Hollow spindle of wind turbine generator and energy-saving heat treatment method thereof

Abstract

The invention provides a heat treatment method for a hollow spindle of a super-power wind turbine generator. The wind turbine generator comprises the following components in percentage by weight: 0.38-0.52% of C, 0.22-0.72% of Mn, 0.54-0.88% of Cr, 0.32-0.52% of V, 0.42-0.65% of Ni and the balance of Fe and inevitable impurities. The heat treatment process comprises the following steps: firstly, carrying out sectional heating and heat preservation on the forging forming main shaft; covering the surface of the main shaft with flaky nickel hydroxide, and melting to form a NiOx layer; the main shaft is vertically placed, PAG medium liquid is injected from an inner hole for quenching, and the flow gradient of a water pump is controlled to rise; and finally, carrying out segmented tempering. The method provided by the invention can release stress at a fixed point at the quenching stress concentration position of the main shaft structure, improves the strength, toughness and corrosion resistance of the main shaft, can adapt to a complex environment, and prolongs the service life of the wind power main shaft.

Description

Technical Field

[0001] The present invention relates to the technical field of wind turbine manufacturing, specifically to the hollow main shaft of an extra-large power wind turbine and its manufacturing technology, and more specifically to the heat treatment method of the hollow main shaft. Background Art

[0002] A wind turbine includes a hollow main shaft. Its manufacturing and assembly preferably adopt an integrated structure, which can effectively reduce the connection points, thereby improving the strength and rigidity of the entire structure. This design method can better transfer and disperse the load, reduce the stress concentration phenomenon, thereby extending the service life of the equipment. And the integrated design helps to optimize the internal structure and streamline design, reduce air resistance and wind power loss, thereby improving the power generation efficiency. The integrated structural design can also enable the wind turbine to better adapt to the environment in offshore or mountainous areas, improving the durability and reliability of the equipment.

[0003] The invention patent application with the publication number CN116179805A discloses a heat treatment method for a lightweight and high-performance hollow main shaft of an extra-large power wind turbine. By setting a two-stage forging process, preparing an austenite matrix and then quenching with PAG medium, and cooperating with two-stage tempering to prepare sorbite, the problem of quenching cracking of the wind power main shaft is solved. At the same time, PAG medium is used for internal cooling, improving the quenching effect of the hollow main shaft and reducing the problems of inner hole edge cracks and crack angles. However, the effect of effectively treating quenching stress of this technical solution depends on the flow rate control of PAG, which has a high pertinence for through holes and cannot be used to release the quenching stress at specific points. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a hollow main shaft of an extra-large power wind turbine and its heat treatment method, which can release the quenching stress at fixed points for different quenching stress concentration points of the wind power main shaft structure.

[0005] To achieve the above purpose, the technical solution provided by the present invention is as follows: A hollow main shaft of an extra-large power wind turbine, by weight percentage, includes: C 0.38 - 0.52%, Mn 0.22 - 0.72%, Cr 0.54 - 0.88%, V 0.32 - 0.52%, Ni 0.42 - 0.65%, NiO x 1.25 - 3.22%; The NiO x is an oxidized nickel layer that at least partially covers the outer surface of the wind power main shaft, where the value range of X is 0.95 - 1.05, and the balance is Fe and other inevitable impurities.

[0006] Further, the flaky nickel hydroxide is β-Ni(OH)2.

[0007] Further, the NiO x covers the quenching stress concentration areas of the wind power main shaft, and the quenching stress concentration areas include parts such as the edge of the through hole of the wind power main shaft, the shaft shoulder, the keyway, the thread, the transition fillet, etc.

[0008] Further, the nickel oxide layer completely covers the wind power main shaft.

[0009] Further, the average thickness of the nickel oxide layer is 50 - 150 μm.

[0010] A heat treatment method for a hollow main shaft of an extra-large power wind turbine, which includes: S1: Gradually raise the forged wind power main shaft to 640 - 660 °C at a heating rate gradient of ≤ 70 °C / h, keep it warm for 3 - 5 h, then continue to heat it to 840 - 860 °C, and then keep it warm again for 6 - 8 h; S2: Horizontally rotate the wind power main shaft, evenly cover the surface of the wind power main shaft with flaky nickel hydroxide, the flaky nickel hydroxide melts on the wind power main shaft and releases water molecules, and solidifies to form a NiO x layer attached to the surface of the wind power main shaft, and the rotation speed of the wind power main shaft is adapted to the solidification speed of the flaky nickel hydroxide; S3: Lift the wind power main shaft to the vertical state by hoisting, and then inject PAG medium liquid into the middle of the through hole of the wind power main shaft through a water pump, and the PAG medium liquid quenches the wind power main shaft in a continuously flowing state; S4: Control the flow rate of the water pump to rise in a gradient, and the rising speed of the gradient is adapted to the cooling state of the wind power main shaft; S5: When the surface temperature of the wind power main shaft drops to 250 - 300 °C, stop injecting the PAG medium liquid and temper the wind power main shaft.

