A method for smelting bearing steel GCr15 by a non-aluminum deoxidization process

Abstract

This invention provides a method for smelting bearing steel GCr15 using a non-aluminum deoxidation process. The invention constructs a non-aluminum composite deoxidation system consisting of pre-deoxidation with a silicon-manganese alloy, diffusion deoxidation with a silicon-based deoxidizer in an LF furnace, and final deoxidation with a RH vacuum barium alloy cored wire. Combined with stepwise oxygen potential control and optimization of a low-alkalinity composite slag system, the entire process does not involve the addition of aluminum-based deoxidizers. This transforms inclusions in the steel into fine, dispersed plastic inclusions, achieving both ultra-low oxygen control and efficient detitanium removal, thereby significantly improving the contact fatigue life of the bearing steel and demonstrating promising industrial application prospects.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, specifically to a method for smelting bearing steel GCr15 using a non-aluminum deoxidation process. Background Technology

[0002] GCr15 bearing steel, as the most widely used high-carbon chromium bearing steel, is extensively used in important industrial fields such as metallurgy and mining, rail transportation, wind power and hydropower, and precision machine tools. Its microscopic cleanliness directly determines the fatigue life and service reliability of bearings under cyclic loads. Currently, the aluminum deoxidation process is commonly used in the smelting of GCr15 bearing steel both domestically and internationally. This involves adding aluminum particles during the ladle refining stage for deep deoxidation, combined with the formation of high-alkalinity slag to rapidly reduce the oxygen content in the molten steel. Through long-term technological accumulation, the total oxygen mass fraction in high-quality bearing steel can now be controlled at 5×10⁻⁶. -6 the following.

[0003] However, the aluminum deoxidation process has inherent defects. During deoxidation, a large amount of Al2O3 inclusions are generated. These inclusions are hard and brittle, and easily aggregate in molten steel to form large particles or dot-like inclusions. Simultaneously, aluminum deoxidation leads to a higher content of acid-soluble aluminum in the molten steel, which readily combines with residual nitrogen to form AlN inclusions, becoming a preferential nucleation source for fatigue cracks under cyclic stress.

[0004] Studies have shown that, under the same size conditions, the fatigue life damage coefficient of Al2O3 inclusions is about 30% higher than that of TiN inclusions. In addition, Al2O3 inclusions generated by aluminum deoxidation significantly reduce the fluidity of molten steel, and are very likely to cause nozzle blockage during the continuous casting of small billets, affecting the continuity of casting.

[0005] To address the aforementioned issues, some studies have attempted to employ non-aluminum deoxidation processes. For example, a smelting approach combining ferrosilicon-manganese pre-deoxidation, slag surface diffusion deoxidation, and vacuum final deoxidation with low-basicity slag has been developed. Results show that this process can stably control Ds-type inclusions in bearing steel to below 0.5. However, existing non-aluminum deoxidation processes still have limitations: firstly, the deoxidation capacity of ferrosilicon-manganese alloys is weaker than that of aluminum; how to stably control total oxygen levels to 5 × 10⁻⁵ without using aluminum remains a challenge. -6 For the following ultra-low oxygen levels, mature industrial solutions are still lacking; secondly, existing processes lack sufficient understanding of the synergistic relationship between deoxidation and titanium control: thermodynamic studies show that the titanium removal rate is positively correlated with the oxygen activity of the molten steel. Excessive deoxidation in the early stages of refining will inhibit the oxidative migration of titanium and reduce the titanium removal efficiency in the subsequent vacuum treatment stage. How to achieve efficient titanium control while ensuring ultra-low oxygen levels is a core technical challenge restricting the production of high-quality bearing steel.

[0006] Therefore, how to achieve ultra-low oxygen control and efficient titanium control while maintaining good fluidity of molten steel without using aluminum deoxidizers is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for smelting bearing steel GCr15 using a non-aluminum deoxidation process, thereby solving the technical problem of "difficulty in simultaneously achieving ultra-low oxygen control and efficient detitanium removal in bearing steel GCr15 without using aluminum deoxidizers".

