Low-cost 420MPa-grade hot-rolled wheel steel and preparation method thereof

Abstract

The invention discloses low-cost 420MPa-grade hot-rolled wheel steel and a preparation method thereof, and belongs to the technical field of materials and metallurgy, the low-cost 420MPa-grade hot-rolled wheel steel comprises the following components in percentage by weight: 0.12%-0.16% of C, 0.05%-0.10% of Si, 0.80%-0.90% of Mn, less than or equal to 0.020% of P, less than or equal to 0.015% of S, 0.018%-0.033% of Al, 0.0035%-0.0055% of N and the balance of Fe and inevitable impurities, and (C + Mn / 6) is more than or equal to 0.25 and less than or equal to 0.30. The 420 MPa grade wheel steel plate with the thickness of 10-25 mm and the low cost is produced, the 420 MPa grade wheel steel plate has the characteristics of excellent low-temperature toughness, high surface quality, low cost, high strength and toughness and the like, the problems of high alloy cost and the like are solved, and the service safety of the wheel steel plate can be guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of materials and metallurgy, and more particularly to a low-cost 420MPa-grade hot-rolled wheel steel and a preparation method thereof. Background Art

[0002] Wheels are crucial safety components for vehicles. Steel wheel assemblies are made from steel sheets through a rigorous manufacturing process involving roll forming or spinning, welding, and painting. They offer advantages such as high precision, light weight, long fatigue life, and reliable safety. The hot-rolled steel sheets used to make wheels are required to possess high strength, toughness, and ductility, as well as high fatigue resistance, impact resistance, and surface quality. Currently, high-strength wheel steels with a tensile strength of 500 MPa and above are rarely used in the market, while hot-rolled steel sheets with a tensile strength of 500 MPa and below remain the mainstream material for automotive wheel manufacturing. Wheel steels with a tensile strength of 420 MPa, which currently account for a large proportion, generally use a low-carbon, low-manganese composition. To ensure a low yield-to-tensile ratio and high ductility, steel mills add expensive alloying elements such as niobium, chromium, and molybdenum to enhance strength. However, this represents excessive quality for wheel applications, resulting in high costs and poor market competitiveness.

[0003] Faced with the challenging market conditions of the steel industry, reducing the manufacturing cost of 420MPa-grade wheel steel while ensuring product quality and maximizing production line capacity is crucial. Ultimately, achieving maximum efficiency and minimizing energy and alloy costs while maintaining the required performance and technical specifications for the steel plate is crucial, while ensuring production and equipment safety. Therefore, developing a low-cost, high-strength and tough 420MPa-grade wheel steel is crucial for improving steel mill profitability. Currently, to ensure the low-temperature toughness of 420MPa-grade wheel steel, high alloying elements (such as Mn, Nb, and Cr) are typically used, along with a thick intermediate billet thickness and a two- or even three-stage controlled rolling process. This results in the plate finishing temperature being controlled below 800°C, or even lower, significantly increasing rolling complexity. Firstly, mill load, plate temperature uniformity, and plate shape control all face significant challenges. Secondly, improving plate performance depends primarily on controlling the content of impurities such as phosphorus and sulfur in the steel, the content of alloying elements in the steel, and the control of key process parameters during smelting and rolling. It can be seen that how to organically combine phase transformation strengthening, solid solution strengthening and fine grain strengthening to solve the above-mentioned problems in the production of 420MPa grade wheel steel, reduce alloy costs, improve market competitiveness, and at the same time ensure its excellent strength and toughness is the key to the development of low-cost 420MPa grade wheel steel.

[0004] To date, there have been few reports domestically and internationally on the production and manufacturing methods of low-cost 420 MPa hot-rolled wheel steel. The journal articles "The Role of Titanium in Automotive Wheel Steel and the Alloying Process" (Steel, Vol. 36 (2001), p. 48) and "Development of Automotive Wheel Steel at Anshan Iron and Steel's ASP Line" (Automotive Technology and Materials, Vol. 6 (2004), p. 57) respectively describe the addition of Ti and Nb to automotive wheel steel, achieving tensile strength that meets technical requirements after hot rolling. However, the addition of Ti and Nb, both precious elements, and the use of controlled-deep rolling methods, result in low production efficiency and significantly increased manufacturing costs. Furthermore, the low-temperature impact properties remain unclear.

