High-strength wheel steel and preparation method thereof

Abstract

The invention discloses a preparation method of high-strength wheel steel, which comprises the following steps: providing an initial steel billet which comprises the following components in percentage by mass: 0.045%-0.055% of C, less than or equal to 0.03% of Si, 0.30%-0.50% of Al, 1.60%-1.80% of Mn, 0.05%-0.07% of Ti, 0.010%-0.015% of Nb, 0.02%-0.04% of V, 0.003%-0.025% of Y, less than or equal to 0.002% of S, less than or equal to 0.008% of P, less than or equal to 0.0016% of N and the balance of Fe; the initial steel billet is subjected to multiple times of hot rolling treatment, a hot rolled plate is obtained, hot rolling treatment comprises rough rolling and finish rolling, and the finish rolling temperature of rough rolling is higher than the initial rolling temperature of finish rolling; cooling the hot-rolled plate to a first temperature at a first cooling speed to obtain a first steel plate; cooling the first steel plate to a second temperature at a second cooling speed to obtain a second steel plate; the second steel plate is cooled to the coiling temperature at a third cooling speed, a third steel plate is obtained, and the first cooling speed and the third cooling speed are both higher than the second cooling speed; coiling the third steel plate to obtain a first steel coil; and the first steel coil is subjected to acid pickling flattening treatment, and the high-strength wheel steel is obtained. The invention further discloses the high-strength wheel steel.

Description

Technical Field

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

[0002] Automobile wheels are important safety components in the automobile driving system, playing the role of load-bearing, steering, driving, etc. Their lightweight energy-saving effect is remarkable, and there is an urgent need to develop economical and high-performance lightweight wheel steel to achieve lightweight. At present, the tensile strength of steel wheel materials on the market is mainly between 300~600MPa, such as the common 380CL, 420CL, 540CL, 330 / 580DP and other wheel steel materials. At the same time, wheel steel products also have a series of problems such as low strength and high weight, easy cracking during the forming and welding process resulting in high product scrap rate, and unsatisfactory fatigue performance.

[0003] With the increasing requirements for lightweight technology, there is an urgent need to improve the strength of wheel steel. The wheel steel currently produced mainly has low strength level, high alloy cost, poor performance stability, and the related rolling process used is relatively strict and complex, with extremely high requirements for cooling speed, resulting in greater production difficulties and restricting the production and application of high-strength wheel steel products. In addition, fatigue damage is the main form of wheel damage, of which more than 80% is caused by fatigue damage, so fatigue life is one of the most important performance indicators of wheels.

[0004] Therefore, developing and designing a new method for preparing wheel steel and wheel steel, improving the strength of wheel steel, and reducing structural defects, thereby increasing fatigue life are issues that urgently need to be addressed 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 method for preparing 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: 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 process includes rough rolling and finish rolling, and the final rolling temperature of the rough rolling is greater than the start rolling temperature of the finish rolling; Cooling the hot-rolled plate to a first temperature at a first cooling rate to obtain a first steel plate; Cooling the first steel plate to a second temperature at a second cooling rate to obtain a second steel plate; 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; 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.

[0007] Furthermore, in the step of subjecting the initial steel billet to multiple hot rolling processes to obtain a hot rolled sheet, The initial steel billet is subjected to at least four passes of rough rolling to obtain a hot-rolled intermediate plate, wherein the final rolling temperature of the fourth pass of rough rolling is between 1000° C. and 1040° C., and the starting rolling temperature of the first pass of rough rolling is between 1220° C. and 1280° C.; The hot-rolled intermediate plate is subjected to multiple finish rolling to obtain the hot-rolled plate.

[0008] Furthermore, 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, 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%.

[0009] Furthermore, in the step of rough rolling the initial steel billet for at least 4 passes, The method also includes subjecting the initial steel billet to a high-pressure water dephosphorization treatment before the first two rough rolling passes.

[0010] Further, 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. 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. 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.

[0011] Furthermore, 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%; The pretreated molten iron is subjected to converter smelting treatment to obtain primary molten steel; The primary molten steel is refined in an LF ladle furnace to obtain refined molten steel; The refined molten steel is continuously cast to obtain the initial steel billet.

