Material for harmonic reducer flexible gear and blank machining method

Abstract

The invention discloses a material for a harmonic reducer flexible gear and a blank machining method. The material for the harmonic reducer flexible gear comprises 0.3 wt% to 0.5 wt% of manganese, 0.03 wt% to 0.1 wt% of titanium, 0.05 wt% to 0.15 wt% of niobium, 0.002 wt% to 0.01 wt% of boron, 0.02 wt% to 0.08 wt% of cerium and 0.01 wt% to 0.03 wt% of magnesium. According to the machining method, an integrated manufacturing route of powder electrostatic purification, MIM near-net forming, hot isostatic pressing densification and local strengthening and heat treatment is adopted, the inclusion content is controlled from the source, the material utilization rate and compactness are improved, targeted strengthening is conducted on stress concentration parts, and overall toughness, local ultrahigh strength and abrasion resistance are considered. According to the scheme, the fatigue life of the flexible gear is remarkably prolonged, the comprehensive performance of the flexible gear is remarkably improved, the material utilization rate is greatly increased, the machining procedure is simplified, the machining efficiency is improved, and the production cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of harmonic reducer technology, and in particular to a material and blank processing method for a harmonic reducer flexspline. Background Technology

[0002] As a core component of high-precision mechanical transmission systems, the mechanical properties and fatigue life of the flexible wheel in a harmonic reducer directly affect the transmission accuracy, operational stability, and fatigue life of the entire machine. Currently, flexible wheels are mostly manufactured by forging 40CrNiMoA medium-carbon alloy steel bars. This process has several inherent defects that restrict further improvement in the performance of the flexible wheel. First, although the steel undergoes purification treatment during smelting, it is still difficult to completely avoid the residue of brittle inclusions such as Al2O3. These inclusions are prone to becoming initiation sources of fatigue cracks under cyclic loading, significantly reducing the fatigue performance of the flexible wheel. Second, traditional smelting and solidification processes easily lead to uneven distribution of alloying elements, resulting in compositional segregation and inconsistencies in the overall microstructure and properties of the material. Third, during forging, uneven deformation easily leads to uneven distribution of the internal microstructure (such as grain size and texture) of the billet; at the same time, during subsequent overall heat treatment, the uneven temperature field of the heating equipment often causes abnormal grain growth, with grain sizes typically exceeding 20μm. Coarse grains not only reduce the fatigue resistance of materials but also weaken their overall mechanical properties. Furthermore, existing processes typically use bar stock as the starting material, requiring multiple processing steps such as forging, quenching, turning, and gear hobbing, resulting in lengthy processes, long processing cycles, and low manufacturing efficiency. Due to the complex structure and thin-walled nature of flexible gears, material utilization is generally less than 5%, leading to significant resource waste.

[0003] Several improvement schemes have been proposed to address the above-mentioned technical problems, but all of them have limitations:

[0004] Chinese patent CN112359187A discloses a flexible wheel material and its heat treatment process. Through processes such as homogenization annealing, multi-directional forging, double normalizing, cyclic isothermal annealing, rapid cyclic quenching, and stress-relief annealing, it can refine grain size, eliminate substrate defects, refine carbide size, achieve a supercrystalline structure, and improve the material's impact and fatigue properties. However, this method does not effectively solve the problems of controlling inclusions in raw materials and the unevenness of steel microstructure and properties, and it still relies on traditional forging processes, resulting in low material utilization and high process complexity.

[0005] Chinese patent CN119243031A discloses a fine-grained, high-purity steel for the flexible wheel of a harmonic reducer in an industrial robot and its preparation method. The chemical composition and mass percentage of this steel are as follows: C: 0.38–0.42%, Si: 0.20–0.30%, Mn: 0.60–0.90%, P≤0.015%, S≤0.010%, Cr: 0.60–0.90%, Mo: 0.15–0.25%, Ni: 1.50–1.80%, Nb: 0.015–0.035%, O≤0.0006%, with the remainder being iron and unavoidable impurities. The preparation method includes: vacuum induction furnace smelting, electroslag remelting, billet forging, bar heating, bar rolling, and rolled product cooling. This method uses electroslag remelting, which has limited effect on controlling inclusions and results in low material utilization.

[0006] Chinese patent CN202411147038 discloses a MIM (Metal Injection Molding) process for a harmonic reducer flexure. This process uses metal powder injection molding, involving mixing alloy powder with a binder, granulation, injection molding, debinding the blank, atmospheric sintering, solution treatment, and rapid cooling to achieve integrated molding of the harmonic reducer flexure. However, this method does not address alloy composition adjustment and lacks control over powder purity. These unfavorable factors, along with residual porosity from atmospheric sintering, can accelerate flexure failure. Furthermore, the overall solution treatment and rapid cooling easily introduce thermal stress, reducing component lifespan.

[0007] Chinese patent CN201610404515 discloses a material for flexible wheels and a method for preparing flexible wheels. The material is composed of 72-84 parts of low-carbon steel water-atomized iron powder, 6-10 parts of graphene, 3-5 parts of nano-silicon carbide, 6-10 parts of polyamide-imide, and 1-3 parts of coupling agent. The powder is placed in a mixer and mixed at 80-120 rpm for at least 6 hours. Then, it is ball-milled in a vacuum ball mill, and subsequently melted into an alloy broth in a crucible of a vacuum solidification furnace under inert gas protection. Finally, the broth is poured into a flexible wheel mold, cooled and shaped, then die-cast and extruded, followed by heat treatment and annealing. Flexible wheels produced by this method have many material impurities, are intrinsically cast, are prone to segregation, and exhibit poor performance.

[0008] Chinese patent CN202010789581 discloses a high-entropy alloy for manufacturing flexible wheels and a processing method for the flexible wheels. The high-entropy alloy is FeCoCrNiMo with an FCC-type single-phase solid solution structure. 0.2 C 0.1 High-entropy alloys. This composition incorporates large amounts of elements such as Co, Cr, Ni, and Mo, resulting in high raw material costs and hindering large-scale application.

[0009] In summary, existing technologies still have significant shortcomings in terms of the cleanliness of flexible wheel materials, grain refinement, molding efficiency, and cost control, and have not yet provided a comprehensive solution that balances high performance, high reliability, high material utilization, and low cost. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a material and a method for processing a flexible wheel for a harmonic reducer, in view of the above-mentioned defects of the prior art.

[0011] To achieve the above objectives, in a first aspect, the present invention provides a material for the flexible gear of a harmonic reducer, comprising, by mass percentage: 0.36–0.43% carbon, 0.15–0.35% silicon, 0.3–0.5% manganese, 0–0.03% phosphorus, 0.01–0.03% sulfur, 1.6–2.0% nickel, 0.6–1.0% chromium, 0.15–0.3% molybdenum, 0–0.3% copper, 0.03–0.1% titanium, 0.05–0.15% niobium, 0.002–0.01% boron, 0.02–0.08% cerium, and 0.01–0.03% magnesium, with the balance being iron and unavoidable impurities.

[0012] Secondly, the present invention provides a method for processing a flexure blank for a harmonic reducer, characterized in that the method includes the following steps:

[0013] Step S1: Prepare master alloy powder, wherein the master alloy powder comprises, by mass percentage: carbon 0.36-0.43%, silicon 0.15-0.35%, manganese 0.3-0.5%, phosphorus 0-0.03%, sulfur 0.01-0.03%, nickel 1.6-2.0%, chromium 0.6-1.0%, molybdenum 0.15-0.3%, copper 0-0.3%, titanium 0.03-0.1%, niobium 0.05-0.15%, boron 0.002-0.01%, cerium 0.02-0.08%, magnesium 0.01-0.03%, with the balance being iron and unavoidable impurities;

[0014] Step S2: Remove oxide inclusions from the master alloy powder by electrostatic separation to obtain purified powder;

[0015] Step S3: The purified powder and binder are mixed and injected into a flexible wheel preform by metal injection molding process. The thickness of the flexible wheel preform is 2-3.5 mm. After degreasing treatment, a flexible wheel blank is obtained.

