High-sulfur steel for automobile hub and preparation method of high-sulfur steel

Abstract

The invention relates to high-sulfur steel for an automobile hub and a preparation method of the high-sulfur steel. The preparation method comprises the following steps: converter smelting (taking quantitative non-desulfurized molten iron and high-quality scrap steel as raw materials for primary smelting and tapping in a converter, sequentially adding silicomanganese and high-carbon ferromanganese according to the sequence, and adjusting the S content according to the S content of molten steel at the end point of the converter and by adding ferrous sulfide in the tapping process), LF refining, continuous casting and steel rolling. By using the high-sulfur steel for the automobile hub produced by the invention, the Mo element and a large amount of Ti element do not need to be independently added, so that a large amount of cost can be saved. The steel has good cutting performance, meanwhile, the steel needs to have excellent obdurability to keep part stability, and the mechanical performance in the hot rolling state can meet the following requirements that the tensile strength is larger than or equal to 735 Mpa, the lower yield strength is larger than or equal to 420 Mpa, the ductility is larger than or equal to 16%, and the hot rolling hardness ranges from 210 HB to 240 HB.

Description

Technical Field

[0001] The invention relates to the field of automobile steel manufacturing, and in particular to a high-sulfur steel for automobile wheel hubs and a preparation method thereof. Background Art

[0002] The wheel hub is an important part of the car and an important part of the car's driving process. All the forces and torques between the car and the ground are borne and transmitted by the wheel hub. It directly affects the overall driving stability, safety, reliability, smoothness, traction and appearance of the car. It has a great impact on the overall energy consumption of the car and the life of the tire. The wheel hub is also a very important part of the car chassis system. It transmits the force and torque between the wheel and the frame through the suspension system, stabilizes the car's steering, and buffers the impact of road bumps on the frame or body. The car's driving torque eventually transmits the driving force to the car hub to drive the car to rotate and ensure the smooth driving of the car. The wheel hub bears the entire weight of the car and bears the alternating impact load generated by the rotating torque. For the car, the stability of the wheel hub determines the most important safety of the car, so the strength of the wheel hub is crucial to the car. At present, there are two main types of car hubs on the market: aluminum alloy and steel. The main advantages of the former are good heat dissipation, protection of tires, extended tire life, good grip, and high friction coefficient. However, aluminum alloy wheels are expensive. Compared with steel wheels, the performance is not much different from aluminum alloy wheels, but the cost is much cheaper than aluminum alloy wheels. Steel wheels have considerable economic benefits. At present, about 95% of foreign cars have adopted steel wheels. Improving the cutting performance of steel wheels also makes it easier to process the finished wheels into beautiful shapes comparable to aluminum alloy wheels.

[0003] Based on the above reasons and considering the economic efficiency, it is urgent to design a steel for automobile wheel hub that has high uniformity, high toughness, good machinability and sufficient strength. Summary of the invention

