High-hydrogen embrittlement resistance, fatigue resistance, and easy-carburization wind power gear and manufacturing method thereof

Abstract

The application discloses a high-hydrogen embrittlement resistance, fatigue resistance and easy-carburization wind power gear and a manufacturing method thereof. Through micro-alloying design and rare earth elements Ce+La, combined with smelting, forging, heat treatment whole-process process synergistic control, the technical problems of hydrogen-induced delayed brittle fracture, grain boundary hydrogen embrittlement, low carburization efficiency, grain boundary embrittlement / early peeling of carburized layer, insufficient fatigue life and the like of the high-power wind power gear in service are solved; steel liquid deep purification, fine-grain high-density, carbon diffusion speed-up, carburized layer structure optimization and grain boundary strengthening are realized, and the strict working condition requirements of the wind power gear, such as heavy load, long service life and high reliability, are met.

Description

Technical Field

[0001] This invention relates to a wind turbine gear and its manufacturing method, belonging to the field of iron and steel metallurgy technology. Background Technology

[0002] Wind energy, as a vast, clean, and renewable green energy source, has become a core pillar of the global energy transition strategy and has received high attention and active development from countries around the world, including China. As a key component of wind turbines, the performance of the wind turbine gearbox directly affects the overall operating efficiency and service life of the wind turbine unit.

[0003] Wind turbine gears are core transmission components of wind turbine units. These gears operate in harsh environments, bearing high loads and complex alternating stresses, requiring materials with high strength, high toughness, high wear resistance, excellent carburizing processability, and long fatigue life. As wind power equipment develops towards higher power, heavier loads, higher speeds, and lighter weights, conventional gear steels can no longer meet the demands.

[0004] CN113549866A discloses a carburizing and quenching process for planetary gears on the raceway of a wind turbine generator set. This invention uses traditional Cr-Ni-Mo gear steel and performs high-carbon potential carburizing at 940±10℃ with segmented controlled carbon potential (strong carburizing 1.2%~1.3%, diffusion 0.9%~1.1%), followed by solution treatment + high-temperature aging or slow cooling + spheroidizing annealing. This process can make the carburized layer of the workpiece form a structure of tempered martensite + retained austenite + fine alloy carbides, with a surface carbon concentration ≥0.85%, hardness ≥HRC60.0, and a 59.0HRC hardened layer accounting for more than half of the effective hardened layer depth. The planetary gear teeth and inner holes still retain high contact fatigue strength and excellent comprehensive mechanical properties after grinding.

[0005] CN115386790A discloses a niobium-containing high-temperature carburized gear steel and its production process. Its chemical composition is as follows: C: 0.16–0.22%, Si: 0.05–0.16%, Mn: 0.45–0.75%, P≤0.020%, S≤0.02%, Cr: 0.3–0.6%, Ni: 0.8–1.25%, Mo: 0.12–0.25%, Nb: 0.02–0.045%, V: 0.04–0.1%, Ti: 0.006–0.025%, Al≤0.035%, Cu≤0.15%, B≤0.006%, Co≤0.006%, Zr≤0.006%, N: 100–200 ppm, H≤2.0 ppm, O≤20 ppm. This invention optimizes the steel composition by utilizing the synergistic effects of low Si, Mo, V-Ti-Nb and elements such as B, Cu, Co, and Zr to improve the black network structure, refine carbonitrides and grains, form dispersed and fine second-phase particles, increase the density and refinement of oxides and nitrides, optimize the high-temperature carburizing structure, and improve the strength and toughness of gear steel.

[0006] CN110846580A discloses a high-Mo, high-performance Mn-Cr series wind turbine output gear steel and its production method. Its chemical composition is as follows: C: 0.21-0.28%, Si: 0.15-0.35%, Mn: 0.70-1.10%, Cr: 1.25-1.40%, Mo: 0.30-0.50%, Nb: 0.030-0.045%, Ni: 0.25-0.45%, Al: 0.020-0.040%, P: ≤0.010%, S: 0.005-0.035%, O: ≤10ppm, [H]: ≤1.0ppm, [N]: 90-160ppm, Al / [N]: 2.0-4.0, Al f =Al-1.93×[N]≤0.02%, 4.25%≤[Si+1.4(Mn+Cr)+2Mo+1.2Ni]≤5.35%, with the remainder being Fe and unavoidable impurity elements. This invention uses an alloy composition formula that maintains hardenability to determine the alloy composition. By appropriately reducing the Mn content and increasing the Mo content, the hardenability of the material is maintained while reducing the risk of brittleness. Furthermore, the combined use of Mo and Nb elements further refines the grain size, ensuring that the material is less prone to grain coarsening during subsequent high-temperature, long-term carburizing processes.