[0008] To achieve the above objectives, the present invention is implemented using the following technical solution: This invention provides a method for smelting bearing steel GCr15 using a non-aluminum deoxidation process, comprising the following steps: (1) Converter smelting and pre-deoxidation of steel: During the steel tapping process in the converter, silicon manganese alloy is added to the molten iron in the blast furnace for pre-deoxidation, and the oxygen content of the molten steel is controlled within the first oxygen content range. (2) LF furnace refining and diffusion deoxidation: The pre-deoxidized molten steel is transferred into the LF furnace, a low-basicity composite slag system is added for refining, and a silica deoxidizer is added to the slag surface in batches for diffusion deoxidation. After the LF refining is completed, the oxygen content of the molten steel is controlled to be within the second oxygen content range, and the acid-soluble aluminum content is within the first acid-soluble aluminum content range. (3) RH vacuum final deoxidation and titanium control: The molten steel after LF refining is transferred to an RH vacuum device for vacuum treatment. Final deoxidation is carried out by vacuum carbon, and barium alloy cored wire is fed into the molten steel to supplement the final deoxidation. The oxygen content of the molten steel after RH vacuum treatment is controlled to be within the third oxygen content range, and the titanium content is ≤5×10 -6 ; (4) Continuous casting: Under an argon atmosphere, the RH vacuum-treated molten steel is continuously cast to obtain bearing steel GCr15 billet.

[0009] In this invention, the first oxygen content ranges from 120 to 150 ppm; the second oxygen content ranges from 80 to 100 ppm; the third oxygen content ranges from 5 to 9 ppm; and the first acid-soluble aluminum content ranges from 0.011 to 0.031%.

[0010] In this invention, the siliceous deoxidizer is a silicon-iron alloy with a particle size ≤3mm; the barium alloy cored wire is a silicon-barium-calcium alloy cored wire, consisting of an alloy powder core wrapped by a steel strip with a steel strip thickness of 0.3~0.5mm, a cored wire diameter of 13mm, and a steel strip mass percentage of approximately 20~25%. The particle size of the alloy powder core is ≤3mm.

[0011] In step (1), the amount of silicon-manganese alloy added is 8-12 kg / t steel.

[0012] In step (2), the low-alkalinity composite slag system comprises, by mass percentage: SiO2: 18~23%, Al2O3: 20~30%, MgO: 3~6%, and CaO balance.

[0013] In step (2), the amount of silicon deoxidizer added is 1.5 to 2.5 kg / t steel, added in 2 to 3 times, with an interval of 5 to 8 minutes between each addition.

[0014] In step (3), the feeding speed of the barium alloy cored wire is 2-3 m / s, and the feeding amount is 0.8-1.2 kg / t steel.

[0015] In step (3), the vacuum treatment is to evacuate to a vacuum degree ≤67Pa and maintain it for 15 to 25 minutes.

[0016] In step (4), the continuous casting temperature is 1530-1550℃ and the billet pulling speed is 0.8-1.2m / min.

[0017] Compared with the prior art, the beneficial effects achieved by the present invention are: (1) This invention constructs a non-aluminum composite deoxidation system by pre-deoxidation of silicon manganese, diffusion deoxidation of silicon deoxidizer and final deoxidation of barium alloy cored wire, without adding aluminum deoxidizer throughout the process, which reduces the risk of Al2O3 and AlN inclusions; at the same time, it adopts a step-by-step oxygen potential control strategy, controlling the oxygen content at 80~100ppm in the LF refining stage to drive the oxidation and migration of titanium elements, and gradually deoxidizing to 5~9ppm of total oxygen in the RH vacuum stage, breaking through the antagonistic relationship between deoxidation and titanium control in the traditional aluminum deoxidation process.

[0018] (2) This invention employs a low-alkalinity composite slag system with a specific composition in conjunction with barium alloy cored wire for final deoxidation. Utilizing the synergistic modification effect of barium and calcium elements on inclusions, residual oxide inclusions in the steel are transformed into fine, spherical, and dispersed plastic inclusions, reducing the harmful effects of point-like non-deformable inclusions on fatigue performance. The Ds-class inclusion rating results show that all embodiments of this invention are stably controlled at level 0.5, with a very small amount of fine point-like inclusions of 13~19μm in size, increasing the contact fatigue life of the bearing steel.

