Continuous casting round billet for offshore wind power main shaft bearing and manufacturing method of continuous casting round billet

Abstract

The invention discloses a continuous casting round billet for an offshore wind power main shaft bearing and a manufacturing method of the continuous casting round billet, and belongs to the technical field of metallurgy. The steel comprises the following chemical components in percentage by mass: 0.41-0.46% of C, 0.20-0.40% of Si, 0.80-0.90% of Mn, 1.00-1.20% of Cr, less than or equal to 0.015% of P, less than or equal to 0.010% of S, 0.10-0.40% of Ni, less than or equal to 0.20% of Cu, 0.20-0.30% of Mo, less than or equal to 0.050% of Al, 0.01-0.10% of V, less than or equal to 0.0010% of Ca, less than or equal to 0.003% of Ti, less than or equal to 0.0015% of O, less than or equal to 0.0080% of N, less than or equal to 0.015% of As, less than or equal to 0.010% of Sn, less than or equal to 0.010% of Bi, less than or equal The manufacturing method comprises the working procedures of KR molten iron pretreatment, BOF converter primary smelting, LF ladle refining, RH vacuum circulation degassing, CCM continuous casting, forging, ring rolling, heat treatment and the like, and through component optimization (Ni + V cooperation) and process innovation, the product has the characteristics of ultrahigh purity, compact and uniform structure and excellent toughness, can replace a traditional die casting process and meets the requirements of deep and far sea wind power equipment.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a continuously cast round billet for offshore wind turbine main shaft bearings and its manufacturing method, which is particularly suitable for core components of deep-sea wind power equipment that withstand strong wind loads, vibrations, extreme temperatures and long-term operating conditions. Background Technology

[0002] During the energy structure transformation, green and low-carbon industries such as wind power and hydropower are booming, but they are severely constrained by the quality and specifications of upstream metal raw materials. Currently, most billet manufacturers choose ingot casting, but due to the low production efficiency of the ingot casting process, production costs remain high. The unstable quality of ingot casting is a major cause of product failure. Therefore, continuous casting technology is used to produce offshore wind turbine main shaft bearings, ensuring the supply of key and core components for wind power equipment, breaking through the technical bottlenecks in the industrial chain, manufacturing high-performance, low-energy-consumption, large-scale green materials, and enhancing the core competitiveness of enterprises for high-quality development.

[0003] Wind power is characterized by abundant wind energy resources, high operating efficiency, small footprint, large-scale development, and relatively advanced technology. The main shaft bearing of an offshore wind turbine is a critical component, primarily used to support and transmit the rotational power of the wind turbine (blades) to the generator, while also bearing complex loads. It must withstand strong winds, varying loads, vibrations, extreme temperatures, and long-term operation; its reliability directly impacts the unit's efficiency and maintenance costs. The offshore wind turbine's main shaft bearing is the "joint" of the wind turbine, with high technological barriers and harsh operating conditions, directly affecting power generation efficiency and lifespan.

[0004] Due to the unique characteristics of offshore wind turbine main shaft bearings, high requirements are placed on raw materials. Currently, offshore wind turbine main shaft bearings mainly use high-carbon bearing steel ingot casting or ingot forging. Product failure is complex. In addition to reasons related to assembly and lubrication, the unstable quality of ingot casting is the main factor causing failure, mainly manifested in fatigue failure due to poor steel purity. Ingot casting suffers from low production efficiency, insufficient mechanization and automation, and inconsistent steel purity. Furthermore, with the increasing size and load-bearing capacity of wind turbines, traditional ingot casting products cannot meet current usage demands in terms of quality and specifications. Continuous casting, on the other hand, produces products with high purity and uniform structure. Compared to manual single-furnace production, continuous casting allows for automated multi-furnace continuous production, ensuring stable quality and high efficiency. This guarantees the materials for key and core components of wind power equipment and overcomes the technical bottlenecks in the industry chain. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a continuous casting round billet with ultra-high purity, dense and uniform structure and excellent toughness and its stable production method, which solves the problems of low purity, uneven structure, insufficient toughness, low production efficiency and high cost in the production of offshore wind turbine main shaft bearing steel by existing ingot casting process. At the same time, it overcomes the defects such as center segregation, shrinkage cavity and cracks that are prone to occur when the continuous casting process is applied to this field.

