CN109023105B - Hot-rolled strip steel for automobile structure and manufacturing method thereof - Google Patents
Hot-rolled strip steel for automobile structure and manufacturing method thereof Download PDFInfo
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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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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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
- C21D8/0226—Hot rolling
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- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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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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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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Abstract
The invention discloses a hot-rolled strip steel for an automobile structure and a manufacturing method thereof, wherein the strip steel comprises the following components in percentage by mass: 0.030-0.080 wt%, Si: 0.15-0.25 wt%, Mn: 1.00-1.60 wt%, P: less than or equal to 0.020 wt%, S: less than or equal to 0.005 wt%, Al: 0.02-0.05 wt%, Nb: 0.020-0.060 wt%, Ti: 0.01-0.03 wt%, V: 0.02-0.06 wt%, Cr: 0.10-0.30 wt%, and the balance of Fe and inevitable impurities. The method is used for solving the technical problems that the influence of alloy elements on the surface iron scale of the strip steel is not researched in the prior art, the surface iron scale of the strip steel with high strength and thick specification is easy to fall off, and the controlled rolling and controlled cooling process of the strip steel with high ductility and high surface quality is in conflict with each other, realizes the development of the green environment-friendly hot rolled strip steel with thick specification, high strength and high ductility, has excellent cold formability, meets the forming requirement of complex parts, and has the technical effect that the surface iron scale is not easy to fall off to prevent the surface of a die from being damaged.
Description
Technical Field
The invention relates to the technical field of metallurgy, in particular to a hot-rolled strip steel for an automobile structure and a manufacturing method thereof.
Background
With the progress of steel production technology, the equipment conditions, the dimensional accuracy and the performance quality of steel products in the Chinese steel industry basically reach the international level. However, for a long time, the systematic research on the surface quality of large-scale and wide-range hot rolled steel products in China is lacked, and the problems of the surface quality of hot rolled strip steel, such as the difficult removal of iron scales, the falling of the iron scales, the occurrence of red rust on the surface of the strip steel, the pressing in of the iron scales, the pickling defects and the like, frequently occur, so that the improvement of the grade of the hot rolled steel products is seriously hindered. On the other hand, for some parts with complex shapes, the conventional product design cannot meet the requirements of the parts on the forming performance, and the problem of 'not meeting the standard' is caused, so that the parts with special performance requirements need to be designed in a differentiated and personalized manner. To occupy a niche in a highly competitive market, the surface quality of hot rolled steel must be improved and "custom-made services" must be performed.
In the current steel production flow, acid pickling is mainly used for improving the surface quality of products, but the generated waste acid seriously damages the ecological environment. In order to adapt to the basic policy of energy conservation and emission reduction in China in the face of adjustment of national macro policy, downstream production enterprises, particularly automobile production enterprises, urgently need iron scales which can adapt to 'pickling reduction' and even 'pickling-free' steel raw material products so as to relieve or even eliminate the fundamental damage of waste acid discharge to the ecological environment.
Because the influence of alloy elements on the surface oxide scale of the strip steel is not researched in the prior art, the oxide scale on the surface of the strip steel with high strength and thick specification is easy to fall off, and the technical problems that the high ductility of the strip steel is contradictory to the controlled rolling and controlled cooling process with high surface quality are solved.
Disclosure of Invention
The embodiment of the invention provides a hot-rolled strip steel for an automobile structure and a manufacturing method thereof, which are used for solving the technical problems that the influence of alloy elements on the oxide scales on the surface of the strip steel is not researched in the prior art, the oxide scales on the surface of the high-strength thick-specification strip steel are easy to fall off, and the high ductility of the strip steel is inconsistent with the controlled rolling and cooling process with high surface quality, so that the development of the thick-specification high-strength high-ductility green environment-friendly hot-rolled strip steel is realized, the cold formability is excellent, the forming requirement of complex parts is met, and the oxide scales on the surface are not easy to fall off to prevent the surface damage of a mold.
In order to solve the above problems, in a first aspect, an embodiment of the present invention provides a hot-rolled steel strip for an automobile structure, where the steel strip includes, by mass, C: 0.030-0.080 wt%, Si: 0.15-0.25 wt%, Mn: 1.00-1.60 wt%, P: less than or equal to 0.020 wt%, S: less than or equal to 0.005 wt%, Al: 0.02-0.05 wt%, Nb: 0.020-0.060 wt%, Ti: 0.01-0.03 wt%, V: 0.02-0.06 wt%, Cr: 0.10-0.30 wt%, and the balance of Fe and inevitable impurities.
Preferably, the microstructure of the strip steel is a full ferrite structure and a nanoscale precipitated phase, wherein the average grain size of the ferrite structure is 2.0-6.0 mu m, and the range of the nanoscale precipitated phase with the average grain diameter of 1-60 nm in the microstructure is 90-100%.
