Low-cost 380mpa grade hot-rolled wheel steel and method for producing the same

Abstract

The application discloses a low-cost 380MPa-grade hot-rolled wheel steel and a preparation method thereof, and belongs to the field of materials and metallurgy technology. The low-cost 380MPa-grade hot-rolled wheel steel comprises the following components in percentage by weight: C: 0.09%-0.15%, Si: 0.06%-0.09%, Mn: 0.65%-0.75%, P: 0.020% or less, S: 0.015% or less, Al: 0.019%-0.035%, N: 0.0033%-0.0053%, and the balance of Fe and inevitable impurities, and 0.21<= (C+Mn / 6) <=0.26. The low-cost 380MPa-grade wheel steel plate with a thickness of 10-25mm is realized, and the low-cost 380MPa-grade wheel steel plate has the characteristics of excellent low-temperature toughness, high surface quality, low cost, high strength and toughness and the like, solves the problems of high alloy cost and the like, and guarantees the service safety of the wheel steel plate.

Description

Technical Field

[0001] This invention relates to the fields of materials and metallurgy, and more specifically, to a low-cost 380MPa grade hot-rolled wheel steel and its preparation method. Background Technology

[0002] Wheels are crucial safety components for automobiles. Steel wheel assemblies are produced through a series of rigorous manufacturing processes, including rolling or spinning, welding, and painting, resulting in high precision, light weight, long fatigue life, and reliable safety. The hot-rolled steel plates used to manufacture wheels require high strength, toughness, and plasticity, as well as high fatigue resistance, impact resistance, and surface quality. Currently, the use of high-strength wheel steel (500MPa and above) is relatively limited; hot-rolled steel plates with tensile strength below 500MPa remain the mainstream material for automobile wheel manufacturing. The most prevalent wheel steel, with a tensile strength of 380MPa, typically employs a low-carbon, low-manganese composition. To ensure a low yield strength ratio and high plasticity, steel mills add expensive alloying elements such as niobium and chromium to increase strength, but this is somewhat excessive for wheel steel, leading to high costs and poor market competitiveness.

[0003] Faced with the severe market situation in the steel industry, it is crucial to reduce the manufacturing cost of 380MPa grade wheel steel while ensuring product quality and maximizing production line capacity. Under the premise of ensuring production and equipment safety, the ultimate goal is to achieve maximum efficiency and minimum energy and alloy cost consumption while meeting the technical requirements of steel plate performance. Therefore, developing a low-cost, high-strength and high-toughness 380MPa grade wheel steel is essential for steel mills to improve profitability. Currently, to ensure the low-temperature toughness of 380MPa grade wheel steel, higher alloy compositions (Mn, Nb, etc.) are typically used, a thicker intermediate billet is maintained for heating, and a two-stage or even three-stage controlled rolling process is employed. This results in the final rolling temperature of the steel plate potentially being controlled below 800℃, or even lower, significantly increasing the rolling difficulty. Firstly, mill load, steel plate temperature uniformity, and plate shape control all face severe challenges. Secondly, improving steel plate performance mainly depends on the content of impurities such as phosphorus and sulfur, the content of alloying elements, and the control of key process parameters in smelting and rolling. Therefore, the key to developing low-cost 380MPa grade wheel steel lies in how to organically combine phase transformation strengthening, solid solution strengthening, and grain refinement strengthening to solve the problems existing in the production of 380MPa grade wheel steel, reduce alloy costs, improve market competitiveness, and at the same time ensure its excellent strength and toughness.

[0004] To date, there are very few reports, both domestically and internationally, on the manufacturing of low-cost 380MPa grade hot-rolled wheel steel and its manufacturing methods. Chinese patent application number 201010183475.0 discloses a high-strength automotive wheel steel and its manufacturing method, whose main components include: C 0.07–0.12%, Si 0.01–0.1%, Mn 1.0–1.2%, P 0.008–0.015%, S≤0.006%, and Alt 0.020–0.040%. However, this patent has low production efficiency and does not clearly define its low-temperature impact performance. The paper "The Role of Titanium in Automotive Wheel Steel and Discussion on Alloying Process" analyzes the influence of titanium on the mechanical properties of automotive wheel steel plates through titanium microalloying experiments and production practice, and analyzes the titanium microalloying process and its existing problems. Experimental results show that titanium microalloying not only refines grains but also combines with sulfur in steel to form Ti₄C₂S₂ inclusions, altering the morphology of these inclusions and improving the elongation flange properties of the steel plate. When the Ti / S ratio in the steel is 2–3, the elongation flange performance is significantly improved. Adding 0.05%–0.12% titanium is sufficient to meet the mechanical property requirements of automotive wheel steel. However, Ti is a valuable element, which obviously increases manufacturing costs.

