Steel for wind power main shaft bearing rolling element and preparation method thereof

Abstract

The application belongs to the technical field of metallurgy, and particularly relates to a kind of steel for wind power main shaft bearing rolling body and a preparation method thereof.The chemical composition of the steel is optimally proportioned, including elements such as C, Si, Mn, Cr, Ni, Mo and Cu, and high purity is achieved by strictly controlling the impurity content.The steel is smelted by an electric furnace, refined by an LF furnace, vacuum degassed by VD, protected by a tundish, cast by continuous casting, heated by a casting blank, rolled, annealed, finished, quenched and the like, to obtain round steel with compact and uniform structure and extremely low impurities.After bainite quenching and tempering, the finished steel has a bainite structure of ≥95% and excellent grain size.The method significantly improves the wear resistance, fatigue strength and impact toughness of the steel, and is particularly suitable for offshore wind power main shaft bearing rolling body that bears extreme load and complex environment, effectively prolongs the service life, reduces the maintenance cost, and provides a high-performance bearing steel material solution for large-scale wind power equipment.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, and in particular relates to a steel for rolling elements of wind turbine main shaft bearings and its preparation method. Background Technology

[0002] With the rapid development of the global clean energy industry, the scale and single-unit capacity of offshore wind turbines are continuously increasing. The reliability and lifespan of the main shaft bearings have become key factors affecting the economics of wind power operation and maintenance. Once a bearing fails in an offshore wind turbine, on-site hoisting and replacement are extremely inconvenient and costly, often reaching hundreds of thousands or even millions of yuan for a single installation and dismantling. Therefore, the industry has imposed far more stringent requirements on the rolling element materials of the main shaft bearings than on general mechanical bearings, generally requiring a service life of no less than 25 years and maintaining high reliability even under long-term, extremely harsh environments.

[0003] Offshore wind turbines are exposed to complex natural environments with high humidity and drastic temperature fluctuations, enduring enormous and varied loads. The main shaft bearings not only continuously support the weight of the rotor and nacelle but also resist torque, axial thrust, aerodynamic bending moment transmitted during rotor rotation, and overturning moment caused by shaft bending and oscillation. Furthermore, the turbines may start or stop at any time, and the bearings are frequently subjected to strong impact loads during operation, posing a significant challenge to the strength and toughness of the materials. In recent years, the single-unit capacity of wind turbines has gradually increased, with 10MW-class offshore wind turbines becoming mainstream. Domestically, even 20MW-class turbines have been successfully tested, further increasing the stringent requirements for the performance of main shaft bearing materials.

[0004] In existing technologies, both domestically and internationally, carburized bearing steel or high-carbon chromium bearing steel is commonly used to manufacture the rolling elements of wind turbine main shaft bearings. These traditional bearing steels are generally obtained through electroslag remelting or die casting and forging. However, while electroslag remelting can improve the purity of the steel, it consumes a lot of energy and significantly increases production costs, which is not conducive to large-scale applications. Although die casting steel has a relatively flexible manufacturing process, it is difficult to control the purity of the steel in actual production, which can easily lead to problems such as a large number of non-metallic inclusions, large fluctuations in composition, and uneven microstructure, resulting in unstable product quality. In addition, although carburized bearing steel and high-carbon chromium bearing steel have good wear resistance and contact fatigue strength, their impact toughness often cannot meet the stringent requirements of high-power, heavy-load conditions, especially when subjected to frequent impacts or in low-temperature environments, making them more prone to brittle fracture and other failure phenomena.

[0005] With the increasing size of wind power equipment, the performance requirements for rolling element steel in main shaft bearings are continuously rising. High wear resistance and high strength alone are no longer sufficient for the applications of larger wind turbines; materials must simultaneously possess high impact toughness, high hardenability, high microstructure uniformity, and high purity. At the same time, with the rapid growth of wind power installed capacity, the industry is placing higher demands on bearing steel for low cost, mass production feasibility, and process adaptability. Currently, mainstream bearing steels and their production processes still have shortcomings in cost control, microstructure density, carbide uniformity, and inclusion content, making it difficult to balance high performance and economy. Especially in the manufacturing of large-size bearing rolling elements, the performance fluctuations, carbide coarsening, residual stress, and short fatigue life of traditional steels during subsequent heat treatment and use have become prominent bottlenecks affecting the safety and reliability of offshore wind turbine main shaft bearings.