[0007] In the aforementioned patents, CN113549866A employs conventional high-carbon-potential carburizing, which results in low carburizing efficiency, slow carbon diffusion, and a tendency for grain boundary carbide network precipitation in the carburized layer, leading to embrittlement, early spalling, and hydrogen-induced crack propagation along grain boundaries. Lacking rare-earth purification and grain boundary strengthening mechanisms, the grain boundaries are easily weakened by the segregation of harmful elements such as H, S, and P, resulting in insufficient resistance to hydrogen embrittlement and fatigue. CN115386790A relies solely on Nb microalloying to refine grains, lacking rare-earth Ce+La synergistic purification and hydrogen trap regulation, thus failing to fundamentally suppress hydrogen-induced delayed cracking. During high-temperature carburizing, the grains tend to be coarse and mixed, resulting in low microstructure density and insufficient purity. The problem of grain boundary carbide network precipitation in the carburized layer remains unresolved, and its fatigue life and resistance to hydrogen embrittlement cannot meet the requirements of high-power applications. CN110846580A uses a Mn-Cr series composition, completely lacking hydrogen embrittlement control measures, and has no hydrogen trap or grain boundary protection design, resulting in a high risk of hydrogen-induced cracking; it lacks rare earth purification and fine grain control, resulting in low purity of molten steel, poor inclusion morphology, and easy formation of fatigue crack initiation; the carburizing process is traditional, with slow carbon diffusion, low efficiency, and insufficient stability of the carburized layer structure and interface. Summary of the Invention

[0008] To address the aforementioned technical challenges, this invention provides a high-resistance, fatigue-resistant, and easily carburized wind turbine gear and its manufacturing method. This invention utilizes microalloying design and rare earth elements Ce+La, combined with coordinated control of the entire process from smelting and forging to heat treatment, to solve technical problems in high-power wind turbine gears during service, such as hydrogen-induced delayed embrittlement, grain boundary hydrogen embrittlement, low carburizing efficiency, grain boundary embrittlement / early spalling of the carburized layer, and insufficient fatigue life. It achieves deep purification of molten steel, fine and dense microstructure, accelerated carbon diffusion, optimized carburized layer microstructure, and grain boundary strengthening, meeting the stringent requirements of heavy-load, long-life, and high-reliability operating conditions for wind turbine gears.

[0009] The technical solution of this invention is: a wind turbine gear with high resistance to hydrogen embrittlement, fatigue, and easy carburization, and its manufacturing method, comprising the following chemical composition by mass percentage: C: 0.15-0.20%, Si: 0.17-0.35%, Mn: 0.60-0.90%, Cr: 1.55-1.80%, Ni: 1.50-1.70%, Mo: 0.25-0.35%, Al: 0.020-0.040%, P≤0.012%, S≤0.006%, Ce+La≤300ppm and Ce / La=1-3, H≤1.5ppm, O≤15ppm, N: 70-100ppm and Al / N=2-4, with the balance being Fe and unavoidable impurities.

[0010] Manufacturing method: 1) Smelting and casting The smelting process uses an electric arc furnace to melt scrap steel, LF refining and VD vacuum treatment to ensure the cleanliness of the molten steel, and the casting process uses continuous casting or ingot casting; lanthanum-cerium alloy is added during the VD vacuum treatment process. 2) Processing and shaping 3) High-temperature carburizing + quenching and tempering after carburizing 4) After heat treatment, the gears are machined on a lathe to obtain the gear products.

[0011] Furthermore, the high-purity lanthanum-cerium alloy (La+Ce content ≥99.5%) is added at a rate of 70-120 × ([%S]+[%O]) kg per ton of steel.

