Short-process heat treatment process for megawatt wind power main shaft

Abstract

According to the megawatt wind power short-process main shaft heat treatment process provided by the invention, the manufacturing process is effectively shortened and the energy consumption is reduced by optimizing material components and forging steps. The main shaft comprises the following components in percentage by weight: 0.35 to 0.55 percent of C, 0.42 to 0.85 percent of Mn, 0.32 to 0.52 percent of V, 1.15 to 1.57 percent of Cr, 0.44 to 0.85 percent of Ti, 0.25 to 0.38 percent of Nb, 0.32 to 0.58 percent of Ni, less than or equal to 0.01 percent of S, less than or equal to 0.01 percent of P and the balance of Fe. A metal raw material with specific components is poured into a steel ingot, and after heat preservation, heating, upsetting and other procedures, the steel ingot is further treated in two parts. Wherein one part is upset into a rod-shaped structure, the other part is processed into a through hole, and then the rod-shaped structure is inserted into the through hole to form a combined body. And the combined body is heated again, upset and subjected to surface rolling finishing, the rolling initial temperature ranges from 800 DEG C to 850 DEG C, the rolling final temperature ranges from 500 DEG C to 550 DEG C, finally, slow heating and returning are conducted, cooling is conducted to the room temperature, and the finished steel ingot is obtained. By means of the segmented heating and combined forging mode, the forging process is optimized, working hours are shortened, and energy waste is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of manufacturing hollow main shafts of wind turbines, and particularly to a short-process heat treatment process for megawatt-level wind power main shafts. Background Art

[0002] With the development of wind power technology, wind turbines are developing towards the direction of large-scale and high-efficiency. Large wind turbines have advantages such as higher power generation efficiency and lower unit cost, and can meet the demand for large-scale energy supply. Therefore, the research and manufacturing of megawatt-level wind power main shafts that match them have become an inevitable trend.

[0003] The traditional manufacturing process of wind power main shafts has the following problems. Casting can enable workpieces to be formed quickly in one time, with high production efficiency and relatively high material utilization rate. However, the mechanical properties of forgings of the same material are lower than those of castings of the same material. Forging can ensure the continuity of the internal metal structure of forgings, making the forgings have good mechanical properties and a long service life. However, the forging process is long. In addition to the necessary forging process, post-forging normalizing-tempering treatment is also required to refine grains and homogenize the structure, so as to achieve the purpose of hydrogen diffusion and internal stress removal, resulting in a long and energy-consuming overall process.

[0004] The invention patent with publication number CN115608908A discloses a short-process manufacturing process for an extra-large power rectangular wind power hollow main shaft. The technical feature is to place the heated perforated forging inside the mold, insert a mandrel into the central holes of the perforated forging and the mold, extrude to obtain a flange and a shaft body connected integrally, perform rotary upsetting on the flange and draw out the shaft body, and finally perform surface rolling finishing on the forging. The starting temperature of rolling is 800 - 850°C, the ending temperature of rolling is 500 - 550°C, and then return to the furnace to make the internal and external structures of the forging tend to be uniform, forming a dispersed distribution of ultrafine precipitation phases. At the same time, the effect of improving the irreversible hydrogen trap density and other effects to prevent hydrogen embrittlement is achieved by using the large plastic deformation effect to refine the material grains to produce a large number of grain boundaries and phase interfaces; through low-temperature rolling finishing, with the starting temperature of rolling being 800 - 850°C and the ending temperature of rolling being 500 - 550°C, and without normalizing, a short-process manufacturing process is realized. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a short-process heat treatment process for megawatt-level wind power main shafts to improve the technical problems of the existing forging process being too long and consuming a large amount of energy.

[0006] To achieve the above purpose, the technical solution provided by the present invention is as follows: A megawatt-level wind power main shaft, by weight percentage, its composition includes: C: 0.45 - 0.55%, Mn: 0.42 - 0.85%, V: 0.32 - 0.52%, Cr: 1.15 - 1.57%, Ti: 0.44 - 0.85%, Nb: 0.25 - 0.38%, Ni: 0.32 - 0.58%, S ≤ 0.01%, P ≤ 0.01%, the balance being Fe and unavoidable impurities.