[0005] In summary, the existing technology has the problem of high production costs, and is therefore not suitable for producing low-cost, high-quality, strong and tough 420MPa grade wheel steel. In view of the above situation, it is urgent to design a low-cost 420MPa grade hot-rolled wheel steel and its manufacturing method. Summary of the Invention

[0006] The purpose of the present invention is to overcome the above-mentioned defects of the prior art, provide a low-cost 420MPa grade hot-rolled wheel steel and a preparation method thereof, and realize the production of 10~25mm thick, low-cost 420MPa grade wheel steel plates using continuous casting billets with a thickness of 170-230mm, and the steel plates have excellent low-temperature toughness and high surface quality, thereby solving the problem of high alloy cost. The steel plates obtained by the present invention have the advantages of low cost and high strength and toughness, and can ensure the service safety of wheel steel plates.

[0007] To achieve the above object, the technical solution of the present invention is as follows: A low-cost 420 MPa grade hot-rolled wheel steel comprises the following components in weight percentage: C: 0.12% to 0.16%, Si: 0.05% to 0.10%, Mn: 0.80% to 0.90%, P≤0.020%, S≤0.015%, Al: 0.018% to 0.033%, N: 0.0035% to 0.0055%, the balance being Fe and unavoidable impurities, and 0.25≤(C+Mn / 6)≤0.30.

[0008] Optionally, the hot-rolled wheel steel has a transverse tensile yield strength of 310-355 MPa, a tensile strength of 420-500 MPa, an elongation ≥26%, a transverse Charpy impact energy at -20°C ≥135 J, and a yield strength ratio ≤0.83.

[0009] Optionally, the thickness of the hot-rolled wheel steel is 10-25 mm.

[0010] The present invention also discloses a method for preparing the above-mentioned low-cost 420MPa grade hot-rolled wheel steel, comprising the following steps: molten steel smelting, LF refining, RH vacuum degassing, continuous casting, billet heating, hot rolling, controlled cooling and coiling; During the continuous casting, the continuous casting superheat is 7-11° C., the continuous casting billet drawing rate is 0.8-1.1 m / min, the electromagnetic stirring current intensity in the secondary cooling zone during the continuous casting stage is controlled to be 200-250 A, the secondary cooling water volume is controlled to be 2.1 L / kg-2.6 L / kg, and soft reduction is applied at the end of solidification in the horizontal sector, with a continuous casting billet reduction of 6-10 mm. The billets are stacked for 24-48 hours after leaving the production line. The billet heating process includes: passing the billet 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 300-600°C, the temperature range of the heating section is 1235-1270°C, and the temperature range of the soaking section is 1100-1120°C; the heating and soaking section time in the furnace is controlled to be 2.5-3.3 hours, the opening of the upper and lower burners in the soaking section is adjusted, and the air-fuel ratio is controlled to be 1:1.7-1:2.2, ensuring that the temperature difference between the upper and lower surfaces of the billet is ≤15°C, and the soaking section time is 1-2 hours; In the hot rolling, in the rough rolling stage, the reduction rate of each of the first two passes of rough rolling is 30-50%, and the first three passes of rolling are sprayed with water to remove scale, each pass time is 0.2-0.5 min, and the pressure is 10-15 MPa; after the rough rolling is completed, the finishing rolling stage is directly carried out, and the finishing rolling temperature is 830-860° C. The total reduction rate of the finishing rolling stage is greater than 70%, of which the reduction rate of the last two passes of finishing rolling is greater than 18%; In the controlled cooling and coiling, a controlled cooling mode combining head rapid cooling and laminar cooling is adopted, the head rapid cooling final rolling temperature is 780-800°C, the final cooling temperature range is 650-720°C, the cooling rate is 50-60°C / s, and then laminar cooling is entered, the coiling temperature range is 480-520°C, and the cooling rate is 10-20°C / s; the initial running speed at each 10-60m length of the head and tail is 1.2-1.4 times the normal roller running speed, the normal roller running speed is 1.2-1.5m / s, the initial running speed at each 10-60m length of the head and tail is 1.44-2.1m / s, the head and tail shielding value is 200-500mm, and is maintained for 1-2s, and then the roller running speed is restored to 1.2-1.5m / s.