[0012] Furthermore, 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; 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 billet is drawn and straightened and then cut into blocks to obtain the initial billet, wherein, during the process of drawing and straightening the intermediate billet, the solidification 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.

[0013] Furthermore, in the step of pickling and leveling the first steel coil, the leveling reduction rate is between 1.5% and 2.5%. As a second aspect of the present application, a high-strength wheel steel is disclosed, which is prepared by the above-mentioned preparation method.

[0014] 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.

[0015] 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 plus Al composition, and the tensile strength is significantly improved through low C rare earth microalloying, and the composite addition of Ti, Nb, V and other elements, and 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, which solves the problems of low tensile strength, insufficient elongation, high yield strength ratio, and excessively high cracking rate of traditional wheel steel. 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, most of which are below 5μm in size, and purifying the steel quality. And strictly control the N content to be less than 0.0016%, compositely add Ti, Nb, V and other elements, increase the Ti content in the steel, and add a small amount of Nb and V elements, while reducing the alloy cost, improving the strength of the steel plate. Microalloying Ti elements have the advantages of large reserves, low prices and significant strengthening effects, but their advantages are limited by the fact that their large TiN particles, which are difficult to control, deteriorate the plastic toughness and fatigue properties due to liquid precipitation. By adding rare earth element Y to refine and modify inclusions, deeply purify molten steel and refine grains, rare earth microalloying technology based on coordinated control of cost and performance is realized, which significantly improves the plastic toughness and fatigue life of wheel steel. Combined with process optimization, the solid solution precipitation behavior of nanoscale 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 a 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 nanoscale 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

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative work.

[0017] Figure 1 This is a flow chart of an implementation method of the method for preparing high-strength wheel steel provided by the present invention; Figure 2 It is a flow chart of an implementation method of the method for preparing high-strength wheel steel provided by the present invention. DETAILED DESCRIPTION

[0018] Embodiments of the present invention are described in detail below, 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 with the same or similar functions. The embodiments in the implementation manner are intended to be used to explain the present invention and should not be construed as limiting the present invention.

[0019] References to "one embodiment" or "example" or "example" in this specification mean that a particular feature, structure, or characteristic described in conjunction with the embodiment itself may be included in at least one embodiment disclosed herein. The appearance of the phrase "in one embodiment" in various places in the specification does not necessarily refer to the same embodiment.

[0020] Automobile wheels are important safety components in the automobile driving system, playing the role of load-bearing, steering, driving, etc., and their lightweight energy-saving effect is remarkable. Therefore, under the increasingly stringent standards such as "energy saving, low emissions, high safety and long life", it is urgent to develop economical and high-performance lightweight wheel steel to achieve lightweight. At present, the tensile strength of steel wheel materials on the market is mainly between 300 and 600 MPa, such as the common 380CL, 420CL, 540CL, 330 / 580DP and other wheel steel materials. At the same time, wheel steel products also have a series of problems such as low strength and heavy weight, easy cracking during forming and welding, resulting in high product scrap rate, and unsatisfactory fatigue performance. In the related art, some wheel steels and their production methods have been published. Some of them are produced by strict controlled rolling and controlled cooling process, using the deformation of the austenite non-recrystallization zone and the strain-induced ferrite phase transformation mechanism to achieve low-temperature large reduction and multi-pass deformation near the Ar3 temperature to produce ferrite + pearlite structure 490MPa grade fine-grained wheel steel. The patent has low strength and cannot meet the wheel parts with high strength performance requirements. The other part is to strictly control the temperature and cooling rate during the rolling process, and use ultra-fast cooling in the laminar cooling stage to reduce the Ar3 temperature, increase the number of phase transformation cores, and inhibit the growth of grains after phase transformation, thereby refining the ferrite grains and producing wheel steel with excellent welding performance. Although this patent can produce thicker wheel steel, the tensile strength is 470~630MPa, which still cannot meet the requirements of lightweight wheel steel. At the same time, the rolling process it adopts is relatively strict and complex, and the cooling rate requirements are extremely high, which makes production more difficult.

[0021] With the increase in lightweight technology requirements, there is an urgent need to improve the strength of wheel steel. The main problems of the 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 damage is the main form of wheel damage, of which more than 80% is caused by fatigue damage, so 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.

