Low-cost 590mpa grade hot-rolled wheel steel and method of making same

Abstract

The application discloses a kind of low-cost 590MPa grade hot-rolled wheel steel and preparation method thereof, belong to material, metallurgical technology field, including the following weight percentage of components: C:0.1%~0.14%, Si:0.1%~0.15%, Mn:1.35%~1.45%, P≤0.020%, S≤0.015%, Al:0.015%~0.035%, V:0.04%~0.06%, N:0.01%~0.02%, and 0.29≤C+{0.75+0.25tanh [20 (C-0.12) ]}×{Si / 24+Mn / 6+V / 5}≤0.35, the balance is Fe and inevitable impurities.The application realizes production low-cost 590MPa grade wheel steel plate, with low cost, high strength toughness, can guarantee the service safety of wheel steel plate.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of materials and metallurgy, and more particularly to a low-cost 590MPa grade hot-rolled wheel steel and a preparation method thereof. BACKGROUND

[0002] The wheel is an important safety structure in automobile driving, and the steel wheel assembly is obtained by a series of strict manufacturing processes such as rolling or spinning forming, welding, paint spraying treatment, etc., and has the advantages of high precision, light weight, long fatigue life and reliable safety. The hot-rolled raw material steel plate for manufacturing the wheel is required to have high strength, toughness and plasticity, high fatigue resistance, impact resistance, and high surface quality. At present, the use of 600MP grade or above high-strength wheel steel is less in the market, and the use of hot-rolled steel plate with a tensile strength of less than 600MPa is still the mainstream material for manufacturing automobile wheels in the market. The steel plate with a tensile strength of 590MPa, which accounts for a large proportion at present, generally adopts a low-carbon low-manganese composition system, and each steel plant requires the steel plate to have a low yield ratio and high plasticity to ensure the safety of the steel strip during service, and adds expensive alloy elements such as niobium, chromium and molybdenum to increase the strength, but for the wheel steel, it seems that the quality is excessive, and the cost is high and the market competitiveness is poor.

[0003] In the face of the severe market situation of the steel industry, how to reduce the manufacturing cost of the 590MPa grade wheel steel, while ensuring the product quality, and make the production line play the maximum capacity becomes particularly important. Under the condition of ensuring the safety of production and equipment, the steel plate can finally be produced with the maximum efficiency, the lowest energy and alloy cost consumption while meeting the technical requirements of the steel plate performance. Based on this, it is very important for the steel plant to develop a 590MPa grade wheel steel with low cost and high strength and toughness to improve the profit level. At present, in order to ensure the low-temperature toughness of the 590MPa grade wheel steel, a process with high alloy composition (Mn, Nb, Cr, Mo, etc.), thick intermediate billet and two-stage or even three-stage controlled rolling is usually adopted, which results in that the final rolling temperature of the steel plate may be controlled below 800℃, or even lower; and the rolling difficulty is greatly increased. First, the rolling mill load, steel plate temperature uniformity and plate shape control are all under severe test, and second, the improvement of the steel plate performance mainly depends on the content of impurities such as phosphorus and sulfur in the steel, the content of alloy elements in the steel and the control of key process parameters in the production process such as smelting and rolling. Therefore, how to systematically combine the strengthening mechanisms such as phase transformation strengthening, solid solution strengthening and fine-grain strengthening, solve the above problems in the production of 590MPa grade wheel steel, reduce the alloy cost, improve the market competitiveness, and at the same time ensure the excellent strength and toughness, is the key to the development of low-cost 590MPa grade wheel steel.

