A hot-rolled steel for automobile wheels having a tensile strength greater than 490 MPa and a thickness of 3-6 mm and a method for producing the same

Abstract

The application discloses a hot-rolled automobile wheel steel with tensile strength greater than 490 MPa and thickness of 3-6 mm and a production method thereof, wherein the chemical components of the hot-rolled automobile wheel steel are as follows in percentage by mass: C: 0.06-0.08%, Si: 0.03-0.10%, Mn: 0.85-1.00%, P: less than or equal to 0.018%, S: less than or equal to 0.005%, Alt: 0.020-0.045%, Nb: 0.030-0.045%, Ti: 0.015-0.025%, Ca: 0.0010-0.0030%, and the rest is Fe and inevitable inclusions. The hot-rolled automobile wheel steel with thickness of 3-6 mm has the advantages of high strength, high toughness, high forming precision and the like, can realize reduction of the self weight and energy consumption of a vehicle, and meets the demand of the automobile wheel steel very well.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical plate production technology, specifically relating to a hot-rolled automotive wheel steel with a tensile strength greater than 490MPa and a thickness of 3-6mm and its production method. Background Technology

[0002] With the rapid development of my country's automotive industry, automobile wheels, as one of the main components of a car, not only require sturdiness, durability, and aesthetic appeal, but also increasingly adopt lightweight and complex designs for energy conservation and emission reduction. This leads to more complex wheel designs, demanding that wheel steel possess excellent formability to meet the requirements of complex deformation during stamping. Under the dual pressures of rapid economic development, resource shortages, energy crises, and environmental protection, the development demands for automobiles are safety, energy efficiency, environmental friendliness, comfort, and low cost. Data shows that lightweighting is the most important way to reduce fuel consumption and carbon dioxide emissions. Analysis indicates that a 10% reduction in vehicle weight can save 3-7% on fuel, and the energy-saving effect of using high-strength steel to reduce the weight of automobile wheels, as a running gear, is equivalent to 1.2-1.3 times that of other components. Driven by this trend towards lightweighting, wheel steel will inevitably develop towards higher strength.

[0003] For example, patent document CN 101812637 A (hereinafter referred to as Document 1) discloses a high-strength, high-toughness automotive wheel steel and its production method. However, this document does not mention the specific key process parameters such as the continuous casting superheat and the cooling rate after finishing rolling, as well as the microstructure of the product. Patent document CN 113981319 A (hereinafter referred to as Document 2) discloses a low-alloy, high-strength automotive wheel steel with the following chemical composition: C: 0.15–0.20%, Si: 0.20–0.30%, Mn: 0.35–0.50%, Ti: 0.030–0.050%, Als: 0.015–0.050%, P≤0.025%, S≤0.010%. The composition design in Document 2 improves strength by increasing C and Si content. While increasing carbon content is beneficial for strength, excessive carbon content leads to the formation of numerous coarse and brittle carbide particles in the steel, which is detrimental to plasticity and toughness. Excessive carbon content also creates segregation zones in the center of the steel plate, negatively impacting bending and formability. Furthermore, excessive carbon content increases the welding carbon equivalent and welding crack sensitivity index, hindering welding. Excessive Si content makes descaling during rolling difficult and also reduces weldability. Patent document CN 114574771A (hereinafter referred to as Document 3) discloses a wheel-specific steel with high elongation flange performance and fatigue resistance, along with its production process. However, Document 3 does not mention key process parameters such as continuous casting superheat, cooling rate after finishing rolling, and cooling mode during production. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a hot-rolled automotive wheel steel with a tensile strength greater than 490MPa and a thickness of 3-6mm, and its production method. The automotive wheel steel mentioned in this invention has advantages such as high strength, high toughness, and high forming precision. By improving the strength of the material and reducing the thickness of the steel plate, the vehicle's weight and energy consumption can be reduced, which perfectly meets the requirements of automotive wheel steel. Moreover, all performance characteristics meet the relevant standard requirements and user needs.