[0022] As a first aspect of the present invention, a method for preparing high-strength wheel steel is provided, such as Figure 1 As shown, including: S100, providing an initial steel billet, 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.; S110, performing multiple hot rolling treatments on the initial steel billet to obtain a hot rolled plate, wherein the hot rolling treatment includes rough rolling and finish rolling, and the final rolling temperature of the rough rolling is greater than the start rolling temperature of the finish rolling; S120, cooling the hot-rolled plate to a first temperature at a first cooling rate to obtain a first steel plate; S130, cooling the first steel plate to a second temperature at a second cooling rate to obtain a second steel plate; 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; S150, coiling the first steel plate to obtain a first steel coil; S160, performing pickling and leveling treatment on the first steel coil to obtain high-strength wheel steel.

[0023] 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, for example.

[0024] In some embodiments, the initial steel billet is prepared by smelting molten steel, specifically, Figure 2 As shown, before providing the initial steel billet, the preparation method further includes: S010, the initial molten iron is pretreated to remove impurities to obtain pretreated molten iron, which can be pretreated by KR method for molten iron desulfurization, which refers to immersing a cross-shaped stirring head that is cast with refractory materials and baked into a certain depth of the molten iron pool, and using the vortex generated by its rotation, a weighed desulfurizer is added to the surface of the molten iron from a feeder, and is drawn into the molten iron by the vortex to make the calcium oxide-based desulfurization powder 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 technology. It can reduce the coke ratio of continuous steel casting and improve productivity, reduce the lime consumption and slag amount of steelmaking, etc., thereby reducing production costs; S020, subjecting the pretreated molten iron to converter smelting treatment to obtain primary molten steel. The converter refers to a process in which the pretreated molten iron is used as raw material in the converter, and high-pressure air or oxygen is blown into the converter from the top, bottom, and side of the converter to oxidize and remove impurities in the pretreated molten iron in the furnace, mainly decarburizing, dephosphorizing, desulfurizing, deoxidizing, removing harmful gases and non-metallic inclusions, increasing the temperature and adjusting the composition, and ensuring that the sulfur content of the pretreated molten iron is not higher than 0.002% before entering the converter; S030, refining the primary molten steel by using an LF ladle furnace to obtain refined molten steel, and transferring the primary molten steel obtained by the converter smelting into an LF furnace for refining, and using multiple electrodes for submerged arc heating. On the one hand, high-basicity reducing slag can be produced by electrode heating to purify the molten steel; on the other hand, the LF furnace can further deoxidize and desulfurize, adjust the composition of the molten steel, and blow argon inert gas into the bottom of the LF furnace to stir the molten steel to make the temperature of the molten steel uniform; S040, continuously casting the refined molten steel to obtain an initial steel billet. Specifically, in the step of continuously casting the refined molten steel, First, the refined molten steel passes through the tundish, and the tundish then injects the molten steel into each crystallizer through the water inlet for the first cooling treatment to obtain the initial ingot. The superheat of the molten steel in the continuous casting tundish is 10~25℃. The crystallizer is the core component of continuous casting. It consists of a metal shell with cooling water continuously flowing inside. This crystallizer that continuously supplies cooling water will initially solidify the liquid molten steel in contact with it to obtain the initial ingot with a solidified shell on the outside and molten steel in the core.

[0025] The initial ingot in the crystallizer is pulled into the casting channel by the straightening machine for the second cooling treatment (also called the second cooling zone) to obtain the intermediate ingot. The role 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. Among them, 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 improve product quality. As a preferred embodiment, the frequency of electromagnetic stirring is between 5.0HZ and 8.0HZ. The role of electromagnetic stirring in the second cooling zone is to break up the dendrite bridge in the liquid core cavity, eliminate the looseness and shrinkage cavity in the center of the ingot, and the broken dendrite crystals serve as equiaxed crystal cores to expand the equiaxed crystal area in the center of the ingot, eliminate the center segregation, and promote the floating of inclusions in the liquid phase cavity of the ingot, and reduce the accumulation of inner arc inclusions.

[0026] The intermediate ingot is further drawn and straightened and then cut into blocks to obtain an initial steel billet. In the process of drawing and straightening the intermediate ingot, 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 pressure-solid phase ratio is between 0.4 and 1.0, which reduces component segregation and inhibits the size and number of large TiN particles precipitated during solidification.