[0016] Step S4: The flexible wheel blank is subjected to hot isostatic pressing densification treatment to obtain the flexible wheel blank.

[0017] Step S5: Perform local rolling on the toothed ring and its transition part, and the cup bottom transition area of ​​the flexible wheel blank;

[0018] Step S6: The toothed ring and its transition part and the cup bottom transition area of ​​the flexible wheel blank are rapidly heated to 800-850°C and then rapidly cooled.

[0019] Step S7: Perform overall homogenization tempering treatment on the flexible wheel blank.

[0020] In the method for processing the flexspline blank of the harmonic reducer of the present invention, step S1 includes:

[0021] Step S101: Prepare the required alloys for each component of industrial pure iron, electrolytic nickel plate and master alloy powder, and crush the block raw materials to uniform size.

[0022] Step S102: Put industrial pure iron and electrolytic nickel plates into the bottom of the crucible, put Fe-Cr and Fe-Mo master alloys into the middle layer, and put Fe-C, Fe-Si and Fe-Mn master alloys into the top layer.

[0023] Step S103: Repeatedly evacuate and fill with inert gas to stabilize the vacuum level inside the furnace within the preset pressure threshold.

[0024] Step S104: The furnace charge is completely melted by slowly increasing the power.

[0025] Step S105: Refining and degassing the molten furnace charge to obtain molten steel;

[0026] Step S106: The temperature of the molten steel is reduced to 1520-1540℃, and Fe-Ti and Fe-Nb master alloys are added through the feeding hopper, followed by electromagnetic stirring.

[0027] Step S107: Continue to lower the temperature of the molten steel to 1480-1500℃, add Fe-B master alloy, and then perform electromagnetic stirring.

[0028] Step S108: Control the temperature of the molten steel within the range of 1460 to 1480°C, add Ce-Fe alloy, and then perform static and electromagnetic stirring treatments in sequence.

[0029] Step S109: Adjust the temperature of the molten steel to 1440-1460℃, add Ni-Mg alloy, and then perform electromagnetic stirring.

[0030] In step S110, add 0.05-0.08 wt% of Ca-Si alloy, control the temperature at 1420-1440℃, and then perform electromagnetic stirring to ensure sufficient deoxidation.

[0031] Step S111: The temperature of the molten steel is lowered to 1400-1420℃, and electromagnetic stirring and settling are performed in sequence to obtain molten steel with uniform composition distribution.

[0032] Step S112: Adjust the temperature of the molten steel to 150-200°C above the liquidus line;

[0033] Step S113: Start the atomization system to perform powder production.

[0034] In the method for processing the flexure blank of the harmonic reducer of the present invention, step S2 includes:

[0035] Step S201: The raw powder obtained by atomization is sieved and classified, and powder with a particle size range of 15-53 μm is taken and dried. Then, a surface modifier is added to the powder to optimize the difference in conductivity.

[0036] Step S202: Start the ventilation system to maintain a slightly negative pressure environment, start the drum drive motor to reach the set speed, turn on the high voltage power supply, slowly increase the voltage to the set value, start the vibrating feeder, so that the powder falls evenly into the sorting area for sorting and processing to obtain purified powder.

[0037] In the method for processing the flexure blank of the harmonic reducer of the present invention, step S3 includes:

[0038] Step S301: The purified powder and binder are mixed and then cooled before being crushed.

[0039] Step S302: The pulverized feed material is formed into a flexible preform in an injection molding die;

[0040] Step S303: The flexible wheel blank is placed in a hydrocarbon cleaning agent at a temperature of 50-60°C for solvent degreasing treatment;

[0041] Step S304: Perform hot degreasing treatment on the flexible wheel green blank after step S303.

[0042] In the method for processing the flexible wheel blank of the harmonic reducer of the present invention, in step S301, the volume ratio of the purified powder to the binder is 80:20 to 90:10, the mixing temperature is 160 to 180°C, and the mixing time is 2 to 5 hours.

[0043] In the method for processing the flexspline blank of the harmonic reducer of the present invention, step S304 includes:

[0044] Keep warm at 180–250℃ for 1–4 hours;

[0045] Keep warm at 550-600℃ for 1-2 hours.

[0046] In the method for processing the flexure blank of the harmonic reducer of the present invention, the specific method of step S4 is as follows:

[0047] The flexible wheel blank is placed in a hot isostatic pressing furnace for densification treatment to obtain a flexible wheel blank. The hot isostatic pressing temperature is 1120-1300℃, the atmosphere pressure is 100-120MPa, the holding time is 2-3h, and argon protection is used.

[0048] The present invention has the following beneficial effects: By controlling the Mn content in the ultra-low range of 0.3-0.5% and supplementing it with elements such as Ni and Mo, the present invention greatly reduces the temper brittleness sensitivity of the material while ensuring necessary hardenability, providing extremely high toughness reserves for the flexible wheel. The use of Ti and Nb to form nanoscale composite carbides and B to form Fe2B, together pinning grain boundaries, achieves ultra-fine grains; simultaneously, the introduction of Ce and Mg transforms brittle Al2O3 inclusions into more tough Ce2O3 and MgAl2O4, significantly reducing the detrimental effects of inclusions on fatigue performance. This invention employs an integrated manufacturing route of "powder electrostatic purification + MIM near-net-shape forming + hot isostatic pressing densification + localized strengthening and heat treatment." Specifically: electrostatic sorting provides high-purity pretreatment of the MIM powder, controlling inclusions at the source; MIM technology is used to integrally form complex thin-walled flexible wheel blanks, achieving a material utilization rate of over 85%, overcoming the limitations of traditional forging and machining; hot isostatic pressing completely closes residual pores within the material, achieving near-complete densification; and innovatively, localized strengthening and localized high-frequency quenching are used to specifically strengthen the gear ring and its transition areas and cup bottom transition zone, which suffer from severe stress concentration, replacing traditional integral quenching and balancing overall toughness with localized ultra-high strength / wear resistance. This invention effectively refines grain size, reduces the number and size of inclusions, improves inclusion types, and enhances the uniformity of microstructure and properties, thereby significantly improving the fatigue life and overall performance of the flexible wheel. Furthermore, it greatly improves material utilization, simplifies processing steps, increases processing efficiency, and reduces production costs, making it suitable for large-scale promotion. Attached Figure Description

[0049] The accompanying drawings, which are provided to further illustrate the invention and constitute a part of this invention, are illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention.

[0050] Figure 1 This is a schematic diagram illustrating the steps of a harmonic reducer flexure blank processing method provided in an embodiment of the present invention.

[0051] Figure 2 This is a schematic diagram of the grain morphology of the flexible wheel blank under a metallographic microscope, provided in an embodiment of the present invention.