[0005] The above-mentioned materials have high production costs, making them unsuitable for producing low-cost, high-strength, and high-toughness 380MPa grade wheel steel. Therefore, it is urgent to design a low-cost hot-rolled wheel steel with a thickness of 10-25mm and a tensile strength of 380MPa, and to develop its production method. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned defects in the prior art and provide a low-cost 380MPa grade hot-rolled wheel steel and its preparation method. This invention enables the production of 10-25mm thick, low-cost 380MPa grade wheel steel plates using continuously cast billets with a thickness of 170-230mm. The steel plates have excellent low-temperature toughness, high surface quality, low cost, and high strength and toughness, solving the problem of high alloy cost and ensuring the service safety of wheel steel plates.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A low-cost 380MPa grade hot-rolled wheel steel comprises the following components by weight percentage: C: 0.09%–0.15%, Si: 0.06%–0.09%, Mn: 0.65%–0.75%, P≤0.020%, S≤0.015%, Al: 0.019%–0.035%, N: 0.0033%–0.0053%, with the balance being Fe and unavoidable impurities, and 0.21≤(C+Mn / 6)≤0.26.

[0009] Optionally, the hot-rolled wheel steel has a transverse tensile yield strength of 300-330 MPa, a tensile strength of 380-410 MPa, an elongation of ≥28%, a transverse Charpy impact energy of ≥150 J at -20℃, and a yield strength ratio of ≤0.85.

[0010] Optionally, the thickness of the hot-rolled wheel steel is 10~25mm.

[0011] This invention also discloses a method for preparing low-cost 380MPa grade hot-rolled wheel steel as described above, comprising the following steps: steelmaking, LF refining, RH vacuum degassing, continuous casting, billet heating, rolling, controlled cooling and coiling;

[0012] In the continuous casting process: the superheat is 7-11℃, and the casting speed is 0.7-1.0m / min; in the fan-shaped section, strong cooling is used, with a total cooling water volume of 1500-2000L / min for the first half (sections 1-4) and 1300-1800L / min for the second half (sections 5-8); at the same time, light reduction is applied at the end of solidification, with a reduction of 7-12mm for the continuous casting billet.

[0013] In the billet heating process: the billet is passed through a preheating section, a heating section, and a soaking section in sequence before being taken out of the furnace; wherein, the temperature range of the preheating section is 300-550℃, the temperature range of the heating section is 1235-1260℃, and the temperature range of the soaking section is 1100-1130℃; the time in the heating and soaking sections is 2.5-3.3 hours, ensuring that the temperature difference between the upper and lower surfaces of the billet is ≤15℃, and the soaking section time is 0.5-1.0 hours;

[0014] In the rolling process: during the roughing stage, the reduction rate of each of the first two passes is greater than 30%, and the mill is sprayed with descaling water during the first two passes for 0.5–1 min at a pressure of 20–25 MPa. The total reduction rate during the roughing stage is controlled at 75%–85%. After the roughing stage, the finishing stage is carried out directly, with a finishing temperature of 840–870℃. The total reduction rate during the finishing stage is >70%, of which the reduction rate of the last two stands is >15%.

[0015] In the controlled cooling and winding process: laminar flow cooling is adopted, with an initial cooling temperature range of 730-760℃ and a final cooling winding temperature range of 510-530℃. The cooling rate is controlled at 30-45℃ / s. The initial running speed for the first 10-60m of the head and tail sections is 1.2-1.3 times the normal roller conveyor running speed, which is 1.2-1.5m / s. The initial running speed for the first 10-60m of the head and tail sections is 1.44-1.95m / s, with a head and tail occlusion value of 200-500mm, which is maintained for 1-2s. Then, the roller conveyor running speed returns to the normal roller conveyor running speed.

