CN112626421A - 650 MPa-grade steel for automobile wheels and preparation method thereof - Google Patents
650 MPa-grade steel for automobile wheels and preparation method thereof Download PDFInfo
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- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
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- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
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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
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- 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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- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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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
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- C21D2211/005—Ferrite
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Abstract
The invention provides 650MPa grade steel for automobile wheels, which comprises the following components: 0.05-0.12 wt% of C, 1.00-2.00 wt% of Mn, 0.05-0.30 wt% of Si, 0.04-0.07 wt% of Nb, 0.02-0.05 wt% of Ti, 0.01-0.06 wt% of Als, less than or equal to 0.020 wt% of P, less than or equal to 0.010 wt% of S, and the balance of Fe. The application also provides a preparation method of the 650 MPa-grade steel for the automobile wheels. The 650 MPa-grade steel for the automobile wheels is Nb microalloying, the strength and the toughness are improved through fine grain strengthening and precipitation strengthening, and the number and the size of precipitates of Nb are stable, so that the mechanical property stability is good; meanwhile, the metallographic structure of the steel plate is ultrafine ferrite and trace pearlite and contains fine dispersed precipitated phases, and the type structure has the characteristics of good forming and welding performance.
Description
Technical Field
The invention relates to hot continuous rolled steel for automobile wheels, in particular to 650 MPa-grade automobile wheel steel and a preparation method thereof.
Background
Under the conditions that the automobile yield and the holding capacity are continuously increased, the automobile energy consumption and the harmful gas emission are gradually increased, the reduction of the automobile self-mass is the most effective measure for energy conservation and environmental protection. The foreign relevant experimental data show that the mass of the vehicle is reduced by 10 percent, namely the oil consumption is reduced by 5 to 8 percent. Therefore, on the premise of ensuring the overall strength and the use reliability of the automobile, the high strength and the light weight of the automobile body are one of important ways for achieving energy conservation and emission reduction.
In order to adapt to the development trend of light weight of automobiles, the novel high-strength steel plate for wheels has the performance characteristics of high strength and toughness, excellent energy absorption and good formability. The research and development hotspots of the steel plate for the high-strength wheel at present comprise: microalloyed dual phase steel, low alloy high strength steel, and the like. The microstructure of the dual-phase steel is ferrite and martensite, and the dual-phase steel has the performance characteristics of low yield strength, higher initial work hardening rate, poorer stretch flangeability and easy occurrence of the problem of softening of a heat affected zone in the welding process. The low-alloy high-strength steel is mainly prepared by Nb and Ti microalloying or Nb and V microalloying, the microstructure is ferrite and a small amount of pearlite or trace pearlite, and the steel is strengthened and toughened by forming ferrite with fine grains and nano-scale precipitates which are dispersed. The low-alloy high-strength steel has stable mechanical property, good formability and weldability. At present, research and development hot spots of the steel plate for the hot-rolled high-strength wheel are concentrated on the following advanced high-strength steels: microalloyed dual phase steels (FMDP and FBDP steels), low alloy high strength steels (HSLA steels), and the like.
According to research, alloy elements such as Ti, Cr and the like are added into 590-780 MPa class automobile chassis steel plates of Nippon Sumitomo company. In high elongation hot rolled steel of 590 to 780MPa class by NKK corporation, alloying elements such as Ti and Mo are added. The India Tata Steel works produced 600MPa grade ferritic and bainitic steels using low C, high Mn and 0.04% Nb chemistries. The steel types are mostly microalloyed dual phase steels (FMDP steel and FBDP steel), and the dual phase steel, particularly FMDP steel, has poor welding process matching and is easy to generate the phenomenon of softening of a heat affected zone. Low alloy high strength steels (HSLA steels) are good at circumventing this drawback.
By search, CN103031493B discloses a 650 MPa-grade low-Si Cr-containing hot-rolled dual-phase steel plate and a manufacturing method thereof, and the chemical components are as follows: 0.06-0.15% of C, 1.0-1.8% of Mn and 0.3-1.5% of Cr, wherein the finished steel is ferrite and martensite dual-phase steel with the thickness of 3-10 mm. CN105950984B discloses a hot-rolled complex phase steel with 650 MPa-level tensile strength and a production method thereof, and the hot-rolled complex phase steel comprises the following chemical components: 0.06-0.10% of C, 0.90-1.3% of Mn and 0.01-0.03% of Nb, wherein the finished steel is complex phase steel containing bainite, martensite and a certain amount of ferrite. The steel of the invention is dual-phase steel or complex-phase steel, and has the defects of complex production process and difficult control of microstructure. CN104981551B discloses a high strength hot rolled steel strip or sheet with excellent formability and fatigue property and a method for producing the same, which adopts a composition of Nb and V in combination, adopts a single phase ferrite microstructure, strengthens ferrite with carbonitride containing Nb and V, and has the disadvantage of difficult process control because N is easy to form inclusion in steel and affects the surface quality of steel billet in order to ensure the precipitation effect of V, and the content of N in steel is controlled to be high.