[0006] Therefore, the wind power industry urgently needs to develop a new type of low-cost, high-performance steel for the rolling elements of wind turbine main shaft bearings, which can comprehensively improve wear resistance, impact toughness, and fatigue life, and has high purity, high microstructure uniformity, and process adaptability for industrial mass production. Summary of the Invention

[0007] The purpose of this invention is to provide a steel for the rolling elements of wind turbine main shaft bearings and its preparation method, aiming to address the shortcomings of existing offshore wind turbine main shaft bearing steels in terms of high reliability, long service life, and high strength and toughness. By optimizing the steel's composition design and metallurgical process, the invention achieves safe and stable operation of the rolling elements of wind turbine main shaft bearings under extremely complex working conditions, extends their service life, reduces maintenance costs, and meets the development needs of larger and more advanced wind power equipment.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] The first aspect of this invention provides a steel for rolling elements of wind turbine main shaft bearings, the chemical composition and its mass percentage being: C: 0.90–1.10%, Si: 0.40–0.80%, Mn: 0.90–1.0%, Cr: 1.80–2.10%, Ni: 0.40–0.50%, Mo: 0.35–0.45%, Cu: 0.15–0.25%, Al ≤ 0.0020%, Ti ≤ 0.0020%, Ca≤0.0010%, P≤0.015%, S≤0.010%, O≤0.0009%, H≤0.001%, N≤0.005%, As≤0.015%, Sn≤0.010%, Sb≤0.01%, Pb≤0.002%, Bi≤0.005%, As+Sn+Sb+Pb+Bi≤0.030%, balance being Fe and unavoidable impurities.

[0010] Furthermore, the steel used for the rolling elements of the wind turbine main shaft bearing, after bainitic quenching and tempering treatment, can obtain a bainitic structure with ≥95% bainitic content and a grain size of 8 or higher.

[0011] The steel for rolling elements of wind turbine main shaft bearings provided by this invention has the following functions and controls for each component:

[0012] C: Carbon in steel ensures hardness after quenching and forms carbides with Cr, Mo, etc., such as (FeCrMo)3C, (FeCr)7C3, etc., which improve the wear resistance and contact fatigue strength of steel. However, excessive carbon will not only lead to coarsening of carbides and uneven distribution, reducing fatigue life, but also increase the amount of residual austenite after heat treatment, reducing the hardness and wear resistance of steel. The carbon content in this invention is controlled within the range of 0.90-1.10%.

[0013] Si: Adding Si to steel can improve its strength, elastic limit, and hardenability, as well as its low-temperature tempering stability. However, Si increases the steel's overheating sensitivity, cracking tendency, and decarburization tendency. The Si content in this invention is determined to be in the range of 0.40% to 0.80%.

[0014] Mn: Mn can effectively improve the strength of steel and significantly improve the hardenability of steel. For wind turbine main shaft bearings, it can improve the strength and toughness of the ring center after tempering. However, excessive Mn will increase grain coarsening and temper brittleness. The Mn content of this invention is controlled at 0.90 to 1.0%.

[0015] Cr: It can improve the hardenability of steel. Cr is also a carbide-forming element. It forms alloy carbides such as (FeCrMo)3C and (FeCr)7C3 with C and Mo, which improves the wear resistance and contact fatigue strength of steel. However, if the Cr content is too high, it is easy to form large carbides. These insoluble carbides reduce the toughness of steel and reduce the bearing life.

[0016] Ni: Ni improves plasticity and toughness, especially at low temperatures. Ni is also an effective element for improving austenite stability and inhibiting austenite transformation, ensuring the presence of bainite or martensite after quenching. However, Ni is a precious alloy, and excessive content increases cost. Therefore, this invention controls its content at 0.40–0.50% to achieve optimal cost-effectiveness while meeting design performance requirements.

[0017] Mo (Mo): Molybdenum can refine the grains of steel, refine carbides, inhibit carbide aggregation, improve hardenability and hot strength, improve the microstructure of bearing cores, and enhance the toughness and impact resistance of bearing core materials. Mo is not only a valuable alloy, but molybdenum is also a ferrite-forming element. When the molybdenum content is high, ferrite δ phase or other brittle phases are more likely to appear, reducing toughness. In this invention, the Mo content is determined to be in the range of 0.35%–0.45%.