Preferably, the mass percentages of a part of the components of the strip steel are C: 0.35 to 0.07 wt%, Mn: 1.0-1.5 wt%, Nb: 0.03-0.45 wt%, Ti: 0.01 to 0.025 wt%, V: 0.025 to 0.04 wt%, Cr: 0.15 to 0.25 wt%.
Preferably, the mass percentages of a part of the components of the strip steel are C: 0.04-0.07 wt%, Mn: 1.1-1.5 wt%, Nb: 0.03-0.05 wt%, Ti: 0.015-0.025 wt%, V: 0.025 to 0.045 wt%, Cr: 0.15 to 0.25 weight percent.
Preferably, the mass percentages of a part of the components of the strip steel are C: 0.03 to 0.07 wt%, Mn: 1.0-1.4 wt%, Nb: 0.03-0.04 wt%, Ti: 0.01-0.02 wt%, V: 0.02-0.04 wt%, Cr: 0.15 to 0.2 wt%.
In a second aspect, embodiments of the present invention provide a method for manufacturing a hot-rolled strip for an automobile structure, where the method includes obtaining a continuous casting slab by smelting molten steel; the continuous casting slab comprises the following components in percentage by mass: 0.030-0.080 wt%, Si: 0.15-0.25 wt%, Mn: 1.00-1.60 wt%, P: less than or equal to 0.020 wt%, S: less than or equal to 0.005 wt%, Al: 0.02-0.05 wt%, Nb: 0.020-0.060 wt%, Ti: 0.01-0.03 wt%, V: 0.02-0.06 wt%, Cr: 0.10 to 0.30 weight percent, and the balance of Fe and inevitable impurities; heating a continuous casting plate blank, wherein the temperature of the continuous casting plate blank is 1180-1230 ℃ after heating, and the heat preservation time is 2.0-2.5 h; carrying out rough rolling on the heated continuous casting plate blank to obtain an intermediate blank, wherein the rough rolling adopts an R1 rough rolling mill set for one-pass rolling and an R2 rough rolling mill set for five-pass rolling, and the outlet temperature range of the rough rolling is 950-1050 ℃; performing precision rolling on the intermediate plate blank to obtain a strip steel, wherein the inlet temperature of the precision rolling is 920-1000 ℃, and the finishing temperature is controlled to be 870-930 ℃; after hot rolling is finished, carrying out laminar cooling and coiling on the strip steel, wherein the coiling temperature is 530-600 ℃; and (4) independently stacking and cooling the strip steel to room temperature.
Preferably, the rough rolling is performed with a 5-pass dephosphorization process, wherein the R1 rough rolling mill set carries out one-pass descaling, the R2 rough rolling mill set carries out 1, 2, 3 and 5-pass descaling, air cooling is performed before the 5 th pass of the R2 rough rolling mill set, and the air cooling time is 20-50 s.
Preferably, the intermediate slab is fine descaled using high pressure water of greater than 18MPa prior to finish rolling.
Preferably, the finish rolling adopts an acceleration rolling mode, and the steel throwing speed of the final stand is controlled to be more than 6 m/s.
Preferably, the laminar cooling adopts a mode of combining front-section sparse cooling with U-shaped cooling, wherein the head and the tail of the strip steel adopt weak cooling within the range of 30-50 m, and the weak cooling temperature is 20-50 ℃.
One or more technical solutions in the embodiments of the present invention at least have one or more of the following technical effects:
the embodiment of the invention provides a hot-rolled strip steel for an automobile structure and a manufacturing method thereof, wherein the method adopts molten steel smelting to obtain a continuous casting slab; the continuous casting slab comprises the following components in percentage by mass: 0.030-0.080 wt%, Si: 0.15-0.25 wt%, Mn: 1.00-1.60 wt%, P: less than or equal to 0.020 wt%, S: less than or equal to 0.005 wt%, Al: 0.02-0.05 wt%, Nb: 0.020-0.060 wt%, Ti: 0.01-0.03 wt%, V: 0.02-0.06 wt%, Cr: 0.10 to 0.30 weight percent, and the balance of Fe and inevitable impurities; heating a continuous casting plate blank, wherein the temperature of the continuous casting plate blank is 1180-1230 ℃ after heating, and the heat preservation time is 2.0-2.5 h; carrying out rough rolling on the heated continuous casting plate blank to obtain an intermediate blank, wherein the rough rolling adopts an R1 rough rolling mill set for one-pass rolling and an R2 rough rolling mill set for five-pass rolling, and the outlet temperature range of the rough rolling is 950-1050 ℃; performing precision rolling on the intermediate plate blank to obtain a strip steel, wherein the inlet temperature of the precision rolling is 920-1000 ℃, and the finishing temperature is controlled to be 870-930 ℃; after hot rolling is finished, carrying out laminar cooling and coiling on the strip steel, wherein the coiling temperature is 530-600 ℃; and (4) independently stacking and cooling the strip steel to room temperature. The strength, plasticity and fatigue property of the intermediate billet are ensured by controlling the heating temperature of the continuous casting slab; then R1 is adopted for one-time rolling, and R2 is adopted for five-time rolling, so that the iron scale on the surface of the intermediate billet is completely removed; fine descaling is adopted to further improve the removal of the iron scale; the control of the finish rolling inlet temperature and outlet temperature can reach higher steel throwing speed so as to obtain uniform and fine ferrite tissues and thinner iron scales; and then the excellent plate-shaped quality is ensured through laminar cooling; finally, the iron scale is not easy to fall off by controlling the coiling temperature; the obtained strip steel with the components meets the requirements of thick specification, high strength and high ductility, does not have edge warping and red iron scale on the surface of the strip steel, and has the technical effect of excellent cold formability.