[0004] So far, there are few reports on the manufacture of low-cost 590MPa grade hot-rolled wheel steel and its manufacturing method at home and abroad. The Chinese patent with application number 201711156024.6 discloses a high-strength thin-gauge wheel and a production method with good fatigue resistance. The chemical composition and the percentage by weight content are as follows: C: 0.05~0.07%, Si: 0.15~0.30%, Mn: 1.40~1.60%, P≤0.008%, S≤0.002%, Als: 0.020~0.060%, Nb: 0.046~0.055%. The production method is as follows: after converter smelting, the molten steel is refined and Ca treated in the LF furnace; the cast blank is heated after continuous casting; hot rolling is carried out; the cooling mode of fast cooling in the front and slow cooling in the rear is adopted; coiling is carried out; finishing and post-process are carried out. However, the steel plate adds a large amount of Nb element, and adopts a two-stage controlled rolling method, which leads to low production efficiency and obviously increases the manufacturing cost. Meanwhile, the yield ratio and low-temperature impact performance are not clear. The Chinese patent with application number 201910102546.0 discloses a hot-rolled ferritic bainite dual-phase steel strip for wheels with a tensile strength of 590MPa and a preparation method thereof. According to the percentage by weight, it comprises: C: 0.05~0.10%, Si: 0.40~0.70%, Mn: 1.40~1.70%, P≤0.020%, S≤0.004%, Al: 0.020~0.060%, Nb: 0.015~0.035%, Cr: 0.20~0.40%, N≤0.0060, O≤0.0020%, and the balance is Fe and inevitable impurities. According to another aspect of the present application, a preparation method of the steel strip is provided, comprising the following steps: hot metal pretreatment→ converter smelting→ LF+RH external refining→ slab continuous casting→ heating→ rough rolling, finish rolling→ controlled cooling→ coiling→ finished product inspection→ factory delivery. However, the steel plate adds a large amount of Nb, Cr and other elements, and also adopts a two-stage controlled rolling method, which leads to low production efficiency and high manufacturing cost. Meanwhile, the yield ratio, low-temperature impact and other performance indicators are not clear.

[0005] Although the steel disclosed in the above patent documents meets the strength requirement, the production cost is high, so it is not suitable for producing low-cost, excellent tough 590MPa grade wheel steel. SUMMARY

[0006] The present application aims to overcome the above-mentioned defects in the prior art, and provides a low-cost 590MPa grade hot-rolled wheel steel and a preparation method thereof, which realizes the production of low-cost 590MPa grade wheel steel plate with a thickness of 4~10mm from a continuous casting blank with a thickness of 150~200mm, and the steel plate has excellent low-temperature toughness and other characteristics, solves the problem of high alloy cost, and the steel plate has low cost, high strength and toughness, and can ensure the service safety of the wheel steel plate.

[0007] To achieve the above object, the technical scheme of the present application is as follows:

[0008] A low-cost 590MPa grade hot-rolled wheel steel, comprising the following components by weight percentage: C: 0.1%~0.14%, Si: 0.1%~0.15%, Mn: 1.35%~1.45%, P≤0.020%, S≤0.015%, Al: 0.015%~0.035%, V: 0.04%~0.06%, N: 0.01%~0.02%, and 0.29≤C+{0.75+0.25tanh[20(C-0.12)]}×{Si / 24+Mn / 6+V / 5}≤0.35, the balance being Fe and unavoidable impurities.

[0009] Optionally, the hot-rolled wheel steel has a transverse tensile yield strength of 450~520MPa, a tensile strength of 590~690MPa, an elongation≥23%, a -40℃ transverse Charpy impact energy≥85J, and a yield strength ratio≤0.85.

[0010] Optionally, the hot-rolled wheel steel has a thickness of 4~10mm.

[0011] The present application also discloses a preparation method of the low-cost 590MPa grade hot-rolled wheel steel as described above, comprising the following steps: molten steel smelting, LF refining, RH vacuum degassing, continuous casting, casting blank heating, high-pressure water descaling, rolling, cooling and coiling;

[0012] In the continuous casting, the continuous casting superheat is 10~15℃, the strand pulling rate is 0.8~1.1m / min, electromagnetic stirring is used in the control of the secondary cooling zone in the continuous casting stage, the molten steel is subjected to continuous casting to obtain a continuous casting blank, the intermediate axis crystal ratio in the continuous casting blank is≥80%, meanwhile, in the fan-shaped section, strong cooling is used, the total cooling water amount of the 1st~3rd section is 500~800L / min, the total cooling water amount of the 4th~8th section is 1000~1200L / min, meanwhile, the solidification end is subjected to light press-down, the press-down amount of the continuous casting blank is 9~12mm, and the blank is subjected to 48~72h slow cooling after being stacked;