[0027] In step S110, in the step of performing multiple hot rolling processes on the initial steel billet to obtain a hot rolled sheet, The initial steel billet is subjected to at least 4 passes of rough rolling to obtain a hot-rolled intermediate plate. In some embodiments, the rough rolling adopts a 1+3 pass distribution mode, that is, two rough rolling mills R1 and R2 are used, R1 is used for the first rough rolling, and then R2 is used for 3 rough rollings. Reasonable rough rolling load distribution can make production more stable, control accuracy more precise, increase the service life of the rolling mill, and improve production efficiency. It can also achieve the effect of reducing heat loss of the slab and saving energy. Among them, the final rolling temperature of the fourth pass of rough rolling is between 1000℃ and 1040℃, and the starting rolling temperature of the first pass of rough rolling is between 1220℃ and 1280℃.

[0028] In some embodiments, in the step of performing at least 4 rough rolling passes on the initial steel billet, the initial steel billet is further subjected to high-pressure water dephosphorization treatment before the first two rough rolling passes. Specifically, a high-pressure water descaling treatment is performed once before the start of the above-mentioned rough rolling R1 and the rough rolling R2. High-pressure water descaling removes iron oxide scale to prevent defects caused by pressing into the surface, thereby improving the surface quality of the product.

[0029] After the above-mentioned rough rolling is completed, the hot-rolled intermediate plate is subjected to multiple finishing rolling to obtain a hot-rolled plate. Rough rolling usually has a larger roll diameter and a lower rolling speed to provide a larger rolling force and a higher rolling pressure. The width of the slab is accurately adjusted by the rough rolling vertical width to provide a hot-rolled intermediate plate with a good version, a flat surface and a uniform width for finishing rolling. Finishing rolling is used to roll the rough-rolled intermediate plate into a product with a smooth surface, uniform thickness and good performance. Finishing rolling adopts a continuous rolling process, usually 7-stand continuous rolling. Specifically, the hot-rolled intermediate plate is subjected to multi-stand finishing rolling to a set thickness to obtain a hot-rolled plate. The start rolling temperature of the finishing rolling is between 930°C and 960°C, the final rolling temperature of the finishing rolling is between 840°C and 860°C, and the reduction rate of each of the last two passes is between 13% and 22%.

[0030] 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, and then 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, and then the second steel plate is 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 cooling is carried out in a segmented cooling mode of fast cooling-slow cooling-fast cooling. By controlling the cooling rate and coiling temperature, the microstructure of the steel plate is controlled to promote the sufficient precipitation of Ti, Nb, and V elements, and avoid the ripening and growth of the precipitated second phase particles, 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 less than 10nm accounts for more than 85%, thereby maximizing the precipitation strengthening effect of micro-alloying elements and improving strength and plasticity.

[0031] In step S160, the first steel coil is pickled and flattened to obtain high-strength wheel steel, wherein the flattening reduction rate is between 1.5% and 2.5%.

[0032] The thickness of the steel plate finally obtained is 4mm~16mm. After adding rare earth element Y to the steel, the harmful inclusions in the steel are modified and refined, reducing the impact on the plastic toughness and fatigue performance of the wheel steel. The microstructure of the steel plate is uniformly refined polygonal ferrite, acicular ferrite, bainite and nano-scale precipitation phase, which fully exerts the fine grain strengthening and precipitation strengthening effect of nano-scale second phase particles, significantly improving the strength and forming performance of the wheel steel, with tensile strength ≥670MPa, elongation A50 ≥24%, hole expansion rate ≥75%, yield strength ratio ≤0.86, and excellent fatigue performance, meeting the use requirements of more than 1 million times of wheel fatigue life. The product has low alloy cost, stable mechanical properties, excellent strength and plasticity matching, high hole expansion rate and fatigue resistance, can significantly improve the forming performance and product qualification rate, and has obvious advantages over traditional wheel steel.

[0033] As a second aspect of the present application, a high-strength wheel steel is disclosed, which is prepared by the above-mentioned 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 rate 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.