[0052] Figure 3 This is a schematic diagram of inclusions in a flexible wheel blank provided in an embodiment of the present invention under a metallographic microscope. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] The embodiments of the present invention will now be described in further detail with reference to the accompanying drawings. It should be understood that the embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0055] This invention provides a material for the flexible gear of a harmonic reducer, comprising, by mass percentage: 0.36–0.43% carbon, 0.15–0.35% silicon, 0.3–0.5% manganese, 0–0.03% phosphorus, 0.01–0.03% sulfur, 1.6–2.0% nickel, 0.6–1.0% chromium, 0.15–0.3% molybdenum, 0–0.3% copper, 0.03–0.1% titanium, 0.05–0.15% niobium, 0.002–0.01% boron, 0.02–0.08% cerium, and 0.01–0.03% magnesium, with the balance being iron and unavoidable impurities.

[0056] The basic components of the aforementioned flexible gear material include: 0.36–0.43% carbon, 0.15–0.35% silicon, 0.3–0.5% manganese, 0–0.03% phosphorus, 0.01–0.03% sulfur, 1.6–2.0% nickel, 0.6–1.0% chromium, 0.15–0.3% molybdenum, 0–0.3% copper, iron, and unavoidable impurities; grain refiners include 0.03–0.1% titanium, 0.05–0.15% niobium, and 0.002–0.01% boron, belonging to a composite strengthening phase composition design; inclusion modification components include 0.02–0.08% cerium and 0.01–0.03% magnesium.

[0057] Carbon is the core strengthening element and the most critical element to ensure the hardenability of the material and obtain high strength and high hardness. The content range of 0.36 to 0.43 wt% ensures that the material can obtain a tempered troostite structure with excellent comprehensive properties through heat treatment (quenching + tempering), which provides the basis for the load-bearing capacity and fatigue resistance of the flexible wheel.

[0058] Silicon is a solid solution strengthening element with beneficial effects. When dissolved in ferrite, silicon can increase strength; at the same time, it can suppress temper brittleness, but its content should not be too high to avoid impairing toughness and cold workability.

[0059] Manganese can significantly improve hardenability. In existing technologies, flexible wheel blanks need to be forged and tempered as a whole. To prevent deformation, the thickness of the flexible wheel blank is generally large (typically 5-8 mm). To ensure that the entire cross-section can be hardened through in subsequent quenching to obtain a uniform microstructure, the manganese content is usually required to be between 0.6% and 0.9%. However, manganese is an element that reduces the grain boundary cohesion of steel. It will synergistically segregate with the unavoidable trace impurity elements in the system, and co-enrich on the austenite grain boundaries. This segregation significantly aggravates the temper brittleness of steel, causing a sharp decrease in impact toughness and making it brittle. To reduce temper brittleness, the technical solution of this invention innovatively combines subsequent metal injection molding and local heat treatment to control the thickness of the flexible wheel blank within the range of ≤3.5 mm, breaking through the requirement of Mn content greater than 0.6% in existing technical solutions due to hardenability. In the solution of this invention, the designed manganese content is 0.3-0.5 wt% to meet the combined effect of hardenability and reduced temper brittleness.

[0060] Phosphorus is a harmful impurity that needs to be strictly controlled. Phosphorus can cause brittleness and reduce low-temperature toughness; keeping it at extremely low levels is a prerequisite for ensuring high fatigue performance.

[0061] Sulfur is a trace and harmful impurity that needs to be strictly controlled. Excessive sulfur can form sulfide inclusions, which become fatigue crack initiation points and severely impair the fatigue life of materials. However, the presence of trace amounts of sulfur is beneficial to improving machinability. In the present invention, the sulfur content is controlled at 0.01-0.03 wt%.

[0062] Nickel is an element that enhances toughness and hardenability. It is an excellent toughening element, significantly improving the low-temperature impact toughness and fracture toughness of materials, which is crucial for flexible wheels subjected to cyclic bending stresses, preventing brittle fracture. Simultaneously, nickel can also help improve hardenability.

[0063] Chromium is an element that provides hardenability, wear resistance, and corrosion resistance. Chromium forms carbides, improving hardenability, strength, and hardness. At the same time, chromium can improve the surface wear resistance of steel and provide a certain degree of corrosion resistance.

[0064] Molybdenum can prevent temper brittleness and enhance hardenability. Molybdenum can very effectively suppress the embrittlement phenomenon (temper brittleness) that occurs in alloy steels during tempering, especially in the range of 350-575℃, ensuring that the material maintains good toughness while obtaining high strength. Molybdenum can also help improve hardenability.

[0065] Copper is a residual element with some beneficial effects. Copper is usually controlled as a residual element, but small amounts of copper can improve atmospheric corrosion resistance and have a certain solid solution strengthening effect. However, excessive amounts may cause problems with hot working.

[0066] The unavoidable impurities include trace elements introduced from raw materials and the smelting process, such as O, N, H, etc., and their total content should be less than 0.1 wt%.

[0067] In this embodiment of the invention, 0.03-0.1 wt% titanium and 0.05-0.15 wt% niobium form titanium-niobium composite carbides with a particle size of 50-200 nm. Their main function is to pin grain boundaries and inhibit grain growth. In synergistic control, 0.002-0.01% boron is added together to combine with iron in the basic component system to form Fe2B distributed along the grain boundaries, further controlling grain growth.

[0068] In this embodiment of the invention, inclusion modification is achieved by introducing 0.02-0.08 wt% Ce and 0.01-0.03 wt% Mg. In the steel used for the flexible wheel of a harmonic reducer, Al2O3, with its sharp-angled shape, is the most destructive inclusion and should therefore be avoided at all costs. However, even with the most thorough purification techniques in the prior art, at least some fine-grained alumina inclusions are still unavoidable. In this embodiment of the invention, inclusion modification is achieved by introducing 0.02-0.08 wt% Ce and 0.01-0.03 wt% Mg, and then, during the subsequent smelting process, through the following reaction: Ce preferentially captures oxygen to form the Ce2O3 phase, replacing the brittle Al2O3; the remaining Mg combines with Al to form MgAl2O4, reducing the amount of Al2O3.

[0069] The material for the flexible wheel of the harmonic reducer provided by this invention has been improved from three aspects: basic composition design, composite reinforcing phase composition design, and inclusion modification composition design. Regarding the basic composition, a low-manganese, high-toughness alloy design based on MIM thin-wall forming technology is adopted. By controlling the Mn content to an ultra-low range of 0.3–0.5 wt%, and supplementing it with elements such as Ni and Mo, the temper brittleness sensitivity of the material is greatly reduced while ensuring necessary hardenability, providing the flexible wheel with extremely high toughness reserves. In terms of composite reinforcing phase composition design, Ti and Nb are used to form nanoscale composite carbides, and B forms Fe2B, jointly pinning grain boundaries to achieve ultra-fine grains. Simultaneously, Ce and Mg are introduced to transform brittle Al2O3 inclusions into more tough Ce2O3 and MgAl2O4, significantly reducing the detrimental effects of inclusions on fatigue performance.

[0070] like Figure 1 As shown in the figure, an embodiment of the present invention provides a method for processing a flexspline blank for a harmonic reducer, the method comprising the following steps:

[0071] Step S1: Prepare master alloy powder, wherein the master alloy powder comprises, by mass percentage: 0.36-0.43% carbon, 0.15-0.35% silicon, 0.3-0.5% manganese, 0-0.03% phosphorus, 0.01-0.03% sulfur, 1.6-2.0% nickel, 0.6-1.0% chromium, 0.15-0.3% molybdenum, 0-0.3% copper, 0.03-0.1% titanium, 0.05-0.15% niobium, 0.002-0.01% boron, 0.02-0.08% cerium, 0.01-0.03% magnesium, with the balance being iron and unavoidable impurities.