Disclosure of Invention
The invention aims to provide 650MPa grade steel for automobile wheels, which has good mechanical property stability and good forming and welding properties.
In view of the above, the present application provides a 650MPa grade steel for automobile wheels, comprising:
preferably, the content of C is 0.06-0.10 wt%, and the content of Mn is 1.20-1.80 wt%.
Preferably, the content of Si is 0.14 to 0.18 wt%.
Preferably, the content of Ti is 0.03-0.04 wt%, and the content of Als is 0.035-0.045 wt%.
The application also provides a preparation method of the 650 MPa-grade steel for the automobile wheels, which comprises the following steps:
A) pre-desulfurizing molten steel smelted by a blast furnace;
B) sequentially carrying out converter smelting, LF refining and continuous casting on the molten iron obtained in the step A) to obtain a casting blank;
C) and heating the casting blank, pressing, rolling, and finally performing laminar cooling to obtain 650 MPa-grade automobile wheel steel.
Preferably, in the smelting process of the converter, aluminum iron is adopted for deoxidation, and active lime is adopted for desulfurization; and in the LF refining process, white slag is adopted for desulfurization.
Preferably, in the continuous casting process, a dynamic light pressing mode is adopted, the pressing amount is more than or equal to 3mm, the secondary cooling water adopts a weak cooling mode, the casting superheat degree is 15-40 ℃, and the drawing speed is 0.8-1.2 m/min.
Preferably, in the step C), the heating temperature is 1100-1300 ℃ and the time is 180-400 min.
Preferably, the side pressure of the side pressure is less than or equal to 160 mm; the rough rolling is performed for 5-10 times, and the deformation of each time is more than or equal to 18%; the finish rolling is performed for 5-10 passes, the initial rolling temperature is 1000-1100 ℃, and the final rolling temperature is 800-900 ℃.
Preferably, the laminar cooling adopts a front-stage cooling mode, and the steel plate is cooled to 580-640 ℃ at a cooling speed of 10-30 ℃/s.
The application provides a 650MPa level automobile wheel steel, it includes: 0.05-0.12 wt% of C, 1.00-2.00 wt% of Mn, 0.05-0.30 wt% of Si, 0.04-0.07 wt% of Nb, 0.02-0.05 wt% of Ti, 0.01-0.06 wt% of Als, less than or equal to 0.020 wt% of P, less than or equal to 0.010 wt% of S, and the balance of Fe. The element C can form precipitates with microalloy elements such as Nb and Ti, and has a precipitation strengthening effect; mn has the functions of solid solution strengthening and plasticity improvement; the main functions of Nb in the steel are grain refinement and precipitation strengthening, Nb (CN) precipitates formed in the hot rolling stage can strongly nail-roll grain boundaries and inhibit the grains from growing, so that the grains of the finished steel are refined, and the nano-size and dispersion-distributed Nb (CN) precipitates formed in the coiling stage can effectively improve the strength; meanwhile, the stability of the Nb (CN) precipitate is good, so that the stability of the mechanical property of the steel is good. Therefore, the 650 MPa-grade steel for automobile wheels with stable mechanical properties can be obtained by controlling the elements.
Further, the application also provides 650 MPa-grade steel for automobile wheels, which comprises the steps of pre-desulfurization, converter smelting, LF refining, continuous casting, side pressing, rolling, laminar cooling and the like, wherein in the preparation process, the smelting processes of pre-desulfurization, vacuum degassing and the like are adopted, impurities are included and central segregation is strictly controlled, the subsequent side pressing, rolling and laminar cooling processes are further carried out, and Nb and Ti systems are adopted to obtain ultrafine ferrite and trace pearlite structures, so that the steel has good formability and weldability, which are difficult to achieve by martensite dual-phase steel with the same strength grade.
