Steel for main shaft bearing of large-scale wind driven generator and production method of steel

Abstract

The invention relates to steel for a main shaft bearing of a large wind driven generator, and belongs to the technical field of iron-based alloys. A continuous casting process is adopted for molten steel casting, a casting blank is sampled, and after thermal refining, the yield strength is larger than or equal to 930 MPa, the tensile strength is larger than or equal to 1180 MPa, the percentage elongation after fracture is larger than or equal to 15%, and the normal-temperature impact absorbing energy AKU is larger than or equal to 60 J; the macrostructure rating of the continuous casting round billet according to GB / T 226 meets the following conditions: the center porosity is less than or equal to 1.5 grade, the general porosity is less than or equal to 1.0 grade, the center crack is less than or equal to 1.0 grade, the center segregation is less than or equal to 1.0 grade, and no shrinkage cavity or subsurface crack exists; the structure of the continuous casting round billet is a ferrite + pearlite + bainite structure. A continuous casting round billet is subjected to blanking, heating, forging, ring rolling, slow cooling, quenching and tempering heat treatment, turning, surface induction quenching, grinding and finished product ferrule obtaining, and the bearing ring piece is obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of metallurgy, and in particular relates to bearing steel and a production method thereof. Background Art

[0002] As an ideal renewable, clean energy source with vast resources, wind power is inevitably developing along the path of high quality, large-scale, lightweight, low-cost, and long life. Due to the harsh operating environment and inconvenient installation, repair, and maintenance of wind turbine equipment, bearings, as core components of wind turbines, face particularly stringent quality requirements. They must not only possess sufficient strength and load-bearing capacity, but also a service life of at least 20 years. Currently, domestically produced wind turbine bearings are limited to yaw and pitch bearings, which require relatively low technical barriers to entry for wind turbines. Main shaft and gearbox bearings are largely imported. The domestic main shaft bearing market is still primarily dominated by traditional international companies from Germany, Sweden, and Japan, with domestically produced bearings holding less than 10% of the market share. Furthermore, the domestic main shaft bearing market for wind turbines below 3MW is primarily focused on turbines with a production capacity of 3MW and above. Due to the high technical complexity, domestic production of main shaft bearings for wind turbines above 3MW is still in its infancy. Bearing material quality is the most important factor in determining wind turbine bearing quality, followed by bearing design, process technology, and equipment manufacturing. Future domestic production of wind turbine main shaft and gearbox bearings in China requires overcoming the technical challenges of wind turbine bearing material production.

[0003] Wind turbines operate outdoors year-round, under harsh operating conditions. Temperature, humidity, and bearing loads fluctuate significantly, requiring bearings with excellent sealing and lubrication properties, impact resistance, long life, and high reliability. Because wind turbine main shaft bearings are subject to axial and radial loads from the weight of the turbine head, as well as impact loads caused by fluctuating wind speeds, the bearing rings and rolling elements experience constant relative motion, subjecting them to severe contact fatigue and frictional wear. Therefore, bearing surfaces must possess not only high hardness but also a well-matched surface finish. Therefore, bearing materials must possess high hardenability, hardenability, and good impact toughness to meet contact fatigue resistance requirements. At present, foreign imported materials mainly use steel produced by electroslag remelting and die casting processes. Since the steel produced by electroslag remelting and die casting processes has certain advantages in purity and structural uniformity, they can produce highly stable materials for wind turbine main shaft bearings. However, these two processes have obvious disadvantages such as low production efficiency, yield rate, and production capacity, high energy consumption and production costs, and the fatigue life of foreign imported materials is not stable, which still leads to early failure of wind turbine main shaft bearings.