[0019] (3) This invention does not use aluminum deoxidizers, and the acid-soluble aluminum content of the molten steel is stably controlled, which reduces the risk of deterioration of the fluidity of the molten steel caused by Al2O3 inclusions. There is no Al2O3 type nozzle blockage during the continuous casting process, which ensures the continuity and stability of continuous casting production. Attached Figure Description

[0020] Figure 1 This is a comparison chart of contact fatigue life of various embodiments and comparative examples of the present invention. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] The following is a detailed description of the preparation method of bearing steel GCr15 using a non-aluminum deoxidation process provided by the present invention.

[0023] Step 1, Converter smelting and pre-deoxidation of steel: The blast furnace hot iron is smelted in a converter to a final temperature of 1620-1650℃, a final carbon content of 0.85-0.95%, and a phosphorus content of ≤0.025%; during the tapping process, silicon-manganese alloy is added in the flow for pre-deoxidation, with an addition amount of 8-12 kg / t steel and a tapping time of 8-12 min. Argon is blown and stirred throughout the process, with an argon flow rate of 15-20 L / min. Step 2, LF Furnace Refining and Diffusion Deoxidation: Transfer the pre-deoxidized molten steel to the LF furnace and add 3-5 kg / t of low-basicity composite slag system. The low-basicity composite slag system, by mass percentage, includes: SiO2: 18-23%, Al2O3: 20-30%, MgO: 3-6%, and CaO balance. Heat to 1580-1600℃, hold and stir for 10-15 min, then add siliceous deoxidizer to the slag surface for diffusion deoxidation. The amount of siliceous deoxidizer added is 1.5-2.5 kg / t of steel, added in 2-3 batches, with an interval of 5-8 min between each batch. The argon gas stirring flow rate is 10-15 L / min, and the diffusion deoxidation stage lasts for 25-35 min. Step 3, RH Vacuum Final Deoxidation and Titanium Control: Transfer the molten steel refined in the LF furnace to the RH vacuum device, evacuate to a vacuum degree ≤67Pa, and maintain for 15-25 minutes for vacuum carbon final deoxidation; after vacuum treatment for 10 minutes, feed barium alloy cored wire at a wire feeding speed of 2-3 m / s, with a wire feeding amount of 0.8-1.2 kg / t steel. During the vacuum treatment, the temperature of the molten steel is 1560-1580℃, and the argon circulation flow rate is 20-25 L / min. Step 4: Continuous casting: The molten steel after RH vacuum treatment is transferred to the continuous casting machine. The continuous casting temperature is controlled at 1530-1550℃, the billet pulling speed is 0.8-1.2m / min, and argon protection is carried out throughout the process. The argon flow rate is 5-8L / min. After cooling, the bearing steel GCr15 billet is obtained.

[0024] In step one, silicon-manganese alloy is added for pre-deoxidation. After pre-deoxidation, the oxygen content of the molten steel is controlled at 120-150 ppm, for example, 123 ppm, 136 ppm, or 141 ppm.

[0025] In step two, after LF refining, the oxygen content of the molten steel is controlled at 80-100 ppm, for example, 80 ppm, 85 ppm, 90 ppm, or 98 ppm. Within this oxygen content range, the molten steel has suitable oxygen activity, which ensures the diffusion deoxidation effect of the silica deoxidizer and reserves sufficient oxygen potential driving conditions for efficient detitanium removal in the RH stage. The acid-soluble aluminum content is controlled at 0.011-0.031%, for example, 0.011%, 0.013%, or 0.024%. Within this acid-soluble aluminum content range, it can be ensured that there is no excessive residual aluminum in the molten steel, while meeting the allowable residual requirements of GCr15 bearing steel for acid-soluble aluminum.

[0026] In step three, the oxygen content of the molten steel after RH vacuum final deoxidation is controlled at 5–9 ppm, for example, 6 ppm, 8 ppm, or 9 ppm, and the titanium content is ≤5 × 10⁻⁶. -6 Under these ultra-low oxygen and ultra-low titanium levels, the cleanliness of the molten steel meets the requirements of high-quality bearing steel, effectively avoiding the harm of TiN inclusions to the fatigue performance of bearing steel.

