Heat treatment process for small cylindrical bearing
By using gradient heating and segmented cooling and other technical means in the heat treatment process of small cylindrical bearings to control the carbon potential and temperature, the problem of large and mesh carbides in the carburizing process of small cylindrical bearings is solved, which improves the wear resistance and life of the bearings and reduces production costs.
Patent Information
- Application Number
- CN202411542636.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-31
- Publication Date
- 2025-04-18
AI Technical Summary
Small cylindrical bearings are prone to thick and mesh carbides during carburization, resulting in low fatigue life and high production costs.
A small cylindrical bearing heat treatment process is adopted, which includes five carburizing treatment stages, combining quenching, high-temperature tempering, secondary heating, secondary quenching and low-temperature tempering. The carbon potential and temperature are controlled through technical means such as gradient heating and segmented cooling to form a uniform carburizing layer.
It effectively solves the problems of coarse and mesh carbides, improves the wear resistance and life of the bearings, and reduces the cost of raw materials.
Smart Images
Figure CN119843213A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of bearing heat treatment, and in particular relates to a heat treatment process for a small cylindrical bearing. Background Art
[0002] The industry standard for small cylindrical bearings requires that the surface carbon content of carburizing steel be relatively high, at 0.8-1.05%. Coarse carbides and network carbides are prone to appear during the carburizing process, which often leads to a short fatigue life of the bearing and high production costs. Summary of the invention
[0003] In view of the defects of the above-mentioned prior art, the present invention develops a heat treatment process for small cylindrical bearings to improve bearing life and reduce production costs. The process is mainly used in applications requiring high reliability and stability, extremely high wear resistance and long life, such as wind power gearbox components.
[0004] To achieve the above-mentioned purpose, the present invention provides a heat treatment process for a small cylindrical bearing. The cylindrical bearing adopts carburizing steel as raw material, and the cylindrical bearing is carburized. After the carburizing treatment, the cylindrical bearing is subjected to primary quenching, high-temperature tempering, secondary heating, secondary quenching and low-temperature tempering; the carburizing treatment includes five stages, the first stage temperature is 650°C, no carbon potential, and the time is 1h; the second stage temperature is 860°C, the carbon potential is 0.85%, and the time is 1h; the third stage temperature is 940°C±10°C, the carbon potential is 1.2%, and the time is 17h; the fourth stage temperature is 940°C±10°C, the carbon potential is 0.8%, and the time is 2h; the fifth stage temperature is reduced to 860°C, the carbon potential is 0.8%, and the temperature is kept for 1 hour.
[0005] Based on the above technical solution, it should be noted that in the first stage, due to the large amount of small rings loaded into the furnace, the time it takes for each product to reach the temperature is different, so it is necessary to use gradient heating to achieve uniform temperature of each ring in the carburizing furnace. The second stage is also a gradient heating process like the first stage. At the same time, the second stage must start to supply carbon potential to lay the foundation for the establishment of high carbon potential in the subsequent strong carburizing process. The third stage is the strong carburizing stage, the purpose is to use a high carbon potential method to carburize the surface of low-carbon carburizing steel to form a certain carburized layer on the surface of the product. The fourth stage is the diffusion stage, the purpose is to solve the problem of coarse and network carbides caused by carbon oversaturation on the surface of the product during the strong carburizing stage. The fifth stage needs to be cooled to a certain temperature to prevent the precipitation of network carbides.
[0006] Furthermore, the primary quenching is performed by oil quenching, and the quenching oil temperature is 30-80°C.
[0007] Furthermore, the oil quenching process adopts segmented cooling, and the segmented cooling adjusts the cooling rate through different stirring frequencies. The stirring time of the first stage of cooling in the oil quenching is 30 minutes, and the stirring frequency is 1600rmp. The stirring time of the second stage of cooling in the oil quenching is 10 minutes, and the stirring frequency is 600rmp.
[0008] Furthermore, the high temperature tempering process is divided into two stages, the temperature of the first stage is 620° C., the time is 12 hours, and the temperature of the second stage is raised to 650° C., the time is 15 hours.