[0004] In view of the above situation, the present invention proposes a steel for main shaft bearings of large wind turbines and a manufacturing method thereof, which meets the use requirements of steel for main shaft bearings of large wind turbines by optimizing material properties. Summary of the Invention

[0005] The purpose of the present invention is to provide steel for main shaft bearings of large wind turbines and a production method thereof, involving an optimal continuous casting process design for producing high-alloy steel continuous casting round billets with specifications of φ600mm and above. Through reasonable composition design, the internal quality of the continuous casting round billets is effectively controlled. This product is suitable for the processing and manufacturing of main shaft bearings of large wind turbines.

[0006] The technical solution adopted by the present invention is: a method for producing continuous casting round billets for large-scale wind turbine main shaft bearings, adopting a smelting method of molten iron pretreatment → oxygen converter smelting → ladle refining → vacuum circulation degassing, and casting into round billets through an arc continuous casting machine. The chemical composition of the continuous casting round billets is as follows by mass percentage: C: 0.52-0.56%, Si: 0.10-0.30%, Mn: 0.70-0.80%, P≤0.020%, S≤0.010%, Cr: 1.0-1.20%, Mo: 0.35-0.50%, Ni: 0.15-0.40%, Cu≤0.20%, Ti≤0.003%, N: 0.0060-0.0090%, Al≤0.050%, H≤0.0002%, O≤0.0015%, Ca≤0.0010%, and the balance is Fe and other inevitable impurity elements.

[0007] The continuous casting round billet meets the following requirements: sampling, after quenching and tempering, the yield strength of the sample is ≥930MPa, the tensile strength is ≥1180MPa, the elongation after fracture is ≥15%, and the impact absorption energy AKU at room temperature is ≥60J.

[0008] The macrostructure of the continuous casting round billet is graded according to GB / T 226, meeting the following requirements: central porosity ≤ Grade 1.5, general porosity ≤ Grade 1.0, central crack ≤ Grade 1.0, central segregation ≤ Grade 1.0, no shrinkage cavity or subcutaneous crack, and the extreme carbon content of the full cross-section of the bearing product shall not exceed 10% of the normal smelting carbon content.

[0009] A method for processing large-scale wind turbine main shaft bearings comprises the following steps: continuously cast round billets are blanked → heated → forged (roughening, drawing, center punching) → ring rolling → slow cooling → tempering heat treatment (quenching + tempering) → turning → surface induction hardening → grinding → finished rings.

[0010] Samples are taken from forgings after forging for non-metallic inclusion testing according to GB / T 10561 Method A. Brittle, non-deformable inclusions must meet the following criteria: B Fine ≤ 1.5, B Coarse ≤ 1.0, D Fine ≤ 1.0, D Coarse ≤ 1.0, and Ds ≤ 1.5. Grain size is measured on forgings according to ASTM E112, with a grain size of ≥ 6. End quenching is performed on ferrules after quenching and tempering treatment, with requirements for J1.5 ≥ 62 HRC, J3 ≥ 60 HRC, and J5 ≥ 59 HRC.

[0011] In terms of metallographic structure: the continuous casting round billet structure is ferrite + pearlite + bainite. After forging and quenching and tempering, the round billet structure is tempered bainite + bainite. After induction quenching, the surface metallographic structure of the ring is martensite + retained austenite.

[0012] The elemental composition of this application is set based on: 1) Determination of C content Carbon is an essential element for ensuring the wear resistance of steel. Increasing the carbon content in steel increases its martensitic transformation ability, thereby improving its hardness and strength, and thus its wear resistance. However, excessive carbon content is detrimental to the toughness of the steel. Furthermore, excessive carbon content can lead to severe central carbon segregation, which affects the toughness of the steel's core. The present invention controls the carbon content to 0.52-0.56%. The steel of the present invention falls within the category of medium-carbon steel.

[0013] 2) Determination of Si content Si is a key element in the present invention. Si is solid-dissolved in the ferrite phase and has a strong solid-solution strengthening effect, which can significantly improve the strength of ferrite, but at the same time reduces the plasticity and toughness of ferrite. Si is added to steel as a deoxidizing element during steelmaking. The steel of the present invention is used for cold working purposes, which requires the material to have good cold working properties, that is, the ferrite in the steel must have excellent plasticity and toughness. Therefore, the Si content of the steel of the present invention should be as low as possible, in order to reduce the content of solid-dissolved Si in ferrite as much as possible and to exert the plastic limit of ferrite, so the setting range of the Si content is 0.10~0.30%.