[0011] Optionally, during the molten steel smelting: smelting raw materials are configured according to the chemical composition, and the molten iron is pretreated by KR to control the S content to ≤0.015%, and then the slag is removed before entering the converter; during the converter smelting, the double slag method is used to remove P to control the P content to ≤0.02%, and the C content at the end point of the converter smelting is controlled to be 0.12%~0.16%, and argon is blown for 10~25 minutes when tapping.

[0012] Optionally, during 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 to 30 minutes.

[0013] Optionally, during the heating of the ingot, the thickness of the ingot is 170~230mm.

[0014] Optionally, during the hot rolling: before starting rolling, the cast slab is descaled for 1 to 2 minutes using high-pressure water, with a descaling machine pressure of 20 to 25 MPa; the total reduction rate in the rough rolling stage is controlled at 75% to 85%, with 3 to 5 rough rolling passes.

[0015] The implementation of the present invention will have the following beneficial effects: 1. The smelting process utilizes KR hot metal pretreatment for deep desulfurization followed by clean slag skimming. The converter utilizes a double-slag method for P removal, resulting in low P and S content in the ingot. Controlled argon blowing time and consistent RH vacuum degassing mitigate defects such as central segregation, inclusions, and excessive H and O content caused by high Mn and C contents, thereby improving the ductility and toughness of the steel plate. Reducing superheat and continuous casting speeds improves macrosegregation in the ingot and reduces the spacing between secondary dendrite arms in the solidified structure, thereby minimizing segregation and internal structural defects. Controlling the electromagnetic stirring current intensity and secondary cooling water volume in the secondary cooling zone effectively reduces the average carbon segregation index, inhibiting segregation and the development of central cracks in the ingot. Applying soft reduction at the end of solidification effectively reduces central porosity and segregation in the ingot. This also promotes core grain breakage, ensuring the subsequent strength and toughness of the steel plate. Furthermore, stacking the ingots after they are rolled off the production line reduces the accumulation of residual H and inhibits the formation of microcracks within the ingot.

[0016] 2. Ingot heating: The temperature and time of the ingot in the preheating section, heating section and soaking section are limited to ensure the full diffusion of various elements and reduce the influence of composition segregation on the structure and performance. At the same time, the heating section provides high-temperature heating and air-fuel ratio to ensure the temperature uniformity of various parts of the ingot and improve the uniformity of metal flow in the horizontal and vertical directions on the surface of the steel plate. In combination with the composition of the steel billet, the heating temperature of the soaking section of the ingot is lowered to reduce energy consumption. The temperature and time of the heating section and soaking section are controlled to inhibit the excessive growth of the original austenite grains and increase the contribution of fine grain strengthening to the strength of the steel plate. In addition, low-temperature heating is adopted in the soaking section to avoid the steel plate waiting for temperature in the second stage of rolling.

[0017] 3. The present invention has a reasonable chemical composition design, reduces the amount of alloy added, replaces precipitation strengthening with fine grain strengthening, does not add expensive alloy elements, and adopts a low-temperature heating + hot rolling manufacturing mode, which greatly reduces the alloy cost and the high-temperature deformation resistance in the rough rolling and finishing rolling stages, is conducive to increasing the reduction per pass, and is conducive to ensuring the comprehensive performance of the super steel plate.

[0018] 4. The mill's capacity is maximized during the first two roughing passes, with a high reduction ratio adopted to promote dynamic re-crystallization of austenite and refine the original austenite grains. High-pressure water descaling is used in the mill to create a temperature gradient from the surface to the core of the steel plate. This promotes uniform deformation and microstructure distribution in the core during the subsequent finishing rolling process, thereby improving the strength and toughness of the steel plate. Furthermore, the low-temperature heating process eliminates the need for warming the intermediate bar during the finishing rolling phase, ensuring that the final two passes of the finishing rolling process are within the austenite non-recrystallization temperature range. This ensures that a high reduction ratio is adopted in these final two passes, further refining the austenite grains and improving the steel plate's performance.

