Preparation process of large-specification long-service-life bearing steel bar

Abstract

The invention relates to the technical field of bearing steel, and discloses a preparation process of a large-size long-life bearing steel bar, which comprises the following steps: carrying out primary smelting on iron ore, high-carbon molten iron and high-quality scrap steel, adding aluminum and other deoxidizing agents to obtain liquid steel, and carrying out secondary refining on the liquid steel, the molten steel is further desulfurized and deoxidized, nonmetallic inclusions and trace impurities are removed by adding an alloy into the molten steel, adjusting the performance of the molten steel and carrying out electroslag remelting to obtain a consumable ingot, the consumable ingot is subjected to homogenizing annealing, forging, rolling and quenching to obtain a martensite bar-shaped steel ingot, and the surface of the bar-shaped steel ingot is treated by turning or grinding to obtain the martensite bar-shaped steel ingot. And stress relief annealing is carried out, the temperature of the rod-shaped steel ingot is increased to 500-650 DEG C, residual stress formed in the material is partially released or redistributed, and after stress relief annealing, the size and shape are more stable, and the high-precision requirement of the bearing steel is met.

Description

Technical Field

[0001] The invention relates to the technical field of bearing steel, and in particular to a preparation process of a large-size and long-life bearing steel bar. Background Art

[0002] High-carbon bearing steel is the main material for manufacturing bearings, accounting for more than 80% of the production and sales of bearing steel, and is an essential key basic material for manufacturing bearings. However, the fatigue life of traditional bearing steel decreases significantly as the size of the bearing steel increases, especially when the size of the bearing steel bar exceeds 60mm, the contact fatigue life of the bearing steel decreases exponentially.

[0003] According to the disclosed large-size, long-life, high-carbon bearing steel bar and its preparation method (Announcement No.: CN113755766A), in the above application, the bearing steel is micro-alloyed with Nb, V, Mo and Zr to greatly refine the original austenite structure and carbide size, thereby achieving a significant improvement in the contact fatigue life of large-size bearing steel and meeting the quality and life requirements of large bearings for large-size bearing steel bars.

[0004] However, in the actual bearing steel preparation process, there is little research on the hot deformation control method, hot processing and heat treatment of consumable ingots in consumable smelting, which is not enough to solve the quality problems of existing bars. In view of this, we proposed a preparation process for large-size and long-life bearing steel bars. Summary of the invention

[0005] The purpose of the present invention is to provide a preparation process for large-size and long-life bearing steel bars to solve the problems raised in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solution: A preparation process of large-size and long-life bearing steel bars, comprising the following steps:

[0007] S1. Prepare raw materials and micro-alloying elements;

[0008] S2, perform primary smelting, desulfurize and dephosphorize the molten iron, add deoxidizers such as aluminum, and obtain liquid steel;

[0009] S3, secondary refining to obtain consumable ingots;

[0010] S4, hot processing, homogenizing annealing of the steel ingot, then forging and rolling, after the steel ingot is uniformly heated, upsetting and stretching the steel ingot multiple times;

[0011] S5, heat treatment, sequentially performing spheroidizing annealing, quenching and tempering;

[0012] S6, surface finishing and ultrasonic flaw detection;

[0013] S7. Perform stress relief annealing.

[0014] Preferably, the raw materials are iron ore, high-carbon molten iron and high-quality scrap steel, wherein the carbon content of the high-carbon molten iron is 0.8%-1.2%, and the micro-alloying elements include Cr, Mn, Si, Mo, etc., so that the Si≤0.65wt%, Mn≤0.65wt%, Ni≤0.30wt%, Cu≤0.25wt% in the large-size and long-life bearing steel bar, and the content of Si, Mn, Ni and Cu is not 0.

[0015] Preferably, the deoxidizer includes Al or Si, Mn, etc., wherein the content of Al cannot be higher than 0.05wt%, and the temperature of the molten metal is less than 1550°C during the addition of the deoxidizer. The primary smelting is carried out by a converter or an electric arc furnace, using molten iron and scrap steel for batching, and impurities such as carbon and silicon are removed by blowing oxygen to reduce the oxygen content and oxide inclusions.

[0016] Preferably, the secondary refining includes vacuum degassing, refining outside the furnace and electroslag remelting. The stirring time of the vacuum degassing is between 30 minutes and 60 minutes, the stirring temperature is less than 1600°C, the number of alternating stirring operations is greater than 3 times, the vacuum degassing makes N≤0.0040wt%, T.0≤10ppm, and the refining outside the furnace further desulfurizes and deoxidizes to improve the purity of the molten steel.