The foregoing description is only an overview of the technical solutions of the present invention, and the embodiments of the present invention are described below in order to make the technical means of the present invention more clearly understood and to make the above and other objects, features, and advantages of the present invention more clearly understandable.
Drawings
FIG. 1 is a schematic diagram showing a metallographic structure of a hot-rolled steel strip for an automobile structure according to an embodiment of the present disclosure;
FIG. 2 is a flowchart of a method of manufacturing a hot rolled steel strip for automobile structures according to an embodiment of the present specification;
FIG. 3 is a schematic diagram showing the thickness of the scale of a hot-rolled strip steel for a 6.0mm automobile structure in an example of the present specification;
FIG. 4 is a schematic diagram showing the thickness of the scale of a hot-rolled strip steel for an 8.0mm automobile structure in an embodiment of the present specification;
FIG. 5 is a schematic diagram showing the thickness of scale in a hot-rolled steel strip for an automobile structure of 12.0mm in the examples of the present specification.
Detailed Description
The embodiment of the invention provides a hot-rolled strip steel for an automobile structure and a manufacturing method thereof, which are used for solving the technical problems that the influence of alloy elements on the oxide scales on the surface of the strip steel is not researched in the prior art, the oxide scales on the surface of the high-strength thick-specification strip steel are easy to fall off, and the high ductility of the strip steel is inconsistent with the controlled rolling and cooling process with high surface quality, so that the development of the thick-specification high-strength high-ductility green environment-friendly hot-rolled strip steel is realized, the cold formability is excellent, the forming requirement of complex parts is met, and the oxide scales on the surface are not easy to fall off to prevent the surface damage of a mold.
According to the technical scheme in the embodiment of the invention, the strip steel comprises the following components in percentage by mass: 0.030-0.080 wt%, Si: 0.15-0.25 wt%, Mn: 1.00-1.60 wt%, P: less than or equal to 0.020 wt%, S: less than or equal to 0.005 wt%, Al: 0.02-0.05 wt%, Nb: 0.020-0.060 wt%, Ti: 0.01-0.03 wt%, V: 0.02-0.06 wt%, Cr: 0.10-0.30 wt%, and the balance of Fe and inevitable impurities. The method is used for solving the technical problems that the influence of alloy elements on the surface iron scale of the strip steel is not researched in the prior art, the surface iron scale of the strip steel with high strength and thick specification is easy to fall off, and the controlled rolling and controlled cooling process of the strip steel with high ductility and high surface quality is in conflict with each other, realizes the development of the green environment-friendly hot rolled strip steel with thick specification, high strength and high ductility, has excellent cold formability, meets the forming requirement of complex parts, and has the technical effect that the surface iron scale is not easy to fall off to prevent the surface of a die from being damaged.
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example one
The embodiment of the invention provides a hot-rolled strip steel for an automobile structure, and with reference to a figure 1, the strip steel comprises the following components in percentage by mass: 0.030-0.080 wt%, Si: 0.15 to 0.25 wt%, Mn: 1.00-1.60 wt%, P: less than or equal to 0.020 wt%, S: less than or equal to 0.005 wt%, Al: 0.02-0.05 wt%, Nb: 0.020 to 0.060 wt%, Ti: 0.01-0.03 wt%, V: 0.02-0.06 wt%, Cr: 0.10 to 0.30 wt%, and the balance Fe and inevitable impurities.
Further, the mass percentages of a part of the components of the strip steel are C: 0.35 to 0.07 wt%, Mn: 1.0-1.5 wt%, Nb: 0.03-0.45 wt%, Ti: 0.01 to 0.025 wt%, V: 0.025 to 0.04 wt%, Cr: 0.15 to 0.25 wt%.
Further, the mass percentages of a part of the components of the strip steel are C: 0.04-0.07 wt%, Mn: 1.1-1.5 wt%, Nb: 0.03-0.05 wt%, Ti: 0.015 to 0.025 wt%, V: 0.025-0.045 wt%, Cr: 0.15 to 0.25 wt%.
Further, the mass percentages of a part of the components of the strip steel are C: 0.03 to 0.07 wt%, Mn: 1.0-1.4 wt%, Nb: 0.03-0.04 wt%, Ti: 0.01-0.02 wt%, V: 0.02-0.04 wt%, Cr: 0.15 to 0.2 wt%.
