CN110484827B - Hot-rolled pickled steel plate with tensile strength of 600MPa and low yield ratio - Google Patents
Hot-rolled pickled steel plate with tensile strength of 600MPa and low yield ratio Download PDFInfo
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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
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- 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
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- 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
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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- C22C33/04—Making ferrous alloys by melting
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- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- 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
- C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
- C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
- C23G1/08—Iron or steel
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Abstract
The invention discloses a hot-rolled pickled steel plate with 600 MPa-level tensile strength and low yield ratio, which mainly solves the technical problems that the stamping performance and the hole expanding performance of the conventional 600 MPa-level hot-rolled pickled steel plate are not matched and the manufacturing requirements of automobile parts with complex shapes cannot be met. The hot-rolled pickled steel plate provided by the invention comprises the following chemical components in percentage by weight: c: 0.06-0.08%, Mn: 0.8-1.2%, Si: 0-0.10%, P: 0-0.020%, S: 0-0.006%, Alt: 0.015-0.050%, N: 0-0.005%, Ti: 0.03 to 0.05 percent, and the balance of Fe and inevitable impurity elements. The yield ratio of the hot-rolled pickled steel plate with the thickness of 2.0-4.0 mm is less than or equal to 0.80, and the elongation percentage A after fracture50mm25-35%, and the hole expansion performance lambda is more than or equal to 75%. The steel plate is used for manufacturing automobile structural parts.
Description
Technical Field
The invention relates to a hot-rolled pickled steel plate, in particular to a hot-rolled pickled steel plate with tensile strength of 600MPa and low yield ratio and a manufacturing method thereof.
Background
The hot-rolled and pickled automobile structural steel is one of hot-rolled steel plates, and the surface quality is greatly improved after pickling treatment, so that the steel plate has the advantages of low cost, good size and plate shape precision of a hot plate, and is widely applied to structural members such as automobile chassis, wheels and the like. The weight of such structural components amounts to about 25% of the weight of the vehicle body, so that the automobile industry has an increasing desire for high strength and weight reduction of the material. The plasticity of the parts is greatly influenced by the reduction of plasticity after the strength level is improved, the equipment pressure is increased, the punching is not facilitated, and therefore the yield strength of the materials is expected to be lower by processing enterprises. Meanwhile, since many parts have complicated shapes and often have various molding requirements, such as punching property and hole expansibility, the material is also desired to have good composite moldability.
The existing hot rolled steel plate with 600 MPa-level tensile strength mainly has two production technologies, one is low-alloy high-strength steel (HSLA), and the low-alloy high-strength steel is mainly reinforced by Mn and added Nb, V and Ti elements, and has the advantages that the manufacturing process is relatively easy to realize, and the defects are that: the yield ratio is high and is more than or equal to 0.85; the elongation is low and is less than or equal to 20 percent; the stamping performance is poor, and the requirement on parts with large stamping amplitude is difficult to meet; the other is dual-phase steel (DP) with a main F + M structure, and has the advantages of low yield ratio of less than or equal to 0.6, high elongation of more than or equal to 25 percent and excellent punching performance, and the defect that the hole expanding performance is not high and is generally lower than 50 percent.
The Chinese patent application publication No. CN106834949A discloses a low-silicon titanium-containing pickled plate with a yield strength of 500MPa and a preparation method thereof, wherein the pickled plate comprises the following chemical components in percentage by weight: c: 0.06-0.09%, Mn: 0.35-0.80%, Als: 0.03-0.06%, Ti: 0.07-0.09%, less than or equal to 0.05% of Si, less than or equal to 0.01% of Nb, less than or equal to 0.008% of S, less than or equal to 0.015% of P, less than or equal to 0.004% of N, less than or equal to 0.003% of O, and the balance of iron and inevitable impurities. The preparation method comprises the following steps: converter smelting, ladle argon blowing, LF furnace refining, RH vacuum treatment, continuous casting, hot continuous rolling, laminar cooling, coiling and acid pickling in a continuous pickling line. The steel has the structure form of ferrite, a small amount of carbide and a small amount of pearlite, the grain size grade is 11-12 grade, the yield strength is 535-550 MPa, the tensile strength is 625-645 MPa, the elongation is 22-25 percent, and the steel has the surface quality of band steel of grade above FB (02) and good processing performance. The yield ratio of the scheme is higher than 0.85, the punching performance is not facilitated, the addition amount of Ti is large, the performance fluctuation is large if Ti cannot be completely dissolved, and the control difficulty is large.