[0013] In the casting blank heating, the casting blank is sequentially subjected to preheating, heating and soaking, and then discharged; the preheating temperature interval is 600~900℃, the heating temperature interval is 1260~1290℃, and the soaking temperature interval is 1130~1150℃; the heating and soaking time in the furnace is 3~4h, the opening degree of the upper and lower burners in the soaking section is adjusted, the air-fuel ratio is controlled to be 1:1.7~1:2.1, the temperature difference between the upper and lower surfaces of the blank is ensured to be≤15℃, and the soaking time is 1~2h.

[0014] In the rolling process: during the roughing stage, the reduction rate of each of the first three passes is greater than 30%, and the descaling water is sprayed onto the mill during the first three passes, with a time of 0.5 to 1 minute and a pressure of 10 to 15 MPa; during the finishing stage, the total reduction rate is >75%, and the reduction rate of the last two stands is >15%; the finishing temperature is 800 to 830℃.

[0015] During the cooling and coiling process: the steel plate throwing speed after rolling is controlled at 5–6.5 m / s, the initial cooling temperature is controlled at 710–730℃, the final cooling coiling temperature range is 480–510℃, the cooling rate is 25–40℃ / s, and the side spray pressure and water flow rate are 2–5 MPa and 50–70 m³ / s, respectively. 3 / h.

[0016] Optionally, in the continuous casting process: the electromagnetic stirring method is alternating forward and reverse stirring, wherein the forward stirring time is 20-30s, the reverse stirring time is 10-20s, the current is 500-800A, and the frequency is 30-50Hz.

[0017] Optionally, during the heating of the billet, the thickness of the billet is 150~200mm.

[0018] Optionally, in the high-pressure water descaling and rolling process: before rolling, high-pressure water is used to descale the billet after it exits the furnace for 1-2 minutes, with the descaling machine pressure being 20-25 MPa; the total reduction rate during the rough rolling stage is controlled at 75%-85%, with 4-5 rough rolling passes; and 5-7 finish rolling passes.

[0019] Optionally, in steelmaking: the smelting raw materials are prepared 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, the double slag method is used to remove P, and the P content is controlled to be ≤0.02%. The C content is controlled to be 0.1% to 0.14% at the end of the converter smelting. Argon gas is blown for 20 to 30 minutes when tapping the steel.

[0020] Optional, during LF refining and RH vacuum degassing: RH vacuum is maintained for 30~40 min.

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

[0022] 1. The smelting process 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 billet. Controlling the argon blowing time and maintaining RH vacuum degassing time overcomes defects such as central segregation, inclusions, and excessive H and O content in the 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 billet, decreases the spacing of secondary dendrite arms in the solidification structure, and helps reduce billet segregation and internal structural defects. Optimizing the electromagnetic stirring process during continuous casting significantly increases the equiaxed crystal ratio of the billet. Strong cooling ensures a temperature gradient along the billet thickness. Light pressure at the end of solidification effectively reduces central porosity and segregation, while heavy pressure promotes core grain breakage, ensuring the strength and toughness of the subsequent steel plate. Furthermore, billet stacking after casting reduces residual H accumulation and inhibits the formation of microcracks within the billet.

[0023] 2. The temperatures and times of the preheating, heating, and soaking zones of the billet are limited to ensure sufficient diffusion of all elements and reduce the impact of component segregation on the microstructure and properties. At the same time, the heating zone provides high-temperature heating and air-fuel ratio 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 temperatures and times 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 waiting for the rolling temperature during the finishing rolling stage of the steel plate.