[0014] 3) Determination of Mn content Manganese, as a deoxidizing element in the steelmaking process, is an effective element for strengthening steel, exerting a solid solution strengthening effect. Furthermore, manganese increases the hardenability of steel and improves its hot workability. Manganese can also counteract the effects of sulfur (S): during steelmaking, Mn reacts with S to form high-melting-point MnS, thereby weakening and eliminating the adverse effects of S. However, high Mn contents can reduce the toughness of steel. In the present invention, the Mn content is controlled to 0.70-0.80%.

[0015] 4) Determination of Al content Al is added to steel as a deoxidizing element. Besides reducing dissolved oxygen in molten steel, Al and N form dispersed, fine aluminum nitride inclusions, which refine grain size. However, excessive Al content can easily form brittle inclusions such as large Al₂O₃ particles during smelting, reducing the purity of the molten steel and shortening the service life of the finished product. The Al content in this invention is specified to be ≤0.05%.

[0016] 5) Determination of Ni content Nickel in steel can reduce the surface's ability to absorb carbon atoms, accelerate the diffusion of carbon atoms into austenite, and reduce the carbon concentration in the carburized layer. Therefore, nickel can slow the carburization rate. Furthermore, the addition of nickel can improve the toughness of the steel. The Ni content in the present invention is determined to be within a range of 0.15% to 0.40%.

[0017] 6) Determination of Cr content Cr is a carbide-forming element that can improve the hardenability, wear resistance and corrosion resistance of steel. However, Cr content is too high and, combined with the carbon in the steel, easily forms bulk carbides, which insoluble carbides reduce the toughness of the steel. In carburized bearing steel, chromium can adjust hardenability, improve the wear resistance of the carburized layer, and improve the mechanical properties of the steel. In addition, chromium can also stabilize the heat treatment process of steel, obtain good carburizing performance, and reduce the heterogeneity of carbides. The scope of Cr content of the present invention is determined as 1.00-1.20%.

[0018] 7) Determination of Mo content Molybdenum's primary role in carburized bearing steel is to enhance hardenability and improve the steel's mechanical properties, particularly toughness. It also improves the steel's wear resistance and carburization performance. The Mo content in this invention is preferably within a range of 0.35% to 0.50%.

[0019] 8) Determination of N content When supersaturated nitrogen is dissolved in steel, nitrogen will precipitate in the form of nitrides after being placed for a long period of time, and the hardness and strength of the steel will increase, while the plasticity will decrease and aging will occur. Adding an appropriate amount of aluminum to the steel can generate stable AlN, which can suppress the generation and precipitation of Fe4N, not only improving the aging of the steel, but also preventing the growth of austenite grains and playing a role in refining the grains. However, nitrogen will generate nitride non-metallic inclusions with the alloying elements in the steel, and more importantly, it reduces the effect of the alloying elements. When the nitrogen content in the steel is high, the strength of the steel increases and the impact toughness decreases. The N content of the present invention is determined to be 0.0060-0.0090% 9) Determination of Ti content Ti forms hard, angular inclusions in steel called TiN, which severely impact the material's fatigue life. However, Ti preferentially reacts with nitrogen in molten steel, mitigating the failure of added boron due to the reaction between nitrogen and boron. Therefore, the present invention requires the addition of Ti. Comprehensive calculations have determined the Ti content to be ≤0.0030%.

[0020] 10) Determination of Ca content Ca content increases the number and size of point-like oxides in steel. Furthermore, because these oxides are hard and have poor plasticity, they resist deformation during steel deformation, easily forming voids at interfaces and degrading steel performance. The Ca content in this invention is limited to 0.001% or less.

