Economical 650mpa grade high strength hot-rolled wheel steel and production method thereof

Abstract

The present application relates to a kind of economic 650MPa grade high-strength hot-rolled wheel steel and its production method, wheel steel chemical composition is as follows by weight percentage:C:0.04%~0.08%, Si:0.05%~0.16%, Mn:0.60%~1.8%, P≤0.018%, S≤0.003%, Als:0.01%~0.05%, N≤0.006%, Nb:0.01%~0.04%, Ti:0.01%~0.04%, the rest is Fe and inevitable impurities.The wheel steel produced by the present application compared with similar products, with good economy, high fatigue strength, low yield ratio, good strength and formability, can meet the current development of lightweight automobile to the high strength, high elongation, excellent fatigue performance requirements of steel for wheel.

Description

Technical Field

[0001] This invention relates to the field of high-strength steel production technology for automobiles, and in particular to an economical 650MPa grade high-strength hot-rolled wheel steel and its production method. Background Technology

[0002] In recent years, with the continuous improvement of people's living standards, the car ownership rate has been increasing, which has also directly led to the accelerated growth of energy consumption and harmful gas emissions, resulting in increasing harm to human health and the environment. Studies have found that vehicle exhaust emissions are directly proportional to vehicle weight; therefore, lightweighting of the entire vehicle is an important way to reduce vehicle exhaust emissions and resource consumption.

[0003] Lightweighting of a vehicle is achieved through the lightweighting of its individual components. Wheels are crucial rotating parts of a car, transmitting all forces and torques between the car and the ground. The structural performance of the wheels significantly impacts the overall safety and reliability of the vehicle. With advancements in vehicle lightweighting technology, wheel lightweighting has also become a research focus. Currently, domestically produced wheels generally suffer from quality issues such as high weight, poor formability, and susceptibility to cracking during welding, as well as performance problems such as substandard fatigue resistance.

[0004] Therefore, it is necessary to develop a high-strength wheel steel with excellent formability, good weldability, and fatigue resistance. Compared with the traditional 590MPa wheel steel, the development of the new 650MPa grade high-strength hot-rolled wheel steel has profound significance for the gradual development of automobile steel wheels towards higher strength and thinner specifications.

[0005] Chinese patent application CN101603153A discloses "A hot-rolled ferritic bainitic duplex steel and its production method," which can be used to manufacture high-strength automotive wheels and other structural components. The main components and their weight percentages in the steel are: C: 0.06–0.08%, Si: 0.40–0.60%, Mn: 1.40–1.60%, P: <0.02%, S: <0.02%, Cr: 0.40–0.60%, Nb: 0.02–0.04%. The rolling process controls the cumulative deformation in the non-recrystallization zone to be >60%, with a final rolling temperature of 800–830℃. The post-rolling segmented cooling process involves a first stage of water cooling at a rate of 30–50℃ / s to 700℃, followed by air cooling for 12–15 seconds. A second stage of water cooling is then performed at a rate of 30–50℃ / s to 500℃. The steel is then coiled and slowly cooled to room temperature. The finished product has a yield strength of 450 MPa, a tensile strength of 665 MPa, an elongation of 22%, and a yield-to-tensile ratio of 0.68, exhibiting a good balance between strength and plasticity, as well as good fracture performance. However, the actual examples do not specify the thickness of the finished steel, and its elongation is relatively low, resulting in higher production costs.

[0006] Chinese patent application CN113957359A discloses a "high-strength automotive wheel steel and its preparation method." The wheel steel comprises the following components by weight percentage: C: 0.05–0.10%, Si: 0.10–0.20%, Mn: 1.40–1.60%, P≤0.020%, S≤0.008%, Cr: 0.15–0.30%, Nb: 0.04–0.06%, Ti: 0.020–0.040%, Als: 0.015–0.050%, with the balance being Fe and unavoidable impurities. The preparation method of the wheel steel follows these steps: hot metal desulfurization → converter smelting → LF refining → RH → slab continuous casting → hot rolling → coiling → cooling. The finished product has a yield strength ≥500 MPa, tensile strength ≥650 MPa, and elongation after fracture ≥18%. The steel used for this wheel has a high microalloying content, resulting in a low elongation rate. Furthermore, using the same composition for different thicknesses can easily lead to significant strength fluctuations and unstable performance.