[0024] 3. The composition of this invention is reasonable, with low alloy addition and no expensive alloying elements (Nb, Mo, etc.) added. It employs a low-temperature heating + hot rolling manufacturing mode, significantly reducing alloy costs and high-temperature deformation resistance during roughing and finishing rolling. This facilitates increased reduction per pass and ensures the comprehensive performance of the super-strength steel plate. By maximizing the mill's capacity in the first three passes of the roughing stage with a high reduction rate, dynamic austenite re-crystallization is promoted, refining the original austenite grains. Simultaneously, the high-temperature deformation-induced effect promotes the precipitation of the VN phase within the austenite grains, providing nucleation sites for acicular ferrite, thus promoting the formation of intragranular acicular ferrite and improving strength and toughness. Furthermore, the use of 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, further enhancing the steel plate's strength and toughness. In addition, by adopting a low-temperature heating process, the intermediate billet waiting temperature in the finishing rolling stage is eliminated, ensuring that the last two stands of finishing rolling are in the austenite non-recrystallization temperature range, ensuring that the last two stands adopt a large reduction rate, ensuring the dislocation density, vacancies and deformation bands in the austenite body, promoting VN precipitation, providing more nucleation sites, promoting ferrite phase transformation, refining the ferrite structure, and ensuring the strength and toughness of the steel plate.

[0025] 4. Through calculation and experimentation, the fastest precipitation temperature range for VN is 740–760℃. By controlling the steel-blasting speed and ensuring the starting cooling temperature, the density of VN nanoprecipitates is guaranteed. This precipitation-strengthened VN significantly improves the mechanical properties of the steel while ensuring that the steel plate microstructure is ferrite + austenite. During the cooling process, controlling the cooling rate ensures that the microstructure of the cooled steel plate is ferrite + pearlite + bainite, thus ensuring the coordination of deformation and further improving the strength and toughness of the steel plate. Side-spraying facilitates the control of the steel plate shape and improves the uniformity of the steel plate 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 4-10mm and a strength of 590MPa by controlling the steelmaking, continuous casting, heating, and rolling cooling processes. It exhibits good low-temperature toughness. Specific properties include: transverse tensile yield strength between 450-520MPa, tensile strength between 590-690MPa, elongation ≥23%, transverse Charpy impact energy ≥85J at -40℃, and yield strength ratio ≤0.85. 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 590MPa grade hot-rolled wheel steel, comprising the following components by weight percentage: C: 0.1%–0.14%, Si: 0.1%–0.15%, Mn: 1.35%–1.45%, P≤0.020%, S≤0.015%, Al: 0.015%–0.035%, V: 0.04%–0.06%, N: 0.01%–0.02%, and 0.29≤C+{0.75+0.25tanh[20(C-0.12)]}×{Si / 24+Mn / 6+V / 5}≤0.35, with the balance being Fe and unavoidable impurities.

[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 basic 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 0.1% to 0.14%.

[0031] Mn: It enhances the strength of steel through solid solution strengthening, while compensating for the strength loss caused by the reduction in carbon content. Furthermore, it lowers the γ-α phase transformation temperature, thereby refining ferrite grains and contributing to the acquisition of fine low-temperature phase transformation products, thus improving toughness. However, increasing the Mn content exacerbates center segregation and layered martensite formation in continuously cast billets, which is detrimental to improving the low-temperature toughness of the steel plate and also affects its hole-expanding performance. Therefore, the Mn content range of this invention is designed to be 1.35%–1.45%.

[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 0.1% to 0.15% 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 0.01% to 0.02%.

[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 0.015%.

[0035] V (V): A strong solid nitrogen element, existing in the form of VN in continuously cast billets. Fine VN particles can effectively inhibit austenite grain growth during reheating of the continuously cast billet. Furthermore, the addition of V will precipitate in austenite and ferrite to form V(C,N), which can significantly improve the strength and toughness of the steel. When the V addition exceeds a certain value, the VN particles will coarsen, increasing the stress concentration level at the particle interface and the matrix. Therefore, this invention selects a V content range of 0.04% to 0.06%.

