Ti into the steel, the formed TiC can prevent austenite grains from excessively growing when the steel billet is heated, thereby achieving the purpose of refining the original austenite grains. Ti can also exist in the form of second phase particles in the steel to play a role in strengthening precipitation, so that the content range of the titanium in the invention is 0.030-0.132%.
B, the hardenability of the steel can be obviously improved, and when the content of B is higher than 0.0050%, excessive B and N in the steel form a B compound to reduce the performance of the steel plate, so that the content of boron in the invention is 0.0020-0.0050%.
P: the temperature for forming the alpha phase is increased to expand the temperature range for forming the alpha phase. However, the content of phosphorus is too high, which deteriorates the workability of the steel sheet, and is limited to 0.020% in order to obtain a high elongation.
S: since sulfur forms sulfide inclusions such as MnS and becomes a starting point of cracks to deteriorate workability, the content is preferably as small as 0.007%.
RE, rare earth has strong deoxidizing and desulfurizing capacity, can change the appearance of sulfide inclusions, can improve the plasticity of the steel plate, reduce the anisotropy of the steel plate, and can improve the fatigue property of the steel plate, improve the welding property of the steel plate and improve the cold forming property of the steel plate. Therefore, the content of the rare earth La + Ce is 0.010-0.050%.
A production method of 800 MPa-grade hot-rolled pickled complex phase steel with low yield ratio and high hole expansibility comprises the following steps:
1) heating the continuous casting plate blank with the thickness of 80-300 mm to 1130-1270 ℃ in a stepping heating furnace, and preserving heat for 5-6 hours.
2) The controlled rolling method is adopted, the initial rolling temperature of rough rolling is not higher than 1080 ℃, the thickness of the intermediate blank is 25-50mm, the final rolling temperature is 840-900 ℃, the thickness of the finished product is 1.8-5.3mm, and the total reduction rate is not less than 85%.
3) And after the final rolling, adopting front-section rapid continuous laminar cooling, wherein the cooling rate is more than 120 ℃/s, and the coiling temperature is 580-650 ℃.
4) And (3) immediately entering a slow cooling cover for slow cooling after the steel plate is coiled, slowly cooling to below 130 ℃, taking out the steel coil at a slow cooling speed of not more than 14 ℃/h, and air cooling to room temperature.
5) And then carrying out acid pickling, wherein before acid pickling, the steel plate is subjected to tension straightening, the tension straightening elongation is 0.2-1.6%, the pickling solution is hydrochloric acid, the pickling tank is divided into 3 tanks, the concentration of free acid in the tank 1 is 80-120 g/l, the temperature of the pickling solution in the tank 1 is 80.0-86.0 ℃, the concentration of free acid in the tank 2 is 120-150 g/l, the temperature of the pickling solution in the tank 2 is 75.0-80.0 ℃, the concentration of free acid in the tank 3 is 150-185 g/l, the temperature of the pickling solution in the tank 3 is 68.0-75.0 ℃, the steel plate threading speed is 60-120 m/min, and the steel plate is pickled under the belt tension in the acid pickling process, wherein the tension is 20-50 kN.
Heating temperature: the proper heating temperature and the proper heat preservation time enable alloy elements in the plate blank to be completely dissolved in solid solution and the plate blank components to be uniform, and the effects of controlling the size of original austenite grains, saving energy and the like are achieved. The defects of large austenite crystal grain growth, overheating, overburning, increased iron scale, decarburization and the like can be caused by overhigh heating temperature or overlong time of the steel billet; and the heating temperature is too low, which can prevent the alloy elements such as V, Ti, Mo, B and the like from fully dissolving and the austenite grains from homogenizing. Therefore, the hot rolling heating temperature range of the continuous casting billet is 1130-1270 ℃.
The finishing temperature is as follows: is a key parameter influencing the steel structure performance in the thermal deformation process. In order to ensure that the crystal grains are uniform after rolling and achieve a good thinning effect, the finishing temperature range of the invention is 840-900 ℃.
Coiling temperature: to obtain a complex phase structure, the steel grade is selected to be coiled in the bainite region. Therefore, the rolling temperature range of the invention is 580-650 ℃. And the front-section rapid continuous laminar cooling is adopted after the final rolling, and the cooling rate is more than 120 ℃/s. In order to reduce the internal stress of the steel plate structure and improve the toughness, the steel plate immediately enters a slow cooling cover for slow cooling after being coiled, the steel plate is slowly cooled to below 130 ℃, the slow cooling speed is not more than 14 ℃/h, and the steel coil is taken out and cooled to the room temperature by air.
[ examples ] A method for producing a compound
The smelted chemical composition continuous casting slab with the thickness of 80-300 mm meeting the requirement in the table 1 is rolled into a steel plate with the thickness specification of 1.8-5.3mm on a hot continuous rolling mill, and the steel plate is cooled by adopting a front-section rapid continuous laminar flow after rolling. Wherein, fig. 1 is a metallographic structure diagram of example 1, bainite is distributed on a ferrite matrix and a martensite structure is mixed, the structure is a typical complex phase steel structure under the invention, and the structures under other systems are similar to the complex phase steel structure.