Drawings
FIG. 1 is a metallographic structure photograph of a steel for an automobile wheel of grade 650MPa prepared in example 1 of the present invention;
FIG. 2 is a metallographic structure photograph of a steel for an automobile wheel of grade 650MPa prepared in example 2 of the present invention;
FIG. 3 is a metallographic structure photograph of a steel for an automobile wheel of grade 650MPa according to comparative example 1 of the present invention;
FIG. 4 is a metallographic structure photograph of a steel for an automobile wheel of grade 650MPa according to comparative example 2 of the present invention.
Detailed Description
For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention by way of example, and it is to be understood that the description is intended to further illustrate features and advantages of the invention, and not to limit the scope of the claims.
In view of the requirements of 650 MPa-grade steel for automobile wheels on high strength, light weight and molding, and in order to comprehensively consider the process control difficulty and the high requirements of finished steel forming and welding performance, the application designs a low-carbon, high-manganese and niobium-titanium microalloying component route, improves the welding performance and flange performance by reducing the carbon content, refines ferrite grains by niobium microalloying, and obtains a finished structure of ultrafine ferrite, trace pearlite and precipitated phase, wherein the mechanical properties of the 650 MPA-grade steel for automobile wheels meet the following requirements: the yield strength is more than or equal to 500MPa, the tensile strength is more than or equal to 650MPa, the elongation is more than or equal to 20 percent, d is qualified after 180-degree cold bending test, and the inclusion is less than or equal to 1.5 grade. Specifically, the application firstly provides 650 MPa-grade automobile wheel steel, which comprises the following components:
in the invention, the main function of C is to form precipitates with Nb, Ti and the like, the invention adopts the metallographic structure of ultrafine ferrite and trace pearlite, the content of C is not too high, otherwise the core structure of the steel plate is easy to be abnormal, so the content of C is controlled to be 0.05-0.12 percent, and in the specific embodiment, the content of C is 0.06-0.10 percent by weight.
The main role of Mn is solid solution strengthening and plasticity improvement, but the higher Mn content may cause segregation of the core component of the steel sheet, resulting in the formation of ferrite band-shaped structure, so the Mn content is controlled to 1.0-2.0 wt%, and in the specific embodiment, the Mn content is 1.20-1.80 wt%.
The main functions of Nb in the steel are grain refinement and precipitation strengthening, Nb (CN) precipitates formed in the hot rolling stage can strongly pin-roll grain boundaries and inhibit the grain growth, so that the grains of the finished steel are refined, and the nano-size and dispersion-distributed Nb (CN) precipitates formed in the coiling stage can effectively improve the strength. Meanwhile, the stability of the Nb (CN) precipitate is good, so that the mechanical property stability of the finished steel is good. The content of Nb is controlled to be 0.04-0.07%; in a specific embodiment, the content of Nb is 0.050 to 0.055 wt%.
The main functions of Ti in steel are austenite grain refinement, welding performance improvement and precipitation strengthening, TiN precipitates formed in the heating process of a casting blank can nail a grain boundary and inhibit austenite coarsening, and similarly, the TiN precipitates formed in the welding process can inhibit the structure coarsening of a heat affected zone and improve the welding performance. Meanwhile, the strength of the nanometer-level Ti (CN) precipitate formed in the coiling stage can be effectively improved, so that the content of Ti is controlled to be 0.020-0.050%; in a specific embodiment, the content of Ti is 0.030-0.040 wt%.
The main functions of Al in steel are deoxidation and grain refinement, and an AlN precipitated phase formed by Al and N can refine original austenite grains, so that the content of Als is controlled to be 0.010-0.060%; in a specific embodiment, the content of the Als is 0.035-0.045 wt%.
In addition, Si element is related to the plasticity of steel, P element is related to grain boundary segregation, S element is related to inclusion, particularly sulfide inclusion, and the forming crack of wheel steel is easily caused when the S content is higher and the A type inclusion is higher, so that the S content is controlled to be less than or equal to 0.010%.
If the content of P is higher, grain boundary segregation is easily caused, and if the content of S is higher, the level of inclusions exceeds the standard, the plasticity and the formability of the steel are easily reduced, so that the content of P is controlled to be less than or equal to 0.010 percent.
The invention also provides a preparation method of the 650MPa grade steel for automobile wheels, which comprises the following steps:
A) pre-desulfurizing molten steel smelted by a blast furnace;
B) sequentially carrying out converter smelting and LF refining continuous casting on the molten iron obtained in the step A) to obtain a casting blank;
C) and heating the casting blank, pressing, rolling, and finally performing laminar cooling to obtain 650 MPa-grade automobile wheel steel.