[0009] Furthermore, after the high temperature tempering, the temperature is cooled to room temperature, and then a secondary quenching process is performed, and the temperature is naturally cooled by air to 30-40°C.
[0010] Furthermore, in the secondary quenching process, the cylindrical bearing is first heated to 810°C, with a total heating time of 130 minutes, and then cooled by salt quenching. The quenching salt bath temperature is 170-180°C, and the cylindrical bearing is cooled to 170°C by salt quenching.
[0011] Based on the above technical solution, the total heating time of 130 minutes means that the total heating + insulation time is 130 minutes. The purpose of heating is to gradually austenitize the product from the tempered troostite structure. The purpose of insulation is to complete the austenitization and prevent the appearance of non-martensitic structures such as troostite during cooling.
[0012] Furthermore, the salt quenching process adopts segmented cooling, and the segmented cooling adjusts the cooling rate through different stirring frequencies. The stirring time of the first cooling stage of the secondary salt quenching is 4 minutes, the stirring frequency is 200rmp, and the stirring time of the second stage is 10 minutes, and the stirring frequency is 300rmp.
[0013] Furthermore, the low temperature tempering process temperature is 150° C. and the time is 4 hours.
[0014] Furthermore, the cylindrical bearings are quenched without a mold during both the primary quenching and the secondary quenching processes.
[0015] Based on the above technical solution, moldless quenching can achieve full relative flow of the product with the cooling medium during the cooling process, which is more complete than mold-limited quenching.
[0016] The beneficial effects of the present invention are as follows: the small cylindrical bearing uses carburized steel as raw material, and innovatively uses 0.85-1.2% carbon potential for carburization during the process, which solves the problem of coarse and network carbides appearing on the product surface, while reducing the cost of raw materials. BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Figure 1 The process flow chart of the heat treatment process of the small cylindrical bearing of the present invention; Figure 2This is a product drawing of a small cylindrical roller. DETAILED DESCRIPTION
[0018] In order to make the structure and function of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.
[0019] See attached Figure 1 A heat treatment process for a small cylindrical bearing, wherein the cylindrical bearing uses carburizing steel as raw material, and the cylindrical bearing is carburized. After the carburizing treatment, the cylindrical bearing is subjected to primary quenching, high temperature tempering, secondary heating, secondary quenching and low temperature tempering; the carburizing treatment includes five stages, the first stage temperature is 650°C, no carbon potential, and the time is 1h; the second stage temperature is 860°C, the carbon potential is 0.85%, and the time is 1h; the third stage temperature is 940°C±10°C, the carbon potential is 1.2%, and the time is 17h; the fourth stage temperature is 940°C±10°C, the carbon potential is 0.8%, and the time is 2h; the fifth stage temperature is reduced to 860°C, the carbon potential is 0.8%, and the temperature is kept for 1 hour. Then a quenching is performed, and the first quenching adopts oil quenching.
[0020] Based on the above technical solution, it should be noted that in the first stage, due to the large amount of small rings in the furnace, the time for each product to reach the temperature is different, so it is necessary to use gradient heating to achieve uniform temperature of each ring in the carburizing furnace. The second stage is also a gradient heating process like the first stage. At the same time, the second stage must start to supply carbon potential to lay the foundation for the establishment of high carbon potential in the subsequent strong penetration process. The third stage is the strong penetration stage, the purpose of which is to form a certain carburized layer on the surface of the carburized product using a high carbon potential on the surface of the low-carbon carburizing steel. The fourth stage is the diffusion stage, the purpose of which is to solve the problem of carbon supersaturation on the surface of the product in the strong penetration stage, resulting in the elimination of coarse and network carbides. The fifth stage needs to be cooled to a certain temperature for cooling to prevent the precipitation of network carbides. The small cylindrical bearing of the present invention uses carburizing steel as raw material, and innovatively uses 0.85-1.2% carbon potential for carburizing in the process, which solves the problem of coarse and network carbides on the surface of the product, while reducing the cost of raw materials.
