A high-strength wheel steel and its preparation method

Abstract

The present invention discloses a preparation method of high-strength wheel steel, comprising: providing an initial steel billet, wherein the components of the initial steel billet include, by mass percentage, C: 0.045% to 0.055%, Si≤0.03%, Al: 0.30% to 0.50%, Mn: 1.60% to 1.80%, Ti: 0.05% to 0.07%, Nb: 0.010% to 0.015%, V: 0.02% to 0.04%, Y: 0.003% to 0.025%, S: ≤0.002%, P: ≤0.008%, N: ≤0.0016%, Fe: bal.; the initial steel billet is subjected to multiple hot rolling processes to obtain a hot-rolled plate, the hot rolling process including rough rolling and finish rolling, the final rolling temperature of the rough rolling being greater than the start rolling temperature of the finish rolling; the hot-rolled plate is cooled to a first temperature at a first cooling rate to obtain a first steel plate; the first steel plate is cooled to a second temperature at a second cooling rate to obtain a second steel plate; the second steel plate is cooled to a coiling temperature at a third cooling rate to obtain a third steel plate, the first cooling rate and the third cooling rate both being greater than the second cooling rate; the third steel plate is coiled to obtain a first steel coil; the first steel coil is pickled and leveled to obtain the high-strength wheel steel. The present invention also discloses high-strength wheel steel.

Description

Technical Field

[0001] The present invention belongs to the field of automobile steel production and application, and in particular relates to a rare earth microalloyed thick gauge high-strength wheel steel with excellent fatigue performance and a preparation method thereof. Background Art

[0002] Automobile wheels are crucial safety components in the vehicle's driving system, providing load-bearing, steering, and driving functions. Their lightweighting offers significant energy-saving benefits, necessitating the urgent need to develop economical, high-performance, lightweight wheel steels. Currently, the tensile strength of steel wheel materials on the market primarily ranges from 300 to 600 MPa, such as the common 380CL, 420CL, 540CL, and 330 / 580DP wheel steels. However, wheel steel products also suffer from a range of issues, including low strength and high weight, high scrap rates due to cracking during forming and welding, and suboptimal fatigue performance.

[0003] With increasing demands for lightweighting technology, there's an urgent need to increase the strength of wheel steel. Currently produced wheel steel suffers from low strength levels, high alloy costs, and poor performance stability. Furthermore, the associated rolling processes are rigorous and complex, requiring extremely high cooling rates, making production difficult and restricting the production and application of high-strength wheel steel products. Furthermore, fatigue failure is the primary form of wheel failure, accounting for over 80% of all wheel failures. Therefore, fatigue life is one of the most important performance indicators for wheels.

[0004] Therefore, developing and designing a new method for preparing wheel steel and wheel steel to improve the strength of wheel steel while reducing tissue defects, thereby increasing fatigue life, is an urgent problem to be solved in this field. Summary of the Invention

[0005] The present invention aims to solve one of the technical problems in the related art to a certain extent, and to provide a preparation method of high-strength wheel steel and a high-strength wheel steel.

[0006] As a first aspect of the present invention, a method for preparing high-strength wheel steel is provided, comprising:

[0007] An initial steel billet is provided, wherein the components of the initial steel billet include, by mass percentage:

[0008] C: 0.045%~0.055%, Si≤0.03%, Al: 0.30%~0.50%, Mn: 1.60%~1.80%, Ti: 0.05%~0.07%, Nb: 0.010 %~0.015%, V: 0.02%~0.04%, Y: 0.003%~0.025%, S: ≤0.002%, P: ≤0.008%, N: ≤0.0016%, Fe: bal.;

[0009] The initial steel billet is subjected to multiple hot rolling processes to obtain a hot-rolled plate, wherein the hot rolling process includes rough rolling and finish rolling, and the final rolling temperature of the rough rolling is higher than the start rolling temperature of the finish rolling;

[0010] Cooling the hot-rolled plate to a first temperature at a first cooling rate to obtain a first steel plate;

[0011] Cooling the first steel plate to a second temperature at a second cooling rate to obtain a second steel plate;

[0012] cooling the second steel plate to a coiling temperature at a third cooling rate to obtain a third steel plate, wherein the first cooling rate and the third cooling rate are both greater than the second cooling rate;

[0013] Coiling the third steel plate to obtain a first steel coil;

[0014] The first steel coil is pickled and leveled to obtain the high-strength wheel steel.

[0015] Furthermore, in the step of performing multiple hot rolling treatments on the initial steel billet to obtain a hot rolled plate,

[0016] The initial steel slab is subjected to at least four rough rolling passes to obtain a hot-rolled intermediate plate, wherein the final rolling temperature of the fourth rough rolling pass is between 1000° C. and 1040° C., and the starting rolling temperature of the first rough rolling pass is between 1220° C. and 1280° C.;

[0017] The hot-rolled intermediate plate is subjected to multiple finish rolling processes to obtain the hot-rolled plate.