[0005] This invention is specifically achieved through the following technical solutions:

[0006] In one aspect of the present invention, a hot-rolled automotive wheel steel with a tensile strength greater than 490 MPa and a thickness of 3-6 mm is provided, the chemical composition of which, by mass percentage, is: C: 0.06-0.08%, Si: 0.03-0.10%, Mn: 0.85-1.00%, P≤0.018%, S≤0.005%, Alt: 0.020-0.045%, Nb: 0.030-0.045%, Ti: 0.015-0.025%, Ca: 0.0010-0.0030%, with the remainder being Fe and unavoidable inclusions.

[0007] In some embodiments, the chemical composition of the hot-rolled automotive wheel steel, by mass percentage, is: C: 0.062–0.080%, Si: 0.05–0.10%, Mn: 0.85–1.00%, P ≤ 0.018%, S ≤ 0.004%, Alt: 0.025–0.045%, Nb: 0.030–0.044%, Ti: 0.016–0.023%, Ca: 0.0015–0.0026%, with the remainder being Fe and unavoidable inclusions.

[0008] In some embodiments, the chemical composition of the hot-rolled automotive wheel steel, by mass percentage, is: C: 0.070%, Si: 0.05%, Mn: 0.85%, P: 0.018%, S: 0.004%, Alt: 0.045%, Nb: 0.036%, Ti: 0.016%, Ca: 0.0015%, with the remainder being Fe and unavoidable inclusions.

[0009] In some embodiments, the chemical composition of the hot-rolled automotive wheel steel, by mass percentage, is: C: 0.075%, Si: 0.08%, Mn: 0.88%, P: 0.016%, S: 0.003%, Alt: 0.040%, Nb: 0.030%, Ti: 0.020%, Ca: 0.0026%, with the remainder being Fe and unavoidable inclusions.

[0010] In some embodiments, the chemical composition of the hot-rolled automotive wheel steel, by mass percentage, is: C: 0.066%, Si: 0.10%, Mn: 0.90%, P: 0.015%, S: 0.003%, Alt: 0.030%, Nb: 0.042%, Ti: 0.017%, Ca: 0.0018%, with the remainder being Fe and unavoidable inclusions.

[0011] In some embodiments, the chemical composition of the hot-rolled automotive wheel steel, by mass percentage, is: C: 0.062%, Si: 0.06%, Mn: 0.93%, P: 0.017%, S: 0.002%, Alt: 0.035%, Nb: 0.035%, Ti: 0.023%, Ca: 0.0018%, with the remainder being Fe and unavoidable inclusions.

[0012] In some embodiments, the chemical composition of the hot-rolled automotive wheel steel, by mass percentage, is: C: 0.080%, Si: 0.07%, Mn: 1.00%, P: 0.018%, S: 0.002%, Alt: 0.025%, Nb: 0.044%, Ti: 0.022%, Ca: 0.0016%, with the remainder being Fe and unavoidable inclusions.

[0013] In some embodiments, the microstructure of the hot-rolled automotive wheel steel consists of ferrite and a small amount of pearlite, and its mechanical properties meet the following requirements: yield strength 450-480 MPa, tensile strength 512-565 MPa, and elongation 28-32%.

[0014] In another aspect, the present invention also provides a method for producing hot-rolled steel for automobile wheels, comprising the following processes: smelting—continuous casting—slab heating—rolling—cooling—coiling; wherein:

[0015] The smelting-continuous casting process includes: KR desulfurization—converter—LF refining—RH vacuum treatment—slab continuous casting—slow cooling. The composition of the molten steel supplied to the casting machine is C: 0.06~0.08%, Si: 0.03~0.10%, Mn: 0.85~1.00%, P≤0.018%, S≤0.005%, Alt: 0.020~0.045%, Nb: 0.030~0.045%, Ti: 0.015~0.025%, Ca: 0.0010~0.0030%, with the remainder being Fe and unavoidable inclusions. The superheat of the slab continuous casting is controlled at 25-32℃.

[0016] The slab heating process includes feeding the slab, after surface cleaning, into a heating furnace, strictly controlling the slab heating temperature, furnace time, and furnace exit temperature. The heating temperature is controlled at 1200±30℃, the furnace time is controlled at 160~270min, and the furnace exit temperature is controlled at 1200±20℃.