[0007] Further, the content of V is 0.42 - 0.46%, the content of Ti is 0.68 - 0.72%, and the content of Nb is 0.28 - 0.32%.

[0008] Further, the ratio of V, Ti, and Nb is 3:4:2.

[0009] A short - process forging process for an extra - large power horizontal wind power spindle is as follows: S1, Pour the metal raw materials into a metal ingot according to the formula. After the ingot is demolded and cooled to 680 - 720 °C, keep it warm. S2, Heat the insulated ingot at a heating rate of 100 - 160 °C / h to 1150 - 1280 °C, keep it warm for 6 - 10 h, and then take it out of the furnace. S3, Shape the ingot taken out of the furnace. After shaping, perform rotary upsetting. The upsetting forging ratio is (5 - 7):1, and the final forging temperature is 980 - 850 °C. S4, Divide the ingot into ingot A and ingot B. Upset ingot A into a rod - like structure, and punch a through - hole in the middle of ingot B. After cleaning the residues on the surfaces of ingot A and ingot B, insert the rod - like ingot A into the through - hole of ingot B to form an ingot AB combination. S5, Heat the ingot AB combination at a heating rate of 100 - 160 °C / h to 1150 - 1280 °C, keep it warm for 6 - 10 h, and then take it out of the furnace. S6, Place the heated and insulated ingot AB combination in multiple flips and perform upsetting to obtain a forging. The upsetting forging ratio is (6 - 8):1, and the final forging temperature is 1050 - 980 °C. S7, Perform surface rolling and finishing on the forging. The starting temperature of rolling is 800 - 850 °C, the ending temperature of rolling is 500 - 550 °C, then return it to the furnace at 310 - 360 °C and slowly heat it at 50 - 80 °C / h to 540 - 560 °C. After keeping it warm for 18 - 24 h, cool it with the furnace to 120 - 150 °C, and then take it out of the furnace and air - cool it to room temperature to obtain the finished ingot.

[0010] Further, in S4, ingot A adopts a rod - like structure with a polygonal cross - section, and the through - hole of ingot B is adapted to the shape of ingot A.

[0011] Further, in S4, splines are machined on the surfaces of ingot A and ingot B, and the two are tightly fitted through the splines.

[0012] Further, in S2 and / or S5, segmented heating is adopted. First, the ingot is heated to a lower temperature at a relatively fast rate, and then the heating rate is reduced.

[0013] Further, in S3 and / or S6, the forging speed is 0.02 - 0.05 m / s.

[0014] The present invention also relates to a wind power main shaft forged by adopting the above component ratios and processes, and the application of such a wind power main shaft in a wind turbine unit.

[0015] The advantages and beneficial effects of the present invention are as follows: 1. Through the optimization of the forging process with materials of specific components, the present invention not only eliminates the normalizing process, but also effectively utilizes the remaining heat of the heat-preserved ingot through the segmented heating of ingot A and ingot B and the combined forging method. By combining ingot A, the manufacturing process is shortened and the energy consumption is reduced.

[0016] 2. During the rotary upsetting process, the metal is compressed and deformed in three dimensions, and the grains are elongated and broken to form a fibrous-like structure. This fibrous-like structure is distributed along the deformation direction of the metal. When ingot A is upset into a rod-like structure and inserted into the through hole of ingot B to form an ingot AB combination, the fibrous-like structure also plays a key "stitching" role at the connection part of the two. Since the fibrous structure is distributed along the deformation direction, after ingot A is inserted into ingot B and upset, the ingot AB combination is intertwined with each other in the contact area through the fibrous-like structure. Through subsequent forging, the fibrous-like structure can be evenly dispersed throughout the combined structure. In the forging process, stress can be transmitted and dispersed to a larger volume range through the fibrous-like structure, reducing the cracking risk caused by local stress concentration, and thus improving the load-bearing capacity of the entire ingot AB combined structure.