[0072] In this embodiment of the invention, the powder is smelted according to the designed composition in a vacuum induction melting-vacuum atomization integrated powder forming furnace, and then atomized into powder using inert gas. Step S1 includes:

[0073] Step S101: Prepare the required alloys for each component of industrial pure iron, electrolytic nickel plate, and master alloy powder, and crush the block raw materials to a uniform size. In this embodiment of the invention, industrial pure iron with a C content ≤0.01wt%, S content ≤0.005wt%, and P content ≤0.005wt% is selected as the base material. Intermediate alloys such as Fe-C, Fe-Si, Fe-Mn, Fe-Cr, Fe-Mo, and Fe-Ni are prepared. Pure metal raw materials such as electrolytic nickel plate and metallic chromium blocks are prepared. Trace element additives such as Fe-Ti, Fe-Nb, Fe-B, and Ce-Mg alloys are prepared. All raw materials are vacuum dried at 150–200℃ for 2 hours, and the block raw materials are crushed to a uniform size of 20–50 mm.

[0074] Step S102: Put industrial pure iron and electrolytic nickel plates into the bottom of the crucible, put Fe-Cr and Fe-Mo master alloys into the middle layer, and put Fe-C, Fe-Si and Fe-Mn master alloys into the top layer.

[0075] Step S103 involves repeatedly evacuating and filling the furnace with inert gas to stabilize the vacuum level within a preset pressure threshold. In some embodiments of the present invention, the vacuum system is activated to evacuate the furnace pressure to 5 × 10⁻² Pa, and then high-purity argon is introduced until the furnace pressure reaches 5000 Pa. This evacuation-argon filling process is repeated 2-3 times until the furnace vacuum level is finally stabilized at 1 × 10⁻² Pa. 2 Within Pa.

[0076] Step S104: The furnace charge is completely melted by slowly increasing the power. In this embodiment of the invention, the furnace charge is heated to 1550±10℃ uniformly within 30 minutes by slowly increasing the power, and then held at this temperature for 10 to 15 minutes to ensure that the furnace charge is completely melted.

[0077] Step S105 involves refining and degassing the molten furnace charge to obtain molten steel. In this embodiment of the invention, after melting and cleaning, the temperature is raised to 1580–1600°C, the vacuum degree is maintained at ≤5×10⁻²Pa, the refining time is 20–30 minutes, and the electromagnetic stirring system is turned on with a frequency of 0.5–1.0Hz, using an intermittent stirring mode.

[0078] In this embodiment of the invention, between step S105 and step S106, the following steps are usually included: extracting a steel molten sample using a vacuum sampler, performing rapid spectral analysis to determine the content of each element, adjusting the content of elements such as C, Si, and Mn according to the analysis results, and continuing refining for 10 to 15 minutes after adjustment to ensure uniform composition.

[0079] In step S106, the temperature of the molten steel is reduced to 1520–1540°C, and Fe-Ti and Fe-Nb master alloys are added through a feeding hopper, followed by electromagnetic stirring. In this embodiment of the invention, the stirring frequency is 0.3–0.5 Hz, and the duration is 5–8 minutes.

[0080] Step S107: Continue to lower the temperature of the molten steel to 1480–1500°C, add the Fe-B master alloy, and then perform electromagnetic stirring. In this embodiment of the invention, the B content in the Fe-B master alloy is 20 wt%, a gentle stirring mode is used, and the stirring time is 2–3 minutes.

[0081] Step S108: Control the temperature of the molten steel within the range of 1460–1480°C, add the Ce-Fe alloy, and then perform static settling and electromagnetic stirring treatments sequentially. In this embodiment of the invention, the Ce content in the Ce-Fe alloy is 30 wt%, and the mixture is allowed to stand for 2–5 minutes, followed by gentle stirring for 2–3 minutes.

[0082] Step S109: Adjust the temperature of the molten steel to 1440–1460°C, add the Ni-Mg alloy, and then perform electromagnetic stirring. In this embodiment of the invention, the Mg content in the Ni-Mg alloy is 15 wt%, the stirring frequency is 0.2–0.3 Hz, and the stirring time is 2–3 minutes.

[0083] In step S110, 0.05–0.08 wt% of Ca-Si alloy is added, the temperature is controlled at 1420–1440 °C, and then electromagnetic stirring is performed to ensure sufficient deoxidation. In this embodiment of the invention, the stirring time is 3–5 minutes.

[0084] Step S111: The temperature of the molten steel is lowered to 1400–1420°C, and electromagnetic stirring and settling are performed sequentially to obtain molten steel with uniform composition distribution. In this embodiment of the invention, the temperature of the molten steel is lowered to 1400–1420°C, electromagnetic stirring is turned on at a frequency of 0.1–0.2 Hz for 10–15 minutes, and after stirring is stopped, the mixture is allowed to stand for 5 minutes to promote the floating of inclusions.

[0085] Step S112: Adjust the temperature of the molten steel to 150-200°C above the liquidus line.

[0086] Step S113: Start the atomization system to perform powder production. In this embodiment of the invention, the diameter of the guide tube is set to 4-6 mm, the atomization pressure is adjusted to 3.5-4.5 MPa, the atomizing gas is heated to 250-350°C, the metal flow rate is controlled within the range of 15-25 kg / min, and the atomization system is started to perform powder production.

[0087] Step S2: Remove oxide inclusions from the master alloy powder by electrostatic separation to obtain purified powder.

[0088] Step S2 includes:

[0089] Step S201: The raw powder obtained by atomization is sieved and classified, and powder with a particle size range of 15-53 μm is selected and dried. Then, a surface modifier is added to the powder to optimize the difference in conductivity. In this embodiment of the invention, the raw powder obtained by gas atomization is sieved and classified, and powder with a particle size range of 15-53 μm is sorted. The powder is dried in a vacuum oven at 100°C for 2 hours, and 0.1-0.5% of a surface modifier (such as zinc stearate) is added to the powder to optimize the difference in conductivity.

[0090] Step S202: Start the ventilation system to maintain a slightly negative pressure environment, start the drum drive motor to reach the set speed, turn on the high-voltage power supply, slowly increase the voltage to the set value, and start the vibrating feeder to make the powder fall evenly into the sorting area for sorting to obtain purified powder. In some embodiments of the present invention, the electric field strength is 10-20kV / cm, the drum speed is 100±20rpm, and the feeding rate is 8-10kg / h. During the sorting process, metal powder with good conductivity quickly gains charge and discharges rapidly through the grounding of the drum, falling into the qualified product collection bin under the action of centrifugal force; oxide inclusions have poor conductivity, remain charged, are adsorbed on the drum surface, and move with the drum to the brushing area, falling into the tail material collection bin; the intermediate state particles, which are partially oxidized metal powder, fall into the intermediate product collection bin and can be returned for reprocessing.

[0091] In this embodiment of the invention, electrostatic sorting is used to perform high-purity pretreatment on MIM powder, which significantly reduces the number of large-size oxide inclusions in the powder and controls the content of inclusions from the source.

[0092] Step S3: The purified powder and binder are mixed and injected using a metal injection molding process to form a flexible wheel blank with a thickness of 2-3.5 mm. The blank is then degreased to obtain a flexible wheel blank.

[0093] Step S3 includes:

[0094] Step S301: The purified powder and binder are mixed and kneaded, and then the feed is crushed after cooling. The volume ratio of the purified powder to the binder is 80:20 to 90:10, the mixing temperature is 160 to 180°C, and the mixing time is 2 to 5 hours.

[0095] Step S302: The pulverized feedstock is used to form a flexible preform in an injection molding die. In this embodiment of the invention, the pulverized feedstock is used to form the flexible preform in an injection molding die. The injection molding process parameters are adjusted according to the product shape. The thickness of the flexible preform is 2-3.5 mm. After injection molding, the sprue is removed.

