A low-cost steel for a flexspline of a harmonic reducer for robots and a method of manufacturing the same

Abstract

The present application relates to a kind of low-cost robot harmonic reducer flexible wheel steel and its manufacturing method, the component in steel is: 0.4%≤C≤0.7%, 0.2%≤Si≤1.0%, 0.5%≤Mn≤1.0%, 0.5%≤Cr≤1.5%, 0.003%≤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;Production process includes smelting, continuous casting, billet heating, rolling and cooling, normalizing and pickling.The microstructure of finished steel plate is uniform and fine sorbite, the hardness of finished steel plate is 40-45HRC, the surface hardness difference is within ±0.5HRC, the tensile strength is 1100-1300MPa, the yield strength is 800-1000MPa, and the elongation after fracture is ≥15%.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, and in particular to a low-cost steel for the flexible wheel of a harmonic reducer for 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 guillotine 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 material. 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, flexible wheels are typically manufactured using ingots of high-purity special steels such as 40CrMo and 40CrNiMo, which are molded into bars. These bars are then precision forged and tempered with nitriding to meet the demands for high precision, ultra-thin walls, long lifespan, and high reliability. However, mold casting suffers from low production efficiency, yield, and capacity, as well as high energy consumption and production costs. Furthermore, the precision forging of the bars and the heat treatment of individual flexible wheels not only result in low production efficiency and yield but also in complex processes. Compared to advanced foreign companies like Harmonic Drive Systems of Japan, domestically produced flexible wheels lag significantly in mechanical properties, microstructure control, and service life. Consequently, high-end flexible wheels have long relied on imports, greatly increasing the manufacturing cost of domestic industrial robots and severely hindering the development of my country's intelligent robot industry. Therefore, there is an urgent need to research and develop a low-cost steel and manufacturing process for harmonic reducer flexible wheels to promote the localization of key robot materials.

[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 rolling - slow cooling - softening annealing - finishing. The finished product is annealed bar stock with a yield strength ≥980 MPa, elongation ≥12%, reduction of area ≥55%, room temperature impact resistance AKV ≥78J, annealed hardness ≤269 HBW, and steel grain size ≥6. Non-metallic inclusions: B fine series ≤1.5 grade, B coarse series ≤1.0 grade, D fine series ≤1.0 grade, D coarse series ≤1.0 grade, DS series ≤1.0 grade; central porosity ≤1.5 grade, general porosity ≤1.0 grade, ingot segregation ≤1.0 grade, central segregation ≤1.5 grade, and banded inclusions after annealing ≤2.0 grade. However, the high variety and content of alloys in this scheme lead to high costs and are prone to defects such as segregation, which seriously affect fatigue life. In addition, both the billets and bars require slow cooling and softening annealing, resulting in long production cycles and low efficiency. The bars also need to be forged and precision machined into flexible wheels, which is 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%, and Al / N≥3.0, 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 meet the requirements of hardness ≥48HRC, yield strength ≥1500MPa, and elongation after fracture ≥12%. Before forging the flexible wheel blank, the raw materials need 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 between 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. The rolled steel has an austenite grain size of grade 9.5 or higher, and after a single quenching heat treatment, the austenite grain size of the flexible wheel product reaches grade 10.5 or higher. The rolled steel for flexible wheels has a D-class inclusion size of 0.5 and no A, B, or C-class inclusions. The steel for flexible wheels is also in bar form, requiring annealing of the raw materials followed by forging and precision machining of the flexible wheels. This process is complex, resulting in low production efficiency, low yield, and high cost.

