Steel for a flexible gear of a harmonic reducer for an industrial robot and a method of manufacturing the same

Abstract

The present application relates to a kind of harmonic reducer flexible wheel for industrial robot and its manufacturing method, the chemical composition in steel is: 0.35%≤C≤0.60%, 0.2%≤Si≤1.5%, 0.5%≤Mn≤1.0%, 0.5%≤Cr≤1.5%, 0.1%≤Mo≤1.0%, 0.05%≤V≤0.50%, 0.002%≤Ce≤0.050%, Al≤0.015%, P≤0.015%, S≤0.01%, H≤0.0001%, O≤0.0015%, N≤0.005%, the balance is Fe and impurity.The finished steel plate organization is uniform fine tempering troostite structure, hardness ≥48HRC, surface hardness difference is within ±0.5HRC, tensile strength 1500~1800MPa, yield strength 1300~1500MPa, elongation after break ≥10%.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, and in particular to a steel for the flexible wheel of a harmonic reducer for industrial robots and its manufacturing method. Background Technology

[0002] With the rapid development of the intelligent manufacturing industry, the demand for robots is growing rapidly. Motion controllers, servo drive motors, and precision reducers are the three core components of intelligent robots, among which precision reducers are the most critical, accounting for more than 35% of the manufacturing cost. Harmonic reducers have advantages such as compact structure, light weight, small size, large reduction ratio, high transmission efficiency, and high transmission accuracy, and are widely used in joints such as the forearm and wrist of robots.

[0003] Harmonic reducers consist of a rigid wheel, a flexible wheel, and a wave generator. The flexible wheel is the component with the highest technological barrier in a harmonic reducer, and its fatigue life determines the overall service life of the reducer. The flexible wheel needs to continuously move at high speed, undergo elliptical deformation, and mesh with the rigid wheel to transmit torque and achieve speed changes. Each part of the flexible wheel must withstand various forms of alternating stress over a long period. Therefore, the flexible wheel requires extremely high strength, toughness, fatigue performance, purity, and dimensional accuracy of the materials used. The high-end market has long been dominated by Japanese and German special steel companies, with Japan holding approximately 80% of the global harmonic reducer market share.

[0004] Currently, high-purity 40CrMo and other special steel ingots are typically cast into bars, which are then precision forged and tempered with nitriding to process flexible wheels, meeting the requirements for high precision, ultra-thin walls, long lifespan, and high reliability. However, on the one hand, casting has low production efficiency, yield, and capacity, and high energy consumption and production costs; on the other hand, the bars require precision forging and individual flexible wheel heat treatment, resulting in low production efficiency and yield, as well as complex processes. Compared with advanced foreign companies such as Harmonic Drive Systems of Japan, domestically produced flexible wheels lag significantly in terms of mechanical properties, microstructure control, and service life. The long-term reliance on imports for high-end flexible wheels has greatly increased the manufacturing cost of domestic industrial robots, severely restricting the development of my country's industrial robot industry. There is an urgent need to research and develop a low-cost steel and processing technology for harmonic reducer flexible wheels to promote the localization of key materials for industrial robots.

[0005] Chinese patent application No. 202210584327.2 discloses "a medium carbon bearing steel for the flexible wheel of a robot harmonic reducer and its production method". The chemical composition of the steel is C: 0.36%~0.43%, Si: 0.15%~0.35%, Mn: 0.60%~0.90%, Cr: 0.60%~1.00%, S≤0.015%, P≤0.025%, Ni: 1.60%~2.00%, Cu≤0.25%, Mo: 0.15%~0.35%, Ca≤0.0010%, Ti≤0.003%, O≤0.0010%, As≤0.01%, Sn≤0.015%, Sb≤0.005%, with the balance being Fe and impurities. The production process is as follows: molten iron pretreatment - converter smelting - LF refining - RH refining - continuous casting - slow cooling of continuously cast billets - rough rolling, intermediate rolling and finishing to obtain round bars - slow cooling - softening annealing - finishing. The yield strength of the finished bars is ≥980MPa, elongation is ≥12%, reduction of area is ≥55%, and room temperature impact resistance is A. KV The steel has a hardness of ≥78J, an annealed hardness of ≤269HBW, and a grain size of ≥6. Non-metallic inclusions include B fine series ≤1.5, B coarse series ≤1.0, D fine series ≤1.0, D coarse series ≤1.0, and DS series ≤1.0. However, its high alloy types and content lead to high costs and a tendency to form defects such as segregation, severely affecting fatigue life. Both cast billets and bars require slow cooling and softening annealing, resulting in long production cycles and low efficiency. Furthermore, bars require forging and precision machining to produce flexible wheels, a complex process that is not only costly but also prone to machining defects.

