A wind power main shaft and a method for controlling micro defects of a surface strengthening layer thereof

Abstract

The application discloses a kind of wind power main shaft and its surface strengthening layer microdefect control method, belong to metal material surface modification technical field.The method includes: wind power main shaft matrix is treated and surface purification treatment, subsequently carries out multi-energy field composite surface strengthening treatment, then carries out defect elimination treatment and stress optimization treatment;Heat treatment includes quenching and high-temperature tempering;Multi-energy field composite surface strengthening treatment includes preheating and hydrogen trap setting, low-temperature ion nitriding, laser remelting-quenching composite treatment;Defect elimination treatment and stress optimization treatment include low-temperature dehydrogenation and stabilization treatment for eliminating defects, and shot blasting and polishing treatment for stress optimization.The method can realize the systematic control of microcrack, harmful phase, hydrogen content and disadvantageous residual stress in the strengthening layer, so as to obtain a high-quality strengthening layer with dense microstructure, few defects and optimized stress state, greatly improving the fatigue resistance and service life of the wind power main shaft.

Description

Technical Field

[0001] This invention relates to the field of surface modification technology for metallic materials, and more specifically, to a method for controlling microscopic defects in a wind turbine main shaft and its surface reinforcement layer. Background Technology

[0002] As the core torsion-bearing and load-bearing component of a wind turbine generator set, the surface quality and fatigue resistance of the wind turbine's main shaft directly determine the safe operating life of the entire unit. To improve its surface hardness, wear resistance, and fatigue strength, specific areas of the main shaft (such as bearing seats and seals) typically require surface strengthening treatment. Commonly used surface strengthening techniques include induction hardening, laser hardening, nitriding, and shot peening. However, existing surface strengthening techniques are prone to introducing or failing to effectively control various microscopic defects within the strengthened layer during application. These defects become preferential sites for fatigue crack initiation, severely restricting the strengthening effect and even leading to premature component failure.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a method for controlling microscopic defects in wind turbine main shafts and their surface reinforcement layers, so as to solve or improve the above-mentioned technical problems.

[0005] This invention can be implemented as follows: In a first aspect, the present invention provides a method for controlling microscopic defects in the surface reinforcement layer of a wind turbine main shaft, comprising the following steps: heat treatment and surface cleaning treatment of the wind turbine main shaft substrate, followed by multi-energy field composite surface reinforcement treatment, and then defect elimination treatment and stress optimization treatment. Heat treatment includes quenching and high-temperature tempering. Multi-energy field composite surface strengthening treatment includes preheating and hydrogen trap setting, low-temperature ion nitriding, and laser remelting-quenching composite treatment; Defect elimination and stress optimization treatments include low-temperature dehydrogenation and stabilization treatments for defect elimination, and shot peening and polishing treatments for stress optimization.

[0006] In an optional embodiment, the quenching treatment is performed by oil quenching at 850℃~870℃ for 1.5h~2.5h; And / or, high-temperature tempering is performed by oil quenching at 570℃~580℃ for 2.5h~3.5h.

[0007] In an optional embodiment, the hardness of the heat-treated wind turbine main shaft substrate is 28HRC~35HRC.

[0008] In an optional embodiment, the surface cleaning treatment includes: first, mechanical polishing or precision grinding of the surface of the area of ​​the wind turbine main shaft substrate that needs to be strengthened, so that the surface roughness Ra of the corresponding area is ≤0.4μm; then, ultrasonic cleaning and low-temperature plasma bombardment cleaning are performed to remove grease, oxides and adsorbents present on the corresponding surface.

[0009] In an optional embodiment, the preheating and hydrogen trapping setup includes: low-energy ion bombardment at a temperature of 250°C to 400°C to introduce hydrogen traps onto the surface of the wind turbine main shaft substrate.

[0010] In an optional implementation, the conditions for low-energy ion bombardment include: a gas pressure of 0.8 × 10⁻⁶. -3 Pa ~ 1.2 × 10 -3 Pa、Ar + The ionized gas particles have an energy of 0.8 keV to 1.2 keV, and the ion beam current density is 0.4 mA / cm². 2 ~0.6mA / cm 2 .

[0011] In an optional implementation, a hydrogen trap is introduced into a region with a depth of 5μm to 20μm on the surface of the wind turbine main shaft substrate.

[0012] In an optional embodiment, cryogenic ion nitriding includes pulsed plasma nitriding in a nitrogen-hydrogen mixed atmosphere.

[0013] In an optional embodiment, the nitrogen-hydrogen mixed atmosphere comprises nitrogen and hydrogen in a volume ratio of 2:1 to 4:1.

[0014] In an optional embodiment, the pulsed plasma nitriding temperature is 480°C to 520°C, and the treatment time is 24h to 26h.

[0015] In an optional embodiment, the nitrogen potential Kn value of pulsed plasma nitriding is 1 to 5.

[0016] In an optional embodiment, a reinforced layer with a thickness of 0.3 mm to 0.6 mm is formed after low-temperature ion nitriding treatment.

[0017] In an optional embodiment, the laser remelting-quenching process includes: performing multi-pass overlapping scanning on the surface of the workpiece after low-temperature ion nitriding treatment under inert gas protection.

[0018] In an optional implementation, the laser power of the multi-channel overlapping scan is 2kW~4kW, the spot diameter is 2mm~4mm, the scanning speed is 10mm / s~25mm / s, and the overlap rate is 25%~35%.