The chinese patent application publication No. CN106086627A discloses a 600MPa grade hot-rolled dual-phase steel, which comprises the following chemical components by mass percent: 0.05 to 0.07%, Si: 0.1 to 0.3%, Mn: 1.10-1.50%, Cr: 0.5-0.8% and the balance Fe. The dual-phase steel is a ferrite and martensite structure, the yield strength is 300-375 MPa, the tensile strength is 590-650 MPa, the yield ratio is 0.56-0.60, the total elongation after fracture is 24-30%, the index of the hole expansion rate is not given, and the hole expansion rate of the product is low in structure view and is not suitable for parts with relatively complex shapes and flanging characteristics.
The application publication number CN107099739A of the chinese patent application discloses a low-cost high-hole-expansion steel plate with 600MPa tensile strength and a production method thereof, wherein the high-hole-expansion steel plate comprises the following chemical components in percentage by mass: c: 0.15-0.20%, Si is less than or equal to 0.30%, Mn: 0.80-1.00%, P is less than or equal to 0.020%, S is less than or equal to 0.010%, Als: 0.020 to 0.050%, Ti: 0.010-0.030 percent of the total weight of the alloy, less than or equal to 0.0060 percent of N and the balance of Fe and inevitable impurities; the production method comprises the working procedures of steel making, heating, rolling and cooling. According to the invention, a cooling path is controlled to obtain a ferrite and bainite dual-phase structure, and the strength is improved by adding C, so that the hot rolled steel strip with the tensile strength of 600-. The proposal improves the strength at low cost by increasing the content of C, but the high C is unfavorable for plasticity, and banded structures are easy to appear, and simultaneously, the yield ratio is improved, and the yield ratio is about 0.85 seen from the embodiment of the proposal.
The chinese patent application publication No. CN105220065A discloses a high-porosity low-yield-ratio hot-rolled high-strength steel plate, the microstructure of which is ferrite + martensite + bainite, and the high-porosity low-yield-ratio hot-rolled high-strength steel plate has the following chemical elements by mass: c: 0.02-0.08%; mn: 1.0-2.0%; al: 0.025 to 0.060%; the balance being Fe and other unavoidable impurities. The invention also discloses a manufacturing method of the hot-rolled high-strength steel plate with high hole expansion rate and low yield ratio, which sequentially comprises the following steps: (1) smelting and casting into a plate blank; (2) heating; (3) rolling; (4) cooling in sections; (5) coiling; (6) and air-cooling to room temperature. The invention is improved on the basis of DP dual-phase steel, obtains a three-phase structure of ferrite, martensite and bainite, overcomes the defects of insufficient strength of the ferrite and bainite structure and excessively low hole expansion rate of the ferrite and martensite in the past, and ensures that the tensile strength is more than or equal to 590MPa, the yield ratio is less than or equal to 0.6, the hole expansion rate is more than or equal to 60 percent, and the comprehensive performance is very excellent. However, from the embodiment examples, in order to promote ferrite production in the multi-phase steel, the Si content in the composition system reaches 1.0%, and the red sheet iron on the surface of the steel plate with the Si content of more than 0.5% is relatively serious, so that the multi-phase steel is difficult to accept for parts with high surface quality requirements. In addition, for the double (three) -phase steel, the phase composition in the structure is controlled by two-stage laminar cooling, the high precision and stable performance of the structure are difficult to realize, and the production control difficulty is large.
