Fine-grain high-cleanliness steel for harmonic reducer flexible gear of industrial robot and preparation method of fine-grain high-cleanliness steel

Abstract

The invention discloses fine-grain high-cleanliness steel for a harmonic reducer flexible gear of an industrial robot and a preparation method, and belongs to the technical field of metallurgy. The steel for the flexible gear comprises the following chemical components in percentage by mass: 0.38 to 0.42 percent of C, 0.20 to 0.30 percent of Si, 0.60 to 0.90 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.010 percent of S, 0.60 to 0.90 percent of Cr, 0.15 to 0.25 percent of Mo, 1.50 to 1.80 percent of Ni, 0.015 to 0.035 percent of Nb, less than or equal to 0.0006 percent of O and the balance of iron and inevitable impurity elements. The production method comprises the working procedures of vacuum induction furnace smelting, electroslag remelting, casting blank forging, bar heating, bar rolling and rolled material cooling. The steel for the flexible gear has fine austenite grains and high cleanliness, and the technical requirements of the steel for the harmonic reducer flexible gear of the industrial robot are met.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to fine-grained high-cleanliness steel for a flexible wheel of a harmonic reducer of an industrial robot and a preparation method thereof. Background Art

[0002] Precision reducers are the most critical components in industrial robots, and RV reducers and harmonic reducers are the two most common precision reducers for industrial robots. Among them, harmonic reducers have the advantages of compact structure, light weight, small size, large reduction ratio, and high transmission efficiency, and are widely used in the forearms and wrists of industrial robots.

[0003] The harmonic reducer for industrial robots consists of three basic components: a rigid wheel, a flexwheel and a wave generator. As one of the three core components of the harmonic reducer, the flexwheel is the part with the highest technical barriers. Since the flexwheel needs to continuously deform at high speed to transmit torque, it is most prone to failure, and its life determines the life of the reducer.

[0004] At present, Japan's Harmonic reducer accounts for about 80% of the global market share. Due to factors such as raw materials, there is a significant gap in the products of domestic enterprises. Compared with Japanese flexible wheels, the poor cleanliness, coarse and uneven structure of domestic flexible wheels are the main reasons for short fatigue life and poor stability. Therefore, the development of a high-cleanliness steel for flexible wheels of harmonic reducers for industrial robots has broad application prospects. Summary of the invention

[0005] The present invention provides fine-grained high-cleanliness steel for flexible pulleys of industrial robot harmonic reducers and a preparation method thereof. By adopting a new process, the steel for flexible pulleys has fine austenite grains and high cleanliness, and the austenite grain size of the rolled material reaches 9.5. After a single quenching heat treatment, the austenite grain size of the flexible pulley product reaches 10.5. The steel has a high cleanliness, with a total [O] content of ≤0.0006%, a D-type inclusion of ≤0.5, and no A, B, or C-type inclusions, meeting the technical requirements for steel for flexible pulleys of industrial robot harmonic reducers.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a fine-grained, high-cleanliness industrial robot harmonic reducer flexible wheel steel, the chemical composition of the flexible wheel steel and its mass percentage are: 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%, and the remainder is Fe and unavoidable impurities.

[0007] The austenite grain size of the steel rolled material for the flexible pulley of the present invention reaches above grade 9.5, and after a single quenching heat treatment, the austenite grain size of the flexible pulley product reaches above grade 10.5.

[0008] The D-type inclusions of the steel rolled material for the flexible wheel of the present invention are ≤0.5 level, and there are no A, B, C-type inclusions.

[0009] Another object of the present invention is to provide a method for preparing the above-mentioned fine-grained, high-cleanliness industrial robot harmonic reducer flexible wheel steel, the production method comprising vacuum induction furnace smelting, electroslag remelting, ingot forging, bar heating, bar rolling, and rolled material cooling processes; the vacuum induction furnace smelting process comprises a vacuum degree of 10 to 15 Pa in the vacuum induction furnace smelting, and argon protection for the electroslag remelting; the bar heating process comprises a heating temperature of 1150 to 1200°C and a total heating time of 180 to 240 minutes.

[0010] The casting billet forging process of the present invention has a heating temperature of 1180-1220° C., a forging temperature of 1150-1180° C., and a forging billet cross-sectional size of 140*140-160*160 mm square billet.

[0011] In the bar rolling process of the present invention, the square billet is continuously rolled into a bar with a diameter of 30 to 60 mm after leaving the heating furnace.

[0012] In the rolling material cooling process of the present invention, the rolled bar material passes through a cooling bed quickly and then enters a pit for slow cooling, and the temperature entering the pit is controlled to be ≥500°C.