[0021] 11) Determination of O content Oxygen content represents the total amount of oxide inclusions. Oxide brittle inclusions limit the service life of finished products. Extensive testing has shown that reducing oxygen content significantly improves steel purity, particularly reducing the content of oxide brittle inclusions within a given steel grade. The oxygen content in this invention is specified to be ≤0.0015%.

[0022] 12) Determination of P and S content Phosphorus (P) causes severe segregation during solidification in steel. P dissolves in ferrite, causing grain distortion and coarsening, and increasing cold brittleness. The P content in this invention is set to ≤ 0.020%. Sulphur (S) causes hot brittleness in steel, reducing its ductility and toughness. The S content in this invention is set to ≤ 0.010%.

[0023] 13) Determination of H content Hydrogen easily dissolves into molten steel at high temperatures. During cooling, it has no time to escape and accumulates in the steel structure, forming high-pressure micropores that reduce the steel's plasticity, toughness, and fatigue strength. Furthermore, hydrogen can easily cause white spots on the steel. Therefore, the hydrogen content in this invention is required to be ≤ 0.0002%.

[0024] The specific production steps of continuous casting round billets are as follows: Step 1: Primary smelting: First, the smelting raw materials are pre-treated by KR. After pre-treatment, the molten iron must meet the following requirements: Si≤0.1%, S≤0.002%, to provide high-quality molten iron raw materials for the converter. The molten iron and scrap steel are prepared in a weight ratio of 4:1 or more to prepare the smelting raw materials. During the primary smelting of the smelting raw materials, the converter should ensure that the P content in the molten steel is ≤0.018% when tapping, and C ≥0.05% to prevent over-oxidation of the molten steel. The tapping temperature should be ≥1600℃, and the five harmful elements: Sn, As, Sb, Pb, and Bi should be less than 0.006%. In order to prevent P from returning to the subsequent process and to ensure the P requirements of the finished product, a portion of baked ferromanganese and ferroaluminum should be added in advance when tapping from the converter. The tapping time should be controlled at 5-7min, and slag should be blocked during the tapping process. Step 2: Molten steel refining: Bottom-blown argon is used to stir the molten steel throughout the refining process. The molten steel enters the refining furnace for slagging, stirring, deoxidation, and alloying. Lime and fluorite are added to the furnace during the smelting process. SiC is used for diffusion deoxidation on the surface of the refined slag. The slag viscosity and stability are adjusted to control the FeO+MnO content in the slag to less than 1%. The white slag time is controlled to be ≥20 minutes to ensure that the total [O] in the steel is ≤20ppm. Step 3 Vacuum degassing: The refined molten steel is treated with high vacuum degassing, and the vacuum degree is maintained for ≥15min at a vacuum degree of ≤133Pa. The alloy element content is not adjusted during the vacuum degassing process. The atmosphere of the molten steel after vacuum degassing should meet the following requirements: H ≤ 1.5ppm, O ≤ 15ppm, N: 60ppm ~ 90ppm, wherein nitrogen is used as the lifting gas to control the N content during the vacuum degassing process.

[0025] Step 4: Continuous Casting: The refined molten steel is continuously cast into round billets with diameters of 600mm or larger. Argon is blown through a long nozzle from the ladle to the tundish during the continuous casting process, and ladle slag detection technology is used to prevent residual metallurgical slag from the ladle from entering the tundish and contaminating the pure steel. The molten steel in the tundish is protected by a double layer of tundish cover and carbonized rice husks, isolating it from air, preventing secondary oxidation of the steel, and minimizing the temperature drop within the tundish, maintaining a stable superheat of ≤40°C. A slag retaining wall within the tundish filters and traps some harmful impurities. A computer system precisely controls the opening of the stopper rod, allowing the molten steel to flow through the submerged nozzle and into the mold. The mold level fluctuation is controlled within a range of -5mm to +5mm. Special mold powder is added to the mold, and the molten steel rapidly forms a shell under the cooling conditions of the mold cooling water. The molten steel in the mold is electromagnetically stirred by an external electromagnetic stirring device. The casting machine draws billets at a speed of 0.5-1.0 mm / min. The secondary cooling zone cools the round billets in sections, depending on the cooling capacity required at different times during the solidification process. An electromagnetic stirrer at the end of the cooling zone stirs the liquid core of the continuous casting billet, breaking up coarse columnar crystals to form more equiaxed crystals and reduce positive segregation at the 1 / 2R position. The billets are cut vertically into fixed-length billets by a flame cutting machine synchronized with the casting speed. The billets are then transferred to a horizontal roller conveyor via a conveyor roller table and removed by a large-tonnage crane. After removal, the billets are placed in a pit for slow cooling for at least 48 hours, with a temperature of no less than 500°C at the bottom and no more than 200°C at the exit. The metallographic structure of the billets after removal is ferrite, pearlite, and bainite.

