Low-cost 420mpa grade hot-rolled wheel steel and method of making same

Abstract

The application discloses a low-cost 420MPa-grade hot-rolled wheel steel and a preparation method thereof, and belongs to the field of materials and metallurgy technology, and comprises the following components in percentage by weight: C: 0.12% to 0.16%, Si: 0.05% to 0.10%, Mn: 0.80% to 0.90%, P: 0.020% or less, S: 0.015% or less, Al: 0.018% to 0.033%, N: 0.0035% to 0.0055%, and the balance of Fe and inevitable impurities, and 0.25 <= (C+Mn / 6) <= 0.30. The low-cost 420MPa-grade wheel steel plate with a thickness of 10 to 25 mm is realized, and the 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 can guarantee the service safety of the 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 420MPa-grade hot-rolled wheel steel and a preparation method thereof. BACKGROUND

[0002] A wheel is an important safety structure in automobile driving, and a steel wheel assembly is obtained through a series of strict manufacturing processes such as rolling or spinning forming, welding, paint spraying treatment, and has the advantages of high precision, light weight, long fatigue life, and reliable safety. The hot-rolled raw material steel plate for manufacturing a wheel is required to have high strength, toughness and plasticity, high fatigue resistance, impact resistance, and high surface quality. At present, the use of 500MP-grade or above high-strength wheel steel is less in the market, and the use of a 500MPa or below strength hot-rolled steel plate is still the mainstream material for manufacturing automobile wheels in the market. The 420MPa-grade wheel steel currently accounting for a large proportion generally adopts a low-carbon low-manganese composition system, and in order to ensure that the steel strip has a low yield ratio and high plasticity, expensive alloy elements such as niobium, chromium and molybdenum are added to increase the strength, but for 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 420MPa-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 production and equipment safety, the final goal is to realize the maximum efficiency, the lowest energy and alloy cost consumption while ensuring the performance technical requirements of the steel plate. Based on this, it is very important to develop a 420MPa-grade wheel steel with low cost and high strength and toughness for steel plants to improve the profit level. At present, in order to ensure the low-temperature toughness of 420MPa-grade wheel steel, a higher alloy composition (Mn, Nb, Cr, etc.) is usually used, the intermediate blank is kept thick, and a two-stage or even three-stage controlled rolling process is used, which results in that the final rolling temperature of the steel plate may be controlled below 800℃, or even lower; which greatly increases the rolling difficulty. First of all, the rolling mill load, the uniformity of the steel plate temperature, the shape control and the like are all facing severe challenges, and secondly, the improvement of the performance of the steel plate 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 organically combine the phase transformation strengthening, solid solution strengthening and fine-grain strengthening, solve the above problems in the production of 420MPa-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 420MPa-grade wheel steel.

[0004] So far, there are few reports on manufacturing low-cost 420MPa grade hot-rolled wheel steel and its manufacturing method at home and abroad. The journal paper "Titanium in the Role of Automobile Wheel Steel and Alloying Process Discussion" (Steel, Vol. 36 (2001), p. 48) and "Anshan ASP Line Automobile Wheel Steel Development" (Automobile Technology and Materials, Vol. 6 (2004), p. 57) introduce the addition of Ti and Nb in the manufacture of automobile wheel steel, and the tensile strength after hot rolling can meet the technical requirements. However, Ti and Nb are both valuable elements, and deep controlled rolling method is used, which leads to low production efficiency and obviously increases the manufacturing cost. At the same time, the low-temperature impact performance is not clear.

[0005] In summary, the prior art has the problem of high production cost, so it is not suitable for producing low-cost, excellent toughness 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

[0006] The purpose of the present application is to overcome the above-mentioned defects existing in the prior art, provide a low-cost 420MPa grade hot-rolled wheel steel and its preparation method, realize the production of low-cost 420MPa grade wheel steel plate with a thickness of 10~25mm using a continuous casting billet with a thickness of 170-230mm, and the steel plate has excellent low-temperature toughness, high surface quality and other characteristics, solves the problem of high alloy cost, the steel plate obtained by the present application has the advantages of low cost and high strength and toughness, and can ensure the service safety of the wheel steel plate.