[0013] The austenite grain size of the flexspline steel rolled material obtained by the method of the present invention reaches above grade 9.5, and after a single quenching heat treatment, the austenite grain size of the flexspline product reaches above grade 10.5; the D-type inclusions are ≤ grade 0.5, and there are no A, B, or C-type inclusions.

[0014] The chemical composition design of the present invention is based on the following: C: Carbon has a significant solid solution strengthening effect, which can improve the hardenability and strength of steel. Considering the service characteristics of the harmonic reducer flexible wheel, the steel is required to have not only high strength but also good toughness and impact resistance. The C content of the present invention is in the range of 0.38-0.42%.

[0015] Si: Silicon plays a role in solid solution strengthening in steel and can improve the stability of austenite. As a non-carbide forming element, silicon can be dissolved into carbides to stabilize carbides, slow down the aggregation rate of carbides, and hinder the growth of carbides, thereby helping to improve the strength and hardness of steel. However, too high a silicon content will lead to a decrease in the toughness of steel. The Si content of the present invention is in the range of 0.20 to 0.30%.

[0016] Mn: Manganese can expand the austenite region, stabilize the austenite structure, improve hardenability, and reduce the critical cooling rate of martensite formation. However, excessive manganese content will increase the tendency of grain coarsening and increase the temper brittleness of steel. The Mn content of the present invention is in the range of 0.60-0.90%.

[0017] P, S, [O]: Phosphorus and sulfur as impurity elements seriously damage the plasticity and toughness of steel. Oxygen exists in steel in the form of B or D oxide inclusions and is not easily deformed. During the service life of the flexible wheel, cracks are easily generated near the oxide inclusions, resulting in a reduced life. In the present invention, P≤0.015%, S≤0.010%, O≤0.0006%.

[0018] Cr: Chromium can improve hardenability. As a medium carbide-forming element, it improves the stability of carbides. It can prevent or slow down the precipitation and aggregation of carbides during tempering, improve the tempering stability of steel, and improve the strength and hardness of steel. However, too high a chromium content reduces the impact toughness of steel. The Cr content of the present invention is in the range of 0.60 to 0.90%.

[0019] Ni: Nickel is an element that stabilizes austenite, can improve hardenability, strength and hardness, and improve the toughness of steel, especially low-temperature toughness. Considering that nickel is a precious alloy, the Ni content of the present invention is in the range of 1.50-1.80%.

[0020] Mo: Molybdenum can improve hardenability and significantly refine grains, improve strength and toughness, reduce or inhibit the first and second temper brittleness of steel, and precipitate very fine carbides during tempering to strengthen the steel matrix. Since molybdenum is very expensive, the Mo content of the present invention is in the range of 0.15-0.25%.

[0021] Nb: Niobium is a strong carbide, nitride and carbonitride forming element. The precipitated carbonitride particles can effectively pin the grain boundary, inhibit grain growth, and play a role in grain refinement. Among them, fine grain strengthening can not only improve the strength of the material, but also improve plasticity and toughness. At the same time, in order to prevent the precipitation of large particles of niobium carbonitride from affecting the service life of the flexible wheel, the present invention strictly limits the content range of niobium, and the content range of Nb in the present invention is 0.015-0.035%.

[0022] The beneficial effects of the above technical scheme are as follows: 1. The present invention appropriately adds Mn, Cr, Ni, and Mo hardenability elements on the basis of medium carbon steel to ensure the strength and toughness of the flexible wheel of the harmonic reducer of the industrial robot. In addition, the grain refinement element Nb is added, and the amount of Nb added is strictly limited, so that the austenite grain size of the rolled material reaches 9.5. After a quenching heat treatment, the austenite grain size of the flexible wheel product reaches 10.5. Compared with the medium carbon low alloy steel without Nb addition, the austenite grain size can be refined by 1.5 to 2.0 levels, and the grains are finer. 2. The present invention adopts a vacuum induction furnace and an electroslag remelting method for smelting, and the total [O] content is ≤0.0006%, the D-type inclusions are ≤0.5, and there are no A, B, and C-type inclusions. Compared with the ordinary production process, the cleanliness of the steel is higher, which is beneficial to improve the service life of the flexible wheel of the harmonic reducer of the industrial robot. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Austenite grain size and inclusions of the flexspline steel obtained in Example 1 of the present invention; Figure 2 Austenite grain size and inclusions of the flexspline steel obtained in Example 2 of the present invention; Figure 3 Austenite grain size and inclusions image of the flexspline steel obtained in Example 3 of the present invention. DETAILED DESCRIPTION