[0012] Furthermore, in step 1), continuous casting or ingot casting is used. Continuous casting uses low superheat casting, with the superheat of the molten steel controlled at 20-30℃ and the average cooling rate in the crystallizer section controlled at 170-202℃ / min. Ingot casting uses high superheat casting, with the superheat of the molten steel strictly controlled at 38-40℃ and a medium-strong cooling regime adopted, with the segmented cooling rate of the mold at 25-35℃ / min.

[0013] Furthermore, the processing and shaping in step 2) specifically includes: Post-casting machining: The steel ingot is first sawn to cut the sprue and riser so that the ingot body meets the weight requirements of the gear; the gear is formed by free forging + ring rolling. After each forging is completed, the surface of the forging is cooled to ≤950℃ before it can be put into the furnace for heating. The heat treatment adopts normalizing + tempering process. The normalizing temperature is 880±20℃, the tempering treatment adopts water quenching, and the tempering temperature is selected to perform high-temperature tempering treatment at 500-600℃.

[0014] Post-continuous casting processing: The continuously cast billet is first sawed to meet the specifications of the gear blank. The gear is formed by free forging and ring rolling. After each forging is completed, the surface of the forging is cooled to ≤950℃ before it can be heated in the furnace. The heat treatment adopts normalizing + tempering process. The normalizing temperature is 920±20℃, the tempering treatment adopts water quenching, and the tempering temperature is selected to perform high-temperature tempering treatment at 600-700℃.

[0015] Step 3) High-temperature carburizing + quenching and tempering after carburizing: ① Preheating of workpieces in furnace: Preheating temperature 820℃, hold for 60-90 minutes; ② Strong carburizing stage: Carburizing temperature 930±10℃, carbon potential controlled at 1.15%-1.25%; ③ Diffusion stage: Temperature maintained at 930±10℃, carbon potential decreases to 0.85%-1.00%; ④ Carburizing followed by quenching: After carburizing, directly cool to 840±10℃ and hold for 20-40 minutes, then oil quench. ⑤ Low-temperature tempering: Temper at 180-220℃ for 120-180 minutes to stabilize the diffusion layer structure and eliminate quenching stress.

[0016] The wind turbine gear prepared by the above method has a high resistance to hydrogen embrittlement and fatigue and is easy to carburize, with a tensile strength ≥1200MPa, a yield strength ≥900MPa, and an impact energy ≥42J at -40℃.

[0017] This invention achieves the coupling of rare earth purification and suppression technologies through micro-alloying design, combined with full-process control from smelting to heat treatment, ultimately yielding fine-grained, highly dense gear forgings that are easily carburized. Specifically: First, adding Ce+La elements during the steel refining process allows them to react with O and S elements in the steel to form (Ce+La)S. x O y Non-metallic inclusions; these inclusions can spontaneously float to the surface and be removed from the molten steel, significantly reducing the O and S content of the molten steel, achieving deep purification of the molten steel, and providing a good foundation for obtaining a clean and uniform microstructure of steel.

[0018] Secondly, during the solidification stage of molten steel, some of the (Ce+La)S that did not float to the surface remained. x O y Non-metallic inclusions can serve as heterogeneous nucleation sites, promoting nucleation precipitation, effectively refining the solidification structure, improving the density of the matrix, and weakening the segregation of micro-components.

[0019] Furthermore, after steel is forged, Ce+La atoms in the steel tend to agglomerate and accumulate at the grain boundaries. On the one hand, this can effectively restrict grain coarsening and growth during subsequent heat treatment, achieving the effect of grain refinement and strengthening; on the other hand, it can block the enrichment and diffusion of harmful impurities such as H, S, P, and Pb at the grain boundaries, thus purifying the grain boundary structure and effectively preventing the occurrence of hydrogen embrittlement at the grain boundaries.

[0020] Finally, the solid-solution Ce+La atoms can modulate the interfacial energy of the nanoscale AlN and Nb(C,N) precipitates within the grains, hindering particle agglomeration and coarsening, and promoting their uniform dispersion within the matrix. These fine precipitates can act as efficient hydrogen traps, binding hydrogen atoms, and also act as grain boundary pinning, further refining the grains and producing a dispersion strengthening effect on the steel matrix.