[0017] 3. The final forging temperature of the metal material composition and ratio provided by the present invention is relatively low and its stability is high. During the forging process, it can be combined with a faster heating rate without causing the problem that the rejection rate increases when the heating rate is too high as in the prior art; finally, excellent properties of the finished ingot can be achieved through medium and low temperature rolling and finishing without going through the normalizing process; in the manufacturing process of the entire forging, the forging temperature is lower than that of the prior art (about 50 - 100 °C), and the process is shorter (saving 48 - 72 h). Description of the Drawings

[0018] Figure 1 is a flow chart of the forging method of the wind power main shaft provided by the present invention. Detailed Embodiments

[0019] The present invention provides a hollow main shaft for a giant (over 48 tons) wind turbine with an ultra-high power (above 50 kW), and the functions of each component are as follows.

[0020] Carbon (C: 0.45 - 0.55%) forms a solid solution during forging, which helps to enhance the strength and hardness of ferrite. At the same time, an appropriate carbon content can also promote the formation of pearlite during subsequent heat treatment. The carbon content in the present invention belongs to medium carbon steel (carbon content is 0.25% - 0.60%), but the reason for the relatively high carbon content is that C also forms carbide metals with other metal elements during forging, serving as alloy strengthening phases and lubricating and assisting the dispersion effect of the strengthening phases.

[0021] Manganese (Mn: 0.42 - 0.85%) mainly plays the role of deoxidizing (O), desulfurizing (S), and dephosphorizing (P) in steel, effectively reducing harmful impurities in the steel. It should be noted that the present invention has relatively high requirements for the contents of impurity elements sulfur (S ≤ 0.01%) and phosphorus (P ≤ 0.01%). The key lies in that, on the one hand, sulfur makes the steel have hot brittleness, that is, it is easy to crack during hot processing; phosphorus makes the steel have cold brittleness, reducing the toughness of the steel. On the other hand, S and P will also have an unnecessary impact on the carbon content. Specifically, their competitive effect on C is stronger than that of other metal elements, which easily leads to a reduction in the content of carbide strengthening phases and is not conducive to their dispersion in the alloy. Therefore, it is necessary to strictly control the initial contents of S and P. Within this composition range, manganese can also refine the pearlite structure to a certain extent in the initial stage of forging heating, which is beneficial for the forged product of the wind power main shaft to withstand complex alternating loads.

[0022] Chromium (Cr: 1.15 - 1.57%) can form various types of carbides (such as CrC, Cr3C2, Cr7C3, and Cr 23 C6), and these carbides are generated as strengthening phases during casting and are evenly distributed in the matrix, playing a role of dispersion strengthening. In addition, chromium helps to improve the oxidation resistance and corrosion resistance of the steel, extending the service life of the wind power main shaft.

[0023] Nickel (Ni: 0.32 - 0.58%) is mainly used in the alloy to expand the austenite phase region, enabling the steel to obtain more austenite structure even at low temperatures.

[0024] Titanium (Ti: 0.44 - 0.85%, more preferably 0.68 - 0.72%) is an active element and is prone to forming compounds such as titanium carbide (TiC) with C prior to other metal elements during the forging process provided by the present invention. TiC has high hardness and high melting point. During the cooling and solidification of forgings, it can serve as non-spontaneous nucleation, maintain the structure at high temperatures to promote heterogeneous substrates for non-uniform nucleation, and improve the fluidity of ingot casting. At the same time, during the subsequent high-temperature processing and service of wind power spindle forgings, these compounds can stably exist, prevent grain coarsening, and enhance the thermal stability of the material. Vanadium (V: 0.32 - 0.52%, more preferably 0.42 - 0.46%) is mainly used in the alloy to reduce the reheating temperature of forgings and shorten the forging process. The content of niobium (Nb: 0.25 - 0.38%, more preferably 0.28 - 0.32%) is lower than that of V, and the reduction in the reheating temperature of forgings caused by Nb is less than the influence brought by V. In addition, another important role of Nb is that during forging, as the temperature gradually rises, these three elements migrate and diffuse from the inside of the ingot to the surface of the forging. Due to the lower migration rates of the remaining elements, these three elements are more likely to form segregation on the surface of the ingot.