[0027] In this invention, the silicon-based deoxidizer is a silicon-iron alloy, and its chemical composition by mass percentage is: Si 72%~80%, C≤0.2%, P≤0.04%, S≤0.02%, with the balance being Fe and unavoidable impurities; the silicon-based deoxidizer has a particle size ≤3mm and is added to the LF slag surface in powder form for diffusion deoxidation.

[0028] In this invention, the barium alloy cored wire is a silicon-barium-calcium alloy cored wire. The alloy powder core wrapped in the steel strip has the following chemical composition by mass percentage: Si 40-50%, Ba 10-15%, Ca 10-15%, Al ≤ 1.0%, C ≤ 0.5%, P ≤ 0.05%, S ≤ 0.05%, with the balance being Fe and unavoidable impurities. The outer steel strip is ordinary low-carbon steel strip with a thickness of 0.3-0.5 mm. The cored wire diameter is 13 mm, and the steel strip accounts for approximately 20-25% of the total mass. The particle size of the alloy powder core is ≤ 3 mm to ensure rapid melting after the molten steel is fed in, allowing elements such as barium and calcium to be released and participate in the reaction within a short time.

[0029] Example 1; (1) Converter smelting and pre-deoxidation of steel: The blast furnace iron is smelted in the converter to the final temperature of 1620℃, the final carbon content of 0.85% and the phosphorus content of ≤0.025%; during the tapping process, silicon manganese alloy is added with the flow for pre-deoxidation. The amount of silicon manganese alloy added is 8kg / t steel, the tapping time is 8min, and argon is blown and stirred throughout the process. The argon flow rate is 15L / min. After pre-deoxidation, the oxygen content of the molten steel is controlled at 123ppm. (2) LF furnace refining and diffusion deoxidation: The pre-deoxidized molten steel is transferred to the LF furnace and a low-basicity composite slag system of 3 kg / t steel is added. The low-basicity composite slag system includes, by mass percentage: SiO2: 18%, Al2O3: 30%, MgO: 3%, and CaO balance. The temperature is raised to 1580℃, and after holding and stirring for 10 min, a silica deoxidizer is added to the slag surface for diffusion deoxidation. The amount of silica deoxidizer added is 1.5 kg / t steel, added in two batches with an interval of 8 min between each batch. The argon stirring flow rate is 10 L / min, and the diffusion deoxidation stage lasts for 25 min. After the process, the oxygen content of the molten steel is controlled at 82 ppm, and the acid-soluble aluminum content is controlled at 0.016%. (3) RH Vacuum Final Deoxidation and Titanium Control: The molten steel refined in the LF furnace was transferred to the RH vacuum device and evacuated to a vacuum degree ≤67Pa. Vacuum carbon final deoxidation was carried out for 15 minutes. After vacuum treatment for 10 minutes, barium alloy cored wire was fed in at a wire feeding speed of 2m / s. The wire feeding amount was 0.8kg / t steel. During the vacuum treatment, the temperature of the molten steel was 1560℃, the argon circulation flow rate was 20L / min, and the oxygen content of the molten steel after treatment was controlled at 6ppm and the titanium content ≤5×10 -6 ; (4) Continuous casting: The molten steel after RH vacuum treatment is transferred to the continuous casting machine, the continuous casting temperature is controlled at 1530℃, the billet pulling speed is 0.8m / min, the whole process is protected by argon blowing, the argon flow rate is 5L / min, and the bearing steel GCr15 billet is obtained after cooling.