[0006] Chinese patent application No. 202311743341.3 discloses "a steel for a flexible wheel of a harmonic reducer and its heat treatment method." The chemical composition of the steel is C: 0.42%–0.48%, Si: 1.6%–2.0%, Mn: 2.0%–2.5%, Al: 0.03%–0.07%, S≤0.002%, P≤0.002%, Cr≤0.10%, Mo≤0.10%, Ti≤0.01%, O≤0.002%, N≥0.010%, with the remainder being Fe and impurities. The flexible wheel is manufactured using forging and heat treatment processes. Precise control of the retained austenite content (3%–5%), original austenite grain size (≥10), and banded structure (W0.5) is required to achieve the following performance requirements: hardness ≥48 HRC, yield strength ≥1500 MPa, and elongation after fracture ≥12%. Before forging the flexible wheel blank, the raw material needs to be homogenized and annealed. After forging, the flexible wheel blank needs to be normalized twice and then quenched and distributed heat treatment to obtain a good match of high strength and high toughness. The process is complicated, inefficient and has a low yield.

[0007] Chinese patent application No. 202411348591.1 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 of the steel is: C: 0.38%–0.42%, Si: 0.2%–0.30%, Mn: 0.60%–0.90%, Cr: 0.60%–0.90%, S≤0.010%, P≤0.015%, Ni: 1.50%–1.80%, Mo: 0.15%–0.25%, Nb: 0.015%–0.035%, O≤0.0006%, with the remainder being iron and impurities. The preparation method includes: vacuum induction furnace smelting of ingots – electroslag remelting into steel billets – forging the steel billets into square billets – heating – continuous roughing, intermediate, and finishing rolling into bars – slow cooling – collection. By adding Nb to refine the austenite in the rolled material (grain size reaching grade 9.5 or higher), the austenite grain size of the flexible wheel product reaches grade 10.5 or higher after a single quenching heat treatment. Electroslag remelting improves cleanliness, resulting in a D-class inclusion level of 0.5 and no A, B, or C-class inclusions in the rolled steel for the flexible wheel. However, the steel used for the flexible wheel is still bar stock, requiring annealing of the raw material followed by forging and precision machining before it can be manufactured into a flexible wheel. This process is complex, has low production efficiency, low yield, and high cost. Furthermore, the stability of the production process is difficult to control, and the uniformity of the flexible wheel's hardness is hard to guarantee. Summary of the Invention

[0008] This invention addresses the problems of high production cost and unstable quality of flexible wheels for industrial robots in my country. It provides a steel for flexible wheels in harmonic reducers for industrial robots and its manufacturing method. The finished product has a thickness of 1.5–3.0 mm, a hardness ≥48 HRC, a surface hardness difference within ±0.5 HRC, a tensile strength of 1500–1800 MPa, a yield strength of 1300–1500 MPa, and an elongation after fracture ≥10%. Flexible wheels produced using the steel described in this invention have a fatigue life ≥10 years. 7 Second, high-cycle fatigue strength ≥600MPa.