[0025] Nb, V, and Ti are adjacent in the periodic table of elements and have similar crystal structures and lattice parameters. This enables them to fuse well with each other in the solid-state alloy to form a relatively uniform solid solution or compound. During the forging process, as the temperature rises, the thermal motion of atoms intensifies, and atoms with similar crystal structures are more likely to migrate and diffuse with each other. The lattice distortion between them is small, and the interaction force between atoms will not be overly hindered due to the mismatch of atomic sizes. The addition of Nb can change the electronic structure and the interaction between atoms in the alloy, thereby reducing the diffusion activation energy of V and Ti, making the element distribution in the alloy more uniform, reducing composition segregation and concentration gradients, and guiding other elements to diffuse along the forging direction, reducing the possibility of their random diffusion inside the lattice.

[0026] The preferred content ratio of the three elements V (vanadium), Ti (titanium), and Nb (niobium) in the alloy is 3:4:2, which can ensure the maximization of the synergistic effect of these elements in the alloy, contribute to optimizing the heat treatment response of the alloy, and improving the hardness, strength, and toughness of the forged ingot. By redistributing the segregated elements through subsequent AB combined forging, it is beneficial to reduce the anisotropy of the material, make the metal flow more uniform, thereby reducing the formation of defects such as cracks, improving the plasticity of the material at high temperatures, facilitating complex shape processing, and at the same time reducing energy consumption and production costs.

[0027] The present invention further provides a short-process forging process achieved through the above components, and the technical principle of this process is as follows.

[0028] In S1, first, various metal raw materials are melted according to a specific formula and then cast into ingots. This process requires precise control of the chemical composition to ensure that the contents of various alloying elements meet the requirements. The distribution and interaction of different elements in the steel will affect the final microstructure and properties. For example, some elements may form segregation, resulting in non-uniform local composition, and subsequent forging and heat treatment processes are aimed at eliminating these non-uniformities to make the microstructure more uniform and dense.

[0029] After the ingot is demolded, it is cooled to 680 - 720 °C and held at this temperature. This temperature range is selected to avoid excessive thermal stress inside the ingot, which may cause cracking. Holding at this temperature can make the temperature distribution inside the ingot more uniform, creating good conditions for subsequent heating and forging. At the same time, some solid-state phase transformations may occur at this stage, such as pearlite transformation, initially affecting the microstructure of the steel.

[0030] In S2, the present invention can use a relatively fast heating rate to raise the ingot temperature above the austenitizing temperature while keeping the thermal stress inside the ingot within a certain range so as not to cause the ingot to crack. Hold for a sufficient length of time to ensure that the austenite transformation proceeds fully and that the alloying elements diffuse evenly in the austenite, providing a suitable microstructure state for subsequent forging.

[0031] In S3, the shaping treatment of the as-cast ingot is to remove the defects and irregularities on the surface of the ingot, specifically including chamfering the ingot, cutting off the riser and the bottom of the ingot, and cleaning if there is slag. The principle is to make the shape of the ingot regular for subsequent rotary upsetting. The upsetting forging ratio should be such that the grains inside the ingot can be broken and refined without being (5 - 7):1. This forging ratio. During the rotary upsetting process, the metal is compressed and deformed in three dimensions, and the grains are elongated and broken, forming a fibrous structure. This fibrous structure is distributed along the direction of metal deformation, which can improve the strength and toughness of the material. The final forging temperature is in the range of 980 - 850 °C. This temperature range is selected to ensure that the material has sufficient plasticity while avoiding excessive grain growth due to too high a temperature.