[0004] In order to solve the above problems, the present invention discloses a high-sulfur steel for automobile wheel hub and a preparation method thereof, and the specific technical scheme thereof is as follows: A method for preparing high-sulfur steel for automobile wheel hubs comprises the following steps: (1) Converter smelting: Non-desulfurized hot metal and high-quality scrap steel are used as raw materials for primary smelting in a converter. When tapping steel, silicon manganese (FeMn 68 Si 18 ): 8.5~10.5kg / t, high carbon ferromanganese (FeMn 68 C 7.0 ): 13~15kg / t, according to the S content of the molten steel at the end of the converter, sulfur iron is added during the steel-making process to adjust the S content; Before 20 tons of steel is tapped from the converter, aluminum cakes for pre-deoxidation are added to prevent alloy oxidation and waste. Alloys are added after 30 tons; the speed of adding alloys is controlled to ensure that all alloys are added to the ladle when the amount of steel tapped reaches 1 / 2, and the bottom blowing argon stirring is adjusted to 500-600NL / min. After all the alloys are melted, 3 / 4 of the slag is added. At this time, the stirring time of the bottom blowing argon is controlled at 1min, and then the bottom blowing argon stirring is quickly adjusted to 200-300NL / min. The deoxidizer calcium aluminum iron is added to the impact area. After the deoxidizer is added for 1min, the argon stirring is adjusted to 100-200NL / min, and the remaining 1 / 4 of the slag is added to the ladle; after the slag is added, soft blow for 2-3 minutes at the argon blowing station, and aluminum wire is fed into the molten steel. 100m of aluminum wire with a specification of φ9mm is fed into the first furnace of the tundish, and 70m of aluminum wire with a specification of φ9mm is fed into the continuous casting furnace; (2) LF refining: 2.1) In the early stage of LF refining and when adjusting the composition, use argon blowing and stirring (preferably without overturning or exposing the molten steel) to make the composition uniform. Otherwise, keep the argon blowing soft. The bottom blowing and stirring flow rate during the refining process is less than 600NL / min. 2.2) Slag adjustment: In principle, no slag is added during the LF refining process, and no desulfurization is done intentionally. If the S content of the first batch of molten steel in LF refining is low, ferrosulphur is added to adjust the S content. The refining slag must have good fluidity and the white slag time must be ≥25min. 2.3) Use silicon carbide, calcium carbide and aluminum particles to deoxidize the slag surface. The amount of calcium carbide added is 40-60 kg / furnace and the amount of silicon carbide added is 100-120 kg / furnace; the Al mass content of the second sample is controlled to be 0.010%-0.015%; 2.4) Use high carbon ferrochrome to adjust the Cr content in refining; use ferrotitanium to adjust the Ti content in the case of white slag in the later stage of refining; 2.5) No denaturation treatment is performed, and the sulfur content is adjusted to the internal control range by feeding the sulfur line at the end of LF refining; 2.6) Soft blowing for 20 to 30 minutes; 2.7) During the refining process, the requirements for bottom blowing argon stirring are: when adding alloys to adjust the chemical composition, the bottom blowing argon flow rate is controlled at 400-500NL / min, and the slag surface blowing area is controlled at 100-200mm; during other refining times, the bottom blowing argon flow rate is controlled at 100-200NL / min, the slag surface is slightly moved and the molten steel is not exposed, and the bottom blowing argon flow rate is prohibited to exceed 200NL / min; (3) Continuous casting: The superheat of the first ladle is 25-45℃, and the pulling speed is 1.20m / min; the superheat of the continuous casting furnace is 20-30℃, and the pulling speed is 1.35m / min. The temperature drop of each ladle of molten steel from the beginning to the end of casting is ≤5℃; (4) Steel rolling: The continuous casting billet is cold charged into the furnace, and the walking-beam heating furnace is re-divided from the original three heating zones into six heating zones; the temperature of the preheating section is ≤850℃, the temperature of the first heating section is 950±10℃, the temperature of the second heating section is 1100±10℃, the temperature of the third heating section is 1140±10℃, the temperature of the first soaking section is 1160±10℃, and the temperature of the second soaking section is 1150±10℃. From the perspective of the division of heating areas, the preheating section, the first heating section, and the second heating section are the billet uniform heating sections; the third heating section, the first soaking section, and the second soaking section are the billet homogenization high-temperature diffusion stages; the starting rolling temperature is ≥1050℃, the final rolling temperature is ≥950℃, the upper cooling bed temperature is ≥850℃, the slow cooling temperature of the steel entering the pit is ≥430℃, the slow cooling time of the steel entering the pit must be ≥72h, and the surface temperature of the steel is ≤100℃ when the steel is out of the pit, and it is out of the pit.

[0005] Furthermore, the chemical composition and mass content of the molten steel in step (1) are as follows: C: 0.40%-0.43%, Mn: 1.57%-1.65%, Cr: 0.12%-0.15%, Ti: 0.02%-0.03%; there is no need to add Mo and a large amount of Ti elements separately, As≤0.0070%, Sn≤0.005%, Pb≤0.009%, Sb≤0.0008%, Bi≤0.0005%.

[0006] Furthermore, in the step (1), in order to prevent the molten steel from being over-oxidized, a high carbon drawing operation is performed at the end of the converter, so that the mass content of C is ≥ 0.08%, the tapping temperature is 1620-1670°C, and the mass content of phosphorus is ≤ 0.012% when tapping.

[0007] Furthermore, in the step (1), when the converter is tapping steel, aluminum blocks are added for precipitation deoxidation according to the oxygen determination result at the end of blowing. The slag material is made by using lime, refined slag and quartz sand, with the amount of lime added being 500 kg / furnace, the amount of refined slag added being 200 kg / furnace and the amount of quartz sand added being 100 kg / furnace.

[0008] Furthermore, in the step (2), argon blowing is used for stirring in the early stage of refining and when adjusting the composition. The intensity of stirring and blowing argon is suitable to ensure that the molten steel is not greatly stirred and exposed, and the composition is uniform. Otherwise, soft argon blowing is maintained. The bottom blowing stirring flow rate during the refining process is less than 600NL / min.

[0009] Furthermore, in the step (2), the temperature of the first ladle is 1557-1577°C, the temperature of the ladle in the continuous casting furnace is 1537-1567°C, the superheat of the first ladle is 25-45°C, and the superheat of the continuous casting furnace is 20-30°C.