[0008] In addition, the production process stability of flexible wheels using the above methods is difficult to control, the uniformity of the hardness of the flexible wheels is difficult to guarantee, and none of the above solutions mention hardness uniformity and control technology. Summary of the Invention

[0009] This invention addresses the problems of high production cost and unstable quality of existing robot flexible wheels in my country. It provides a low-cost steel for robot harmonic reducers and its manufacturing method, eliminating the need for cold rolling and heat treatment. The finished steel plate has a thickness of 2.0–4.0 mm, a hardness of 40–45 HRC, a surface hardness difference within ±0.5 HRC, a tensile strength of 1100–1300 MPa, a yield strength of 800–1000 MPa, and an elongation after fracture ≥15%. Flexible wheels processed using the steel described in this invention have a fatigue life ≥10 years. 7 Second, high-cycle fatigue strength ≥400MPa.

[0010] To achieve the above objectives, the present invention employs the following technical solution: A low-cost steel for flexible wheels in harmonic reducers for robots, wherein the chemical composition of the steel by weight percentage is: 0.4%≤C≤0.7%, 0.2%≤Si≤1.0%, 0.5%≤Mn≤1.0%, 0.5%≤Cr≤1.5%, 0.003%≤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.

[0011] The finished steel plate has a uniform and fine sorbite structure with a spheroidized pearlite diameter not exceeding 1 μm; the various non-metallic inclusions in the finished steel plate do not exceed grade 1.0; the hardness of the finished steel plate is 40-45 HRC, the surface hardness difference is within ±0.5 HRC, the tensile strength is 1100-1300 MPa, the yield strength is 800-1000 MPa, and the elongation after fracture is ≥15%.

[0012] A method for manufacturing steel for a low-cost harmonic reducer flexspline in a robot 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 8-12mm, 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 stirring alternation time of 5-10min; the continuous casting speed is 1.1-1.7m / min, the secondary cooling water flow rate is 0.15-0.35L / kg, the equiaxed crystal ratio is above 50%; the 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 1130~1200℃, the soaking zone temperature is 1150~1200℃, and the total time in the furnace is more than 180 minutes. (4) Rolling and cooling: The roughing mill starts at 1130–1200℃, with a first pass reduction of 30–50 mm and a rolling speed of 5–8 m / s. The finishing mill runs at 8–12 m / s, starts at 1050–1100℃, with a first pass reduction of 25–35 mm and a final rolling temperature of 800–880℃. The steel plate is then subjected to laminar flow cooling 3–10 seconds after exiting the finishing mill, cooled to 650–700℃ at a rate of 30–100℃ / s before being coiled. Within 20 minutes of coiling, the plate is placed in a slow cooling pit for at least 90 hours to obtain a mixed microstructure of fine lamellar pearlite, sorbite, and ferrite, where the volume ratio of fine lamellar pearlite does not exceed 30% and the volume ratio of ferrite does not exceed 20%. (5) Normalizing and pickling: When the steel coil is slowly cooled to 70-100℃, it is put into the normalizing and pickling unit at a speed of 20-50m / min. The normalizing temperature is 800-900℃ and the temperature is held for 2-6min. The first cooling is at a cooling rate of 1.5-3℃ / s to 500-600℃, and the second cooling is at a cooling rate of 3-8℃ / s to 50-100℃. After pickling, fine sorbite structure is obtained.

[0013] In step (1), lime and lightly calcined dolomite are added during the converter smelting process to produce alkaline slag with an alkalinity R of 2.5 to 3.5 and a slag thickness of ≤80mm; silica, lime and fluorite are added during the LF electric furnace refining process to produce acidic slag with an alkalinity R of ≤1.0.

[0014] 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.

[0015] Compared with the prior art, the beneficial effects of the present invention are: Through improvements in chemical composition and processing, a flexible wheel steel with a thickness of 2.0–4.0 mm was produced. It is alloyed with elements such as Cr and Ce, and process parameters for smelting, continuous casting, billet heating, rolling and cooling, normalizing, and pickling were controlled simultaneously. No cold rolling or heat treatment is required. The finished product has a uniform and fine sorbite microstructure with spheroidized pearlite diameter not exceeding 1 μm, a hardness of 40–45 HRC, a surface hardness difference within ±0.5 HRC, a tensile strength of 1100–1300 MPa, a yield strength of 800–1000 MPa, and an elongation after fracture ≥15%. Flexible wheels processed using the steel described in this invention exhibit excellent strength-toughness matching, excellent fatigue strength and life, with a high-cycle fatigue strength ≥400 MPa and a fatigue life ≥10. 7 Second-rate. Attached Figure Description