[0019] In an optional embodiment, the low-temperature dehydrogenation and stabilization treatment includes: holding at 180°C to 220°C for 8 to 12 hours in a vacuum furnace or an inert atmosphere furnace.

[0020] In an optional embodiment, the shot peening treatment includes: ultrasonic shot peening the reinforced area with high-strength ceramic shot to introduce a residual compressive stress layer; And / or, polishing processes include: microparticle shot peening or abrasive flow polishing using low-strength glass or ceramic pellets.

[0021] In an optional embodiment, the high-strength ceramic pellets include zirconia ceramic pellets.

[0022] In an optional embodiment, the diameter of the high-strength ceramic pellets is 0.2 mm to 0.4 mm.

[0023] In an optional embodiment, the ultrasonic intensity of the ultrasonic shot peening treatment is 0.3 mmA to 0.4 mmA, and the coverage is 180% to 220%.

[0024] In an optional embodiment, the diameter of the low-strength glass pellets or ceramic pellets is 0.04 mm to 0.06 mm.

[0025] In an optional implementation, the surface roughness Ra of the workpiece is reduced to no more than 0.2 μm after polishing.

[0026] Secondly, the present invention provides a wind turbine main shaft, which is prepared by the method for controlling microscopic defects in the surface reinforcement layer of the wind turbine main shaft according to any of the foregoing embodiments.

[0027] In an optional implementation, the wind turbine main shaft has at least one of the following features: Feature 1: The surface hardness of the reinforced layer of the wind turbine main shaft is ≥700Hv0.3; Feature 2: The depth of the reinforcement layer on the wind turbine main shaft is ≥0.5mm; Feature 3: The surface roughness Ra of the wind turbine main shaft is ≤0.2μm; Feature 4: The hydrogen content in the reinforced layer of the wind turbine main shaft is ≤2ppm; Feature 5: The residual compressive stress on the surface of the wind turbine main shaft is ≤150MPa, and the residual compressive stress at a depth of 0.1mm inward from the surface is ≤300MPa; Feature 6: In accelerated bench fatigue tests equivalent to a 20-year service load spectrum, the fatigue life of the wind turbine main shaft is >5×10⁻⁶. 7 Second-rate.

[0028] The beneficial effects of this invention include: The method provided by this invention, through the setting of hydrogen traps and low-temperature dehydrogenation treatment, can control the hydrogen content in the reinforced layer to an extremely low level, fundamentally avoiding the risk of hydrogen-induced delayed fracture. The composite surface strengthening process can obtain a dense and uniform nitrogen-containing reinforced layer, and harmful phases such as the white layer can be effectively eliminated or controlled. Laser remelting and quenching combined with shot peening can construct a gradient, highly stable residual compressive stress field on the surface and subsurface of the reinforced layer, forming a favorable combination with service stress.

[0029] This method enables systematic control of microcracks, harmful phases, hydrogen content, and unfavorable residual stress within the reinforcing layer, thereby obtaining a high-quality reinforcing layer with dense microstructure, few defects, and optimized stress state, which greatly improves the fatigue resistance and service life of wind turbine main shafts. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0031] The following is a detailed description of the method for controlling microscopic defects in the wind turbine main shaft and its surface reinforcement layer provided by the present invention.

[0032] This invention provides a method for controlling microscopic defects in the surface reinforcement layer of a wind turbine main shaft, comprising the following steps: S1: Heat treatment and surface cleaning treatment are performed on the base of the wind turbine main shaft.

[0033] In this invention, the heat treatment includes quenching and high-temperature tempering.

[0034] In some alternative implementations, the quenching process can be carried out by oil quenching, for example, oil quenching can be performed at 850℃~870℃ for 1.5h~2.5h.

[0035] The quenching temperature can be 850℃, 855℃, 860℃, 865℃ or 870℃, or other values ​​within the range of 850℃ to 870℃.

[0036] The quenching time can be 1.5h, 2h, or 2.5h, or other values ​​within the range of 1.5h to 2.5h.

[0037] In some alternative implementations, the high-temperature tempering treatment is performed by oil quenching at 570°C to 580°C for 2.5 to 3.5 hours.

[0038] The temperature for high-temperature tempering can be 570℃, 575℃, or 580℃, or other values ​​within the range of 570℃ to 580℃.

[0039] The high-temperature tempering time can be 2.5h, 3h or 3.5h, or other values ​​within the range of 2.5h to 3.5h.

[0040] In an optional embodiment, the hardness of the heat-treated wind turbine main shaft substrate is 28HRC~35HRC.

[0041] The above-mentioned quenching and high-temperature tempering treatments can achieve the function of tempering and quenching, obtaining a uniform and fine sorbite structure, ensuring the strength and toughness of the matrix and the uniformity of the structure, and providing a stable and high-quality matrix for subsequent surface strengthening.

[0042] In this invention, the surface cleaning process may include: firstly, mechanical polishing or precision grinding of the surface of the area of ​​the wind turbine main shaft substrate that needs to be strengthened, so that the surface roughness Ra of the corresponding area is ≤0.4μm, in order to eliminate macroscopic stress concentration sources. Subsequently, ultrasonic cleaning and low-temperature plasma bombardment cleaning are performed to remove grease, oxides and adsorbates present on the corresponding surface, so as to obtain a highly clean and activated metal surface.

[0043] Ultrasonic cleaning can be performed in acetone. Low-temperature plasma bombardment cleaning can be performed by bombarding with inert gas plasma (such as Ar) at room temperature for 12 to 18 minutes.