[0010] Furthermore, in the step (3), the billet is cast in an arc continuous casting machine, the billet specification is 210*210 mm, and a tundish covering agent and a mold protection slag are used to implement 100% protection casting throughout the whole process to avoid secondary oxidation of the molten steel.

[0011] Furthermore, in step (3), a cold water flow rate is controlled at 120±5m 3 / h, the M-EMS electromagnetic stirring current is 350A, the frequency is 2.5Hz, and the F-EMS electromagnetic stirring current is 250A, the frequency is 10Hz.

[0012] Furthermore, in step (4), the 210*210 mm square continuous casting billet is cold loaded into the furnace, and the total heating time is controlled within 2.5 to 3.0 h, of which the high temperature diffusion time is 1.25 to 1.5 h.

[0013] A high-sulfur steel for automobile wheel hubs prepared by the preparation method of the high-sulfur steel for automobile wheel hubs, wherein the elements of the high-sulfur steel for automobile wheel hubs include, in order by mass percentage: C: 0.40%-0.43%, Si: 0.25%-0.33%, Mn: 1.57%-1.65%, Cr: 0.12%-0.15%, Ti: 0.02%-0.03%, P≤0.012%, S: 0.095%-0.11%, Cu≤0.05%, Ni≤0.04%, As≤0.0070%, Sn≤0.005%, Pb≤0.009%, Sb≤0.0008%, Bi≤0.0005%, and the balance is Fe and unavoidable impurity elements.

[0014] The beneficial effects of the present invention are: (1) The high-sulfur steel for automobile wheel hub and the preparation method thereof of the present invention, after fully considering the requirements of the mechanical properties of the steel, reduces the amount of precious alloy Ti iron added by increasing the C and Mn contents and appropriately adding Cr elements, and no longer adds Mo iron separately, which can greatly reduce the production cost and reduce the difficulty of smelting. By calculating, the cost can be reduced by 200 yuan per ton of steel.

[0015] (2) The present invention takes into account the "hot brittleness" of medium carbon high sulfur steel and the influence of a large amount of sulfides on the continuity of steel, while also meeting the requirements of automobile wheel hubs for mechanical properties. It is difficult to meet the above three conditions at the same time, and the chemical composition and process method have been redesigned with full consideration of the above situation.

[0016] (3) The high-sulfur steel for automobile wheel hubs of the present invention has a tendency to grow grains during high-temperature heating. Elements for controlling high-temperature grain growth must be added to the high-sulfur steel for automobile wheel hubs of the present invention. Considering that the molten steel contains a certain amount of nitrogen and cost considerations, a certain amount of titanium is added to the steel of the present invention to form TiN, which can prevent grain growth and thus achieve the effect of fine grain strengthening. In order to control the size of the titanium nitride inclusions formed, the Ti content is determined to be 0.02% to 0.03%.

[0017] (4) The present invention strictly controls the residual element content of molten iron, selects high-quality scrap steel for smelting, optimizes the smelting process to achieve ultra-low control of five harmful elements: As≤0.0070%, Sn≤0.005%, Pb≤0.009%, Sb≤0.0008%, and Bi≤0.0005%, thereby ensuring the stability of the processed automobile wheel hub.

[0018] (5) The method for preparing high-sulfur steel for automobile wheel hubs of the present invention does not require desulfurization of molten iron, which effectively reduces production costs. The inherent advantage of the uniform distribution of sulfur in high-sulfur molten iron is fully utilized, thereby improving the uniform distribution of the morphology of sulfides in steel and ensuring uniform mechanical properties.

[0019] (6) The method for preparing high-sulfur steel for automobile wheel hubs of the present invention adopts a six-stage ultra-precise temperature-controlled heating furnace for high-temperature heating, so that the original continuous casting billet is heated evenly on all four sides to prevent the generation of "yin-yang surface", improve the homogenization effect of the continuous casting billet, and make the rolling deformation rate consistent to prevent the generation of "splitting" defects during the rolling process. The temperature drop rate is consistent during the slow cooling process, and the microstructure transformation is uniform and effective, which stabilizes the uniformity of product performance.

[0020] (7) The high-sulfur steel for automobile wheel hub and the preparation method thereof of the present invention optimize the superheat and casting speed parameters in the continuous casting process, improve the core structure of the ingot, use a large compression ratio to increase the density of the steel, and ensure that the ultrasonic flaw detection can reach the AA level.

[0021] (8) The method for preparing high-sulfur steel for automobile wheel hub of the present invention optimizes the cooling strength of the first and second cooling water during continuous casting, slows down the growth of columnar crystals, increases the equiaxed crystal ratio, and improves the uniformity of the composition of the entire cross-section of the ingot.