[0032] In S4, the ingot is divided into ingot A and ingot B, and they are processed differently. Ingot A is upset into a rod-like structure. The cross-section of the rod-like structure is polygonal, which can increase the contact area with the through-hole of ingot B and improve the connection stability. A through-hole is formed in the middle of ingot B by impact machining. This machining method can form a certain stress distribution and microstructure change inside ingot B. The rod-like ingot A is inserted into the through-hole of ingot B to form an ingot AB combination. This way can change the overall structural form, optimize the mechanical properties of the forging and provide convenience for subsequent processing. At the same time, a tight fit with a polygonal structure or spline connection can be preferably adopted between ingot A and ingot B to avoid relative rotation, reduce the risk of separation of the two during forging, and further enhance the connection strength between the two.

[0033] S5 is similar to S2. It is heated to 1150 - 1280 °C again at a heating rate of 100 - 160 °C / h and held for 6 - 10 h. This is to readjust the microstructure state of the ingot AB combination to make it reach the temperature and microstructure conditions suitable for forging again. After the first forging, the microstructure of the material has changed. By this heating, the new microstructure can be homogenized to prepare for the next upsetting. Similarly, adopting a segmented heating method (rapidly heating to a lower temperature first and then reducing the heating rate) can better control the temperature change according to the actual situation and reduce the generation of thermal stress.

[0034] In S6, the forging ratio is (5 - 7):1, and the final forging temperature is 980 - 850 °C. The second upsetting further refines the grains and improves the microstructure. During the forging process, the forging speed is controlled at 0.02 - 0.05 m / s. An appropriate forging speed can ensure that the metal has enough time for deformation and recrystallization processes. If the forging speed is too fast, the deformation inside the metal may be uneven, resulting in microstructure defects; if the forging speed is too slow, it may lead to excessive grain growth and affect the properties of the material.

[0035] In S7, the forging is tempered at 310 - 360 °C and slowly heated to 540 - 560 °C at 50 - 80 °C / h, held for 18 - 24 h, and then cooled in the furnace. Tempering is one of the important links in heat treatment. Its main purpose is to eliminate the internal stress generated during forging. During the tempering process, the atoms inside the material will migrate and rearrange, releasing the internal stress. At the same time, tempering in this temperature range can also adjust the microstructure of the material to a certain extent, such as decomposing martensite into tempered troostite and other microstructures, further improving the toughness and comprehensive mechanical properties of the material. Slowly heating and holding can ensure that the temperature inside the material changes evenly and avoid generating new thermal stress.

[0036] The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings and embodiments. 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.

[0037] Embodiment 1 A megawatt-level wind power spindle, by weight percentage, its composition includes: C: 0.45%, Mn: 0.65%, V: 0.42%, Cr: 1.32%, Ti: 0.44%, Nb: 0.30%, Ni: 0.32%, S≤0.01%, P≤0.01%, the balance is Fe and unavoidable impurities.

[0038] The preparation steps are as follows: S1, Pour the metal raw materials into a metal ingot according to the formula, and keep it warm after the ingot is demolded and cooled to 680°C; S2, Heat the insulated ingot to 1200°C at a heating rate of 100°C / h, keep it warm for 10h, and then take it out of the furnace; S3, Shape the ingot taken out of the furnace, and then perform rotary upsetting after shaping. The upsetting forging ratio is 5:1, the forging speed is 0.03m / s, and the final forging temperature is 900°C; S4, Divide the ingot into ingot A and ingot B. Upset ingot A into a rod-shaped structure, punch a through hole in the middle of ingot B, clean the residues on the surfaces of ingot A and ingot B, and then insert the rod-shaped ingot A into the through hole of ingot B to form an ingot AB combination; S5, Heat the ingot AB combination to 1200°C at a heating rate of 100°C / h, keep it warm for 10h, and then take it out of the furnace; S6, Place the heated and insulated ingot AB combination in multiple flips to obtain a forging by upsetting. The upsetting forging ratio is 6:1, the forging speed is 0.03m / s, and the final forging temperature is 1000°C; S7, Perform surface rounding and finishing on the forging. The starting temperature of rounding is 850°C, the ending temperature of rounding is 500°C, then return to the furnace at 360°C, and slowly heat it to 550°C at 50°C / h. After keeping it warm for 24h, cool it in the furnace to 150°C, and then take it out of the furnace and air-cool it to room temperature to obtain a finished ingot.

