Production method of high-carbon bearing steel for spindle bearing of high-rotating-speed precision machine tool

Abstract

The invention relates to a production method of high-carbon bearing steel for a spindle bearing of a high-rotating-speed precision machine tool, and belongs to the field of metallurgy. The process production of KR molten iron pretreatment, converter smelting, converter tapping, LF refining, vacuum degassing and continuous casting is adopted, the whole process collaborative optimization design is adopted, all process control targets are deeply coupled, KR ultra-low sulfur (less than or equal to 0.004%) lays a foundation for low-oxygen and low-sulfur smelting, LF and RH efficient refining is guaranteed through converter accurate end point control (C / P / temperature three elements), and the low-oxygen and low-sulfur low-oxygen and low-sulfur low-oxygen and low-sulfur low-oxygen and low-sulfur low-oxygen and low-sulfur low-oxygen and low-sulfur low-oxygen and low-sulfur low-oxygen The continuous casting electromagnetic stirring and soft reduction technology synergistically improves homogenization, the steel oxygen content is smaller than or equal to 5 ppm, the sulfur content is smaller than or equal to 0.006%, the calcium content is smaller than or equal to 5 ppm, the titanium content is smaller than or equal to 9 ppm, the center porosity is smaller than or equal to 1.0 level, the center segregation is smaller than or equal to 1.0 level, the B fine inclusion is smaller than or equal to 1.0 level, the B coarse inclusion is smaller than or equal to 0.5 level, the DS inclusion is smaller than or equal to 0.5 level, the macroscopic purity is smaller than or equal to 3 mm / dm < 3 >, and the rolling contact fatigue rated life L10 under the contact stress of 4.5 GPa is 2.38 * 107 and is 1.2 times or above that of a die casting material.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a method for producing high-carbon bearing steel. Background Technology

[0002] Modern manufacturing is rapidly developing towards precision, efficiency, and intelligence. High-end fields such as aerospace, precision instruments, semiconductor manufacturing, and medical devices are placing unprecedentedly stringent demands on the machining accuracy, surface quality, and processing efficiency of components. As a core functional component of industrial mother machines, the performance of the machine tool spindle directly determines the overall machining capability of the machine. However, the spindle bearings, as key fundamental components supporting the high-speed rotation of the spindle, bearing complex loads, and ensuring rotational accuracy, have become a bottleneck restricting the performance improvement of high-end precision machine tools due to insufficient performance in high speed, high precision, long life, and high reliability.

[0003] High-speed spindles (typically referring to spindles with speeds exceeding tens of thousands of revolutions per minute) are a core means of improving machining efficiency. However, extremely high speeds bring severe challenges: the enormous centrifugal force subjectes bearing assemblies to extremely high stress, easily leading to deformation or fatigue failure; intense frictional heat causes a sharp rise in operating temperature, triggering material softening, microstructural degradation, and lubrication failure; minute thermal and elastic deformations are significantly amplified, directly threatening the stability of rotational accuracy; vibration and noise problems are also more prominent at high speeds. Under such extreme conditions, traditional general-purpose bearing steels often fail to meet requirements in terms of strength, hardness, dimensional stability, fatigue resistance, and high-temperature performance, leading to premature bearing failure, loss of accuracy, or decreased reliability.

[0004] With the advancement of the "dual carbon" target, replacing ingot casting or electroslag remelting with green and efficient continuous casting technology is an important trend in the low-carbon production of bearing steel. Therefore, developing spindle bearing materials that can meet the requirements of extreme working conditions such as high speed and high precision is of urgent strategic significance.