[0022] (9) The method for preparing high-sulfur steel for automobile wheel hub of the present invention develops a new head-end electromagnetic stirring process to interrupt the growth of dendrites and make the composition of molten steel at the dendrite position as balanced as possible.

[0023] (10) The preparation method of the high-sulfur steel for automobile wheel hub of the present invention has a tensile strength of ≥735 MPa, a lower yield strength of ≥420 MPa, an elongation of ≥16%, and a hot-rolled hardness of 210 to 240 HB in the hot-rolled state. DETAILED DESCRIPTION

[0024] The present invention will be further described below in conjunction with specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0025] Existing high-sulfur automobile wheel hub steel manufacturers have added Mo and a large amount of Ti elements to the traditional main element control to improve the hardenability of steel to ensure the mechanical properties of steel in the hot-rolled state. The additional addition of precious alloys greatly increases the production cost, which is disadvantageous for steel mills. The advantage of using die casting in the steelmaking model is that there will be no problem of immersion nozzle nodules, the casting process is relatively smooth, the steel density is also good, and the flaw detection pass rate is improved. The yield rate of die-cast ingots is only about 80%, while the yield rate of continuous casting billets can reach about 95%, which can greatly improve economic benefits. By redesigning the chemical composition to meet the requirements of hot-rolled mechanical properties of steel, the density of continuous casting billets can be improved by reasonably optimizing the continuous casting process, and the compression ratio of continuous casting billets to steel can further increase the density of steel, and finally the flaw detection pass rate can reach the same effect as die-cast materials.

[0026] For general steel products, sulfur is a harmful element. The presence of sulfur will cause hot brittleness of steel and affect the performance of steel. Therefore, the lower the sulfur content in general steel, the better. However, many downstream users of special steel products need to be cut into various parts. It is well known that although sulfur in steel will affect the performance of steel, it can also greatly improve the cutting performance of steel. Special steel contains a certain amount of sulfur, which is not only easy to process, but also can greatly reduce the life of the cutting head. That is to say, if special steel contains a certain amount of sulfur, the same processing head can process more finished parts. In this way, the production efficiency of downstream processing users can be greatly improved, and a certain amount of processing heads can be saved, reducing production costs and bringing certain benefits to enterprises. From the development experience of steel mills, the higher the sulfur content in normal special steel, the better the cutting performance, but there is no specific value to measure the impact of sulfur content on cutting performance, which can only be verified through the use of downstream users. Therefore, while ensuring the cutting performance of special steel, the performance of steel must also meet the requirements of parts, so designing a composition to match the performance between the two (cutting performance and other properties of steel) is the difficulty in developing this special steel.

[0027] Based on the shortcomings of existing high-sulfur steel for automobile wheels, in the design of chemical composition, after fully considering the requirements of automobile wheels for strength, the carbon content is strictly controlled. On the premise of matching with the production method, the conventional chemical composition design ideas are broken, and the design requirements of high carbon, high manganese, low chromium and low titanium are innovatively introduced; the five harmful elements of As, Sn, Pb, Sb and Bi in steel are strictly controlled to stabilize the performance of steel. Reasonable design of steelmaking process improves the uniformity of molten steel composition and reduces the segregation of chemical composition of steel during solidification. Reasonable heating system for steel rolling further improves the homogenization effect of steel through high-temperature diffusion. Control the heating temperature, starting rolling temperature, final rolling temperature, slow cooling temperature, etc., so that the various mechanical properties of steel in the hot rolling state can meet the standard requirements.

[0028] The high-sulfur steel for automobile wheel hub of the present invention has high uniformity and high strength and toughness. The processing of automobile wheel hub with the steel of the present invention is relatively simple and greatly improves the efficiency of turning processing. The production process is simple to operate, the production cost is low, and the adaptability is strong, and it can be promoted and used in this industry.

[0029] The elements of the high-sulfur steel for automobile wheel hub of the present invention include, in order by mass percentage, C: 0.40%-0.43%, Si: 0.25%-0.33%, Mn: 1.57%-1.65%, Cr: 0.12%-0.15%, Ti: 0.02%-0.03%, P≤0.012%, S: 0.095%-0.11%, Cu≤0.05%, Ni≤0.04%, As≤0.0070%, Sn≤0.005%, Pb≤0.009%, Sb≤0.0008%, Bi≤0.0005%, and the balance is Fe and unavoidable impurity elements.