[0036] 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.

[0037] This invention further controls the content of 0.29≤C+{0.75+0.25tanh[20(C-0.12)]}×{Si / 24+Mn / 6+V / 5}≤0.35 to ensure good weldability of the wheel steel, relatively low hardness of 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.

[0038] In one specific embodiment, the yield strength of the hot-rolled wheel steel in the transverse tensile test is 450-520 MPa, the tensile strength is 590-690 MPa, the elongation is ≥23%, the transverse Charpy impact energy at -40℃ is ≥85 J, and the yield strength ratio is ≤0.85.

[0039] In one specific embodiment, the thickness of the hot-rolled wheel steel is 4~10mm.

[0040] The present invention also discloses a method for preparing low-cost 590MPa grade hot-rolled wheel steel as described above, comprising the following steps: steelmaking, LF refining, RH vacuum degassing, continuous casting, billet heating, high-pressure water descaling, rolling, cooling and coiling.

[0041] 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 0.1%–0.14%. Argon gas is blown for 20–30 minutes during tapping. Argon blowing and killing before continuous casting can promote the removal of inclusions in the molten steel and improve the uniformity of steel composition.

[0042] In S2, LF refining and RH vacuum degassing: RH vacuum is maintained for 30~40 minutes.

[0043] S3. In continuous casting: The superheating temperature is 10–15℃, and the casting speed is 0.8–1.1 m / min. Reducing the superheating temperature and casting speed can improve the macroscopic segregation of the continuously cast billet, reduce the spacing of secondary dendrite arms in the solidification structure of the billet, and help reduce billet segregation and internal structural defects. Electromagnetic stirring is used in the secondary cooling zone during the continuous casting stage, with alternating forward and reverse stirring. The forward stirring time is 20–30 s, and the reverse stirring time is 10–20 s. The current is 500–800 A, and the frequency is 30–50 Hz. The molten steel is continuously cast to obtain a continuously cast billet with an equiaxed grain ratio ≥80%. Strong cooling is used in the fan-shaped sections, with a total cooling water flow of 500–800 L / min for sections 1–3 and 1000–1200 L / min for sections 4–8. Light pressure is applied at the end of solidification, and the reduction of the electromagnetically stirred billet is 9–12 mm. The billets are then stacked and slowly cooled for 48–72 hours after casting. By optimizing the electromagnetic stirring process in the continuous casting stage, the equiaxed grain ratio of the billet is significantly improved. Strong cooling ensures a temperature gradient along the billet thickness. Light pressure helps reduce billet segregation and internal structural defects, while promoting core grain breakage, ensuring the strength and toughness of the subsequent steel plate. The billets are stacked for more than 48 hours after casting to reduce the accumulation of residual hydrogen, inhibit the formation of microcracks inside the billet, and ensure the toughness of the steel plate.

[0044] S4. During billet heating: The billet with a thickness of 150~200mm is passed through the preheating section, heating section, and soaking section before being taken out of the furnace. The temperature range of the preheating section is 600~900℃, which promotes the homogenization of the microstructure in the billet, and the rapid and complete solidification and diffusion of V carbides or nitrides into the matrix, as well as the full diffusion of elements. The temperature range of the heating section is 1260~1290℃, and the temperature range of the soaking section is 1130~1150℃. The time in the heating and soaking sections is 3~4 hours. The opening degree of the upper and lower burners in the soaking section is adjusted to control the air-fuel ratio of 1:1.7~1:2.1, ensuring that the temperature difference between the upper and lower surfaces of the billet is ≤15℃, and the soaking section time is 1~2 hours. Increasing the heating temperature and extending the furnace time further promotes the diffusion of elements Mn, C, V, and N, mitigating their impact on microstructure and properties due to compositional segregation. Simultaneously, the heating section provides high-temperature heating and controls the air-fuel ratio, ensuring temperature uniformity across the billet and 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-grain strengthening contributes to the steel plate's strength. Furthermore, low-temperature heating in the soaking zone avoids the need for preheating during the finishing rolling stage, while also ensuring that the finishing rolling stage takes place in the non-recrystallized austenite region.