[0005] Patent Publication Number: CN110257716A, a high-end bearing steel material for machine tools and its production process; Patent Publication Number: CN110257717A, a high-end bearing steel material for machine tool bearing rings and its manufacturing method. The production process of high-end bearing steel materials for machine tools respectively adopts the process flow of "electric furnace → LF refining and VD process → ingot casting". The ingot casting process has low production efficiency and high costs, and rare earth elements are added to the elemental composition. In addition, there is still room for improvement in the control of residual elements and purity in bearing steel. However, to develop spindle bearing materials that can meet the requirements of extreme working conditions such as high speed and high precision, the most fundamental and important prerequisite is to produce bearing steel with high purity. In the context of the green development of bearing steel, using the continuous casting process to replace ingot casting or electroslag remelting has become an inevitable trend. However, to produce high-quality bearing steel using the continuous casting process, the technical thresholds in many aspects such as purity control and tissue homogenization control are higher and the challenges are greater. Therefore, at present, there are few products of bearing steel produced by the continuous casting process that can replace ingot casting or electroslag remelting bearing steel at the application end. Summary of the Invention

[0006] Aiming at the problems existing in the purity control and tissue homogenization control of long-life and high-stability bearing steel produced by the continuous casting process at present, the present invention provides a high-carbon bearing steel for high-speed precision machine tool spindles and its production method using the continuous casting process.

[0007] Compared with the ingot casting and electroslag remelting processes, the continuous casting process is more suitable for the green and efficient mass production of high-carbon bearing steel. However, the risks such as ladle slagging, tundish slag entrainment, and mold slag entrainment in the continuous casting process are relatively high, which is not conducive to the purity control of high-carbon bearing steel. In addition, the center segregation of continuous casting billets is relatively more obvious, and it is more difficult to control banded carbides, reticulated carbides, and liquid segregation carbides. Moreover, the probability of center shrinkage cavities is higher, which is not conducive to the tissue homogenization control of high-carbon bearing steel. In steelmaking, the primary melting furnaces are mainly electric furnaces and converters, and the refining furnaces are mostly LF refining furnaces. The vacuum degassing methods are mainly RH and VD. To produce high-carbon bearing steel with high purity and high homogenization using the continuous casting process, the selection of the steelmaking process flow and process design supporting the continuous casting process are crucial. Therefore, selecting a reasonable steelmaking process and controlling the smelting process, with each process key point and process detail related to each other before and after, to produce a high-carbon bearing steel for high-speed precision machine tool spindles, and to achieve the production of high-carbon bearing steel with high purity and high homogenization using the continuous casting process to replace the ingot casting and electroslag remelting processes, is the main research content of the present invention.

[0008] To achieve the above objectives, this invention proposes a production method for high-carbon bearing steel for high-speed precision machine tool spindle bearings. The core technology for controlling the purity of the steel structure is "oxygen-sulfur synergistic control." The initial hot metal pretreatment further reduces the sulfur content. The subsequent converter tapping and refining furnace slag composition design can appropriately reduce the sulfur capacity of the slag while ensuring that the slag has sufficient inclusion adsorption and deoxidation capacity, avoiding the problems of poor slag fluidity and excessive inclusions caused by excessively basic slag. The core idea of ​​homogenization control is "high-purity molten steel + continuous casting integrated technology." Under the premise of high-purity molten steel, continuous casting is combined with integrated technologies of superheat control, segregation control, and billet defect control to achieve efficient homogenized continuous casting. The specific technical solution is as follows: The process flow is as follows: "KR hot metal pretreatment → converter smelting → converter tapping → LF refining → vacuum degassing → continuous casting → rolling".

[0009] The primary task of KR hot metal pretreatment is to efficiently remove sulfur from blast furnace hot metal. Oxygen and sulfur in steel have a complex interaction; to achieve ultra-low oxygen content in high-purity bearing steel, the sulfur content must be controlled synergistically. This lays the foundation for low sulfur from the very beginning. Several aspects of the KR desulfurization process revolve around efficient desulfurization.