[0030] Example 2; (1) Converter smelting and pre-deoxidation of steel: The blast furnace iron is smelted in the converter to the final temperature of 1630℃, the final carbon content of 0.9% and the phosphorus content of ≤0.025%; during the tapping process, silicon manganese alloy is added with the flow for pre-deoxidation. The amount of silicon manganese alloy added is 10kg / t steel, the tapping time is 10min, and argon is blown and stirred throughout the process. The argon flow rate is 18L / min. After pre-deoxidation, the oxygen content of the molten steel is controlled at 134ppm. (2) LF furnace refining and diffusion deoxidation: The pre-deoxidized molten steel is transferred to the LF furnace and a low-basicity composite slag system of 4 kg / t steel is added. The low-basicity composite slag system includes, by mass percentage: CaO: 50.18%, SiO2: 21.36%, Al2O3: 24.11%, MgO: 4.35%. The temperature is raised to 1590℃, and after holding and stirring for 12 min, a silica deoxidizer is added to the slag surface for diffusion deoxidation. The amount of silica deoxidizer added is 2 kg / t steel, added in 3 batches with an interval of 7 min between each batch. The argon stirring flow rate is 12 L / min, and the diffusion deoxidation stage lasts for 30 min. After the process, the oxygen content of the molten steel is controlled at 92 ppm, and the acid-soluble aluminum content is controlled at 0.024%. (3) RH Vacuum Final Deoxidation and Titanium Control: The molten steel refined in the LF furnace was transferred to the RH vacuum device, and the vacuum was evacuated to ≤67Pa and maintained for 20min for final carbon deoxidation. After 10min of vacuum treatment, barium alloy cored wire was fed in at a feeding speed of 2.5m / s, with a feeding amount of 1kg / t steel. During the vacuum treatment, the temperature of the molten steel was 1570℃, the argon circulation flow rate was 22L / min, and the oxygen content of the molten steel after treatment was controlled at 8ppm, and the titanium content was ≤5×10 -6 ; (4) Continuous casting: The molten steel after RH vacuum treatment is transferred to the continuous casting machine, the continuous casting temperature is controlled at 1540℃, the billet pulling speed is 1m / min, the whole process is protected by argon blowing, the argon flow rate is 6L / min, and the bearing steel GCr15 billet is obtained after cooling.

[0031] Example 3; (1) Converter smelting and pre-deoxidation of steel: The blast furnace iron is smelted in the converter to the final temperature of 1650℃, the final carbon content of 0.95% and the phosphorus content of ≤0.025%; during the tapping process, silicon manganese alloy is added with the flow for pre-deoxidation. The amount of silicon manganese alloy added is 12kg / t steel, the tapping time is 12min, and argon is blown and stirred throughout the process. The argon flow rate is 15~20L / min. After pre-deoxidation, the oxygen content of the molten steel is controlled at 147ppm. (2) LF furnace refining and diffusion deoxidation: The pre-deoxidized molten steel is transferred to the LF furnace and a low-basicity composite slag system of 5 kg / t steel is added. The low-basicity composite slag system includes, by mass percentage: SiO2: 23%, Al2O3: 20%, MgO: 6%, and CaO balance. The temperature is raised to 1600℃, and after holding and stirring for 15 min, a silica deoxidizer is added to the slag surface for diffusion deoxidation. The amount of silica deoxidizer added is 2.5 kg / t steel, added in 3 batches with an interval of 5 min each time. The argon stirring flow rate is 15 L / min, and the diffusion deoxidation stage lasts for 35 min. After the process, the oxygen content of the molten steel is controlled at 95 ppm, and the acid-soluble aluminum content is controlled at 0.03%. (3) RH Vacuum Final Deoxidation and Titanium Control: The molten steel refined in the LF furnace was transferred to the RH vacuum device and evacuated to a vacuum degree ≤67Pa. Vacuum carbon final deoxidation was carried out for 25 minutes. After vacuum treatment for 10 minutes, barium alloy cored wire was fed in at a wire feeding speed of 3m / s. The wire feeding amount was 1.2kg / t steel. During the vacuum treatment, the temperature of the molten steel was 1580℃, the argon circulation flow rate was 25L / min, and the oxygen content of the molten steel after treatment was controlled at 9ppm and the titanium content ≤5×10 -6 ; (4) Continuous casting: The molten steel after RH vacuum treatment is transferred to the continuous casting machine, the continuous casting temperature is controlled at 1550℃, the billet pulling speed is 1.2m / min, the whole process is protected by argon blowing, the argon flow rate is 8L / min, and the bearing steel GCr15 billet is obtained after cooling.