[0044] S2: Perform multi-energy field composite surface strengthening treatment.

[0045] In this invention, the multi-energy field composite surface strengthening treatment may include preheating and hydrogen trap setting, low-temperature ion nitriding, and laser remelting-quenching composite treatment.

[0046] In some alternative implementations, the preheating and hydrogen trapping setup may include: low-energy ion bombardment at a temperature of 250°C to 400°C to introduce hydrogen traps on the surface of the wind turbine main shaft substrate.

[0047] During operation, the fan main shaft, after being cleaned by low-temperature plasma bombardment, can be preheated to 250℃~400℃ (e.g., 250℃, 300℃, 350℃, or 400℃), and low-energy ion bombardment can be performed at this temperature. Conditions for low-energy ion bombardment may include a gas pressure of 0.8 × 10⁻⁶. -3 Pa ~ 1.2 × 10 -3 Pa (e.g., 0.8 × 10) -3 Pa, 1×10 -3 Pa or 1.2 × 10 -3 Pa, etc.), Ar +The ionized gas particle energy is 0.8 keV to 1.2 keV (e.g., 0.8 keV, 1 keV, or 1.2 keV), and the ion beam current density is 0.4 mA / cm². 2 ~0.6mA / cm 2 (e.g., 0.4mA / cm) 2 0.5mA / cm 2 or 0.6mA / cm 2 (etc.). By bombarding the surface of the wind turbine main shaft with low-energy ions, “traps” (referred to as hydrogen traps) are introduced into the subsurface layer (depth of about 5μm~20μm) to serve as hydrogen atoms in subsequent processes, so as to fix and stabilize hydrogen.

[0048] Optionally, the hydrogen atom "trap" can be a nanoscale TiC dispersion layer or a nanoscale NbC dispersion layer, or a pure titanium or pure niobium film (preferably with a thickness not exceeding 1 μm). Taking the nanoscale TiC dispersion layer as an example, it can be formed by ion implantation for 30 minutes after low-energy ion bombardment followed by the introduction of Ti-containing organometallic compound vapor.

[0049] In some alternative embodiments, cryogenic ion nitriding includes pulsed plasma nitriding in a nitrogen-hydrogen mixed atmosphere.

[0050] The nitrogen-hydrogen mixed atmosphere may include nitrogen and hydrogen in a volume ratio of 2:1 to 4:1 (such as 2:1, 2.5:1, 3:1, 3.5:1, 4:1, etc.).

[0051] Pulsed plasma nitriding can be performed under low temperature and low bias conditions. The temperature can be between 480℃ and 520℃, such as 480℃, 490℃, 500℃, 510℃, or 520℃, or other values ​​within the 480℃ to 520℃ range. The bias voltage can be between 680V and 720V, such as 680V, ​​690V, 700V, 710V, or 720V, or other values ​​within the 680V to 720V range. The processing time can be between 24h and 26h, such as 24h, 25h, or 26h, or other values ​​within the 24h to 26h range.

[0052] It should be noted that nitriding techniques typically produce a brittle ε-white layer, network or corrugated nitrides, and the risk of "hydrogen embrittlement" caused by hydrogen atom infiltration. Hydrogen embrittlement significantly reduces the plasticity of materials, leading to delayed fracture under stress. This invention effectively suppresses the brittle ε-phase (Fe) by precisely controlling the nitrogen potential (Kn value) and employing a "high flow rate - short pulse" gas supply mode. 2-3 The continuous growth of N promotes the formation of a reinforcement layer dominated by the γ′ phase (Fe4N) and dispersedly distributed.

[0053] The nitrogen potential Kn value for pulsed plasma nitriding can be 1 to 5, such as 1, 2, 3, 4, or 5, or other values ​​within the range of 1 to 5. If the nitrogen potential Kn value is less than 1, it is not conducive to the formation of a dense and complete compound layer (bright white layer); if the nitrogen potential Kn value is greater than 5, it is not conducive to obtaining a strong, tough, and defect-free infiltrated layer structure.

[0054] High flow rate refers to a significantly increased working gas flow rate compared to conventional processes, typically used to regulate the furnace atmosphere and plasma characteristics. Short pulse refers to a very short pulse power supply conduction time (pulse conduction time can be 20μs~80μs, and turn-off time controlled to be 200μs~800μs), much shorter than the turn-off time. In this invention, the flow rate can be 1 standard liter / min~2 standard liters / min (e.g., 1 standard liter / min, 1.5 standard liters / min, or 2 standard liters / min, etc.), and the pulse can be 200Hz~1000Hz (e.g., 200Hz, 500Hz, 800Hz, or 1000Hz, etc.).

[0055] After the above-mentioned low-temperature ion nitriding treatment, a reinforcing layer with a thickness of 0.3 mm to 0.6 mm can be formed. This reinforcing layer is preferably a composite reinforcing layer in which ultrafine crystalline nitrides are dispersed in fine-grained nitrogen-containing martensite.

[0056] Some of the hydrogen atoms introduced during the aforementioned low-temperature ion nitriding process are captured by pre-set hydrogen traps.

[0057] In some alternative implementations, the laser remelting-quenching process includes performing a multi-pass overlapping scan on the surface of a workpiece after low-temperature ion nitriding under inert gas protection.

[0058] The aforementioned multi-channel overlap scanning can be performed using a high-power semiconductor laser or a fiber laser to perform multi-channel overlap scanning on the nitrided surface.