[0016] Optionally, during the rolling process: before the start of rolling, the billet after exiting the furnace is descaled with high-pressure water for 1-2 minutes, with a descaling machine pressure of 20-25 MPa; and the roughing rolling passes 4-5 times.

[0017] Optionally, in the steel smelting process: the smelting raw materials are configured according to the chemical composition, and the S content is controlled to be ≤0.015% after KR hot metal pretreatment. After slag removal, the steel enters the converter. In the converter smelting process, the P content is controlled to be ≤0.02% by using the double slag method. At the end of the converter smelting process, the C content is controlled to be 0.09% to 0.15%. Argon gas is blown for 10 to 25 minutes when tapping the steel.

[0018] Optionally, in the LF refining and RH vacuum degassing: the molten steel after smelting is subjected to LF refining and RH vacuum degassing, and the RH vacuum is maintained for 20~30 minutes.

[0019] Optionally, in the controlled cooling and winding process: the number of controlled cooling manifold opening groups is 3 to 5, and the water flow rate of a single manifold is 200 to 250 m³. 3 / h.

[0020] Optionally, during the heating of the billet, the thickness of the billet is 170~230mm.

[0021] Implementing the embodiments of the present invention will have the following beneficial effects:

[0022] 1. Steelmaking employs KR hot metal pretreatment for deep desulfurization followed by thorough slag removal. The converter utilizes a double-slag method for P removal, resulting in lower P and S content in the cast billet. Controlling the argon blowing time and maintaining RH vacuum degassing time overcomes defects such as center segregation, inclusions, and excessive H and O content in the cast billet caused by high Mn and C content, thus improving the plasticity and toughness of the steel plate. Reducing superheat and continuous casting speed improves macroscopic segregation in the continuously cast billet, decreases the spacing of secondary dendrite arms in the solidification structure, and helps reduce billet segregation and internal structural defects. Strong cooling is used in the fan-shaped section to maintain the temperature gradient along the billet thickness, while light pressure promotes core grain breakage, ensuring the strength and toughness of the subsequent steel plate.

[0023] 2. Heating the billet during continuous casting: The temperature and time of the billet in the preheating, heating, and soaking zones are limited to ensure sufficient diffusion of elements and reduce the impact of compositional segregation on the microstructure and properties. At the same time, the heating zone provides high-temperature heating to ensure temperature uniformity in all parts of the billet and improve the uniformity of transverse and longitudinal metal flow on the steel plate surface. In combination with the billet composition, the heating temperature of the soaking zone is reduced to decrease energy consumption. The temperature and time of the heating and soaking zones are controlled to inhibit excessive growth of the original austenite grains and increase the contribution of fine grain strengthening to the strength of the steel plate. In addition, the soaking zone adopts low-temperature heating to avoid the need for the steel plate to wait for heating during the second stage of rolling.

[0024] 3. This invention features a rationally designed chemical composition, reducing the amount of alloy added. It replaces precipitation strengthening with fine-grain strengthening, eliminates the addition of expensive alloying elements, and employs a low-temperature heating + hot rolling manufacturing mode. This significantly reduces alloy costs and the resistance to high-temperature deformation during roughing and finishing rolling, facilitating higher reduction per pass and ensuring the overall performance of the high-strength steel plate. By maximizing the mill's capacity in the first two passes of the roughing stage with a high reduction rate, it promotes dynamic recrystallization of austenite, refining the original austenite grains. High-pressure water descaling in the mill creates a temperature gradient from the steel plate surface to the core, promoting core deformation and uniform microstructure distribution during subsequent finishing rolling, thus improving the steel plate's strength and toughness. Furthermore, the low-temperature heating process eliminates the need for intermediate billet warming in the finishing stage, ensuring that the last two stands of finishing rolling are within the austenite non-recrystallization temperature range. This allows for a high reduction rate in the last two stands, further refining the austenite grains and improving the steel plate's performance.