[0006] The technical solution adopted by the present invention to solve the above problems is as follows: a continuously cast round billet for offshore wind turbine main shaft bearings, the chemical composition (mass fraction) of which is: C: 0.41-0.46%, Si: 0.20-0.40%, Mn: 0.80-0.90%, Cr: 1.00-1.20%, P≤0.015%, S≤0.010%, Ni: 0.10-0.40%, Cu≤0.20%, Mo: 0.20-0.30%, Al≤0.050%, V: 0.01-0.10%, Ca≤0.0010%, Ti≤0.003%, O≤0.0015%, N≤0.0080%, As≤0.015%, Sn≤0.010%, Bi≤0.010%, Sb≤0.010%, Pb≤0.008%, with the balance being Fe and unavoidable impurities.

[0007] The chemical composition design basis for the continuously cast round billet used in the offshore wind turbine main shaft bearing of this invention is as follows: C: Controlled between 0.41% and 0.46%, this ensures the hardenability, hardness, and wear resistance required for bearing steel, while avoiding excessive carbon content that could lead to a decrease in toughness, thus meeting the impact performance requirements under heavy load conditions.

[0008] A Si content of 0.20–0.40% can strengthen ferrite, improve strength and elastic limit, and at the same time avoid the deterioration of plasticity and toughness caused by high Si content.

[0009] Mn content of 0.80-0.90% plays a solid solution strengthening role, improving strength and hardenability, while weakening the harmful effects of S and avoiding hot brittleness.

[0010] P≤0.015%: Strictly control the P content to prevent its segregation during solidification, avoid ferrite grain distortion and cold brittleness, and ensure weldability and cold bending performance.

[0011] S≤0.010%: Inhibits the formation of sulfur compounds, avoids hot brittleness and damage to the continuity of the steel matrix, and improves ductility and toughness.

[0012] Synergistic effect of Ni+V: Ni (0.10~0.40%) enhances strength and toughness, improves hardenability and corrosion resistance; V (0.01~0.10%) refines grains, improves strength, toughness and wear resistance, and the two work synergistically to optimize the fatigue resistance of the material.

[0013] Ti≤0.003%: Strictly limit the Ti content to avoid it forming sharp-angled titanium nitride inclusions with N. These inclusions have extremely high hardness and will severely shorten the service life of bearings.

[0014] A Cr content of 1.00–1.20% ensures hardenability, wear resistance, and corrosion resistance, while avoiding excessive Cr content that could form large, insoluble carbides, leading to a decrease in toughness.

[0015] Mo: A content of 0.20-0.30% refines the grains, reduces the tendency to overheat, and improves strength, hardness, and thermal stability.

[0016] Al≤0.050%: As a strong deoxidizer, it generates fine oxides, prevents grain growth and improves hardenability, while avoiding the formation of large-particle brittle Al2O3 inclusions due to excessive Al.

[0017] Harmful trace element control: Low-melting-point elements such as As, Sn, Sb, Bi, and Pb can easily cause soft spots and uneven hardness on the surface of parts. Therefore, their content is strictly limited to ensure the uniformity of material properties.

[0018] Another objective of this application is to provide a method for manufacturing continuously cast round billets for offshore wind turbine main shaft bearings. The method uses continuously cast round billets instead of ingot casting to smelt the billet. The manufacturing process is as follows: KR molten iron pretreatment → BOF converter primary refining → LF ladle refining → RH vacuum circulation degassing → CCM continuous casting (round billet) → finishing → warehousing → forging → ring rolling → heat treatment → flaw detection → finished product. The manufacturing method specifically includes the following steps: 1) KR molten iron pretreatment: Mechanical stirring desulfurization is adopted to remove impurities such as S, Si, and Ti from the molten iron, laying the foundation for purity in subsequent smelting, while reducing the amount of converter slag and improving metal yield.

[0019] 2) BOF converter primary refining: top and bottom blowing process, control the tapping temperature at 1600℃~1700℃, use slag blocking to prevent slag from falling, add Al pre-deoxidation during tapping, and complete the initial alloying adjustment at the same time to ensure that the final C and P content meets the standards.

[0020] 3) LF ladle refining: Submerged arc refining operation, adding slag material to form slag, using Al+SiC composite deoxidation, argon blowing and stirring to make the composition and temperature uniform, and promoting the aggregation and flotation of inclusions.

[0021] 4) RH vacuum circulation degassing: Argon gas is stirred throughout the process, and degassing is carried out for 15 to 35 minutes under a high vacuum of ≤133Pa. A certain soft blowing time of argon is then ensured to fully remove gases such as H, O, and N from the molten steel, promote the flotation of non-metallic inclusions, and improve the purity of the molten steel.

[0022] 5) CCM continuous casting: Casting specifications: Ф280mm~Ф1200mm round billet; Special protective slag is used to fully adsorb inclusions; The casting process is fully argon-sealed to prevent secondary oxidation of the molten steel. Multi-stage electromagnetic stirring (initial stirring + flow stirring + final stirring): By breaking dendrites, accelerating heat and mass transfer, expanding and refining equiaxed crystal zones, eliminating central shrinkage cavities, and reducing central porosity and segregation; Adjust the cooling water volume according to the billet specifications to prevent cracks from forming.