[0026] The specific process steps for processing continuous casting round billets into ferrules are as follows: Step 1: Forging and ring rolling: The continuous casting round billet is placed in a heating furnace for heating at a rate of 20°C per hour to 1250°C ± (0-20°C), and kept warm for ≥5 hours. After being taken out of the furnace, forging is carried out, and the start forging temperature is greater than 1050°C. After five upsetting and four drawing, the upsetting ratio is greater than 2 each time, and the drawing ratio is greater than 1.5 each time, to ensure that the dendritic structure is fully broken during the forging process, and the final structure and alloy elements on the bearing ring forging are evenly distributed to ensure good mechanical properties. Then the center is punched, and the punching diameter is greater than φ200mm. Before ring rolling, it is heated in the furnace again, and the heating temperature is 1250°C ± (0-20°C), and kept warm for 0.5-2 hours. After being taken out of the furnace, ring rolling is carried out, and cooling is carried out after ring rolling. During cooling, a blower is used to quickly cool in the range of 950°C-700°C in the early stage to refine the grains, and then air cooling is used until the ring is air-cooled to room temperature. Step 2: Bearing ring heat treatment (quenching and tempering): The ring is heated to 860°C ± (0-20°C) and held for 4-8 hours. It is then water quenched. After 30-40 seconds, the workpiece is removed from the water. The surface temperature of the workpiece is controlled between 100°C and 200°C. At this surface temperature, martensite forms, which undergoes low-temperature autotempering. After quenching, the workpiece is reheated and tempered. Tempering is performed by heating the workpiece in a cold furnace to 580°C ± (0-20°C) for 5-8 hours, then removing it from the furnace and air cooling it to room temperature. After quenching and tempering, the ring exhibits a tempered bainite structure.

[0027] Step 3: Bearing Ring Turning and Surface Induction Hardening: After rough machining, the above steps are followed by surface induction hardening. After surface induction hardening, the surface microstructure of the bearing ring is martensite and retained austenite. Large wind turbine main shaft bearings are subject to heavy dynamic loads, and the operating conditions of the bearings require stable mechanical properties and a uniform hardened layer across the entire circumferential annular roller surface. In traditional induction hardening, when the end of the scanning induction heating path overlaps with the starting point, the hardened material is tempered, creating a soft zone. This soft zone, with its low surface hardness and mechanical strength, is susceptible to wear, forming a specific area for crack nucleation and propagation. This soft zone can affect the fatigue life of the bearing during heavy-load operation. To address this soft zone issue during track induction hardening, a soft zone-free induction hardening process has been introduced. This soft zone-free quenching process achieves uniform heat treatment without a soft zone. This soft zone-free quenching process utilizes a preheating coil with an independent power supply, allowing for adjustable heating rates to tailor the heating process to the steel's characteristics. The preheating sensor and mechanical tracking system prevent surface overheating and achieve a fine and uniform grain structure in the traditional soft zone, thereby improving the bearing's load capacity and fatigue life.