[0009] To achieve the above objectives, the present invention employs the following technical solution: A type of steel for the flexible wheel of a harmonic reducer for industrial robots, wherein the chemical composition of the steel by weight percentage is: 0.35%≤C≤0.60%, 0.2%≤Si≤1.5%, 0.5%≤Mn≤1.0%, 0.5%≤Cr≤1.5%, 0.1%≤Mo≤1.0%, 0.05%≤V≤0.50%, 0.002%≤Ce≤0.050%, Al≤0.015%, P≤0.015%, S≤0.01%, H≤0.0001%, O≤0.0015%, N≤0.005%, with the balance being Fe and unavoidable impurities.

[0010] The finished steel plate has a uniform and fine tempered troostite structure, a hardness ≥48HRC, a surface hardness difference within ±0.5HRC, a tensile strength of 1500~1800MPa, a yield strength of 1300~1500MPa, and an elongation after fracture ≥10%.

[0011] A method for manufacturing steel for the flexible wheel of a harmonic reducer for industrial robots includes the following steps: (1) Smelting: This includes converter smelting, LF electric furnace refining, and RH vacuum refining; the converter produces alkaline slag with phosphorus ≤0.014%, sulfur ≤0.010%, and residual oxygen ≤0.05% before tapping; the LF produces acidic slag with free oxygen ≤0.015% and residual oxygen ≤0.02% upon exiting the station; the pure RH treatment time is 20–30 min, the net circulation time is 10–20 min, the RH free oxygen is ≤0.0010%, the residual oxygen is ≤0.01%, and the steel killing time is 20–40 min; (2) Continuous casting: The superheat of the tundish casting is ≤25℃; continuous casting adopts light reduction and electromagnetic stirring, with a reduction of 6-10mm, a reduction rate of 1-4mm / m, an electromagnetic stirring current of 200-300A, a stirring frequency of 3-8Hz, and a forward and reverse rotation alternation time of 5-10min; continuous casting speed is 0.9-1.5m / min, secondary cooling water volume is 0.15-0.35L / kg, equiaxed crystal ratio is above 50%, billet thickness is 170-250mm, and the surface temperature deviation of the billet is not greater than 10℃; (3) Heating of the billet: The billet is hot-charged and fed into the heating furnace at a temperature ≥600℃. The heating furnace adopts a reducing atmosphere, with a preheating zone temperature of 600~700℃ and a holding time of more than 30 minutes. The first heating zone temperature is 1000~1100℃, the second heating zone temperature is 1180~1230℃, the soaking zone temperature is 1180~1220℃, and the total time in the furnace is more than 190 minutes. (4) Rolling and cooling: The roughing rolling start temperature is 1180~1230℃, the first pass reduction is 25~40mm, the roughing rolling speed is 3~6m / s, the finishing rolling threading speed is 7~10m / s, the finishing rolling start temperature is 1050~1100℃, the first pass reduction is 20~28mm, and the finishing rolling finish temperature is 850~950℃. The steel plate is cooled in a laminar flow cooling system 3-10 seconds after exiting the finishing mill, and then cooled to 580-680℃ at a cooling rate of 60-150℃ / s before being coiled. It is then air-cooled to room temperature to obtain a fine laminar pearlite mixed structure. The first to fourth laminar flow cooling groups are edge-shielded within 200mm of the two sides of the steel plate, with a cooling rate difference of ≤10℃ / s and a temperature difference of ≤20℃ in the width direction. (5) Pickling and cold rolling: Hot-rolled steel coils are pickled at a speed of 50–70 m / min. The pickled coil is rolled once, with a cold rolling reduction of 0.5-1.0 mm. After winding, it is annealed at a temperature of 680-750℃ for a holding time of ≥20h. (6) Heat treatment: A continuous heat treatment process is adopted, induction heating of cold-rolled steel coils to 750-850℃, cooling to 400-500℃ in a lead-bismuth mixture at a cooling rate of 50-70℃ / s, tempering for ≥3h, and air cooling to room temperature to obtain a uniform and fine tempered troostite structure.

[0012] In step (1), lime and lightly calcined dolomite are added during the converter smelting process to produce alkaline slag, with an alkalinity R of 3.0 to 4.5; silica, lime and fluorite are added during the LF electric furnace refining process to produce acidic slag, with an acidic slag alkalinity R ≤ 1.4.