[0016] Figure 1 This is a typical metallographic image of the steel used for the flexible wheel of a low-cost robot harmonic reducer as described in this invention. Detailed Implementation

[0017] The present invention discloses a low-cost steel for flexible wheels in harmonic reducers for robots. The chemical composition of the steel, by weight percentage, is as follows: 0.4%≤C≤0.7%, 0.2%≤Si≤1.0%, 0.5%≤Mn≤1.0%, 0.5%≤Cr≤1.5%, 0.003%≤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. The production process includes smelting, continuous casting, billet heating, rolling and cooling, normalizing and pickling.

[0018] The mechanism of action of each alloy component in the steel for the flexible wheel of a low-cost harmonic reducer for robots described in this invention is as follows: C: 0.4%~0.7%.

[0019] Carbon (C) is a major solid solution strengthening element in steel. In this invention, C reacts with Ce, Mn, and Cr 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 0.4%, it is difficult to guarantee the strength of the steel plate. On the other hand, if the C content is above 0.7%, the strength is too high, affecting the yield strength ratio, deteriorating the toughness and plasticity of the steel, and making it prone to fracture. Therefore, the C content should be controlled between 0.4% and 0.7%.

[0020] Mn: 0.5%~1.0%.

[0021] 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 lead to hot cracks and affect stamping formability. Furthermore, the fine MnCeS precipitates also enhance strength and impact toughness. Low Mn content cannot meet the requirements for high strength and hardness, while excessive Mn content results in severe segregation, affecting deep-drawing formability and increasing production costs. Therefore, considering both cost and performance requirements, the Mn content should be controlled between 0.5% and 1.0%.

[0022] Si: 0.2%~1.0%.

[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, not a carbide-forming element. Si dissolved in ferrite improves hardenability and tempering resistance, increases strength and hardness, and enhances wear resistance. This invention uses fine precipitates formed by Si and Ce to hinder dislocation movement, improving the elastic limit and yield strength, thus meeting the requirements for flexible gear applications. When the Si content exceeds 1.0%, the steel surface suffers severe oxidation and decarburization, affecting wear resistance.

[0024] Cr: 0.5%~1.5%.

[0025] Chromium is a medium-strong carbide-forming element. In this invention, the addition of Cr forms complex carbides with C, Mn, and Ce, inhibiting the segregation of Cr and Mo and improving the uniformity of the microstructure. Chromium also increases the temperature of Al3 and Al, shifts the GS line to the upper left, slows down Al decomposition, improves hardenability, and enhances 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, and O are unavoidable harmful impurities in steel. Their presence will seriously deteriorate the toughness of steel. Therefore, the content of P, S, H, O, and N in steel should be controlled to be as low as possible.

[0028] Ce: 0.003%~0.050%.

[0029] Ce, as a microalloying element, forms composite precipitates with C, Cr, and Mn, promoting carbide nucleation, pearlite spheroidization and refinement, and improving wear resistance and fatigue strength. 7 The second-highest cycle fatigue strength is ≥600MPa. On the other hand, this invention utilizes the combination of Ce with O and S to form spherical fine inclusions, ensuring sufficient upward floating and avoiding the formation of elongated MnS inclusions from S and Mn, thereby improving fatigue performance and increasing fatigue life to ≥10. 7 Multiple cycles, wear-resistant and anti-seize.