[0024] The present invention will be further described in detail below in conjunction with specific embodiments. Example 1

[0025] A fine-grained, high-cleanliness steel for a flexible wheel of a harmonic reducer of an industrial robot and a preparation method thereof, comprising vacuum induction furnace smelting, electroslag remelting, ingot forging, bar heating, bar rolling, and rolled material cooling processes; wherein: Vacuum induction furnace smelting process: The chemical composition of steelmaking is as follows: C: 0.40%, Si: 0.20%, Mn: 0.72%, P: 0.010%, S: 0.003%, Cr: 0.80%, Ni: 1.70%, Mo: 0.20%, Nb: 0.018%, [O]: 0.00052%, and the rest are iron and unavoidable impurity elements. According to the above composition, it is smelted in a vacuum induction furnace with a vacuum degree of 13Pa.

[0026] Electroslag remelting process: The smelted ingot continues to be electroslag remelted, and argon gas is used for protection during electroslag remelting.

[0027] Ingot forging process: The electroslag remelted steel ingot is heated and forged at a heating temperature of 1210°C and a forging temperature of 1170°C. The electroslag remelted ingot is finally forged into a 150*150mm square ingot.

[0028] Bar heating process: the forged steel billet is heated, rolled and cooled, with a heating temperature of 1160°C and a total heating time of 220 minutes.

[0029] Bar rolling process: After the billet is heated, it undergoes rough rolling, intermediate rolling and finish rolling in sequence. After rolling, the required 40mm diameter bar is achieved.

[0030] Rolled material cooling process: The rolled bars pass through the cooling bed quickly, then enter the pit for slow cooling, the pit temperature is 520℃, and finally collected.

[0031] By adopting the above preparation method, the steel for the flexible wheel of the harmonic reducer of the industrial robot has obtained fine austenite grains and high cleanliness. The austenite grain size of the rolled material is 9.5; after a quenching heat treatment, the austenite grain size of the flexible wheel product is 10.5. The cleanliness of the steel is high, with a total [O] content of 0.00052%, a D-type inclusion of 0.5, and no A, B, or C-type inclusions, which meets the technical requirements for the steel for the flexible wheel of the harmonic reducer of the industrial robot. The austenite grain size of the rolled material is as follows: Figure 1 shown. Example 2

[0032] A fine-grained, high-cleanliness steel for a flexible wheel of a harmonic reducer of an industrial robot and a preparation method thereof, comprising vacuum induction furnace smelting, electroslag remelting, ingot forging, bar heating, bar rolling, and rolled material cooling processes; wherein: Vacuum induction furnace smelting process: The chemical composition of steelmaking is as follows: C: 0.38%, Si: 0.26%, Mn: 0.90%, P: 0.015%, S: 0.006%, Cr: 0.60%, Ni: 1.50%, Mo: 0.25%, Nb: 0.015%, [O]: 0.00060%, and the rest is iron and unavoidable impurity elements. According to the above composition, it is smelted in a vacuum induction furnace with a vacuum degree of 15Pa.

[0033] Electroslag remelting process: The smelted ingot continues to be electroslag remelted, and argon gas is used for protection during electroslag remelting.

[0034] Ingot forging process: The electroslag remelted steel ingot is heated and forged at a heating temperature of 1220°C and a forging temperature of 1180°C. The electroslag remelted ingot is finally forged into a 160*160mm square ingot.

[0035] Bar heating process: the forged billet is heated, rolled, cooled and collected, with a heating temperature of 1200°C and a total heating time of 180 minutes.

[0036] Bar rolling process: After the billet is heated, it undergoes rough rolling, intermediate rolling and finish rolling in sequence. After rolling, the required 30mm diameter bar is achieved.

[0037] Rolled material cooling process: The rolled bars pass through the cooling bed quickly, then enter the pit for slow cooling, the pit temperature is 500℃, and finally collected.

[0038] By adopting the above preparation method, the steel for the flexible wheel of the harmonic reducer of the industrial robot has obtained fine austenite grains and high cleanliness. The austenite grain size of the rolled material is 9.6; after a quenching heat treatment, the austenite grain size of the flexible wheel product is 10.5. The cleanliness of the steel is high, with a total [O] content of 0.00060%, a D-type inclusion of 0.5, and no A, B, or C-type inclusions, which meets the technical requirements for the steel for the flexible wheel of the harmonic reducer of the industrial robot. The austenite grain size of the flexible wheel product is as follows: Figure 2 shown. Example 3

[0039] A fine-grained, high-cleanliness steel for a flexible wheel of a harmonic reducer of an industrial robot and a preparation method thereof, comprising vacuum induction furnace smelting, electroslag remelting, ingot forging, bar heating, bar rolling, and rolled material cooling processes; wherein: Vacuum induction furnace smelting process: The chemical composition of steelmaking is as follows: C: 0.42%, Si: 0.30%, Mn: 0.60%, P: 0.015%, S: 0.0010%, Cr: 0.90%, Ni: 1.80%, Mo: 0.15%, Nb: 0.035%, [O]: 0.00056%, and the rest is iron and unavoidable impurity elements. According to the above composition, it is smelted in a vacuum induction furnace with a vacuum degree of 10Pa.