[0011] Further, in step S2, the surface roughness Ra of the NiO x layer formed by the flaky nickel hydroxide is ≤ 0.2 mm.

[0012] Further, in step S2, the corona treatment time for the solidified NiO x layer is 5 - 60 s with a voltage of 5 - 15 kV.

[0013] Further, in step S3, the distance between the output end of the water pump and the top surface of the through hole of the wind power main shaft is 10 - 15 cm.

[0014] Further, in step S5, the tempering is carried out in a segmented manner, which includes: The first tempering: Raise the wind power main shaft to 435 - 455 °C and keep it warm for 3 - 5 h; Second tempering: Heat the wind power main shaft to 635 - 655 °C and keep it warm for 18 - 30 h; Cooling: Air-cool the wind power main shaft to room temperature.

[0015] The advantages and beneficial effects of the present invention are as follows: 1. By covering nickel hydroxide flakes at fixed points, the quenching stress concentration points of different structures of the wind power main shaft, such as the edges of through holes, shoulders, keyways, threads, transition fillets, etc., can be targeted for quenching stress release. This solves the problem in the traditional technology that it is difficult to effectively handle the quenching stress at specific points, and avoids defects such as cracking and deformation caused by excessive stress in these stress concentration areas, improving the structural and performance reliability of the wind power main shaft.

[0016] 2. By precisely controlling the quenching stress, the wind power main shaft can better maintain the balance between strength and rigidity in the overall structure. The stresses in different parts are reasonably released and controlled, which helps to distribute the load more evenly throughout the structure, reduce the weakening effect on the structural strength caused by excessive local stress, and thus extend the service life of the equipment. Description of the Drawings

[0017] Figure 1 is a flowchart of the heat treatment method for the wind power main shaft provided by the present invention. Detailed Embodiments

[0018] The present invention provides a hollow main shaft for an extra-large power wind turbine, and its components include C (carbon) 0.38 - 0.52%, Mn (manganese) 0.22 - 0.72%, Cr (chromium) 0.54 - 0.88%, V (vanadium) 0.32 - 0.52%, Ni (nickel) 0.42 - 0.65%, NiO x (nickel oxide) 1.25 - 3.22%, and the balance is Fe (iron) and other inevitable impurities. The ideal ratio of nickel to oxygen in NiO is 1:1, but in the actual preparation process, this ratio may deviate due to various reasons. In the present invention, the value range of X should be between 0.95 and 1.05 to ensure the basic chemical properties and structural stability of the material. For this main shaft forging, the main functions of various elements are as follows.

[0019] Iron is the main element of the hollow spindle forging, which gives the spindle a high strength and rigidity, enabling it to maintain a stable structure in a complex working environment, not prone to deformation or fracture, and its good mechanical properties also help maintain the shape of the spindle. As a basic element, iron can also respond well to temperature changes and structural transformations during heat treatment. During heat treatment, the microstructure of Fe will change, such as the transformation of austenite and martensite. In addition, Fe is also related to alloying elements such as C, Mn, Cr, V, and Ni. Specifically, these alloying elements partially form solid solutions or compounds with Fe as the matrix to enhance the performance of the spindle, as follows.

[0020] Carbon is a key element that determines the strength and hardness of the main shaft. Within the appropriate content range, carbon can improve the strength and hardness of forgings by solid solution strengthening and forming carbides, so that they have sufficient load-bearing capacity to cope with the huge torque and stress during the operation of wind turbines. However, too high a content will lead to a decrease in material toughness and increase the risk of brittle fracture, so it is more appropriate to control it within 0.38-0.52%.

[0021] Manganese is used to improve the hardenability of steel, making it easier for forgings to obtain uniform martensitic structure during heat treatment, thereby improving the strength and hardness of the material. At the same time, manganese can also eliminate the adverse effects of sulfur in impurities to a certain extent, reduce the hot brittleness of the material, improve the hot processing performance of steel, and help the wind turbine main shaft obtain good quality during hot processing such as forging or hot forming.

[0022] The role of chromium is to improve the material's oxidation resistance and corrosion resistance. In the operating environment of wind turbines, the main shaft may be corroded by various corrosive media. An appropriate amount of chromium can form a dense oxide film on the surface to improve the material's strength and wear resistance. This protective effect is conducive to extending the service life of the main shaft.

