1. Material composition adaptation basis
Processing of bearing inner and outer rings mostly uses high-carbon chromium bearing steel, and its initial composition determines the potential of heat treatment. Reasonable carbon content can provide guarantee for hardness improvement, and chromium enhances wear resistance and hardenability. According to the hardness and toughness range required by the product, strictly control the fluctuation of composition in the steel procurement link to ensure that the basic material has the conditions for precise regulation, laying a good foundation for subsequent heat treatment process.
2. Key points for controlling heating speed
The heating process affects the transformation of the organization. Rapid heating can inhibit grain growth and help retain toughness, but too fast may cause excessive thermal stress and cause crack hazards; slow heating can reduce thermal stress, but it is easy to coarsen grains and affect hardness. For small processing of bearing inner and outer rings, the heating speed can be appropriately increased, while large and complex structural parts need to be heated in stages and slowly transitioned, and the heating rhythm should be accurately controlled to balance the changes in hardness and toughness caused by organizational changes.
3. Fine adjustment of quenching temperature
Quenching temperature is the key control point. When the temperature is too high, the austenite grains are coarse, the hardness increases but the toughness decreases; when the temperature is too low, the hardness is insufficient. According to the specific steel grade and product technical requirements, with the help of the precise temperature control system of the quenching furnace, the quenching temperature error is controlled within a very small range. For example, the quenching temperature of GCr15 steel is usually between 830℃ and 860℃. Fine-tune in this range to find the best balance between hardness and toughness.
4. Selection of cooling medium and method
The cooling link determines the final organizational form. The oil-cooled quenching has a moderate cooling speed, which can obtain a good combination of hardness and toughness, and is suitable for most conventional bearings; for special working condition bearings with extremely high toughness requirements, graded quenching or isothermal quenching can be used, using salt baths, nitrate baths and other media to first slow cool and then fast cool, to avoid the loss of toughness caused by too fast martensitic transformation, and accurately shape the ideal organization.
5. Tempering process optimization strategy
Tempering is used to eliminate quenching stress and adjust performance. Low-temperature tempering can maintain high hardness, and medium-high temperature tempering can improve toughness. According to the service conditions of the processing of bearing inner and outer rings, the tempering temperature, time and number of times are reasonably designed. For bearings with large impact loads, high temperature tempering is used; for high-precision bearings, low temperature tempering is mainly used, and tempering parameters are accurately adjusted to stabilize the hardness and toughness balance.
6. Real-time tracking of quality inspection
After heat treatment, hardness and toughness indicators are immediately tested using hardness testers, impact testers, etc. A database is established to compare the process preset values with the actual measured values. Once the deviation exceeds the allowable range, each link of the heat treatment is traced back, from heating, quenching to tempering to find the cause, and correct it in time to ensure that the performance of each batch of products meets the standards.
7. Accumulation and inheritance of process experience
The experience of heat treatment operators is crucial. Encourage old masters to share practical skills, organize internal training and exchanges, so that newcomers can quickly master the subtle adjustments of different specifications of processing of bearing inner and outer rings at each process node, and transform experience into stable productivity with precise control of hardness and toughness.