The application firstly describes the smelting method of 650MPa grade steel for automobile wheels in detail:
in the smelting process, firstly, molten iron pre-desulfurization is carried out, and specifically, the method comprises the following steps: the molten iron obtained by blast furnace smelting is pre-desulfurized to control the S content and reduce the grade of A-type inclusions, so that the wheel steel is prevented from forming and cracking due to the high-level inclusions, and the S content is controlled to be less than or equal to 0.005 percent.
According to the invention, the pre-desulfurized molten iron is smelted in a converter, which specifically comprises the following steps: the pre-desulfurized molten iron is put into a converter for smelting, aluminum and iron are adopted for deoxidation in the smelting process of the converter, and meanwhile Al and trace N elements (below 50 ppm) remained in the steel are polymerized into a nano AlN precipitated phase, so that a good nail rolling effect can be achieved on a crystal boundary, and the grain size of finished steel is reduced. In addition, it is also important not to introduce C element in the alloying process, because the steel grade of the invention has high strength grade, and the toughness and the formability of the steel grade are difficult to control due to the contradiction between the strength and the toughness, therefore, the C content must be reduced to avoid forming a carbon-rich phase structure with poor toughness.
In the continuous casting stage, low-superheat-degree casting is adopted, dynamic soft reduction is required, the casting superheat degree is controlled to be 15-40 ℃, and the soft reduction amount is controlled to be more than or equal to 3 mm; because the steel for the automobile wheel is microalloyed steel and alloy elements such as Nb, Ti and the like are added, the process means is adopted to prevent the segregation of the components of a casting blank and avoid influencing the forming performance in the subsequent use process.
The smelting process aims at the high requirement of the wheel steel on the forming performance, and provides a component target with low sulfur content and an inclusion deformation means; the control requirement of N is provided for the Ti microalloyed high-strength wheel steel so as to avoid the formation of liquated titanium nitride and avoid the problems of poor performance and forming cracking; a related continuous casting process is established for the problem that the wheel steel has high alloy content and possibly has composition segregation.
The steel for the 650 MPa-grade automobile wheel is obtained by processing the plate blank obtained by smelting, and specifically comprises the following steps: reheating the plate blank in a heat accumulating type heating furnace, wherein the heating temperature is 1100-1300 ℃, the heating time is 180-400 min, the side pressing is carried out on the steel blank through a fixed width press after the steel blank is taken out of the furnace, then 5-10 times of rough rolling and 5-10 times of finish rolling are carried out, the initial rolling temperature is 1000-1100 ℃, the final rolling temperature is 800-900 ℃, and the laminar cooling is carried out after the rolling.
The reheating is to ensure that the alloy elements are fully dissolved in the solid solution, and relieve the center segregation and the dendritic segregation of the billet in the casting process. When the tapping temperature is low and the furnace time is short, alloy elements cannot be fully dissolved in a solid manner, segregation in a billet cannot be completely eliminated, and the excessive load is easily caused during subsequent rolling; when the tapping temperature is higher and the time in the furnace is longer, the original austenite grains of the billet are easy to be coarse, so that the original austenite grains are inherited into finished steel, and the final structure is coarse. In a specific embodiment, the reheating temperature is 1190-1240 ℃.
In the process of side pressing, the adaptability of a hot continuous rolling production line to the section specification of a billet can be improved by adopting a fixed width press to carry out the side pressing, but when the side pressing amount of a slab is too large, the edge of the slab in the width direction is easy to bulge, the deformation of the subsequent rough-rolled edge is low, and the texture of the slab in the width direction is thick and even mixed crystals are caused. The purpose of rough rolling is to refine grains through austenite dynamic recrystallization, and the deformation of a single pass of rough rolling must be larger than the critical deformation, otherwise, the central deformation of the steel plate is insufficient, and the grains are promoted to grow to form a mixed crystal structure. Therefore, the side pressure of the plate blank is limited to be less than or equal to 160mm, and the deformation of the rough rolling pass is limited to be more than or equal to 18%. When the thickness of the rough-rolled plate blank is low, the accumulated deformation of finish rolling is low, and the final structure is not refined favorably, so that the thickness of the rough-rolled plate blank is controlled to be 35-55 mm.