[0023] Vanadium can form fine dispersed carbides in steel, which can effectively hinder dislocation movement, thereby improving the strength and toughness of the material. At the same time, vanadium can also refine the grains, further improving the comprehensive mechanical properties of the material, so that the wind turbine main shaft has better performance when bearing complex loads.

[0024] Nickel is an austenite-forming element that can expand the austenite phase region, allowing the material to maintain more austenite structure at room temperature, thus having good toughness and plasticity. Nickel can also improve the hardenability and corrosion resistance of the material, and work synergistically with elements such as chromium to further enhance the comprehensive performance of the wind turbine main shaft.

[0025] NiO xThe (nickel oxide layer) is obtained by covering the wind power main shaft with flaky sodium hydroxide during the heat treatment process. In this process, the flaky sodium hydroxide melts on the surface of the high-temperature wind power main shaft, nickel hydroxide loses water at high temperature, and water molecules escape in the form of steam, and nickel oxide solidifies to form NiO attached to the surface of the wind power main shaft. x layer. This conversion process can achieve precise control of the NiO x layer, ensuring its uniformity and quality, so as to better play the role of protection and performance improvement. As a preferred technical solution, the flaky nickel hydroxide adopts β-Ni(OH)2 with higher stability.

[0026] The nickel oxide layer melted on the surface of the high-temperature wind power main shaft has relatively good adhesion and can closely cover the surface of the main shaft. During heat treatment or use, alloy elements in the wind power main shaft will diffuse, segregating towards the grain boundaries and the surface of the wind power main shaft. The segregation of alloy elements located on the surface of the wind power main shaft will lead to an increase in the concentration of alloy elements at the surface, forming a special microstructural region. The segregation of alloy elements and the reorganization of the microstructure may change the chemical state and physical properties of the surface of the wind power main shaft, thereby affecting the bonding force between the nickel oxide layer and the substrate. This change is beneficial to enhancing the adhesion between the nickel oxide layer and the substrate, making it adhere more firmly to the surface of the main shaft.

[0027] The present invention also provides a heat treatment method for the above-mentioned wind power main shaft, and the principle is as follows.

[0028] In step S1, the forged wind power main shaft is heated to 640 - 660 °C at a heating rate gradient of ≤70 °C / h and held for 3 - 5 h. This process is mainly to eliminate the residual stress generated during forging, homogenize the structure, and prepare for subsequent heat treatment. Then it is continuously heated to 840 - 860 °C and held again for 6 - 8 h. This temperature range is close to the phase transformation point of the material, which can cause the microstructure of the material to change and prepare the structure for quenching. The slow heating rate can prevent excessive thermal stress generated inside the material due to too rapid temperature change, and avoid problems such as deformation and cracking.

[0029] In step S2, flaky nickel hydroxide is covered on the surface of the wind power main shaft to form a NiO x layer. The specific operation process is to place the wind power main shaft horizontally, evenly cover flaky nickel hydroxide on the side of the wind power main shaft away from the ground and wait for it to melt. During this process, controlling the rotation speed of the wind power main shaft to adapt to the solidification speed of the flaky nickel hydroxide is to ensure the NiO xThe layer can evenly cover the surface of the main shaft, avoiding the situation of local over-thickness or under-thickness. The reason for using flaky nickel hydroxide is its unique flaky structure, presenting a hexagonal crystal system. Its crystal structure enables it to have a relatively large size and specific surface area in a specific direction. Conventional nickel hydroxide is in the form of spherical particles with a relatively small specific surface area. When spherical particles are stacked, they may form a relatively compact structure, which is not conducive to the rapid diffusion of the nickel oxide layer.

[0030] As a preferred embodiment, the NiO formed by flaky nickel hydroxide x layer has a surface roughness Ra ≤ 0.2 mm: The lower surface roughness can make the NiO x layer more dense and flat, reducing the surface defects and stress concentration points of the nickel oxide layer itself, improving its protective effect and being conducive to achieving better technical effects in cooperation with the subsequent PAG medium liquid.

[0031] As a preferred technical solution, in order to more easily perform a corona treatment on the NiOx layer cured with a voltage of 5 - 15 kV for 5 - 60 s, the surface quality and performance of the NiO x layer can be further improved. The corona treatment can generate a certain polarization effect on the surface of the NiO x layer, enhancing its bonding force with the substrate, and at the same time, it can also improve the surface finish and corrosion resistance.