[0007] Chinese patent application CN107904501A discloses "a high-strength thin-gauge wheel steel with good fatigue resistance and its production method." The chemical composition and weight percentage content of the steel are as follows: C: 0.05-0.07%, Si: 0.15-0.30%, Mn: 1.40-1.60%, P≤0.008%, S≤0.002%, Als: 0.020-0.060%, Nb: 0.046-0.055%. The production method involves: smelting in a converter and then refining and Ca treatment in an LF furnace; hot rolling of the continuously cast billet; cooling and coiling using a fast-to-slow cooling method; and finishing and subsequent processes. The final product exhibits a fine-grained ferrite + pearlite microstructure with a grain size of 13.5. The finished product has a lower yield strength ≥500 MPa, tensile strength of 590–700 MPa, elongation A ≥30%, and a welded side bending elongation ≥28%. Its lower limit of fatigue strength is 140 MPa. However, the strength of the produced high-strength wheel steel is still relatively low, and its fatigue performance cannot meet the requirements for thin-gauge 650 MPa grade high-strength wheel steel. Summary of the Invention

[0008] This invention provides an economical 650MPa grade high-strength hot-rolled wheel steel and its production method. Compared with similar products, the produced wheel steel has the advantages of good economy, high fatigue strength, low yield strength ratio, good strength and toughness and formability, and can meet the requirements of the current development of automotive lightweighting for high strength, high elongation and excellent fatigue performance of wheel steel.

[0009] To achieve the above objectives, the present invention employs the following technical solution:

[0010] An economical 650MPa grade high-strength hot-rolled wheel steel, the chemical composition of the wheel steel by weight percentage is C: 0.04%~0.08%, Si: 0.05%~0.16%, Mn: 0.60%~1.8%, P≤0.018%, S≤0.003%, Als: 0.01%~0.05%, N≤0.006%, Nb: 0.01%~0.04%, Ti: 0.01%~0.04%, with the remainder being Fe and unavoidable impurities.

[0011] The microstructure of the finished steel plate consists of bainite and ferrite, with ferrite accounting for 80% to 90% of the volume; the grain size grade is ≥13.

[0012] The finished steel plate has a tensile strength of 650–750 MPa, a yield strength ≥500 MPa, a yield-to-tensile ratio ≤0.75, and an elongation A. 50 ≥30%, lower limit of fatigue strength ≥270MPa.

[0013] The thickness of the finished steel plate is 3.0 to 5.0 mm.

[0014] An economical production method for 650MPa grade high-strength hot-rolled wheel steel, controlling the following processes:

[0015] 1) Converter smelting: Top and bottom blowing method is adopted, with oxygen pressure of 0.8-2.0 MPa and oxygen flow rate of 30,000-40,000 Nm³. 3 / h, oxygen lance position: high-low-high; concentrated argon blowing in the second half of smelting;

[0016] 2) LF furnace refining; desulfurization and deoxidation operations are performed;

[0017] 3) Continuous casting: Employing light reduction technology, with a reduction rate of 4% to 10%;

[0018] 4) Billet heating: The billet is hot-charged and hot-delivered, with a heating temperature of 1150~1220℃;

[0019] 5) Rolling and coiling: The roughing rolling adopts the "1+4" rolling method, with a first pass reduction rate of 30% to 60%; the finishing rolling temperature is 830 to 880℃; and the coiling temperature is 570 to 640℃.

[0020] 6) Laminar flow cooling and slow cooling: Laminar flow cooling adopts a centralized cooling method in the later stage, and slow cooling adopts a stacked slow cooling method.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] 1) Compared with other similar products, the steel used for wheels produced has a lower content of microalloying and adopts a hot charging and hot delivery method to reduce production costs, thus making it more economical.

[0023] 2) Compared with other similar products, the steel produced for wheels is cleaner, has fewer inclusions, and has more uniform grains. Therefore, the finished product has better fatigue strength, with a conditional fatigue strength ≥270MPa.