[0039] Embodiment 2 A megawatt-level wind power spindle, by weight percentage, its composition includes: C: 0.50%, Mn: 0.85%, V: 0.32%, Cr: 1.15%, Ti: 0.85%, Nb: 0.38%, Ni: 0.58%, S≤0.01%, P≤0.01%, the balance is Fe and unavoidable impurities.

[0040] The preparation steps are as follows: S1. Cast the metal raw materials into a metal ingot according to the formula, and keep it warm after the ingot is demolded and cooled to 720 °C. S2. Heat the insulated ingot to 1150 °C at a heating rate of 150 °C / h, keep it warm for 10 h, and then take it out of the furnace. S3. Shape the ingot taken out of the furnace, and then perform rotary upsetting after shaping. The upsetting forging ratio is 7:1, the forging speed is 0.02 m / s, and the final forging temperature is 850 °C. S4. Divide the ingot into ingot A and ingot B. Upset ingot A into a square rod-like structure, and impact-process a square through-hole in the middle of ingot B. After cleaning the residues on the surfaces of ingot A and ingot B, insert the rod-like ingot A into the through-hole of ingot B to form an ingot AB combination. S5. Heat the ingot AB combination to 1250 °C at a heating rate of 100 °C / h, keep it warm for 8 h, and then take it out of the furnace. S6. Place the heated and insulated ingot AB combination in multiple flips and perform upsetting to obtain a forging. The upsetting forging ratio is 6:1, the forging speed is 0.05 m / s, and the final forging temperature is 1050 °C. S7. Perform surface rounding and finishing on the forging. The starting temperature for rounding is 860 °C, the ending temperature for rounding is 500 °C, then return it to the furnace at 60 °C and slowly heat it to 560 °C at a rate of 80 °C / h. After keeping it warm for 24 h, cool it with the furnace to 130 °C and then take it out of the furnace and air-cool it to room temperature to obtain the finished ingot.

[0041] Example 3 A megawatt-level wind power main shaft, by weight percentage, its composition includes: C: 0.55%, Mn: 0.65%, V: 0.42%, Cr: 1.35%, Ti: 0.72%, Nb: 0.32%, Ni: 0.48%, S≤0.01%, P≤0.01%, and the balance is Fe and unavoidable impurities.

[0042] Its preparation steps are as follows: S1. Cast the metal raw materials into a metal ingot according to the formula, and keep it warm after the ingot is demolded and cooled to 680 °C. S2. Heat the insulated ingot to 900 °C at a heating rate of 160 °C / h, and then heat it to 1150 °C at a heating rate of 100 °C / h and keep it warm for 8 h, and then take it out of the furnace. S3. Shape the ingot taken out of the furnace, and then perform rotary upsetting after shaping. The upsetting forging ratio is 7:1, the forging speed is 0.05 m / s, and the final forging temperature is 950 °C. S4. Divide the ingot into ingot A and ingot B. Upset ingot A into a regular pentagon rod-like structure, and impact-process a regular pentagon through-hole in the middle of ingot B. After cleaning the residues on the surfaces of ingot A and ingot B, insert the rod-like ingot A into the through-hole of ingot B to form an ingot AB combination. S5. Combine the ingots A and B and heat them to 1150°C at a heating rate of 160°C / h, hold for 8 h, and then take them out of the furnace. S6. Place the combined and heat-insulated ingots A and B in multiple flips and upset them to obtain forgings. The forging ratio of upsetting is 7:1, the forging speed is 0.05 m / s, and the final forging temperature is 1050°C. S7. Carry out surface rounding and finishing on the forgings. The starting temperature of rounding is 800°C, the ending temperature of rounding is 550°C, then return them to the furnace at 310°C and slowly heat them to 540°C at a rate of 50°C / h. After holding for 18 h, cool them in the furnace to 140°C and then take them out of the furnace and air-cool them to room temperature to obtain the finished ingots.