[0032] Comparative Example 1; The difference between Comparative Example 1 and Example 2 lies in the difference between steps (2) and (3). Step (2) is changed to: LF furnace refining and diffusion deoxidation: the pre-deoxidized molten steel is transferred to the LF furnace and a low-basicity composite slag system of 4 kg / t steel is added; the low-basicity composite slag system includes, by mass percentage: CaO: 50.18%, SiO2: 21.36%, Al2O3: 24.11%, MgO: 4.35%; the temperature is raised to 1590℃, and the mixture is kept at the temperature and stirred for 12 min. Aluminum deoxidizer was added to the slag surface for diffusion deoxidation. The amount of aluminum deoxidizer added was 2 kg / t steel, added in 3 times with an interval of 7 min each time. The argon stirring flow rate was 12 L / min. The diffusion deoxidation stage lasted for 30 min. After the end, the oxygen content of the molten steel was controlled at 92 ppm and the acid-soluble aluminum content was controlled at 0.048%. In step (3), since the diffuse particles generated by aluminum deoxidation will act as heterogeneous nucleation cores of TiN, it will aggravate the fixation of titanium and the titanium content cannot meet the standard. The remaining steps are the same as in Example 2.

[0033] Comparative Example 2; The difference between Comparative Example 2 and Example 2 lies in the difference in step (2). Step (2) is changed to: LF furnace refining and diffusion deoxidation: The pre-deoxidized molten steel is transferred to the LF furnace and a high-basicity composite slag system of 4 kg / t steel is added; the high-basicity composite slag system includes, by mass percentage: CaO: 62%, SiO2: 8%, Al2O3: 25%, MgO: 5%; the temperature is raised to 1590℃, and after holding and stirring for 12 min, a silica deoxidizer is added to the slag surface for diffusion deoxidation. The amount of silica deoxidizer added is 2 kg / t steel, added in 3 times, with an interval of 7 min each time. The argon stirring flow rate is 12 L / min, and the diffusion deoxidation stage lasts for 30 min. After the end, the oxygen content of the molten steel is controlled at 92 ppm, and the acid-soluble aluminum content is controlled at 0.024%; the remaining steps are the same as in Example 2.

[0034] Comparative Example 3; The difference between Comparative Example 3 and Example 2 lies in the difference between steps (2) and (3). Step (2) is changed to: LF furnace refining and diffusion deoxidation: the pre-deoxidized molten steel is transferred to the LF furnace and a low-basicity composite slag system of 4 kg / t steel is added; the low-basicity composite slag system includes, by mass percentage: CaO: 50.18%, SiO2: 21.36%, Al2O3: 24.11%, MgO: 4.35%; the temperature is raised to 1590℃ and stirred for 1 hour. Two minutes later, a silica deoxidizer was added to the slag surface for diffusion deoxidation. The amount of silica deoxidizer added was 4.5 kg / t steel, added in three batches with a 7-minute interval between each batch. The argon stirring flow rate was 12 L / min, and the diffusion deoxidation stage lasted for 30 minutes. After the process, the oxygen content of the molten steel was controlled at 30 ppm, and the acid-soluble aluminum content was controlled at 0.026%. In step (3), excessive deoxidation by LF resulted in insufficient oxygen to combine and generate titanium oxides, and the titanium content could not meet the standard. The remaining steps were the same as in Example 2.

[0035] Comparative Example 4; The difference between Comparative Example 4 and Example 2 lies in step (3). Step (3) is changed to: RH vacuum final deoxidation and titanium control: The molten steel refined in the LF furnace is transferred to the RH vacuum device, and the vacuum is evacuated to a vacuum degree ≤67Pa. Vacuum carbon final deoxidation is carried out for 20 minutes, and the titanium content is 5×10 -6 ~8×10 -6 The remaining steps are the same as in Example 2.

[0036] Test and Results Analysis Contact fatigue life test method: Samples were cut from the same location of the bearing steel GCr15 billet obtained in the embodiments and comparative examples of this invention, and processed into standard contact fatigue samples. The sample dimensions were 60 mm outer diameter, 40 mm inner diameter, and 5 mm thickness. The working surface was ground to a surface roughness Ra ≤ 0.2 μm. The test was conducted on a thrust plate contact fatigue testing machine, with the Hertzian contact stress set at 5.5 GPa, the rotation speed at 3000 r / min, the slip ratio at 10%, and mechanical oil circulating lubrication used, with the oil temperature controlled at 60 ± 2℃. The appearance of fatigue spalling pits ≥ 0.1 mm on the working surface of the sample was used as the failure criterion. The number of cycles to failure for each sample was recorded. The test data were statistically analyzed using the Weibull distribution. Ten parallel samples were taken for each test group, and the rated life L under a 10% failure probability was calculated using the Weibull distribution. 10 The results are shown Figure 1 .