[0028] Step 4: Grinding the bearing ring to form a finished bearing ring. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below with reference to the examples. The examples are illustrative and intended to explain the present invention, but are not to be construed as limiting the present invention.

[0030] The purpose of the present invention is to protect a continuous casting round billet and its production method, which can replace the billet remelted by electroslag or mold casting to process bearings, and the final bearings meet the use requirements of large wind turbine main shaft bearings.

[0031] The chemical composition (wt%) of 50CrMo produced by the die casting process currently used in the market in various embodiments of the present invention and (as a comparative example) is shown in Table 1.

[0032] Table 1

[0033] Table 2 Inclusion levels of steels in Examples 1-3 and Comparative Example

[0034] Table 3 End hardenability of steel materials of Examples 1-3 and Comparative Example, HRC

[0035] Table 4 Grain size, hardness and mechanical properties of steels in Examples 1-3 and Comparative Example

[0036] Table 5 Macrostructure rating data of the ingots of Examples 1-3 and Comparative Example

[0037] The manufacturing process for large-scale wind turbine main shaft bearing steel in the embodiments of the present invention involves arc continuous casting of large-scale continuous cast round billets for wind turbine main shaft bearings and a method for preparing the same. The process utilizes a smelting process consisting of molten iron pretreatment, oxygen converter smelting, ladle refining, and RH vacuum cycle degassing. Round billets are then cast using an arc continuous casting machine. The continuously cast round billets undergo subsequent processes: blanking, heating, forging (upsetting, drawing, and center punching), ring rolling, slow cooling, heat treatment (tempering), lathing, surface induction hardening, grinding, and finally the finished rings.

[0038] Specifically, high-quality molten iron, scrap steel, and raw and auxiliary materials are selected during smelting, along with high-quality deoxidizers and refractory materials. During the converter production process, the three embodiments achieve a tapping endpoint C of ≥0.05%, an endpoint P of ≤0.018%, and a continuous casting superheat within 20-40°C. The continuously cast round billets are then pitted for slow cooling, with a pit temperature exceeding 500°C, a slow cooling time exceeding 48 hours, and a pit exit temperature below 200°C. The metallographic structure after pit exit is ferrite, pearlite, and bainite.

[0039] The continuous casting billet undergoes a process of forging, ring rolling, quenching and tempering, turning, surface induction hardening, and grinding to produce the final bearing. Before forging, the billet is heated to 1250°C ± (0-20°C) and held at this temperature for 5-7 hours. The initial forging temperature is above 1100°C, and the billet undergoes five upsetting and four drawing cycles, with each upsetting ratio exceeding 2 and each drawing ratio exceeding 1.5. Center punching is then performed, with a diameter of φ350mm or larger, depending on the billet size. Before ring rolling, the billet is heated again in the furnace to 1250°C ± (0-20°C) and held at this temperature for 0.5-2 hours. After exiting the furnace, the billet is ring rolled. After ring rolling, the billet is cooled using air blast for the initial cooling period between 950°C and 700°C, followed by air cooling until it reaches room temperature. The rings are then subjected to quenching and tempering heat treatment, resulting in a tempered bainite structure. After turning and surface induction hardening, the surface structure of the rings is martensite with retained austenite. Induction hardening uses a soft-band-free induction hardening process to avoid the formation of soft band areas on the rings, which will affect the ultimate bearing service life. During heating, the ring position is mechanically adjusted to ensure uniform heating.

[0040] As can be seen from the comparison in Tables 1-5, the performance indicators of the wind spindle bearings in various embodiments of the present invention are significantly better than those of 50CrMo steel produced by die casting, with significantly better control of harmful elements such as oxygen and titanium, as well as non-metallic inclusions. This means that the steel purity is significantly improved. Low-magnification inspection results show superior low-magnification quality, reflecting the present invention's improved uniformity and density. Based on the above analysis, the present invention utilizes a vacuum degassing and continuous casting process to produce continuously cast billets, which can replace the original die casting process, significantly improving production efficiency, reducing production costs, and significantly enhancing product competitiveness.