[0032] In steps S3 and S4, the wind power main shaft is hoisted to a vertical state, and PAG medium liquid is injected into the middle of the through hole of the wind power main shaft for quenching. The PAG medium liquid refers to polyalkylene glycol, which has good cooling characteristics and quenching performance. It can ensure the quenching effect while reducing the tendency of material deformation and cracking. Controlling the distance between the output end of the water pump and the top surface of the through hole of the wind power main shaft to be 10 - 15 cm is to ensure that the PAG medium liquid can evenly fill the entire through hole and achieve effective cooling of the inside of the wind power main shaft. By controlling the water pump flow rate to increase gradually, when the water pump flow rate is in the later stage of the gradient increase, the flow rate should be sufficient to make the PAG medium liquid overflow from the through hole and then flow from the top surface of the main shaft to the outer surface of the main shaft. By making the rising speed of the water pump flow rate gradient adapt to the cooling state of the wind power main shaft, the wind power main shaft can be evenly cooled during the quenching process. If the cooling speed is too fast or uneven, it may cause uneven thermal stress inside the material, resulting in problems such as deformation and cracking. A reasonable cooling speed and a uniform cooling process can ensure good control of the microstructure and properties of the material.

[0033] During the quenching process of the PAG medium liquid, the nickel oxide layer can act as a barrier layer to slow down the heat dissipation rate, thereby helping to control the cooling rate of the wind power spindle. This significantly avoids the generation of quenching cracks and improves the quenching quality. Specifically, the thermal conductivity of the nickel oxide layer is different from that of the base metal and the PAG medium liquid. Macroscopically, the nickel oxide layer structure can, to a certain extent, slow down the heat transfer rate on the surface of the wind power spindle, reducing the temperature difference between the spindle surface and the interior, that is, reducing the temperature gradient. A smaller temperature gradient means that the generated thermal stress will also be correspondingly reduced, thus reducing the generation of cracks caused by excessive thermal stress; the nickel oxide layer, as a physical barrier, isolates the spindle surface from the PAG medium liquid, reducing the possible microscopic structure erosion of the medium liquid on the spindle, protecting the quality of the spindle surface, and reducing the occurrence of cracks caused by surface damage. Further, there are some microscopic defects or stress concentration sources on the surface of the wind power spindle forging. During the quenching process, these stress concentration sources are likely to become the starting points of cracks. The nickel oxide layer can cover these defects and stress concentration sources, playing a certain role in repair and bridging, preventing them from further expanding into macroscopic cracks under the action of quenching stress. Microscopically, the nickel oxide layer makes the quenching process relatively mild, reducing the lattice distortion and volume change during the phase transformation process, making the structure of newly formed phases such as martensite more uniform and fine, improving the toughness and strength of the material, thus avoiding the martensite transformation being too intense due to too fast a cooling rate, generating large tissue stress, and further reducing the cracking of the forging caused by the stress during the quenching process.

[0034] In step S5, when the surface temperature of the wind power spindle drops to 250 - 300 °C, stop injecting the PAG medium liquid and perform tempering treatment. The purpose of tempering is to eliminate the residual stress generated during the quenching process, stabilize the organizational structure of the material, and improve the toughness and comprehensive mechanical properties of the material.

[0035] First tempering: Heat the wind power spindle to 435 - 455 °C and hold for 3 - 5 h. In this temperature range, the atoms inside the material begin to rearrange and diffuse, part of the residual stress is released, and at the same time, some unstable structures begin to transform into stable states, improving the toughness of the material.

[0036] Second tempering: Heat the wind power spindle to 635 - 655 °C and hold for 18 - 30 h. At this higher temperature, the atoms inside the material diffuse more fully, the residual stress is further eliminated, the organizational structure is more stable, and the comprehensive properties such as the toughness, strength, and corrosion resistance of the material are further improved.

[0037] Cooling method: Finally, air-cool the wind power spindle to room temperature. Air-cooling can allow the material to cool slowly in the natural environment, avoiding the generation of new residual stress and deformation problems due to rapid cooling.

[0038] In summary, through the composition design of the hollow main shaft of the wind turbine and precise control of the heat treatment process, the present invention can achieve an optimized balance of various properties such as material strength, toughness, wear resistance, and corrosion resistance. The reasonable chemical composition ensures that the material has basic mechanical properties and protective properties, while the carefully designed heat treatment method further improves the microstructure and properties of the material, enabling it to meet the long-term stable operation requirements of ultra-large power wind turbines under complex working conditions.

[0039] The following will further describe the specific implementation manners of the present invention in conjunction with the accompanying drawings and embodiments. Each embodiment uses β-Ni(OH)2. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and cannot be used to limit the protection scope of the present invention.