[0025] 4. Control the initial cooling temperature to ensure the steel plate's microstructure upon entering the water is austenitic + ferrite. During cooling, control the cooling rate and final cooling temperature to avoid ferrite volume expansion or martensitic transformation due to uneven cooling, which can affect the steel plate's toughness and cause "edge waviness" defects. To achieve temperature uniformity control along the steel plate's length, samples are divided into groups every 0.1–0.2 m from the head. Based on this, various models (temperature, flow rate, etc.) perform speed optimization calculations for each sample interval. The control model obtains the optimal operating speed trend for each sample based on the steel plate's longitudinal temperature measurement, the target final cooling temperature process requirements, and the head and tail shielding value calculation formula (head and tail shielding value = HMI interface set shielding distance - shielding time * roller speed). For the low-temperature zones at the head and tail of the steel plate, when the head of the steel plate enters the laminar flow region or the tail leaves the laminar flow region, the roller speed is appropriately increased and the water flow rate at the head and tail positions is controlled according to the thickness group interval to reduce excessive cooling of the steel plate's head and tail by the cooling water, which is beneficial for improving the uniformity of the steel plate's performance.

[0026] This invention reduces alloy costs through simple composition design and achieves low-cost manufacturing of hot-rolled wheel steel plates with a thickness of 10-25mm and a strength of 380MPa by controlling the steelmaking, continuous casting, heating, and rolling cooling processes. It exhibits good low-temperature toughness. Specific properties include: a yield strength of 300-330MPa in the transverse tensile range, a tensile strength of 380-410MPa, a yield-to-tensile ratio ≤0.85, an elongation ≥28%, and a transverse Charpy impact energy ≥150J at -20℃. Detailed Implementation

[0027] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0028] This invention discloses a low-cost 380MPa grade hot-rolled wheel steel, comprising the following components by weight percentage: C: 0.09%–0.15%, Si: 0.06%–0.09%, Mn: 0.65%–0.75%, P≤0.020%, S≤0.015%, Al: 0.019%–0.035%, N: 0.0033%–0.0053%, with the balance being Fe and unavoidable impurities, and 0.21≤(C+Mn / 6)≤0.26.

[0029] Specifically, the roles of the main elements in the chemical composition of the steel plate of this invention are as follows:

[0030] Carbon (C): The most economical and fundamental strengthening element in steel. It has a significant effect on improving the strength of steel through solid solution strengthening and precipitation strengthening. However, increasing the C content has a negative impact on the plasticity, toughness, and weldability of steel. Therefore, this invention sets the C content range to 0.09% to 0.15%.

[0031] Mn: Mn strengthens steel through solid solution treatment, compensating for the strength loss caused by reduced carbon content. Furthermore, it lowers the γ-α phase transformation temperature, refining ferrite grains and contributing to finer low-temperature transformation products, thus improving toughness. However, increasing Mn content exacerbates center segregation and layered martensite formation in continuously cast billets, hindering low-temperature toughness and affecting the expansion properties of the steel plate. Therefore, the Mn content range in this invention is designed to be 0.65%–0.75%.

[0032] Si (Si) plays a role in deoxidation in steelmaking and improving the strength of the matrix. However, excessive Si will reduce the toughness of the heat-affected zone in the base metal. Increasing the Si content can purify ferrite and reduce the content of pearlite, which is beneficial for reducing the Bauschinger effect in the matrix material. Therefore, the Si content is set to 0.06% to 0.09% in this invention.

[0033] N: In steel, the element N has no other significant role besides forming fine NbN particles to refine the austenite grains. Therefore, it needs to be kept at a low content level. The N content range selected in this invention is 0.0033% to 0.0053%.

[0034] Al: Commonly used as a deoxidizer in steel, it can also refine the microstructure if it forms AlN. When the Al content exceeds 0.035%, excessive alumina inclusions will reduce the cleanliness of the steel. If the Al content is too low, deoxidation will be insufficient; therefore, the lower limit for Al content is set at 0.019%.

[0035] P and S are unavoidable impurity elements in steel, and their content should be as low as possible. However, due to considerations of smelting costs and processes, their levels cannot be infinitely low. Therefore, this invention sets the upper limits for P and S content at 0.020% and 0.015%, respectively.

[0036] This invention further controls the content of C+Mn / 6 to 0.21≤(C+Mn / 6)≤0.26, ensuring good weldability of the wheel steel, relatively low hardness in the heat-affected zone, and a low probability of welding cracks. Outside this range, welding cracks will occur, further affecting the weldability of the wheel steel.