And (3) rolling the rough rolled fine rolling for 5-10 times, wherein the rolling start temperature of the fine rolling is controlled to be 1040-1100 ℃, and the rolling finish temperature is controlled to be 830-880 ℃. The finish rolling is to promote austenite flattening through rolling in a non-recrystallization region, form a dispersed and fine Nb (CN) precipitated phase through deformation induced precipitation energy, effectively nail-roll austenite grain boundaries, promote austenite grain refinement, provide a nucleation core for subsequent ferrite phase transformation and promote finished ferrite structure refinement. When the finish rolling initial rolling temperature is lower, the rolling load is too heavy when the thin gauge steel is rolled, and when the finish rolling initial rolling temperature is higher, the thin gauge steel enters an incomplete recrystallization region to generate a mixed crystal structure, so that the finish rolling initial rolling temperature is controlled to be 1000-1100 ℃. When the finish rolling temperature is low, the austenite and ferrite two-phase region enters after finish rolling to generate a mixed crystal structure, and when the finish rolling temperature is high, the austenite structure after finish rolling is coarse, so that the finish rolling temperature is limited to 830-880 ℃.
And further, carrying out laminar cooling after rolling, wherein when the thickness of the steel type finished product is 2-8 mm, the cooling strength can be improved by adopting front-section cooling, so that the surface and the core of the steel plate are fully cooled, and the steel plate is deformed into fine ferrite grains under a larger supercooling degree, thereby improving the strength and the toughness of the finished steel. The laminar cooling speed and the final cooling temperature both influence the phase change process; when the cooling rate is relatively low or the final cooling temperature is relatively high, coarse pro-eutectoid ferrite is likely to be formed, and a large-sized pearlite structure, even grain boundary cementite, is likely to form an abnormal structure such as martensite when the cooling rate is relatively high or the final cooling temperature is relatively low. The above-mentioned abnormal structures all affect the mechanical properties and formability of the finished steel. Therefore, the laminar cooling speed is controlled to be 10-30 ℃/s, and the final cooling temperature is controlled to be 580-640 ℃.
The strength and the toughness are contradictory, the 650MPa wheel steel has higher strength level, and the problem of toughness matching is a great technical difficulty, so the method adopts the idea of rolling at low temperature and high pressure, and clearly specifies the rolling reduction, the thickness of an intermediate billet, the rolling temperature and the like so as to obtain fine and uniform metallographic structures, thereby obtaining the toughness matching on the performance. Meanwhile, 650MPa grade high strength wheel steel has high requirements on forming performance, and the forming performance can be obviously reduced by grain boundary cementite, banded structure and the like which may appear in a metallographic structure. Therefore, the present application clearly defines the laminar cooling method, the cooling rate, the final cooling temperature, and the like, in view of the high sensitivity of the steel grade to the laminar cooling process.
The preparation method has good process stability, and the steel produced by the preparation method has good mechanical property stability; the 650 MPa-grade steel for the automobile wheels is low-alloy high-strength steel, adopts a Nb and Ti component system and combines a controlled rolling and controlled cooling process, can obtain an ultrafine ferrite and trace pearlite structure, has good formability and weldability, is difficult to achieve by martensite dual-phase steel of the same strength grade, and meets high requirements of the high-strength steel for the automobile wheels on formability and flange hole expansibility by strictly controlling inclusion, particularly sulfide inclusion. The preparation method is simple, has strong technological adaptability, and is suitable for common hot continuous rolling production lines and continuous casting and rolling production lines.
For further understanding of the present invention, the steel for 650MPa grade automobile wheels and the preparation method thereof provided by the present invention are described in detail below with reference to the following examples, and the scope of the present invention is not limited by the following examples.