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

[0008] A low-cost 420MPa grade hot-rolled wheel steel, comprising the following components by 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 being Fe and unavoidable impurities, and 0.25≤(C+Mn / 6)≤0.30.

[0009] Optionally, the hot-rolled wheel steel has a transverse tensile yield strength of 310~355MPa, a tensile strength of 420~500MPa, an elongation of ≥26%, a -20℃ transverse Charpy impact energy of ≥135J, and a yield strength ratio of ≤0.83.

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

[0011] The application further discloses a preparation method of the low-cost 420MPa-grade hot-rolled wheel steel.

[0012] In the continuous casting, the overheat degree of the continuous casting is 7-11 DEG C, the casting speed is 0.8-1.1 m / min, the current intensity of electromagnetic stirring in the secondary cooling zone in the continuous casting stage is 200-250 A, the secondary cooling water quantity is 2.1-2.6 L / kg, the light press-down is performed at the solidification end in the horizontal fan-shaped section, the press-down amount of the continuous casting blank is 6-10 mm, and the blank is stacked for 24-48 h after being discharged.

[0013] In the casting blank heating, the casting blank is sequentially discharged after passing through a preheating section, a heating section and a soaking section; the temperature range of the preheating section is 300-600 DEG C, the temperature range of the heating section is 1235-1270 DEG C, and the temperature range of the soaking section is 1100-1120 DEG C; the time of the heating and soaking sections in the furnace is controlled to be 2.5-3.3 h, the opening degree of the upper and lower burners in the soaking section is adjusted, the air-fuel ratio is controlled to be 1:1.7-1:2.2, the temperature difference between the upper and lower surfaces of the blank is ensured to be less than or equal to 15 DEG C, and the time of the soaking section is 1-2 h.

[0014] In the hot rolling, the reduction rate of each pass of the first two passes before rough rolling is 30-50%, the scale is removed by spraying water in the first three passes of rolling, the time of each pass is 0.2-0.5 min, and the pressure is 10-15 MPa; rough rolling is directly followed by finish rolling, and the finish rolling temperature is 830-860 DEG C; the total reduction rate in the finish rolling stage is greater than 70%, and the reduction rate of the last two passes in the finish rolling stage is greater than 18%.

[0015] In the controlled cooling and coiling, the head fast cooling and laminar cooling are combined to form a controlled cooling mode, the finish rolling temperature of the head fast cooling is 780-800 DEG C, the final cooling temperature range is 650-720 DEG C, the cooling speed is 50-60 DEG C / s, then the laminar cooling is performed, the coiling temperature range is 480-520 DEG C, and the cooling speed is 10-20 DEG C / s; the initial running speed of the 10-60 m length at the head and tail is 1.2-1.4 times of the normal roller running speed, the normal roller running speed is 1.2-1.5 m / s, the initial running speed of the 10-60 m length at the head and tail is 1.44-2.1 m / s, the head and tail shielding value is 200-500 mm, and is maintained for 1-2 s, and then the roller running speed is restored to 1.2-1.5 m / s.

[0016] Optionally, in the molten steel smelting: smelting raw materials are configured according to chemical composition, KR molten iron pretreatment is performed, the content of S is controlled to be less than or equal to 0.015%, and after slagging, the molten steel enters a converter; in the converter smelting, a double-slag method is used to remove P, the content of P is controlled to be less than or equal to 0.02%, the content of C at the end of the converter smelting is controlled to be 0.12% to 0.16%, and argon gas is blown for 10 to 25 minutes when the molten steel is tapped.

[0017] 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 to 30 minutes.

[0018] Optionally, in the casting blank heating: the thickness of the casting blank is 170 to 230 mm.