[0037] In one specific embodiment, the yield strength of the hot-rolled wheel steel in the transverse tensile test is 300-330 MPa, the tensile strength is 380-410 MPa, the elongation is ≥28%, the transverse Charpy impact energy at -20℃ is ≥150 J, and the yield strength ratio is ≤0.85.

[0038] In one specific embodiment, the thickness of the hot-rolled wheel steel is 10~25mm.

[0039] This invention also discloses a method for preparing low-cost 380MPa grade hot-rolled wheel steel as described above, comprising the following steps: steelmaking, LF refining, RH vacuum degassing, continuous casting, billet heating, rolling, controlled cooling, and coiling.

[0040] S1. In steelmaking: Smelting raw materials are prepared according to chemical composition. After KR hot metal pretreatment, the sulfur (S) content is controlled to be ≤0.015%. After slag removal, the steel enters the converter. In converter smelting, a double-slag method is used to remove phosphorus (P), controlling the P content to be ≤0.02%. At the end of converter smelting, the carbon (C) content is controlled to be 0.09%–0.15%. Argon gas is blown for 10–25 minutes during tapping. Argon blowing and calming before continuous casting promotes the removal of inclusions in the molten steel and improves the uniformity of the steel composition.

[0041] In S2, LF refining and RH vacuum degassing: the molten steel after smelting is subjected to LF refining and RH vacuum degassing, and the RH vacuum is maintained for 20~30 minutes.

[0042] S3. In continuous casting: The superheat is 7–11℃, and the casting speed is 0.7–1.0 m / min. Reducing the superheat and casting speed can improve macroscopic segregation of the billet, reduce the spacing of secondary dendrite arms in the solidification structure, and help reduce billet segregation and internal structural defects. In the fan-shaped section, strong cooling is used. The total cooling water volume in the first half (sections 1-4) is 1500–2000 L / min, and in the second half (sections 5-8) it is 1300–1800 L / min. At the same time, light reduction is applied at the end of solidification, with a billet reduction of 7–12 mm. Strong cooling ensures the temperature gradient in the thickness direction of the billet, and the light reduction helps reduce billet segregation and internal structural defects, while promoting core grain breakage, thus ensuring the strength and toughness of the subsequent steel plate.

[0043] S4. During billet heating: Billets with a thickness of 170~230mm are fed into a walking beam furnace for heating. The billets pass through a preheating section, a heating section, and a soaking section before exiting the furnace. The temperature range of the preheating section is 300~550℃, which promotes the homogenization of the microstructure in the billet and facilitates the full diffusion of elements. The temperature range of the heating section is 1235~1260℃, and the temperature range of the soaking section is 1100~1130℃. The time spent in the heating and soaking sections in the furnace is 2.5~3.3h, ensuring that the temperature difference between the upper and lower surfaces of the billet is ≤15℃, and the soaking section time is 0.5~1.0h. Increasing the heating temperature and extending the furnace time further promotes the diffusion of alloying elements Mn and C, reducing their impact on microstructure and properties due to compositional segregation. Simultaneously, the heating section provides high-temperature heating to ensure temperature uniformity across all parts of the billet, improving the uniformity of transverse and longitudinal metal flow on the steel plate surface. Combined with the billet composition, reducing the heating temperature of the soaking zone decreases energy consumption. Limiting the temperature and time of the heating and soaking zones inhibits excessive growth of the original austenite grains, ensuring that fine-grained strengthening contributes to the steel plate's strength. Furthermore, low-temperature heating in the soaking zone avoids the waiting time required during the finishing rolling stage of the steel plate.

[0044] S5. During rolling: Before the start of rolling, the billet after exiting the furnace is descaled with high-pressure water for 1-2 minutes, with a descaling machine pressure of 20-25 MPa. In the roughing stage, the reduction rate of each of the first two passes is greater than 30%. Descaling water is sprayed onto the mill for 0.5-1 minutes at a pressure of 20-25 MPa in the first two passes. The mill capacity is maximized in the first two passes, with a large reduction rate to promote dynamic austenite recrystallization and refine the original austenite grains. By using high-pressure water descaling, a temperature gradient is created from the surface to the core of the steel plate, which promotes core deformation and uniform microstructure distribution in the subsequent finishing rolling process, improving the strength and toughness of the steel plate. The total reduction rate in the roughing stage is controlled at 75%-85%, with 4-5 roughing passes. After roughing, the finishing stage is carried out directly, with a finishing rolling temperature of 840-870℃. The total reduction rate in the finishing stage is >70%, with a reduction rate of >15% in the last two finishing stands. By adopting a low-temperature heating process, the intermediate billet waiting time in the finishing rolling stage is eliminated, ensuring that the last two stands of finishing rolling are in the austenite non-recrystallization temperature range, and ensuring that the last two stands adopt a large reduction rate, further refining the austenite grains and improving the steel plate performance.