Example 1
(1) Pre-desulfurization of molten iron: pre-desulfurizing molten iron obtained by blast furnace smelting, and controlling the S content to be 0.003 wt%;
(2) smelting in a converter: smelting the pre-desulfurized molten iron in a converter, wherein the weight of the loaded molten iron is 180-250 t, 300kg of aluminum iron is deoxidized, manganese is added into the molten iron, and 800-1200 kg of active lime is used for desulfurization;
(3) LF refining: performing LF refining on the molten steel smelted by the converter, and desulfurizing by using white slag, wherein the S content is controlled to be less than or equal to 0.005 wt%, and the desulfurizing time is 41 min;
(4) continuous casting: transferring the molten steel refined by LF into a tundish for casting, producing into a casting blank through a crystallizer, putting the casting blank under dynamic soft reduction, controlling the reduction amount to be more than or equal to 3mm, controlling the superheat degree of casting to be 26 ℃ and controlling the slab pulling speed to be 1.0m/min by using secondary cooling water in a weak cooling mode, and obtaining a steel blank with the thickness of 200-230 mm;
(5) reheating the obtained plate blank at 1247 deg.C for 254 min; the rough rolling adopts 6-pass rolling, the pass reduction is 18%, 20%, 20%, 31%, 30% and 29%, the thickness of the plate blank after the rough rolling is 41mm, the finish rolling is 7-stand hot continuous rolling, the pass reduction is 43%, 39%, 30%, 23%, 20%, 15% and 12%, the initial rolling temperature is 1045 ℃, the final rolling temperature is 855 ℃, and after the finish rolling is finished, the plate blank is cooled to 593 ℃ at the cooling speed of 25 ℃/s by adopting a front-section cooling mode to obtain the 650MPa steel for the automobile wheel.
Through detection, the mechanical properties of the 650MPa grade steel for automobile wheels produced by the embodiment are as follows: the yield strength is 585MPa, the tensile strength is 658MPa, the elongation is 24.0 percent, and the cold bending test at 180 degrees is qualified when the d is equal to the a. The metallographic structure is ferrite plus trace pearlite (see figure 1), and the grain size is grade 13.
Example 2
(1) Pre-desulfurization of molten iron: pre-desulfurizing molten iron obtained by blast furnace smelting, and controlling the S content to be 0.003 wt%;
(2) smelting in a converter: smelting the pre-desulfurized molten iron in a converter, wherein the weight of the loaded molten iron is 180-250 t, 290kg of aluminum iron is deoxidized, manganese is added into the molten iron, and 800-1200 kg of active lime is used for desulfurization;
(3) LF refining: performing LF refining on the molten steel smelted by the converter, and desulfurizing by using white slag, wherein the S content is controlled to be less than or equal to 0.003 wt%, and the desulfurizing is performed for 36 min;
(4) continuous casting: transferring the molten steel refined by LF into a tundish for casting, producing into a casting blank through a crystallizer, putting the casting blank under dynamic soft reduction, controlling the reduction amount to be more than or equal to 3mm, controlling the superheat degree of casting to be 24 ℃ and controlling the slab pulling speed to be 1.0m/min by using secondary cooling water in a weak cooling mode, and obtaining a steel blank with the thickness of 200-230 mm;
(5) reheating the obtained plate blank at 1236 ℃ for 265 min; the rough rolling adopts 5-pass rolling, the thickness of the plate blank after the rough rolling is 43mm, and the deformation of each pass of the rough rolling is 22%, 29%, 29%, 32% and 30%; the finish rolling is 7-frame hot continuous rolling, and the deformation of each pass of the finish rolling is 42%, 39%, 30%, 23%, 20%, 15% and 11%; the initial rolling temperature is 1051 ℃, the final rolling temperature is 869 ℃, after finishing rolling, laminar cooling adopts front-section cooling, and the steel is cooled to 587 ℃ at the cooling speed of 28 ℃/s, so as to obtain 650MPa steel for automobile wheels.
Through detection, the mechanical properties of the 650MPa steel for automobile wheels produced by the embodiment are as follows: the yield strength is 592MPa, the tensile strength is 658MPa, the elongation is 24.5 percent, and the cold bending test at 180 degrees is qualified when the d is a. The metallographic structure is ferrite plus trace pearlite (see figure 2), and the grain size is grade 13.
Example 3
(1) Pre-desulfurization of molten iron: pre-desulfurizing molten iron obtained by blast furnace smelting, and controlling the S content to be 0.002 wt%;
(2) smelting in a converter: smelting the pre-desulfurized molten iron in a converter, wherein the weight of the loaded molten iron is 180-250 t, 285kg of aluminum iron is deoxidized, manganese is added into metal manganese, and 800-1200 kg of active lime is used for desulfurization;
(3) LF refining: performing LF refining on the molten steel smelted by the converter, and desulfurizing by using white slag, wherein the S content is controlled to be less than or equal to 0.003 wt%, and the desulfurizing time is 35 min;
(4) continuous casting: transferring the molten steel refined by LF into a tundish for casting, producing into a casting blank through a crystallizer, putting the casting blank under dynamic soft reduction, controlling the reduction amount to be more than or equal to 3mm, controlling the superheat degree of casting to be 27 ℃ and controlling the slab pulling speed to be 1.05m/min by using secondary cooling water in a weak cooling mode, and obtaining a steel blank with the thickness of 200-230 mm;
(5) reheating the obtained plate blank at 1247 deg.C for 254 min; the rough rolling adopts 6-pass rolling, the pass reduction is 18%, 20%, 20%, 31%, 30% and 29%, the thickness of the plate blank after the rough rolling is 41mm, the finish rolling is 7-stand hot continuous rolling, the pass reduction is 43%, 39%, 30%, 23%, 20%, 15% and 12%, the initial rolling temperature is 1045 ℃, the final rolling temperature is 855 ℃, and after the finish rolling is finished, the plate blank is cooled to 593 ℃ at the cooling speed of 25 ℃/s by adopting a front-section cooling mode to obtain the 650MPa steel for the automobile wheel.