[0043] Example 4 A megawatt-level wind power main shaft, by weight percentage, its composition includes: C: 0.55%, Mn: 0.62%, V: 0.46%, Cr: 1.20%, Ti: 0.68%, Nb: 0.28%, Ni: 0.44%, S≤0.01%, P≤0.01%, and the balance is Fe and unavoidable impurities.

[0044] The preparation steps are as follows: S1. Pour the metal raw materials into metal ingots according to the formula, and keep them warm after the ingots are demolded and cooled to 720°C. S2. Heat the insulated ingots to 1150°C at a heating rate of 150°C / h, hold for 9 h, and then take them out of the furnace. S3. Shape the ingots taken out of the furnace, and then carry out rotary upsetting after shaping. The forging ratio of upsetting is 5:1, the forging speed is 0.04 m / s, and the final forging temperature is 920°C. S4. Divide the ingots into ingot A and ingot B. Upset ingot A into a regular pentagon rod-like structure, punch splines on the connection surface between the surface of ingot A and ingot B, punch a regular pentagon through hole in the middle of ingot B, clean the residues on the surfaces of ingot A and ingot B, and then insert the rod-like ingot A into the through hole of ingot B to form the combined ingots AB. S5. Heat the combined ingots AB to 850°C at a heating rate of 150°C / h, and then heat them to 1150°C at a heating rate of 80°C / h, hold for 6 h, and then take them out of the furnace. S6. Place the combined and heat-insulated ingots AB in multiple flips and upset them to obtain forgings. The forging ratio of upsetting is 8:1, the forging speed is 0.04 m / s, and the final forging temperature is 1000°C. S7. Carry out surface rounding and finishing on the forgings. The starting temperature of rounding is 820°C, the ending temperature of rounding is 550°C, then return them to the furnace at 360°C and slowly heat them to 560°C at a rate of 70°C / h. After holding for 18 h, cool them in the furnace to 130°C and then take them out of the furnace and air-cool them to room temperature to obtain the finished ingots.

[0045] Example 5 A megawatt-level wind power main shaft, by weight percentage, its composition includes: C: 0.55%, Mn: 0.68%, V: 0.45%, Cr: 1.22%, Ti: 0.60%, Nb: 0.30%, Ni: 0.43%, S≤0.01%, P≤0.01%, the balance is Fe and unavoidable impurities.

[0046] The preparation steps are as follows: S1, Pour the metal raw materials into a metal ingot according to the formula. After the ingot is demolded and cooled to 700 °C, keep it warm. S2, Heat the insulated ingot to 950 °C at a heating rate of 160 °C / h, and then heat it to 1100 °C at a heating rate of 80 °C / h, keep it warm for 6 h, and then take it out of the furnace. S3, Shape the ingot taken out of the furnace, and then perform rotary upsetting after shaping. The upsetting forging ratio is 5:1, the forging speed is 0.05 m / s, and the final forging temperature is 930 °C. S4, Divide the ingot into ingot A and ingot B. Upset ingot A into a regular pentagon rod-like structure, punch a regular pentagon through hole in the middle of ingot B, punch splines on the connecting surfaces of ingot A and ingot B, clean the residues on the surfaces of ingot A and ingot B, and then insert the rod-like ingot A into the through hole of ingot B to form an ingot AB combination. S5, Heat the ingot AB combination to 920 °C at a heating rate of 150 °C / h, and then heat it to 1150 °C at a heating rate of 90 °C / h, keep it warm for 6 h, and then take it out of the furnace. S6, Place the heated and insulated ingot AB combination in multiple flips and perform upsetting to obtain a forging. The upsetting forging ratio is 8:1, the forging speed is 0.05 m / s, and the final forging temperature is 1050 °C. S7, Perform surface rolling and finishing on the forging. The starting temperature of rolling is 800 °C, the ending temperature of rolling is 550 °C, then return to the furnace at 330 °C, and slowly heat it to 560 °C at 80 °C / h. After keeping it warm for 24 h, cool it with the furnace to 120 °C, and then take it out of the furnace and air-cool it to room temperature to obtain the finished ingot.