[0018] Furthermore, in the step of performing multiple finish rolling on the hot-rolled intermediate plate to obtain the hot-rolled plate,

[0019] The hot-rolled intermediate plate is subjected to multi-stand finish rolling to a set thickness to obtain the hot-rolled plate, the start rolling temperature of the finish rolling is between 930° C. and 960° C., the final rolling temperature of the finish rolling is between 840° C. and 860° C., and the reduction rate of each of the last two passes is between 13% and 22%.

[0020] Furthermore, in the step of rough rolling the initial steel billet for at least 4 passes,

[0021] The method also includes performing high-pressure water dephosphorization treatment on the initial steel billet before the first two rough rolling passes.

[0022] Furthermore, in the step of cooling the hot-rolled plate to a first temperature at a first cooling rate to obtain a first steel plate, the first cooling rate is between 60°C / s and 100°C / s, and the first temperature is between 680°C and 700°C.

[0023] In the step of cooling the first steel plate to a second temperature at a second cooling rate to obtain a second steel plate, the second cooling rate is between 5°C / s and 10°C / s, and the second temperature is between 640°C / s and 660°C.

[0024] In the step of cooling the second steel plate to a coiling temperature at a third cooling rate to obtain the third steel plate, the third cooling rate is not less than 25°C / s, and the coiling temperature is between 450°C / s and 470°C.

[0025] Furthermore, before providing the initial steel billet, the preparation method further comprises:

[0026] Performing impurity removal pretreatment on the initial molten iron to obtain pretreated molten iron, wherein the sulfur content of the pretreated molten iron is not higher than 0.002%;

[0027] performing converter smelting treatment on the pretreated molten iron to obtain primary molten steel;

[0028] Refining the primary molten steel in an LF ladle furnace to obtain refined molten steel;

[0029] The refined molten steel is continuously cast to obtain the initial steel billet.

[0030] Furthermore, in the step of continuously casting the refined molten steel,

[0031] injecting the refined molten steel into a crystallizer for a first cooling treatment to obtain an initial casting;

[0032] Drawing the initial cast billet into a casting channel for a second cooling treatment to obtain an intermediate cast billet, wherein the second cooling treatment further includes subjecting the initial cast billet to electromagnetic stirring, wherein the frequency of the electromagnetic stirring is between 5.0 Hz and 8.0 Hz;

[0033] The intermediate billet is drawn and straightened and then cut into blocks to obtain the initial steel billet. During the drawing and straightening process of the intermediate billet, the solidified end of the intermediate billet is pressed down, the pressing amount is between 5 mm and 12 mm, and the pressed solid phase ratio is between 0.4 and 1.0.

[0034] Furthermore, in the step of pickling and leveling the first steel coil, the leveling reduction rate is between 1.5% and 2.5%.

[0035] As a second aspect of the present application, a high-strength wheel steel is disclosed, which is prepared using the above-mentioned preparation method.

[0036] Furthermore, the tensile strength of the high-strength wheel steel is not less than 670 MPa, the elongation A50 is not less than 24%, the hole expansion rate is not less than 75%, the yield strength ratio is not higher than 0.86, and the fatigue life is not less than 1 million cycles.

[0037] Compared to existing wheel steels, this invention achieves superior surface quality through low-Si (≤0.03%) or even Si-free and Al-added composition design and control. Low-C rare earth microalloying and the combined addition of elements such as Ti, Nb, and V significantly enhance tensile strength, further stabilize mechanical properties, achieve high hole expansion, a yield ratio ≤0.86, and excellent formability. This addresses the issues of conventional wheel steels with low tensile strength, insufficient elongation, high yield ratio, and excessive cracking during complex forming. The invention adds the rare earth element Y to the steel to modify and refine harmful inclusions, forming spherical or spherical rare earth inclusions, most of which are sized below 5μm, thus purifying the steel quality. Furthermore, the nitrogen content is strictly controlled to below 0.0016%. The combined addition of elements such as Ti, Nb, and V increases the Ti content in the steel while adding small amounts of Nb and V, reducing alloy costs while improving the strength of the steel plate. Microalloying Ti has the advantages of large reserves, low price and significant strengthening effect, but its advantages are limited by the fact that its large TiN particles that are difficult to control due to liquid precipitation deteriorate the plasticity, toughness and fatigue properties. By adding rare earth element Y to refine and modify inclusions, deeply purify the molten steel and refine the grains, a rare earth microalloying technology based on the coordinated control of cost and performance is realized, which significantly improves the plasticity, toughness and fatigue life of wheel steel. Combined with process optimization, the solid solution precipitation behavior of nano-scale second phase particles in steel is controlled, and the fine grain strengthening and precipitation strengthening effects of microalloying elements are fully utilized to improve the strength and performance stability of the product, improve the product qualification rate, and meet the current market demand. In the hot rolling process, the present invention adopts a lower final rolling temperature and large deformation control in the last two passes. Through the segmented cooling mode of rapid cooling-slow cooling-rapid cooling, the coiling temperature is set to 450~470℃, which realizes the refinement and homogenization control of multiphase structures such as polygonal ferrite, acicular ferrite, bainite and nano-scale precipitation phases. Due to the lower coiling temperature, the difference in cooling rate of different parts of the steel coil is reduced, and the stability of the mechanical properties of the product is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0039] Figure 1This is a flow chart of an embodiment of the method for preparing high-strength wheel steel provided by the present invention;