[0045] S6. Controlled cooling and winding: Laminar flow cooling is used, with an initial cooling temperature range of 730–760℃ and a final cooling winding temperature range of 510–530℃. The number of controlled cooling manifold groups is 3–5, and the water flow rate per manifold is 200–250m³. 3The cooling rate is controlled at 30~45℃ / s per hour. The steel plate is divided into samples every 0.1~0.2m from the head. The initial running speed of the steel plate after entering the laminar flow is set according to the thickness of the steel plate at 1 / 30 of the length from the head and tail. The initial running speed at 10~60m from the head and tail is 1.2~1.3 times the normal roller conveyor running speed. The normal roller conveyor running speed is 1.2~1.5m / s. The initial running speed at 10~60m from the head and tail is 1.44~1.95m / s. The head and tail shielding value is 200~500mm and is maintained for 1~2s. Then the roller conveyor running speed is restored to the normal roller conveyor running speed. To ensure the steel plate's microstructure remains austenitic and ferritic upon entering the water cooling process, the cooling rate and final cooling temperature are controlled to suppress martensitic phase formation and prevent surface martensitic transformation from affecting the steel plate's toughness. To achieve temperature uniformity along the steel plate's length, samples are divided into groups of 0.1–0.2 meters from the head. Based on this, various models (temperature, flow rate, etc.) perform speed optimization calculations for each sample group. The control model obtains the optimal operating speed trend for each sample based on the longitudinal temperature measurement of the steel plate, the target final cooling temperature process requirements, and the head and tail shielding value calculation formula (head and tail shielding value = HMI interface set shielding distance - shielding time * roller speed). For the low-temperature zones at the head and tail of the steel plate, when the head enters the laminar flow region or the tail leaves the laminar flow region, the roller speed is appropriately increased and the water flow rate at the head and tail positions is controlled according to the thickness group spacing to reduce over-cooling of the steel plate's head and tail by the cooling water, which helps improve the uniformity of the steel plate's performance.

[0046] The following are specific embodiments.

[0047] Table 1 shows the chemical composition of the steel in the examples; Table 2 shows the smelting process of the steel in the examples; Table 3 shows the heating process of the billet and the high-pressure water descaling process before rolling of the continuously cast billet in the examples; Table 4 shows the rolling parameters of the steel in the examples; Table 5 shows the controlled cooling and coiling process parameters of the steel in the examples; Table 6 shows the performance indicators of the steel plates in the examples.

[0048] Table 1 Chemical composition (wt, %) of embodiments of the present invention

[0049]

[0050] Note: P≤0.02% in steel; S≤0.015%.

[0051] Table 2. Smelting process of steel in the examples

[0052]

[0053] Table 3 Heating regime of steel billets and high-pressure water descaling process before rolling of continuously cast billets in the examples

[0054]

[0055] Table 4 Rolling parameters of the steel in the examples

[0056]

[0057] Table 5. Steel controlled cooling and coiling process parameters in embodiments of the present invention

[0058]

[0059] Table 6 Performance indicators of steel plates in embodiments of the present invention

[0060]

[0061] Therefore, compared with existing technologies, the composition design, steelmaking continuous casting, heating, and controlled rolling and cooling scheme of this invention overcomes the shortcomings of existing technologies, providing a hot-rolled wheel steel with a thickness of 10~25mm and a strength of 380MPa, and its manufacturing method. It solves the problem of high alloy costs, and this steel plate is low-cost, high-strength and tough, ensuring the safe service of wheel steel plates.