[0018] Al: Al is a good deoxidizer in smelting, but Al is also the main source of Al2O3, CaO and Al2O3 inclusions in steel, which seriously affects the fatigue life of bearings. Therefore, in order to ensure the purity of steel, the Al content is required to be ≤0.0020%.

[0019] Ca: The Ca content increases the number and size of dot oxides in steel. Since dot oxides have high hardness and poor plasticity, they do not deform during plastic deformation, which affects the service life of bearings. Therefore, the Ca content of this invention is required to be ≤0.0010%.

[0020] Ti: Ti easily reacts with N to produce TiN inclusions. Due to its high hardness and sharp angles, Ti can easily cause stress concentration and affect the service life of bearings. Therefore, the Ti content in this invention is required to be ≤0.0020%.

[0021] O is the source of oxide inclusions in steel, therefore the O content in this invention is required to be ≤0.0009%. H is the main factor causing white spots and hydrogen embrittlement in steel, and it is extremely harmful to steel, therefore the H content in this invention is required to be ≤0.001%.

[0022] As, Sn, Sb, Pb, and Bi are low-melting-point elements. These elements affect the plasticity, toughness, and pressure processing properties of steel. Therefore, this invention requires that: As ≤ 0.015%, Sn ≤ 0.010%, Sb ≤ 0.01%, Pb ≤ 0.002%, Bi ≤ 0.005%, and As + Sn + Sb + Pb + Bi ≤ 0.030%.

[0023] The second aspect of this invention provides a method for preparing the steel for rolling elements of a wind turbine main shaft bearing, comprising the following steps:

[0024] (1) Electric furnace smelting: Iron and scrap steel are mixed in proportion and smelted in an electric furnace. When tapping the steel, aluminum is added for pre-deoxidation, followed by top slag, high-purity ferrosilicon, metallic manganese, low-titanium high-carbon ferrochrome and carbon raiser to obtain primary molten steel.

[0025] (2) LF ladle refining: The primary steel is transferred to the LF refining furnace, where carbon powder is used for diffusion deoxidation and aluminum, ferrosilicon alloy and calcium alloy deoxidation are prohibited. The ternary slag is treated with foam slag to obtain refined steel.

[0026] (3) VD vacuum degassing: The refined molten steel is transferred into a VD vacuum tank and vacuum degassed under an argon atmosphere. After degassing, rare earth modifiers are added for modification treatment.

[0027] (4) Tundish metallurgy and continuous casting protection casting: The molten steel treated in step (3) is cast through a long nozzle under an argon protective atmosphere. Alkaline covering agent and heat preservation agent are added to the tundish. The molten steel is purified by slag washing and slag blocking measures. The steel is continuously cast into round billets by stirring and light pressure technology.

[0028] (5) Hot delivery and heating of billet: After the continuous casting round billet is cut to length, it is hot delivered to the heating furnace for segmented heating and high-temperature diffusion to homogenize carbides and microstructure;

[0029] (6) Rolling: The heated steel billet is descaled, rolled into a billet, and the intermediate billet is kept warm. Then, continuous rolling is carried out, with controlled rolling and cooling, to obtain round steel with a rolling ratio of not less than 20.

[0030] (7) Annealing and finishing: The rolled steel is subjected to slow cooling, annealing and heat preservation and cooling treatment, and then straightening, peeling, flaw detection and finishing to obtain the steel for the rolling elements of the wind turbine main shaft bearing.

[0031] Further, the elemental mass percentages in the molten iron in step (1) are as follows: P≤0.15%, Ti≤0.06%, As≤0.005%, Sn≤0.003%, Sb≤0.003%, Pb≤0.005%, Bi≤0.005%; the molten iron accounts for 80%-85% of the total mass, and the scrap steel accounts for 15-20% of the total mass; during the smelting process, slag dephosphorization is performed to control the phosphorus content of the tapped steel to ≤0.009%, and the final carbon content is controlled at 0.15%~0.35%.

[0032] Further, the ternary slag system in step (2) is a CaO (50-55%) + SiO2 (5-10%) + Al2O3 (32-35%) ternary slag system, with the alkalinity controlled at 5-7; the refining process is stirred by argon gas throughout.