[0013] In step (4), high-pressure water descaling is used before roughing and finishing, and the descaling water pressure is not less than 20MPa; roughing is carried out by 3+1 rolling, and finishing is carried out by 7-pass continuous rolling.

[0014] In step (5), the hot-rolled steel coil is pickled by a push-pull pickling unit, then rolled once on a reversible cold rolling mill, and then annealed in a full-hydrogen bell-type annealing furnace after being coiled.

[0015] In step (6), the mass ratio of lead to bismuth in the lead-bismuth mixture is 3:1 to 4:1.

[0016] Compared with the prior art, the beneficial effects of the present invention are: A steel strip for flexible wheels with a thickness of 1.5–3.0 mm is produced through improvements in chemical composition and process. It is alloyed with elements such as Cr, Mo, Ce, and V, while controlling process parameters in smelting, continuous casting, billet heating, rolling and cooling, pickling and cold rolling, and heat treatment. This results in a uniform and fine tempered troostite structure. The finished product has a hardness ≥48 HRC, a surface hardness difference within ±0.5 HRC, a tensile strength of 1500–1800 MPa, a yield strength of 1300–1500 MPa, and an elongation after fracture ≥10%. Flexible wheels processed from the steel described in this invention exhibit excellent strength and toughness matching, superior fatigue strength and life, with a high-cycle fatigue strength ≥600 MPa and a fatigue life ≥10. 7 Second-rate. Attached Figure Description

[0017] Figure 1 This is a typical metallographic photograph of the steel used for the flexible wheel of a harmonic reducer for industrial robots, as described in this invention. Detailed Implementation

[0018] The present invention discloses a steel for the flexible wheel of a harmonic reducer for industrial robots. The chemical composition of the steel, by weight percentage, is as follows: 0.35%≤C≤0.60%, 0.2%≤Si≤1.5%, 0.5%≤Mn≤1.0%, 0.5%≤Cr≤1.5%, 0.1%≤Mo≤1.0%, 0.05%≤V≤0.50%, 0.002%≤Ce≤0.050%, Al≤0.015%, P≤0.015%, S≤0.01%, H≤0.0001%, O≤0.0015%, N≤0.005%, with the balance being Fe and unavoidable impurities.

[0019] The mechanism of action of each alloy component in the steel for the flexible wheel of a harmonic reducer for industrial robots described in this invention is as follows: C: 0.35%~0.60%.

[0020] Carbon (C) is a major solid solution strengthening element in steel. In this invention, C also reacts with Ce and V to form fine carbides, improving strength and hardness, especially high-temperature resistance, ensuring that hardness and wear resistance do not decrease at high temperatures. If the C content is below 0.35%, it is difficult to guarantee the strength and hardness of the steel plate. On the other hand, if the C content is above 0.60%, the excessive strength will affect the yield strength ratio, worsen the toughness and plasticity of the steel, and make it prone to fracture. Therefore, this invention controls the C content between 0.35% and 0.60%.

[0021] Mn: 0.5%~1.0%.

[0022] Manganese (Mn) is relatively inexpensive and is an excellent deoxidizer and desulfurizer, essential for ensuring the strength and toughness of steel. Manganese and iron can form a solid solution indefinitely, increasing hardness and strength. In this invention, Mn combines with Ce and S to form MnCeS. This avoids the formation of FeS at grain boundaries, which can cause hot cracks and affect stamping formability. Furthermore, the fine MnCeS precipitates also enhance strength and impact toughness. Too low an Mn content will not meet the requirements for high strength and hardness, while too high an Mn content will severely affect deep-drawing formability due to segregation and increase production costs. Therefore, considering both cost and performance requirements, this invention controls the Mn content to be between 0.5% and 1.0%. Si: 0.2%~1.5%.