[0023] 6) Forging: The billet is heated to 1250℃ and then undergoes blanking → heating → upsetting → center punching processes to improve the density of the microstructure.

[0024] 7) Ring rolling: After forging, the ring is heated in a furnace to 1240℃, rolled into a ring, and then air-cooled to room temperature.

[0025] 8) Heat treatment: Avoid quenching cracks, and subsequent tempering treatment eliminates internal stress and optimizes mechanical properties.

[0026] Compared with the prior art, the present invention has the following beneficial effects: 1. Significantly improved purity: Through full-process impurity control and inclusion removal technology, the O content of molten steel is ≤0.0015%, and the level of non-metallic inclusions is better than that of molded products, avoiding the risk of fatigue failure.

[0027] 2. Excellent microstructure and properties: The low-magnification microstructure is dense and uniform, and the central porosity, shrinkage cavities and crack levels all meet the stringent requirements. The Ni+V synergistic effect greatly improves the toughness of the material, with an impact energy Akv≥60J and a fatigue life that is more than 30% higher than that of molded products.

[0028] 3. Improved production efficiency: Continuous casting process enables automated multi-furnace continuous production, which increases production efficiency by more than 50% compared with ingot casting, and reduces production costs by 20-30%.

[0029] 4. Comprehensive specifications: It can stably produce large-sized round billets from Ф280mm to Ф1200mm, which can meet the needs of large-scale deep-sea wind power equipment.

[0030] 5. Enhanced reliability: Ultrasonic testing eliminates dense defects, with individual defects ≤Ф2mm, resulting in a product qualification rate ≥98%, significantly reducing wind turbine maintenance costs. Detailed Implementation

[0031] The technical solution of the present invention will be described in more detail below with reference to preferred embodiments. However, these embodiments are merely descriptions of preferred implementations of the present invention and should not be construed as limiting the scope of the present invention.

[0032] The chemical composition (wt%) of the present invention and (for comparison) currently used mold castings in the market is shown in Table 3.

[0033] Table 3

[0034] Continued from Table 3

[0035] Low-magnification data of the steel in each embodiment are shown in Table 4. Table 4

[0036] Table 5 shows a comparison of non-metallic inclusions after forging and rolling in each embodiment. Table 5

[0037] The manufacturing process of the continuous casting round billet for the main shaft bearing of offshore wind power in each embodiment is as follows: KR molten iron pretreatment, BOF converter, LF ladle refining furnace, RH vacuum circulation degassing, CCM continuous casting (round billet), finishing, and warehousing.

[0038] In the specific smelting process, high-quality molten iron, scrap steel, raw and auxiliary materials, deoxidizers, and refractory materials are selected. During the converter production process, the tapping temperature and alloying are carefully controlled to prevent the formation of oxide slag. The molten steel is then transferred to the LF refining furnace, a special refining vessel that employs submerged arc refining to heat, deoxidize, desulfurize, and alloy the molten steel. Argon blowing is used for stirring to ensure uniform composition and temperature of the steel stream and to accelerate the metallurgical reaction. A sufficient LF refining time is ensured so that inclusions in the molten steel are removed primarily by agglomeration and floating to the slag. Through these operations, molten steel with the required composition and temperature is obtained and then transferred to the RH furnace for vacuum treatment, ultimately yielding molten steel with improved purity, which is then poured into the CCM continuous casting furnace. The produced continuous casting round billets are cold-loaded into a heating furnace for heating, followed by forging, ring rolling, heat treatment, flaw detection, and warehousing.

[0039] The forging, ring rolling, and heat treatment processes are as follows: Forging: The billet is heated to 1250℃, held at that temperature, and then forged: blanking - heating - upsetting - center punching; Ring rolling: After forging, the ring is heated to 1240℃ in a furnace, held at that temperature, and then rolled: heating-ring rolling; Heat treatment: Quenching + Tempering - Cooling to room temperature.