[0041] In summary, this invention, by improving steel purity, employs a high-efficiency, high-capacity, low-cost process involving vacuum degassing, continuous casting, and rolling, optimizing and controlling key processes. This results in steel with high purity, high structural uniformity, and high density, making it a perfect replacement for the traditional die-casting process. This makes it more competitive in terms of production efficiency, production costs, and product quality stability.

Claims

1. A continuous casting round billet for bearings, characterized by: The chemical composition by mass percentage is C: 0.52~0.56%, Si: 0.10~0.30%, Mn: 0.70~0.80%, P≤0.020%, S≤0.010%, Cr: 1.0~1.20%, Mo: 0.35~0.50%, Ni: 0.15~0.40%, Cu≤0.20%, Ti≤0.003%, N: 0.0060~0.0090%, Al≤0.050%, H≤0.0002%, O≤0.0015%, Ca≤0.0010%, and the balance is Fe and other inevitable impurity elements.

2. The continuous casting round billet for bearings according to claim 1, characterized in that: Samples are taken from the ingot, and after quenching and tempering, the yield strength is ≥930MPa, the tensile strength is ≥1180MPa, the elongation after fracture is ≥15%, and the impact absorption energy AKU at room temperature is ≥60J; the macrostructure of the continuous casting round billet is graded according to GB / T 226, and meets the following requirements: central porosity ≤1.5 level, general porosity ≤1.0 level, central crack ≤1.0 level, central segregation ≤1.0 level, and no shrinkage cavity or subcutaneous crack; the microstructure of the continuous casting round billet is ferrite + pearlite + bainite.

3. A bearing, characterized in that: The bearing ring is obtained by the continuous casting round billet according to claim 1 or 2 through the following steps: blanking → heating → forging → ring rolling → slow cooling → tempering heat treatment → turning → surface induction hardening → grinding → finished ring.

4. The bearing according to claim 3, characterized in that: After forging, samples are taken from the forgings for non-metallic inclusion inspection according to GB / T 10561 A method. Brittle non-deformable inclusions are B fine ≤ 1.5, B coarse ≤ 1.0, D fine ≤ 1.0, D coarse ≤ 1.0, and Ds ≤ 1.

5. Grain size is measured on the forgings according to ASTM E112 method. The grain size is ≥ 6. End quenching is tested on the rings after quenching and tempering heat treatment. The test meets the requirements of J1.5 ≥ 62HRC, J3 ≥ 60HRC, and J5 ≥ 59HRC. The metallographic structure of the ring surface is martensite + retained austenite.