[0040] Example 1 A hollow main shaft for an ultra-large power wind turbine, by weight percentage, its composition is C 0.52%, Mn 0.55%, Cr 0.78%, V 0.40%, Ni 0.65%, NiO 1.02 1.25%, and the balance is Fe and other inevitable impurities.

[0041] NiO 1.02 Covers the edges of through holes, shoulders, keyways, threads, and transition fillets on the outer surface of the wind power main shaft, and its average thickness is 50μm.

[0042] The heat treatment method of this wind power main shaft is as follows: S1: Gradually heat the forged wind power main shaft to 660°C at a heating rate of 50°C / h, keep it warm for 5h, then continue to heat to 840°C, and then keep it warm for 6h again; S2: Horizontally rotate the wind power main shaft, and evenly cover flaky nickel hydroxide on the edges of through holes, shoulders, keyways, threads, and transition fillets of the wind power main shaft, so that the flaky nickel hydroxide melts on the high-temperature wind power main shaft and releases water molecules, and solidifies to form a NiO layer attached to the surface of the wind power main shaft; the surface roughness Ra of the NiO layer formed by the flaky nickel hydroxide ≤ 0.2mm; among them, the flaky nickel hydroxide is α-Ni(OH)2; 1.02 layer; the NiO 1.02 layer formed by the flaky nickel hydroxide; S3: Lift the wind power main shaft to a vertical state by hoisting, and then inject PAG medium liquid into the middle of the through hole of the wind power main shaft through a water pump. The PAG medium liquid quenches the wind power main shaft in a continuously flowing state; the distance between the output end of the water pump and the top surface of the through hole of the wind power main shaft is 10cm.

[0043] S4: Control the water pump flow rate to increase dynamically at a gradient of 0.5m³ / h, and the dynamic change speed is linearly positively correlated with the cooling rate of the wind power main shaft; S5: When the surface temperature of the wind power main shaft drops to 300 °C, stop injecting the PAG dielectric fluid and temper the wind power main shaft: The first tempering: Heat the wind power main shaft to 435 °C and hold for 5 h; The second tempering: Heat the wind power main shaft to 655 °C and hold for 30 h; Cooling: Air-cool the wind power main shaft to room temperature.

[0044] Example 2 A hollow main shaft of an extra-large power wind turbine, by weight percentage, its composition is C 0.47%, Mn 0.32%, Cr 0.54%, V 0.32%, Ni 0.65%, NiO 1.05 2.25%; NiO 1.05 is a nickel oxide layer covering the outer surface of the wind power main shaft with an average thickness of 50 - 150 μm, and the balance is Fe and other inevitable impurities.

[0045] NiO 1.05 covers the edges of through holes, shoulders, keyways, threads, and transition fillets on the outer surface of the wind power main shaft, and its average thickness is 100 μm.

[0046] The heat treatment method of this wind power main shaft is: S1: Gradually heat the forged wind power main shaft to 640 °C at a heating rate of 20 °C / h, hold for 3 h, then continue heating to 850 °C, and then hold for 8 h again; S2: Rotate the wind power main shaft horizontally, and evenly cover flaky nickel hydroxide on the edges of through holes, shoulders, keyways, threads, and transition fillets of the wind power main shaft, so that the flaky nickel hydroxide melts on the high-temperature wind power main shaft and releases water molecules, and solidifies to form NiO 1.05 layer attached to the surface of the wind power main shaft, and then corona-treat the solidified NiO 1.05 layer with a voltage of 5 kV for 30 s, and the surface roughness Ra of the NiO 1.05 layer formed by flaky nickel hydroxide ≤ 0.15 mm; S3: Lift the wind power main shaft to a vertical state by hoisting, and then inject the PAG dielectric fluid into the middle of the through hole of the wind power main shaft through a water pump. The PAG dielectric fluid quenches the wind power main shaft in a continuously flowing state; the distance between the output end of the water pump and the top surface of the through hole of the wind power main shaft is 15 cm.

[0047] S4: Control the water pump to increase at a dynamic flow rate gradient of 0.3 m³ / h, and its dynamic change speed is linearly positively correlated with the cooling rate of the wind power main shaft; S5: When the surface temperature of the wind power main shaft drops to 250 °C, stop injecting the PAG dielectric fluid and temper the wind power main shaft.

[0048] The first tempering: Heat the wind power main shaft to 455 °C and hold for 4 h; The second tempering: Heat the wind power main shaft to 635 °C and hold for 24 h; Cooling: Air-cool the wind power main shaft to room temperature.