[0033] Furthermore, the vacuum degassing treatment in step (3) is carried out under a vacuum degree of less than 67 Pa and the treatment time is not less than 15 minutes; the rare earth modifier is rare earth cerium carbonate iron wire, and 0.2 to 0.3 kg of rare earth cerium carbonate iron wire is added per ton of steel; after the modification treatment, argon gas is continuously blown softly for a time of not less than 25 minutes, and carbonized rice husk heat preservation agent is covered on the top slag layer to ensure that the inclusions float up fully and the temperature of the molten steel is uniform.

[0034] Furthermore, in step (4), the continuous casting is carried out at a low superheat of 15℃-25℃; the reduction amount under light pressure is 10-20mm of the billet diameter.

[0035] Further, in step (5), the surface temperature of the billet entering the heating furnace is controlled at 500-650℃ when the heat is delivered to the heating furnace; the segmented heating includes: the billet is preheated at 850-950℃, heated at 950-1150℃ for one stage, heated at 1200-1250℃ for the second stage, and heated at 1200-1230℃ for homogenization, heated to the rolling temperature in four stages, and diffused at 1200-1230℃ for 8-10 hours to promote uniform distribution of carbides and uniform structure.

[0036] Further, in step (6), the billet rolling is carried out by a reversible billet rolling mill for multiple passes. During the rolling process, the steel is turned over in even passes to ensure uniform deformation. A large reduction of 25% to 30% is implemented in the main deformation pass to achieve plastic penetration rolling. The temperature of the intermediate billet is 850 to 900°C. The temperature of the continuous rolling is controlled at 800 to 950°C. The controlled rolling and controlled cooling are as follows: the rolled steel is cooled by water through 3-5 water tanks. The water pressure, water volume and rolling speed are adjusted to control the red temperature of the steel at 600 to 700°C. After the steel is removed from the cooling bed, the temperature is 450 to 550°C. The steel is then sent to the slow cooling pit for cooling.

[0037] Furthermore, the annealing and heat preservation in step (7) is carried out at 750-800℃ for 4-6 hours.

[0038] Furthermore, after the steel used for the rolling elements of the wind turbine main shaft bearing is further processed into bearing rolling elements, it undergoes spheroidizing annealing, isothermal quenching in a bainitic salt bath, and tempering treatment to obtain a bainitic structure with ≥95% bainitic content.

[0039] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0040] Compared with existing technologies, this invention improves the hardenability, refines and homogenizes carbides, and enhances the wear resistance and fatigue strength of bearing steel by increasing the amounts of Mn, Cr, and Mo in the composition system of ordinary high-carbon chromium bearing steel. Furthermore, by adding an appropriate amount of nickel, it improves the impact toughness, especially the low-temperature impact toughness. After bainitic quenching, the low-impact toughness AkV (-40℃) is 3-5 times that of ordinary high-carbon chromium bearing steel, with AkV (-40℃) ≥ 27J. This doubles the fatigue life of the bearing, reaching 0.8 × 10⁻⁶ J. 8 The wear resistance is three times that of ordinary high-carbon chromium bearing steel. The high-purity, highly homogeneous, and wear-resistant bearing steel produced by the method of this invention is free of micropores and carbide precipitation. The carbide network structure is ≤CZ4.2, the carbide band structure is ≤CZ7.2, and the carbide particle size is less than 2μm. The high-hardenability wear-resistant bearing steel produced by this invention fully meets the requirements of wind turbine shaft bearings for impact resistance, reliability, and long service life. Attached Figure Description

[0041] Figure 1 A low-magnification photograph of the steel used for the rolling elements of the wind turbine main shaft bearing prepared in Example 1.

[0042] Figure 2 Metallographic image of the steel used for rolling elements of wind turbine main shaft bearings prepared in Example 1.