[0023] Si (silicon) is a common element in steel, used as a reducing agent and deoxidizer in the steelmaking process. Si is a ferrite-forming element and a non-carbide-forming element. Si dissolved in ferrite can improve hardenability and tempering resistance, increase strength and hardness, and improve wear resistance. This invention utilizes the fine precipitates formed by Si and Ce to hinder dislocation movement, thereby improving the elastic limit and yield strength to meet the requirements of flexible gears. When the Si content exceeds 1.5%, severe oxidation and decarburization occur on the steel surface, affecting wear resistance.

[0024] Cr: 0.5%~1.5%.

[0025] Chromium is a medium-strong carbide-forming element. In this invention, Cr is added to form composite carbides with C, Si, and Ce, which inhibits the segregation of Cr and Mo and improves the uniformity of the microstructure. Chromium can also increase the A3 and A1 temperatures, shift the GS line to the upper left, slow down austenite decomposition, improve hardenability, and enhance the oxidation resistance and corrosion resistance of the steel.

[0026] Harmful elements: P≤0.015%, S≤0.01%, H≤0.0001%, O≤0.0015%, Al≤0.015%, N≤0.005%.

[0027] P, S, H, O, etc. are all unavoidable harmful impurities in steel. Their presence will seriously deteriorate the toughness of steel. Therefore, the content of P, S, H, O, N, etc. in steel should be controlled to be as low as possible.

[0028] Ce: 0.002%~0.050%.

[0029] Ce, as a microalloying element, forms complex precipitates with C, Cr, Mo, and V, promoting carbide nucleation and pearlite spheroidization and refinement, thus improving wear resistance and fatigue strength. This is crucial for ensuring a fatigue life of at least 1000 mm for flexible wheels. 7 The key is achieving a high-cycle fatigue strength of ≥600MPa. On the other hand, this invention utilizes the combination of Ce and S to form spherical fine precipitates, reducing the strip-shaped MnS inclusions formed by S and Mn, improving fatigue performance, further increasing the fatigue life of the flexible wheel, and making it wear-resistant and anti-galling.

[0030] Mo: 0.1%~1.0%.

[0031] Mo is a solid solution strengthening element that significantly improves strength and hardness. It also enhances the hardenability and tempering stability of flexible wheels, ensuring strength during high-temperature tempering. Furthermore, it strongly suppresses temper brittleness at 450–550℃, preventing the segregation of impurities such as P and As at grain boundaries. Combined with Cr and Mn, it completely eliminates temper embrittlement, improving impact toughness and fatigue life. Mo forms stable carbides such as Mo2CeC with carbon and Ce, refining the microstructure, suppressing Mo segregation, and improving wear resistance and anti-galling properties. Mo also enhances resistance to pitting and hydrogen embrittlement, increases fatigue limit and contact fatigue strength, and reduces tooth surface wear and crack initiation, making it suitable for the complex working conditions of humanoid robots.

[0032] V: 0.05%~0.50%.

[0033] Vanadium is a strong carbide-nitride forming element, which comprehensively improves the strength, toughness, wear resistance, and thermal stability of steel through grain refinement and precipitation strengthening. Vanadium forms stable precipitates with C, N, and Ce, pinning grain boundaries, preventing austenite grain growth, pinning dislocations, significantly improving strength, wear resistance, creep resistance, and thermal fatigue resistance, lowering the brittle transition temperature, and greatly enhancing tempering stability and red hardness (high-temperature hardness). On the other hand, vanadium makes cementite finer and denser, controls segregation, and enhances resistance to hydrogen-induced cracking. Therefore, in the flexible wheel of a harmonic reducer for industrial robots, vanadium can significantly improve the overall performance of large-section flexible wheels, including high-temperature wear resistance and toughness.