[0049] Example 3 A hollow main shaft of an extra-large power wind turbine, by weight percentage, its composition is C 0.38%, Mn 0.22%, Cr 0.88%, V 0.48%, Ni 0.55%, NiO 0.98 3.22%; NiO 0.98 is a nickel oxide layer with an average thickness of 150 μm covering the entire outer surface of the wind power main shaft, and the balance is Fe and other inevitable impurities.

[0050] The heat treatment method of this wind power main shaft is: S1: Gradually heat the forged wind power main shaft to 650 °C at a heating rate of 70 °C / h, hold for 5 h and then continue to heat to 840 °C, and then hold for 7 h again; S2: Horizontally rotate the wind power main shaft, evenly cover flaky nickel hydroxide on the surface of the wind power main shaft, the flaky nickel hydroxide melts on the wind power main shaft and releases water molecules, and solidifies to form a NiO 0.98 layer attached to the surface of the wind power main shaft, and then corona-treat the solidified NiO 0.98 layer for 60 s with an 8 kV voltage, and the surface roughness Ra of the NiO 0.98 layer formed by the flaky nickel hydroxide ≤ 0.15 mm; S3: Lift the wind power main shaft to a vertical state by hoisting, and then inject PAG medium liquid into the middle of the through hole of the wind power main shaft through a water pump. The PAG medium liquid quenches the wind power main shaft in a continuously flowing state; the distance between the output end of the water pump and the top surface of the through hole of the wind power main shaft is 15 cm; S4: Control the water pump to rise at a dynamic flow rate gradient of 0.4 m³ / h, and its dynamic change speed is linearly positively correlated with the cooling rate of the wind power main shaft; S5: When the surface temperature of the wind power main shaft drops to 270 °C, stop injecting the PAG medium liquid and temper the wind power main shaft.

[0051] The first tempering: Heat the wind power main shaft to 445 °C and hold for 5 h; The second tempering: Heat the wind power main shaft to 645 °C and hold for 30 h; Cooling: Air-cool the wind power main shaft to room temperature.

[0052] Example 4 A hollow main shaft for an extra-large power wind turbine, by weight percentage, is composed of C 0.46%, Mn 0.72%, Cr 0.88%, V 0.52%, Ni 0.48%, NiO 0.95 2.35%; NiO 0.95 is a nickel oxide layer with an average thickness of 100 μm covering the entire outer surface of the wind power main shaft, and the balance is Fe and other inevitable impurities.

[0053] The heat treatment method of this wind power main shaft is as follows: S1: Gradually raise the forged wind power main shaft to 660 °C at a heating rate of 65 °C / h, hold for 3 h and then continue to heat to 860 °C, and then hold again for 6 h; S2: Horizontally rotate the wind power main shaft, evenly cover flaky nickel hydroxide on the surface of the wind power main shaft, the flaky nickel hydroxide melts on the wind power main shaft and releases water molecules, and solidifies to form NiO attached to the surface of the wind power main shaft 0.95 layer, and then corona-treat the solidified NiO 0.98 layer for 5 s, and the surface roughness Ra of the NiO 0.98 layer formed by the flaky nickel hydroxide is ≤ 0.18 mm; S3: Lift the wind power main shaft to the vertical state by hoisting, and then inject PAG medium liquid into the middle of the through hole of the wind power main shaft through a water pump. The PAG medium liquid quenches the wind power main shaft in a continuously flowing state; the distance between the output end of the water pump and the top surface of the through hole of the wind power main shaft is 13 cm.

[0054] S4: Control the water pump to rise at a dynamic flow rate gradient of 0.4 m³ / h, and the dynamic change speed is linearly positively correlated with the cooling rate of the wind power main shaft; S5: When the surface temperature of the wind power main shaft drops to 280 °C, stop injecting the PAG medium liquid and temper the wind power main shaft.

[0055] The first tempering: Raise the wind power main shaft to 440 °C and hold for 3 h; The second tempering: Raise the wind power main shaft to 635 °C and hold for 30 h; Cooling: Air-cool the wind power main shaft to room temperature.

[0056] Example 5 A hollow main shaft for an extra-large power wind turbine, by weight percentage, is composed of C 0.46%, Mn 0.35%, Cr 0.66%, V 0.38%, Ni 0.42%, NiO 0.99 2.75%; NiO0.99 It is a nickel oxide layer with an average thickness of 122 μm covering the entire outer surface of the wind power spindle, and the balance is Fe and other inevitable impurities.