Through detection, the mechanical properties of the 650MPa grade steel for automobile wheels produced by the embodiment are as follows: the yield strength is 602MPa, the tensile strength is 703MPa, the elongation is 23.5 percent, and the cold bending test at 180 degrees proves that d is qualified as a. The metallographic structure is ferrite plus trace pearlite, and the grain size is grade 13.
Comparative example 1
(1) Pre-desulfurization of molten iron: pre-desulfurizing molten iron obtained by blast furnace smelting, wherein the S content is controlled to be 0.020 wt%;
(2) smelting in a converter: smelting the pre-desulfurized molten iron in a converter, wherein the weight of the loaded molten iron is 180-250 t, 310kg of aluminum iron is deoxidized, medium-carbon ferromanganese is used for matching manganese, and 800-1200 kg of active lime is used for desulfurization;
(3) LF refining: performing LF refining on the molten steel smelted by the converter, and desulfurizing by using white slag, wherein the S content is controlled to be less than or equal to 0.020 wt%, and the desulfurizing is performed for 11 min;
(4) continuous casting: transferring the molten steel refined by LF into a tundish for casting, producing into a casting blank through a crystallizer, putting the casting blank under dynamic soft reduction, controlling the reduction amount to be more than or equal to 3mm, controlling the superheat degree of casting to be 35 ℃ and controlling the slab pulling speed to be 0.9m/min by using secondary cooling water in a weak cooling mode, and obtaining a steel slab with the thickness of 200-230 mm;
(5) reheating the obtained plate blank at 1231 deg.C for 201 min; the rough rolling adopts 6-pass rolling, the pass reduction is 20%, 21%, 22%, 28%, 28% and 27%, the thickness of the plate blank after the rough rolling is 42mm, the finish rolling is 7-stand hot continuous rolling, the pass reduction is 43%, 37%, 32%, 24%, 21%, 14% and 12%, the start rolling temperature of the finish rolling is 1064 ℃, the finish rolling temperature is 870 ℃, and after the finish rolling is finished, the plate blank is cooled to 614 ℃ at the cooling speed of 16 ℃/s by adopting a sparse cooling mode to obtain the 650MPa automobile wheel steel.
Through detection, the mechanical properties of the 650MPa grade steel for automobile wheels produced by the comparative example are as follows: the yield strength is 599MPa, the tensile strength is 667MPa, the elongation is 19.5 percent, and the cold bending test d at 180 degrees is unqualified. The metallographic structure is ferrite plus pearlite, the pearlite grows up abnormally, and the grain size is grade 12.
The 650MPa grade steel for automobile wheels produced by the comparative example has unqualified elongation and cold bending property, and has unqualified structure, and forms abnormally long pearlite (shown in figure 3). The reason for the formation is that laminar cooling adopts a sparse cooling mode, and the cooling intensity is low.