[0030] The present invention discloses a method for manufacturing steel for a low-cost harmonic reducer flexspline in a robot, comprising 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 enhanced stirring during refining, resulting in 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 is ≤0.0010%, and the residual oxygen is ≤0.01%. The steel calming time is 20–40 min, promoting sufficient flotation of inclusions, improving steel purity, reducing inclusions in the steel (all non-metallic inclusions in the finished steel do not exceed grade 1.0), and eliminating anisotropy in the microstructure.

[0031] 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 2.5 to 3.5. During the converter tapping process, slag blocking operations are performed to reduce the amount of slag discharged during tapping and to control the slag thickness to ≤80mm. Silica, lime, and fluorite are added during the LF electric furnace refining process to create acidic slag, with an acidic slag basicity R ≤1.0.

[0032] (2) Continuous casting: The superheat of the tundish casting is ≤25℃; continuous casting adopts light reduction and electromagnetic stirring, with a reduction of 8-12mm, 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 stirring alternation time of 5-10min; the continuous casting speed is 1.1-1.7m / min, the secondary cooling water volume is 0.15-0.35L / kg, the equiaxed crystal ratio is above 50%, and the microsegregation of the alloy liquid at the end of the columnar crystals is controlled; the billet thickness is 170-250mm, the surface temperature deviation of the billet is not greater than 10℃, the billet cooling rate is uniform, and the microstructure is uniform.

[0033] (3) Heating of the billet: The billet is hot-charged and fed into the heating furnace at a temperature ≥600℃ to reduce the surface temperature difference and mitigate microsegregation. The heating furnace employs a reducing atmosphere. The preheating section temperature is 600–700℃ with a holding time of at least 30 minutes. The first heating section temperature is 1000–1100℃, the second heating section temperature is 1130–1200℃, and the soaking section temperature is 1150–1200℃. The total time in the furnace is at least 180 minutes to ensure billet surface quality, prevent oxidation and decarburization, and simultaneously ensure the rolling temperature to form various Ce carbides, thereby improving strength and toughness.

[0034] (4) Rolling and cooling: The roughing rolling start temperature is 1130–1200℃, the first pass reduction is 30–50 mm, and the roughing rolling speed is 5–8 m / s. The roughing rolling adopts low temperature and high reduction to promote the precipitation of Cr carbides and uniformly refine the microstructure. The finishing rolling strip threading speed is 8–12 m / s, the finishing rolling start temperature is 1050–1100℃, the first pass reduction is 25–35 mm, and the finishing rolling finish temperature is 800–880℃. The finishing rolling adopts low temperature and high reduction, which helps to uniformly refine the microstructure, promote the precipitation of Cr and Ce carbides, and control the banding to not exceed grade 1.5.

[0035] The steel plate enters laminar flow cooling 3-10 seconds after exiting the finishing mill, with concentrated cooling in the front section, and is cooled to 650-700℃ at a cooling rate of 30-100℃ / s before being coiled. After coiling, it is placed in a slow cooling pit for slow cooling for more than 90 hours within 20 minutes to obtain a mixed microstructure of fine lamellar pearlite + sorbite + ferrite, wherein the volume ratio of fine lamellar pearlite does not exceed 30% and the volume ratio of ferrite does not exceed 20%, so as to ensure uniform austenitization during subsequent normalizing treatment.

[0036] As a preferred method, high-pressure water descaling is performed before both roughing and finishing rolling, with a descaling water pressure of not less than 20 MPa, in order to ensure the surface quality of the steel plate. Roughing is carried out using a 3+1 rolling process, and finishing rolling is carried out using a 7-pass continuous rolling process.

[0037] (5) Normalizing and pickling: When the steel coil is slowly cooled to 70-100℃, it is put into the normalizing and pickling unit at a speed of 20-50m / min. The normalizing temperature is 800-900℃ and the temperature is held for 2-6min to homogenize the austenite. The first cooling is at a cooling rate of 1.5-3℃ / s to 500-600℃, and the second cooling is at a cooling rate of 3-8℃ / s to 50-100℃. After pickling, a fine sorbite structure is obtained, and the diameter of the spheroidized pearlite does not exceed 1μm. It can be directly stamped and formed.