[0034] The present invention discloses a method for manufacturing steel for the flexible wheel of a harmonic reducer for industrial robots, comprising the following steps: (1) Smelting: This includes converter smelting, LF electric furnace refining, and RH vacuum refining. The converter produces alkaline slag; slag-blocking operations are implemented during the converter tapping process to reduce the amount of slag discharged during tapping, requiring a slag thickness ≤80mm. Before tapping, phosphorus ≤0.014%, sulfur ≤0.010%, and residual oxygen ≤0.05%. The LF produces acidic slag; stirring is strengthened during the refining process, ensuring free oxygen ≤0.015% and residual oxygen ≤0.02% at the outlet, controlling the formation of brittle inclusions and improving the surface quality of the steel plate. The RH pure treatment time is 20–30 min, the net circulation time is 10–20 min, the RH free oxygen ≤0.0010%, and the residual oxygen ≤0.01%. The steel calming time is 20–40 min to promote sufficient flotation of inclusions, improve steel purity, reduce inclusions in the steel, and ensure that all non-metallic inclusions in the finished steel do not exceed grade 1.0, eliminating anisotropy in the microstructure.

[0035] As a preferred method, lime and lightly calcined dolomite are added during the converter smelting process to create alkaline slag with an alkalinity R of 3.0 to 4.5; silica, lime, and fluorite are added during the LF electric furnace refining process to create acidic slag with an alkalinity R ≤ 1.4.

[0036] (2) Continuous casting: The superheat of the tundish casting is ≤25℃; continuous casting employs light reduction and electromagnetic stirring, with a reduction of 6-10mm, a reduction rate of 1-4mm / m, an electromagnetic stirring current of 200-300A, a stirring frequency of 3-8Hz, and a forward / reverse rotation time of 5-10min; the continuous casting speed is 0.9-1.5m / min, the secondary cooling water flow rate is 0.15-0.35L / kg, the equiaxed crystal ratio is above 50%, and micro-segregation of the alloy liquid at the columnar crystal ends is controlled. The billet thickness is 170-250mm, the surface temperature deviation of the billet is no more than 10℃, the cooling rate of the billet is uniform, and the microstructure is homogeneous.

[0037] (3) Heating of the billet: The billet is hot-charged and fed into the heating furnace at a temperature ≥600℃ to reduce the temperature difference on the billet surface and mitigate microsegregation. The heating furnace uses a reducing atmosphere, with a preheating zone temperature of 600–700℃ and a holding time of at least 30 minutes. The first heating zone temperature is 1000–1100℃, the second heating zone temperature is 1180–1230℃, and the soaking zone temperature is 1180–1220℃. The total time in the furnace is at least 190 minutes to ensure the surface quality of the billet, prevent oxidation and decarburization, and ensure the rolling temperature to form various Ce carbides, thereby improving strength and toughness.

[0038] (4) Rolling and cooling: The roughing rolling temperature is 1180–1230℃, the initial reduction is 25–40 mm, and the rolling speed is 3–6 m / s. The slow, low-speed roughing rolling promotes the precipitation of V and Ce carbides and refines the microstructure. The finishing rolling speed is 7–10 m / s, the initial finishing rolling temperature is 1050–1100℃, the initial reduction is 20–28 mm, and the final finishing rolling temperature is 850–950℃. The low-temperature, slow finishing rolling helps promote the precipitation of V and Ce carbides and controls the banded microstructure to no more than grade 1.5.

[0039] The steel plate is subjected to lamellar cooling 3-10 seconds after exiting the finishing mill. The initial cooling stage is concentrated, with a cooling rate of 60-150℃ / s (cooling rates exceeding 150℃ / s will form martensite, while cooling rates below 60℃ / s will result in coarse pearlite clusters with poor toughness and plasticity) to a temperature of 580-680℃ before coiling. This facilitates carbide nucleation. After air cooling to room temperature, a fine lamellar pearlite mixed microstructure is obtained, with banded microstructure not exceeding grade 1.5. In the lamellar cooling stages 1-4, edge shielding is used within 200mm of the edges of the steel plate on both sides, with a cooling rate difference ≤10℃ / s and a temperature difference ≤20℃ along the width of the band. Preferably, high-pressure water descaling is used before both roughing and finishing rolling, with a descaling water pressure of not less than 20MPa, to ensure the surface quality of the steel plate. Roughing is performed using a 3+1 rolling process, and finishing rolling is performed using 7 consecutive passes.