[0017] Preferably, the refining outside the furnace adds alloys to the molten steel, and the added alloys include Si, Mn, etc. The temperature of the molten steel is maintained in the range of 1600°C to 1650°C during the refining outside the furnace, and the time of the refining outside the furnace is controlled within 30 minutes to 60 minutes. The properties of the molten steel are adjusted by adding alloys, wherein impurities in the alloy enter the molten steel, S in the molten steel should not exceed 0.002wt%, P should not exceed 0.004wt%, and Ti should not exceed 0.0015wt%. In the electroslag remelting, the molten steel is remelted in the form of a consumable electrode, the hydrogen content in the molten steel is controlled to be below 2ppm, the oxygen content is controlled to be below 10ppm, and the current density is 1.5 to 3A / cm 2 , non-metallic inclusions and trace impurities are removed by electroslag, the internal density and organizational uniformity of the ingot are improved, and the fatigue performance is improved.

[0018] Preferably, during the upsetting and stretching process, the grains are refined and heated uniformly, the ingot is heated to about 1100°C, and finally the ingot is forged to be close to the requirements of the bar. The stretching adopts a symmetrical pressing method. The upsetting and stretching are performed multiple times to refine the grains, break up segregation, improve the grain structure, eliminate casting defects, and improve the density of the structure through large deformation and low rolling temperature. The symmetrical pressing ensures that the center position of the ingot is not offset.

[0019] Preferably, the temperature of the rod-shaped steel ingot is maintained between 1100°C and 1250°C during the homogenization annealing, the cooling method adopted by the homogenization annealing is slow furnace cooling, the holding time is between 10 hours and 24 hours, the delta ferrite content in the rod-shaped steel ingot is not more than 3%, and the maximum size of the carbide is not more than 3μm. The temperature is maintained at 780°C to 820°C during the spheroidizing annealing, the cooling method adopted by the spheroidizing annealing is furnace cooling to below 500°C, and then air cooling, and the holding time is between 8 hours and 20 hours. The slow furnace cooling avoids cracks and residual stresses, improves the uniformity of the internal structure of the rod-shaped steel ingot, eliminates the component segregation that may be formed during the ingot casting or rolling process, such as uneven distribution of elements such as C, S, and P, so that the material composition is more consistent, which is conducive to uniform forging and rolling deformation. The high-temperature diffusion effect of the homogenization annealing can reduce the time required for subsequent annealing or normalizing.

[0020] Preferably, during the quenching, the temperature of the rod-shaped steel ingot is heated to between 840°C and 870°C, and the rod-shaped steel ingot is kept in this temperature range for 30 minutes to 2 hours, and then cooled by oil cooling. During the tempering, the temperature of the rod-shaped steel ingot is heated to between 150°C and 200°C, and the rod-shaped steel ingot is kept in this temperature range for 2 hours to 4 hours, and the hardness of the steel ingot is adjusted to between 58 and 64HRC. The quenching improves the hardness and wear resistance of the rod-shaped steel ingot, and the temperature of the steel ingot is heated to between 840°C and 870°C, so that the temperature of the rod-shaped steel ingot reaches the austenitizing temperature, more carbon and alloy elements are dissolved in the austenite, and the structure is homogenized. Through the rapid cooling of oil cooling, the austenite can be transformed into martensite with higher hardness, thereby improving the strength and hardness of the rod-shaped steel ingot. The tempering is used to reduce the internal stress of the martensite after quenching, improve the toughness and impact resistance, and avoid hardness deviation or insufficient toughness.

[0021] Preferably, the finishing includes turning or grinding to remove the oxide scale and defect layer on the surface of the rod-shaped steel ingot. The finishing improves the surface quality of the rod-shaped steel ingot and processes the rod-shaped steel ingot to the required diameter and length. The ultrasonic flaw detection is used to check the internal defects of the bar to ensure that there are no cracks, inclusions and other defects inside the bar, thereby ensuring the quality of large-size and long-life bearing steel bars.