[0021] The product of this embodiment is as follows Figure 2 As shown, the embodiment can be used not only for double-row cylindrical roller bearings, but also for single-row cylindrical roller bearings. The heat treatment method of this embodiment is generally applicable to the heat treatment of cylindrical bearings with carburized steel rings having an outer diameter of 200-400 mm and a bearing width of 200-300 mm.
[0022] In order to control the surface carbon content, the present invention strictly controls the carburizing speed of the second stage carburizing process (temperature 860℃, carbon potential 0.85%), uses low temperature and low carbon potential to ensure a gentle carbon concentration gradient in the first carburizing, and the fourth stage carburizing process (temperature 940℃±10℃, carbon potential 0.8%) uses a carbon potential 0.2-0.3% lower than the carbon content requirement for diffusion. The product requires a carbon content of 0.8-1.05%, and the carbon content requirement is fixed. The corresponding carburizing carbon potential will be adjusted according to the different product structures during the process.
[0023] In order to improve the surface hardness of the product, the carburizing process of the present invention includes a first stage and a second stage of gradient heating to refine the surface structure, and at the same time, the segmented medium and high carbon potential is used for strong infiltration and diffusion to obtain a higher surface hardness, which can basically reach 64HRC or above. The gradient heating and segmented medium and high carbon potential are adjusted by program software, and the specific process parameters are optimized in combination with the structure of the actual product, such as the rib and oil groove.
[0024] Furthermore, the oil quenching process adopts segmented cooling, and the segmented cooling adjusts the cooling rate through different stirring frequencies. The stirring time of the first stage of cooling in the oil quenching is 30 minutes, and the stirring frequency is 1600rmp. The stirring time of the second stage of cooling in the oil quenching is 10 minutes, and the stirring frequency is 600rmp. The quenching oil temperature is 30-80°C, and the cylindrical bearing is cooled to 30-40°C.
[0025] Furthermore, the high temperature tempering process is divided into two stages, the temperature of the first stage is 620° C., the time is 12 hours, and the temperature of the second stage is raised to 650° C., the time is 15 hours.
[0026] Furthermore, after the high temperature tempering, the temperature is cooled to room temperature, and then a secondary quenching process is performed, and the temperature is naturally cooled by air to 30-40°C.
[0027] Furthermore, in the secondary quenching process, the cylindrical bearing is first heated to 810°C, with a total heating time of 130 minutes, and then cooled by salt quenching. The quenching salt bath temperature is 170-180°C, and the cylindrical bearing is cooled by salt quenching to about 170°C.
[0028] Furthermore, the salt quenching process adopts segmented cooling, and the segmented cooling adjusts the cooling rate through different stirring frequencies. The stirring time of the first cooling stage of the secondary salt quenching is 4 minutes, the stirring frequency is 200rmp, and the stirring time of the second stage is 10 minutes, and the stirring frequency is 300rmp.
[0029] Furthermore, the low temperature tempering process temperature is 150° C. and the time is 4 hours.
[0030] Furthermore, during the primary quenching and secondary quenching processes, the cylindrical bearing is quenched without a mold.
[0031] For carburized bearings, uniform distribution of finished carburized layer in raceway functional area must be ensured, so small heat treatment deformation must be ensured. Salt bath dieless quenching is used in the heat treatment process. There are two main things to pay attention to when using dieless quenching. One is the diameter variation in the diameter direction, and the other is the taper in the axial direction.
[0032] a. Reduce the diameter variation The present invention uses two cooling processes during the carburizing process. The first cooling process uses oil cooling to control the stirring frequency to avoid structural stress deformation caused by a large cooling rate. The second cooling process uses salt quenching without a mold to ensure cooling uniformity and reduce deformation caused by the superposition of structural stress and thermal stress.