[0019] 5. Control the final rolling temperature to ensure that the steel plate enters the water with an austenite + ferrite structure. During the cooling process, different cooling rates are used. A high cooling rate ensures the transformation of the core structure, and then a low cooling rate is used to ensure that the core returns to red and affects the surface temperature. By controlling the cooling rate and the red temperature, the formation of bainite and martensite phases on the steel plate surface and the amount of bainite phase in the core structure are suppressed, avoiding the impact of bainite or martensite phase transformation on the surface on the strength and toughness of the steel plate. In order to achieve temperature uniformity control in the longitudinal direction of the steel plate, the sample is divided into a sample at a length of 0.1 to 0.2 meters from the head. On this basis, various models (temperature, flow rate) perform speed optimization calculations for each sample interval. The control model obtains the optimal operating speed trend for each sample based on the longitudinal temperature measurement value 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 = shielding distance set on the HMI interface - shielding time * roller speed). For the low-temperature areas at the head and tail of the steel plate, when the head of the steel plate enters the laminar flow area or the tail leaves the laminar flow area, 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 the excessive cooling of the cooling water on the head and tail of the steel plate, which is beneficial to improving the uniformity of the steel plate performance.

[0020] This invention reduces alloy costs through simple composition design. By controlling the steelmaking, continuous casting, heating, and rolling controlled cooling processes, it achieves low-cost production of 420 MPa-grade hot-rolled wheel steel plates with thicknesses of 10-25 mm. This steel exhibits excellent low-temperature toughness. Specific properties include a transverse tensile yield strength of 310-355 MPa, a tensile strength of 420-500 MPa, a yield ratio of ≤0.83, an elongation of ≥26%, and a transverse Charpy impact energy of ≥135 J at -20°C. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to specific examples, but the present invention is not limited thereto in any way.

[0022] The present invention discloses a low-cost 420MPa grade hot-rolled wheel steel, comprising the following components in weight percentage: C: 0.12% to 0.16%, Si: 0.05% to 0.10%, Mn: 0.80% to 0.90%, P≤0.020%, S≤0.015%, Al: 0.018% to 0.033%, N: 0.0035% to 0.0055%, the balance being Fe and unavoidable impurities, and 0.25≤(C+Mn / 6)≤0.30.

[0023] Specifically, the functions of the main elements in the chemical composition of the steel plate of the present invention are as follows: C: The most economical and fundamental strengthening element in steel, it significantly increases steel strength through solid solution strengthening and precipitation strengthening. However, increasing C content negatively impacts the steel's plasticity, toughness, and weldability. Therefore, the present invention sets the C content within a range of 0.12% to 0.16%.

[0024] Mn: It increases steel strength through solid solution strengthening, compensating for the loss of steel plate strength caused by reduced carbon content. It also lowers the γ-α transformation temperature, thereby refining ferrite grains, contributing to the production of fine low-temperature transformation products and improving toughness. However, increasing the Mn content exacerbates central segregation and the formation of lamellar martensite in the continuous casting ingot, hindering low-temperature toughness and affecting the plate's hole expansion performance. Therefore, the Mn content in the present invention is designed to be between 0.80% and 0.90%.

[0025] Si: It deoxidizes steel during steelmaking and improves matrix strength. However, excessive Si content can reduce the toughness of the base material's heat-affected zone (HAZ). Increasing Si content can purify ferrite, reduce pearlite content, and help mitigate the Bauschinger effect in the base material. Therefore, the Si content in this invention is set at 0.05% to 0.10%.

[0026] N: The N element in steel has no other significant function except forming fine NbN particles to refine austenite grains. Therefore, the N content needs to be kept at a relatively low level. The N content selected in the present invention is in the range of 0.0035% to 0.0055%.

[0027] Al: Typically used as a deoxidizer in steel, it also refines the structure by forming AlN. When the Al content exceeds 0.033%, excessive aluminum oxide inclusions can reduce the cleanliness of the steel. Lower Al contents result in inadequate deoxidation, so the lower limit for Al is set at 0.018%.

[0028] P and S are unavoidable impurity elements in steel and should be as low as possible. However, due to smelting costs and process considerations, they cannot be kept indefinitely low. Therefore, the present invention sets the upper limits of P and S content at 0.020% and 0.015% respectively.

[0029] The present invention further controls the ratio 0.25 ≤ (C + Mn / 6) ≤ 0.30 to ensure good wheel steel weldability, a relatively low hardness in the heat-affected zone, and a low likelihood of weld cracking. Outside this range, weld cracks can occur, further impacting the wheel steel's weldability.

[0030] In a specific embodiment, the hot-rolled wheel steel has a transverse tensile yield strength of 310-355 MPa, a tensile strength of 420-500 MPa, an elongation of ≥26%, a transverse Charpy impact energy at -20°C of ≥135 J, and a yield strength ratio of ≤0.83.

[0031] In a specific embodiment, the thickness of the hot-rolled wheel steel is 10-25 mm.