[0017] The rolling process includes a roughing stage and a finishing stage. The roughing stage uses a 3+3 mode two-stand mill for roughing, and the finishing stage uses a 7-stand continuously variable crown (CVC) mill for finishing. The finishing stage uses speed-increasing rolling. The entry thickness of the finishing mill is 40 mm, the starting rolling temperature of the finishing mill is not less than 1030℃, and the finishing rolling temperature is 900±15℃.

[0018] The cooling process employs laminar flow cooling equipment, and the cooling mode is based on the self-learning calculation results of a computer-based secondary system; the cooling rate is controlled at 25-28℃ / s.

[0019] The winding temperature is 580±20℃.

[0020] The above technical solution, through reasonable composition design and optimized production process parameters, provides a hot-rolled automotive wheel steel with a tensile strength greater than 490 MPa and a thickness of 3-6 mm. This steel's microstructure consists of ferrite and a small amount of pearlite, and its mechanical properties meet the following requirements: yield strength 450-480 MPa, tensile strength 512-565 MPa, and elongation 28-32%. This steel possesses comprehensive properties such as high strength and good formability, not only achieving a good match between strength and formability but also exhibiting excellent surface quality. Furthermore, the production method is simple and easy to implement, suitable for industrial mass production, and perfectly meets the needs of lightweight automotive wheel steel. All performance characteristics meet relevant standards and user requirements. Moreover, compared to References 1 and 3, this invention not only specifically describes the control of superheat and cooling rate but also provides a detailed analysis of the product's microstructure. Additionally, compared to Reference 2, this invention uses a low-C, low-Si composition design, avoiding the issues encountered in Reference 2. Attached Figure Description

[0021] Figure 1 Micrograph of hot-rolled automotive wheel steel with a tensile strength greater than 490 MPa and a thickness of 3-6 mm produced in Example 1. Detailed Implementation

[0022] The present invention will be described in detail below through specific embodiments. These embodiments are intended to help understand the present invention and are not intended to limit the scope of the present invention.

[0023] Molten iron undergoes desulfurization pretreatment, followed by decarburization and dephosphorization in a top-and-bottom blown converter to obtain steel. Argon blowing is performed throughout the converter smelting process, with scrap steel added. The converter tapping temperature is 1653℃. The molten steel is then subjected to LF ladle refining at a refining temperature ≥1564℃. Temperature measurement and composition fine-tuning are performed during LF ladle refining. The chemical composition supplied to the casting machine after LF ladle refining is shown in Table 1. The slab superheat is 28℃, followed by slab cleaning, slow cooling, and continuous casting slab quality inspection. The slab heating temperature is 1218℃ for 265 minutes, and the heated slab is then subjected to high-pressure water dephosphorization. Width is determined using a width-fixing press, followed by a 2-stand roughing mill and a 7-stand CVC finishing mill. The finishing mill starting temperature is 1032℃, the finishing mill finishing temperature is 890℃, and the finished product thickness is 3.0mm. Laminar flow cooling employs pre-dispersion cooling at a rate of 28℃ / s, reducing the steel strip temperature to 570℃ before winding. Finally, product performance is tested, as shown in Table 2 below. Figure 1 As shown, a microstructure diagram of the hot-rolled automotive wheel steel obtained in this embodiment is shown, which shows that the microstructure consists of ferrite and a small amount of pearlite.

[0024] Example 2

[0025] Molten iron undergoes desulfurization pretreatment, followed by decarburization and dephosphorization in a top-and-bottom blown converter to obtain steel. Argon blowing is performed throughout the converter smelting process, with scrap steel added. The converter tapping temperature is 1647℃. The molten steel is then subjected to LF ladle refining at a refining temperature ≥1566℃. Temperature measurement and composition fine-tuning are performed during LF ladle refining. The chemical composition supplied to the casting machine after LF ladle refining is shown in Table 1. The slab superheat is 26℃, followed by slab cleaning, slow cooling, and continuous casting slab quality inspection. The slab heating temperature is 1213℃ for 258 minutes, and the heated slab is then subjected to high-pressure water dephosphorization. Width is determined using a width-fixing press, followed by a 2-stand roughing mill and a 7-stand CVC finishing mill. The finishing mill starting temperature is 1030℃, the finishing mill finishing temperature is 900℃, and the finished product thickness is 4.0mm. Laminar flow cooling adopts pre-dispersion cooling with a cooling rate of 26℃ / s. The steel strip temperature is reduced to 583℃ before winding. Finally, product performance is tested, as shown in Table 2 below.