[0043] Figure 3 The image shows the metallographic structure of the steel used for the rolling elements of the wind turbine main shaft bearing prepared in Example 1 after heat treatment. Detailed Implementation

[0044] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] A method for preparing steel for rolling elements of wind turbine main shaft bearings includes the following steps:

[0046] (1) Electric furnace smelting

[0047] High-quality molten iron and high-purity scrap steel are rationally mixed in a ratio of 80%–85% molten iron and 15%–20% scrap steel, and then charged into an electric furnace for smelting. The elemental mass percentages in the molten iron are as follows: P≤0.15%, Ti≤0.06%, As≤0.005%, Sn≤0.003%, Sb≤0.003%, Pb≤0.005%, Bi≤0.005%, ensuring the purity of the raw materials. Hot charging technology is used, and the molten iron temperature is maintained at 1300℃ or above. Slag-flowing operation is employed during the smelting process, with slag formation and dephosphorization occurring simultaneously to ensure that the phosphorus content of the tapped steel does not exceed 0.009%. The furnace atmosphere is also controlled to prevent over-oxidation, and the carbon content at the tapping point is maintained at 0.15%–0.35%. An eccentric bottom tapping technique is used to prevent slag from entering the molten steel, ensuring the cleanliness of the molten steel. Immediately after tapping, the steel undergoes alloying treatment, with aluminum added for pre-deoxidation, followed by the addition of top slag, high-purity ferrosilicon (TFESi75-A), metallic manganese (JMn96-A), low-titanium high-carbon ferrochrome (FeCr55C1000Ti3), and carbon raiser (C90) to obtain primary molten steel.

[0048] (2) LF ladle refining

[0049] The molten steel, smelted in the electric arc furnace, is transferred to the LF refining furnace for ladle refining. During the refining stage, carbon powder diffusion deoxidation is employed; the use of aluminum, ferrosilicon alloys, and calcium alloys for deoxidation is strictly prohibited to avoid the formation of inclusions such as silicates, Al2O3, and CaO·Al2O3. Foamed white slag is created to effectively adsorb inclusions in the steel, improving the purity of the molten steel. The refining slag uses a ternary slag system of CaO (50–55%), SiO2 (5–10%), and Al2O3 (32–35%), with the slag basicity controlled between 5 and 7. Throughout the refining process, argon gas is continuously introduced for stirring to ensure uniform steel composition and temperature and to promote the flotation and adsorption of inclusions by the slag.

[0050] (3) VD vacuum degassing

[0051] The molten steel refined by LF is transferred to a VD vacuum tank, and the argon flow rate is automatically adjusted. Before the vacuum level drops below 67 Pa, the argon flow rate is controlled at 10 ± 5 NL / min to prevent the molten steel from breaking the slag surface and causing secondary oxidation. When the vacuum level drops below 67 Pa, the argon flow rate is adjusted to 70 ± 5 NL / min, and hydrogen in the steel is carried away by a large number of dispersed argon bubbles. The high vacuum is maintained for no less than 15 minutes to achieve effective dehydrogenation of the molten steel and ensure that the hydrogen content is below 1.0 ppm. After the vacuum treatment is completed, the argon flow rate is adjusted to a soft-blowing state, the vacuum pump is turned off to break the vacuum, and constant hydrogen temperature is measured in time. Then, 0.2-0.3 kg / t cerium carbonate rare earth wire is added to the steel using a wire feeder to modify inclusions. After the wire feeding is completed, 50-80 kg of carbonized rice husk insulation agent is sprinkled on the top slag layer for insulation. After the rare earth wire feed is completed, the soft blowing time should be no less than 25 minutes to promote the full floating of inclusions and uniform heat preservation of molten steel.

[0052] (4) Tundish metallurgy and continuous casting protective casting

[0053] After VD treatment, when the molten steel temperature is suitable, the ladle is hoisted to the casting platform. A long nozzle is used for protection during casting between the ladle and the tundish, and an argon gas protection ring is installed between the long nozzle and the ladle's lower nozzle to prevent secondary oxidation of the steel stream by air. After the first heat is poured, when the molten steel reaches 1 / 3 of the tundish's capacity, an alkaline covering agent (the composition and mass content of the alkaline covering agent are as follows: CaO 50.0%, Al2O3 35.0%, MgO 8.0%, SiO2 6.0%, Fe2O3 1%) and carbonized rice husk insulating agent are added to the tundish for insulation and slag washing, further adsorbing inclusions in the molten steel. The tundish adopts a T-shaped tundish and slag-blocking wall structure, effectively preventing slag from flowing into the casting area and facilitating the floating of inclusions and adsorption by the covering agent. After the tundish reaches the required level for casting, pouring begins, introducing the molten steel into the crystallizer. An integral submerged nozzle is used between the tundish and the crystallizer. A special crystallizer protective slag is used inside the crystallizer to prevent contact between the molten steel and air, thus avoiding secondary oxidation. Continuous casting employs a low superheat (15–25°C) casting process, incorporating electromagnetic stirring in the crystallizer (initial stirring), flow stirring (casting stirring), and final electromagnetic stirring (final stirring), along with a rationally configured primary and secondary cooling water system for billet cooling, to reduce billet compositional segregation and improve its density. During the final stage of billet solidification, a light reduction technique is used, with a reduction of 10–20 mm of the nominal billet diameter. After the billet enters the straightening machine, four straightening machines are used for continuous light reduction.