[0040] Electroslag remelting process: The smelted ingot continues to be electroslag remelted, and argon gas is used for protection during electroslag remelting.

[0041] Ingot forging process: The electroslag remelted steel ingot is heated and forged at a heating temperature of 1180°C and a forging temperature of 1150°C. The electroslag remelted ingot is finally forged into a 140*140mm square ingot.

[0042] Bar heating process: the forged billet is heated, rolled, cooled and collected, with a heating temperature of 1150°C and a total heating time of 240 minutes.

[0043] Bar rolling process: After the billet is heated, it undergoes rough rolling, intermediate rolling and finish rolling in sequence. After rolling, the required 60mm diameter bar is achieved.

[0044] Rolled material cooling process: The rolled bars pass through the cooling bed quickly, then enter the pit for slow cooling, the pit temperature is 550℃, and finally collected.

[0045] By adopting the above preparation method, the steel for the flexible wheel of the harmonic reducer of the industrial robot has obtained fine austenite grains and high cleanliness. The austenite grain size of the rolled material is 9.7; after a quenching heat treatment, the austenite grain size of the flexible wheel product is 10.5. The cleanliness of the steel is relatively high, with a total [O] content of 0.00056%, a D-type inclusion of 0.5, and no A, B, or C-type inclusions, which meets the technical requirements for the flexible wheel steel of the harmonic reducer of the industrial robot. The inclusion rating of the rolled material is as follows: Figure 3 shown. Example 4

[0046] A fine-grained, high-cleanliness steel for a flexible wheel of a harmonic reducer of an industrial robot and a preparation method thereof, comprising vacuum induction furnace smelting, electroslag remelting, ingot forging, bar heating, bar rolling, and rolled material cooling processes; wherein: Vacuum induction furnace smelting process: The chemical composition of steelmaking is as follows: C: 0.39%, Si: 0.23%, Mn: 0.75%, P: 0.011%, S: 0.0007%, Cr: 0.83%, Ni: 1.63%, Mo: 0.18%, Nb: 0.035%, [O]: 0.00050%, and the rest is iron and unavoidable impurity elements. According to the above composition, it is smelted in a vacuum induction furnace with a vacuum degree of 11Pa.

[0047] Electroslag remelting process: The smelted ingot continues to be electroslag remelted, and argon gas is used for protection during electroslag remelting.

[0048] Ingot forging process: The electroslag remelted steel ingot is heated and forged at a heating temperature of 1190°C and a forging temperature of 1165°C. The electroslag remelted ingot is finally forged into a 145*145mm square ingot.

[0049] Bar heating process: the forged billet is heated, rolled, cooled and collected, with a heating temperature of 1155°C and a total heating time of 215 minutes.

[0050] Bar rolling process: After the billet is heated, it undergoes rough rolling, intermediate rolling and finish rolling in sequence. After rolling, the required 35mm diameter bar is achieved.

[0051] Rolled material cooling process: The rolled bars pass through the cooling bed quickly, then enter the pit for slow cooling, the pit temperature is 545℃, and finally collected.

[0052] By adopting the above preparation method, the steel for the flexible wheel of the harmonic reducer of the industrial robot has obtained fine austenite grains and high cleanliness. The austenite grain size of the rolled material is 9.6; after a quenching heat treatment, the austenite grain size of the flexible wheel product is 10.5. The cleanliness of the steel is high, the total [O] content is 0.00050%, the D-type inclusion is 0, and there are no A, B, and C-type inclusions, which meets the technical requirements for the flexible wheel steel of the harmonic reducer of the industrial robot. The inclusion rating of the rolled material is similar to that of the attached Figure 1 Similar, so omitted. Example 5

[0053] A fine-grained, high-cleanliness steel for a flexible wheel of a harmonic reducer of an industrial robot and a preparation method thereof, comprising vacuum induction furnace smelting, electroslag remelting, ingot forging, bar heating, bar rolling, and rolled material cooling processes; wherein: Vacuum induction furnace smelting process: The chemical composition of steelmaking is as follows: C: 0.39%, Si: 0.27%, Mn: 0.68%, P: 0.010%, S: 0.0007%, Cr: 0.78%, Ni: 1.58%, Mo: 0.21%, Nb: 0.022%, [O]: 0.00043%, and the rest is iron and unavoidable impurity elements. According to the above composition, it is smelted in a vacuum induction furnace with a vacuum degree of 12Pa.