[0010] To ensure effective desulfurization of molten iron, the silicon content is controlled at 0.20%-0.40%, laying a foundation for temperature control and slag composition control during the converter steelmaking process. Before starting the stirring process, a specialized slag remover is used to remove surface slag from the molten iron, with a slag removal rate controlled above 80% to guarantee subsequent desulfurization effectiveness and efficiency. Insufficient slag control will result in mismatched calculated desulfurizing agent dosage, affecting the final sulfur content. During the stirring process, the desulfurizing agent is added in two equal batches when the stirring paddle reaches its maximum speed. The addition of enhanced desulfurizing agent takes into account parameters such as iron composition, temperature, weight, initial sulfur content, and target sulfur content. The specific addition amount is obtained by machine learning prediction and empirical formula verification method to accurately control consumption and reduce costs. The final sulfur content is controlled to be ≤0.004%, and a lower final sulfur content creates good conditions for achieving ultra-low oxygen control. After the stirring treatment, a special slag remover is used to remove the slag on the surface of the molten iron. The removal rate of slag on the surface of the molten iron is controlled to be above 90%, reducing the sulfur increase caused by the addition of desulfurization slag to the converter.

[0011] Converter smelting process: As a primary smelting furnace, the converter's main tasks are decarburization, dephosphorization, and temperature increase. Therefore, the carbon content, phosphorus content, and temperature at the converter's endpoint are three important indicators reflecting the converter's control level. This invention proposes that the converter endpoint should simultaneously meet the following requirements: carbon content 0.15%-0.35%, phosphorus content ≤0.012%, and temperature 1610℃-1660℃. The converter smelting process is designed based on the target control requirements of the converter endpoint. To ensure the converter endpoint temperature, the mass of molten iron added to the converter is controlled to reach more than 80% of the total mass of molten iron and scrap steel. The design and implementation of this ratio is based on narrow composition control of silicon content in the molten iron. To ensure the endpoint phosphorus content, the oxidizing properties and temperature of the slag during the smelting process are controlled. To ensure the endpoint carbon content, a converter endpoint prediction model with static prediction model and machine learning-assisted correction is used to predict the endpoint carbon content, and oxygen blowing smelting is stopped in a timely manner to ensure the stability of the endpoint carbon content. The measured oxygen content at the endpoint provides a reference for the amount of deoxidizer added in the steel tapping process.

[0012] Converter tapping process: Slag blocking is achieved using slag plugs. The density of the slag plugs is between that of molten steel and slag, effectively blocking the taphole during tapping to prevent slag from flowing into the ladle with the molten steel and contaminating it. This method is also cost-effective. A special ladle for smelting bearing steel is used. The refractory material in contact with the molten steel uses improved magnesia-carbon materials, with the MgO+Al2O3 mass fraction controlled above 75%. Before smelting high-carbon bearing steel for high-speed precision machine tool spindle bearings, other high-carbon bearing steels must be smelted in the previous heat, ensuring a clean lining with clear surfaces and brick joints. The tapping process is carried out in three stages: deoxidation, alloying, and slag formation. Each stage is strictly separated according to the total tapping volume. The deoxidation stage tapping volume is controlled within the first 30% of the total tapping volume, the alloying stage within 30%-60%, and the slag formation stage within 60%-85%. An aluminum-iron alloy is used for deoxidation, resulting in a dissolved oxygen content in the steel of less than 20 ppm after deoxidation. Alloying utilizes low-calcium, low-sulfur, low-phosphorus, and low-titanium ferrochrome, ferromanganese, and ferrosilicon alloys. Slag formation employs a special slag-forming agent for high-carbon bearing steel, with the mass fraction of CaO+Al2O3 controlled above 80% and the mass fraction of MgO+SiO2 controlled below 20%. This composition design is based on low-sulfur steel tapping from the converter, ensuring appropriate sulfur capacity while maximizing inclusion adsorption.