[0040] Figure 2 This is a flow chart of an implementation method of the method for preparing high-strength wheel steel provided by the present invention. DETAILED DESCRIPTION

[0041] The following describes embodiments of the present invention in detail, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described in the embodiments are intended to explain the present invention and are not to be construed as limiting the present invention.

[0042] References in this specification to "one embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with the embodiment itself can be included in at least one embodiment disclosed herein. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.

[0043] Automobile wheels are critical safety components in the vehicle's driving system, providing load-bearing, steering, and driving functions. Their lightweighting offers significant energy-saving benefits. Therefore, under increasingly stringent standards for energy conservation, low emissions, high safety, and long life, there is an urgent need to develop economical, high-performance, lightweight wheel steels to achieve this goal. Currently, the tensile strength of steel wheel materials on the market primarily ranges from 300 to 600 MPa, such as the common 380CL, 420CL, 540CL, and 330 / 580DP wheel steels. Furthermore, these wheel steels suffer from a number of issues, including low strength and high weight, high scrap rates due to cracking during forming and welding, and suboptimal fatigue performance. Related technologies have disclosed several wheel steels and their production methods. Some utilize a rigorous controlled rolling and cooling process, utilizing deformation in the unrecrystallized austenite zone and strain-induced ferrite transformation mechanisms, to produce 490 MPa-grade fine-grained wheel steels with a ferrite-pearlite structure, achieved through low-temperature, high-reduction compression and multi-pass deformation near the Ar3 temperature. However, these patents offer relatively low strength and are not suitable for wheel components requiring high-strength performance. Another approach involves strictly controlling the temperature and cooling rate during the rolling process and employing ultra-rapid cooling during the laminar cooling phase to reduce the Ar3 temperature, increase the number of phase transformation nuclei, and inhibit grain growth after the phase transformation, thereby refining the ferrite grains and producing wheel steel with excellent weldability. While this patent allows for the production of thicker wheel steel, the tensile strength ranges from 470 to 630 MPa, which still cannot meet lightweight wheel steel requirements. Furthermore, the rolling process employed is rigorous and complex, requiring extremely high cooling rates, making production difficult.

[0044] With the increasing requirements for lightweight technology, there is an urgent need to improve the strength of wheel steel. The main problems of currently produced wheel steel are low strength level, high alloy cost and poor performance stability, which restrict the production and application of high-strength wheel steel products. In addition, fatigue failure is the main form of wheel failure, of which more than 80% is caused by fatigue failure. Therefore, fatigue life is one of the most important performance indicators of wheels. The inventors of this application have found that large-sized alumina inclusions of 20μm and above significantly reduce the fatigue strength of the material and should be strictly controlled.

[0045] As a first aspect of the present invention, a method for preparing high-strength wheel steel is provided, such as Figure 1 Shown, including:

[0046] S100, providing an initial steel billet, wherein the components of the initial steel billet include, by mass percentage:

[0047] C: 0.045%~0.055%, Si≤0.03%, Al: 0.30%~0.50%, Mn: 1.60%~1.80%, Ti: 0.05%~0.07%, Nb: 0.010 %~0.015%, V: 0.02%~0.04%, Y: 0.003%~0.025%, S: ≤0.002%, P: ≤0.008%, N: ≤0.0016%, Fe: bal.;

[0048] S110, performing multiple hot rolling processes on the initial steel billet to obtain a hot-rolled plate, wherein the hot rolling process includes rough rolling and finish rolling, and the final rolling temperature of the rough rolling is higher than the start rolling temperature of the finish rolling;

[0049] S120, cooling the hot-rolled plate to a first temperature at a first cooling rate to obtain a first steel plate;

[0050] S130, cooling the first steel plate to a second temperature at a second cooling rate to obtain a second steel plate;

[0051] S140, cooling the second steel plate to a coiling temperature at a third cooling rate to obtain a third steel plate, wherein the first cooling rate and the third cooling rate are both greater than the second cooling rate;

[0052] S150, coiling the first steel plate to obtain a first steel coil;

[0053] S160: Perform pickling and leveling treatment on the first steel coil to obtain high-strength wheel steel.

[0054] In step S100, the present application does not impose any special limitation on the initial steel billet, which may be prepared by smelting molten steel or purchased from outside.