[0034] The present invention uses rare earth microalloying and strictly controls the N content in the steel to be less than 0.0016%, and the harmful inclusions in the steel are modified and refined, thereby reducing the impact on the plastic toughness and fatigue performance of the wheel steel. The composite addition of Ti, Nb, V and other elements controls the microstructure of the wheel steel to be uniformly refined polygonal ferrite, acicular ferrite, bainite and nano-scale precipitation phase through process optimization, fully exerts the fine grain strengthening and precipitation strengthening effects of nano-scale second phase particles, and significantly improves the strength and forming performance 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 requirements of more than 1 million times of wheel fatigue life. The product has low alloy cost, stable mechanical properties, excellent strength and plasticity matching, a high hole expansion rate and fatigue resistance, can significantly improve the forming performance, and improve the product qualification rate, and has obvious advantages over traditional wheel steel.

[0035] (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 through low C addition of rare earth microalloying 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, which solves the problems of low tensile strength, insufficient elongation, high yield strength ratio, and excessively high cracking rate in complex forming of traditional wheel steel.

[0036] (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 5 μm, thereby purifying the steel quality. The N 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 and add a small amount of Nb and V elements, thereby reducing the alloy cost and improving the strength of the steel plate. Microalloying Ti elements have the advantages of large reserves, low prices and significant strengthening effects, but their 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.

[0037] By adding rare earth element Y to refine and modify inclusions, deeply purify molten steel and refine grains, rare earth microalloying technology based on cost and performance synergistic control 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 products, improve product qualification rate, and meet current market demand.

[0038] (3) In the hot rolling process, the present invention adopts a relatively low final rolling temperature and a large deformation control in the last two passes. Through a segmented cooling mode of rapid cooling-slow cooling-rapid cooling, the coiling temperature is set to 450-470°C, thereby achieving the refinement and homogenization control of multiphase structures such as polygonal ferrite, acicular ferrite, bainite and nanoscale precipitation phases. Due to the relatively low coiling temperature, the difference in cooling rate of different parts of the steel coil is reduced, and the mechanical property stability of the product is improved.

[0039] The functions of each element and main process in the present invention are as follows: C: The most basic strengthening element, plays an important role in improving the strength of materials. However, when the C content in steel is too high, the plasticity of the steel will decrease and the welding performance will deteriorate, so the carbon content in steel should be reasonably controlled.

[0040] Mn: It is an important alloying element in high-strength steel and a typical austenite stabilizing element. It can effectively inhibit the austenite recrystallization process and play a role in solid solution strengthening and refining ferrite grains. However, too high a Mn content will lead to severe central segregation and banded structure, which needs to be coordinated with other elements and processes. The present invention selects a Mn content of 1.60% to 1.80%.

[0041] Si: Si can significantly improve the strength and hardness of steel, while enhancing corrosion resistance and high-temperature oxidation resistance, but Si can also reduce the welding performance of steel. Too high Si content will affect the surface quality and coating performance, so the Si content is strictly limited. Therefore, the present invention controls the Si content to ≤0.03%.

[0042] 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 quality of ingot smelting, 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%.

[0043] Ti, Nb, and V elements: Ti, Nb, and V form nano-sized carbonitrides with C and N elements in steel and precipitate evenly dispersed in the matrix, which plays a role in grain refinement and precipitation strengthening, and significantly improves the strength.

[0044] 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%.

[0045] P: It is an impurity element in steel and needs to be strictly controlled, with a requirement of ≤0.008%.

[0046] S: It is an impurity element in steel and needs to be strictly controlled, with a requirement of ≤0.002%.

[0047] The present invention provides a method for preparing rare earth microalloyed thick-gauge high-strength wheel steel with excellent fatigue performance. Rare earth elements are added to refine and modify inclusions, deeply purify molten steel and refine grains, thereby realizing a rare earth microalloying technology based on coordinated control of cost and performance.

[0048] The present invention will be further described below through specific examples and comparative examples.