[0037] like Figure 1As shown in Examples 1-3, the non-aluminum deoxidation process described in this invention for smelting bearing steel GCr15 can significantly improve the contact fatigue life of bearing steel through the synergistic effect of silicon-manganese pre-deoxidation, silicon diffusion deoxidation and barium alloy final deoxidation, combined with step-by-step oxygen potential regulation and optimization of low-alkalinity composite slag system.

[0038] Comparative Example 1 shows that when alumina-based deoxidizer is used for diffusion deoxidation instead of silica-based deoxidizer, a large number of Al2O3 and AlN inclusions are generated in the steel, forming point-like Ds-type inclusions. These inclusions become preferential initiation sources of fatigue cracks under cyclic contact stress, resulting in the lowest contact fatigue life. This indicates that replacing alumina-based deoxidizer with silica-based deoxidizer can significantly reduce harmful inclusions and effectively improve the fatigue life of bearing steel.

[0039] Comparative Example 2 uses a high-basicity slag system instead of a low-basicity composite slag system. The inclusions in the steel are mainly brittle phases with high Al2O3 content, lacking plastic deformation ability, and the fatigue life is lower than that of the other examples. This shows that the low-basicity composite slag system of the present invention can promote the plastic transformation of inclusions, improve the morphology and distribution of inclusions, and thus improve the fatigue life of bearing steel.

[0040] Comparative Example 3 shows that excessive deoxidation to 30 ppm in the LF stage disrupts the step-by-step oxygen potential control strategy, resulting in ineffective titanium removal in the RH stage due to excessively low oxygen activity. This leads to residual TiN inclusions in the steel, whose high hardness becomes a stress concentration source under cyclic stress, significantly shortening fatigue life. This demonstrates that the step-by-step oxygen potential control strategy can achieve efficient titanium removal while ensuring ultra-low oxygen levels, reducing the harm of titanium inclusions to fatigue life, and thus significantly improving the service life of bearing steel.

[0041] Comparative Example 4 shows that no barium alloy cored wire was fed during the RH vacuum treatment stage. The residual oxide inclusions in the steel were irregular in shape and easily agglomerated and grew. The fatigue life was significantly lower than that of the other examples. This indicates that the feeding of barium alloy cored wire can modify the inclusions, causing them to transform into fine, dispersed plastic inclusions, thereby further extending the contact fatigue life of the bearing steel.

[0042] Ds-type inclusion rating test method: According to the test method of GB / T10561-2005, the Ds-type (point-like non-deformable inclusions) in the bearing steel GCr15 billet samples of each embodiment and comparative example were rated under an optical microscope. The results are shown in Table 1 below.

[0043] Table 1

[0044] As shown in Table 1, in Examples 1-3, bearing steel GCr15 was smelted using the non-aluminum deoxidation process described in this invention. The Ds inclusion rating was consistently controlled at level 0.5, with only a very small amount of fine dot-like inclusions present.

[0045] Comparative Example 1, which lacked a silica deoxidizer and used an alumina deoxidizer for diffusion deoxidation, generated a large amount of Al2O3 inclusions in the steel. These inclusions then combined with CaO during the slag-steel reaction to form calcium aluminate dot-shaped non-deformable inclusions, with a rating as high as 2.0. This indicates that the alumina deoxidizer is the root cause of the formation of Ds-type coarse dot-shaped inclusions. In contrast, the present invention uses a silica deoxidizer to replace the alumina deoxidizer, which can reduce the formation of calcium aluminate dot-shaped inclusions from the source and significantly reduce the Ds-type inclusion rating.

[0046] Comparative Example 2 used a high-basicity slag system instead of a low-basicity composite slag system, and the Ds-type inclusion rating was 1.0. Analysis suggests that the high-basicity slag reduces the activity of Al2O3 in the steel, which is conducive to the formation and aggregation of calcium aluminate inclusions. In contrast, the low-basicity composite slag system of this invention can inhibit the formation of point-like non-deformable inclusions and stably control the Ds-type inclusions within a small size range.