[0019] Optionally, in the hot rolling: the casting blank after tapping is descaled by using high-pressure water for 1 to 2 minutes before opening rolling, and the descaling machine pressure is 20 to 25 MPa; the total reduction rate in the rough rolling stage is controlled to be 75% to 85%, and the rough rolling passes are 3 to 5 passes.

[0020] By implementing the embodiment of the present application, the following beneficial effects can be achieved:

[0021] 1. The smelting process adopts KR molten iron pretreatment deep desulfurization and clean slagging, the converter adopts a double-slag method to remove P, the P and S contents of the casting blank are low, the argon gas blowing time is controlled, and the RH vacuum degassing time is maintained, thereby overcoming the defects of casting blank center segregation, inclusions and H and O content exceeding the standard due to high Mn and C contents, and being beneficial to improving the plasticity and toughness of the steel plate. Reducing the superheat and the continuous casting speed can improve the macrosegregation of the continuous casting blank, reduce the secondary dendrite arm spacing in the solidification structure of the continuous casting blank, help to reduce the segregation of the steel blank and reduce internal organizational defects. Controlling the electromagnetic stirring current intensity of the secondary cooling zone and the secondary cooling water quantity can effectively reduce the average index of carbon segregation, inhibit the trend of segregation and center crack deterioration of the casting blank; the light press is poured at the solidification end, which effectively reduces the center porosity level and segregation of the casting blank, and the light press is poured at the same time, which promotes the breaking of the core grain, provides guarantee for the strength and toughness of the subsequent steel plate, and in addition, the stacking of the offline steel blank is lowered to reduce the aggregation of residual H and inhibit the generation of internal micro cracks of the steel blank.

[0022] 2. Casting blank heating: the temperature and time of the casting blank in the preheating section, the heating section and the soaking section are limited, the full diffusion of each element is ensured, the influence of composition segregation on the structure and performance is reduced, the high-temperature heating and air-fuel ratio of the heating section are provided, the uniformity of the temperature of each part of the casting blank is ensured, and the uniformity of the metal flow in the transverse and longitudinal directions of the steel plate surface is improved; combined with the composition of the steel blank, the heating temperature of the soaking section of the casting blank is reduced to reduce energy consumption; the temperature and time of the heating section and the soaking section are controlled to inhibit the excessive growth of the original austenite grain, 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 two-stage rolling of the steel plate.

[0023] 3、The present application designs reasonable chemical composition, reduces alloy addition amount, replaces precipitation strengthening with fine-grain strengthening, does not add expensive alloy elements, adopts low-temperature heating + hot rolling manufacturing mode, greatly reduces alloy cost and high-temperature deformation resistance in rough rolling and finish rolling stages, is beneficial to improving each pass reduction, and is beneficial to guaranteeing the comprehensive performance of the super steel plate.

[0024] 4、Through the first two passes before rolling in the rough rolling stage, the rolling mill capacity is used as much as possible, a large reduction rate is adopted, austenite dynamic crystallization is promoted, and the original austenite grains are refined, the high-pressure water descaling of the rolling mill is adopted, a temperature gradient is generated from the surface to the center of the steel plate, the core deformation and the uniformity of the structure distribution are promoted in the subsequent finish rolling process, and the strength and toughness of the steel plate are improved. In addition, since the low-temperature heating process is adopted, the intermediate billet waiting is cancelled in the finish rolling stage, the last two passes of rolling are guaranteed to be in the austenite non-recrystallization temperature range, the last two passes are guaranteed to adopt a large reduction rate, the austenite grains are further refined, and the performance of the steel plate is improved.