[0013] LF refining process: In order to ensure the stability of the LF refining slag composition, a process of slag removal and re-slag formation is adopted to reduce oxidation and temperature drop. During slag removal, the slag removal rate on the surface of molten steel is controlled at more than 90%. After slag removal, a low-melting-point LF refining slag-forming agent is added in time. The amount of low-melting-point slag-forming agent added is 8.5kg-10.0kg per ton of steel, which covers 100% of the surface of molten steel to reduce oxidation and temperature drop of molten steel. In the early stages of LF refining, a rapid slag-forming process is employed to ensure sufficient effective refining time and improve purity. The slag composition design serves to control slag oxidizability, inclusion adsorption capacity, foaming performance, fluidity, and conductivity. The power supply is matched with the bottom-blown argon flow rate to form a uniformly molten foam slag with a certain viscosity within 20 minutes. The mass fraction ratio of CaO / Al2O3 in the slag is controlled between 1.6 and 2.8, and the mass fraction of FeO+MnO+TiO2 is controlled below 1.5%. This slag composition design is also based on the control of low sulfur content in the molten steel in the early stages. Lower slag oxidizability and sufficiently high slag basicity ensure better deoxidation effect. The total amount of alloy added is controlled to be less than 3 kg per ton of steel, and the number of adjustments is controlled to within 3 times to reduce inclusions introduced into the alloy and ensure the purity of the molten steel. The low amount of refining addition is based on the control of the converter tapping temperature.

[0014] Vacuum degassing process: Before vacuuming begins, slag below the impregnation tube is cleared to prevent slag entrapment from affecting the purity of the molten steel. This technology significantly reduces the generation of low-melting-point inclusions, fully utilizing the inclusion removal capability of vacuum degassing. Argon is used as the lifting gas, with 8-16 outlets evenly distributed along the circumference of the inner wall of the riser. The lifting gas flow rate is controlled at 7.5 NL / min-13 NL / min per ton of steel. The gas flow rate is calculated based on the required molten steel circulation efficiency. Too fast circulation leads to rapid erosion of the refractory material, affecting purity; too slow circulation requires a longer time, resulting in a large temperature drop and prolonged erosion time. The high vacuum state is controlled below 130 Pa, and the holding time is controlled at more than 15 minutes. After vacuum treatment, the vacuum is broken. After breaking the vacuum, a bottom argon blowing device is used for soft blowing, controlling the flow rate at 0.1 NL / min-0.4 NL / min per ton of steel, and the soft blowing time is controlled at more than 10 minutes.

[0015] Continuous casting process: For continuously cast billets with a cross-section of 390mm × 510mm or larger, a ladle slag detection device is used to prevent slag from entering the tundish and contaminating the molten steel; argon protection technology for long nozzles is used to prevent secondary oxidation of the molten steel caused by air entering at the connection between the ladle and the long nozzle, and argon protection technology for the tundish is used to prevent secondary oxidation of the molten steel caused by air entering the tundish; a superheat control model is used in conjunction with the tundish induction heating system to control the difference between the actual superheat and the target superheat within ±5℃; a multi-hole submerged entry nozzle is used to avoid slag entrapment in the crystallizer and promote the floating of inclusions; a combination of first-end electromagnetic stirring + end-end electromagnetic stirring + light reduction technology is used to improve the uniformity and density of the central structure; a water distribution model is used to automatically calculate and control the water volume in each cooling zone, controlling the solidification process and casting speed to match the combination of first-end electromagnetic stirring + end-end electromagnetic stirring + light reduction technology.

[0016] Rolling process: Qualified continuously cast billets are hot-fed into a heating furnace at 1180-1280℃ for ≥6 hours, rolling them into intermediate billets with a cross-section of 230mm×230mm. After slow cooling, they are reintroduced into the heating furnace at 1160-1260℃ for ≥2 hours, rolling them again into bars with a diameter <100mm. After slow cooling, they undergo magnetic flux leakage surface inspection and ultrasonic core inspection to ensure bar quality. The rolling process ensures sufficient heating temperature and high-temperature diffusion time, and the multiple rolling passes further ensure uniform microstructure.