[0024] 3) The microstructure of the produced wheel steel consists of bainite and ferrite, with finer grains (≥13), resulting in better strength and toughness; compared with other similar products, it has better formability and lower yield strength ratio. Attached Figure Description

[0025] Figure 1 This is a metallographic photograph of the steel used for wheels produced in Embodiment 1 of the present invention. Detailed Implementation

[0026] The present invention discloses an economical 650MPa grade high-strength hot-rolled wheel steel. The chemical composition of the wheel steel, by weight percentage, is: C: 0.04%~0.08%, Si: 0.05%~0.16%, Mn: 0.60%~1.8%, P≤0.018%, S≤0.003%, Als: 0.01%~0.05%, N≤0.006%, Nb: 0.01%~0.04%, Ti: 0.01%~0.04%, with the remainder being Fe and unavoidable impurities.

[0027] The main reasons for selecting the chemical composition and content of the wheel steel described in this invention are as follows:

[0028] C: Carbon is the most important solid solution strengthening element in steel and the most economical and effective element to ensure high strength performance. Considering the high requirements for weldability and fatigue performance of high-strength wheel steel, the carbon content in the steel cannot be too high or too low. If the carbon content is too high, the toughness of the steel will decrease, and if the carbon content is too low, the solid solution strengthening effect will not be achieved. Therefore, this invention controls the carbon content in the steel at 0.04%~0.08%.

[0029] Silicon (Si): As a non-carbide-forming element and a solid solution strengthening element, silicon can increase the strength of steel plates. However, high silicon content in steel can reduce the hot-rolling performance of the steel plate and decrease its surface quality. Therefore, this invention controls the silicon content to 0.05%~0.16%.

[0030] Mn: Manganese in steel mainly plays a role in solid solution strengthening and refining ferrite grains. However, excessive manganese content in steel increases the probability of white spots during smelting and rolling, while also enhancing the tendency for banded structures and grain coarsening, thus reducing the steel's plasticity and toughness. Therefore, this invention controls the manganese content to 0.60%~1.8%.

[0031] Al: Aluminum can improve the tensile strength and elongation of steel plates and inhibit the precipitation of penetrating carbides, but its solid solution strengthening effect is not as good as that of silicon. Aluminum forms fine, dispersed, insoluble particles with elements such as carbon and nitrogen, forming AlN precipitation, which can play a certain role in refining grains. In this invention, the aluminum content is controlled at 0.01%~0.05%.

[0032] P: Phosphorus can increase the formation temperature of the α phase and expand the temperature range for α phase formation. However, excessive phosphorus content in steel will deteriorate the processing performance of the steel plate. In order to obtain a higher elongation, this invention sets its upper limit to 0.018%.

[0033] S: Sulfide inclusions such as MnS formed by sulfur can become the starting point of cracks and deteriorate the processing performance of steel plates. Therefore, the lower its content, the better. This invention sets its upper limit to 0.003%.

[0034] Nb has the effect of refining grains and its precipitation strengthening ability is moderate. Adding a low content of Nb to wheel steel has a significant grain refining effect. When the content continues to increase, the increase in strength and toughness is not obvious. Therefore, the present invention controls the Nb content at 0.01%~0.04%.

[0035] Ti has precipitation strengthening and grain refinement strengthening effects, which can improve the yield strength and grain coarsening temperature of wheel steel. It also has a good effect on improving the performance of the heat-affected zone in welding. Therefore, the Ti content is controlled at 0.01%~0.04% in this invention.

[0036] N: Nitrogen has a significant impact on the weldability of wheel steel. As its content increases, the toughness of the steel decreases significantly, while also increasing the tendency to age, cold brittleness and hot brittleness, which impairs the weldability and cold bending performance of the steel. Therefore, this invention sets its upper limit at 0.006%.

[0037] The present invention discloses an economical method for producing 650MPa grade high-strength hot-rolled wheel steel, which includes processes such as molten iron smelting, converter steelmaking, LF furnace refining, continuous casting, hot rolling, and cooling. The main controlled steps are as follows:

[0038] 1) Converter smelting: Top and bottom blowing is adopted to accelerate the floating of inclusions in the molten steel to the protective slag with the air bubbles; oxygen lance parameters are: oxygen pressure 0.8~2.0MPa, oxygen flow rate 30000~40000Nm³. 3 / h, oxygen lance position is high-low-high; argon gas is concentrated in the second half of the smelting process.

[0039] 2) LF furnace refining; rapid desulfurization and deoxidation operations to improve alloy yield.