[0022] Preferably, the stress relief annealing heats the temperature of the rod-shaped steel ingot to 500°C-650°C, and the cooling method adopted by the stress relief annealing is slow furnace cooling to room temperature, and the insulation time is between 1 hour and 4 hours. Large-sized bars are more likely to form greater stress under the action of the internal and external temperature difference. Stress relief annealing can reduce the risk of cracking. By heating to 500°C-650°C, the residual stress formed in the material is partially released or redistributed to eliminate the residual stress generated during the hot working process. Slow furnace cooling to room temperature avoids the reintroduction of new stress due to rapid cooling, and prevents cracking during subsequent processing or use. After stress relief annealing, the size and shape are more stable, which meets the high precision requirements of bearing steel.

[0023] Compared with the prior art, the present invention provides a preparation process for large-size and long-life bearing steel bars, which has the following beneficial effects:

[0024] 1. The preparation process of the large-size long-life bearing steel bar is to remove impurities such as carbon and silicon through primary refining, secondary refining and hot processing, and to reduce the oxygen content and oxide inclusions in an electric arc furnace to make N≤0.0040wt%, T.0≤10ppm. The refining outside the furnace is further desulfurized and deoxidized to improve the purity of the molten steel. The properties of the molten steel are adjusted by adding alloys during the secondary refining process, non-metallic inclusions and trace impurities are removed, the internal density and uniformity of the ingot are improved, and the fatigue performance is improved. The hot processing, upsetting and stretching are repeated for multiple times to refine the grains, break up segregation, improve the grain structure, and eliminate casting defects. , through large deformation and low rolling temperature, the density of the organization is improved, the symmetrical pressing stretching method ensures that the center position of the steel ingot does not shift, and ensures that the steel ingot is subjected to uniform and symmetrical force, so that the deformation process is consistent inside and outside, avoiding the formation of cracks or voids in the center area, and ensuring the internal quality of the material is intact. Through heat treatment, the purity of the molten steel is improved, the internal density and uniformity of the ingot are improved, and the rod-shaped steel ingot dissolves more carbon and alloy elements at the austenite temperature to homogenize the organization and improve the strength and hardness of the rod-shaped steel ingot. Tempering is used to reduce the internal stress of the martensite after quenching, improve toughness and impact resistance, and avoid hardness deviation or insufficient toughness.

[0025] 2. The preparation process of the large-size and long-life bearing steel bar is to perform fine processing on the surface after heat treatment to remove the oxide scale and defect layer on the surface of the rod-shaped steel ingot. The fine processing improves the surface quality of the rod-shaped steel ingot, and the rod-shaped steel ingot is processed to the required diameter and length. The internal defects of the bar are checked by ultrasonic testing to ensure that there are no cracks, inclusions and other defects inside the bar, thereby ensuring the quality of the large-size and long-life bearing steel bar.

[0026] 3. The preparation process of the large-size and long-life bearing steel bar is to release or redistribute the residual stress formed in the material by re-stress relief annealing after surface finishing, so as to eliminate the residual stress generated during hot working and turning, and then slowly cool it to room temperature in the furnace to avoid the introduction of new stress due to rapid cooling, so as to prevent cracking during subsequent processing or use. After stress relief annealing, the size and shape are more stable, which meets the high-precision requirements of large-size bearing steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the preparation process of the present invention. DETAILED DESCRIPTION

[0028] like Figure 1 As shown, the present invention provides a technical solution: a preparation process of a large-size and long-life bearing steel bar, comprising the following steps:

[0029] First, prepare the raw materials and micro-alloying elements, then perform primary smelting on the raw materials, desulfurize and dephosphorize the molten iron, add deoxidizers such as aluminum to obtain liquid steel, and perform secondary refining on the liquid steel. During the secondary refining, the molten steel is further desulfurized and deoxidized, and alloys are added to the molten steel to adjust its properties. Non-metallic inclusions and trace impurities are removed by electroslag remelting to obtain consumable ingots.

[0030] Then the consumable ingot is heat-treated to homogenize the annealing of the ingot, and then forged and rolled. After the ingot is evenly heated to about 1100°C, it is upset and stretched several times to forge the ingot into a shape close to that of a bar. The ingot is then heat-treated, and the ingot is sequentially spheroidized annealed, quenched and tempered. The ingot temperature is heated to between 840°C and 870°C to make the temperature of the rod-shaped ingot reach the austenitizing temperature, dissolve more carbon and alloy elements in the austenite, and homogenize the structure. After quenching, a martensitic rod-shaped ingot is obtained. Tempering is used to reduce the internal stress of the martensite after quenching, improve toughness and impact resistance, and avoid hardness deviation or insufficient toughness.