[0021] Under high-temperature carburizing processes, the Ce+La dissolved in steel can increase the diffusion rate of carbon in the matrix by 25%-35%, and simultaneously improve the carburizing process efficiency by 20%-30%. It also improves carburizing kinetics, optimizes the internal microstructure and interface stability of the carburized layer, and inhibits the formation of a continuous network of carbides at grain boundaries, effectively avoiding defects such as grain boundary embrittlement, premature surface shedding, and hydrogen-induced crack propagation along grain boundaries. During carburizing and quenching, the Ce+La solution further refines the martensite and retained austenite microstructure of the carburized layer, promoting the precipitation of carbides in fine spherical shapes, significantly improving the hardenability, wear resistance, and overall strength and toughness of the steel. During tempering, the Ce+La atoms segregate at grain boundaries, inhibiting the enrichment and segregation of harmful elements at grain boundaries, strengthening grain boundary bonding, and increasing the fatigue life of the steel matrix by 2-3 times. This fully meets the high-standard operating requirements of high-power wind turbine gears for carburized layer quality, carburizing efficiency, strength and toughness, and long-term service life.

[0022] In summary, through the synergistic effect of alloy element regulation and preparation process, the microstructure of the steel matrix and the comprehensive mechanical properties can be refined throughout the entire production process of wind turbine gear steel. This significantly enhances the material's resistance to hydrogen embrittlement and fatigue, and can meet the stringent requirements of high-power wind turbine gears for carburized layer quality, carburizing efficiency, and service life. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of inclusions in the present invention; where A: control steel 1# has no rare earth inclusions (100 times the amount); B: sample steel 4# has rare earth inclusions (100 times the amount); the scale bar in the figure is 100µm. Figure 2 This is a schematic diagram of the metallographic structure of the present invention; where A: 1000x metallographic image of control steel #1 without rare earth; B: 1000x metallographic image of sample steel #4 with rare earth; the scale bar in the figure is 100µm; Figure 3 The diagram shows the effect of Ce on the H content of 18CrNiMo7-6 steel. Detailed Implementation

[0024] The effects are illustrated below with reference to the embodiments and accompanying drawings. The embodiments and accompanying drawings are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0025] Example 1: A high-resistance to hydrogen embrittlement, fatigue, and easy carburization wind turbine gear and its manufacturing method, comprising the following chemical composition by mass percentage: C: 0.15-0.20%, Si: 0.17-0.35%, Mn: 0.60-0.90%, Cr: 1.55-1.80%, Ni: 1.50-1.70%, Mo: 0.25-0.35%, Al: 0.020-0.040%, P≤0.012%, S≤0.006%, Ce+La≤300ppm and Ce / La=1-3, H≤1.5ppm, O≤15ppm, N: 70-100ppm and Al / N=2-4, with the balance being Fe and unavoidable impurities.

[0026] Preparation method: 1) Smelting and casting The smelting process uses an electric arc furnace to melt scrap steel, LF refining and VD vacuum treatment to ensure the cleanliness of the molten steel, and the casting process uses continuous casting or ingot casting. Smelting: The smelting process uses an electric arc furnace to melt scrap steel; during electric arc furnace smelting, scrap steel is mixed with carbon and coke powder, and the tapping temperature is <1650℃; LF refining: LF refining uses a large amount of slag (approximately 4 kg / t of lime, approximately 1.5 kg / t of composite deoxidizer, and approximately 3 kg / t of refining slag) for slag formation to ensure that the S content is ≤0.002%; VD vacuum treatment: VD vacuum treatment time is greater than 30 min, N content is controlled to be ≤100 ppm, and H is guaranteed to be ≤0.8 ppm; high-purity lanthanum-cerium alloy (La+Ce content ≥99.5%, molar ratio La / Ce is 1-3, and the amount added per ton of steel is 70-120 × ([%S]+[%O]) kg) is added during VD vacuum treatment to ensure deep vacuum circulation time of molten steel. After vacuum treatment, slag surface protectant (carbonized rice husks completely cover the slag surface) is immediately added to prevent slag surface oxidation, and argon soft blowing time is greater than 20 min. Casting: Continuous casting or ingot casting is used. Continuous casting employs low superheat casting, with the superheat of the molten steel controlled at 20-30℃ and the cooling water flow rate in the crystallizer controlled at 270-300 m / s. 3 / h, the average cooling rate of the crystallizer section is controlled at 170-202℃ / min; the ingot casting adopts high superheat casting, the superheat of the molten steel is strictly controlled at 38-40℃, and a medium-strong cooling system is adopted, with the segmented cooling rate of the mold being 25-35℃ / min.