[0062] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A low-cost 380MPa grade hot-rolled wheel steel, characterized in that, Includes the following components by weight percentage: C: 0.09%~0.15%, Si: 0.06%~0.09%, Mn: 0.65%~0.75%, P≤0.020%, S≤0.015%, Al: 0.019%~0.035%, N: 0.0033%~0.0053%, with the balance being Fe and unavoidable impurities, and 0.21≤(C+Mn / 6)≤0.26; The hot-rolled wheel steel has a transverse tensile yield strength of 300-330 MPa, a tensile strength of 380-410 MPa, an elongation of ≥28%, a transverse Charpy impact energy of ≥150 J at -20℃, and a yield strength ratio of ≤0.

85. The method for preparing low-cost 380MPa grade hot-rolled wheel steel includes the following steps: steelmaking, LF refining, RH vacuum degassing, continuous casting, billet heating, rolling, controlled cooling and coiling. In the continuous casting process: the superheat is 7-11℃, and the casting speed is 0.7-1.0m / min; in the fan-shaped section, strong cooling is used, with a total cooling water volume of 1500-2000L / min in the first half and 1300-1800L / min in the second half, and light reduction is applied at the end of solidification, with a reduction of 7-12mm for the continuous casting billet; In the billet heating process: the billet is passed through a preheating section, a heating section, and a soaking section in sequence before being taken out of the furnace; wherein, the temperature range of the preheating section is 300-550℃, the temperature range of the heating section is 1235-1260℃, and the temperature range of the soaking section is 1100-1130℃; the time in the heating and soaking sections is 2.5-3.3 hours, ensuring that the temperature difference between the upper and lower surfaces of the billet is ≤15℃, and the soaking section time is 0.5-1.0 hours; In the rolling process: during the roughing stage, the reduction rate of each of the first two passes is greater than 30%, and the mill is sprayed with descaling water during the first two passes for 0.5–1 min at a pressure of 20–25 MPa. The total reduction rate during the roughing stage is controlled at 75%–85%. After the roughing stage, the finishing stage is carried out directly, with a finishing temperature of 840–870℃. The total reduction rate during the finishing stage is >70%, of which the reduction rate of the last two stands is >15%. In the controlled cooling and winding process: laminar flow cooling is adopted, with an initial cooling temperature range of 730-760℃ and a final cooling winding temperature range of 510-530℃. The cooling rate is controlled at 30-45℃ / s. The initial running speed for the first 10-60m of the head and tail sections is 1.2-1.3 times the normal roller conveyor running speed, which is 1.2-1.5m / s. The initial running speed for the first 10-60m of the head and tail sections is 1.44-1.95m / s, with a head and tail occlusion value of 200-500mm, which is maintained for 1-2s. Then, the roller conveyor running speed returns to the normal roller conveyor running speed.

2. The low-cost 380MPa grade hot-rolled wheel steel according to claim 1, characterized in that, The thickness of the hot-rolled wheel steel is 10~25mm.

3. The low-cost 380MPa grade hot-rolled wheel steel according to claim 1, characterized in that, During the rolling process: before the start of rolling, the billet after exiting the furnace is descaled with high-pressure water for 1-2 minutes, with a descaling machine pressure of 20-25 MPa; the roughing rolling passes 4-5 times.

4. The low-cost 380MPa grade hot-rolled wheel steel according to claim 1, characterized in that, In the steelmaking process: the smelting raw materials are prepared according to the chemical composition, and the KR hot metal is pretreated to control the S content ≤0.015%. After slag removal, the steel enters the converter. In the converter smelting, the double slag method is used to remove P, and the P content is controlled ≤0.02%. The C content is controlled at the end of the converter smelting process to be 0.09%~0.15%. Argon gas is blown for 10~25 minutes when tapping the steel.

5. The low-cost 380MPa grade hot-rolled wheel steel according to claim 1, characterized in that, In the LF refining and RH vacuum degassing process: the molten steel after smelting is subjected to LF refining and RH vacuum degassing, and the RH vacuum is maintained for 20~30 minutes.

6. The low-cost 380MPa grade hot-rolled wheel steel according to claim 1, characterized in that, During the heating of the billet, the thickness of the billet is 170~230mm.

7. The low-cost 380MPa grade hot-rolled wheel steel according to claim 1, characterized in that, During the controlled cooling and winding process: the number of controlled cooling manifold opening groups is 3 to 5, and the water flow rate of a single manifold is 200 to 250 m³. 3 / h.

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