Along with the improvement of the processing efficiency of the automobile industry, the requirements of part integration and process shortening are increased day by day, and parts with high strength and complex shapes are processed more and more, so that the hot-rolled pickled steel plate with high strength, good stamping performance and hole expanding performance has greater market requirements.
Disclosure of Invention
The invention aims to provide a hot-rolled pickled steel plate with 600 MPa-level tensile strength and low yield ratio and a manufacturing method thereof, and mainly solves the technical problems that the stamping performance and the hole expanding performance of the conventional 600 MPa-level hot-rolled pickled steel plate are not matched and the manufacturing requirements of automobile parts with complex shapes cannot be met. The hot-rolled pickled steel plate has good stamping performance and hole expansion performance and good surface quality, meets the manufacturing requirement of automobile parts with complex shapes, and meets the requirement of lightweight automobile structural parts.
The design idea of the invention is that the structure design of ferrite, a small amount of pearlite and dispersed carbide is adopted, the hole expansion performance is good, and on the basis, the fine grain strengthening effect is weakened appropriately, the precipitation strengthening effect is promoted, the yield ratio is reduced comprehensively by using the withdrawal and straightening process, and the stamping performance is improved.
The invention adopts the technical scheme that a hot-rolled pickled steel plate with 600 MPa-level tensile strength and low yield ratio comprises the following chemical components in percentage by weight: c: 0.06-0.08%, Mn: 0.8-1.2%, Si: 0-0.10%, P: 0-0.020%, S: 0-0.006%, Alt: 0.015-0.050%, N: 0-0.005%, Ti: 0.03 to 0.05 percent, and the balance of Fe and inevitable impurity elements.
The hot-rolled pickled steel plate has a metallographic structure comprising ferrite, a small amount of pearlite and dispersed titanium carbide particles, wherein the volume content of the pearlite in the metallographic structure is 5-8%, and the grain size of the ferrite is 10.5-11.5 grades; yield strength R of hot-rolled pickled steel plate with thickness of 2.0-4.0 mmp0.2460 to 520MPa, tensile strength Rm600 to 660MPa, a yield ratio of less than or equal to 0.80 and a post-fracture elongation A50mm25-35%, and the hole expansion performance lambda is more than or equal to 75%.
The reason why the chemical composition of the hot-rolled pickled steel sheet with the tensile strength of 600MPa and the low yield ratio is limited within the above range is as follows:
carbon: carbon is the most effective element for improving the strength of steel. The invention adopts a low-carbon design route, when the C content is higher than 0.085%, the steel making enters a crystal-wrapping area, the quality of a plate blank is difficult to control, the defects of slag entrapment and the like are easy to occur, meanwhile, the pearlite content in the steel is increased, and the ductility, toughness and welding performance of the steel are poor; when the amount of C is less than 0.06%, the strength of the steel is difficult to secure. In order to ensure the strength, toughness and welding performance of the steel, the content of C is set to be 0.06-0.08%.
Silicon: silicon is used as a harmful element, the plasticity is damaged due to the high silicon content, red iron sheet on the surface is easily generated due to the high silicon content, and the surface quality is influenced, and the Si is set to be less than or equal to 0.1 percent.
Manganese: manganese is a deoxidizing element, large-size inclusions in steel are removed to ensure the purity of the steel, and meanwhile manganese and sulfur form manganese sulfide, so that the adverse effect of FeS on plasticity can be avoided. Manganese has a solid solution strengthening effect on the steel performance, ferrite grains can be refined, the manganese content is reduced as much as possible on the basis of keeping the content which is several times of that of sulfur, the alloy cost is reduced, the material strength is reduced, and the formability is improved. Compared with a fine-grain strengthening mode and a precipitation strengthening mode, the rate of improving the yield ratio by the solid solution strengthening mode is the lowest, so that the strength is ensured by the solid solution strengthening to be most beneficial to obtaining low yield ratio, but when the content of Mn is too high, the structure segregation in the steel is increased, the structure uniformity and the impact property of the steel are influenced, and the welding performance is also influenced. Therefore, the Mn content is controlled to be 0.8 to 1.2% in the invention.