The chemical components of the hot-rolled and pickled complex phase steel of the embodiment of the invention comprise the following components in percentage by weight, and are shown in Table 1:
TABLE 1 chemical composition wt% of hot-rolled pickled complex phase steel in the inventive example
TABLE 2 main production process parameters of hot-rolled pickled complex phase steel of the embodiment of the invention
TABLE 3 main pickling process parameters of hot-rolled pickled complex-phase steel in the inventive example
TABLE 4 Hot-rolled pickled complex phase steel Properties and microstructures of the examples of the present invention
According to the invention, by adding alloy elements such as V, Ti, Mo and B and combining a corresponding rolling schedule and a cooling schedule, the production of the hot-rolled and pickled complex-phase steel with fine-grain strengthening, precipitation strengthening and phase-change strengthening is realized. The produced hot-rolled pickled steel plate has a ferrite, bainite and martensite multiphase structure, wherein the bainite structure is 70-80% by volume percentage, the yield strength is more than or equal to 540MPa, the tensile strength is more than or equal to 800MPa, the elongation A80 is more than or equal to 20%, the yield ratio is less than or equal to 0.70, the hole expansion ratio is more than or equal to 90%, and the roughness is 0.80-1.86 μm. The rare earth element La + Ce is added by 0.010-0.050 percent, so that the plasticity of the steel plate is improved, the anisotropy of the steel plate is reduced, the fatigue performance of the steel plate is improved, the welding performance of the steel plate is improved, and the cold forming performance of the steel plate is improved.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.
Claims (5)
1. The hot-rolled and pickled multiphase steel with the low yield ratio and the high hole expansion rate of 800MPa is characterized by comprising the following chemical components in percentage by weight:
c: 0.075-0.132%, Si: 0.08-0.40%, Mn: 1.15% -2.02%, Al: 0.10% -0.30%, Mo: 0.08 to 0.35 percent of Ti, 0.010 to 0.042 percent of V, 0.030 to 0.132 percent of Ti, 0.0020 to 0.0050 percent of B, 0.010 to 0.050 percent of rare earth element La + Ce, less than or equal to 0.020 percent of P, less than or equal to 0.007 percent of S and the balance of Fe and inevitable impurities.
2. The production method of the 800 MPa-grade hot-rolled and pickled complex phase steel with the low yield ratio and the high hole expansibility as claimed in claim 1 is characterized by comprising the following steps of:
1) putting a continuous casting plate blank with the thickness of 80-300 mm into a heating furnace, heating to 1130-1270 ℃, and preserving heat for 5-6 hours;
2) the rolling control means is adopted, the initial rolling temperature of rough rolling is not higher than 1080 ℃, the thickness of an intermediate blank is 25-50mm, the final rolling temperature is 840-900 ℃, the thickness of a finished product is 1.8-5.3mm, and the total rolling reduction rate is more than or equal to 85%;
3) after final rolling, adopting front-section rapid continuous laminar cooling and coiling;
4) after the steel plate is coiled, the steel plate immediately enters a slow cooling cover to be slowly cooled to below 130 ℃, the slow cooling speed is not more than 14 ℃/h, the steel coil is taken out, and the steel coil is cooled to room temperature in an air cooling mode;
5) and then pickling, wherein the steel plate is subjected to pulling and straightening before pickling, the pulling and straightening elongation is 0.2% -1.6%, the steel plate passing speed is 60-120 m/min, and the steel plate is pickled with tension in the pickling process, wherein the tension is 20-50 kN.
3. The method for producing the hot-rolled and pickled multiphase steel with the low yield ratio and the high hole expansibility of 800MPa according to claim 2, wherein the heating furnace in the step 1) is a walking beam type heating furnace.
4. The production method of the 800 MPa-grade hot-rolled and pickled complex phase steel with the low yield ratio and the high hole expansibility as claimed in claim 2, wherein the front section of the step 3) is rapidly and continuously cooled by laminar flow, the cooling rate is more than 120 ℃/s, and the coiling temperature is 580-650 ℃.
5. The production method of the hot-rolled and pickled complex phase steel with low yield ratio and high hole expansion rate of 800MPa according to claim 2, wherein the pickling in the step 5) sequentially passes through 3 pickling tanks, the pickling solution is hydrochloric acid, the concentration of free acid in the tank No. 1 is 80-120 g/l, and the temperature of the pickling solution is 80.0-86.0 ℃; the concentration of free acid in the No. 2 tank is 120-150 g/l, and the temperature of the acid pickling liquid is 75.0-80.0 ℃; the concentration of free acid in the No. 3 tank is 150-185 g/l, and the temperature of the pickling solution is 68.0-75.0 ℃.
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