[0057] The heat treatment method of this wind power spindle is as follows: S1: Gradually increase the temperature of the forged wind power spindle to 650 °C at a heating rate gradient of 25 °C / h, keep it warm for 5 h, then continue to heat it to 850 °C, and then keep it warm for 8 h again; S2: Rotate the wind power spindle horizontally, evenly cover the surface of the wind power spindle with flaky nickel hydroxide, the flaky nickel hydroxide melts on the wind power spindle and releases water molecules, and solidifies to form NiO attached to the surface of the wind power spindle 0.99 layer, and then corona-treat the solidified NiO 0.99 layer for 50 s, and the surface roughness Ra of the NiO 0.99 layer formed by the flaky nickel hydroxide ≤ 0.12 mm; S3: Lift the wind power spindle to the vertical state by hoisting, and then inject PAG medium liquid into the middle of the through hole of the wind power spindle through a water pump. The PAG medium liquid quenches the wind power spindle in a continuously flowing state; the distance between the output end of the water pump and the top surface of the through hole of the wind power spindle is 15 cm.

[0058] S4: Control the water pump to rise at a dynamic flow rate gradient of 0.3 m³ / h, and its dynamic change speed is linearly positively correlated with the cooling rate of the wind power spindle; S5: When the surface temperature of the wind power spindle drops to 280 °C, stop injecting the PAG medium liquid and temper the wind power spindle.

[0059] The first tempering: Heat the wind power spindle to 455 °C and keep it warm for 3 h; The second tempering: Heat the wind power spindle to 635 °C and keep it warm for 24 h; Cooling: Air-cool the wind power spindle to room temperature.

[0060] Comparative Example 1 A hollow spindle of an extra-large power wind turbine, by weight percentage, its composition is C 0.45%, Mn 0.52%, Cr 0.72%, V 0.32 - 0.52%, Ni 0.42 - 0.65%, The balance is Fe and other inevitable impurities.

[0061] The heat treatment method of this wind power spindle is as follows: S1: Gradually increase the temperature of the forged wind power spindle to 650 °C at a heating rate gradient of ≤ 50 °C / h, keep it warm for 4 h, then continue to heat it to 850 °C, and then keep it warm for 8 h again; S2: Lift the wind power main shaft to the vertical state by hoisting, and then inject PAG medium liquid into the middle of the through-hole of the wind power main shaft through a water pump. The PAG medium liquid quenches the wind power main shaft in a continuously flowing state; the distance between the output end of the water pump and the top surface of the through-hole of the wind power main shaft is 15 cm.

[0062] S3: Control the water pump to rise at a dynamic flow rate gradient of 0.4 m³ / h, and the dynamic change speed is linearly positively correlated with the cooling rate of the wind power main shaft; S4: When the surface temperature of the wind power main shaft drops to 280 °C, stop injecting the PAG medium liquid and temper the wind power main shaft.

[0063] The first tempering: Heat the wind power main shaft to 445 °C and keep it warm for 4 h; The second tempering: Heat the wind power main shaft to 645 °C and keep it warm for 24 h; Cooling: Air-cool the wind power main shaft to room temperature.

[0064] Comparative Example 2 A hollow main shaft of an extra-large power wind turbine, by weight percentage, its composition is C 0.45%, Mn 0.52%, Cr 0.72%, V 0.32 - 0.52%, Ni 0.42 - 0.65%, NiO 0.98 2.13%; NiO 0.98 is a nickel oxide layer with an average thickness of 94 μm covering the entire outer surface of the wind power main shaft, and the balance is Fe and other inevitable impurities.

[0065] The heat treatment method of this wind power main shaft is: S1: Gradually heat the forged wind power main shaft to 650 °C at a heating rate gradient of ≤40 °C / h, keep it warm for 5 h and then continue to heat to 850 °C, and then keep it warm for 7 h again; S2: Rotate the wind power main shaft horizontally, evenly cover nickel hydroxide on the surface of the wind power main shaft. The nickel hydroxide melts on the wind power main shaft and releases water molecules, and solidifies to form a NiO layer attached to the surface of the wind power main shaft. Then, corona-treat the solidified NiO layer with a voltage of 15 kV for 30 s. The surface roughness Ra of the NiO layer formed by flaky nickel hydroxide is ≤0.20 mm; 0.98 layer, and then corona-treat the solidified NiO 0.98 layer for 30 s. The surface roughness Ra of the NiO 0.98 layer formed by flaky nickel hydroxide is ≤0.20 mm; S4: Lift the wind power main shaft to the vertical state by hoisting, and then inject PAG medium liquid into the middle of the through-hole of the wind power main shaft through a water pump. The PAG medium liquid quenches the wind power main shaft in a continuously flowing state; the distance between the output end of the water pump and the top surface of the through-hole of the wind power main shaft is 10 cm.