[0096] Step S303: The flexible wheel blank is placed in a hydrocarbon cleaning agent at a temperature of 50-60°C for solvent degreasing treatment.

[0097] Step S304 involves performing a thermal degreasing treatment on the flexible wheel blank after step S303. The thermal degreasing treatment includes: holding at 180–250°C for 1–4 hours to remove low-melting-point components from the blank and fully remove internal stress; then holding at 550–600°C for 1–2 hours to remove high-melting-point components from the blank, thereby obtaining a flexible wheel blank with most of the binder removed, possessing a certain shape strength, and suitable for subsequent processing.

[0098] In this embodiment of the invention, the complex thin-walled flexible wheel blank is integrally formed using MIM technology, with a material utilization rate of over 85%, which is significantly higher than the material utilization rate of traditional forging processes, breaking through the limitations of traditional forging + cutting.

[0099] Step S4: The flexible wheel blank is subjected to hot isostatic pressing (HIP) densification treatment to obtain a flexible wheel blank. In this embodiment of the invention, the flexible wheel blank is placed in a hot isostatic pressing furnace for densification treatment to obtain a flexible wheel blank. The HIP temperature is 1120–1300℃, the atmosphere pressure is 100–120 MPa, the holding time is 2–3 h, and argon protection is used to obtain a blank with a density ≥99.5%.

[0100] In this embodiment of the invention, hot isostatic pressing is used to completely close the residual pores inside the material, achieving near-complete density.

[0101] Step S5 involves locally rolling the toothed ring and its transition portion, as well as the cup bottom transition area of ​​the flexible wheel blank, to further break down the grains. In this embodiment of the invention, the locally rolled material includes, but is not limited to, conventional rolling and ultrasonic-assisted deep rolling.

[0102] Step S6 involves rapidly heating the gear ring, its transition portion, and the cup bottom transition area of ​​the flexible gear blank to 800–850°C, followed by rapid cooling. In this embodiment of the invention, a high-frequency induction coil is used to heat the gear ring, its transition portion, and the cup bottom transition area to 800–850°C, followed by rapid cooling. The cooling medium includes argon, water mist, or oil mist. In some embodiments of the invention, the heating rate is 150°C / s.

[0103] In this embodiment of the invention, local strengthening and local high-frequency quenching are innovatively used to target the gear ring and its transition parts and the transition area at the bottom of the cup, which are subject to severe stress concentration. This replaces the traditional overall quenching and achieves the goal of "using good steel on the cutting edge", taking into account overall toughness, local ultra-high strength and wear resistance.

[0104] Step S7: Perform overall homogenization tempering on the flexible wheel blank. In this embodiment of the invention, the flexible wheel blank undergoes overall homogenization tempering at 450–520°C for 2–6 hours to obtain a troostite or sorbite matrix. Typically, tempering at 450–500°C mainly yields a troostite structure with higher hardness; tempering at 500–520°C mainly yields a sorbite structure with better toughness and fatigue properties.

[0105] After step S7, the flexible gear blank is obtained. Precision turning, gear hobbing, and other finishing processes are then performed on the flexible gear blank to obtain the final flexible gear product. From the flexible gear blank to the finished product, the material utilization rate is 50-70%.

[0106] The flexible wheel blank prepared according to the embodiments of the present invention can achieve a fatigue life of ≥5×10⁻⁶. 7 In one cycle, the fatigue life of a flexible wheel prepared by traditional processes is generally 3 × 10⁻⁶. 7 This effectively solves the problem of poor fatigue resistance in flexible wheels prepared by traditional processes. For example... Figure 2 As shown, the grain size of the key parts of the flexible wheel blank prepared in this embodiment of the invention is only 5-8 μm, which is much smaller than the grain size of more than 20 μm in traditional processes, thereby improving the overall mechanical properties of the flexible wheel. Figure 3 As shown, the arrow points to the inclusions. The inclusion size of the flexible wheel blank prepared in this embodiment of the invention is reduced to ≤3μm. Compared with the prior art, the remaining inclusions have higher toughness, which effectively solves the problem that inclusions become crack initiation sources in traditional processes.

[0107] Example 1

[0108] In this embodiment, the material of the flex wheel in the harmonic reducer is as follows:

[0109] Basic components (by mass percentage): 0.38% carbon, 0.25% silicon, 0.40% manganese, 0.02% phosphorus, 0.02% sulfur, 1.8% nickel, 0.8% chromium, 0.2% molybdenum, 0.2% copper, with the balance being iron and unavoidable impurities;

[0110] Composite strengthening phase: Grain refiner, with the addition of 0.06% titanium and 0.1% niobium to form titanium and niobium carbide composite carbides with a particle size of 100nm. Its main function is to pin grain boundaries and inhibit grain growth; synergistic control, with the addition of 0.005% boron, which combines with iron in the basic component system to form Fe2B distributed along the grain boundaries.

[0111] Inclusion modification components: Through precise oxygen control, the oxygen content of the powder is controlled at 80ppm to inhibit the formation of Al2O3. The residual inclusions are mainly titanium and niobium carbides with a size ≤2μm. At the same time, 0.05wt%Ce+0.02wt%Mg is introduced.

[0112] This embodiment provides a method for machining a flexspline blank for a harmonic reducer, the steps of which are as follows:

[0113] Step a1: Master Alloy Atomization: After melting according to the designed composition, the alloy is atomized into powder under inert argon gas. Specifically, a vacuum induction melting-gas atomization integrated furnace is used; the alloy is charged in the following order: industrial pure iron → Ni plate → Fe-Cr / Fe-Mo → Fe-C / Fe-Si / Fe-Mn. After evacuating to 5.0×10-2 Pa, 99.999% high-purity Ar is introduced to a positive pressure of 50 kPa. The gas is purged three times. Finally, under a vacuum of 2.0×10-2 Pa, the temperature is raised to 1580℃ for refining for 25 minutes, during which electromagnetic stirring is performed at a frequency of 0.8 Hz, with a 2-minute on / 1-minute off cycle. The temperature is then lowered to 1520℃, and a Fe-Ti master alloy with a Ti content of 30% and a Fe-Nb alloy with a Nb content of 50% are added. The intermediate alloy was gently stirred for 5 minutes; the temperature was then lowered to 1480℃, and a Fe-B alloy with a B content of 20% was added and stirred for 3 minutes; the temperature was lowered to 1460℃, and a Ce-Fe alloy with a Ce content of 30% was added, allowed to stand for 2 minutes, and then gently stirred for 2 minutes; the temperature was lowered to 1440℃, and a Ni-Mg alloy with a Mg content of 15% was added using the bell jar method, and immediately stirred at a frequency of 0.3Hz for 3 minutes; a Ca-Si alloy was added for deoxidation treatment, and the molten steel was superheated to 1420℃ (liquidity line approximately 1365℃), and electromagnetic stirring was started at a frequency of 0.1Hz for 10 minutes. After stirring was stopped, the mixture was allowed to stand for 5 minutes to promote the flotation of inclusions. Then, the mixture was atomized through a 5mm diameter guide tube under a high-purity Ar gas flow of 4.0MPa and 300℃. The resulting powder was sieved, and the oxygen content was measured to be 78ppm.

[0114] Step b1: Powder purification, including electrostatic separation. The equipment used is a double-drum high-voltage electrostatic separator with an electric field strength of 12kV / cm, a drum speed of 110rpm, and a feeding rate of 9kg / h.