[0031] After hot working and heat treatment, the surface of the bar-shaped steel ingot is finely processed, and the surface of the bar-shaped steel ingot is processed by turning or grinding. After turning and grinding, the bar is subjected to ultrasonic flaw detection to check for internal defects in the bar to ensure that there are no defects such as cracks and inclusions inside the bar.

[0032] Finally, stress relief annealing is carried out, and the temperature of the rod-shaped steel ingot is heated to 500℃~650℃ to partially release or redistribute the residual stress formed in the material. The cooling method adopted for stress relief annealing is slow furnace cooling to room temperature to avoid the introduction of new stress due to rapid cooling. The holding time is between 1 hour and 4 hours. After stress relief annealing, the size and shape are more stable, which meets the high precision requirements of bearing steel.

[0033] The raw materials are iron ore, high-carbon molten iron and high-quality scrap steel, wherein the carbon content of the high-carbon molten iron is 0.8%-1.2%, and the micro-alloying elements include Cr, Mn, Si, Mo, etc., so that the Si in the large-size and long-life bearing steel bars is ≤0.65wt%, Mn ≤0.65wt%, Ni ≤0.30wt%, Cu ≤0.25wt%, and the content of Si, Mn, Ni and Cu is not zero.

[0034] Among them, the deoxidizer includes Al or Si, Mn, etc., wherein the content of Al cannot be higher than 0.05wt%. During the process of adding the deoxidizer, the temperature of the molten metal is less than 1550°C. The primary smelting is carried out by a converter or an electric arc furnace, using molten iron and scrap steel for batching, and impurities such as carbon and silicon are removed by blowing oxygen to reduce the oxygen content and oxide inclusions.

[0035] Among them, secondary refining includes vacuum degassing, refining outside the furnace and electroslag remelting. The stirring time of vacuum degassing is between 30 minutes and 60 minutes, the stirring temperature is less than 1600°C, the number of alternating stirring operations is greater than 3 times, and the vacuum degassing makes N≤0.0040wt%, T.0≤10ppm. Refining outside the furnace further desulfurizes and deoxidizes to improve the purity of the molten steel.

[0036] Among them, the refining outside the furnace adds alloys to the molten steel, the added alloys include Si, Mn, etc., the temperature of the molten steel is maintained in the range of 1600°C to 1650°C during the refining outside the furnace, the time of the refining outside the furnace is controlled within 30 minutes to 60 minutes, the performance of the molten steel is adjusted by adding alloys, impurities in the alloy enter the molten steel, S in the molten steel should not exceed 0.002wt%, P should not exceed 0.004wt%, and Ti should not exceed 0.0015wt%.

[0037] Among them, the molten steel in the electroslag remelting is remelted in the form of consumable electrodes, the hydrogen content in the molten steel is controlled below 2ppm, the oxygen content is controlled below 10ppm, and the current density is 1.5~3A / cm 2 , non-metallic inclusions and trace impurities are removed by electroslag, the internal density and organizational uniformity of the ingot are improved, and the fatigue performance is improved.

[0038] Among them, during the upsetting and stretching process, the grains are refined and heated evenly, and the ingot is heated to about 1100℃. Finally, the ingot is forged to be close to the requirements of the bar. The stretching adopts the method of symmetrical pressing. The upsetting and stretching are carried out multiple times to refine the grains, break up segregation, improve the grain structure, eliminate casting defects, and improve the density of the structure through large deformation and low rolling temperature. Symmetrical pressing ensures that the center position of the ingot does not shift.

[0039] The temperature of the rod-shaped steel ingot is maintained between 1100°C and 1250°C during homogenization annealing, the cooling method adopted for homogenization annealing is slow furnace cooling, the holding time is between 10 hours and 24 hours, the delta ferrite content in the rod-shaped steel ingot is not more than 3%, and the maximum size of the carbide is not more than 3μm. The temperature is maintained at 780°C to 820°C during spheroidizing annealing, the cooling method adopted for spheroidizing annealing is furnace cooling to below 500°C, and then air cooling, the holding time is between 8 hours and 20 hours, the slow furnace cooling avoids cracks and residual stress, improves the uniformity of the internal structure of the rod-shaped steel ingot, eliminates the component segregation that may be formed during the ingot casting or rolling process, such as uneven distribution of elements such as C, S, and P, so that the material composition is more consistent, which is conducive to uniform forging and rolling deformation, and the high-temperature diffusion effect of the homogenization annealing can reduce the time required for subsequent annealing or normalizing.