[0066] S4: Control the water pump to increase with a dynamic flow rate gradient of 0.3 m³ / h, and the speed of its dynamic change is linearly and positively correlated with the cooling rate of the wind power main shaft; S5: When the surface temperature of the wind power main shaft drops to 280 °C, stop injecting the PAG medium liquid and temper the wind power main shaft.

[0067] The first tempering: Heat the wind power main shaft to 440 °C and keep it warm for 5 h; The second tempering: Heat the wind power main shaft to 640 °C and keep it warm for 28 h; Cooling: Air-cool the wind power main shaft to room temperature.

[0068] For each of the above examples and comparative examples, specimens were obtained synchronously during casting. The specimens were subjected to tensile tests at room temperature according to GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature"; For each example, three specimens were taken to conduct impact tests according to GB / T 229-2020 "Metallic materials - Charpy pendulum impact test method", and the results are recorded in Table 1 and Table 2 respectively.

[0069] Table 1 Table 2 The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. An ultra-high power wind turbine hollow main shaft, characterized in that By weight percentage, it includes: C, 0.38 - 0.52%, Mn, 0.22 - 0.72%, Cr, 0.54 - 0.88%, V, 0.32 - 0.52%, Ni, 0.42 - 0.65%, NiO x , 1.25 - 3.22%; The NiO x is a nickel oxide layer that at least partially covers the outer surface of the wind power spindle, where the value range of X is 0.95 - 1.05, and the balance is Fe and other inevitable impurities.

2. The wind turbine hollow main shaft according to claim 1, characterized in that The nickel oxide layer is prepared from nickel hydroxide, and the nickel hydroxide is flaky nickel hydroxide β-Ni(OH)₂.

3. The wind turbine hollow main shaft according to claim 1 or 2, characterized in that The NiO x is covered on the quenching stress concentration area of the wind power main shaft.

4. The wind turbine hollow main shaft according to claim 1 or 2, characterized in that The nickel oxide layer completely covers the wind power main shaft.

5. The wind turbine hollow main shaft according to claim 1 or 2, characterized in that The average thickness of the nickel oxide layer is 50 - 150 μm.

6. A heat treatment method for a hollow main shaft of a wind turbine as described in claim 1, characterized in that, Including: S1: Gradually increase the temperature of the forged wind power main shaft to 640 - 660 °C at a heating rate gradient of ≤70 °C / h, keep it warm for 3 - 5 h, then continue to heat to 840 - 860 °C, and then keep it warm again for 6 - 8 h; S2: Horizontally rotate the wind power main shaft, evenly cover the surface of the wind power main shaft with flaky nickel hydroxide, the flaky nickel hydroxide melts on the wind power main shaft and releases water molecules, and solidifies to form a NiO layer attached to the surface of the wind power main shaft. The rotation speed of the wind power main shaft is adapted to the solidification speed of the flaky nickel hydroxide. x layer, and the rotation speed of the wind power main shaft is adapted to the solidification speed of the flaky nickel hydroxide; S3: Lift the wind power main shaft to a vertical state by hoisting, and then inject PAG medium liquid into the middle of the through hole of the wind power main shaft through a water pump. The PAG medium liquid quenches the wind power main shaft in a continuously flowing state; S4: Control the flow rate of the water pump to increase in a gradient manner, and the gradient increase speed is adapted to the cooling state of the wind power main shaft; S5: When the surface temperature of the wind power main shaft drops to 250 - 300 °C, stop injecting the PAG medium liquid and temper the wind power main shaft.

7. The wind turbine hollow main shaft according to claim 6, characterized in that In step S2, the NiO formed by the flaky nickel hydroxide x has a surface roughness Ra ≤ 0.2 mm for the layer.

8. The wind turbine hollow main shaft according to claim 6, characterized in that In step S2, a voltage of 5 - 15 kV is also applied for corona treatment of the cured NiO x layer for 5 - 60 s.

9. The wind turbine hollow main shaft according to any one of claims 6 - 8, characterized in that In step S3, the distance between the output end of the water pump and the top surface of the through hole of the wind power main shaft is 10 - 15 cm.

10. The wind turbine hollow main shaft according to any one of claims 6 - 8, characterized in that In step S5, the tempering is carried out in a segmented manner, which includes: The first tempering: Raise the temperature of the wind power main shaft to 435 - 455 °C and keep it warm for 3 - 5 h; The second tempering: Raise the temperature of the wind power main shaft to 635 - 655 °C and keep it warm for 18 - 30 h; Cooling: Air-cool the wind power main shaft to room temperature.

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