[0115] Step c1: Metal injection molding, including: mixing the purified powder and wax-based binder (PW:68%-LDPE:20%-SA:12%) in a mixer at a volume ratio of 92:8 for 4 hours at a mixing temperature of 175℃, followed by cooling and granulation; using an injection molding machine at a mold temperature of 75℃ to injection mold a flexible wheel preform with a wall thickness of 3.2mm; solvent degreasing the preform in n-heptane at 50℃ for 6 hours; thermal degreasing in a vacuum degreasing sintering furnace, raising the temperature to 220℃ at 1℃ / min and holding for 3 hours (to remove residual paraffin), and then raising the temperature to 600℃ at 2℃ / min and holding for 2 hours (to remove the polymer and perform preliminary pre-sintering), to obtain a flexible wheel preform with most of the binder removed, possessing certain shape strength, and suitable for subsequent processing.

[0116] Step d1: The flexible wheel blank obtained in step c1 is placed in a hot isostatic pressing furnace for hot isostatic pressing densification treatment with parameters of 1200℃ / 110MPa / 2.5h and argon protection, and the density of the flexible wheel blank is ≥99.8%.

[0117] Step e1: For the flexible wheel blank formed by injection molding and hot isostatic pressing, use a five-axis linkage CNC rolling equipment to perform local ultrasonic-assisted deep rolling on the gear ring, transition part, and cup bottom transition area. The rolling force is 350N, the rolling speed is 300mm / min, the ultrasonic frequency is 28kHz, the amplitude is 15μm, and the rolling is repeated 3 times.

[0118] Step f1: Local rapid heat treatment, using a high-frequency induction coil to heat the tooth ring and transition part of the flexible wheel blank, and the transition area of ​​the cup bottom, at a heating rate of 150℃ / s, and then cooling with water mist after heating to 820±5℃ to form fine lath martensite;

[0119] Step g1: The flexible wheel blank is subjected to overall homogenization tempering in an air circulation furnace, held at 480±5℃ for 2 hours to obtain a troostitic matrix with a hardness of HRC 37.5.

[0120] Step h1: Finish the flexible wheel blank, including precision turning, gear hobbing and other processes, to obtain the final flexible wheel product.

[0121] This embodiment achieves an optimal balance of overall performance. The low Mn content (0.4%) ensures excellent toughness, the moderate Ti / Nb / B content effectively refines the grains, and the addition of Ce / Mg effectively controls inclusion morphology. Hot isostatic pressing (HIP) at 1200℃ / 110MPa / 2.5h achieves sufficient densification with high efficiency, and tempering at 480℃ yields a troostite microstructure with a good balance of strength and toughness. Testing shows that the flexural wheel product achieves a fatigue life of 6.8 × 10⁻⁶. 7 This solution offers high reliability, a wide process window, and is suitable for large-scale, stable production.

[0122] Example 2

[0123] In this embodiment, the material of the flex wheel in the harmonic reducer is as follows:

[0124] Basic components (by mass percentage): 0.4% carbon, 0.3% silicon, 0.45% manganese, 0.015% phosphorus, 0.03% sulfur, 1.9% nickel, 0.9% chromium, 0.28% molybdenum, 0.15% copper, with the balance being iron and unavoidable impurities;

[0125] Composite strengthening phase: Grain refiner, with the addition of 0.09wt% titanium and 0.14wt% niobium, forming titanium and niobium carbide composite carbides with a particle size of 150nm. Its main function is to pin grain boundaries and inhibit grain growth; synergistic control, with the addition of 0.009wt% boron, which combines with iron in the basic composition system to form Fe2B distributed along the grain boundaries.

[0126] Inclusion modification components: Through precise oxygen control, the oxygen content of the powder is controlled at 60ppm to inhibit the formation of Al2O3. The residual inclusions are mainly titanium and niobium carbides with a size ≤3μm. At the same time, 0.07wt%Ce+0.028wt%Mg is introduced.

[0127] This embodiment provides a method for machining a flexspline blank for a harmonic reducer, the steps of which are as follows:

[0128] Step a2: Master Alloy Atomization: After melting according to the designed composition, the alloy is atomized into powder under inert argon gas. Specifically, a vacuum induction melting-gas atomization integrated furnace is used; the materials are charged in the following order: industrial pure iron → Ni plate → Fe-Cr / Fe-Mo → Fe-C / Fe-Si / Fe-Mn. After evacuating to 5.0 × 10⁻² Pa, high-purity Ar with a content of 99.999% is introduced to a positive pressure of 50 kPa. The gas is purged three times. Finally, under a vacuum of 2.0 × 10⁻² Pa, the temperature is raised to 1590℃ for refining for 20 minutes, with electromagnetic stirring at a frequency of 1.0 Hz, running for 1.5 min and stopping for 1 min. The temperature is then lowered to 1530℃, and Fe-Ti and Fe-Nb master alloys are added. Subsequent additions and stirring processes are the same as in Example 1. The molten steel was superheated to 1430℃ and then atomized through a 4.5mm diameter guide tube under a high-purity argon flow of 4.2MPa and 280℃. The resulting powder had an oxygen content of 55ppm.

[0129] Step b2: Powder purification, including electrostatic separation. The equipment used is a double-drum high-voltage electrostatic separator with an electric field strength of 20kV / cm, a drum speed of 110rpm, and a feeding rate of 9kg / h.

[0130] Step c2: Metal injection molding, including: mixing purified powder with polypropylene-based binder and injecting it into a flexible wheel blank with a material utilization rate of 90%, then removing the binder to obtain a flexible wheel blank with most of the binder removed, having a certain shape strength and being able to undergo subsequent processing.

[0131] Step d2: The flexible wheel blank obtained in step c1 is placed in a hot isostatic pressing furnace for hot isostatic pressing densification treatment with parameters of 1180℃ / 115MPa / 3h and argon protection. The density of the flexible wheel blank is ≥99.7%.

[0132] Step e2: Local rolling is performed on the tooth root and transition position, and cup bottom transition area of ​​the flexible wheel blank formed by injection molding and hot isostatic pressing to further break down the grains;

[0133] Step f2: Local rapid heat treatment, using a high-frequency induction coil to heat the flexible wheel blank gear ring and its transition area and cup bottom transition area to 840℃, followed by quenching and oil mist cooling to reduce the risk of deformation and cracking, and to form fine lath martensite;

[0134] Step g2: The flexible wheel blank is subjected to overall homogenization tempering and held at 450℃ for 3 hours to obtain a troostitic matrix with a hardness of HRC 42.3.

[0135] Step h2: Finish the flexible wheel blank, including precision turning, gear hobbing and other processes, to obtain the final flexible wheel product.

[0136] This embodiment achieves extreme surface hardness and wear resistance by increasing the content of C, Mo, and microalloying elements (Ti, Nb, B) and using a lower final tempering temperature. The composition design is biased towards higher strength. The HIP uses a slightly lower temperature to prevent coarsening of the reinforcing phase, while higher pressure ensures density. The fatigue test life of the flexible wheel product reaches 5.2 × 10⁻⁶. 7 Suitable for extreme working conditions requiring high load and high wear resistance, but at the cost of some toughness.

[0137] Example 3

[0138] Basic components (by mass percentage): 0.41% carbon, 0.2% silicon, 0.35% manganese, 0.025% phosphorus, 0.01% sulfur, 1.7% nickel, 0.7% chromium, 0.18% molybdenum, 0.25% copper, with the balance being iron and unavoidable impurities;

[0139] Composite strengthening phase: Grain refiner, with the addition of 0.04wt% titanium and 0.07wt% niobium, forming titanium and niobium carbide composite carbides with a particle size of 80nm. Its main function is to pin grain boundaries and inhibit grain growth; synergistic control, with the addition of 0.0025wt% boron, which combines with iron in the basic composition system to form Fe2B distributed along the grain boundaries, further refining the grains to 5.5μm.