[0038] like Figure 1 As shown, the microstructure of the finished steel plate is a uniform and fine sorbite structure, with the diameter of spheroidized pearlite not exceeding 1 μm; the various non-metallic inclusions in the finished steel plate do not exceed grade 1.0; the hardness of the finished steel plate is 40-45 HRC, the surface hardness difference is within ±0.5 HRC, the tensile strength is 1100-1300 MPa, the yield strength is 800-1000 MPa, and the elongation after fracture is ≥15%.

[0039] Unless otherwise specified, all percentages in this invention are percentages by mass.

[0040] 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.

[0041]

Example

[0042] Table 1 - Chemical composition of steel (%)

[0043] Table 2 - Smelting Process Parameters

[0044] Table 3 - Continuous casting and billet heating process parameters

[0045] Table 4 - Hot rolling and cooling process parameters

[0046] Table 5 - Normalizing Process Parameters

[0047] Table 6 - Properties of Finished Steel Plates

[0048] 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 low-cost steel for the flexible wheel of a harmonic reducer for robots, characterized in that, The chemical composition of the steel, by weight percentage, is as follows: 0.4%≤C≤0.7%, 0.2%≤Si≤1.0%, 0.5%≤Mn≤1.0%, 0.5%≤Cr≤1.5%, 0.003%≤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 low-cost steel for the flexible wheel of a harmonic reducer for robots according to claim 1, characterized in that, The finished steel plate has a uniform and fine sorbite structure with a spheroidized pearlite diameter not exceeding 1 μm; the various non-metallic inclusions in the finished steel plate do not exceed grade 1.0; the hardness of the finished steel plate is 40-45 HRC, the surface hardness difference is within ±0.5 HRC, the tensile strength is 1100-1300 MPa, the yield strength is 800-1000 MPa, and the elongation after fracture is ≥15%.

3. A method for manufacturing steel for a low-cost harmonic reducer flexspline for 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 8-12mm, 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 stirring alternation time of 5-10min; the continuous casting speed is 1.1-1.7m / min, the secondary cooling water flow rate is 0.15-0.35L / kg, the equiaxed crystal ratio is above 50%; the 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 1130~1200℃, the soaking zone temperature is 1150~1200℃, and the total time in the furnace is more than 180 minutes. (4) Rolling and cooling: The roughing mill starts at 1130–1200℃, with a first pass reduction of 30–50 mm and a rolling speed of 5–8 m / s. The finishing mill runs at 8–12 m / s, starts at 1050–1100℃, with a first pass reduction of 25–35 mm and a final rolling temperature of 800–880℃. The steel plate is then subjected to laminar flow cooling 3–10 seconds after exiting the finishing mill, cooled to 650–700℃ at a rate of 30–100℃ / s before being coiled. Within 20 minutes of coiling, the plate is placed in a slow cooling pit for at least 90 hours to obtain a mixed microstructure of fine lamellar pearlite, sorbite, and ferrite, where the volume ratio of fine lamellar pearlite does not exceed 30% and the volume ratio of ferrite does not exceed 20%. (5) Normalizing and pickling: When the steel coil is slowly cooled to 70-100℃, it is put into the normalizing and pickling unit at a speed of 20-50m / min. The normalizing temperature is 800-900℃ and the temperature is held for 2-6min. The first cooling is at a cooling rate of 1.5-3℃ / s to 500-600℃, and the second cooling is at a cooling rate of 3-8℃ / s to 50-100℃. After pickling, fine sorbite structure is obtained.

4. The method for manufacturing steel for a low-cost harmonic reducer flexspline for 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 2.5 to 3.5 and a slag thickness of ≤80mm; silica, lime and fluorite are added during the LF electric furnace refining process to produce acidic slag with an alkalinity R of ≤1.

0.

5. A method for manufacturing steel for a low-cost harmonic reducer flexspline for 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.

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