[0054] (5) Hot delivery heating of cast billet

[0055] After being cut to length, the continuously cast round billets are directly hot-sent to the rolling mill heating furnace. The surface temperature upon entering the furnace is controlled at 550–650℃. The heating process is divided into four stages: a preheating stage at 850–950℃, a first heating stage at 950–1150℃, a second heating stage at 1200–1250℃, and finally, a homogenization treatment at 1200–1230℃. The billets undergo high-temperature diffusion in the homogenization stage for an extended period (8–10 hours) to eliminate carbide precipitation and reduce carbide inhomogeneity, ensuring a uniform microstructure before rolling.

[0056] (6) Rolling

[0057] The heated steel billet first undergoes descaling, then is repeatedly rolled on a 1320 reversible billet mill to obtain the required intermediate billet. During the rolling process, even-pass turning is used to ensure uniform deformation, and a large reduction of 25%–30% is used in the main deformation passes for plastic penetration rolling to improve the density of the finished product. After the intermediate billet has reached the desired temperature, it is fed into a 9-stand continuous rolling mill at 850–900℃ for continuous multi-pass rolling, with the final rolling temperature controlled at 800–950℃. After exiting the continuous rolling mill, the rolled piece is sequentially cooled by water through 3–5 sections of water tanks. By adjusting the water pressure, water volume, and rolling speed of each section of water tank, the reheating temperature of the rolled piece on the cooling bed after water cooling is maintained at 600–700℃. The finished steel is removed from the cooling bed at a temperature of 450–550℃ and is promptly placed in a slow cooling pit for slow cooling. Throughout the overall rolling process, the cross-sectional area ratio from the billet to the finished round steel is not less than 20.

[0058] (7) Annealing and finishing

[0059] The rolled steel is slowly cooled and removed from the furnace, then transferred to an annealing furnace for annealing within 48 hours. During annealing, the steel is held at a soaking temperature of 780℃ for 4–6 hours, and then slowly cooled to below 450℃ at a rate of ≤30℃ / h before being air-cooled. The annealed steel then undergoes straightening, peeling, ultrasonic and magnetic flux leakage testing, and finishing processes to obtain the steel for the rolling elements of the wind turbine main shaft bearing.

[0060] The steel for the rolling elements of the wind turbine main shaft bearings obtained through the above processes is then machined into bearing rolling elements through blanking, heating, forging, and other machining processes. The finished rollers are first subjected to spheroidizing annealing, followed by bainitic isothermal quenching in a salt bath. The quenching heating and holding temperature is 870℃, and the isothermal quenching salt bath temperature is 235±1℃. After the isothermal holding is completed, tempering is performed promptly at a tempering temperature of 190±5℃.

[0061] The steel for rolling elements of wind turbine main shaft bearings was prepared using the above method. The chemical composition of the steel in Examples 1-3 and Comparative Examples 1-3 is shown in Table 1, and the process parameters are shown in Table 2.

[0062] Table 1. Chemical composition of steel (wt%)

[0063]

[0064] Table 2 Process parameters

[0065]

[0066] A low-magnification photograph of the steel used for the rolling elements of the wind turbine main shaft bearing prepared in Example 1 is shown below. Figure 1 As shown in the metallographic photograph, Figure 2As shown, Figure 2 No obvious banded tissue was observed in the metallographic images. Figure 1 The rating results are as follows: central looseness 1.0, general looseness 0.5, spindle segregation 0.5, central segregation 0.5, and punctate segregation 0. Figure 2 The rating results are as follows: no micropores, carbide liquid precipitation CZ6.0, carbide banding CZ7.2, and carbide network CN4.2.