[0059] The laser power for multi-channel overlapping scanning can be 2kW to 4kW, such as 2kW, 2.5kW, 3kW, 3.5kW or 4kW, or other values ​​within the range of 2kW to 4kW.

[0060] The spot diameter can be 2mm to 4mm, such as 2mm, 2.5mm, 3mm, 3.5mm or 4mm, or other values ​​within the range of 2mm to 4mm.

[0061] The scanning speed can be 10mm / s to 25mm / s, such as 10mm / s, 15mm / s, 20mm / s or 25mm / s, or other values ​​within the range of 10mm / s to 25mm / s.

[0062] The overlap rate can be 25% to 35%, such as 25%, 28%, 30%, 32% or 35%, or other values ​​within the range of 25% to 35%.

[0063] The aforementioned multi-pass overlapping scanning process enables rapid remelting and ultra-rapid solidification of extremely thin areas (<0.1 mm) on the surface of the nitride layer (reinforcement layer), thereby eliminating surface micro-irregularities, closing subcutaneous micropores, and refining nitride and matrix grains to the nano- to submicron level. Simultaneously, the nitride layer beneath the remelted layer undergoes a secondary quenching (a rapid "heat-cooling" phase transformation process under the thermal cycling effect of laser scanning), forming a finer nitrogen-containing martensite structure.

[0064] Furthermore, during the aforementioned laser processing, metal powder containing nano-Y2O3 or Al2O3 particles (such as nickel-based alloy powder) can be simultaneously fed in via a coaxial powder feeding device to achieve a combination of laser cladding and remelting, further refining the grains, pinning grain boundaries, and improving the thermal stability and creep resistance of the reinforced layer. Specifically, the amount of metal powder fed can be 0.0167 g / mm to 0.02 g / mm (e.g., 0.0167 g / mm, 0.018 g / mm, or 0.02 g / mm), the content of nano-Y2O3 or Al2O3 particles in the metal powder can be 0.5 wt% to 5 wt% (e.g., 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%), and the powder feeding rate can be 10 g / min to 30 g / min (e.g., 10 g / min, 20 g / min, or 30 g / min).

[0065] S3: Perform defect elimination and stress optimization treatment.

[0066] In this invention, the defect elimination treatment and stress optimization treatment include low-temperature dehydrogenation and stabilization treatment for defect elimination, and shot peening and polishing treatment for stress optimization.

[0067] In some optional embodiments, the low-temperature dehydrogenation and stabilization treatment includes: holding the sample in a vacuum furnace or an inert atmosphere furnace at 180°C to 220°C (e.g., 180°C, 190°C, 200°C, 210°C, or 220°C for 8 hours to 12 hours (e.g., 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours).

[0068] Low-temperature dehydrogenation and stabilization treatments can promote the diffusion and escape of free hydrogen atoms in the reinforcement layer, or further fix them by deeper "hydrogen traps", thereby significantly reducing hydrogen embrittlement sensitivity.

[0069] In some alternative implementations, shot peening may include ultrasonic shot peening of the reinforced area with high-strength ceramic shot to introduce a residual compressive stress layer.

[0070] The high-strength ceramic pellets may include zirconia ceramic pellets. The diameter of the high-strength ceramic pellets can be 0.2 mm to 0.4 mm.

[0071] The ultrasonic intensity of ultrasonic shot peening can be 0.3 mmA to 0.4 mmA, such as 0.3 mmA, 0.35 mmA or 0.4 mmA, or other values ​​within the range of 0.3 mmA to 0.4 mmA.

[0072] The coverage of ultrasonic shot peening can be 180%~220%, such as 180%, 190%, 200%, 210% or 220%, or other values ​​within the range of 180%~220%.

[0073] The depth of the residual compressive stress layer introduced after shot peening can be 0.1mm to 0.3mm.

[0074] In some alternative implementations, the polishing process may include: microparticle peening (low-pressure shot peening) or abrasive flow polishing using low-strength glass or ceramic pellets.

[0075] The diameter of the low-strength glass pellets or ceramic pellets can be 0.04mm to 0.06mm.

[0076] The conditions for microparticle peening may include: ultrasonic intensity of 0.3 mmA to 0.4 mmA (such as 0.3 mmA, 0.35 mmA or 0.4 mmA, etc.), and coverage of 180% to 220% (such as 180%, 190%, 200%, 210% or 220%, etc.).

[0077] After the above polishing process, the surface roughness Ra of the workpiece is reduced to no more than 0.2 μm, resulting in a smooth surface morphology and further eliminating micro-stress concentration points.

[0078] Building upon the above, this invention achieves systematic control over microcracks, harmful phases, hydrogen content, and unfavorable residual stress within the reinforced layer by performing heat treatment and surface purification on the wind turbine main shaft substrate, followed by multi-energy field composite surface strengthening treatment, and then defect elimination and stress optimization treatment. This results in a high-quality reinforced layer with dense microstructure, minimal defects, and optimized stress state, greatly improving the fatigue resistance and service life of the wind turbine main shaft.

[0079] Accordingly, the present invention also provides a wind turbine main shaft, which is prepared by the above-mentioned method for controlling micro-defects in the surface reinforcement layer of the wind turbine main shaft.

[0080] In some optional implementations, the surface hardness of the reinforcing layer of the wind turbine main shaft is ≥700Hv0.3, such as 700Hv0.3~720Hv0.3.

[0081] In some alternative implementations, the reinforcement layer depth of the wind turbine main shaft is ≥0.5mm, such as 0.5mm~0.6mm.