[0140] Inclusion modification components: Through precise oxygen control, the oxygen content of the powder is controlled at 90ppm to inhibit the formation of Al2O3. The residual inclusions are mainly titanium and niobium carbides with a size ≤2.5μm. At the same time, 0.03wt%Ce+0.012wt%Mg is introduced.

[0141] This embodiment provides a method for machining a flexspline blank for a harmonic reducer, the steps of which are as follows:

[0142] Step a3: Master Alloy Atomization: After melting according to the designed composition, the alloy is atomized into powder under inert helium gas. Specifically, the charging and gas washing processes are the same as in Example 1. Finally, under a vacuum of 1.5 × 10⁻² Pa, the temperature is raised to 1570℃ for refining for 30 minutes, with electromagnetic stirring at a frequency of 0.5 Hz, on for 3 minutes and off for 2 minutes. The temperature is then lowered to 1510℃, and Fe-Ti and Fe-Nb master alloys are added. Subsequent additions and stirring processes are the same as in Example 1. The molten steel is superheated to 1410℃ and atomized through a 5.5 mm diameter guide tube under a high-purity helium gas flow of 3.8 MPa and 320℃. The resulting powder has an oxygen content of 85 ppm.

[0143] Step b3: Powder purification, including electrostatic separation. The equipment used is a double-drum high-voltage electrostatic separator with an electric field strength of 18kV / cm, a drum speed of 110rpm, and a feeding rate of 9kg / h.

[0144] Step c3: Metal injection molding, including: metal injection molding (MIM), mixing the purified powder with the wax-based binder and injecting it into a flexible wheel blank with a material utilization rate of 86%, and then removing the binder to obtain a flexible wheel blank with most of the binder removed, having a certain shape strength and being able to undergo subsequent processing.

[0145] Step d3: The flexible wheel blank obtained in step c1 is placed in a hot isostatic pressing furnace for hot isostatic pressing densification treatment with parameters of 1250℃ / 100MPa / 2h and argon protection, and the density of the flexible wheel blank is ≥99.6%.

[0146] Step e3: Perform local ultrasonic-assisted deep rolling on the flexible wheel blank formed by injection molding and hot isostatic pressing, the gear ring and its transition part, and the cup bottom transition area to further break down the grains;

[0147] Step f3: Local rapid heat treatment, using a high-frequency induction coil to heat the flexible wheel blank gear ring and its transition area and cup bottom transition area to 810℃ and then cool with argon gas to form fine lath martensite;

[0148] Step g3: The flexible wheel blank is subjected to overall homogenization tempering and held at 520℃ for 5 hours to obtain a sorbite matrix with a hardness of HRC 35.5.

[0149] Step h3: Finish the flexible wheel blank, including precision turning, gear hobbing and other processes, to obtain the final flexible wheel product.

[0150] This embodiment utilizes a lower Mn content, a higher Ni content, and a higher tempering temperature to obtain a flexible wheel blank with high toughness and fatigue limit. The fatigue test life of the flexible wheel product reaches 7.2 × 10⁻⁶. 7 Suitable for applications requiring extremely high reliability and subjected to severe impact loads.

[0151] Example 4

[0152] Basic components (by mass percentage): 0.36% carbon, 0.15% silicon, 0.3% manganese, 0.028% phosphorus, 0.01% sulfur, 1.6% nickel, 0.6% chromium, 0.15% molybdenum, 0.28% copper, with the balance being iron and unavoidable impurities;

[0153] Composite strengthening phase: Grain refiner, with the addition of 0.03wt% titanium and 0.05wt% niobium to form titanium and niobium carbide composite carbides, whose main function is to pin grain boundaries and inhibit grain growth; synergistic control, with the addition of 0.002wt% boron, which combines with iron in the basic composition system to form Fe2B distributed along the grain boundaries.

[0154] Inclusion modification components: 0.02wt% Ce + 0.01wt% Mg were introduced.

[0155] This embodiment provides a method for machining a flexspline blank for a harmonic reducer, the steps of which are as follows:

[0156] Step a4: Master alloy atomization: After melting according to the designed composition, atomize the alloy into powder under inert argon gas. Specifically, the process parameters are the same as in Example 1, but the refining temperature is 1580℃, the atomization pressure is 3.5MPa, and the oxygen content of the resulting powder is approximately 95ppm.

[0157] Step b4: Powder purification, including electrostatic separation. The equipment used is a double-drum high-voltage electrostatic separator with an electric field strength of 10kV / cm, a drum speed of 110rpm, and a feeding rate of 8kg / h.

[0158] Step c4: Metal injection molding, including: the volume ratio of feed powder to binder is 88:12, the wall thickness of the flexible wheel blank is designed to be 3.5mm, and then the binder is removed to obtain a flexible wheel blank with most of the binder removed, having a certain shape strength and being able to undergo subsequent processing.

[0159] Step d4: The flexible wheel blank obtained in step c1 is placed in a hot isostatic pressing furnace for hot isostatic pressing densification treatment with parameters of 1120℃ / 100MPa / 2h and argon protection.

[0160] Step e4: Perform conventional rolling on the flexible wheel blank formed by injection molding and hot isostatic pressing, the gear ring and its transition part, and the cup bottom transition area, with a rolling force of 280N to further break down the grains;

[0161] Step f4: Local rapid heat treatment, using a high-frequency induction coil to heat the flexible wheel blank gear ring and its transition area and cup bottom transition area to 800℃ and then cool with argon gas to form fine lath martensite;

[0162] Step g4: The flexible wheel blank is subjected to overall homogenization tempering and held at 520℃ for 6 hours to obtain a sorbite matrix with a hardness of HRC 34.0.

[0163] Step h4: Finish the flexible wheel blank, including precision turning, gear hobbing and other processes, to obtain the final flexible wheel product.

[0164] Although this embodiment has the lowest strength and hardness among all examples, its toughness and fatigue performance still far exceed those of traditional materials, with a fatigue test life of 5.8 × 10⁻⁶. 7 Second-rate.

[0165] Example 5

[0166] Basic components (by mass percentage): 0.43% carbon, 0.35% silicon, 0.5% manganese, 0.025% phosphorus, 0.03% sulfur, 2.0% nickel, 1.0% chromium, 0.3% molybdenum, 0.05% copper, with the balance being iron and unavoidable impurities;

[0167] Composite strengthening phase: Grain refiner, with the addition of 0.1wt% titanium and 0.15wt% niobium to form titanium and niobium carbide composite carbides, whose main function is to pin grain boundaries and inhibit grain growth; synergistic control, with the addition of 0.01wt% boron, which combines with iron in the basic composition system to form Fe2B distributed along the grain boundaries.

[0168] Modifying components: 0.08wt% Ce + 0.03wt% Mg were introduced.

[0169] This embodiment provides a method for machining a flexspline blank for a harmonic reducer, the steps of which are as follows:

[0170] Step a5: Master alloy atomization: After melting according to the designed composition, atomize to form powder under inert argon gas. Specifically, the process parameters are the same as in Example 2, but the refining temperature is 1600℃ and the atomization pressure is 4.5MPa. The resulting powder has an oxygen content of approximately 50ppm.

[0171] Step b5: Powder purification, including electrostatic separation. The equipment used is a double-drum high-voltage electrostatic separator with an electric field strength of 15kV / cm, a drum speed of 110rpm, and a feeding rate of 10kg / h.