[0026] Example 3

[0027] Molten iron undergoes desulfurization pretreatment, followed by decarburization and dephosphorization in a top-and-bottom blown converter to obtain steel. Argon blowing is performed throughout the converter smelting process, with scrap steel added. The converter tapping temperature is 1641℃. The molten steel is then subjected to LF ladle refining at a refining temperature ≥1562℃. Temperature measurement and composition fine-tuning are performed during LF ladle refining. The chemical composition supplied to the casting machine after LF ladle refining is shown in Table 1. The slab superheat is 32℃, followed by slab cleaning, slow cooling, and continuous casting slab quality inspection. The slab heating temperature is 1215℃ for 263 minutes, and the heated slab is then subjected to high-pressure water dephosphorization. Width is determined using a width-fixing press, followed by a 2-stand roughing mill and a 7-stand CVC finishing mill. The finishing mill starting temperature is 1031℃, the finishing mill ending temperature is 893℃, and the finished product thickness is 5.0mm. Laminar flow cooling adopts pre-dispersion cooling with a cooling rate of 27℃ / s. The steel strip temperature is reduced to 578℃ before winding. Finally, product performance is tested, as shown in Table 2 below.

[0028] Example 4

[0029] Molten iron undergoes desulfurization pretreatment, followed by decarburization and dephosphorization in a top-and-bottom blown converter to obtain steel. Argon blowing is performed throughout the converter smelting process, with scrap steel added. The converter tapping temperature is 1645℃. The molten steel is then subjected to LF ladle refining at a refining temperature ≥1560℃. Temperature measurement and composition fine-tuning are performed during LF ladle refining. The chemical composition supplied to the casting machine after LF ladle refining is shown in Table 1. The slab superheating temperature for continuous casting is 27℃, followed by slab cleaning, slow cooling, and continuous casting slab quality inspection. The slab heating temperature is 1220℃ for 258 minutes, and the heated slab is then subjected to high-pressure water dephosphorization. Width is determined using a width-fixing press, followed by a 2-stand roughing mill and a 7-stand CVC finishing mill. The finishing mill starting temperature is 1036℃, the finishing mill ending temperature is 902℃, and the finished product thickness is 6.0mm. Laminar flow cooling adopts pre-dispersion cooling with a cooling rate of 25℃ / s. The steel strip temperature is reduced to 572℃ before winding. Finally, product performance is tested, as shown in Table 2 below.

[0030] Example 5

[0031] Molten iron undergoes desulfurization pretreatment, followed by decarburization and dephosphorization in a top-and-bottom blown converter to obtain steel. Argon blowing is performed throughout the converter smelting process, with scrap steel added. The converter tapping temperature is 1650℃. The molten steel is then subjected to LF ladle refining at a refining temperature ≥1565℃. Temperature measurement and composition fine-tuning are performed during LF ladle refining. The chemical composition supplied to the casting machine after LF ladle refining is shown in Table 1. The slab superheating is 30℃, followed by slab cleaning, slow cooling, and continuous casting slab quality inspection. The slab heating temperature is 1218℃ for 257 minutes, and the heated slab is then subjected to high-pressure water dephosphorization. Width is determined using a width-fixing press, followed by a 2-stand roughing mill and a 7-stand CVC finishing mill. The finishing mill starting temperature is 1033℃, the finishing mill finishing temperature is 896℃, and the finished product thickness is 7.0mm. Laminar flow cooling adopts pre-dispersion cooling with a cooling rate of 26℃ / s. The steel strip temperature is reduced to 576℃ before winding. Finally, product performance is tested, as shown in Table 2 below.