[0040] During quenching, the temperature of the rod-shaped steel ingot is heated to between 840°C and 870°C, and the rod-shaped steel ingot is kept in this temperature range for 30 minutes to 2 hours, and then cooled by oil cooling. During tempering, the temperature of the rod-shaped steel ingot is heated to between 150°C and 200°C, and the rod-shaped steel ingot is kept in this temperature range for 2 hours to 4 hours, and the hardness of the steel ingot is adjusted to between 58 and 64HRC. Quenching improves the hardness and wear resistance of the rod-shaped steel ingot. The temperature of the steel ingot is heated to between 840°C and 870°C, so that the temperature of the rod-shaped steel ingot reaches the austenitizing temperature, more carbon and alloy elements are dissolved in the austenite, and the structure is homogenized. Through rapid cooling by oil cooling, the austenite can be transformed into martensite with higher hardness, thereby improving the strength and hardness of the rod-shaped steel ingot. Tempering is used to reduce the internal stress of the martensite after quenching, improve the toughness and impact resistance, and avoid hardness deviation or insufficient toughness.

[0041] Among them, finishing includes turning or grinding to remove the oxide scale and defect layer on the surface of the rod-shaped steel ingot, finishing to improve the surface quality of the rod-shaped steel ingot, processing the rod-shaped steel ingot to the required diameter and length, and ultrasonic testing to check the internal defects of the bar to ensure that there are no cracks, inclusions and other defects inside the bar, thereby ensuring the quality of large-size and long-life bearing steel bars.

[0042] In addition, stress relief annealing is carried out after tempering. First, the temperature of the rod-shaped steel ingot is heated to 500℃~650℃. The cooling method adopted for stress relief annealing is slow furnace cooling to room temperature. The holding time is between 1 hour and 4 hours. Large-sized bars are more likely to form greater stress under the action of internal and external temperature differences. Stress relief annealing can reduce the risk of cracking. By heating to 500℃~650℃, the residual stress formed in the material is partially released or redistributed to eliminate the residual stress generated during the hot working process. Slowly furnace cooling to room temperature avoids the introduction of new stress due to rapid cooling, and prevents cracking during subsequent processing or use. After stress relief annealing, the size and shape are more stable, which meets the high precision requirements of bearing steel.

[0043] In the present invention, raw materials and micro-alloying elements are prepared, the raw materials are iron ore, high-carbon molten iron and high-quality scrap steel, the micro-alloying elements include Cr, Mn, Si, Mo, etc., the raw materials are subjected to primary refining, desulfurization and dephosphorization, and deoxidizers such as aluminum are added to obtain liquid steel, the liquid steel is subjected to secondary refining, and vacuum degassing, refining outside the furnace and electroslag remelting are used to further desulfurize and deoxidize, reduce the oxygen content and oxide inclusions, and improve the purity of the molten steel, and non-metallic inclusions and trace impurities are removed by electroslag to obtain a consumable ingot, and then the consumable ingot is subjected to heat treatment to homogenize the ingot and anneal it, eliminate the component segregation that may be formed during the ingot casting or rolling process, such as uneven distribution of elements such as C, S, and P, so that the material composition is more consistent, which is conducive to uniform forging and rolling deformation, and after the ingot is uniformly heated to about 1100°C, the ingot is subjected to multiple upsetting and drawing. The steel ingot is stretched, forged into a shape close to that of a bar, and then heat treated. The steel ingot is sequentially subjected to spheroidizing annealing, quenching and tempering to obtain a martensitic rod-shaped steel ingot to improve toughness and impact resistance. The surface of the rod-shaped steel ingot is fine-machined. The surface of the rod-shaped steel ingot is processed by turning or grinding to remove the oxide scale and defect layer on the surface of the rod-shaped steel ingot. The fine machining improves the surface quality of the rod-shaped steel ingot. The rod-shaped steel ingot is processed to the required diameter and length. Ultrasonic flaw detection is used to check the internal defects of the bar to ensure that there are no cracks, inclusions and other defects inside the bar. Finally, stress relief annealing is performed after ultrasonic flaw detection to partially release or redistribute the residual stress formed in the material to eliminate the residual stress generated during the hot working process. The furnace is slowly cooled to room temperature to avoid the introduction of new stress due to rapid cooling, so as to prevent cracking during subsequent processing or use.

[0044] The above generally describes the present invention in detail, but it is obvious to a person skilled in the art that some modifications or improvements can be made to the present invention. Therefore, modifications or improvements that do not depart from the spirit of the present invention are within the scope of protection of the present invention.