[0055] In some embodiments, the initial steel billet is prepared by smelting molten steel, specifically, Figure 2As shown, before providing the initial steel billet, the preparation method further includes:

[0056] S010. Pre-treating the initial molten iron to remove impurities to obtain pre-treated molten iron. The KR method can be used for molten iron desulfurization pre-treatment, which involves immersing a cross-shaped stirring head, which has been cast with refractory materials and baked, into a molten iron pool to a certain depth. The vortex generated by the stirring head's rotation is used to add a weighed desulfurizer to the surface of the molten iron from a feeder. The desulfurizer is then drawn into the molten iron by the vortex, allowing the calcium oxide-based desulfurization powder to fully contact and react with the molten iron to achieve the purpose of desulfurization. Pre-desulfurization of molten iron is one of the indispensable processes for optimizing metallurgical production processes. It can reduce the coke ratio of continuous steelmaking and improve productivity, reduce lime consumption and slag volume in steelmaking, and thus reduce production costs.

[0057] S020, subjecting the pretreated molten iron to a converter smelting treatment to obtain primary molten steel. The converter is a process in which the pretreated molten iron is used as raw material in a converter, and high-pressure air or oxygen is blown into the converter from the top, bottom, or sides to oxidize and remove impurities in the pretreated molten iron in the converter, primarily for decarburization, dephosphorization, desulfurization, and deoxidation, and to remove harmful gases and non-metallic inclusions. The temperature is increased and the composition is adjusted to ensure that the sulfur content of the pretreated molten iron is no more than 0.002% before entering the converter.

[0058] S030. The primary molten steel is refined in an LF ladle furnace to obtain refined molten steel. The primary molten steel obtained in the converter is transferred to an LF furnace for refining. Submerged arc heating is performed using multiple electrodes. The electrode heating can produce high-basicity reducing slag to purify the molten steel. Furthermore, the LF furnace can further deoxidize and desulfurize the molten steel to adjust its composition. Inert gas such as argon is blown into the bottom of the LF furnace to stir the molten steel and ensure a uniform temperature.

[0059] S040, continuously casting the refined molten steel to obtain an initial steel billet. Specifically, in the step of continuously casting the refined molten steel,

[0060] First, the refined molten steel passes through the tundish, and the tundish then injects the molten steel into each crystallizer through the water nozzle for the first cooling treatment to obtain the initial casting billet. The superheat of the molten steel in the continuous casting tundish is 10~25℃. The crystallizer is the core component of continuous casting. It is composed of a metal shell with cooling water continuously flowing inside. This crystallizer that continuously supplies cooling water causes the liquid molten steel in contact with it to initially solidify the steel liquid to obtain an initial casting billet with a solidified billet shell on the outside and molten steel in the core.

[0061] The initial ingot in the crystallizer is pulled into the casting channel by a straightening machine for a second cooling treatment (also known as the secondary cooling zone) to obtain an intermediate ingot. The purpose of the secondary cooling is to force and uniformly cool the surface of the ingot, so that the ingot solidifies in a relatively short time. The second cooling process also includes electromagnetic stirring of the initial ingot. Electromagnetic stirring is an effective means to improve the metal solidification structure and enhance product quality. Preferably, the frequency of electromagnetic stirring is between 5.0HZ and 8.0HZ. The purpose of electromagnetic stirring in the secondary cooling zone is to break up the dendrite bridges in the liquid core cavity, eliminate the looseness and shrinkage cavity in the center of the ingot, and the broken dendrites serve as equiaxed crystal cores, expand the equiaxed crystal zone in the center of the ingot, eliminate central segregation, promote the floating of inclusions in the liquid phase cavity of the ingot, and reduce the accumulation of inner arc inclusions.

[0062] The intermediate ingot is further drawn and straightened and then cut into blocks to obtain an initial steel billet. During the drawing and straightening process, the solidification end of the intermediate ingot is pressed down. Proper mechanical pressure at the solidification end can compensate for the shrinkage of the solidified body in the two-phase region at the end, thereby alleviating and eliminating the center segregation and looseness problems. In some embodiments, the amount of pressure reduction is between 5 mm and 12 mm, and the solid phase ratio of the pressure reduction is between 0.4 and 1.0, which reduces component segregation and inhibits the size and number of large TiN particles precipitated during the solidification process.

[0063] In step S110, in the step of performing multiple hot rolling processes on the initial steel billet to obtain a hot rolled plate,

[0064] The initial steel slab is subjected to at least four rough rolling passes to obtain a hot-rolled intermediate plate. In some embodiments, the rough rolling adopts a 1+3 pass distribution mode, i.e., two roughing mills, R1 and R2, are used, with R1 performing the first rough rolling, followed by R2 performing three rough rolling passes. Reasonable rough rolling load distribution can ensure more stable production, more precise control accuracy, increase rolling mill life, improve production efficiency, reduce slab heat loss, and save energy. The final rolling temperature of the fourth rough rolling pass is between 1000°C and 1040°C, and the starting rolling temperature of the first rough rolling pass is between 1220°C and 1280°C.