[0047] Comparative Example 3's excessive deoxidation to 30 ppm during the LF stage disrupted the stepwise oxygen potential control strategy, resulting in residual TiN inclusions during the RH stage's titanium removal. The TiN inclusions were square or rectangular angular in shape. Although not typical of the Ds class, their large size earned them a rating of 1.0. This indicates that stepwise oxygen potential control not only achieves efficient titanium removal and reduces the hazards of titanium inclusions, but also helps prevent the formation of large inclusions, ensuring the cleanliness of the molten steel.

[0048] Comparative Example 4 did not have barium alloy cored wire fed during the RH vacuum treatment stage, and its Ds-class inclusion rating was 1.5. Without the addition of barium alloy, the residual oxide inclusions in the steel, without modification treatment, easily aggregated and grew into larger dot-like inclusions; however, after the barium alloy cored wire was fed, the barium element reacted with the oxide inclusions, causing them to transform into fine, dispersed plastic inclusions.

[0049] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for smelting bearing steel GCr15 using a non-aluminum deoxidation process, characterized in that, Includes the following steps: (1) Converter smelting and pre-deoxidation of steel: During the steel tapping process in the converter, silicon manganese alloy is added to the molten iron in the blast furnace for pre-deoxidation, and the oxygen content of the molten steel is controlled within the first oxygen content range. (2) LF furnace refining and diffusion deoxidation: The pre-deoxidized molten steel is transferred into the LF furnace, a low-basicity composite slag system is added for refining, and a silica deoxidizer is added to the slag surface in batches for diffusion deoxidation. After the LF refining is completed, the oxygen content of the molten steel is controlled to be within the second oxygen content range, and the acid-soluble aluminum content is within the first acid-soluble aluminum content range. (3) RH vacuum final deoxidation and titanium control: The molten steel after LF refining is transferred to an RH vacuum device for vacuum treatment. Final deoxidation is carried out by vacuum carbon, and barium alloy cored wire is fed into the molten steel to supplement the final deoxidation. The oxygen content of the molten steel after RH vacuum treatment is controlled to be within the third oxygen content range, and the titanium content is ≤5×10 -6 ; (4) Continuous casting: Under an argon atmosphere, the RH vacuum-treated molten steel is continuously cast to obtain bearing steel GCr15 billet.

2. The method according to claim 1, characterized in that, The first oxygen content ranges from 120 to 150 ppm; the second oxygen content ranges from 80 to 100 ppm; the third oxygen content ranges from 5 to 9 ppm; and the first acid-soluble aluminum content ranges from 0.011 to 0.031%.

3. The method according to claim 1, characterized in that, In step (2), the low-alkalinity composite slag system comprises, by mass percentage: SiO2: 18~23%, Al2O3: 20~30%, MgO: 3~6%, and CaO balance.

4. The method according to claim 1, characterized in that, In step (2), the amount of silicon deoxidizer added is 1.5 to 2.5 kg / t steel, added in 2 to 3 times, with an interval of 5 to 8 minutes between each addition.

5. The method according to claim 1, characterized in that, In step (3), the feeding speed of the barium alloy cored wire is 2-3 m / s, and the feeding amount is 0.8-1.2 kg / t steel.

6. The method according to claim 1, characterized in that, In step (1), the amount of silicon-manganese alloy added is 8-12 kg / t steel.

7. The method according to claim 1, characterized in that, In step (3), the vacuum treatment is to evacuate to a vacuum degree ≤67Pa and maintain it for 15 to 25 minutes.

8. The method according to claim 1, characterized in that, In step (4), the continuous casting temperature is 1530-1550℃ and the billet pulling speed is 0.8-1.2m / min.

9. The method according to claim 1, characterized in that, The silicon-based deoxidizer is a silicon-iron alloy with a particle size ≤3mm.

10. The method according to claim 1, characterized in that, The barium alloy cored wire is a silicon-barium-calcium alloy cored wire, consisting of an alloy powder core wrapped by a steel strip. The steel strip thickness is 0.3~0.5mm, the cored wire diameter is 13mm, and the steel strip accounts for approximately 20~25% of the total mass. The particle size of the alloy powder core is ≤3mm.

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