[0017] The high-carbon bearing steel for high-speed precision machine tool spindle bearings produced using the above-mentioned production method can replace the mold casting material. The main alloy composition (mass fraction) is C: 0.95~1.05%, Si: 0.15~0.35%, Mn: 0.25~0.45%, Cr: 1.40~1.65%, Mo: ≤0.10%, Al: ≤0.050%, meeting the application requirements. The actual mass has the following properties: oxygen content ≤5ppm, sulfur content ≤0.006%, calcium content ≤5ppm, titanium content ≤9ppm, central porosity ≤1.0 grade, central segregation ≤1.0 grade, fine B inclusions ≤1.0 grade, coarse B inclusions ≤0.5 grade, DS inclusions ≤0.5 grade, and the macroscopic purity of the bar stock ≤3mm / dm. 3 Rated rolling contact fatigue life L under 4.5 GPa contact stress 10 =2.38*10 7 It reaches more than 1.2 times that of molded materials.

[0018] Compared to the current production processes used for high-end bearing steel in machine tools, the innovation of this invention is reflected in: 1. The process of producing high-carbon bearing steel for high-speed precision machine tool spindle bearings by adopting the process of "hot metal desulfurization → converter → ladle refining → vacuum degassing → continuous casting → rolling" replaces the die casting process. The production cycle is short, the production efficiency and yield are high, and large-scale production can be achieved, which meets the requirements of green development.

[0019] 2. The whole process is designed with collaborative optimization. In response to the quality requirements of high carbon bearing steel for high-speed precision machine tool spindle bearings, the control targets of each process are deeply coupled. KR ultra-low sulfur (≤0.004%) lays the foundation for low oxygen and low sulfur smelting. Converter control (C / P / temperature three elements) ensures efficient refining outside the furnace and vacuum degassing. Continuous casting electromagnetic stirring + light reduction technology synergistically improves homogenization.

[0020] 3. KR hot metal pretreatment's intelligent desulfurization control reduces consumption by over 10% and improves efficiency by over 10%; narrow-window control of the three key elements at the converter smelting endpoint improves the stability of subsequent refining; LF refining rapid slag formation technology extends the effective refining time and improves refining efficiency while maintaining the same smelting cycle; vacuum degassing and slag removal technology reduces steel contamination caused by slag entrapment, improves gas porosity distribution, and enhances steel circulation efficiency; integrated continuous casting composite technology significantly reduces billet defects and improves homogenization.

[0021] 4. This invention achieves breakthroughs in purity, improved homogenization, and dual optimization of efficiency and cost in the field of bearing steel smelting through full-process redesign, deep process collaboration, and intelligent control. It breaks the dilemma of "high cost and low efficiency" in high-end bearing steel and provides an industrial mass production solution for a new generation of ultra-high performance bearing steel for high-end equipment manufacturing. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the embodiments. The embodiments are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention.

[0023] The present invention will be further described in detail below with reference to the embodiments.

[0024] Five heats of the steel of this invention were produced using the process flow of "KR hot metal pretreatment → converter → LF refining → RH vacuum degassing → continuous casting → rolling".

[0025] 1. The silicon content of the molten iron used in KR molten iron pretreatment is 0.25%-0.40%; the surface slag removal rate before treatment is >80%; the enhanced desulfurizing agent is added in two batches in equal amounts, with the amount of desulfurizing agent added being 12.4kg-15.7kg per ton of steel; the final sulfur content is 0.002%-0.004%; and the slag removal rate after treatment is >90%.

[0026] 2. The proportion of molten iron in converter smelting is 80%-85%, the final carbon content is 0.15%-0.32%, the phosphorus content is <0.012%, the temperature is 1620℃-1650℃, and the final oxygen content is 176ppm-284ppm.

[0027] 3. The refractory materials used in the steel ladle for converter tapping meet the requirements. The previous heat is smelted with high-carbon bearing steel. When the steel output reaches 20%-30% of the total steel output, deoxidizer is added. Aluminum-iron alloy is added at a rate of 1.8kg-3.2kg per ton of steel. When the steel output reaches 40%-55% of the total steel output, ferrochrome, ferromanganese, and ferrosilicon alloys are added. When the steel output reaches 60%-76% of the total steel output, deoxidizer is added. Slagging agents that have passed the incoming inspection are used.