[0065] In some embodiments, the step of performing at least four rough rolling passes on the initial steel slab further includes performing a high-pressure water dephosphorization treatment on the initial steel slab before the first two rough rolling passes. Specifically, a high-pressure water descaling treatment is performed before each of the rough rolling passes R1 and R2. High-pressure water descaling removes iron oxide scale to prevent it from penetrating the surface and causing defects, thereby improving the surface quality of the product.

[0066] After the rough rolling is completed, the hot-rolled intermediate plate undergoes multiple finishing rolls to produce hot-rolled plate. Rough rolling typically involves a larger roll diameter and a lower rolling speed to provide greater rolling force and pressure. The rough rolling process precisely adjusts the slab width to produce a hot-rolled intermediate plate with a smooth surface and uniform width for finishing. Finishing rolls transform the rough-rolled intermediate plate into a product with a smooth surface, uniform thickness, and excellent performance. Finishing rolls utilize a continuous rolling process, typically seven stands. Specifically, the hot-rolled intermediate plate undergoes multiple finish rolls to a set thickness to produce the hot-rolled plate. The start rolling temperature for finishing rolls is between 930°C and 960°C, the final rolling temperature for finishing rolls is between 840°C and 860°C, and the reduction ratio for each of the last two passes is between 13% and 22%.

[0067] In steps S120 to S150, the hot-rolled plate is cooled after finish rolling, wherein the hot-rolled plate is first cooled to a first temperature at a first cooling rate to obtain a first steel plate, wherein the first cooling rate is between 60°C / s and 100°C / s, and the first temperature is between 680°C and 700°C; the first steel plate is then cooled to a second temperature at a second cooling rate to obtain a second steel plate, wherein the second cooling rate is between 5°C / s and 10°C / s, and the second temperature is between 640°C / s and 660°C; the second steel plate is then cooled to a coiling temperature at a third cooling rate to obtain a third steel plate, wherein the third cooling rate is not less than 25°C / s, and the coiling temperature is between 450°C / s and 470°C. The steel is cooled in a segmented cooling mode of rapid cooling-slow cooling-rapid cooling. By controlling the cooling rate and coiling temperature, the microstructure of the steel plate is controlled, the sufficient precipitation of Ti, Nb, and V elements is promoted, and the ripening and growth of the precipitated second-phase particles are avoided, ensuring that small and sufficient second-phase particles such as TiC, NbC, and VC are obtained. Among them, the proportion of second-phase particles with a size of less than 10nm reaches more than 85%, thereby maximizing the precipitation strengthening effect of microalloying elements and improving strength and plasticity.

[0068] In step S160, the first steel coil is pickled and leveled to obtain high-strength wheel steel, wherein the leveling reduction rate is between 1.5% and 2.5%.

[0069] The resulting steel plate has a thickness of 4mm to 16mm. The addition of rare earth element Y modifies and refines harmful inclusions in the steel, reducing their impact on the wheel steel's plasticity, toughness, and fatigue performance. The steel plate's microstructure consists of uniformly refined polygonal ferrite, acicular ferrite, bainite, and nanoscale precipitates. This fully utilizes the effects of grain refinement and precipitation strengthening of nanoscale second-phase particles, significantly improving the wheel steel's strength and formability. The tensile strength is ≥670MPa, the elongation A50 is ≥24%, the hole expansion ratio is ≥75%, and the yield strength ratio is ≤0.86. The product also exhibits excellent fatigue performance, meeting the requirement for a wheel fatigue life of more than 1 million cycles. This product offers low alloy cost, stable mechanical properties, an excellent balance of strength and plasticity, a high hole expansion ratio, and fatigue resistance. This significantly enhances formability and product qualification, offering significant advantages over traditional wheel steels.

[0070] As a second aspect of this application, a high-strength wheel steel is disclosed, produced using the aforementioned preparation method. The high-strength wheel steel has a tensile strength of not less than 670 MPa, an elongation A50 of not less than 24%, a hole expansion ratio of not less than 75%, a yield strength ratio of not more than 0.86, and a fatigue life of not less than 1 million cycles.

[0071] The present invention uses rare earth microalloying and strictly controls the nitrogen content in the steel to be less than 0.0016%, and modifies and refines the harmful inclusions in the steel, thereby reducing the impact on the plastic toughness and fatigue performance of the wheel steel. By adding elements such as Ti, Nb, and V in combination, the microstructure of the wheel steel is controlled to be uniformly refined polygonal ferrite, acicular ferrite, bainite, and nanoscale precipitation phases through process optimization, giving full play to the effects of grain refinement and precipitation strengthening of nanoscale second-phase particles, significantly improving the strength and forming properties of the wheel steel, with a tensile strength of ≥670MPa, an elongation A50 of ≥24%, a hole expansion rate of ≥75%, a yield strength ratio of ≤0.86, and excellent fatigue performance, meeting the use requirement of a wheel fatigue life of more than 1 million times. This product has low alloy cost, stable mechanical properties, excellent strength-plasticity matching, a high hole expansion rate and fatigue resistance, can significantly improve forming properties, and increase product qualification rate, and has obvious advantages over traditional wheel steel.