[0025] 5、The final rolling temperature is controlled to guarantee that the steel plate enters the water in the austenite + ferrite state, different cooling speeds are adopted during the cooling process, the core structure is transformed by using a large cooling speed, then a small cooling speed is used to guarantee the influence of the core redness on the surface temperature, the formation of bainite and martensite phases on the surface of the steel plate is inhibited by controlling the cooling speed and the redness temperature, the number of bainite phases in the core structure is inhibited, and the influence of bainite or martensite phase change on the surface on the strength and toughness of the steel plate is avoided; in order to realize the temperature uniformity control in the length direction of the steel plate, samples are divided into one sample according to every 0.1-0.2 m length from the head, on this basis, each model (temperature, flow) is optimized for each sample interval, and the optimal running speed trend of each sample is obtained according to the calculation formula of the steel plate longitudinal temperature measurement value, the target final cooling temperature process requirement and the head and tail shielding value (head and tail shielding value = HMI interface shielding distance set - shielding time * roller speed). For the low-temperature area existing in 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 head and tail water flow is controlled according to the thickness group distance to reduce the excessive cooling of the cooling water on the head and tail of the steel plate, and the performance uniformity of the steel plate is improved.

[0026] The present application realizes low-cost manufacturing of a 10-25 mm thick 420 MPa grade hot-rolled wheel steel plate through simple composition design, alloy cost reduction, and regulation and control of steelmaking, continuous casting, heating and rolling and controlled cooling processes. The steel plate has good low-temperature toughness. The specific performance is that the yield strength performance of transverse tension is between 310-355 MPa, the tensile strength is between 420-500 MPa, the yield strength ratio is ≤0.83, the elongation is ≥26%, and the transverse Charpy impact energy at-20℃ is ≥135 J. DETAILED DESCRIPTION

[0027] The present application is further illustrated in conjunction with specific examples, but does not limit the present application in any way.

[0028] The present application discloses a low-cost 420MPa grade hot-rolled wheel steel, comprising the following components by 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 being Fe and inevitable impurities, and 0.25≤(C+Mn / 6)≤0.30.

[0029] Specifically, the role of each main element in the chemical composition of the steel plate of the present application is as follows:

[0030] C: the most economical and basic strengthening element in steel, which has a significant effect on improving the strength of the steel through solid solution strengthening and precipitation strengthening, but increasing the C content has a negative impact on the plasticity, toughness and weldability of the steel. Therefore, the C content range is set to 0.12%~0.16% in the present application.

[0031] Mn: improves the strength of the steel through solid solution strengthening, while compensating for the loss of plate strength caused by the reduction of C content. In addition, it can also reduce the γ-α phase transition temperature, thereby refining the ferrite grains, which helps to obtain fine low-temperature phase transformation products and improve their toughness. However, increasing the content of Mn will exacerbate the center segregation of continuous casting billet and the formation of lamellar martensite, which is not conducive to the improvement of the low-temperature toughness of the steel plate and also affects the hole expansion performance of the steel plate. Therefore, the Mn content range is designed to be 0.80%~0.90% in the present application.

[0032] Si: has the effects of steelmaking deoxidization and improving the strength of the matrix. However, excessive Si will reduce the toughness of the base material in the weld heat-affected zone, and increasing the Si content can purify the ferrite and reduce the content of pearlite, which is beneficial to reducing the Bauschinger effect of the base material. Therefore, the Si content is set to 0.05%~0.10% in the present application.

[0033] N: in steel, N has no other obvious effect except forming fine NbN particles to refine austenite grains, so it needs to be maintained at a relatively low content level, and the N content range selected in the present application is 0.0035%~0.0055%.

[0034] Al: is usually used as a deoxidizer in steel, and has the effect of refining the structure when AlN is formed. When the content of Al exceeds 0.033%, excessive alumina inclusions will reduce the cleanliness of the steel. Therefore, the lower limit of the Al content is set to 0.018%.

[0035] P, S: are inevitable impurity elements in steel, should be as low as possible. But for the consideration of smelting cost and process, it can not be unlimitedly low. Therefore, the upper limit of P, S content in the application is set to 0.020% and 0.015%.

[0036] The application further controls 0.25≤(C+Mn / 6)≤0.30, ensures that the wheel steel has good welding performance, the hardness of the heat-affected zone is relatively low, and the possibility of welding crack is low. If it is not in this range, welding crack will occur, which further affects the welding performance of the wheel steel.