[0030] The design reasons for the chemical composition of high-sulfur steel for automobile wheel hubs of the present invention are described in detail below: C: The mutual influence between carbon and the strength and toughness of metal materials makes the setting of C content very cautious. According to previous studies, the increase of carbon can quickly increase the carbon equivalent of steel, which significantly improves the strength of steel but significantly reduces the toughness. The impact resistance of steel is reduced, which is not conducive to the service life of parts. If the carbon element is low, the mechanical properties of steel cannot be improved. The mechanical properties can be improved by alloying molten steel, but the cost of steelmaking will increase greatly. Comprehensive consideration is to keep the carbon content in a more appropriate range to maintain strength while having good toughness, so the carbon content is designed to be 0.40% to 0.43%.

[0031] Si: Silicon can increase the yield strength, improve the hardenability, tempering stability and oxidation resistance of steel, but when the silicon content is too high, it is easy to cause serious decarburization on the steel surface and increase the brittle transition temperature of the steel. Taking into account the influence of silicon on the performance of steel, the Si content is determined to be 0.25% to 0.33% during the composition design.

[0032] Mn: Considering that when the Mn content is lower than 1.8%, as its content increases, manganese is added as a particularly important alloying element. Therefore, the Mn content is determined to be 1.57% to 1.65%.

[0033] Ti: Considering the characteristics of the production process in terms of heating temperature, the steel will have a tendency to grow grains during high-temperature heating, and elements to control high-temperature grain growth must be added to the invention steel. Considering that molten steel generally contains a certain amount of nitrogen and cost considerations, a certain amount of titanium is added to this patented steel to form TiN, which can prevent grain growth and thus achieve the effect of fine grain strengthening. In order to control the size of the titanium nitride inclusions formed, the Ti content is determined to be 0.02% to 0.03%.

[0034] Cr: In order to compensate for the lack of strength in the low-carbon composition design, the steel of the present invention adds a proper amount of chromium element in the composition design, and the Cr content is determined to be 0.12% to 0.15%.

[0035] P: In view of the high requirements for hot-rolled mechanical properties of the invented steel, comprehensive consideration of smelting costs and prevention of cold brittleness by controlling phosphorus as a harmful residual element, the P content is determined to be ≤0.012%.

[0036] S: In order to improve the turning performance of automobile wheel hub, sulfur is appropriately added to the invented steel. Considering the good turning performance, the S content is determined to be 0.095% to 0.11%.

[0037] In order to ensure the stability of the processed automobile wheels, the five harmful elements in the steel are controlled to be ultra-low: As≤0.0070%, Sn≤0.005%, Pb≤0.009%, Sb≤0.0008%, and Bi≤0.0005%.

[0038] Take furnace 5 as an example to explain the application process in detail: In actual production, the following production process is used: (1) Hot metal is not subjected to KR quantitative desulfurization treatment: According to the usage of the steel grade, this steel needs to have good machinability, so the steel must contain a higher sulfur content. The blast furnace molten iron does not need desulfurization treatment, which can reduce one process and reduce production costs compared with normal steel grades.

[0039] (2) Converter smelting: High-quality non-desulfurized molten iron and high-quality scrap steel (the molten iron mass can be 80% and the high-quality scrap steel mass can be 20%) are used as raw materials for primary smelting in the converter. In order to prevent the molten steel from being overoxidized, the converter end point high carbon drawing operation is adopted (the high carbon drawing operation is to ensure the removal of harmful elements, increase the carbon content of the charged molten steel out of the furnace to prevent the molten steel from being overoxidized). When tapping, C: 0.11%~0.13%, P: 0.008%~0.011%, and the tapping temperature is 1640~1660℃. When tapping the converter, aluminum blocks are added for precipitation deoxidation according to the oxygen determination results at the end of blowing, and lime, refined slag and quartz sand are used for slag making, with 500kg of lime / furnace, 200kg of refined slag / furnace, and 100kg of quartz sand / furnace. When tapping, silicon manganese (FeMn 68 Si 18 ): 8.5~10.5kg / t, high carbon ferromanganese (FeMn 68 C 7.0 ): 13~15kg / t. According to the S content of the molten steel at the end of the converter, ferrosulphur is added during the steel-making process to adjust the S content.

[0040] Aluminum cakes are added before 20 tons of steel is tapped from the converter, and alloys are added after 30 tons. The speed of adding alloys is controlled to ensure that all alloys are added to the ladle when the amount of steel tapped reaches 1 / 2. At the same time, the bottom blowing argon stirring is adjusted to 550NL / min. After all the alloys are melted, 3 / 4 of the slag is added. At this time, the bottom blowing argon stirring time is controlled to 1min, and then the bottom blowing argon stirring is quickly adjusted to 250NL / min. Deoxidizer calcium aluminum iron is added to the impact area. After the deoxidizer is added for 1min, the argon stirring is adjusted to 150NL / min, and the remaining 1 / 4 of the slag is added to the ladle. After the slag is added, it is soft-blown at the argon blowing station for 2 to 3 minutes, and aluminum wire is fed into the molten steel. 100m is fed into the first furnace of the tundish, and 70m is fed into the continuous casting furnace.