[0040] (5) Pickling and cold rolling: Hot-rolled steel coils are pickled. Because the LF furnace uses acidic slag, the inclusions in the steel plate are fully deformed and floated to the surface, and the iron oxide scale on the surface is loose. The pickling speed is controlled at 50-70m / min to ensure excellent surface quality of V-containing steel.

[0041] The pickled coil undergoes a single rolling process with a cold rolling reduction of 0.5–1.0 mm to break up the lamellar cementite and increase the dislocation density. After coiling, it is annealed at 680–750℃ for at least 20 hours. This process fully softens and relieves stress, achieving a spheroidization rate of over 98% and eliminating intergranular oxidation on the surface, effectively improving impact toughness, fatigue strength, and service life.

[0042] As a preferred option, the hot-rolled steel coil is pickled by a push-pull pickling unit, then rolled once on a reversible cold rolling mill, and finally annealed in a full-hydrogen bell-type annealing furnace.

[0043] (6) Heat treatment: The continuous heat treatment process is highly efficient, energy-saving, and reduces production costs. Cold-rolled steel coils are induction heated to 750–850℃, then cooled in a lead-bismuth mixture at a rate of 50–70℃ / s to 400–500℃ for tempering for ≥3 hours. After air cooling to room temperature, a uniform and fine tempered troostite structure is obtained, exhibiting excellent strength and toughness, superior fatigue strength and lifespan, and can be directly stamped into shape.

[0044] As a preferred option, the mass ratio of lead to bismuth in the lead-bismuth mixture is 3:1 to 4:1, which provides good hardenability.

[0045] like Figure 1 As shown, the finished steel plate has a uniform and fine tempered troostite structure, a hardness ≥48HRC, a surface hardness difference within ±0.5HRC, a tensile strength of 1500~1800MPa, a yield strength of 1300~1500MPa, and an elongation after fracture ≥10%.

[0046] Unless otherwise specified, all percentages in this invention are percentages by mass.

[0047] To more intuitively illustrate the present invention, the embodiments of the present invention will be further described in conjunction with the examples. The following examples are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technical solutions that can be obviously obtained by those skilled in the art within the scope of the technology disclosed in the present invention, including simple variations or equivalent substitutions, are all within the scope of protection of the present invention.

[0048]

Example

[0049] Table 1 - Chemical composition of steel (%)

[0050] Table 2 - Smelting Process Parameters

[0051] Table 3 - Continuous Casting and Heating Process Parameters

[0052] Table 4 - Rolling and Cooling Process Parameters

[0053] Table 5 Pickling and Cold Rolling Process Parameters

[0054] Table 6 - Heat Treatment Process Parameters and Properties of Finished Steel Plates

[0055] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A type of steel for the flexible wheel of a harmonic reducer for industrial robots, characterized in that, The chemical composition of the steel, by weight percentage, is as follows: 0.35%≤C≤0.60%, 0.2%≤Si≤1.5%, 0.5%≤Mn≤1.0%, 0.5%≤Cr≤1.5%, 0.1%≤Mo≤1.0%, 0.05%≤V≤0.50%, 0.002%≤Ce≤0.050%, Al≤0.015%, P≤0.015%, S≤0.01%, H≤0.0001%, O≤0.0015%, N≤0.005%, with the balance being Fe and unavoidable impurities.

2. The steel for the flexible wheel of a harmonic reducer for industrial robots according to claim 1, characterized in that, The finished steel plate has a uniform and fine tempered troostite structure, a hardness ≥48HRC, a surface hardness difference within ±0.5HRC, a tensile strength of 1500~1800MPa, a yield strength of 1300~1500MPa, and an elongation after fracture ≥10%.