Phosphorus: p is a harmful element in steel, and is likely to cause severe segregation, lowering the toughness of the steel sheet, and causing brittle fracture. In addition, too high a P content will significantly reduce the weldability of the steel and should generally be removed. Therefore, in the present invention, P is controlled to be 0.020%.
Sulfur: s is a harmful element in steel, is easy to form sulfide inclusion and structure segregation with elements such as Mn and the like in the steel, reduces the strength and toughness of the steel, deteriorates fatigue and welding performance, and needs to reduce the content of S as much as possible. Therefore, the S content is controlled to be less than 0.006% in the present invention.
Titanium: ti is a strong carbonitride forming element, and carbon and nitride particles are precipitated in ferrite, so that the strength of a ferrite matrix can be effectively improved. The Ti alloy content is set in consideration of cost and required strength, and when Ti is less than 0.03%, the precipitation strengthening effect is insufficient, and when Ti exceeds 0.05%, the excessive Ti deteriorates the toughness of the steel. Therefore, the Ti content is controlled to be 0.03-0.05%.
Nitrogen: the nitrogen and the carbon are equivalent to interstitial atoms, and the nitrogen and the carbon are required to be fixed for the formability of the steel, so that the N and the Ti can be solidified at high temperature, large-particle TiN is easily formed during continuous casting, the waste of Ti alloy is caused, and the subsequent dispersion precipitation strengthening of Ti is influenced. Therefore, the content of nitrogen is limited, and the invention controls N to be less than or equal to 0.005 percent.
The manufacturing method of the hot-rolled pickled steel plate with the tensile strength of 600MPa and the low yield ratio comprises the following steps:
continuously casting molten steel to obtain a continuous casting slab, wherein the molten steel comprises the following chemical components in percentage by weight: c: 0.06-0.08%, Mn: 0.8-1.2%, Si: 0-0.10%, P: 0-0.020%, S: 0-0.006%, Alt: 0.015-0.050%, N: 0-0.005%, Ti: 0.03 to 0.05 percent of Fe and the balance of inevitable impurity elements;
heating the continuous casting plate blank to 1200-1250 ℃ by a heating furnace, and then carrying out hot rolling, wherein the hot rolling is a two-stage rolling process, the rough rolling is 5-pass continuous rolling, the rolling is carried out at a temperature above the austenite recrystallization temperature, and the finish temperature of the rough rolling is 1030-1050 ℃; the finish rolling is 7-pass continuous rolling, the finish rolling is carried out in an austenite non-recrystallization region, the finish rolling temperature is 850-880 ℃, the finish rolling reduction rate is 85-95%, after the finish rolling, the thickness of the steel plate is controlled to be 2.0-4.0 mm, the laminar cooling adopts front-section cooling, and a hot rolled steel coil is obtained when the coiling temperature is 580-620 ℃;
and re-uncoiling the hot-rolled steel coil on an uncoiler, and coiling to obtain a finished hot-rolled pickled steel plate through straightening, pickling, wherein the straightening elongation is 0.40-0.60%.
The production process adopted by the invention has the following reasons:
1. setting of heating temperature of continuous casting slab
In the composition design, Ti is added to obtain dispersed fine two-phase particles, while TiN and Ti4C2S2Because the melting point is high, the large particles are generated and aggregated in the continuous casting process, and the high slab heating temperature is needed to ensure that the large two-phase particles can be re-fused into the substrate and dispersed and separated out, so the continuous casting slab heating temperature is set to be 1200-1250 ℃.
2. Setting of roughing finishing temperature
In the rough rolling process, in order to recover and recrystallize the crystal grains, the rough rolling finishing temperature is higher than the austenite recrystallization temperature of the steel, the austenite recrystallization temperature of the steel is about 930 ℃, and in order to realize austenite zone rolling by subsequent finish rolling, the rough rolling finishing temperature cannot be too low, but the rough rolling finishing temperature cannot be too high, otherwise, the heating temperature of the continuous casting plate blank must be increased, and the energy consumption is increased. Therefore, the rough rolling finishing temperature is set to 1030 to 1050 ℃.