[0041] Table 1 below shows the specific values ​​of the parameters of the converter tapping in the converter smelting operation and the soft blowing time after the slag is added in each embodiment.

[0042] Table 1

[0043] (3) LF refining: 1) In the early stage of refining and when adjusting the composition, use appropriate stirring and argon blowing intensity (preferably without excessive overturning and exposure of molten steel) to uniformly distribute the composition. Otherwise, maintain soft argon blowing. The bottom blowing stirring flow rate during the refining process is 500NL / min.

[0044] 2) Slag adjustment: No additional slag is added during the LF refining process, and the refined slag has good fluidity. The white slag time is 30 to 40 minutes.

[0045] 3) Use silicon carbide, calcium carbide and aluminum particles to deoxidize the slag surface. The amount of calcium carbide added is 40-60 kg / furnace and the amount of silicon carbide added is 100-120 kg / furnace. The mass content of Al in the second sample is 0.011%-0.015%.

[0046] When the molten steel enters the LF refining process, it is first sampled to detect the element content and convert the amount of alloy added. According to the converted alloy amount, the molten steel is alloyed in the subsequent process, and the added alloy is completely dissolved evenly. After the alloying is completed, the molten steel is sampled for the second time to detect the content of each element in the molten steel. The mass content of Al in the second sample refers to the Al content detected in the second sampling of the molten steel after the molten steel is alloyed.

[0047] Table 2 shows the specific values ​​of the slag amount of slag surface deoxidation in the LF refining operation and the mass content of Al in the second sample in each embodiment.

[0048] Table 2

[0049] 4) Use high carbon ferrochrome to adjust the Cr content in refining; in the case of white slag in the later stage of refining, use ferrotitanium to adjust the Ti content, the dosage is: 0.55kg / t.

[0050] 5) No denaturation treatment is performed. At the end of refining, the sulfur content is adjusted to the internal control range by feeding the sulfur line (the internal control range is the range that the enterprise strictly controls on the basis of the standard requirements, that is, higher than the standard requirements).

[0051] 6) Soft blowing time is 25 to 35 minutes.

[0052] 7) The temperature of the first bag is 1557~1577℃, and the temperature of the continuous casting furnace bag is 1537~1567℃.

[0053] During the refining process, the requirements for bottom blowing argon stirring are: when adding alloys to adjust the chemical composition, the bottom blowing argon flow rate is controlled at 450NL / min, and the slag surface blowing area is controlled at 150NL / min; during other refining times, the bottom blowing argon flow rate is controlled at 150NL / min, the slag surface moves slightly, and the bottom blowing argon flow rate exceeds 100NL / min.

[0054] Table 3 shows the specific values ​​of the soft blowing time and the ladle temperature in the LF refining operation in each embodiment.

[0055] Table 3

[0056] (4) Continuous casting: 1) Billet casting is carried out in an arc continuous casting machine with a billet size of 210*210mm. Tundish covering agent and mold protection slag are used to implement 100% protective casting throughout the whole process to prevent secondary oxidation of molten steel.

[0057] 2) The superheat of the first ladle is 25-40℃, and the pulling speed is 1.20m / min; the superheat of the continuous casting furnace is 20-30℃, and the pulling speed is 1.35m / min. The temperature drop of each ladle of molten steel from the beginning to the end of casting is ≤5℃.

[0058] 3) Cold water flow control 120±5m 3 / h, M-EMS electromagnetic stirring current 350A, frequency 2.5Hz, F-EMS electromagnetic stirring current 250A, frequency 10Hz.

[0059] Table 4 gives the specific values ​​of the first ladle superheat, continuous casting furnace superheat, temperature drop and cooling water flow rate in each embodiment during the continuous casting operation.

[0060] Table 4

[0061] (5) Steel rolling: 210*210mm square continuous casting billet is cold loaded into the furnace, and a six-heating zone step-beam heating furnace is used. The preheating section temperature is 700~800℃, the heating section temperature is 950±10℃, the heating section temperature is 1100±10℃, the heating section temperature is 1140±10℃, the soaking section temperature is 1160±10℃, and the soaking section temperature is 1150±10℃. The total heating time is controlled at 2.5~3.0h, of which the high temperature diffusion time is 1.25~1.5h. The rolling temperature is 1060~1080℃, the final rolling temperature is 960~980℃, the upper cooling bed temperature is 860~880℃, the slow cooling temperature of steel entering the pit is 435~455℃, the slow cooling time of steel entering the pit must be 72~80h, and the surface temperature of the steel is ≤100℃ when the steel is out of the pit.