Claims

1. A process for preparing large-size and long-life bearing steel bars, characterized in that: The steps include: S1. Prepare raw materials and micro-alloying elements; S2, perform primary smelting, desulfurize and dephosphorize the molten iron, add deoxidizers such as aluminum, and obtain liquid steel; S3, secondary refining to obtain consumable ingots; S4, hot processing, homogenizing annealing of the steel ingot, then forging and rolling, after the steel ingot is uniformly heated, upsetting and stretching the steel ingot multiple times; S5, heat treatment, sequentially performing spheroidizing annealing, quenching and tempering; S6, surface finishing and ultrasonic flaw detection; S7. Perform stress relief annealing.

2. The process for preparing a large-size and long-life bearing steel bar according to claim 1 is characterized in that: The raw materials are iron ore, high-carbon molten iron and high-quality scrap steel, wherein the carbon content of the high-carbon molten iron is 0.8%-1.2%, and the micro-alloying elements include Cr, Mn, Si, Mo and the like.

3. The process for preparing a large-size and long-life bearing steel bar according to claim 1 is characterized in that: The deoxidizer includes Al or Si, Mn, etc., wherein the content of Al cannot be higher than 0.05wt%. During the process of adding the deoxidizer, the temperature of the molten metal is less than 1550°C, and the primary smelting is carried out by a converter or an electric arc furnace.

4. The process for preparing a large-size and long-life bearing steel bar according to claim 1 is characterized in that: The secondary refining includes vacuum degassing, refining outside the furnace and electroslag remelting. The stirring time of the vacuum degassing is within 30 minutes to 60 minutes, the stirring temperature is less than 1600° C., and the number of alternating stirring operations is greater than 3 times.

5. The process for preparing a large-size and long-life bearing steel bar according to claim 5 is characterized in that: The refining outside the furnace adds alloys to the molten steel, and the added alloys include Si, Mn, etc. During the refining outside the furnace, the temperature of the molten steel is maintained in the range of 1600° C. to 1650° C., and the time of the refining outside the furnace is controlled within 30 minutes to 60 minutes.

6. The process for preparing a large-size and long-life bearing steel bar according to claim 5 is characterized in that: In the electroslag remelting, the molten steel is remelted in the form of a consumable electrode, the hydrogen content in the molten steel is controlled below 2ppm, the oxygen content is controlled below 10ppm, and the current density is 1.5-3A / cm 2 .

7. The process for preparing a large-size and long-life bearing steel bar according to claim 1 is characterized in that: During the upsetting and stretching process, the grains are refined and heated evenly, the steel ingot is heated to about 1100° C., and finally the steel ingot is forged to be close to the requirements of the bar. The stretching adopts a symmetrical pressing method.

8. The process for preparing a large-size and long-life bearing steel bar according to claim 1 is characterized in that: During the homogenization annealing, the temperature of the rod-shaped steel ingot is maintained between 1100°C and 1250°C, the cooling method adopted by the homogenization annealing is slow furnace cooling, the holding time is between 10 hours and 24 hours, the delta ferrite content in the rod-shaped steel ingot is not more than 3%, and the maximum size of the carbide is not more than 3μm. During the spheroidizing annealing, the temperature is maintained at 780°C to 820°C, the cooling method adopted by the spheroidizing annealing is cooling the furnace to below 500°C and then air cooling, and the holding time is between 8 hours and 20 hours.

9. The process for preparing a large-size and long-life bearing steel bar according to claim 1, characterized in that: During the quenching, the temperature of the rod-shaped steel ingot is heated to between 840°C and 870°C, and the rod-shaped steel ingot is kept in this temperature range for 30 minutes to 2 hours, and then cooled by oil cooling. During the tempering, the temperature of the rod-shaped steel ingot is heated to between 150°C and 200°C, and the rod-shaped steel ingot is kept in this temperature range for 2 hours to 4 hours, and the hardness of the steel ingot is adjusted to between 58 and 64HRC.

10. The process for preparing a large-size and long-life bearing steel bar according to claim 1, characterized in that: The finishing includes turning or grinding to remove the oxide scale and defect layer on the surface of the rod-shaped steel ingot. The stress relief annealing heats the temperature of the rod-shaped steel ingot to 500°C to 650°C. The cooling method adopted by the stress relief annealing is slow furnace cooling to room temperature, and the insulation time is between 1 hour and 4 hours.

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