[0040] 3) Continuous casting: Light reduction technology is adopted to reduce center segregation, with a reduction rate of 4% to 10%.

[0041] 4) Billet heating: The billet is heated by hot charging, which greatly reduces the fuel consumption of the heating furnace. The heating temperature is 1150~1220℃.

[0042] 5) Rolling and Coiling: Rough rolling employs high temperature and high reduction, and a "1+4" rolling method. The reduction rate in the first pass is 30%–60% to refine the grain size. The finishing rolling temperature is 830–880℃, above the Ar3 temperature, ensuring the final rolling temperature is within the austenitic phase region. The coiling temperature is 570–640℃, which is between the bainite and ferrite phases to improve the strength and toughness of the product.

[0043] 6) Laminar flow cooling and slow cooling: Laminar flow cooling adopts a centralized cooling method in the rear section to reduce the yield strength ratio of the product and improve the stamping qualification rate of wheel parts. Slow cooling adopts a stacked slow cooling method to improve the elongation of the product.

[0044] The finished product properties and parameters of the economical 650MPa grade high-strength hot-rolled wheel steel described in this invention are as follows:

[0045] The microstructure of the finished steel plate consists of bainite and ferrite, with ferrite accounting for 80% to 90% of the volume; the grain size grade is ≥13.

[0046] The finished steel plate has a tensile strength of 650–750 MPa, a yield strength ≥500 MPa, a yield-to-tensile ratio ≤0.75, and an elongation A. 50 ≥30%, lower limit of fatigue strength ≥270MPa.

[0047] The thickness of the finished steel plate is 3.0 to 5.0 mm.

[0048] To more intuitively illustrate the present invention, the embodiments of the present invention will be further described in conjunction with the examples. The following examples are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technical solutions that can be obviously obtained by those skilled in the art within the scope of the technology disclosed in the present invention, including simple variations or equivalent substitutions, are all within the scope of protection of the present invention.

[0049] Example:

[0050] The chemical composition of the steel in each embodiment is shown in Table 1, and the main process parameters are shown in Table 2; the mechanical properties of the finished steel plates are shown in Table 3, and the metallographic structure of the wheel steel produced in Example 1 is shown in Table 3. Figure 1 .

[0051] Table 1 Chemical composition of steel (wt, %)

[0052]

[0053] Table 2 Main Process Parameters

[0054]

[0055] Table 3. Microstructure and Mechanical Properties of Finished Steel Plates

[0056]

[0057] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for producing an economical 650 MPa grade high-strength hot-rolled wheel steel, characterized by, The chemical composition of the wheel steel is C: 0.04%~0.08%, Si: 0.05%~0.16%, Mn: 0.60%~1.8%, P≤0.018%, S≤0.003%, Als: 0.01%~0.05%, N≤0.006%, Nb: 0.01%~0.04%, Ti: 0.01%~0.04% by weight percentage, and the rest is Fe and inevitable impurities; the production method of the economic 650MPa grade high-strength hot-rolled wheel steel controls the following procedures: 1) Converter smelting: using top and bottom combined blowing mode, oxygen lance oxygen pressure is 0.8-2.0 MPa, oxygen flow is 30000-40000 Nm 3 / h, oxygen lance position: high-low-high; concentrated argon blowing in the second half of smelting; 2) LF furnace refining; desulfurization and deoxidation operation is performed; 3) continuous casting: light pressing down technology is adopted, and the pressing down rate is 4%~10%; 4) casting blank heating: the casting blank is heated and sent, and the heating temperature is 1150~1220℃; 5) rolling and coiling: the rough rolling adopts "1+4" rolling mode, the first pass rolling pressing down rate is 30%~60%; the final rolling temperature is 830~880℃; and the coiling temperature is 570~610℃; 6) laminar flow cooling and slow cooling: the laminar flow cooling adopts the mode of concentrated cooling in the later stage, and the slow cooling adopts the mode of stacking slow cooling. The thickness of the finished steel plate is 3.0-5.0 mm; the tensile strength of the finished steel plate is 650-750 MPa, the yield strength is ≥500 MPa, the yield ratio is ≤0.75, the elongation A 50 ≥30%, and the fatigue strength lower limit is ≥270 MPa.

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