3. A method for manufacturing steel for the flexible wheel of a harmonic reducer for industrial robots as described in claim 1 or 2, characterized in that, Includes the following steps: (1) Smelting: This includes converter smelting, LF electric furnace refining, and RH vacuum refining; the converter produces alkaline slag with phosphorus ≤0.014%, sulfur ≤0.010%, and residual oxygen ≤0.05% before tapping; the LF produces acidic slag with free oxygen ≤0.015% and residual oxygen ≤0.02% upon exiting the station; the pure RH treatment time is 20–30 min, the net circulation time is 10–20 min, the RH free oxygen is ≤0.0010%, the residual oxygen is ≤0.01%, and the steel killing time is 20–40 min; (2) Continuous casting: The superheat of the tundish casting is ≤25℃; continuous casting adopts light reduction and electromagnetic stirring, with a reduction of 6-10mm, a reduction rate of 1-4mm / m, an electromagnetic stirring current of 200-300A, a stirring frequency of 3-8Hz, and a forward and reverse rotation alternation time of 5-10min; continuous casting speed is 0.9-1.5m / min, secondary cooling water volume is 0.15-0.35L / kg, equiaxed crystal ratio is above 50%, billet thickness is 170-250mm, and the surface temperature deviation of the billet is not greater than 10℃; (3) Heating of the billet: The billet is hot-charged and fed into the heating furnace at a temperature ≥600℃. The heating furnace adopts a reducing atmosphere, with a preheating zone temperature of 600~700℃ and a holding time of more than 30 minutes. The first heating zone temperature is 1000~1100℃, the second heating zone temperature is 1180~1230℃, the soaking zone temperature is 1180~1220℃, and the total time in the furnace is more than 190 minutes. (4) Rolling and cooling: The roughing rolling start temperature is 1180~1230℃, the first pass reduction is 25~40mm, the roughing rolling speed is 3~6m / s, the finishing rolling threading speed is 7~10m / s, the finishing rolling start temperature is 1050~1100℃, the first pass reduction is 20~28mm, and the finishing rolling finish temperature is 850~950℃. The steel plate is cooled in a laminar flow cooling system 3-10 seconds after exiting the finishing mill, and then cooled to 580-680℃ at a cooling rate of 60-150℃ / s before being coiled. It is then air-cooled to room temperature to obtain a fine laminar pearlite mixed structure. The first to fourth laminar flow cooling groups are edge-shielded within 200mm of the two sides of the steel plate, with a cooling rate difference of ≤10℃ / s and a temperature difference of ≤20℃ in the width direction. (5) Pickling and cold rolling: Hot-rolled steel coils are pickled at a speed of 50–70 m / min. The pickled coil is rolled once, with a cold rolling reduction of 0.5-1.0 mm. After winding, it is annealed at a temperature of 680-750℃ for a holding time of ≥20h. (6) Heat treatment: A continuous heat treatment process is adopted, induction heating of cold-rolled steel coils to 750-850℃, cooling to 400-500℃ in a lead-bismuth mixture at a cooling rate of 50-70℃ / s, tempering for ≥3h, and air cooling to room temperature to obtain a uniform and fine tempered troostite structure.

4. A method for manufacturing steel for the flexible wheel of a harmonic reducer for industrial robots according to claim 3, characterized in that, In step (1), lime and lightly calcined dolomite are added during the converter smelting process to produce alkaline slag, with an alkalinity R of 3.0 to 4.5; silica, lime and fluorite are added during the LF electric furnace refining process to produce acidic slag, with an acidic slag alkalinity R ≤ 1.

4.

5. A method for manufacturing steel for the flexible wheel of a harmonic reducer for industrial robots according to claim 3, characterized in that, In step (4), high-pressure water descaling is used before roughing and finishing, and the descaling water pressure is not less than 20MPa; roughing is carried out by 3+1 rolling, and finishing is carried out by 7-pass continuous rolling.

6. A method for manufacturing steel for the flexible wheel of a harmonic reducer for industrial robots according to claim 3, characterized in that, In step (5), the hot-rolled steel coil is pickled by a push-pull pickling unit, then rolled once on a reversible cold rolling mill, and then annealed in a full-hydrogen bell-type annealing furnace after being coiled.

7. A method for manufacturing steel for the flexible wheel of a harmonic reducer for industrial robots according to claim 3, characterized in that, In step (6), the mass ratio of lead to bismuth in the lead-bismuth mixture is 3:1 to 4:1.

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