[0072] (1) Compared with the existing wheel steel, the present invention has excellent surface quality through the design and control of low Si (≤0.03%) or even no Si and Al composition. The tensile strength is significantly improved by adding rare earth microalloying with low C and composite addition of elements such as Ti, Nb, and V. The mechanical properties are more stable, the hole expansion rate is high, the yield strength ratio is ≤0.86, and the forming performance is excellent. The problems of low tensile strength, insufficient elongation, high yield strength ratio, and excessively high cracking rate in complex forming of traditional wheel steel are solved.

[0073] (2) The present invention adds rare earth element Y to the steel to modify and refine the harmful inclusions in the steel, forming spherical or spherical rare earth inclusions with a size of less than 5μm, thereby purifying the steel quality. The nitrogen content is strictly controlled to be less than 0.0016%, and Ti, Nb, V and other elements are added in combination to increase the Ti content in the steel while adding a small amount of Nb and V elements. This reduces the alloy cost while improving the strength of the steel plate. Microalloying Ti elements have the advantages of large reserves, low price and significant strengthening effect, but the advantages are limited by the fact that the large TiN particles that are difficult to control due to liquid precipitation deteriorate the plastic toughness and fatigue properties.

[0074] By adding the rare earth element Y to refine and modify inclusions, deeply purify the molten steel, and refine the grain size, we have achieved a rare earth microalloying technology based on the coordinated control of cost and performance, significantly improving the plasticity, toughness, and fatigue life of wheel steel. Combined with process optimization, this technology controls the solid solution precipitation behavior of nanoscale second-phase particles in the steel, fully leveraging the grain refinement and precipitation strengthening effects of the microalloying element to enhance the product's strength and performance stability, increase product qualification rates, and meet current market demands.

[0075] (3) During the hot rolling process, the present invention adopts a relatively low finishing temperature and large deformation control in the last two passes. Through a staged cooling mode of rapid cooling, slow cooling, and rapid cooling, the coiling temperature is set at 450-470°C, achieving refinement and homogenization of the multiphase structure of polygonal ferrite, acicular ferrite, bainite, and nanoscale precipitation phases. Due to the low coiling temperature, the difference in cooling rate between different parts of the steel coil is reduced, and the mechanical property stability of the product is improved.

[0076] The functions of each element and main process in the present invention are as follows:

[0077] C: The most basic strengthening element, it plays an important role in improving the strength of the material. However, when the C content in steel is too high, it will lead to reduced plasticity and deterioration of welding performance. Therefore, the carbon content in steel should be reasonably controlled.

[0078] Manganese (Mn) is a key alloying element in high-strength steel and a typical austenite stabilizer. It effectively inhibits austenite recrystallization, strengthens the solid solution, and refines ferrite grains. However, excessive Mn content can lead to severe central segregation and banded structure, requiring coordinated control in conjunction with other elements and process control. In this paper, a Mn content of 1.60% to 1.80% is selected.

[0079] Si: Si can significantly improve the strength and hardness of steel, while enhancing its corrosion resistance and high-temperature oxidation resistance. However, Si can also reduce the welding performance of steel. Excessive Si content can affect the surface quality and coating performance. Therefore, the Si content is strictly limited. Therefore, the present invention controls the Si content to ≤0.03%.

[0080] Rare earth elements (Y): can deeply reduce non-metallic inclusions and play a role in purifying molten steel. Adding a small amount of rare earth to the steel can refine the structure, improve the ingot smelting quality, and effectively improve the cold forming performance of the steel plate. Excessive addition will not have a significant effect. Therefore, the content of rare earth element Y is controlled at 0.003%~0.025%.

[0081] Ti, Nb, and V elements: Ti, Nb, and V form nano-sized carbonitrides with C and N elements in steel and precipitate evenly in the matrix, which plays a role in grain refinement and precipitation strengthening, significantly improving strength.

[0082] N: If the N content is too high, coarse TiN will be precipitated, which will significantly reduce the plasticity, toughness and fatigue properties of the steel. Therefore, the present invention controls the N content to ≤0.0016%.

[0083] P: It is an impurity element in steel and needs to be strictly controlled, with a requirement of ≤0.008%.

[0084] S: It is an impurity element in steel and needs to be strictly controlled, with a requirement of ≤0.002%.

[0085] The present invention provides a method for preparing rare earth microalloyed thick-gauge high-strength wheel steel with excellent fatigue performance. By adding rare earth elements, the inclusions are refined and modified, the molten steel is deeply purified, and the grains are refined, thereby realizing a rare earth microalloying technology based on the coordinated control of cost and performance.

[0086] The present invention will be further described below through specific examples and comparative examples.