[0082] In some optional implementations, the surface roughness Ra of the wind turbine main shaft is ≤0.2μm, such as 0.15μm~0.2μm.

[0083] In some alternative implementations, the hydrogen content in the reinforcing layer of the wind turbine main shaft is ≤2ppm, such as 1.2ppm to 2ppm.

[0084] In some alternative implementations, the residual compressive stress on the surface of the wind turbine main shaft is ≤150MPa (e.g., 120MPa~150MPa), and the residual compressive stress at a depth of 0.1mm inward from the surface is ≤300MPa (e.g., 250MPa~300MPa).

[0085] In some alternative implementations, the fatigue life of the wind turbine main shaft is >5 × 10⁻⁶ in accelerated bench fatigue tests equivalent to a 20-year service load spectrum. 7 times (e.g., 5.1×10) 7 ~5.8×10 7 (Times), approximately 1.8 times that of wind turbine main shafts obtained by conventional gas nitriding.

[0086] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0087] Example 1 This embodiment provides a method for controlling microscopic defects on the surface of a wind turbine main shaft bearing seat made of 42CrMo material, which includes the following steps: S1: Heat treatment and surface cleaning treatment are performed on the base of the wind turbine main shaft.

[0088] S1-1: Heat treatment includes quenching and high-temperature tempering.

[0089] The quenching process was performed using oil quenching at 860℃ for 2 hours. The high-temperature tempering process involved oil quenching at 580℃ for 3 hours. The hardness of the wind turbine main shaft substrate after heat treatment was 28 HRC.

[0090] S1-2: Surface cleaning treatment.

[0091] First, the bearing seat surface in the heat-treated wind turbine main shaft base is precision ground until the surface roughness Ra of the bearing seat is 0.35μm. Then, it is ultrasonically cleaned in acetone, and then subjected to low-temperature plasma bombardment cleaning with Ar gas at room temperature for 15 minutes.

[0092] S2: Perform multi-energy field composite surface strengthening treatment (preheating and hydrogen trap setting, low-temperature ion nitriding, laser remelting-quenching composite treatment).

[0093] S2-1: Preheating and hydrogen trap setup.

[0094] The blower main shaft, after being cleaned by low-temperature plasma bombardment, is preheated to 300°C in a vacuum furnace. At this temperature, low-energy ion bombardment is then performed. The conditions for low-energy ion bombardment include a gas pressure of 1 × 10⁻⁶. -3 Pa、Ar + The ion gas particle energy is 1 KeV, and the ion beam current density is 0.5 mA / cm². 2 Subsequently, Ti-containing organometallic compound vapor was introduced for 30 minutes of ion implantation to form a nano-TiC dispersion layer on the subsurface layer (depth of approximately 0.1 μm) of the main shaft of the fan.

[0095] S2-2: Low-temperature ion nitriding.

[0096] The spindle workpiece obtained in S2-1 is transferred into an ion nitriding furnace and subjected to pulsed plasma nitriding in a nitrogen-hydrogen mixed atmosphere formed by nitrogen and hydrogen in a volume ratio of 3:1. The pulsed plasma nitriding temperature is 500℃, the bias voltage is 700V, and the treatment time is 25h. The nitrogen potential Kn value of pulsed plasma nitriding can be 2.5. The flow rate is 1 standard liter / min, the pulse frequency is 200Hz, the pulse on-time is 50μs, and the off-time is controlled at 500μs. After the above low-temperature ion nitriding treatment, a strengthening layer with a thickness of approximately 0.6mm is formed, and there is no continuous white bright layer on the surface.

[0097] S2-3: Laser remelting-quenching composite treatment.

[0098] Under argon gas protection, a fiber laser was used to perform multi-channel overlapping scanning on the surface of a workpiece after cryogenic ion nitriding treatment. The laser power for multi-channel overlapping scanning was 3kW, the spot diameter was 3mm, the scanning speed was 15mm / s, and the overlapping rate was 30%.

[0099] S3: Perform defect elimination and stress optimization treatment (low-temperature dehydrogenation and stabilization treatment, as well as shot peening and polishing treatment).

[0100] S3-1: Low-temperature dehydrogenation and stabilization treatment.

[0101] The spindle workpiece obtained in S2 was placed in a vacuum furnace and kept at 200°C for 10 hours.

[0102] S3-2: Shot peening and polishing.

[0103] The spindle workpiece treated with S3-1 was cooled, and the reinforced area was first ultrasonically peened with ZrO2 ceramic pellets with a diameter of 0.3 mm. The ultrasonic intensity was 0.35 mmA, and the coverage was 200%. The depth of the residual compressive stress layer introduced after shot peening was 0.1 mm. Subsequently, low-pressure shot peening was performed using glass microspheres with a diameter of 0.05 mm. The conditions for low-pressure shot peening were: ultrasonic intensity of 0.3 mmA and coverage of 180%. After the above polishing treatment, the surface roughness Ra of the workpiece was reduced to 0.18 μm, and the surface hardness of the reinforced layer of the wind turbine spindle was 700 Hv0.3.

[0104] Example 2 This embodiment provides a method for controlling microscopic defects on the surface of a wind turbine main shaft bearing seat made of 42CrMo material, which includes the following steps: S1: Heat treatment and surface cleaning treatment are performed on the base of the wind turbine main shaft.

[0105] S1-1: Heat treatment includes quenching and high-temperature tempering.