[0027] 2) Processing and shaping Post-casting machining: The steel ingot is first sawn to cut the sprue and riser so that the ingot body meets the weight requirements of the gear; the gear is formed by free forging + ring rolling. After each forging is completed, the surface of the forging is cooled to ≤950℃ before it can be put into the furnace for heating. The heat treatment adopts normalizing + tempering process. The normalizing temperature is 880±20℃, the tempering treatment adopts water quenching, and the tempering temperature is selected to be 500-600℃ for high-temperature tempering treatment.

[0028] Post-continuous casting processing: The continuously cast billet is first sawed to meet the specifications of the gear blank. The gear is formed by free forging and ring rolling. After each forging is completed, the surface of the forging is cooled to ≤950℃ before it can be heated in the furnace. The heat treatment adopts normalizing + tempering process. The normalizing temperature is 920±20℃, the tempering treatment adopts water quenching, and the tempering temperature is selected to be 600-700℃ for high-temperature tempering treatment.

[0029] 3) High-temperature carburizing + quenching and tempering after carburizing: ① Preheating of workpieces in furnace: Preheating temperature 820℃, hold for 60-90 minutes to eliminate internal stress in forgings and uniform temperature field of the base material; ② Strong Carburizing Stage: Carburizing temperature 930±10℃, carbon potential controlled at 1.15%-1.25%, and heat preservation time set according to the depth of the carburized layer, which is 20% to 30% shorter than the traditional process; ③ Diffusion stage: The temperature is maintained at 930±10℃, the carbon potential is reduced to 0.85%-1.00%, and the holding time is 1 / 2 of the strong diffusion stage. The carbon diffusion rate is increased by Ce+La to avoid the precipitation of grain boundary carbides in a network. ④ Carburizing followed by quenching: After carburizing, directly cool to 840±10℃ and hold for 30 minutes, then oil quench. ⑤ Low-temperature tempering: Temper at 180-220℃ for 120-180 minutes to stabilize the diffusion layer structure and eliminate quenching stress.

[0030] 4) After heat treatment, the gears are machined on a lathe to obtain the gear products.

[0031] The composition of the test steel (four samples, in-mold casting) and the control test steel (one sample) is shown in Table 1. Inclusion dimensions are shown in Table 2, and a schematic diagram of the inclusions is shown below. Figure 1 The tensile strength, yield strength, reduction of area, elongation at break, and impact energy at -40℃ are shown in Table 3. The tensile strength, yield strength, reduction of area, and elongation at break were tested according to GB / T228.1-2021 "Metallic materials, tensile testing—Part 1: Tests at room temperature," and the impact energy at -40℃ (KV2) was tested according to GB / T229-2020 "Metallic materials, Charpy impact test."

[0032] Table 1 Main Components of the Test Steel

[0033] Notes: 1. The control steel was produced using the same smelting process, differing only in the amount of high-purity lanthanum-cerium alloy added; all other components and processes were identical. The chemical composition of the control steel, except for rare earth elements, was the same as the test steel, used to evaluate the impact of lanthanum-cerium alloy addition on material properties. 2. The Ce / La molar ratio of all sample steels was strictly controlled within the range of 1-3, meeting the composition design requirements of this invention.

[0034] Table 2 Dimensions of inclusions in the test steel

[0035] Table 3. Mechanical property data of the experimental steel

[0036] Results analysis: 1. High resistance to hydrogen embrittlement: Hydrogen-induced delayed cracking and grain boundary hydrogen embrittlement are the main failure modes of high-power wind turbine gears. This invention achieves multiple hydrogen control effects through rare earth Ce+La: 1) Hydrogen content control: As shown in Table 1, the hydrogen content of the sample steel with added Ce+La was as low as 0.4-0.6 ppm, far below the standard limit of ≤1.5 ppm; combined with Figure 3 (Ce effect curve on hydrogen content in steel) Under hydrogen charging conditions, the hydrogen enrichment of Ce-containing test steel is significantly lower than that of Ce-free control steel, proving that rare earth elements can effectively reduce the dissolved hydrogen content in steel.