3. Setting of finish Rolling finishing temperature
In order to prevent the occurrence of mixed crystal structure when the finish rolling is rolled in a two-phase region, the finishing rolling temperature is required to be higher than Ar3Transformation point of A of the steelr3The transformation point was 840 ℃. In addition, the finish rolling temperature may be slightly higher to obtain relatively large-sized grains, but too high a temperature makes the grains coarse to be detrimental to the press property. Therefore, the finish rolling finishing temperature is set to be 850-880 ℃.
4. Setting of laminar cooling system and hot rolling coiling temperature
The hot rolling coiling temperature is one of key factors influencing the mechanical property, and the TiC particle precipitation temperature is lower between 580 and 900 ℃, so that the TiC precipitation is greatly influenced by laminar cooling and the hot rolling coiling temperature. The coiling temperature is too high, the crystal grains grow rapidly, and the strength is reduced too much; if the coiling temperature is too low, the precipitation strengthening effect is not exhibited. Therefore, the laminar cooling and the coiling temperature are set by comprehensively considering the grain size and the precipitation strengthening effect, so the invention adopts a front-stage cooling mode and sets the hot rolling coiling temperature to be 580-620 ℃.
5. Setting of withdrawal and straightening elongation
Firstly, mechanical external force is provided to destroy the combination between the iron scale on the surface of the hot plate and the matrix, so that the scale breaking effect is realized, and the efficiency of removing the iron scale by subsequent acid liquor is improved; secondly, the steel plate which originally has inconsistent extension or larger residual stress is subjected to micro plastic deformation to realize consistent extension or reduce the residual stress through repeated bending and straightening, so that the effect of improving the shape of the steel plate is achieved; and thirdly, applying a small amount of plastic deformation to the steel plate through straightening and withdrawal to eliminate a yield platform so as to eliminate the defects of possible sliding lines and the like on the surface of the part in the stamping process. Through a large amount of work of the applicant, the fact that the pulling and straightening process has a large influence on the performance of the hot rolled steel plate is found, the yield platform is eliminated, and the yield strength is also greatly influenced. For the low-carbon microalloyed steel composition system in the scheme, through experimental work of the applicant, the yield strength R of the steel plate is foundp0.2The pulling-straightening elongation rate is in a relation as shown in figure 2, the principle is that through certain small deformation, originally pinned dislocation is depailed and changed into movable dislocation, dislocation slip is promoted, and when plastic deformation is increased, dislocation rapid propagation entanglement can cause slip difficulty and yield strength increase. Therefore, the invention sets the withdrawal and straightening elongation rate to be 0.40-0.60%, the lowest yield strength can be obtained, and the influence on the tensile strength and the elongation rate is not large.
The hot-rolled pickled steel plate produced by the method has a metallographic structure comprising ferrite, a small amount of pearlite and dispersed titanium carbide particles, wherein the volume content of the pearlite in the metallographic structure is 5-8%, and the ferrite isThe grain size of the body is 10.5-11.5 grade; yield strength R of hot-rolled pickled steel plate with thickness of 2.0-4.0 mmp0.2460 to 520MPa, tensile strength R m600 to 660MPa, a yield ratio of less than or equal to 0.80 and a post-fracture elongation A50mm25-35%, and the hole expansion performance lambda is more than or equal to 75%.
According to the invention, by adopting the design of proper components, hot rolling process and pickling process, an ideal metallographic structure is obtained, the steel plate has excellent stamping performance and hole expansion performance while meeting the product strength, and the requirement of an automobile user on the forming of complex parts is ensured. The hot-rolled pickled steel plate is used for manufacturing automobile structural parts formed in a complex way.