[0047] For each of the above examples, test its mechanical properties according to "GB / T 228.1—2023 Metallic materials—Tensile testing—Part 1: Method of test at room temperature"; test the impact energy according to "GB / T 229 - 2025 Metallic materials—Charpy pendulum impact test method"; measure its Rockwell hardness according to "GB / T 230.1—2018 Metallic materials—Rockwell hardness test—Part 1: Test method". The test results are shown in Table 1. Table 1: 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 principles 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. A megawatt-level wind power spindle, characterized in that by weight percentage, its composition includes: C: 0.45 - 0.55%, Mn: 0.42 - 0.85%, V: 0.32 - 0.52%, Cr: 1.15 - 1.57%, Ti: 0.44 - 0.85%, Nb: 0.25 - 0.38%, Ni: 0.32 - 0.58%, S ≤ 0.01%, P ≤ 0.01%, and the balance is Fe and unavoidable impurities.

2. The wind power spindle according to claim 1, characterized in that the content of V is 0.42 - 0.46%, the content of Ti is 0.68 - 0.72%, and the content of Nb is 0.28 - 0.32%.

3. The wind power spindle according to claim 2, characterized in that the ratio of V, Ti, and Nb is 3:4:

2.

4. The wind power main shaft according to claim 1, wherein The preparation process includes: S1, Pour the metal raw materials into a metal ingot according to the formula. After the ingot is demolded and cooled to 680 - 720 °C, keep it warm. S2, Heat the insulated ingot at a heating rate of 100 - 160 °C / h to 1150 - 1280 °C, keep it warm for 6 - 10 h, and then take it out of the furnace. S3, Shape the ingot taken out of the furnace, and then perform rotary upsetting after shaping. The upsetting forging ratio is (5 - 7):1, and the final forging temperature is 980 - 850 °C. S4, Divide the ingot into ingot A and ingot B. Upset ingot A into a rod-shaped structure, punch a through hole in the middle of ingot B, clean the residues on the surfaces of ingot A and ingot B, and then insert the rod-shaped ingot A into the through hole of ingot B to form an ingot AB combination. S5, Heat the ingot AB combination at a heating rate of 100 - 160 °C / h to 1150 - 1280 °C, keep it warm for 6 - 10 h, and then take it out of the furnace. S6, Place the heated and insulated ingot AB combination in multiple flips and perform upsetting to obtain a forging. The upsetting forging ratio is (6 - 8):1, and the final forging temperature is 1050 - 980 °C. S7, Perform surface rolling and finishing on the forging. The starting temperature of rolling is 800 - 850 °C, the ending temperature of rolling is 500 - 550 °C, return to the furnace at 310 - 360 °C, and slowly heat it to 540 - 560 °C at 50 - 80 °C / h. After keeping it warm for 18 - 24 h, cool it with the furnace to 120 - 150 °C, and then take it out of the furnace and air-cool it to room temperature to obtain the finished ingot.

5. The wind power spindle according to claim 4, characterized in that in S4, ingot A adopts a rod-shaped structure with a polygonal cross-section, and the through hole of ingot B is adapted to the shape of ingot A.

6. The wind power spindle according to claim 4, characterized in that in S4, splines are machined on the surfaces of ingot A and ingot B, and ingot A and ingot B are tightly fitted through the splines.

7. The wind power spindle according to claim 1, characterized in that in S2 and / or S5, a segmented heating method is adopted. First, heat the ingot to a lower temperature at a faster rate, and then reduce the heating rate and then heat it up to the set value.

8. The wind power spindle according to claim 1, characterized in that In S3 and / or S6, the forging speed is 0.02 - 0.05 m / s.

9. Application of the wind power main shaft according to claim 1 in a wind turbine unit.

10. The wind power main shaft according to claim 1 or 4, characterized in that The megawatt level ≥ 50 kW.

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