Specifically, C in the components of the strip steel is one of the most economical strengthening elements in the steel. C is favorable for improving the fatigue strength, and when the content of C exceeds 0.03 wt%, the fatigue strength is improved more obviously. However, if the C content is too high, particularly if the C content exceeds 0.08 wt%, the steel strip cannot have a full ferrite structure of 100% and cannot surely have a desired elongation value. Therefore, the mass percent of C in the strip steel in the embodiment of the application is controlled to be 0.03-0.08 wt percent by comprehensively considering the strength and the cold formability of the material, and further. Si is a solid solution strengthening element, and ferrite transformation is promoted in the hot rolling step, and in the present embodiment, it is necessary to appropriately add Si element in order to secure a desired structure and excellent formability. However, when the Si content exceeds 0.26 wt%, an fayalite phase is formed, the adhesiveness of iron sheet is increased, the difficulty in removing in a descaling stage is increased, and the defect of 'red rust' is formed, which is not beneficial to the surface quality of the strip steel. Therefore, the mass percent of Si in the strip steel in the embodiment of the application is controlled to be 0.15 wt% to 0.25 wt% in comprehensive consideration. Mn is a solid solution strengthening element and contributes to increase of the steel strength. However, if the Mn content is too high, a serious band-shaped structure is formed, and the transverse elongation of the steel is lowered, which affects cold formability. In the examples of the present application, the Mn content is designed to be 1.0 wt% to 1.6 wt%. P and S are impurity elements in steel, the P element easily causes the center segregation of steel, the weldability and the plastic toughness of the steel are deteriorated, and the content of the P element is reduced as much as possible; the S element is easy to combine with the Mn element to form MnS inclusion, which can reduce the weldability, the formability, the fatigue property and the low-temperature toughness of the steel, and the content of the S element is reduced as much as possible. The mass percent of P in the strip steel in the embodiment of the application is controlled to be lower than 0.020 wt%, and the mass percent of S is controlled to be lower than 0.005 wt%. Al acts as a deoxidizer during steel making, and since the cold formability of the material is lowered by incomplete deoxidation, the mass percentage of Al is controlled to be more than 0.02 wt%. However, too high Al content results in too many AlN inclusions in the steel, and the elongation of the steel strip is reduced. In the embodiment of the application, the mass percent of Al is controlled to be 0.02 wt% -0.05 wt%. Nb has the effect of suppressing the recovery of austenite and the grain growth of recrystallization in the hot rolling step, and making the ferrite phase have a desired grain size (2.0 to 6.0 μm). In order to achieve this effect, the Nb content should be 0.02 wt% or more. On the other hand, if the mass percentage of Nb exceeds 0.06 wt%, the strength of the steel strip tends to increase, and the ductility tends to decrease. In the embodiment of the application, the Nb content in the strip steel is controlled to be 0.02 wt% -0.06 wt%. Ti bonds with C, N in steel at high temperature to form precipitates and serves to suppress austenite grain coarsening during slab heating, but when the amount of Ti added is too large, coarse precipitates are likely to form, which affects the cold formability of the material. In the embodiment of the application, the content of Ti element in the strip steel is controlled to be 0.01 wt% -0.03 wt%. V is completely dissolved in a solid solution in a high-temperature austenite region, and is combined with C only in a ferrite region to form carbide precipitation, thereby exerting a strong precipitation strengthening effect. In order to obtain such an effect, the content of V is required to be 0.02 wt% or more, but when the mass percentage of V exceeds 0.06%, the formability of the steel strip is lowered. Therefore, the V content in the steel strip is controlled to be 0.02 wt% -0.06 wt% in the embodiment of the application by comprehensively considering the strengthening effect and the cold formability of the steel strip. Cr can form a dense oxide film on the surface of the steel sheet to improve the atmospheric corrosion resistance of the steel sheet, but when the Cr content is high, ductility and toughness are lowered. In the embodiment, the Cr content in the strip steel is controlled to be 0.1 wt% -0.3 wt%. The balance other than the above components is Fe and inevitable impurities. Preferably, the mass percentage of a part of the components of the strip steel is preferably C: 0.35 to 0.07 wt%, Mn: 1.0-1.5 wt%, Nb: 0.03-0.45 wt%, Ti: 0.01 to 0.025 wt%, V: 0.025 to 0.04 wt%, Cr: 0.15 to 0.25 wt%. Or, the mass percentage of one part of the components of the strip steel is C: 0.04-0.07 wt%, Mn: 1.1-1.5 wt%, Nb: 0.03-0.05 wt%, Ti: 0.015 to 0.025 wt%, V: 0.025-0.045 wt%, Cr: 0.15 to 0.25 wt%. Or, the mass percentage of one part of the components of the strip steel is C: 0.03 to 0.07 wt%, Mn: 1.0-1.4 wt%, Nb: 0.03-0.04 wt%, Ti: 0.01-0.02 wt%, V: 0.02-0.04 wt%, Cr: 0.15 to 0.2 wt%.