[0045] S5. During rolling: Before the initial 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 rough rolling stage, the reduction rate of each of the first three passes is greater than 30%, and the descaling water is sprayed onto the mill for 0.5-1 minutes per pass at a pressure of 10-15 MPa. The mill capacity is maximized in the first three passes, using a large reduction rate to promote dynamic austenite re-crystallization, refine the original austenite grains, and simultaneously utilize the high-temperature deformation-induced effect to promote the precipitation of the VN phase within the austenite grains. Acicular ferrite provides nucleation sites, promoting the formation of intragranular acicular ferrite and improving strength and toughness. Furthermore, high-pressure water descaling in the rolling mill creates a temperature gradient from the steel plate surface to the core, promoting core deformation and uniform microstructure distribution during subsequent finishing rolling, further enhancing the steel plate's strength and toughness. The total reduction rate in the roughing stage is controlled at 75%–85%, with 4–5 roughing passes. In the finishing stage, the reduction rate in the last two stands is >15%, with 5–7 finishing passes; the total reduction rate in the finishing stage is >75%; and the finishing rolling temperature is 800–830℃. By employing a low-temperature heating process, the intermediate billet warming process in the finishing stage is eliminated, ensuring that the last two stands are rolled within the austenite non-recrystallization temperature range. This ensures a high reduction rate in the last two stands, maintaining the dislocation density, vacancies, and deformation bands within the austenite, promoting VN precipitation, providing more nucleation sites, facilitating ferrite phase transformation, refining the ferrite microstructure, and ensuring the steel plate's strength and toughness.

[0046] S6. During cooling and coiling: The steel plate throwing speed after rolling is controlled at 5-6.5 m / s, the initial cooling temperature is controlled at 710-730℃, the final cooling coiling temperature range is 480-510℃, the cooling rate is 25-40℃ / s, and the side spray pressure and water flow rate are 2-5 MPa and 50-70 m³ / s, respectively. 3 / h; Through calculation and experiment, the fastest precipitation temperature range of VN is 740~760℃. By controlling the steel pouring speed and ensuring the cooling temperature, the density of VN nanoprecipitation is guaranteed. Precipitation strengthening can significantly improve the mechanical properties of steel. At the same time, it ensures that the microstructure of the steel plate is ferrite + austenite when it enters the water. During the cooling process, controlling the cooling rate ensures that the microstructure of the steel plate after cooling is ferrite + pearlite + bainite, so as to ensure the coordination of deformation and further improve the strength and toughness of the steel plate. Side spraying is beneficial to the control of the steel plate shape and improves the uniformity of the steel plate performance.

[0047] The following are specific embodiments.

[0048] Examples 1-6

[0049] 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.

[0050] Table 1 Chemical composition (wt, %) of embodiments of the present invention

[0051]

[0052] Note: Impurity elements in steel: P≤0.02%; S≤0.015%.

[0053] Table 2. Smelting process of steel in the examples

[0054]

[0055] Table 3 Heating regime of steel billets and high-pressure water descaling process before rolling of continuously cast billets in the examples

[0056]

[0057] Table 4 Rolling parameters of the steel in the examples

[0058]

[0059] Table 5. Steel controlled cooling and coiling process parameters in embodiments of the present invention

[0060]

[0061] Table 6 Performance indicators of steel plates in embodiments of the present invention

[0062]

[0063] 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 4~10mm and a strength of 590MPa, 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.