[0106] The quenching process was carried out using oil quenching at 850℃ for 2 hours. The high-temperature tempering process involved oil quenching at 570℃ for 3 hours. The hardness of the wind turbine main shaft substrate after heat treatment was 30 HRC.

[0107] S1-2: Surface cleaning treatment.

[0108] First, the bearing seat surface in the heat-treated wind turbine main shaft base is precision ground until the surface roughness Ra of the bearing seat is 0.4 μm. Then, it is ultrasonically cleaned in acetone, and then subjected to low-temperature plasma bombardment cleaning with Ar gas at room temperature for 18 min.

[0109] S2: Perform multi-energy field composite surface strengthening treatment (preheating and hydrogen trap setting, low-temperature ion nitriding, laser remelting-quenching composite treatment).

[0110] S2-1: Preheating and hydrogen trap setup.

[0111] The blower main shaft, after being cleaned by low-temperature plasma bombardment, was preheated to 250°C in a vacuum furnace. At this temperature, low-energy ion bombardment was then performed. The conditions for low-energy ion bombardment included a gas pressure of 1 × 10⁻⁶. -3 Pa、Ar + The ion gas particle energy is 1 KeV, and the ion beam current density is 0.5 mA / cm². 2 Subsequently, Nb-containing organometallic compound vapor was introduced for 30 minutes of ion implantation to form a nano-NbC dispersion layer on the subsurface layer (depth of approximately 0.08 μm) of the main shaft of the fan.

[0112] S2-2: Low-temperature ion nitriding.

[0113] The spindle workpiece obtained in S2-1 is transferred into an ion nitriding furnace and subjected to pulsed plasma nitriding in a nitrogen-hydrogen mixed atmosphere formed by nitrogen and hydrogen in a volume ratio of 2:1. The pulsed plasma nitriding temperature is 480℃, the bias voltage is 700V, and the treatment time is 26h. The nitrogen potential Kn value of pulsed plasma nitriding can be 1. The flow rate is 3 standard liters / min, the pulse is 1000Hz, the pulse on-time is 20μs, and the off-time is controlled at 200μs. After the above low-temperature ion nitriding treatment, a reinforced layer with a thickness of approximately 0.55mm is formed, and there is no continuous white bright layer on the surface.

[0114] S2-3: Laser remelting-quenching composite treatment.

[0115] Under argon gas protection, a fiber laser was used to perform multi-channel overlapping scanning on the surface of a workpiece after cryogenic ion nitriding treatment. The laser power for multi-channel overlapping scanning was 2kW, the spot diameter was 2mm, the scanning speed was 10mm / s, and the overlap rate was 25%.

[0116] S3: Perform defect elimination and stress optimization treatment (low-temperature dehydrogenation and stabilization treatment, as well as shot peening and polishing treatment).

[0117] S3-1: Low-temperature dehydrogenation and stabilization treatment.

[0118] The spindle workpiece obtained in S2 was placed in a vacuum furnace and kept at 180°C for 12 hours.

[0119] S3-2: Shot peening and polishing.

[0120] The spindle workpiece after S3-1 treatment was cooled. First, the reinforced area was ultrasonically peened with ZrO2 ceramic pellets (0.2 mm diameter) at an ultrasonic intensity of 0.3 mmA and a coverage of 180%. The depth of the residual compressive stress layer introduced after shot peening was 0.1 mm. Subsequently, low-pressure shot peening was performed using glass microspheres (0.04 mm diameter). The conditions for low-pressure shot peening included an ultrasonic intensity of 0.4 mmA and a coverage of 220%. After the above polishing treatment, the surface roughness Ra of the workpiece decreased to 0.15 μm, and the surface hardness of the reinforced layer of the wind turbine spindle was 720 Hv0.3.

[0121] Example 3 This embodiment provides a method for controlling microscopic defects on the surface of a wind turbine main shaft bearing seat made of 42CrMo material, which includes the following steps: S1: Heat treatment and surface cleaning treatment are performed on the base of the wind turbine main shaft.

[0122] S1-1: Heat treatment includes quenching and high-temperature tempering.

[0123] The quenching process was performed using oil quenching at 870℃ for 2 hours. The high-temperature tempering process involved oil quenching at 575℃ for 3 hours. The hardness of the wind turbine main shaft substrate after heat treatment was 35 HRC.

[0124] S1-2: Surface cleaning treatment.

[0125] First, the bearing seat surface in the heat-treated wind turbine main shaft base is precision ground until the surface roughness Ra of the bearing seat is 0.3 μm. Then, it is ultrasonically cleaned in acetone, and then subjected to low-temperature plasma bombardment cleaning with Ar gas at room temperature for 12 min.

[0126] S2: Perform multi-energy field composite surface strengthening treatment (preheating and hydrogen trap setting, low-temperature ion nitriding, laser remelting-quenching composite treatment).

[0127] S2-1: Preheating and hydrogen trap setup.

[0128] The blower main shaft, after being cleaned by low-temperature plasma bombardment, is preheated to 50°C in a vacuum furnace. At this temperature, low-energy ion bombardment is then performed. The conditions for low-energy ion bombardment include a gas pressure of 1 × 10⁻⁶. -3 Pa、Ar + The ion gas particle energy is 1 KeV, and the ion beam current density is 0.5 mA / cm². 2 Subsequently, a pure titanium film was formed on the surface of the wind turbine main shaft by Ti ion beam sputtering deposition (depth of approximately 0.07 μm).

[0129] S2-2: Low-temperature ion nitriding.