[0032] The present invention also discloses a method for preparing the above-mentioned low-cost 420MPa grade hot-rolled wheel steel, comprising the following steps: molten steel smelting, LF refining, RH vacuum degassing, continuous casting, billet heating, hot rolling, controlled cooling and coiling.

[0033] During steelmaking, raw materials are prepared according to their chemical composition. After KR pretreatment, the molten iron is fed into the converter after slag removal. During converter smelting, phosphorus (P) is removed using the double-slag method to control the P content to ≤0.02%. The carbon content at the converter endpoint is controlled to 0.12% to 0.16%. Argon gas is blown for 10 to 25 minutes during tapping. Argon sedation prior to continuous casting can help remove inclusions from the molten steel and improve its compositional uniformity.

[0034] 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 to 30 minutes.

[0035] S3. During continuous casting: the continuous casting superheat is 7-11°C, and the continuous casting casting rate is 0.8-1.1m / min. Reducing the superheat and the continuous casting casting rate can improve the macro-segregation of the continuous casting billet, reduce the secondary dendrite arm spacing in the solidification structure of the continuous casting billet, help reduce the segregation of the steel billet, and reduce internal structural defects; control the electromagnetic stirring current intensity of the secondary cooling zone in the continuous casting stage to 200-250A, and the secondary cooling water volume to 2.1L / kg-2.6L / kg, reduce the average carbon segregation index, inhibit segregation, and at the same time limit the secondary cooling intensity to inhibit the trend of worsening cracks in the center of the billet. In the horizontal fan-shaped section, light pressure is applied at the end of solidification, and the continuous casting billet reduction is 6-10mm to reduce the central porosity level and segregation of the billet. The billets are stacked for 24-48h after leaving the line to reduce the aggregation of residual H, inhibit the generation of microcracks inside the billet, and ensure the toughness of the steel plate.

[0036] S4. Billet heating: Billets with a thickness of 170~230mm are sent into a walking-beam heating furnace for heating. The billets are taken out of the furnace after passing through the preheating section, heating section and soaking section in sequence. The temperature range of the preheating section is 300~600℃, which promotes the homogenization of the structure in the billet and promotes the full diffusion of elements. The temperature range of the heating section is 1235~1270℃, and the temperature range of the soaking section is 1100~1120℃. The time of heating and soaking sections in the furnace is controlled at 2.5~3.3h, and the opening of the upper and lower burners in the soaking section is adjusted. The air-fuel ratio is controlled at 1:1.7~1:2.2 to ensure that the temperature difference between the upper and lower surfaces of the billet is ≤15℃, and the soaking section time is 1~2h. Increasing the heating temperature and extending the furnace time can further promote the diffusion of alloying elements Mn and C, and reduce the impact of composition segregation on the structure and performance; at the same time, the heating section provides high-temperature heating and controls the air-fuel ratio to ensure temperature uniformity in all parts of the ingot and improve the uniformity of transverse and longitudinal metal flow on the steel plate surface; based on the composition of the steel billet, by lowering the heating temperature of the ingot soaking section, energy consumption is reduced, and the temperature and time of the heating section and soaking section are limited to inhibit the excessive growth of the original austenite grains and ensure the contribution of fine grain strengthening to the strength of the steel plate. In addition, low-temperature heating is adopted in the soaking section to avoid the waiting time for the steel plate to be heated during the finishing rolling stage.

[0037] S5. During hot rolling: before rolling, high-pressure water is used to descale the billet after it leaves the furnace for 1 to 2 minutes, and the descaling machine pressure is 20 to 25 MPa. During the rough rolling stage, the reduction rate of each of the first two passes of rough rolling is 30 to 50%, and the first three passes of rolling are sprayed with water for descaling, each pass time is 0.2 to 0.5 minutes, and the pressure is 10 to 15 MPa. The first three passes of rolling try to give full play to the capacity of the rolling mill, use a large reduction rate, promote the dynamic crystallization of austenite, and refine the original austenite. The steel is then descaled using high-pressure water in the rolling mill to create a temperature gradient from the surface to the core of the steel plate. This promotes deformation and uniform microstructure distribution in the core during the subsequent finishing rolling process, thereby improving the strength and toughness of the steel plate. The total reduction rate in the roughing stage is controlled at 75% to 85%, with 3 to 5 roughing passes. The finishing stage is directly followed by the roughing process, with a total reduction rate of >70% in the finishing stage, including a reduction rate of >18% in the final two passes. The final finishing temperature is 830-860°C. Due to the low-temperature heating process, the intermediate bar is not allowed to warm during the finishing stage, ensuring that the final two passes are rolled in the austenite non-recrystallization temperature range. This ensures that a high reduction rate is used in the final two passes, further refining the austenite grains and improving the steel plate properties.