[0037] In a specific embodiment, the transverse tensile yield strength of the hot-rolled wheel steel is 310-355 MPa, the tensile strength is 420-500 MPa, the elongation is ≥26%, the -20℃ transverse Charpy impact energy is ≥135 J, and the yield strength ratio is ≤0.83.

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

[0039] The application also discloses a preparation method of the low-cost 420MPa-grade hot-rolled wheel steel.

[0040] S1, in the molten steel smelting: the smelting raw materials are configured according to the chemical composition, KR hot metal pretreatment is performed, the content of S is controlled to be ≤0.015%, and after slagging, it is put into the converter; the double-slag method is used for P removal in the converter smelting, the content of P is controlled to be ≤0.02%, the content of C is controlled to be 0.12%-0.16% at the end of the converter smelting, and argon gas is blown for 10-25 min when tapping. The argon blowing and settling before continuous casting can promote the removal of inclusions in the molten steel and improve the composition uniformity of the molten steel.

[0041] S2, 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 min.

[0042] S3, in continuous casting: the continuous casting superheat is 7-11℃, the continuous casting withdrawal rate is 0.8-1.1m / min, reducing the superheat and the continuous casting withdrawal rate can improve the macrosegregation of the continuous casting billet, reduce the secondary dendrite arm spacing in the solidification structure of the continuous casting billet, help to reduce the segregation of the billet and reduce internal structure defects; the current intensity of electromagnetic stirring in the secondary cooling zone in the continuous casting stage is controlled to be 200-250A, the secondary cooling water quantity is 2.1L / kg-2.6L / kg, the average index of carbon segregation is reduced, the segregation is inhibited, at the same time, the secondary cooling intensity is limited, the trend of the center crack of the billet is inhibited, in the horizontal fan-shaped section, the light press-down is put into the solidification end, the press-down quantity of the continuous casting billet is 6-10mm, the center porosity level and the segregation of the billet are reduced, the billet is stacked for 24-48h after being discharged, the aggregation of residual H is reduced, the internal micro-crack of the billet is inhibited, and the toughness of the steel plate is ensured.

[0043] S4, billet heating: the billet with a thickness of 170-230mm is sent into a walking beam furnace for heating, the billet is sequentially discharged after passing through a preheating section, a heating section and a soaking section; wherein 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 in the furnace in the heating and soaking sections is controlled to be 2.5-3.3h, the opening degree of the upper and lower burners in the soaking section is adjusted, the air-fuel ratio is controlled to be 1:1.7-1:2.2, the temperature difference between the upper and lower surfaces of the billet is ensured to be ≤15℃, and the soaking time is 1-2h. Increasing the heating temperature and prolonging the time in the furnace further promotes the diffusion of alloy elements Mn and C, and reduces the influence of composition segregation on the structure and performance; at the same time, the high-temperature heating in the heating section and the control of the air-fuel ratio ensure the uniformity of the temperature of each part of the billet and improve the uniformity of the metal flow in the transverse and longitudinal directions of the steel plate; combined with the composition of the billet, the heating temperature in the soaking section is reduced to reduce energy consumption, the temperature and time of the heating section and the soaking section are limited to inhibit the excessive growth of the original austenite grains, ensure the contribution of fine-grain strengthening to the strength of the steel plate, and in addition, low-temperature heating is adopted in the soaking section to avoid the waiting time for rolling in the finishing rolling stage of the steel plate.