[0067] Samples were taken from the steels prepared in the above examples and comparative examples to examine low-magnification microstructure, non-metallic inclusions, carbide inhomogeneity, and grain size. The test data are shown in Tables 3, 4, and 5.

[0068] Table 3 Low-magnification tissue / grade

[0069]

[0070] Table 3 shows the low-magnification tissue rating results. Compared with the comparative example, the example is 0.5 grade better than the comparative example in terms of general porosity and spindle segregation, which has reached the upper limit of the industry level.

[0071] Table 4 Non-metallic inclusions / grade

[0072]

[0073] Table 5. Carbide inhomogeneity, microporosity, and grain size

[0074]

[0075] The hardness and microstructure data of the steels prepared from Examples 1-3 and Comparative Examples 1-3 after blanking, heating, forging, machining, and bainitic quenching and tempering are shown in Table 6.

[0076] Table 6 Bainitic quenching hardness and hardness difference

[0077]

[0078] The AkV (-40℃) wear resistance and fatigue limit of the steels prepared from Examples 1-3 and Comparative Examples 1-3 were tested after blanking, heating, forging, machining, bainitic quenching and tempering at 250℃. The results are shown in Table 7.

[0079] Table 7. Abrasion resistance and fatigue limit of AkV (-40℃)

[0080]

[0081] The above results demonstrate that by adding an appropriate amount of nickel to high-hardenability wear-resistant bearing steel, this invention significantly improves the impact toughness of the steel, especially its impact resistance under low-temperature conditions, showing a substantial improvement compared to conventional high-hardenability wear-resistant bearing steel. Simultaneously, by optimizing the ratio of carbide-forming elements such as chromium and molybdenum, the carbides in the steel are made finer and more uniformly distributed, thereby effectively improving the material's wear resistance and contact fatigue strength.

[0082] This invention employs a specialized high-purity steel smelting process, which involves the rational design of the refining slag system and the composition ratio of the tundish covering agent, as well as the implementation of rare earth inclusion modification treatment, thus achieving ultra-pure steel smelting and continuous casting throughout the entire production process. Through low superheat control, three-stage electromagnetic stirring, and continuous casting with light reduction technology, the obtained continuously cast round billets exhibit high purity, dense and uniform microstructure, and performance indicators that reach the quality level of electroslag remelted steel, fully ensuring the reliability of subsequent processing and service.

[0083] Furthermore, through long-term high-temperature diffusion during billet heating, plastic penetration rolling with large reduction during billet opening, and controlled rolling and cooling processes, round steel with a dense and uniform microstructure and fine and uniformly distributed carbide particles can be obtained in a single firing process. This not only meets the stringent requirements for high strength, high toughness, and long service life of steel used in the rolling elements of wind turbine main shaft bearings, but also improves the overall service safety and reliability of the material.