[0038] S6, control cooling and coiling: adopt the cooling control mode combining head fast cooling and laminar cooling, head fast cooling final rolling temperature is 780 ~ 800 ℃, final cooling temperature range is 650 ~ 720 ℃, cooling rate is 50 ~ 60 ℃ / s, then enter laminar cooling, coiling temperature range is 480 ~ 520 ℃, cooling rate is 10 ~ 20 ℃ / s, control final rolling temperature, ensure that the steel plate enters the water structure is ferrite + austenite, in the cooling process, adopt different cooling rates, large cooling rate ensures the core structure transformation, then adopts small cooling rate to ensure the core returns to red on the surface temperature, by controlling the cooling Speed ​​and red-return temperature are controlled to inhibit the formation of bainite and martensite phases on the surface of the steel plate and the amount of bainite phase in the core structure, so as to avoid the occurrence of bainite or martensite phase transformation on the surface, which affects the strength and toughness of the steel plate; the initial running speed at the head and tail lengths of 10 to 60 m is 1.2 to 1.4 times the normal roller running speed, and the normal roller running speed is 1.2 to 1.5 m / s. The initial running speed at the head and tail lengths of 10 to 60 m is 1.44 to 2.1 m / s, the head and tail shielding value is 200 to 500 mm, and it is maintained for 1 to 2 seconds, and then the roller running speed is restored to 1.2 to 1.5 m / s. The finishing temperature is controlled to ensure the steel plate is in an austenite + ferrite microstructure upon entering the water. During the cooling process, the cooling rate and final cooling temperature are controlled to inhibit the formation of martensite in the steel plate and avoid surface martensitic transformation that affects the steel plate's toughness. To achieve temperature uniformity along the length of the steel plate, the sample is divided into sections every 0.1 to 0.2 meters from the head. Based on this, various models (temperature, flow rate, etc.) perform speed optimization calculations for each sample interval. The control model determines the optimal operating speed trend for each sample based on the measured longitudinal temperature 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 = shielding distance set on the HMI interface - shielding time * roller speed). For low-temperature zones at the head and tail of the steel plate, when the head enters the laminar flow area or the tail leaves the laminar flow area, the roller speed is appropriately increased based on the thickness group interval, and the water flow rate at the head and tail is controlled to reduce excessive cooling of the cooling water at the head and tail of the steel plate, which is beneficial to improving the uniformity of the steel plate's performance.

[0039] The following are specific embodiments Table 1 shows the chemical composition of the example steel, Table 2 shows the smelting process system of the example steel, Table 3 shows the heating system of the cast slab and the high-pressure water descaling process before continuous casting slab rolling of the example steel; Table 4 shows the rolling parameters of the example steel; Table 5 shows the controlled cooling and coiling process parameters of the example steel; Table 6 shows the performance indicators of the example steel plate.

[0040] Table 1 Chemical composition of the examples of the present invention (wt, %)

[0041] Note: P≤0.02% in steel; S≤0.015%.

[0042] Table 2 Smelting process system of example steel

[0043] Table 3 Heating system of cast steel and high pressure water descaling process before continuous casting

[0044] Table 4 Rolling parameters of example steel

[0045] Table 5 Controlled cooling and coiling process parameters of steel according to the present invention

[0046] Table 6 Performance indexes of steel plates according to embodiments of the present invention

[0047] As can be seen, compared with existing technologies, the composition design, steelmaking and continuous casting, heating, and controlled rolling and cooling schemes of this invention overcome the shortcomings of existing technologies, providing a 420 MPa hot-rolled wheel steel with a thickness of 10-25 mm and a manufacturing method. This solves the problem of high alloy costs, and the steel plate offers high strength and toughness at a low cost, ensuring the safe service life of wheel steel plates.