[0062] Table 4 gives the specific values ​​of the preheating stage temperature, the first heating stage temperature, the second heating stage temperature, the third heating stage temperature, the first soaking stage temperature, the second soaking stage temperature, and the total heating time in each embodiment in the steel rolling operation.

[0063] Table 5

[0064] Table 5 gives the specific values ​​of high temperature diffusion time, start rolling temperature, final rolling temperature, upper cooling bed temperature, slow cooling temperature of steel entering the pit, slow cooling time of steel entering the pit, and surface temperature of steel when steel enters the pit in each embodiment during steel rolling operation.

[0065] Table 6

[0066] The chemical composition of the final product is shown in Table 7 and Table 8 below.

[0067] Table 7 Main chemical components (wt%)

[0068] Table 8 Residual elements (wt%)

[0069] The mechanical properties of hot rolled steel are shown in Table 9.

[0070] Table 9 Mechanical properties of hot rolled state

[0071] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as generally understood by those skilled in the art to which this application belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0072] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for preparing high-sulfur steel for automobile wheel hub, characterized in that: The following steps are involved: (1) Converter smelting: Non-desulfurized hot metal and high-quality scrap steel are used as raw materials for primary smelting in a converter. When tapping steel, silicon and manganese FeMn are added in sequence. 68 Si 18 :8.5~10.5kg / t, high carbon ferromanganese FeMn 68 C 7.0 : 13~15kg / t, according to the S content requirement of the converter end steel liquid, sulfur iron is added during the steel tapping process to adjust the S content; Aluminum cakes for pre-deoxidation are added before 20 tons of steel is tapped from the converter, and alloys are added after 30 tons; the speed of adding alloys is controlled, and when the amount of steel tapped reaches 1 / 2, all the alloys are added to the ladle, and at the same time, the bottom blowing argon stirring is adjusted to 500-600NL / min. After all the alloys are melted, 3 / 4 of the slag is added, and at this time, the bottom blowing argon stirring time is controlled to 1min, and then the bottom blowing argon stirring is quickly adjusted to 200-300NL / min, and the deoxidizer calcium aluminum iron is added to the impact area. After the deoxidizer calcium aluminum iron is added for 1min, the argon stirring is adjusted to 100-200NL / min, and the remaining 1 / 4 of the slag is added to the ladle; after the slag is added, soft blowing is performed at the argon blowing station for 2-3min, and aluminum wire is fed into the molten steel. 100m of aluminum wire with a specification of φ9mm is fed into the first furnace of the tundish, and 70m of aluminum wire with a specification of φ9mm is fed into the continuous casting furnace; (2) LF refining: 2.1) In the early stage of LF refining and when adjusting the composition, argon blowing is used for stirring to make the composition uniform. Otherwise, soft argon blowing is maintained. The bottom blowing stirring flow rate during the refining process is less than 600NL / min; 2.2) Slag adjustment: In principle, no slag is added during the LF refining process, and no desulfurization is done intentionally. If the S content of the first batch of molten steel in LF refining is low, ferrosulphur is added to adjust the S content. The refining slag must have good fluidity and the white slag time must be ≥25min. 2.3) Use silicon carbide, calcium carbide and aluminum particles to deoxidize the slag surface. The amount of calcium carbide added is 40-60 kg / furnace and the amount of silicon carbide added is 100-120 kg / furnace; the Al content of the second sample is controlled to be 0.010%-0.015%; 2.4) Use high carbon ferrochrome to adjust the Cr content in refining; use ferrotitanium to adjust the Ti content in the case of white slag in the later stage of refining; 2.5) No denaturation treatment is performed, and the sulfur line is fed at the end of LF refining to adjust the S content to the internal control range; 2.6) Soft blowing for 20 to 30 minutes; 2.7) During the refining process, the requirements for bottom blowing argon stirring are: when adding alloys to adjust the chemical composition, the bottom blowing argon flow rate is controlled at 400-500NL / min, and the slag surface blowing area is controlled at 100-200mm; during other refining times, the bottom blowing argon flow rate is controlled at 100-200NL / min, and the bottom blowing argon flow rate is prohibited to exceed 200NL / min; (3) Continuous casting: The superheat of the first ladle is 25-45℃, and the pulling speed is 1.20m / min; the superheat of the continuous casting furnace is 20-30℃, and the pulling speed is 1.35m / min. The temperature drop of each ladle of molten steel from the beginning to the end of casting is ≤5℃; (4) Steel rolling: The continuous casting billet is cold charged into the furnace, and the walking-beam heating furnace is re-divided from the original three heating zones into six heating zones; the temperature of the preheating section is ≤850℃, the temperature of the first heating section is 950±10℃, the temperature of the second heating section is 1100±10℃, the temperature of the third heating section is 1140±10℃, the temperature of the first soaking section is 1160±10℃, and the temperature of the second soaking section is 1150±10℃. From the perspective of the division of heating areas, the preheating section, the first heating section, and the second heating section are the billet uniform heating sections; the third heating section, the first soaking section, and the second soaking section are the billet homogenization and high-temperature diffusion stages; the starting rolling temperature is ≥1050℃, the final rolling temperature is ≥950℃, the upper cooling bed temperature is ≥850℃, the slow cooling temperature of the steel entering the pit is ≥430℃, the slow cooling time of the steel entering the pit is ≥72h, and the surface temperature of the steel is ≤100℃ when the steel is out of the pit, and it is out of the pit.