[0033] The first quenching uses oil quenching, the purpose of which is to quickly cool the product from 860°C to prevent the precipitation of network carbides. The second quenching uses salt quenching, which is the cooling method selected in the process of carburizing products undergoing secondary heating after high-temperature tempering and then transforming from austenite to martensite.
[0034] b. Reduce the taper The present invention adjusts the inner raceway and inner diameter size of the product during the production of lathe drawings to ensure consistent expansion and contraction. At the same time, the present invention performs segmented cooling in the secondary cooling of the salt bath to doubly reduce the final deformation of the ring. This method ensures a smaller taper after heat treatment.
[0035] The product is a carburized steel ring with an outer diameter of 200-400mm. The carbon content on the surface of the product is required to be 0.85-1.05%. The actual test results of the product are as follows: 1. Martensite structure: Level 3 2. Decarburization depth: 0.08mm 3. Surface hardness: 60.2HRC, 60.0HRC, 59.4HRC 4. 550HV1 depth: 2.6mm 58HRC depth: 1.4mm 5. Surface carbon content: 0.87% 6. Grain size: 8 levels 7. Retained austenite: 18.3% It should be noted that the parts not described in detail in the present invention are prior art.
[0036] The above examples are only the best embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and many variations are possible. All variations that can be directly derived or associated with the contents disclosed by a person skilled in the art should be considered as the protection scope of the present invention.
Claims
1. A heat treatment process for small cylindrical bearings, characterized in that: The cylindrical bearing uses carburizing steel as raw material, and the cylindrical bearing is carburized. After the carburizing treatment, the cylindrical bearing is subjected to primary quenching, high-temperature tempering, secondary heating, secondary quenching and low-temperature tempering; the carburizing treatment includes five stages, the first stage temperature is 650°C, no carbon potential, and the time is 1h; the second stage temperature is 860°C, the carbon potential is 0.85%, and the time is 1h; the third stage temperature is 940°C±10°C, the carbon potential is 1.2%, and the time is 17h; the fourth stage temperature is 940°C±10°C, the carbon potential is 0.8%, and the time is 2h. The fifth stage is cooled to 860°C, the carbon potential is 0.8%, and the temperature is kept for 1 hour.
2. A heat treatment process for small cylindrical bearings according to claim 1, characterized in that: The primary quenching is performed by oil quenching, and the quenching oil temperature is 30-80°C.
3. A heat treatment process for a small cylindrical bearing according to claim 2, characterized in that: The oil quenching process adopts segmented cooling, and the cooling rate is adjusted by different stirring frequencies. The stirring time of the first stage of cooling of the oil quenching is 30 minutes, and the stirring frequency is 1600rmp. The stirring time of the second stage of cooling of the oil quenching is 10 minutes, and the stirring frequency is 600rmp.
4. A heat treatment process for small cylindrical bearings according to claim 1, characterized in that: The high temperature tempering process is divided into two stages. The temperature of the first stage is 620° C. and the time is 12 hours. The temperature of the second stage is raised to 650° C. and the time is 15 hours.
5. The heat treatment process for a small cylindrical bearing according to claim 1 is characterized in that: In the secondary quenching process, the cylindrical bearing is first heated to 810°C, with a total heating time of 130 minutes, and then cooled by salt quenching. The quenching salt bath temperature is 170-180°C, and the cylindrical bearing is cooled to 170°C by salt quenching.
6. A heat treatment process for small cylindrical bearings according to claim 5, characterized in that: The salt quenching process adopts segmented cooling, and the segmented cooling adjusts the cooling rate through different stirring frequencies. The stirring time of the first cooling stage of the secondary salt quenching is 4 minutes, the stirring frequency is 200rmp, and the stirring time of the second stage is 10 minutes, and the stirring frequency is 300rmp.
7. The heat treatment process for a small cylindrical bearing according to claim 1 is characterized in that: The low temperature tempering process temperature is 150° C. and the time is 4 hours.
8. The heat treatment process for a small cylindrical bearing according to claim 1 is characterized in that: During the primary quenching and the secondary quenching, the cylindrical bearings are quenched without a mold.