[0044] S5, in hot rolling: before opening, the cast blank after tapping is descaled for 1-2 min using high-pressure water, the descaling machine pressure is 20-25 MPa; in the rough rolling stage, the reduction rate of each pass of the first two passes is 30-50%, and the first three passes are sprayed with descaling water, the time of each pass is 0.2-0.5 min, and the pressure is 10-15 MPa; the first three passes are rolled as much as possible to develop the rolling mill capacity, a large reduction rate is adopted to promote the dynamic recrystallization of austenite, refine the original austenite grains, and through the use of high-pressure water descaling of the rolling mill, a temperature gradient is generated from the surface to the center of the steel plate, which promotes the core deformation and uniformity of the microstructure distribution in the subsequent finishing rolling process, and improves the strength and toughness of the steel plate; the total reduction rate in the rough rolling stage is controlled at 75%-85%, and the rough rolling pass is 3-5 passes; after the rough rolling stage, direct finishing rolling is carried out, the total reduction rate in the finishing rolling stage is >70%, and the reduction rate of the last two passes in the finishing rolling stage is >18%; the finishing rolling temperature is 830-860℃. Due to the adoption of low-temperature heating process, the intermediate blank waiting in the finishing rolling stage is cancelled, the last two passes of the finishing rolling are ensured to be in the non-recrystallization temperature range of austenite, the large reduction rate is ensured in the last two passes, the austenite grains are further refined, and the performance of the steel plate is improved.

[0045] S6, in the controlling cooling and coiling: a head fast cooling and laminar cooling combined controlled cooling mode is adopted, the head fast cooling final rolling temperature is 780-800℃, the final cooling temperature interval is 650-720℃, the cooling speed is 50-60℃ / s, then laminar cooling is entered, the coiling temperature interval is 480-520℃, the cooling speed is 10-20℃ / s, the final rolling temperature is controlled, the ferrite + austenite is ensured when the steel plate enters water, in the cooling process, different cooling speeds are adopted, the core organization transformation is ensured by large cooling speed, then small cooling speed is adopted, the influence of the core redness on the surface temperature is ensured, the bainite and martensite phase formation on the surface of the steel plate is inhibited by controlling the cooling speed and the redness temperature, and the influence of the bainite or martensite phase change on the surface on the strength and toughness of the steel plate is avoided; the initial running speed of the head and tail 10-60m length is 1.2-1.4 times of the normal roller running speed, the normal roller running speed is 1.2-1.5m / s, the initial running speed of the head and tail 10-60m length is 1.44-2.1m / s, the head and tail shielding value is 200-500mm, and is maintained for 1-2s, then the roller running speed is restored to 1.2-1.5m / s. The final rolling temperature is controlled, the austenite + ferrite is ensured when the steel plate enters water, in the cooling process, the cooling speed and the final cooling temperature are controlled, the martensite phase formation of the steel plate is inhibited, and the influence of the martensite phase change on the surface on the toughness of the steel plate is avoided; in order to realize the temperature uniformity control in the length direction of the steel plate, the sample is divided into a sample according to every 0.1-0.2m length from the head, on this basis, each model (temperature, flow) is calculated for the speed optimization of each sample interval, and the optimal running speed trend of each sample is obtained according to the steel plate longitudinal temperature measurement value, the target final cooling temperature process requirement 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 zone existing in 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 head and tail position water flow is controlled according to the thickness group distance to reduce the excessive cooling of the cooling water on the head and tail of the steel plate, and the performance uniformity of the steel plate is improved.

[0046] The following is a specific embodiment

[0047] Table 1 is the chemical composition of the example steel, Table 2 is the smelting process system of the example steel, Table 3 is the heating system of the cast blank and the high-pressure water descaling process before rolling of the continuous casting blank of the example steel; Table 4 is the rolling parameter of the example steel; Table 5 is the controlled cooling and coiling process parameter of the example steel; and Table 6 is the performance index of the example steel plate.

[0048] Table 1 is the chemical composition of the example steel, Table 2 is the smelting process system of the example steel, Table 3 is the heating system of the cast blank and the high-pressure water descaling process before rolling of the continuous casting blank of the example steel; Table 4 is the rolling parameter of the example steel; Table 5 is the controlled cooling and coiling process parameter of the example steel; and Table 6 is the performance index of the example steel plate.