[0028] 4. The slag removal rate of LF refining furnace is over 90%. After adding slag-forming agent, it can cover 100% of the molten steel surface. The foam slag formation time is 15-20 minutes. Alloy fine-tuning is less than 3 times. The total amount of alloy added is less than 3 kg per ton of steel.

[0029] 5. RH vacuum degassing was successful in slag removal for each furnace. The argon flow rate was increased to 10-13 NL / min per ton of steel, and the high vacuum was controlled at 80-130 Pa for 15-30 minutes. After rupture, the soft blowing flow rate was 0.1-0.25 NL / min per ton of steel, and the soft blowing time was over 10 minutes.

[0030] 6. The continuous casting section is 390mm×510mm. There is no slag in the ladle. The argon flow rate of the long nozzle and tundish is normal. The difference between the actual superheat and the target superheat is within ±4℃. The electromagnetic stirring at the beginning and end is set with different currents and frequencies. Fixed parameters are used under light pressure. The water distribution model dynamically adjusts the water volume in the secondary cooling zone.

[0031] 7. After hot delivery, the rolling process involves heating at 1200-1270℃ for 6-10 hours to produce intermediate billets with a cross-section of 230mm×230mm. After slow cooling, the billets are reintroduced into the heating furnace at 1180-1260℃ for 2-6 hours to produce bars with a diameter of 70-100mm. After slow cooling, the bars undergo magnetic flux leakage surface testing and ultrasonic core testing, achieving 100% compliance.

[0032] 8. The macroscopic purity of the bars from 5 heats was 0. The rolling contact fatigue test results under 4.5 GPa contact stress showed that the rated life of the steel of the present invention was more than 1.3 times that of the molded material. The test results of the steel in the example are shown in Table 1.

[0033] Table 1 shows the test results of the high-carbon bearing steel in Examples 1-5.

Claims

1. A high-carbon bearing steel for high-speed precision machine tool spindle bearings, characterized in that: Based on Fe, the alloy composition by mass fraction is: C: 0.95~1.05%, Si: 0.15~0.35%, Mn: 0.25~0.45%, Cr: 1.40~1.65%, Mo: ≤0.10%, Al: ≤0.050%, oxygen content ≤5ppm, sulfur content ≤0.006%, calcium content ≤5ppm, titanium content ≤9ppm, central porosity ≤1.0 grade, central segregation ≤1.0 grade, fine boron inclusions ≤1.0 grade, coarse boron inclusions ≤0.5 grade, DS inclusions ≤0.5 grade, and the macroscopic purity of the bar is ≤3mm / dm. 3 .