2. The method for preparing high-sulfur steel for automobile wheel hub according to claim 1, characterized in that: The chemical composition and mass content of the molten steel in step (1) are as follows: C: 0.40%-0.43%, Mn: 1.57%-1.65%, Cr: 0.12%-0.15%, Ti: 0.02%-0.03%, no need to add Mo and Ti elements separately, As≤0.0070%, Sn≤0.005%, Pb≤0.009%, Sb≤0.0008%, Bi≤0.0005%, and the rest are iron and unavoidable impurities.

3. The method for preparing high-sulfur steel for automobile wheel hub according to claim 1, characterized in that: In the step (1), in order to prevent the molten steel from being overoxidized, a high carbon drawing operation is adopted at the end of the converter to make the mass content of C ≥ 0.08%. When tapping, the temperature of the molten steel is 1620-1670°C, and the mass content of phosphorus in the molten steel is ≤ 0.012%.

4. The method for preparing high-sulfur steel for automobile wheel hub according to claim 1, characterized in that: In the step (1), when the converter is tapping steel, aluminum blocks are added for precipitation deoxidation according to the oxygen determination result at the end of blowing; the slag material is slag-making using lime, refined slag and quartz sand, with the amount of lime added being 500 kg / furnace, the amount of refined slag added being 200 kg / furnace, and the amount of quartz sand added being 100 kg / furnace.

5. The method for preparing high-sulfur steel for automobile wheel hub according to claim 1, characterized in that: In the step (2), argon blowing is used for stirring in the early stage of refining and when adjusting the composition to make the composition uniform. Otherwise, soft argon blowing is maintained. During the refining process, the bottom blowing stirring flow rate is less than 600NL / min.

6. The method for preparing high-sulfur steel for automobile wheel hub according to claim 1, characterized in that: In the step (2), the temperature of the first bag is 1557-1577°C, the temperature of the continuous casting furnace is 1537-1567°C, the superheat of the first bag is 25-45°C, and the superheat of the continuous casting furnace is 20-30°C.

7. The method for preparing high-sulfur steel for automobile wheel hub according to claim 1, characterized in that: In the step (3), the billet is cast in an arc continuous casting machine, the billet specification is 210*210 mm, a tundish covering agent and a mold protection slag are used, and 100% protection casting is implemented throughout the whole process to prevent secondary oxidation of the molten steel.

8. The method for preparing high-sulfur steel for automobile wheel hub according to claim 1, characterized in that: In step (3), the flow rate of cold water is controlled at 120±5m 3 / h, the M-EMS electromagnetic stirring current is 350A, the frequency is 2.5Hz, and the F-EMS electromagnetic stirring current is 250A, the frequency is 10Hz.

9. The method for preparing high-sulfur steel for automobile wheel hub according to claim 1, characterized in that: In the step (4), the square continuous casting billet is cold loaded into the furnace, and the total heating time is controlled to be 2.5 to 3.0 hours, of which the high temperature diffusion time is 1.25 to 1.5 hours.

10. A high-sulfur steel for automobile wheel hubs produced by the method for producing high-sulfur steel for automobile wheel hubs according to any one of claims 1 to 9, characterized in that: The elements of the high-sulfur steel for automobile wheel hubs include, in order by mass percentage, C: 0.40% to 0.43%, Si: 0.25% to 0.33%, Mn: 1.57% to 1.65%, Cr: 0.12% to 0.15%, Ti: 0.02% to 0.03%, P≤0.012%, S: 0.095% to 0.11%, Cu≤0.05%, Ni≤0.04%, As≤0.0070%, Sn≤0.005%, Pb≤0.009%, Sb≤0.0008%, Bi≤0.0005%, and the remainder is Fe and unavoidable impurity elements.

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