[0049] Example Example 1 This embodiment provides a method for preparing high-strength wheel steel, comprising: 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%; Step 2, subjecting the pretreated molten iron to converter smelting to obtain primary molten steel; Step 3, refining the primary molten steel in a LF ladle furnace to obtain refined molten steel; 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, and the superheat of the molten steel in the tundish is 10-25° 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 also 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 solidification end of the intermediate cast billet is pressed down, the pressing amount is between 5 mm and 12 mm, and the pressed down solid phase ratio is between 0.4 and 1.0; Step 4, performing multiple hot rolling treatments on the initial steel billet to obtain a hot rolled plate, wherein the hot rolling treatment includes rough rolling and finish rolling, wherein the final rolling temperature of the rough rolling is greater than the start rolling temperature of the warm rolling, wherein the composition of the initial steel billet is shown in Table 1 below; The initial steel billet is subjected to 1+3 passes of rough rolling by using R1 and R2 rough rolling mills to obtain a hot rolled intermediate plate, wherein the final rolling temperature of the fourth pass of rough rolling is between 1000° C. and 1040° C., the starting rolling temperature of the first pass of rough rolling is between 1220° C. and 1280° C., and high pressure water descaling treatment is performed once before the start of rough rolling R1 and rough rolling R2 respectively; 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%; Step 5, cooling the hot-rolled plate to a first temperature at a first cooling rate to obtain a first steel plate; cooling the first steel plate to a second temperature at a second cooling rate to obtain a second steel plate; 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 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 Step 6, coiling the third steel plate to obtain a first steel coil; Step 7: Pickling and leveling the first steel coil to obtain high-strength wheel steel with a steel plate thickness of 4 mm to 16 mm, wherein the leveling reduction rate is between 1.5% and 2.5%.

[0050] Example 2 The high-strength wheel steel was prepared by 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 curling temperature are different, see Table 2.

[0051] Example 3 The high-strength wheel steel was prepared by 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 curling temperature are different, see Table 2.

[0052] Example 4 The high-strength wheel steel was prepared by 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 curling temperature are different, see Table 2.

[0053] Table 1 Chemical composition of specific examples 1 to 4 (wt.%)

[0054] Table 2 Main process parameters of example steel

[0055] Test Case Mechanical properties tests were performed on Examples 1 to 4, and the results are shown in Table 3.

[0056] Table 3 Mechanical properties of example steel

[0057] As shown in Table 3, the mechanical properties of the steel in this embodiment show that the embodiment of the present invention has good comprehensive mechanical properties, high strength, and stable mechanical properties. While meeting the strength index, the embodiment of the present invention has a yield strength ratio of ≤0.86, and has good elongation and hole expansion rate, with an elongation of more than 24% and a hole expansion rate of ≥75%, which is much higher than the mechanical property index of traditional high-strength steel, improves the forming performance, solves the problems of low tensile strength, insufficient elongation, high yield strength ratio, and excessively high cracking rate of complex forming of traditional wheel steel, and greatly improves the product qualification rate and scope of application. The alloy of the present invention has low cost, excellent surface quality, wide production process window, and strong flexibility in process parameter control. It is suitable for large-scale industrial production of traditional hot rolling production lines and has good promotion and applicability.

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope 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 process includes rough rolling and finish rolling, and the final rolling temperature of the rough rolling is greater than the start rolling temperature of the finish rolling; Cooling the hot-rolled plate to a first temperature at a first cooling rate to obtain a first steel plate; Cooling the first steel plate to a second temperature at a second cooling rate to obtain a second steel plate; 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; 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 subjecting the initial steel billet to multiple hot rolling treatments to obtain a hot rolled sheet, The initial steel billet is subjected to at least four passes of rough rolling to obtain a hot-rolled intermediate plate, wherein the final rolling temperature of the fourth pass of rough rolling is between 1000° C. and 1040° C., and the starting rolling temperature of the first pass of rough rolling is between 1220° C. and 1280° C.; The hot-rolled intermediate plate is subjected to multiple finish rolling 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, 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%.

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

5. The preparation method according to claim 1, characterized in that: In the step of cooling the hot-rolled plate 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, 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. 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.

6. The preparation method according to any one of claims 1 to 5, 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%; The pretreated molten iron is subjected to converter smelting treatment to obtain primary molten steel; The primary molten steel is refined in an LF ladle furnace to obtain refined molten steel; The refined molten steel is continuously cast to obtain the initial steel billet.

7. The preparation method according to claim 6, 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; 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 billet is drawn and straightened and then cut into blocks to obtain the initial billet, wherein, during the process of drawing and straightening the intermediate billet, the solidification 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.

8. The preparation method according to any one of claims 1 to 5, characterized in that: In the step of pickling and leveling the first steel coil, the leveling reduction rate is between 1.5% and 2.5%.

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

10. The high-strength wheel steel according to claim 9, 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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