Furthermore, the microstructure of the strip steel is a full ferrite structure and a nanoscale precipitated phase, wherein the average grain size of the ferrite structure is 2.0-6.0 mu m, and the range of the nanoscale precipitated phase with the average grain diameter of 1-60 nm in the microstructure is 90-100%.
Specifically, in order to ensure high strength and excellent cold formability of the steel strip and prevent cracks from occurring during press working or roll working, the microstructure of the steel strip is a full ferrite structure and a nano-scale precipitated phase. The average grain size of the ferrite structure is ensured to be 2.0-6.0 mu m, and the range of the nano precipitated phase with the average grain diameter of 1-60 nm in the microstructure is 90-100%. When the average grain size of the ferrite phase is more than 6.0 μm, the required strength, low-temperature toughness and fatigue property cannot be secured; when the average grain size of the ferrite phase of the strip is less than 2.0 μm, the formability of the strip is reduced. In the examples of the present application, the average particle size of the ferrite phase is limited to a range of 2.0 to 6.0. mu.m. Wherein, the proportion of the average grain diameter of the nano precipitated phase in the ferrite phase between 1nm and 60nm being more than 90 percent is the key for ensuring high strength and excellent cold formability, and when the average grain diameter of the carbide is less than 2nm, the elongation of the strip steel can be reduced, and the formability is reduced; on the other hand, when the average grain size of the nano-sized precipitates in the ferrite phase exceeds 60nm, the coarse precipitates deteriorate cold formability. Therefore, the ratio of the average grain size of the nano-sized carbide in the ferrite phase is limited to 90% or more from 1nm to 60 nm.
The steel strip in the embodiment of the application has thick specification, high strength and high ductility, wherein the thickness of the steel strip is more than 6mm, the yield strength exceeds 550MPa, the tensile strength exceeds 650MPa, and the elongation exceeds 24%. The strip steel belongs to green environment-friendly steel, has no surface defects of red rust and black ash on the surface of the strip steel, basically does not drop iron scale in the subsequent flattening, stamping and rolling processes, can meet the surface quality control process and the high-strength and high-ductility control process of thick-specification complex parts, and meets the requirements of the forming performance of the steel for automobile structures. The mechanical properties of the strip steel provided in this example are shown in table 1. Table 1 shows the mechanical properties of a hot-rolled strip for automobile structure according to examples 1 to 3 of the present application.
As can be seen from Table 1, the yield strength of the hot-rolled strip steel for the automobile structure is greater than 550MPa, the tensile strength is greater than 650MPa, the proportional elongation is greater than or equal to 26.5 percent, and the highest percentage elongation can reach 28.5 percent; meanwhile, the strip steel is qualified in a cold bending test of 180-degree d-1 a, and meanwhile, the scale on the outer arc surface is not dropped off; the thickness of the oxide scales of the strip steel with different thicknesses is controlled within 10 mu m, and the thinnest thickness reaches 3.5 mu m. In examples 1 to 3 of the present application, the ratio of nanosized precipitates having an average grain size of 2 to 5 μm in a ferrite structure and an average grain size of (Nb, Ti, V) complex carbonitride of 1 to 60nm is not less than 90%. The strip steel has no cracking or thinning defects in the process of producing various structural parts, and has excellent cold formability.
TABLE 1 mechanical Properties of the strip
Example two
The present embodiment provides a method for manufacturing a hot-rolled strip for an automobile structure, referring to fig. 2 to 5, the method including:
step 110: smelting molten steel to obtain a continuous casting plate blank; the continuous casting slab comprises the following components in percentage by mass: 0.030-0.080 wt%, Si: 0.15 to 0.25 wt%, Mn: 1.00-1.60 wt%, P: less than or equal to 0.020 wt%, S: less than or equal to 0.005 wt%, Al: 0.02-0.05 wt%, Nb: 0.020 to 0.060 wt%, Ti: 0.01-0.03 wt%, V: 0.02-0.06 wt%, Cr: 0.10 to 0.30 wt%, and the balance Fe and inevitable impurities.
Specifically, in the embodiment of the application, the smelting method such as a converter is adopted to smelt the components with the mass percentage of C: 0.030-0.080 wt%, Si: 0.15 to 0.25 wt%, Mn: 1.00-1.60 wt%, P: less than or equal to 0.020 wt%, S: less than or equal to 0.005 wt%, Al: 0.02-0.05 wt%, Nb: 0.020 to 0.060 wt%, Ti: 0.01-0.03 wt%, V: 0.02-0.06 wt%, Cr: 0.10 to 0.30 wt%, and the balance Fe and inevitable impurities. Smelting molten steel according to set components and casting the molten steel into a continuous casting plate blank, wherein the chemical elements of the continuous casting plate blank are shown in the table 2 according to the mass percentage. Table 2 shows the mass percentage of each chemical element in the hot-rolled strip steel for automobile structures of examples 1 to 3 at different chemical component ratios in the present application.