[0084] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A wind power main shaft bearing rolling element steel, chemical composition and mass percentage thereof are as follows: C: 0.90-1.10%, Si: 0.40-0.80%, Mn: 0.90-1.0%, Cr: 1.80-2.10%, Ni: 0.40-0.50%, Mo: 0.35-0.45%, Cu: 0.15-0.25%, Al≤0.0020%, Ti≤0.0020%, Ca≤0.0010%, P≤0.015%, S≤0.010%, O≤0.0009%, H≤0.001%, N≤0.005%, As≤0.015%, Sn≤0.010%, Sb≤0.01%, Pb≤0.002%, Bi≤0.005%, As+Sn+Sb+Pb+Bi≤0.030%, balance of Fe and inevitable impurities; the wind power main shaft bearing rolling element steel, after being treated by bainite quenching and tempering, can obtain ≥95% bainite structure, and grain size reaches 8 level or above; a preparation method of the wind power main shaft bearing rolling element steel comprises the following steps: (1) electric furnace smelting: proportioning molten iron and scrap steel, smelting in an electric furnace, adding aluminum for pre-deoxidization when tapping, and then adding top slag, high-purity ferrosilicon, metal manganese, low-titanium high-carbon ferrochrome and carbon additive in sequence to obtain primary molten steel; (2) LF furnace external refining: transferring the primary molten steel into an LF refining furnace, performing carbon powder diffusion deoxidization, and disabling aluminum, ferrosilicon and calcium alloy deoxidization, performing three-element slag system foam slag treatment to obtain refined molten steel; the three-element slag system is CaO 50-55%+SiO2 5-10%+Al2O3 32-35% three-element slag system, the basicity is controlled to be 5-7, and argon gas is stirred throughout the refining process; (3) VD vacuum degassing: transferring the refined molten steel into a VD vacuum tank, performing vacuum degassing treatment under an argon atmosphere, and adding a rare earth modifier for modification treatment after degassing; (4) tundish metallurgy and continuous casting protection casting: casting the molten steel treated in the step (3) through a long nozzle under an argon protection atmosphere, adding an alkaline covering agent and a heat preservation agent in a tundish, purifying the molten steel through slag washing and slag blocking measures, and adopting stirring and light pressing down technology to continuously cast a round billet; (5) cast billet hot sending and heating: after the continuous casting round billet is cut to size, the round billet is hot sent to a heating furnace for segmented heating and high-temperature diffusion, and carbides and structures are homogenized. ​ ​ (6) rolling: the heated billet is subjected to descaling, blooming rolling, intermediate billet waiting, continuous rolling, controlled rolling and controlled cooling to obtain round steel, and the rolling ratio is not less than 20; the blooming rolling is carried out by using a reversible blooming mill for multi-pass blooming rolling, and the deformation is uniform by odd-pass turning during the rolling process, and the large reduction of 25%-30% is implemented in the main deformation pass to realize plastic penetration rolling; the temperature of the intermediate billet waiting is 850-900℃; the temperature of the continuous rolling is controlled at 800-950℃; the controlled rolling and controlled cooling are specifically as follows: the steel after rolling is subjected to water cooling through 3-5 water tanks, and the return red temperature of the steel is controlled at 600-700℃ by adjusting the water pressure, water quantity and rolling speed, and the temperature after the cooling bed is 450-550℃, and the steel is sent to the slow cooling pit for cooling; (7) annealing and finishing: the steel after rolling is subjected to slow cooling, annealing, heat preservation and temperature reduction, and then is subjected to straightening, peeling, flaw detection and finishing to obtain the steel for the wind power main shaft bearing rolling body.

2. The windmill main shaft bearing rolling element steel according to claim 1, characterized by, The element mass percentage in the molten iron in step (1) is as follows: P≤0.15%, Ti≤0.06%, As≤0.005%, Sn≤0.003%, Sb≤0.003%, Pb≤0.005%, Bi≤0.005%; the mass percentage of the molten iron is 80%-85%, and the mass percentage of the scrap steel is 15-20%; the flow slag dephosphorization operation is carried out during the smelting process, the phosphorus content of the molten steel is controlled to be less than or equal to 0.009%, and the terminal carbon content is controlled to be 0.15%-0.35%.

3. The windmill main shaft bearing rolling element steel according to claim 2, characterized by, The vacuum degassing treatment in step (3) is carried out under the condition that the vacuum degree is less than 67 Pa, and the treatment time is not less than 15 minutes; the rare earth modifier is rare earth cerium carbonate iron wire, and 0.2-0.3 kg of the rare earth cerium carbonate iron wire is added per ton of steel; after the modification treatment, soft argon blowing is continued for not less than 25 minutes, and the carbonized rice husk heat preservation agent is covered on the top slag layer to ensure that the inclusions float up and the temperature of the molten steel is uniform.

4. The windmill main shaft bearing rolling element steel according to claim 3, characterized by, The continuous casting in step (4) is carried out by using low superheat of 15-25℃; and the light reduction amount is 10-20 mm of the round billet diameter.

5. The windmill main shaft bearing rolling element steel according to claim 4, characterized by, The surface temperature of the billet entering the heating furnace in step (5) is controlled at 500-650℃; the segmented heating includes: the billet is preheated at 850-950℃, heated at 950-1150℃ in the first heating section, heated at 1200-1250℃ in the second heating section, and soaked at 1200-1230℃, and the four heating sections reach the rolling temperature, and the high temperature diffusion at 1200-1230℃ is carried out for 8-10 hours to promote the uniform distribution of carbides and the uniformity of the structure.

6. The windmill main shaft bearing rolling element steel according to claim 5, characterized by, The annealing heat preservation in step (7) is carried out at 750-800℃ for 4-6 hours.

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