[0032] Comparative Example 1

[0033] The production method follows that shown in Example 1, except that the chemical composition of the LF ladle refining feeder is different from that used in Example 1, as shown in Table 1 below. Finally, product performance is tested, as shown in Table 2 below.

[0034] Comparative Example 2

[0035] The production method follows that shown in Example 5, except that the chemical composition of the LF ladle refining feeder is different from that used in Example 5, as shown in Table 1 below. Finally, product performance is tested, as shown in Table 2 below.

[0036] Comparative Examples 3-4

[0037] The production methods for Comparative Examples 3 and 4 followed those shown in Example 1, except that the final rolling temperature differed from that in Example 1. Specifically, the final rolling temperature for Comparative Example 3 was 862°C, and the final rolling temperature for Comparative Example 4 was 923°C. Finally, product performance was tested, as shown in Table 2 below.

[0038] Table 1: Chemical composition (wt%) of Examples 1-5 and Comparative Examples 1-4 of the present invention

[0039] Example C Si Mn P S Alt Nb Ti Ca 1 0.070 0.05 0.85 0.018 0.004 0.045 0.036 0.016 0.0015 2 0.075 0.08 0.88 0.016 0.003 0.040 0.030 0.020 0.0026 3 0.066 0.10 0.90 0.015 0.003 0.030 0.042 0.017 0.0018 4 0.062 0.06 0.93 0.017 0.002 0.035 0.035 0.023 0.0018 5 0.080 0.07 1.00 0.018 0.002 0.025 0.044 0.022 0.0016 Comparative Example 1 0.070 0.05 0.55 0.018 0.004 0.045 0.016 0.016 0.0015 Comparative Example 2 0.080 0.07 1.30 0.018 0.002 0.025 0.044 0.052 0.0016 Comparative Example 3 0.070 0.05 0.85 0.018 0.004 0.045 0.036 0.016 0.0015 Comparative Example 4 0.070 0.05 0.85 0.018 0.004 0.045 0.036 0.016 0.0015

[0040] Table 2: Mechanical properties of steel coils from Examples 1-5 and Comparative Examples 1-4 of the present invention

[0041]

[0042] As shown in Tables 1 and 2 above, the mechanical properties of the hot-rolled automotive wheel steel provided by this invention meet the following requirements: yield strength ≥ 325 MPa, tensile strength 490–600 MPa, elongation ≥ 24%, preferably: yield strength 450–480 MPa, tensile strength 512–565 MPa, elongation 28–32%, and good bending test results. This steel has comprehensive properties such as high strength and good formability, not only meeting the good match between strength and formability in terms of performance, but also having good surface quality. Furthermore, the production method is simple and easy to implement, suitable for industrial mass production, and perfectly meets the needs of automotive wheel steel. All properties meet the relevant standard requirements and user needs. Based on the results of Comparative Examples 1-2, it is evident that when the chemical composition of the hot-rolled automotive wheel steel does not meet the requirements of this invention, the resulting product will fail to meet the predetermined mechanical property requirements. For example, the product obtained in Comparative Example 1 does not meet the predetermined strength requirements; the product obtained in Comparative Example 2 has high strength but low elongation, and its bending test fails, leading to cracking during use. Based on the results of Comparative Examples 3-4, it is evident that when the chemical composition of the hot-rolled automotive wheel steel meets the requirements of this invention, but the production method does not meet these requirements (primarily the final rolling temperature), the resulting product may fail to meet the predetermined plasticity or strength requirements, making it prone to cracking and significantly reducing its load-bearing capacity during subsequent processing and use.

[0043] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A hot-rolled automotive wheel steel with a tensile strength greater than 490 MPa and a thickness of 3-6 mm, wherein the chemical composition by mass percentage is: C: 0.06~0.08%, Si: 0.03~0.10%, Mn: 0.85~1.00%, P≤0.018%, S≤0.005%, Alt: 0.020~0.045%, Nb: 0.030~0.045%, Ti: 0.015~0.025%, Ca: 0.0010~0.0030%, with the remainder being Fe and unavoidable inclusions; The microstructure of the hot-rolled automotive wheel steel consists of ferrite and a small amount of pearlite, and its mechanical properties meet the following requirements: yield strength 450~480MPa, tensile strength 512~565MPa, elongation 28~32%, and its 180° bending test with d=2a is intact.