Table 2 wt.% of the chemical elements of the strip steel, balance Fe and other unavoidable impurities
| Thickness/mm | C | Si | Mn | P | S | Alt | Nb | Ti | V | Cr | N | |
| Example 1 | 6 | 0.05 | 0.24 | 1.2 | 0.011 | 0.002 | 0.035 | 0.025 | 0.015 | 0.045 | 0.28 | 0.0030 |
| Example 2 | 8 | 0.06 | 0.21 | 1.5 | 0.010 | 0.003 | 0.040 | 0.035 | 0.018 | 0.035 | 0.15 | 0.0035 |
| Example 3 | 12 | 0.07 | 0.17 | 1.4 | 0.011 | 0.004 | 0.030 | 0.050 | 0.020 | 0.025 | 0.22 | 0.0040 |
Step 120: and heating the continuous casting plate blank, wherein the temperature of the continuous casting plate blank is 1180-1230 ℃ after heating, and the heat preservation time is 2.0-2.5 h.
Specifically, the heating temperature of the continuous cast slab is set in accordance with the solid solution and precipitation of Nb, Ti, and V in the steel and the grain coarsening behavior of the prior austenite. When the heating temperature is lower than 1180 ℃, coarse carbonitrides of Nb, Ti, and V precipitated during continuous casting remain as undissolved carbonitrides, and the strength, plasticity, and fatigue properties required for the steel strip cannot be ensured. When the heating temperature exceeds 1230 ℃, austenite grains are coarsened, the strength, cold formability and fatigue property required by the strip steel cannot be ensured, and the lower finish rolling inlet temperature cannot be ensured, so that the thickness of the final iron scale is influenced. Therefore, the heating temperature is limited to 1180-1230 ℃. Further, it is preferable to set the soaking time for heating the continuous cast slab to 30 to 40 minutes to sufficiently austenitize and ensure the re-dissolution of the microalloy elements, while ensuring a sufficient solution time for Nb, Ti and V. The heating temperature of the continuously cast slab is shown in table 3. Table 3 lists the relevant process parameters for the method of manufacturing the hot rolled steel strip for automobile structures of examples 1 to 3 of the present application.
TABLE 3 Process parameters relevant to the manufacturing method of the strip
Step 130: and carrying out rough rolling on the heated continuous casting plate blank to obtain an intermediate blank, wherein the rough rolling adopts an R1 rough rolling mill set for one-pass rolling and an R2 rough rolling mill set for five-pass rolling, and the outlet temperature range of the rough rolling is 950-1050 ℃.
Further, the rough rolling is performed with a 5-pass dephosphorization process, wherein the R1 rough rolling mill set carries out one-pass descaling, the R2 rough rolling mill set carries out 1, 2, 3 and 5-pass descaling, air cooling is carried out before the 5 th pass of the R2 rough rolling mill set, and the air cooling time is 20-50 s.
Specifically, the heated continuous casting slab is subjected to rough rolling, wherein the rough rolling adopts a 1+5 mode rolling process, namely, one-pass rolling of an R1 rough rolling unit and five-pass rolling of an R2 rough rolling unit, wherein 5-pass descaling processes are carried out in the rough rolling, namely, one-pass descaling of the R1 rough rolling unit and one-pass descaling of the R2 rough rolling unit, and the descaling of the R2 rough rolling unit is carried out for 1, 2, 3 and 5 passes, so that the scale on the surface of the intermediate slab is completely removed. And air cooling is carried out before the 5 th pass of the R2 roughing mill group, the air cooling time is 20-50 s, and the roughing outlet temperature range is 950-1050 ℃. The technological parameters of the rough rolling of the strip steel are shown in the table 3.
Step 140: and carrying out precision rolling on the intermediate plate blank to obtain the strip steel, wherein the inlet temperature of the precision rolling is 920-1000 ℃, and the finishing temperature is controlled at 870-930 ℃.
Further, before finish rolling, the intermediate billet is subjected to finish descaling by using high-pressure water of more than 18 MPa. Furthermore, the finish rolling adopts a speed-up rolling mode, and the steel throwing speed of the final stand is controlled to be more than 6 m/s.
Specifically, in the embodiment of the present invention, from the viewpoint of ensuring good surface quality of the strip, the intermediate slab is subjected to a finish descaling operation using high-pressure water of 18MPa or more before finish rolling to completely remove scale on the surface of the strip so as not to be pressed into the surface of the strip during finish rolling and affect the surface quality. The inlet temperature of the finish rolling is controlled to be 920-1000 ℃, the finish rolling temperature is 870-930 ℃, the speed-up rolling mode is adopted for the finish rolling, all water between the finish rolling frames is opened, and the steel throwing speed of the last frame is controlled to be more than 6 m/s. The inlet temperature and the outlet temperature of finish rolling are limited, so that a higher steel throwing speed can be achieved, and the aim of improving the rolling control level and providing conditions for obtaining uniform and fine ferrite tissues is achieved; on the other hand, the method can ensure higher rolling speed, inhibit the generation of the iron scale and ensure that thinner iron scale is obtained. When the finish rolling finishing temperature exceeds 930 ℃, the average grain diameter of the ferrite phase of the obtained strip steel is easy to exceed 6 mu m, thereby reducing the strength, the formability and the fatigue performance of the strip steel; on the other hand, when the finish rolling temperature is lower than 870 ℃, the rolling speed of the strip steel is slow, so that the primary scale is likely to be thick, and the desired scale thickness cannot be ensured. Therefore, the finish rolling finishing temperature is preferably in the range of 870 to 930 ℃. The finish rolling temperature is more preferably 880 to 900 ℃. The process parameters of the strip finish rolling are shown in table 3 above.