5. A method for producing the continuous casting round billet for bearings according to claim 1, characterized in that: include: Molten steel primary refining: First, the molten iron is pretreated by KR. After pretreatment, the molten iron meets the following requirements: Si ≤ 0.1%, S ≤ 0.002%. The molten iron and scrap steel are prepared in a weight ratio of 4:1 or above to prepare the smelting raw materials. The smelting raw materials are primarily smelted in a converter to ensure that P ≤ 0.018% and C ≥ 0.05% in the molten steel during tapping to prevent overoxidation of the molten steel. The tapping temperature is ≥ 1600°C, and the contents of harmful elements such as Sn, As, Sb, Pb, and Bi are all controlled to be less than 0.006%. Partially baked ferromanganese and ferroaluminum are added during tapping from the converter. The tapping time is controlled at 5-7 minutes, and slag is used for tapping. Molten steel refining: Bottom-blown argon is used to stir the molten steel throughout the refining process. The molten steel enters the refining furnace for slagging, stirring, deoxidation, and alloying. Lime and fluorite are added to the furnace during the smelting process. SiC is used on the surface of the refining slag for diffusion deoxidation. The slag viscosity and stability are adjusted to control the FeO+MnO content in the slag to less than 1%, and the white slag time is controlled to be ≥20 minutes to ensure that the total [O] in the steel is ≤20ppm; Vacuum degassing: The refined molten steel is subjected to high vacuum degassing treatment, with the vacuum degree ≤133Pa and the vacuum holding time ≥15min. The alloying element content is not adjusted during the vacuum degassing process. The atmosphere of the molten steel after vacuum degassing should meet the following requirements: H ≤1.5ppm, O ≤15ppm, N: 60ppm~90ppm. Nitrogen is used as the lifting gas to control the N content during the vacuum degassing process. Continuous casting: Molten steel is cast into continuous casting round billets with a diameter of more than 600mm by continuous casting. During the continuous casting process, argon blowing is adopted from the ladle to the tundish with a long nozzle. The molten steel in the tundish is protected by a double layer of tundish covering agent and carbonized rice husk to isolate the air, keep the heat, and control the superheat of the molten steel to be ≤40℃. A slag retaining wall is provided in the tundish to filter and block some harmful impurities. The molten steel flows into the submerged nozzle through the stopper rod and is injected into the crystallizer. The fluctuation of the crystallizer liquid level is controlled within the range of -5mm to +5mm. Mold protection slag is added to the crystallizer, and the molten steel quickly forms a billet shell under the cooling condition of the crystallizer cooling water. The steel in the crystallizer The water is electromagnetically stirred by the external crystallizer electromagnetic stirring equipment on the molten steel, and the billet drawing speed is 0.5-1.0mm / min; the secondary cooling zone cools the round billet in sections according to the cooling capacity required at different times during the solidification process of the billet; the end electromagnetic stirring is set to stir the liquid center of the continuous casting billet, and the billet is cut into fixed-length billets in the vertical direction by a flame cutting machine synchronized with the billet drawing speed, and is transferred to the horizontal roller via a conveyor roller. After the billet is discharged, the continuous casting billet is slowly cooled in the pit for more than 48 hours, the temperature in the pit is not lower than 500℃, and the temperature out of the pit is not more than 200℃. After discharge, a continuous casting round billet is obtained.

6. The bearing according to claim 3, characterized in that: The forging and ring rolling are as follows: before forging, the continuous casting round billet is heated in a heating furnace at a heating rate of 20°C per hour to 1250°C ± (0-20°C), and kept warm for more than 5 hours. After being taken out of the furnace, it is forged, the start forging temperature is greater than 1050°C, and it undergoes five upsetting and four drawing, each upsetting ratio is greater than 2, each drawing ratio is greater than 1.5, and then the center is punched with a punching diameter of φ200mm or more. Before ring rolling, it is heated in the furnace again at a heating temperature of 1250°C ± (0-20°C), and kept warm for 0.5-2 hours. After being taken out of the furnace, it is ring rolled and cooled after ring rolling. During cooling, air blowing is used for rapid cooling in the early stage of 950°C-700°C to refine the grains, and then it is air-cooled to room temperature.

7. The bearing according to claim 3, characterized in that: The quenching and tempering heat treatment refers to heating the ring to 860°C ± (0-20°C) and keeping it warm for 4-8 hours, then water quenching, and hanging the workpiece out of the water after quenching in water for 30-40 seconds. The surface temperature of the workpiece out of the water is controlled at 100°C-200°C. Martensite is formed at this surface temperature for low-temperature self-tempering. After quenching, the workpiece is reheated for tempering. After the quenching and tempering heat treatment, the metallographic structure of the ring is tempered bainite structure.

8. The bearing according to claim 7, characterized in that: The tempering is to put the ring into the cold furnace again for heating, the heating temperature is 580℃±(0-20℃), keep the temperature for 5-8 hours, and then take it out of the furnace and air cool it to room temperature.

9. The bearing according to claim 3, characterized in that: The surface induction hardening is a soft belt-free hardening process equipped with a preheating coil, which independently adjusts the heating rate. During the heating process, the coil position is mechanically adjusted to compensate for workpiece deformation, ensuring uniform heating and obtaining a fine and uniform grain structure in the soft belt area.

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