Compared with the prior art, the invention has the following positive effects: 1. the invention adopts a matrix of ferrite, a small amount of pearlite and dispersed carbide, and obtains a yield ratio of below 0.80 on a hot rolled steel grade with a tensile strength of 600MPa by the cooperation of solid solution strengthening and precipitation strengthening and combining a specific straightening and withdrawal process, wherein the hole expansion ratio is more than 75%, and the matrix has good punching performance and hole expansion performance. 2. Compared with the conventional ferrite pearlite structure with the same level strength, the hot-rolled pickled plate has low yield ratio; compared with a two-phase (F + M) tissue with the same grade strength, the hole expansion rate is high; compared with a three-phase (F + B + M) structure with the same grade strength, the three-phase composite material has good surface quality, is easy to produce and has stable performance. 3. The hot-rolled pickled plate with the tensile strength of 600MPa has the advantages of better comprehensive forming performance, good surface quality, low manufacturing cost, easy realization of manufacturing process and stable performance, and is suitable for processing hot-rolled pickled automobile structural parts with complex shapes.
Drawings
FIG. 1 is a photograph of a metallographic structure of a hot-rolled pickled steel sheet according to example 2 of the present invention.
FIG. 2 is a data graph showing the yield strength, tensile strength and withdrawal and straightening elongation of a hot-rolled pickled steel sheet according to example 2 of the present invention.
Detailed Description
The present invention is further illustrated in the following examples 1 to 5, and as shown in tables 1 to 5, it is to be understood that the following specific embodiments are only illustrative and not intended to limit the scope of the present invention.
Table 1 shows the chemical composition (in weight%) of the steels of the examples of the invention, the balance being Fe and unavoidable impurities.
Table 1 chemical composition of the steels of the examples of the invention, in units: and (4) weight percentage.
Smelting in a converter to obtain molten steel meeting the requirements of chemical components, blowing Ar to the molten steel in the refining process of an LF ladle refining furnace, and continuously casting the molten steel under the protection of Ar blowing in the whole process to obtain a continuous casting slab; the thickness of the continuous casting plate blank is 210-230 mm, the width is 800-1300 mm, and the length is 5000-10000 mm.
And (3) sending the fixed-length plate blank produced in the steel-making process to a heating furnace for reheating, discharging from the furnace for dephosphorization, and sending to a continuous hot continuous rolling mill for rolling. Controlling rolling through a rough rolling mill and a finish rolling continuous mill unit, and coiling after laminar cooling, wherein the laminar cooling adopts front-section cooling to produce a qualified hot rolled steel coil; the thickness of the hot rolled steel plate is 2.0-4.0 mm. The hot rolling process control parameters are shown in Table 2.
TABLE 2 Hot Rolling Process control parameters of the inventive examples
The hot rolled steel plate obtained by the invention is subjected to a GB/T228.1-2010 metal material tensile test part 1: room temperature test method "was used for tensile test, and the mechanical properties are shown in Table 3.
TABLE 3 mechanical Properties of Hot rolled Steel sheets according to examples of the present invention
And (3) uncoiling the hot-rolled steel coil on an uncoiler again, and coiling to obtain a finished hot-rolled pickled steel plate after straightening and pickling, wherein the straightening elongation is 0.40-0.60%. The withdrawal and straightening elongation rates adopted in the examples of the present invention are shown in table 4.
TABLE 4 elongation by withdrawal straightening for examples of the invention
| Hot rolling parameters | Thickness/mm of hot-rolled pickled steel sheet | Withdrawal elongation/%) |
| The invention | 2.0-4.0 | 0.40-0.60 |
| Example 1 | 2.0 | 0.60 |
| Example 2 | 2.5 | 0.55 |
| Example 3 | 3.0 | 0.50 |
| Example 4 | 3.5 | 0.45 |
| Example 5 | 4.0 | 0.40 |
Referring to fig. 1 (the structure obtained in example 2), the metallographic structure of the hot-rolled pickled steel plate obtained by the method is ferrite, a small amount of pearlite and dispersed titanium carbide particles, the volume content of the pearlite in the metallographic structure is 5-8%, and the grain size of the ferrite is 10.5-11.5 grade; yield strength R of hot-rolled pickled steel plate with thickness of 2.0-4.0 mmp0.2460 to 520MPa, tensile strength R m600 to 660MPa, a yield ratio of less than or equal to 0.80 and a post-fracture elongation A50mm25-35%, and the hole expansion performance lambda is more than or equal to 75%.