Step 150: and after hot rolling is finished, carrying out laminar cooling on the strip steel and coiling, wherein the coiling temperature is 530-600 ℃.
Further, the laminar cooling adopts a mode of combining front-section sparse cooling with U-shaped cooling, wherein the head and the tail of the strip steel adopt weak cooling within the range of 30-50 m, and the weak cooling temperature is 20-50 ℃.
Specifically, after hot rolling is finished, laminar cooling is adopted for the strip steel, wherein the laminar cooling adopts a mode of combining front-section sparse cooling with U-shaped cooling, and sparse cooling is adopted for the front section, namely one or more headers can be arranged at intervals by a cooling mode that the headers are opened at intervals. The heat conduction in the steel plate is far lower than the convection heat exchange on the surface of the steel plate when the steel plate is in laminar cooling, so that the temperature difference between the surface and the center of the steel plate is overlarge during cooling, and the internal structure of the steel plate is uneven. An air cooling section is arranged in the middle of the water cooling section of the sparse cooling day, so that the temperature of the steel plate can be timely returned during air cooling, and the temperature of the whole steel plate tends to be uniform. When the thickness of the steel plate is larger, the temperature difference between the surface and the center of the steel plate can be reduced by sparse cooling, the homogenization of the structure of the steel plate after cooling is facilitated, and the sparse cooling can be realized by sparse group-by-group and sparse tube-by-tube. And then the strip steel is cooled in sections by combining a U-shaped cooling mode so as to improve the temperature of the head and the tail, properly reduce the yield strength of the head and the tail, reduce the temperature of the middle part of the strip steel, keep the same with the coiling temperature, facilitate the uniformity of the strip steel cooling, and overcome the problem that the inner and outer rings are cooled unevenly after being rolled down, thereby ensuring the excellent plate shape quality, the integral coiling mechanical property and the surface quality uniformity. In the embodiment of the application, the coiling temperature of the strip steel is controlled to be 530-600 ℃, the head-tail weak cooling distance is 30-50 m, and the head-tail weak cooling temperature is 20-50 ℃. The coiling temperature is one of the important factors for determining the structure percentage and size of the ferrite phase of the hot-rolled strip steel and the precipitation state of the (Nb, Ti and V) composite carbide, and is also an important factor for ensuring the transformation of the eutectoid reaction of the ferrous oxide. When the coiling temperature is lower than 530 ℃, precipitation of (Nb, Ti, V) composite carbide in the ferrite region is not facilitated, and the strength is affected. On the other hand, when the coiling temperature exceeds 600 ℃, eutectoid transformation of the coiled ferrous oxide is insufficient, eutectoid proportion in an iron scale structure is insufficient, and an iron scale is thicker, so that the iron scale is easy to fall off in a block shape in the subsequent processing process. Therefore, the coiling temperature is preferably in the range of 530 to 600 ℃. Further, the coiling temperature is more preferably 550 to 580 ℃.
Step 160: and (4) independently stacking and cooling the strip steel to room temperature.
Specifically, in order to control the thickness of the iron scale, the strip steel needs to be separately stacked after being put in storage, and is rapidly cooled to the room temperature.
The technical scheme provided in the embodiment of the application at least has the following technical effects or advantages:
the embodiment of the invention provides a hot-rolled strip steel for an automobile structure and a manufacturing method thereof, wherein the method adopts molten steel smelting to obtain a continuous casting slab; the continuous casting slab comprises the following components in percentage by mass: 0.030-0.080 wt%, Si: 0.15-0.25 wt%, Mn: 1.00-1.60 wt%, P: less than or equal to 0.020 wt%, S: less than or equal to 0.005 wt%, Al: 0.02-0.05 wt%, Nb: 0.020-0.060 wt%, Ti: 0.01-0.03 wt%, V: 0.02-0.06 wt%, Cr: 0.10 to 0.30 weight percent, and the balance of Fe and inevitable impurities; heating a continuous casting plate blank, wherein the temperature of the continuous casting plate blank is 1180-1230 ℃ after heating, and the heat preservation time is 2.0-2.5 h; carrying out rough rolling on the heated continuous casting plate blank to obtain an intermediate blank, wherein the rough rolling adopts R1 one-pass rolling and R2 five-pass rolling, and the outlet temperature range of the rough rolling is 950-1050 ℃; performing precision rolling on the intermediate plate blank to obtain a strip steel, wherein the inlet temperature of the precision rolling is 920-1000 ℃, and the finishing temperature is controlled to be 870-930 ℃; after hot rolling is finished, carrying out laminar cooling and coiling on the strip steel, wherein the coiling temperature is 530-600 ℃; and (4) independently stacking and cooling the strip steel to room temperature. The strength, plasticity and fatigue property of the intermediate billet are ensured by controlling the heating temperature of the continuous casting slab; then R1 is adopted for one-time rolling, and R2 is adopted for five-time rolling, so that the iron scale on the surface of the intermediate billet is completely removed; fine descaling is adopted to further improve the removal of the iron scale; the control of the finish rolling inlet temperature and outlet temperature can reach higher steel throwing speed so as to obtain uniform and fine ferrite tissues and thinner iron scales; and then the excellent plate-shaped quality is ensured through laminar cooling; finally, the iron scale is not easy to fall off by controlling the coiling temperature; the obtained strip steel with the components meets the requirements of thick specification, high strength and high ductility, does not have edge warping and red iron scale on the surface of the strip steel, and has the technical effect of excellent cold formability.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various modifications and variations can be made in the embodiments of the present invention without departing from the spirit or scope of the embodiments of the invention. Thus, if such modifications and variations of the embodiments of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to encompass such modifications and variations.