[0049]

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

[0051] Table 2 Smelting process schedule of example steel

[0052]

[0053] Table 3 Heating schedule of casting blank and high-pressure water descaling process before rolling of continuous casting blank of example steel

[0054]

[0055] Table 4 Rolling parameters of example steel

[0056]

[0057] Table 5 Controlled cooling and coiling process parameters of example steel

[0058]

[0059] Table 6 Performance indicators of example steel plate

[0060]

[0061] It can be seen that, compared with the prior art, the component design, the steelmaking and continuous casting, the heating and the controlled rolling and controlled cooling scheme of the present application overcome the shortcomings of the prior art, and provide a 420MPa grade hot-rolled wheel steel with a thickness specification of 10-25mm and a manufacturing method thereof. The steel plate has low cost, high strength and toughness, and can ensure the service safety of the wheel steel plate.

[0062] The above-described embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the scope of the present application. Therefore, the protection scope of the present application patent should be subject to the appended claims.

Claims

1. A low-cost 420MPa grade hot-rolled wheel steel, characterized in that, Includes the following components by 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%, with the balance being Fe and unavoidable impurities, and 0.25≤(C+Mn / 6)≤0.30; 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 of ≥135 J at -20℃, and a yield strength ratio of ≤0.

83. The method for preparing low-cost 420MPa grade hot-rolled wheel steel includes the following steps: steelmaking, LF refining, RH vacuum degassing, continuous casting, billet heating, hot rolling, controlled cooling and coiling; In the continuous casting process: the superheat is 7-11℃, the casting speed is 0.8-1.1m / min; the electromagnetic stirring current intensity in the secondary cooling zone is controlled at 200-250A, the secondary cooling water volume is 2.1L / kg-2.6L / kg, and light pressure is applied at the end of solidification in the horizontal fan-shaped section, with a billet reduction of 6-10mm. The billets are stacked for 24-48 hours after being removed from the line. The billet heating process involves sequentially passing the billet through a preheating section, a heating section, and a soaking section before exiting the furnace. The preheating section has a temperature range of 300–600℃, the heating section has a temperature range of 1235–1270℃, and the soaking section has a temperature range of 1100–1120℃. The time spent in the heating and soaking sections is controlled to be 2.5–3.3 hours. The opening degree of the upper and lower burners in the soaking section is adjusted to control the air-fuel ratio at 1:1.7–1:2.2, 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 hot rolling process: during the roughing stage, the reduction rate for each of the first two passes is 30-50%, and the first three passes are sprayed with descaling water, with each pass lasting 0.2-0.5 minutes and at a pressure of 10-15 MPa; after roughing, the finishing stage is directly carried out, with a finishing temperature of 830-860℃; the total reduction rate in the finishing stage is >70%, of which the reduction rate in the last two stands is >18%; In the controlled cooling and winding process: a controlled cooling mode combining rapid cooling at the head and laminar flow cooling is adopted. The final rolling temperature of rapid cooling at the head is 780-800℃, the final cooling temperature range is 650-720℃, and the cooling rate is 50-60℃ / s. Subsequently, laminar flow cooling is adopted, with the winding temperature range being 480-520℃ and the cooling rate being 10-20℃ / s. The initial running speed for the first 10-60m of the head and tail is 1.2-1.4 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 is 1.44-2.1m / s, with a head and tail shielding value of 200-500mm, which is maintained for 1-2s. Then, the roller conveyor running speed returns to 1.2-1.5m / s.

2. The low-cost 420MPa 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 420MPa 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%. At the end of the converter smelting, the C content is controlled to be 0.12%~0.16%. Argon gas is blown for 10~25 minutes when tapping the steel.

4. The low-cost 420MPa 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.

5. The low-cost 420MPa 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.

6. The low-cost 420MPa grade hot-rolled wheel steel according to claim 1, characterized in that, During the hot 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 total reduction rate during the rough rolling stage is controlled at 75%-85%, and the rough rolling passes are 3-5 times.

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