[0064] 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 590MPa grade hot-rolled wheel steel, characterized in that, Includes the following components by weight percentage: C: 0.1%~0.14%, Si: 0.1%~0.15%, Mn: 1.35%~1.45%, P≤0.020%, S≤0.015%, Al: 0.015%~0.035%, V: 0.04%~0.06%, N: 0.01%~0.02%, and 0.29≤C+{0.75+0.25tanh[20(C-0.12)]}×{Si / 24+Mn / 6+V / 5}≤0.35, with the balance being Fe and unavoidable impurities; The hot-rolled wheel steel has a transverse tensile yield strength of 450-520 MPa, a tensile strength of 590-690 MPa, an elongation of ≥23%, a transverse Charpy impact energy of ≥85 J at -40℃, and a yield strength ratio of ≤0.

85. The method for preparing low-cost 590MPa grade hot-rolled wheel steel includes the following steps: steelmaking, LF refining, RH vacuum degassing, continuous casting, billet heating, high-pressure water descaling, rolling, cooling and coiling. In the continuous casting process: the superheat is 10-15℃, the billet pulling speed is 0.8-1.1m / min, electromagnetic stirring is used in the secondary cooling zone during the continuous casting stage to obtain a continuous casting billet from the molten steel, and the isometric crystal ratio of the continuous casting billet is ≥80%. At the same time, strong cooling is used in the fan-shaped section, with a total cooling water volume of 500-800L / min for the first to third sections and 1000-1200L / min for the fourth to eighth sections. At the same time, light reduction is applied at the end of solidification, with a reduction of 9-12mm for the continuous casting billet. After the billet is removed from the line, it is stacked and slowly cooled for 48-72 hours. 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; the temperature range of the preheating section is 600-900℃, the temperature range of the heating section is 1260-1290℃, and the temperature range of the soaking section is 1130-1150℃; the time in the heating and soaking sections is 3-4 hours; the opening degree of the upper and lower burners in the soaking section is adjusted to control the air-fuel ratio of 1:1.7-1:2.1, ensuring that the temperature difference between the upper and lower surfaces of the billet is ≤15℃, and the soaking section time is 1-2 hours. In the rolling process: during the roughing stage, the reduction rate of each of the first three passes is greater than 30%, and the descaling water is sprayed onto the mill during the first three passes, with a time of 0.5 to 1 minute and a pressure of 10 to 15 MPa; during the finishing stage, the total reduction rate is >75%, and the reduction rate of the last two stands is >15%; the finishing temperature is 800 to 830℃. During the cooling and coiling process: the steel plate throwing speed after rolling is controlled at 5–6.5 m / s, the initial cooling temperature is controlled at 710–730℃, the final cooling coiling temperature range is 480–510℃, the cooling rate is 25–40℃ / s, and the side spray pressure and water volume are 2–5 MPa and 50–70 m³ / s, respectively. 3 / h.

2. The low-cost 590MPa grade hot-rolled wheel steel according to claim 1, characterized in that, The thickness of the hot-rolled wheel steel is 4~10mm.

3. The low-cost 590MPa grade hot-rolled wheel steel according to claim 1, characterized in that, In the continuous casting process, the electromagnetic stirring method is alternating forward and reverse stirring, wherein the forward stirring time is 20-30s, the reverse stirring time is 10-20s, the current is 500-800A, and the frequency is 30-50Hz.

4. The low-cost 590MPa grade hot-rolled wheel steel according to claim 1, characterized in that, During the heating of the billet, the thickness of the billet is 150~200mm.

5. The low-cost 590MPa grade hot-rolled wheel steel according to claim 1, characterized in that, In the high-pressure water descaling and rolling process: before 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 total reduction rate in the rough rolling stage is controlled at 75%-85%, with 4-5 rough rolling passes; and 5-7 finish rolling passes.

6. The low-cost 590MPa grade hot-rolled wheel steel according to claim 1, characterized in that, In steelmaking: the raw materials are prepared 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, the double slag method is used to remove P, and the P content is controlled to be ≤0.02%. The C content is controlled to be 0.1%~0.14% at the end of the converter smelting. Argon gas is blown for 20~30 minutes when tapping the steel.

7. The low-cost 590MPa grade hot-rolled wheel steel according to claim 1, characterized in that, During LF refining and RH vacuum degassing: RH vacuum is maintained for 30~40 minutes.

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