The hot-rolled pickled steel plate obtained by the invention is subjected to a tensile test according to GB/T228.1-2010 part 1: the tensile test is carried out according to the room temperature test method, the reaming test is carried out according to the GB/T24245631-2009 metal material thin plate and thin strip reaming test method, and the mechanical properties are shown in Table 5.
TABLE 5 mechanical Properties of Hot-rolled pickled Steel sheets according to examples of the present invention
Referring to fig. 2, it can be seen from tables 3 and 5 that the yield strength of the hot rolled steel sheet is decreased, the tensile strength is slightly increased, the elongation is not greatly changed, and the yield ratio is decreased to 0.8 or less after the withdrawal and straightening treatment.
In addition to the above embodiments, the present invention may have other embodiments. All technical solutions formed by adopting equivalent substitutions or equivalent transformations fall within the protection scope of the claims of the present invention.
Claims (3)
1. A hot-rolled pickled steel plate with 600 MPa-level tensile strength and low yield ratio comprises the following chemical components in percentage by weight: c: 0.06-0.08%, Mn: 0.8 to 1.11%, Si: 0-0.10%, P: 0-0.020%, S: 0-0.010%, Alt: 0.015-0.050%, N: 0-0.005%, Ti: 0.03 to 0.05 percent of Fe and the balance of inevitable impurity elements; the metallographic structure of the hot-rolled pickled steel plate is ferrite, a small amount of pearlite and dispersed titanium carbide particles, and the volume content of the pearlite in the metallographic structure is5-8%, and the grain size of ferrite is 10.5-11.5 grade; yield strength R of hot-rolled pickled steel plate with thickness of 2.0-4.0 mmp0.2460 to 520MPa, tensile strength Rm600 to 660MPa, a yield ratio of less than or equal to 0.80 and a post-fracture elongation A50mm25-35%, and the hole expansion performance lambda is more than or equal to 75%.
2. The manufacturing method of the hot-rolled pickled steel plate with the tensile strength of 600MPa and the low yield ratio is characterized by comprising the following steps of:
continuously casting molten steel to obtain a continuous casting slab, wherein the molten steel comprises the following chemical components in percentage by weight: c: 0.06-0.08%, Mn: 0.8 to 1.11%, Si: 0-0.10%, P: 0-0.020%, S: 0-0.006%, Alt: 0.015-0.050%, N: 0-0.005%, Ti: 0.03 to 0.05 percent of Fe and the balance of inevitable impurity elements;
heating the continuous casting plate blank to 1200-1250 ℃ by a heating furnace, and then carrying out hot rolling, wherein the hot rolling is a two-stage rolling process, the rough rolling is 5-pass continuous rolling, the rolling is carried out at a temperature above the austenite recrystallization temperature, and the finish temperature of the rough rolling is 1030-1050 ℃; the finish rolling is 7-pass continuous rolling, the finish rolling is carried out in an austenite non-recrystallization region, the finish rolling finishing temperature is 850-880 ℃, the finish rolling reduction rate is 85-95%, after the finish rolling, laminar cooling adopts front-section cooling, and a hot-rolled steel coil is obtained by coiling when the coiling temperature is 580-620 ℃;
and re-uncoiling the hot-rolled steel coil on an uncoiler, and coiling to obtain a finished hot-rolled pickled steel plate through straightening, pickling, wherein the straightening elongation is 0.40-0.60%.
3. The method for producing a hot-rolled pickled steel sheet having a tensile strength of 600MPa grade and a low yield ratio as claimed in claim 2, wherein the thickness of the steel sheet is controlled to be 2.0 to 4.0mm after the finish rolling.
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