Comparative example 2
(1) Pre-desulfurization of molten iron: pre-desulfurizing molten iron obtained by blast furnace smelting, and controlling the S content to be 0.003 wt%;
(2) smelting in a converter: smelting the pre-desulfurized molten iron in a converter, wherein the weight of the loaded molten iron is 180-250 t, 302kg of aluminum iron is deoxidized, manganese is added into the molten iron, and 800-1200 kg of active lime is used for desulfurization;
(3) LF refining: performing LF refining on the molten steel smelted by the converter, and desulfurizing by using white slag, wherein the S content is controlled to be less than or equal to 0.005 wt%, and the desulfurization is carried out for 26 min;
(4) continuous casting: transferring the molten steel refined by LF into a tundish for casting, producing into a casting blank through a crystallizer, putting the casting blank under dynamic soft reduction, controlling the reduction amount to be more than or equal to 3mm, controlling the superheat degree of casting to be 31 ℃ and controlling the slab pulling speed to be 1.1m/min by using secondary cooling water in a weak cooling mode, and obtaining a steel slab with the thickness of 200-230 mm;
(5) reheating the obtained plate blank at 1242 deg.C for 202 min; the rough rolling adopts 6-pass rolling, the pass reduction is 20%, 21%, 22%, 28%, 28% and 27%, the thickness of the plate blank after the rough rolling is 42mm, the finish rolling is 7-frame hot continuous rolling, the pass reduction is 43%, 37%, 32%, 23%, 20%, 13% and 12%, the initial rolling temperature is 1056 ℃, the finish rolling temperature is 865 ℃, after the finish rolling, laminar cooling adopts front-section cooling, and cooling is 645 ℃ at the cooling speed of 11 ℃/s, so that the 650MPa steel for the automobile wheel is obtained.
Through detection, the mechanical properties of the 650MPa steel for automobile wheels produced by the embodiment are as follows: the yield strength is 597MPa, the tensile strength is 663MPa, the elongation is 18.5 percent, and the cold bending test at 180 degrees fails when d is a. The metallographic structure is ferrite plus pearlite, but grain boundary cementite (see figure 4) with the proportion of 4-5% exists, and the grain size is 12 grades.
The 650MPa grade steel for automobile wheels produced by the comparative example has unqualified performance and structure because of the formation of abnormal structure of grain boundary cementite, and the formation reason is that cementite is precipitated and grown in austenite grain boundary because of higher final cooling temperature and higher phase transition temperature.
The compositions of the 650MPa grade steel for automobile wheels of the above examples and comparative examples are specifically shown in Table 1:
TABLE 1 ingredient data table of 650MPa grade steel for automobile wheels provided in examples and comparative examples
The inclusion grades of the 650MPa grade automotive spoke steels of the above examples and comparative examples are specifically shown in Table 2:
TABLE 2 Inclusion grade data Table for 650MPa grade automotive spoke steels prepared in examples and comparative examples
The above description of the embodiments is only intended to facilitate the understanding of the method of the invention and its core idea. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (10)
1. A650 MPa-grade steel for automobile wheels comprises:
P≤0.020wt％；
S≤0.010wt％；
the balance being Fe.
2. The steel for 650 MPa-grade automobile wheels according to claim 1, wherein the C content is 0.06-0.10 wt%, and the Mn content is 1.20-1.80 wt%.
3. The steel for 650 MPa-grade automobile wheels according to claim 1, wherein the Si content is 0.14 to 0.18 wt%.
4. The steel for 650 MPa-grade automobile wheels according to claim 1, wherein the Ti content is 0.03-0.04 wt%, and the Als content is 0.035-0.045 wt%.
5. The preparation method of the steel for 650 MPa-grade automobile wheels, which is disclosed by claim 1, comprises the following steps:
A) pre-desulfurizing molten steel smelted by a blast furnace;
B) sequentially carrying out converter smelting, LF refining and continuous casting on the molten iron obtained in the step A) to obtain a casting blank;
C) and heating the casting blank, pressing, rolling, and finally performing laminar cooling to obtain 650 MPa-grade automobile wheel steel.
6. The preparation method according to claim 5, wherein in the converter smelting process, aluminum iron is used for deoxidation, and active lime is used for desulfurization; and in the LF refining process, white slag is adopted for desulfurization.
7. The preparation method according to claim 5, wherein in the continuous casting process, a dynamic light pressing mode is adopted, the pressing amount is not less than 3mm, the secondary cooling water is in a weak cooling mode, the casting superheat degree is 15-40 ℃, and the drawing speed is 0.8-1.2 m/min.
8. The method according to claim 5, wherein the heating is carried out at 1100 to 1300 ℃ for 180 to 400min in step C).
9. The production method according to claim 5, wherein a side pressure amount of the side pressure is 160mm or less; the rough rolling is performed for 5-10 times, and the deformation of each time is more than or equal to 18%; the finish rolling is performed for 5-10 passes, the initial rolling temperature is 1000-1100 ℃, and the final rolling temperature is 800-900 ℃.
10. The method according to claim 5, wherein the laminar cooling is performed by a front-end cooling method, and the steel plate is cooled to 580-640 ℃ at a cooling rate of 10-30 ℃/s.
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