[0054] Electroslag remelting process: The smelted ingot continues to be electroslag remelted, and argon gas is used for protection during electroslag remelting.

[0055] Ingot forging process: The electroslag remelted steel ingot is heated and forged at a heating temperature of 1200°C and a forging temperature of 1155°C. The electroslag remelted ingot is finally forged into a 155*155mm square ingot.

[0056] Bar heating process: The forged billet is heated, rolled, cooled and collected, with a heating temperature of 1194°C and a total heating time of 208 minutes.

[0057] Bar rolling process: After the billet is heated, it undergoes rough rolling, intermediate rolling and finish rolling in sequence. After rolling, the required 50mm diameter bar is achieved.

[0058] Rolled material cooling process: The rolled bars pass through the cooling bed quickly, then enter the pit for slow cooling, the pit temperature is 537℃, and finally collected.

[0059] By adopting the above preparation method, the steel for the flexible wheel of the harmonic reducer of the industrial robot has obtained fine austenite grains and high cleanliness. The austenite grain size of the rolled material is 9.8; after a quenching heat treatment, the austenite grain size of the flexible wheel product is 10.5. The cleanliness of the steel is high, the total [O] content is 0.00043%, the D-type inclusion is 0, and there are no A, B, and C-type inclusions, which meets the technical requirements for the flexible wheel steel of the harmonic reducer of the industrial robot. The inclusion rating of the rolled material is similar to that of the attached Figure 1 Similar, so omitted.

[0060] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A fine-grained, high-cleanliness steel for flexible pulleys of harmonic reducers of industrial robots, characterized in that: The chemical composition and mass percentage of the flexible wheel steel are: 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%, and the balance is Fe and unavoidable impurities.

2. The fine-grained, high-cleanliness steel for flexible pulleys of harmonic reducers of industrial robots according to claim 1, characterized in that: The austenite grain size of the steel rolled material for the flexspline reaches above grade 9.5, and after a single quenching heat treatment, the austenite grain size of the flexspline product reaches above grade 10.

5.

3. The fine-grained, high-cleanliness steel for flexible pulleys of harmonic reducers of industrial robots according to claim 1, characterized in that: The D-type inclusions of the steel rolled material for the flexible wheel are ≤ level 0.5, and there are no A, B, or C-type inclusions.

4. The method for preparing fine-grained high-cleanliness steel for flexible pulley of harmonic reducer of industrial robot according to any one of claims 1 to 3, characterized in that: The production method comprises the steps of vacuum induction furnace smelting, electroslag remelting, ingot forging, bar heating, bar rolling and rolled material cooling; in the vacuum induction furnace smelting step, the vacuum degree of the vacuum induction furnace smelting is 10-15 Pa, and the electroslag remelting is argon gas protection; in the bar heating step, the heating temperature is 1150-1200° C. and the total heating time is 180-240 min.

5. The method for preparing fine-grained high-cleanliness industrial robot harmonic reducer flexible wheel steel according to claim 4, characterized in that: In the forging process of the cast billet, the heating temperature is 1180-1220°C and the forging temperature is 1150-1180°C.

6. The method for preparing fine-grained high-cleanliness steel for flexible pulley of harmonic reducer of industrial robot according to claim 4 or 5, characterized in that: In the bar rolling process, the square billet is continuously rolled into a bar with a diameter of 30 to 60 mm after leaving the heating furnace.

7. The method for preparing fine-grained high-cleanliness steel for flexible pulley of harmonic reducer of industrial robot according to claim 4 or 5, characterized in that: In the rolling material cooling process, the rolled bars quickly pass through the cooling bed and then enter the pit for slow cooling, and the temperature entering the pit is controlled to be ≥500°C.

8. The method for preparing fine-grained high-cleanliness steel for flexible pulley of harmonic reducer of industrial robot according to claim 4 or 5, characterized in that: The austenite grain size of the flexspline steel rolled material obtained by the method reaches above grade 9.5, and after a single quenching heat treatment, the austenite grain size of the flexspline product reaches above grade 10.5; the D-type inclusions are ≤ grade 0.5, and there are no A, B, or C-type inclusions.

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