[0087] Example

[0088] Example 1

[0089] This embodiment provides a method for preparing high-strength wheel steel, comprising:

[0090] Step 1: performing impurity removal pretreatment on the initial molten iron to obtain pretreated molten iron, wherein the sulfur content of the pretreated molten iron is not higher than 0.002%;

[0091] Step 2: performing converter smelting on the pretreated molten iron to obtain primary molten steel;

[0092] Step 3, refining the primary molten steel in an LF ladle furnace to obtain refined molten steel;

[0093] The refined molten steel is continuously cast to obtain an initial steel billet. Specifically, the refined molten steel is injected into a crystallizer through a tundish for a first cooling treatment to obtain an initial cast billet, wherein the molten steel in the tundish is superheated by 10 to 25° C. The initial cast billet is drawn into a casting channel for a second cooling treatment to obtain an intermediate cast billet, wherein the second cooling treatment further includes electromagnetic stirring of the initial cast billet, and the frequency of the electromagnetic stirring is between 5.0 Hz and 8.0 Hz; the intermediate cast billet is drawn and straightened, and then cut into blocks to obtain an initial steel billet. wherein, during the drawing and straightening treatment of the intermediate cast billet, the solidified end of the intermediate cast billet is pressed down, the pressing amount is between 5 mm and 12 mm, and the pressed solid phase ratio is between 0.4 and 1.0;

[0094] Step 4: performing multiple hot rolling processes on the initial steel billet to obtain a hot-rolled plate, wherein the hot rolling process includes rough rolling and finish rolling, and the final rolling temperature of the rough rolling is higher than the start rolling temperature of the warm rolling. The composition of the initial steel billet is shown in Table 1 below;

[0095] The initial steel slab is subjected to 1+3 passes of rough rolling using R1 and R2 rough rolling mills to obtain a hot-rolled intermediate plate, wherein the finishing rolling temperature of the fourth pass is between 1000°C and 1040°C, and the starting rolling temperature of the first pass is between 1220°C and 1280°C. A high-pressure water descaling treatment is performed before starting the R1 and R2 rough rollings respectively.

[0096] The hot-rolled intermediate plate is subjected to multiple finish rolling to obtain the hot-rolled plate. Specifically, the hot-rolled intermediate plate is subjected to 7-stand finish rolling to a set thickness to obtain the hot-rolled plate. The start rolling temperature of the finish rolling is between 930° C. and 960° C., the final rolling temperature of the finish rolling is between 840° C. and 860° C., and the reduction rate of each of the last two passes is between 13% and 22%.

[0097] Step 5: Cool the hot-rolled plate to a first temperature at a first cooling rate to obtain a first steel plate; cool the first steel plate to a second temperature at a second cooling rate to obtain a second steel plate; and cool the second steel plate to a coiling temperature at a third cooling rate to obtain a third steel plate, wherein the first cooling rate is between 60°C / s and 100°C / s, the first temperature is between 680°C and 700°C, the second cooling rate is between 5°C / s and 10°C / s, the second temperature is between 640°C / s and 660°C, the third cooling rate is not less than 25°C / s, and the coiling temperature is between 450°C / s and 470°C.

[0098] Step 6: Coil the third steel plate to obtain a first steel coil;

[0099] Step 7: Pickling and leveling the first steel coil to obtain high-strength wheel steel. The steel plate thickness is 4 mm to 16 mm, wherein the leveling reduction rate is between 1.5% and 2.5%.

[0100] Example 2

[0101] High-strength wheel steel was prepared using the same preparation method as in Example 1, except that the composition of the initial steel billet is shown in Table 1, and the specific hot rolling parameters, cooling rate, and coiling temperature are different, as shown in Table 2.

[0102] Example 3

[0103] High-strength wheel steel was prepared using the same preparation method as in Example 1, except that the composition of the initial steel billet is shown in Table 1, and the specific hot rolling parameters, cooling rate, and coiling temperature are different, as shown in Table 2.

[0104] Example 4

[0105] High-strength wheel steel was prepared using the same preparation method as in Example 1, except that the composition of the initial steel billet is shown in Table 1, and the specific hot rolling parameters, cooling rate, and coiling temperature are different, as shown in Table 2.

[0106] Table 1 Chemical composition of specific examples 1 to 4 (wt.%)

[0107]

[0108] Table 2 Main process parameters of the example steel

[0109]

[0110] Test Case

[0111] Mechanical properties tests were performed on Examples 1 to 4, and the results are shown in Table 3.

[0112] Table 3 Mechanical properties of example steel

[0113]

[0114] As shown in Table 3, the mechanical properties of the steel in this embodiment demonstrate that the embodiment of the present invention has excellent comprehensive mechanical properties, high strength, and stable mechanical properties. While meeting strength requirements, the embodiment of the present invention has a yield ratio of ≤0.86 and good elongation and hole expansion, with an elongation of over 24% and a hole expansion ratio of ≥75%, far exceeding the mechanical properties of traditional high-strength steel. This improves formability and addresses the problems of traditional wheel steel, such as low tensile strength, insufficient elongation, high yield ratio, and excessive cracking rate during complex forming. This significantly increases the product qualification rate and scope of application. The alloy of the present invention offers low cost, excellent surface quality, a wide production process window, and strong flexibility in process parameter control. It is suitable for large-scale industrial production on traditional hot rolling lines and has good applicability.