2. A method for producing high-carbon bearing steel for high-speed precision machine tool spindle bearings as described in claim 1, characterized in that: Process flow: KR hot metal pretreatment → converter smelting → converter tapping → LF refining → vacuum degassing → continuous casting → rolling. KR molten iron pretreatment: Desulfurize the molten iron, during which the silicon content in the molten iron is controlled at 0.20%-0.40%. Before stirring, remove the slag from the molten iron, and control the removal rate of surface slag to be above 80%. During the stirring process, when the stirring paddle speed reaches the maximum value, add the desulfurizing agent in two batches in equal amounts, and control the final sulfur content to be ≤0.004%. After stirring, remove ≥90% of the surface slag. Converter smelting: The converter, as the primary smelting furnace, decarburizes, dephosphorizes, and heats the molten steel. The final stage of converter smelting must simultaneously meet the following requirements: carbon content ≤0.15%-0.35%, phosphorus content ≤0.012%, temperature ≤1610℃-1660℃, and the proportion of molten iron to the total mass of molten iron + scrap steel ≥80%. Converter tapping: The tapping process is carried out in three stages in sequence: deoxidation, alloying, and slag formation. Each stage must be strictly separated according to the total amount of steel tapped. The steel tapping amount in the deoxidation stage is controlled to be the first 30% of the total steel tapping amount, the alloying stage is controlled to be 30%-60% of the total steel tapping amount, and the slag formation stage is controlled to be 60%-85% of the total steel tapping amount. After deoxidation, the dissolved oxygen content in the steel is less than 20 ppm, and the mass fraction of CaO+Al2O3 in the slag formation agent is controlled to be above 80%, and the mass fraction of MgO+SiO2 is controlled to be below 20%. LF refining: A new slag-forming process is adopted after slag removal. In the early stages of LF refining, a rapid slag-forming process is used. After removing ≥90% of the slag from the surface of the molten steel, a low-melting-point slag-forming agent is added to form a foamy slag within 20 minutes, with a CaO / Al2O3 (mass ratio) of 1.6-2.8 and FeO+MnO+TiO2 mass fraction ≤1.5%. During the refining process, the alloy composition is adjusted, controlling the total amount of alloy added to less than 3 kg per ton of steel, and the number of adjustments is controlled to within 3 times. Vacuum degassing: Argon is used as the lifting gas, and 8-16 gas outlets are evenly distributed along the circumference of the inner wall of the riser. The flow rate of the lifting gas is controlled at 7.5NL / min-13NL / min per ton of steel, the high vacuum state is controlled within 130Pa, and the holding time is controlled at more than 15 minutes. After the vacuum treatment is completed, the vacuum is broken, and then a soft blowing is performed using an argon blowing device at the bottom of the ladle.

3. The production method according to claim 2, characterized in that: The slag-blocking method for converter tapping is slag-blocking plug. The density of the slag-blocking plug is between that of molten steel and slag. It can effectively block the tapping port during the tapping process and prevent slag from flowing into the ladle along with the molten steel.

4. The production method according to claim 2, characterized in that: The steel ladle used for tapping steel from the converter is a special steel ladle for smelting bearing steel, and the refractory material in contact with the molten steel is an improved magnesium-carbon material, in which the mass fraction of MgO+Al2O3 is controlled to be above 75%.

5. The production method according to claim 2, characterized in that: During LF refining, the amount of low-melting-point slagging agent added is 8.5kg-10.0kg per ton of steel, which 100% covers the surface of the molten steel.

6. The production method according to claim 2, characterized in that: Before vacuum degassing, a slag removal device is used to remove the slag below the impregnation tube. The soft blowing flow rate is controlled at 0.1NL / min-0.4NL / min per ton of steel, and the soft blowing time is controlled at more than 10 minutes.

7. The production method according to claim 2, characterized in that: In the continuous casting process, for continuously cast billets with a cross-section of 390mm × 510mm or larger, a ladle slag detection device is used to prevent slag from entering the tundish and contaminating the molten steel. Argon gas protection at the long nozzle is used to prevent secondary oxidation of the molten steel caused by air entering at the connection between the ladle and the long nozzle, and argon gas protection at the tundish is used to prevent secondary oxidation of the molten steel caused by air entering the tundish. A superheat control model is used in conjunction with the tundish induction heating system to control the difference between the actual superheat and the target superheat within ±5℃. A multi-hole submerged entry nozzle is used to avoid slag entrapment in the crystallizer and promote the floating of inclusions. A combination of initial and final electromagnetic stirring technology, along with light reduction technology, is used. A water distribution model is used to automatically calculate and control the water volume in each cooling zone, controlling the solidification process and casting speed to match the initial and final electromagnetic stirring technology with light reduction technology.

8. The production method according to claim 2, characterized in that: In the rolling process, the continuously cast billet is hot-sent to the heating furnace, heated at 1180-1280℃ for ≥6 hours, and rolled into an intermediate billet with a cross-section of 230mm×230mm. After slow cooling, the intermediate billet is put back into the heating furnace, heated at 1160-1260℃ for ≥2 hours, and rolled into round steel with a diameter of <100mm.

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