[0172] Step c5: Metal injection molding, including: the volume ratio of feed powder to binder is 90:10, the wall thickness of the flexible wheel blank is designed to be 2.0 mm, and then the binder is removed to obtain a flexible wheel blank with most of the binder removed, having a certain shape strength and being able to undergo subsequent processing.

[0173] Step d5: The flexible wheel blank obtained in step c1 is placed in a hot isostatic pressing furnace for hot isostatic pressing densification treatment with parameters of 1300℃ / 120MPa / 3h and argon protection.

[0174] Step e5: The flexible wheel blank formed by injection molding and hot isostatic pressing, the gear ring and its transition part, and the cup bottom transition area are subjected to ultrasonic-assisted deep rolling with a rolling force of 400N to further break the grains.

[0175] Step f5: Local rapid heat treatment, using a high-frequency induction coil to heat the flexible wheel blank gear ring and its transition area and cup bottom transition area to 850℃ and then water mist cooling to form fine lath martensite;

[0176] Step g5: The flexible wheel blank is subjected to overall homogenization tempering and held at 450℃ for 2 hours to obtain a troostitic matrix with a hardness of HRC 44.5.

[0177] Step h5: Finish the flexible wheel blank, including precision turning, gear hobbing and other processes, to obtain the final flexible wheel product.

[0178] The fatigue test life of the flexible wheel product obtained in this embodiment still reaches 4.5 × 10⁻⁶. 7 Second-rate.

[0179] The above are merely specific embodiments of the present invention and should not be construed as limiting the scope of the present invention. Equivalent variations made by those skilled in the art based on this invention, as well as changes well-known to those skilled in the art, should still fall within the scope of the present invention.

Claims

1. A material for a flexspline of a harmonic reducer, characterized by, In terms of mass percentage, the alloying elements include: carbon 0.36-0.43%, silicon 0.15-0.35%, manganese 0.3-0.5%, phosphorus 0-0.03%, sulfur 0.01-0.03%, nickel 1.6-2.0%, chromium 0.6-1.0%, molybdenum 0.15-0.3%, copper 0-0.3%, titanium 0.03-0.1%, niobium 0.05-0.15%, boron 0.002-0.01%, cerium 0.02-0.08%, magnesium 0.01-0.03%, and the balance of iron and inevitable impurities.

2. A method of machining a harmonic reducer flexspline blank, characterized by, The method comprises the following steps: In step S1, a master alloy powder is prepared, which comprises, in terms of mass percentage: carbon 0.36-0.43%, silicon 0.15-0.35%, manganese 0.3-0.5%, phosphorus 0-0.03%, sulfur 0.01-0.03%, nickel 1.6-2.0%, chromium 0.6-1.0%, molybdenum 0.15-0.3%, copper 0-0.3%, titanium 0.03-0.1%, niobium 0.05-0.15%, boron 0.002-0.01%, cerium 0.02-0.08%, magnesium 0.01-0.03%, and the balance of iron and inevitable impurities; In step S2, oxides in the master alloy powder are removed by electrostatic separation to obtain a purified powder; In step S3, the purified powder is mixed with a binder by a metal injection molding process to form a soft gear green body, the thickness of the soft gear green body is 2-3.5 mm, and the soft gear green body is subjected to a debinding treatment to obtain a soft gear brown body; In step S4, the soft gear brown body is subjected to a hot isostatic pressing densification treatment to obtain a soft gear blank; In step S5, the gear ring and the transition part and the cup bottom transition area of the soft gear blank are subjected to local rolling; In step S6, the gear ring and the transition part and the cup bottom transition area of the soft gear blank are rapidly heated to 800-850 DEG C and then rapidly cooled; In step S7, the soft gear blank is subjected to overall homogenization tempering treatment.

3. The harmonic reducer flexspline blank machining method of claim 2, wherein, The step S1 comprises: In step S101, industrial pure iron, electrolytic nickel plate and master alloy powder are prepared, and the block-shaped raw materials are crushed to a uniform size; In step S102, the industrial pure iron and the electrolytic nickel plate are loaded at the bottom of the crucible, the Fe-Cr and Fe-Mo intermediate alloys are loaded in the middle layer, and the Fe-C, Fe-Si and Fe-Mn intermediate alloys are loaded in the uppermost layer; In step S103, vacuum is repeatedly drawn and inert gas is filled, and the vacuum degree in the furnace is stabilized within a preset pressure threshold; In step S104, the furnace charge is completely melted by slowly increasing the power; In step S105, the molten furnace charge is subjected to refining and degassing treatment to obtain a steel liquid; In step S106, the temperature of the steel liquid is reduced to 1520-1540 DEG C, the Fe-Ti and Fe-Nb intermediate alloys are added through a feeding bin, and then electromagnetic stirring treatment is performed; In step S107, the temperature of the steel liquid is continuously reduced to 1480-1500 DEG C, the Fe-B intermediate alloy is added, and then electromagnetic stirring treatment is performed; Step S108, control the temperature of the molten steel in the range of 1460-1480℃, add Ce-Fe alloy, and then sequentially perform standing and electromagnetic stirring treatment; Step S109, adjust the temperature of the molten steel to 1440-1460℃, add Ni-Mg alloy, and then perform electromagnetic stirring treatment; Step S110, add 0.05-0.08wt% Ca-Si alloy, control the temperature in the range of 1420-1440℃, and then perform electromagnetic stirring to ensure sufficient deoxidization; Step S111, reduce the temperature of the molten steel to 1400-1420℃, sequentially perform electromagnetic stirring and standing treatment to obtain molten steel with uniform composition distribution; Step S112, adjust the temperature of the molten steel to be 150-200℃ higher than the liquidus; Step S113, start the atomization system to perform powder production.

4. The harmonic reducer flexspline blank machining method of claim 2, wherein, The step S2 comprises: Step S201, sieve and classify the original powder obtained by atomization, take the powder with a particle size in the range of 15-53μm, perform drying treatment, and then add a surface modifier to the powder to optimize the difference in electrical conductivity; Step S202, start the air extraction system to maintain a micro-negative pressure environment, start the roller driving motor to reach the set speed, turn on the high-voltage power supply, slowly increase the voltage to the set value, start the vibration feeder to make the powder uniformly fall into the sorting area for sorting treatment to obtain purified powder.

5. The harmonic reducer flexspline blank machining method of claim 2, wherein, The step S3 comprises: Step S301, mix the purified powder with a binder, and crush the feedstock after cooling; Step S302, form the crushed feedstock into a flexspline green body in an injection molding mold; Step S303, place the flexspline green body into a hydrocarbon cleaning agent with a temperature of 50-60℃ for solvent degreasing treatment; Step S304, perform thermal degreasing treatment on the flexspline green body treated in step S303.

6. The harmonic reducer flexspline blank machining method according to claim 5, wherein, In the step S301, the volume ratio of the purified powder to the binder is 80:20-90:10, the mixing temperature is 160-180℃, and the mixing time is 2-5 hours.

7. The harmonic reducer flexspline blank machining method of claim 5, wherein, The step S304 comprises: hold at 180-250℃ for 1-4 hours; hold at 550-600℃ for 1-2 hours.

8. The harmonic reducer flexspline blank machining method of claim 2, wherein, The specific method of the step S4 is: place the flexspline brown body into a hot isostatic pressing furnace for densification treatment to obtain a flexspline blank, the hot isostatic pressing temperature is 1120-1300℃, the atmosphere pressure is 100-120MPa, the holding time is 2-3h, and argon protection is performed.

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