[0040] As shown in Tables 3, 4, and 5, the continuously cast round billets for offshore wind turbine main shaft bearings produced in the above embodiments of the present invention exhibit significantly better control levels of harmful elements such as P and S compared to ingot steel produced by die casting. The purity of the continuously cast round billets is significantly superior to that produced by die casting. Low-magnification inspection results show that the low-magnification quality of the present invention is not inferior to that of the comparative steel, reflecting that the uniformity and density of the low-magnification quality of the present invention are comparable to those of ingots produced by die casting. Regarding non-metallic inclusions, the non-metallic inclusions of the present invention are significantly superior to those of ingots produced by die casting, indicating high product purity and uniform microstructure. In summary, the continuously cast round billets for offshore wind turbine main shaft bearings produced by the present invention, using KR molten iron pretreatment, BOF converter, LF ladle refining furnace, RH vacuum circulation degassing, and CCM continuous casting (round billet) processes, can replace the original die casting process, significantly improving production efficiency, reducing production costs, and significantly enhancing product competitiveness.

[0041] In summary, the present invention relates to a continuously cast round billet for offshore wind turbine main shaft bearings. By improving the purity and impact toughness of the steel, and increasing the load-bearing capacity of the material, the invention adopts a high-efficiency, high-capacity, and low-cost process route of vacuum degassing and continuous casting. The key processes are optimized and controlled, thereby enabling the continuously cast round billet to obtain higher purity, uniform and dense structure, and high product toughness, and to replace the original ingot casting process.

[0042] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A continuously cast round billet for offshore wind turbine main shaft bearings, characterized in that, The chemical composition by mass fraction is as follows: C: 0.41–0.46%, Si: 0.20–0.40%, Mn: 0.80–0.90%, Cr: 1.00–1.20%, P≤0.015%, S≤0.010%, Ni: 0.10–0.40%, Cu≤0.20%, Mo: 0.20–0.30%, Al≤0.050%, V: 0.01–0.10%, Ca≤0.0010%, Ti≤0.003%, O≤0.0015%, N≤0.0080%, As≤0.015%, Sn≤0.010%, Bi≤0.010%, Sb≤0.010%, Pb≤0.008%, with the balance being Fe and unavoidable impurities.

2. The continuously cast round billet for offshore wind turbine main shaft bearings according to claim 1, characterized in that, The low-magnification microstructure is rated according to YB / T 153, and meets the following requirements: central porosity ≤ 1.5, shrinkage cavities ≤ 1.0, and central cracks ≤ 1.

5.

3. The continuously cast round billet for offshore wind turbine main shaft bearings according to claim 1, characterized in that, Non-metallic inclusions shall be tested according to GB / T10561 Method A and shall meet the following requirements: A fine ≤ 1.0 grade, A coarse ≤ 1.0 grade, B fine ≤ 1.5 grade, B coarse ≤ 1.0 grade, C fine ≤ 0.5 grade, C coarse ≤ 0.5 grade, D fine ≤ 1.0 grade, D coarse ≤ 1.0 grade, DS ≤ 1.5 grade.

4. The continuously cast round billet for offshore wind turbine main shaft bearings according to claim 1, characterized in that, Ultrasonic testing meets the following requirements: individual defects ≤ Ф2mm, no dense defects.

5. A continuously cast round billet for offshore wind turbine main shaft bearings according to claim 1, characterized in that, The specifications are Ф280mm~Ф1200mm.

6. A method for manufacturing a continuously cast round billet for offshore wind turbine main shaft bearings as described in any one of claims 1 to 5, characterized in that, Includes the following steps: (1) KR molten iron pretreatment: removing S, Si and Ti impurities from molten iron; (2) BOF converter primary refining: top and bottom blowing process, tapping temperature controlled at 1600℃~1700℃, slag blocking during tapping, Al pre-deoxidation during tapping and preliminary alloying adjustment completed; (3) LF ladle refining: submerged arc refining, using Al+SiC composite deoxidation, adding slag material to form slag, blowing argon to stir, and controlling the free oxygen in the molten steel; (4) RH vacuum circulation degassing: Argon gas stirring throughout the process, degassing under vacuum conditions of ≤133Pa for 15-35 minutes; (5) CCM continuous casting: special protective slag, full argon seal protection casting and multi-stage electromagnetic stirring are used to cast continuously cast round billets with diameters of Ф280mm~Ф1200mm; (6) Finishing and warehousing: After surface cleaning and straightening, the continuously cast round billets are put into storage; (7) Forging: The billet is heated to 1250℃ and then undergoes blanking → heating → upsetting → center punching process; (8) Ring rolling: After forging, heat to 1240℃, roll into a ring, and then air cool to room temperature; (9) Heat treatment: Quenching + Tempering - Cooling to room temperature; (10) Flaw detection: Ultrasonic flaw detection is used to remove unqualified products and put qualified products into storage.

7. The manufacturing method according to claim 6, characterized in that, In step (1), self-produced blast furnace iron is used to replace purchased pig iron, and the quality of scrap steel, alloys and auxiliary materials is strictly controlled to reduce the introduction of harmful elements.

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