[0037] 2) Hydrogen traps and grain boundary protection: Ce and La atoms segregate at grain boundaries, forming stable hydrogen traps that bind free hydrogen atoms and prevent hydrogen from accumulating at grain boundaries. On the other hand, they prevent harmful elements such as H, S, and P from segregating at grain boundaries, thus weakening the tendency of hydrogen-induced intergranular cracking.

[0038] 3) Inclusion optimization: Table 2 shows that after adding rare earth elements, the inclusion grade decreased from DS1.0 (the control steel) to DT0.5 / DH0.5 (see Table 2). Figure 1 The inclusion size is significantly reduced. Large inclusions are sources of hydrogen crack initiation, while small, dispersed inclusions can block the hydrogen crack propagation path, further enhancing resistance to hydrogen embrittlement.

[0039] 4) Evidence of low-temperature toughness: The impact energy of the sample steel at -40℃ in Table 3 is 44.4~49.0J, which is much higher than the 33.5J of the control steel; hydrogen embrittlement will significantly deteriorate the low-temperature toughness, and the improvement in impact performance directly proves that the material’s resistance to hydrogen embrittlement has been greatly enhanced.

[0040] 2. High fatigue resistance: Wind turbine gears are subjected to alternating loads for extended periods, with fatigue failure being the primary failure mode. This invention improves fatigue life from three aspects: microstructure, grain boundaries, and mechanical properties. 1) Grain refinement: by Figure 2 Metallographic images show that the steel samples with added Ce+La exhibit significantly refined grains, uniform microstructure, and no mixed grain phenomenon. The fine-grained structure can disperse alternating stress, hindering the initiation and propagation of fatigue cracks, and is a core factor in improving fatigue life.

[0041] 2) Grain boundary strengthening: Ce and La are enriched at grain boundaries, which strengthens the grain boundary bonding force and avoids grain boundary cracking under alternating loads; at the same time, it inhibits harmful impurities such as S and P from weakening the grain boundaries, thereby reducing fatigue crack initiation from the root.

[0042] 3) Improved comprehensive mechanical properties: As shown in Table 3, the tensile strength of the sample steel is ≥1250MPa and the yield strength is ≥943MPa, both of which are higher than the control steel (1180MPa / 855MPa), indicating stronger matrix bearing capacity.

[0043] 4) Improvement of inclusions: by Figure 1 As shown in Table 2, rare earth purification of molten steel transforms large, elongated inclusions into small, spherical inclusions, eliminating the main source of fatigue crack initiation and significantly improving contact fatigue and bending fatigue performance.

[0044] 3. Improved Carburizing Performance: This invention optimizes carburizing kinetics and layer microstructure using rare earth elements, achieving both improved carburizing efficiency and optimized layer quality. 1) Improved carburizing efficiency: The solid solution of Ce+La in steel can activate the diffusion channels of carbon atoms, which increases the diffusion rate of carbon in the matrix by 25%-35%; when combined with the segmented carburizing process of this invention, the overall carburizing production efficiency is increased by 20%-30%, shortening the production cycle and reducing energy consumption.

[0045] 2) Suppressing grain boundary network carbides: Traditional high-carbon-potential carburizing of gear steel easily forms continuous network carbides at grain boundaries, causing embrittlement of the carburized layer and early spalling. Ce+La can regulate the precipitation morphology of carbides, transforming them into fine spherical dispersed distributions, and completely eliminating the network embrittlement structure.

[0046] 3) Optimization of carburized layer structure: After carburizing, rare earth elements further refine the martensite and retained austenite structure of the carburized layer, improve the hardness, wear resistance and interfacial bonding strength of the carburized layer, and avoid defects such as carburized layer peeling and pitting corrosion.