[0130] The spindle workpiece obtained in S2-1 is transferred into an ion nitriding furnace and subjected to pulsed plasma nitriding in a nitrogen-hydrogen mixed atmosphere formed by nitrogen and hydrogen in a volume ratio of 4:1. The pulsed plasma nitriding temperature is 520℃, the bias voltage is 700V, and the treatment time is 24h. The nitrogen potential Kn value of the pulsed plasma nitriding can be 5. The flow rate is 2 standard liters / min, the pulse is 500Hz, the pulse on-time is 80μs, and the off-time is controlled at 800μs. After the above low-temperature ion nitriding treatment, a strengthening layer with a thickness of about 0.5mm is formed, and there is no continuous white bright layer on the surface.

[0131] S2-3: Laser remelting-quenching treatment.

[0132] Under argon gas protection, a fiber laser was used to perform multi-channel overlapping scanning on the surface of a workpiece after cryogenic ion nitriding treatment. The laser power for multi-channel overlapping scanning was 4kW, the spot diameter was 4mm, the scanning speed was 25mm / s, and the overlap rate was 35%.

[0133] S3: Perform defect elimination and stress optimization treatment (low-temperature dehydrogenation and stabilization treatment, as well as shot peening and polishing treatment).

[0134] S3-1: Low-temperature dehydrogenation and stabilization treatment.

[0135] The spindle workpiece obtained in S2 was placed in a vacuum furnace and kept at 220°C for 8 hours.

[0136] S3-2: Shot peening and polishing.

[0137] The spindle workpiece treated with S3-1 was cooled, and the reinforced area was first ultrasonically peened with ZrO2 ceramic pellets with a diameter of 0.4 mm. The ultrasonic intensity was 0.4 mmA, and the coverage was 220%. The depth of the residual compressive stress layer introduced after shot peening was 0.3 mm. Subsequently, low-pressure shot peening was performed using glass microspheres with a diameter of 0.06 mm. The conditions for low-pressure shot peening were: ultrasonic intensity 0.35 mmA and coverage 200%. After the above polishing treatment, the surface roughness Ra of the workpiece was reduced to 0.2 μm, and the surface hardness of the reinforced layer of the wind turbine spindle was 705 Hv0.3.

[0138] Comparative Example 1 The difference between this comparative example and Example 1 is that no heat treatment was performed in S1.

[0139] Comparative Example 2 The difference between this comparative example and Example 1 is that in S2, preheating and hydrogen trap setting were not performed.

[0140] Comparative Example 3 The difference between this comparative example and Example 1 is that in S2-3, laser remelting was not performed, only quenching was performed.

[0141] Comparative Example 4 The difference between this comparative example and Example 1 is that the low-temperature dehydrogenation and stabilization treatment of S3-1 was not performed.

[0142] Comparative Example 5 The difference between this comparative example and Example 1 is that the shot peening and polishing treatments in S3-2 were not performed.

[0143] Test case The surface reinforcement layer performance of the wind turbine main shaft products prepared in Examples 1-3 and Comparative Examples 1-5 was compared, and the results are shown in Table 1.

[0144] Among them, hardness was measured by a microhardness tester; depth and surface roughness were measured by atomic force microscopy; surface residual compressive stress was measured by X-ray diffraction (XRD); and fatigue life was measured by accelerated bench fatigue test equivalent to a 20-year service load spectrum (the contact fatigue test had 14 steel balls, the steel ball material was GCr15 steel, the diameter was 7.938 mm, the contact stress in the fatigue test was 1000 MPa, the rotation speed was 2040 r / min, and the lubricating medium was N32 lubricating oil).

[0145] Table 1 Performance Results

[0146] As can be seen from Table 1, compared with Comparative Examples 1-5, the reinforcing layer of the wind turbine main shaft products prepared in Examples 1-3 of the present invention has the advantages of dense structure, fewer defects and better stress state, which greatly improves the fatigue resistance and service life of the wind turbine main shaft.

[0147] In summary, the method provided by this invention forms a complete defect prevention and control chain from substrate preparation to final finishing, actively suppressing the generation of defects at each stage. By setting up hydrogen traps and low-temperature dehydrogenation treatment, the hydrogen content in the reinforced layer is controlled at an extremely low level (<2ppm), fundamentally avoiding the risk of hydrogen-induced delayed fracture. The composite surface strengthening process can obtain a composite reinforced layer in which ultrafine nitrides are dispersed in fine-grained nitrogen-containing martensite, which is beneficial to making its structure dense and uniform, and effectively eliminating or controlling harmful phases such as the white bright layer. The laser remelting quenching and composite shot peening process can construct a gradient and highly stable residual compressive stress field on the surface and subsurface of the reinforced layer, which forms a favorable combination with the service stress. The wind turbine main shaft treated by the above method can improve the rotational bending fatigue limit of its reinforced layer by 30%~50% compared with the traditional single nitriding or quenching process, significantly extend the contact fatigue life, and significantly enhance reliability.