Claims (3)
1. A manufacturing method of hot rolled strip steel for an automobile structure is applied to manufacturing the hot rolled strip steel for the automobile structure and is characterized in that the method adopts molten steel smelting to obtain a continuous casting slab; the continuous casting slab comprises the following components in percentage by mass: 0.030-0.080 wt%, Si: 0.15 to 0.25 wt%, Mn: 1.00-1.60 wt%, P: less than or equal to 0.020 wt%, S: less than or equal to 0.005 wt%, Al: 0.02-0.05 wt%, Nb: 0.020 to 0.060 wt%, Ti: 0.01-0.03 wt%, V: 0.02-0.06 wt%, Cr: 0.10 to 0.30 wt%, and the balance of Fe and inevitable impurities;
heating a continuous casting plate blank, wherein the temperature of the continuous casting plate blank is 1180-1230 ℃ after heating, and the heat preservation time is 2.0-2.5 h;
carrying out rough rolling on the heated continuous casting plate blank to obtain an intermediate blank, wherein the rough rolling adopts an R1 rough rolling mill set for one-pass rolling and an R2 rough rolling mill set for five-pass rolling, and the outlet temperature range of the rough rolling is 950-1050 ℃;
performing precision rolling on the intermediate plate blank to obtain a strip steel, wherein the inlet temperature of the precision rolling is 920-1000 ℃, the finishing temperature is controlled at 870-930 ℃, the precision rolling adopts a speed-up rolling mode, and the steel throwing speed of a final stand is controlled at more than 6 m/s;
after hot rolling is finished, carrying out laminar cooling and coiling on the strip steel, wherein the coiling temperature is 530-600 ℃;
the strip steel is put in a warehouse and is independently stacked and cooled to room temperature;
the rough rolling is carried out with a 5-pass dephosphorization process, wherein the R1 rough rolling unit carries out one-pass descaling, the R2 rough rolling unit carries out 1, 2, 3 and 5-pass descaling, air cooling is carried out before the 5 th pass of the R2 rough rolling unit, and the air cooling time is 20-50 s;
the hot-rolled strip steel for the automobile structure comprises the following components in percentage by mass: 0.030-0.080 wt%, Si: 0.15 to 0.25 wt%, Mn: 1.00-1.60 wt%, P: less than or equal to 0.020 wt%, S: less than or equal to 0.005 wt%, Al: 0.02-0.05 wt%, Nb: 0.020 to 0.060 wt%, Ti: 0.01-0.03 wt%, V: 0.02-0.06 wt%, Cr: 0.10 to 0.30 wt%, and the balance of Fe and inevitable impurities;
the microstructure of the hot-rolled strip steel for the automobile structure is a full ferrite structure and a nanoscale precipitated phase, wherein the average grain size of the ferrite structure is 2.0-6.0 mu m, and the range of the nanoscale precipitated phase with the average grain size of 1-60 nm in the microstructure is 90-100%;
the thickness of the hot-rolled strip steel for the automobile structure is more than 6 mm.
2. The method of claim 1, wherein the intermediate billet is fine descaled using high pressure water of greater than 18MPa prior to finish rolling.
3. The method of claim 1, wherein the laminar cooling adopts a front-section sparse cooling combined with U-shaped cooling mode, wherein the head and the tail of the strip steel adopt weak cooling within the range of 30-50 m, and the weak cooling temperature is 20-50 ℃.
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| CN114618883B (en) * | 2020-12-10 | 2023-10-10 | 上海梅山钢铁股份有限公司 | Method for improving uniformity of mechanical properties of microalloy high-strength steel hot rolled steel plate |
| CN114054515B (en) * | 2021-06-18 | 2024-02-27 | 德龙钢铁有限公司 | Method for controlling scale of cold rolling base stock after rolling |
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