Claims

1. A method for manufacturing a wind turbine gear with high resistance to hydrogen embrittlement, fatigue resistance, and easy carburization, characterized in that, The high-hydrogen embrittlement-resistant, fatigue-resistant, and easily carburized wind turbine gear comprises the following chemical composition by mass percentage: C: 0.15-0.20%, Si: 0.17-0.35%, Mn: 0.60-0.90%, Cr: 1.55-1.80%, Ni: 1.50-1.70%, Mo: 0.25-0.35%, Al: 0.020-0.040%, P≤0.012%, S≤0.006%, Ce+La≤300ppm with a mass ratio of Ce / La=1-3, H≤1.5ppm, O≤15ppm, N: 70-100ppm, with the balance being Fe and unavoidable impurities.

2. The manufacturing method as described in claim 1, characterized in that, The mass ratio is Al / N = 2-4.

3. The manufacturing method as described in claim 1, characterized in that, Includes the following steps: 1) Smelting and casting The smelting process uses an electric arc furnace to melt scrap steel, LF refining and VD vacuum treatment to ensure the cleanliness of the molten steel, and the casting process uses continuous casting or ingot casting; lanthanum-cerium alloy is added during the VD vacuum treatment process. 2) Processing and shaping; 3) High-temperature carburizing + quenching and tempering after carburizing; 4) After heat treatment, the gears are machined on a lathe to obtain the gear products.

4. The manufacturing method as described in claim 3, characterized in that, The amount of lanthanum-cerium alloy added is 70-120 × ([%S] + [%O]) kg per ton of steel.

5. The manufacturing method as described in claim 3, characterized in that, In step 1), continuous casting is carried out with low superheat casting. The superheat of the molten steel is controlled at 20-30℃, and the average cooling rate in the crystallizer section is controlled at 170-202℃ / min.

6. The manufacturing method as described in claim 5, characterized in that, Step 2) Post-continuous casting processing and forming specifically involves: the continuously cast billet is first sawed to meet the specifications of the gear blank. The gear is formed by free forging + ring rolling. After each forging is completed, the surface of the forging is cooled to ≤950℃ before it can be heated in the furnace. The heat treatment adopts normalizing + tempering process. The normalizing temperature is 920±20℃, the tempering treatment adopts water quenching, and the tempering temperature is selected to be 600-700℃ for high-temperature tempering treatment.

7. The manufacturing method as described in claim 3, characterized in that, Step 1) The ingot casting adopts high superheat casting, the superheat of the molten steel is controlled at 38-40℃, and a medium-strong cooling system is adopted, with the segmented cooling rate of the mold being 25-35℃ / min.

8. The manufacturing method as described in claim 7, characterized in that, Step 2) Post-casting processing: The steel ingot is first sawn to cut off the sprue and riser so that the ingot body meets the weight requirements of the gear; the gear is formed by free forging + ring rolling. After each forging is completed, the surface of the forging is cooled to ≤950℃ before it can be put into the furnace for heating. The heat treatment adopts normalizing + tempering process. The normalizing temperature is 880±20℃, the tempering treatment adopts water quenching, and the tempering temperature is selected to be 500-600℃ for high-temperature tempering treatment.

9. The manufacturing method as described in claim 3, characterized in that, Step 3) High-temperature carburizing + quenching and tempering after carburizing specifically involves: ① Preheating of workpieces in furnace: Preheating temperature 820±10℃, holding for 60-90 minutes; ② Strong carburizing stage: Carburizing temperature 930±10℃, carbon potential controlled at 1.15%-1.25%; ③ Diffusion stage: Temperature maintained at 930±10℃, carbon potential decreases to 0.85%-1.00%; ④ Carburizing followed by quenching: After carburizing, directly cool to 840±10℃ and hold for 20-40 minutes, then oil quench. ⑤ Low-temperature tempering: Temper at 180-220℃ for 120-180 minutes to stabilize the diffusion layer structure and eliminate quenching stress.

10. A wind turbine gear with high resistance to hydrogen embrittlement, fatigue resistance, and easy carburization manufactured by the manufacturing method of any one of claims 3-9, characterized in that, Its tensile strength is ≥1200MPa, yield strength is ≥900MPa, and impact energy at -40℃ is ≥42J.

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