[0115] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing high-strength wheel steel, characterized in that: include: An initial steel billet is provided, wherein the components of the initial steel billet include, by mass percentage: C: 0.045%~0.055%, Si≤0.03%, Al: 0.30%~0.50%, Mn: 1.60%~1.80%, Ti: 0.05%~0.07%, Nb: 0.010 %~0.015%, V: 0.02%~0.04%, Y: 0.003%~0.025%, S: ≤0.002%, P: ≤0.008%, N: ≤0.0016%, Fe: bal.; The initial steel billet is subjected to multiple hot rolling processes to obtain a hot-rolled plate, wherein the hot rolling processes include rough rolling and finish rolling, the final rolling temperature of the rough rolling is greater than the start rolling temperature of the finish rolling, the start rolling temperature of the first rough rolling pass is between 1220° C. and 1280° C., the finish rolling temperature of the last rough rolling pass is between 1000° C. and 1040° C., the start rolling temperature of the first finish rolling pass is between 930° C. and 960° C., the finish rolling temperature of the last finish rolling pass is between 840° C. and 860° C., and the reduction ratio of each of the last two finish rolling passes is between 13% and 22%; The hot-rolled plate is cooled to a first temperature at a first cooling rate to obtain a first steel plate, wherein the first cooling rate is between 60° C. / s and 100° C. / s, and the first temperature is between 680° C. and 700° C.; The first steel plate is cooled to a second temperature at a second cooling rate to obtain a second steel plate, wherein the second cooling rate is between 5°C / s and 10°C / s, and the second temperature is between 640°C / s and 660°C. Cooling the second steel plate to a coiling temperature at a third cooling rate to obtain a third steel plate, wherein the third cooling rate is not less than 25° C. / s, and the coiling temperature is between 450° C. / s and 470° C.; Coiling the third steel plate to obtain a first steel coil; The first steel coil is pickled and leveled to obtain the high-strength wheel steel.

2. The preparation method according to claim 1, characterized in that In the step of performing multiple hot rolling processes on the initial steel billet to obtain a hot rolled plate, performing at least four passes of rough rolling on the initial steel slab to obtain a hot-rolled intermediate plate; The hot-rolled intermediate plate is subjected to multiple finish rolling processes to obtain the hot-rolled plate.

3. The preparation method according to claim 2, characterized in that In the step of performing multiple finish rolling on the hot-rolled intermediate plate to obtain the hot-rolled plate, The hot-rolled intermediate plate is subjected to multi-stand finish rolling to a set thickness to obtain the hot-rolled plate.

4. The preparation method according to claim 2, characterized in that In the rough rolling step of at least 4 passes of the initial steel billet, Before the first two rough rolling passes, the initial steel slab is subjected to a high-pressure water dephosphorization treatment.

5. The preparation method according to any one of claims 1 to 4, characterized in that Before providing the initial steel billet, the preparation method further comprises: Performing impurity removal pretreatment on the initial molten iron to obtain pretreated molten iron, wherein the sulfur content of the pretreated molten iron is not higher than 0.002%; performing converter smelting treatment on the pretreated molten iron to obtain primary molten steel; Refining the primary molten steel in an LF ladle furnace to obtain refined molten steel; The refined molten steel is continuously cast to obtain the initial steel billet.

6. The preparation method according to claim 5, characterized in that In the step of continuously casting the refined molten steel, injecting the refined molten steel into a crystallizer for a first cooling treatment to obtain an initial casting; Drawing the initial cast billet into a casting channel for a second cooling treatment to obtain an intermediate cast billet, wherein the second cooling treatment further includes subjecting the initial cast billet to electromagnetic stirring, wherein the frequency of the electromagnetic stirring is between 5.0 Hz and 8.0 Hz; The intermediate billet is drawn and straightened and then cut into blocks to obtain the initial steel billet. During the drawing and straightening process of the intermediate billet, the solidified end of the intermediate billet is pressed down, the pressing amount is between 5 mm and 12 mm, and the pressed solid phase ratio is between 0.4 and 1.

0.

7. The preparation method according to any one of claims 1 to 4, characterized in that In the step of performing pickling and leveling treatment on the first steel coil, the leveling reduction rate is between 1.5% and 2.5%.

8. A high-strength wheel steel, characterized in that: The preparation method is described in any one of claims 1 to 7.

9. The high-strength wheel steel according to claim 8, characterized in that: The tensile strength of the high-strength wheel steel is not less than 670 MPa, the elongation A50 is not less than 24%, the hole expansion rate is not less than 75%, the yield strength ratio is not higher than 0.86, and the fatigue life is not less than 1 million cycles.

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