2. The hot-rolled automotive wheel steel according to claim 1, wherein the chemical composition by mass percentage is: C: 0.062~0.080%, Si: 0.05~0.10%, Mn: 0.85~1.00%, P≤0.018%, S≤0.004%, Alt: 0.025~0.045%, Nb: 0.030~0.044%, Ti: 0.016~0.023%, Ca: 0.0015~0.0026%, with the remainder being Fe and unavoidable inclusions.

3. The hot-rolled automotive wheel steel according to claim 1, wherein the chemical composition by mass percentage is: C: 0.070%, Si: 0.05%, Mn: 0.85%, P: 0.018%, S: 0.004%, Alt: 0.045%, Nb: 0.036%, Ti: 0.016%, Ca: 0.0015%, with the remainder being Fe and unavoidable inclusions.

4. The hot-rolled automotive wheel steel according to claim 1, wherein the chemical composition by mass percentage is: C: 0.075%, Si: 0.08%, Mn: 0.88%, P: 0.016%, S: 0.003%, Alt: 0.040%, Nb: 0.030%, Ti: 0.020%, Ca: 0.0026%, with the remainder being Fe and unavoidable inclusions.

5. The hot-rolled automotive wheel steel according to claim 1, wherein the chemical composition by mass percentage is: C: 0.066%, Si: 0.10%, Mn: 0.90%, P: 0.015%, S ： 0.003%, Alt: 0.030%, Nb: 0.042%, Ti: 0.017%, Ca: 0.0018%, with the remainder being Fe and unavoidable inclusions.

6. The hot-rolled automotive wheel steel according to claim 1, wherein the chemical composition by mass percentage is: C: 0.062%, Si: 0.06%, Mn: 0.93%, P: 0.017%, S: 0.002%, Alt: 0.035%, Nb: 0.035%, Ti: 0.023%, Ca: 0.0018%, with the remainder being Fe and unavoidable inclusions.

7. The hot-rolled automotive wheel steel according to claim 1, wherein the chemical composition by mass percentage is: C: 0.080%, Si: 0.07%, Mn: 1.00%, P: 0.018%, S: 0.002%, Alt: 0.025%, Nb: 0.044%, Ti: 0.022%, Ca: 0.0016%, with the remainder being Fe and unavoidable inclusions.

8. The method for producing hot-rolled automotive wheel steel according to claim 1, comprising the following processes: Smelting—continuous casting—slab heating—rolling—cooling—coiling; wherein: The smelting-continuous casting process includes: KR desulfurization—converter—LF refining—RH vacuum treatment—slab continuous casting—slow cooling. The composition of the molten steel supplied to the casting machine is C: 0.06~0.08%, Si: 0.03~0.10%, Mn: 0.85~1.00%, P≤0.018%, S≤0.005%, Alt: 0.020~0.045%, Nb: 0.030~0.045%, Ti: 0.015~0.025%, Ca: 0.0010~0.0030%, with the remainder being Fe and unavoidable inclusions. The superheat of the slab continuous casting is controlled at 25-32℃. The slab heating process includes feeding the slab, after surface cleaning, into a heating furnace, strictly controlling the slab heating temperature, furnace time, and furnace exit temperature. The heating temperature is controlled at 1200±30℃, the furnace time is controlled at 160~270min, and the furnace exit temperature is controlled at 1200±20℃. The rolling process includes a roughing stage and a finishing stage. The roughing stage uses a 3+3 mode two-stand rolling mill for roughing, and the finishing stage uses a 7-stand continuous variable crown rolling mill for finishing. The finishing stage adopts speed-increasing rolling. The entry thickness of the finishing mill is 40mm, the starting rolling temperature of the finishing mill is not less than 1030℃, and the finishing rolling temperature is 900±15℃. The cooling process employs laminar flow cooling equipment, and the cooling mode is based on the self-learning calculation results of a computer-based secondary system; the cooling rate is controlled at 25-28℃ / s. The winding temperature is 580±20℃.

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