[0048] The above-described embodiments merely represent several implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A low-cost 420MPa grade hot-rolled wheel steel, characterized in that: The composition comprises the following components in weight percentage: C: 0.12%~0.16%, Si: 0.05%~0.10%, Mn: 0.80%~0.90%, P≤0.020%, S≤0.015%, Al: 0.018%~0.033%, N: 0.0035%~0.0055%, the balance is Fe and unavoidable impurities, and 0.25≤(C+Mn / 6)≤0.

30.

2. The low-cost 420 MPa grade hot-rolled wheel steel according to claim 1, characterized in that: The hot-rolled wheel steel has a transverse tensile yield strength of 310-355 MPa, a tensile strength of 420-500 MPa, an elongation of ≥26%, a transverse Charpy impact energy at -20°C of ≥135 J, and a yield strength ratio of ≤0.

83.

3. The low-cost 420 MPa grade hot-rolled wheel steel according to claim 1, characterized in that: The thickness of the hot-rolled wheel steel is 10-25 mm.

4. A method for preparing a low-cost 420 MPa grade hot-rolled wheel steel according to any one of claims 1 to 3, characterized in that: The following steps are involved: Molten steel smelting, LF refining, RH vacuum degassing, continuous casting, billet heating, hot rolling, controlled cooling and coiling; During the continuous casting, the continuous casting superheat is 7-11° C., the continuous casting billet drawing rate is 0.8-1.1 m / min, the electromagnetic stirring current intensity in the secondary cooling zone during the continuous casting stage is controlled to be 200-250 A, the secondary cooling water volume is controlled to be 2.1 L / kg-2.6 L / kg, and soft reduction is applied at the end of solidification in the horizontal sector, with a continuous casting billet reduction of 6-10 mm. The billets are stacked for 24-48 hours after leaving the production line. The billet heating process includes: passing the billet 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 300-600°C, the temperature range of the heating section is 1235-1270°C, and the temperature range of the soaking section is 1100-1120°C; the heating and soaking section time in the furnace is controlled to be 2.5-3.3 hours, the opening of the upper and lower burners in the soaking section is adjusted, and the air-fuel ratio is controlled to be 1:1.7-1:2.2, ensuring that the temperature difference between the upper and lower surfaces of the billet is ≤15°C, and the soaking section time is 1-2 hours; In the hot rolling, in the rough rolling stage, the reduction rate of each of the first two passes of rough rolling is 30-50%, and the first three passes of rolling are sprayed with water to remove scale, each pass time is 0.2-0.5 min, and the pressure is 10-15 MPa; after the rough rolling is completed, the finishing rolling stage is directly carried out, and the finishing rolling temperature is 830-860° C. The total reduction rate of the finishing rolling stage is greater than 70%, of which the reduction rate of the last two passes of finishing rolling is greater than 18%; In the controlled cooling and coiling, a controlled cooling mode combining head rapid cooling and laminar cooling is adopted, the head rapid cooling final rolling temperature is 780-800°C, the final cooling temperature range is 650-720°C, the cooling rate is 50-60°C / s, and then laminar cooling is entered, the coiling temperature range is 480-520°C, and the cooling rate is 10-20°C / s; the initial running speed at each 10-60m length of the head and tail is 1.2-1.4 times the normal roller running speed, the normal roller running speed is 1.2-1.5m / s, the initial running speed at each 10-60m length of the head and tail is 1.44-2.1m / s, the head and tail shielding value is 200-500mm, and is maintained for 1-2s, and then the roller running speed is restored to 1.2-1.5m / s.

5. The preparation method according to claim 4, characterized in that In the molten steel smelting, smelting raw materials are configured according to the chemical composition, the molten iron is pretreated by KR to control the sulfur content to be less than or equal to 0.015%, and the molten iron is fed into the converter after slag removal; a double slag method is used for P removal in the converter to control the P content to be less than or equal to 0.02%, the carbon content is controlled to be 0.12% to 0.16% at the end point of the converter smelting, and argon gas is blown for 10 to 25 minutes during tapping.

6. The preparation method according to claim 4, characterized in that 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 to 30 minutes.

7. The preparation method according to claim 4, characterized in that During the heating of the cast billet, the thickness of the cast billet is 170-230 mm.

8. The preparation method according to claim 4, characterized in that In the hot rolling, high-pressure water is used to descale the cast slab after it is discharged from the furnace for 1 to 2 minutes before rolling, and the descaling machine pressure is 20 to 25 MPa; the total reduction rate in the rough rolling stage is controlled at 75% to 85%, and the rough rolling passes are 3 to 5.

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