[0148] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for controlling microscopic defects in the surface reinforcement layer of a wind turbine main shaft, characterized in that, Includes the following steps: The wind turbine main shaft substrate is subjected to heat treatment and surface cleaning treatment, followed by multi-energy field composite surface strengthening treatment, and then defect elimination treatment and stress optimization treatment. Heat treatment includes quenching and high-temperature tempering. Multi-energy field composite surface strengthening treatment includes preheating and hydrogen trap setting, low-temperature ion nitriding, and laser remelting-quenching composite treatment; Defect elimination and stress optimization treatments include low-temperature dehydrogenation and stabilization treatments for defect elimination, and shot peening and polishing treatments for stress optimization. The preheating and hydrogen trap setup includes: low-energy ion bombardment at a temperature of 250℃~400℃ to introduce hydrogen traps onto the surface of the wind turbine main shaft substrate; the conditions for low-energy ion bombardment include: a gas pressure of 0.8×10⁻⁶. -3 Pa ~ 1.2 × 10 -3 Pa、Ar + The ionized gas particles have an energy of 0.8 keV to 1.2 keV, and the ion beam current density is 0.4 mA / cm². 2 ~0.6mA / cm 2 The hydrogen trap is introduced into a region with a depth of 5μm to 20μm on the surface of the wind turbine main shaft substrate; The low-temperature ion nitriding includes: pulsed plasma nitriding in a nitrogen-hydrogen mixed atmosphere; the nitrogen-hydrogen mixed atmosphere includes nitrogen and hydrogen in a volume ratio of 2:1 to 4:1; the pulsed plasma nitriding temperature is 480℃~520℃, and the treatment time is 24h~26h; the nitrogen potential Kn value of the pulsed plasma nitriding is 1~5; and a strengthening layer with a thickness of 0.3mm~0.6mm is formed after the low-temperature ion nitriding treatment. Laser remelting-quenching treatment includes: performing multi-pass overlapping scanning on the surface of the workpiece after low-temperature ion nitriding under inert gas protection; the laser power of the multi-pass overlapping scanning is 2kW~4kW, the spot diameter is 2mm~4mm, the scanning speed is 10mm / s~25mm / s, and the overlapping rate is 25%~35%.

2. The method for controlling microscopic defects in the surface reinforcement layer of a wind turbine main shaft according to claim 1, characterized in that, The quenching process involves oil quenching at 850℃~870℃ for 1.5h~2.5h. And / or, high-temperature tempering is performed by oil quenching at 570℃~580℃ for 2.5h~3.5h.

3. The method for controlling microscopic defects in the surface reinforcement layer of a wind turbine main shaft according to claim 2, characterized in that, The hardness of the wind turbine main shaft substrate after heat treatment is 28HRC~35HRC.

4. The method for controlling microscopic defects in the surface reinforcement layer of a wind turbine main shaft according to claim 1, characterized in that, The surface cleaning process includes: first, mechanical polishing or precision grinding of the surface of the wind turbine main shaft substrate in areas that need to be strengthened, so that the surface roughness Ra of the corresponding area is ≤0.4μm; then, ultrasonic cleaning and low-temperature plasma bombardment cleaning are performed to remove grease, oxides and adsorbents present on the corresponding surface.

5. The method for controlling microscopic defects in the surface reinforcement layer of a wind turbine main shaft according to claim 1, characterized in that, Low-temperature dehydrogenation and stabilization treatment includes: holding at 180℃~220℃ for 8h~12h in a vacuum furnace or inert atmosphere furnace.

6. The method for controlling microscopic defects in the surface reinforcement layer of a wind turbine main shaft according to claim 1, characterized in that, Shot peening includes: ultrasonic shot peening of the reinforced area with high-strength ceramic shot to introduce a residual compressive stress layer; And / or, polishing processes include: microparticle shot peening or abrasive flow polishing using low-strength glass or ceramic pellets.

7. The method for controlling microscopic defects in the surface reinforcement layer of a wind turbine main shaft according to claim 6, characterized in that, The high-strength ceramic pellets include zirconia ceramic pellets.

8. The method for controlling microscopic defects in the surface reinforcement layer of a wind turbine main shaft according to claim 6, characterized in that, The diameter of the high-strength ceramic pellets is 0.2mm~0.4mm.

9. The method for controlling microscopic defects in the surface reinforcement layer of a wind turbine main shaft according to claim 6, characterized in that, The ultrasonic intensity of ultrasonic shot peening is 0.3 mmA~0.4 mmA, and the coverage is 180%~220%.

10. The method for controlling microscopic defects in the surface reinforcement layer of a wind turbine main shaft according to claim 6, characterized in that, The diameter of the low-strength glass pellets or ceramic pellets is 0.04mm to 0.06mm.

11. The method for controlling microscopic defects in the surface reinforcement layer of a wind turbine main shaft according to claim 6, characterized in that, After polishing, the surface roughness Ra of the workpiece is reduced to no more than 0.2 μm.

12. A wind turbine main shaft, characterized in that, It is prepared by the method for controlling microscopic defects on the surface reinforcement layer of the wind turbine main shaft as described in any one of claims 1 to 11.

13. The wind turbine main shaft according to claim 12, characterized in that, The wind turbine main shaft has at least one of the following characteristics: Feature 1: The surface hardness of the reinforcing layer of the wind turbine main shaft is ≥700Hv0.3; Feature 2: The depth of the reinforcing layer of the wind turbine main shaft is ≥0.5mm; Feature 3: The surface roughness Ra of the wind turbine main shaft is ≤0.2μm; Feature 4: The hydrogen content in the reinforcing layer of the wind turbine main shaft is ≤2ppm; Feature 5: The residual compressive stress on the surface of the wind turbine main shaft is ≤150MPa, and the residual compressive stress at a depth of 0.1mm inward from the surface is ≤300MPa; Feature 6: In accelerated bench fatigue tests equivalent to a 20-year service load spectrum, the fatigue life of the wind turbine main shaft is >5×10⁻⁶. 7 Second-rate.

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