Cold treatment process
Stay at room temperature after heat treatment and quenching: after quenching, make sure that the inside and outside of the ring are evenly cooled to room temperature before cold treatment, otherwise it is easy to crack. After cooling to room temperature, cold treatment shall be carried out immediately (generally no more than 30min), otherwise the transformation from austenite to martensite will be stopped.
Cold treatment temperature: the temperature of cold treatment is mainly based on the martensitic transformation termination temperature MF of steel, in addition, the influence of cold treatment on mechanical properties and processability should be considered. For GCr15 steel, the cold treatment temperature is – 70 ° C; when the rings with low precision requirements or equipment are limited, the cold treatment temperature can be – 40 ~ – 70 ° C; for ultra precision bearings, the cold treatment temperature can be between – 70 ° C and – 80 ° C. The subcooled temperature affects the impact fatigue and contact life of the bearing.
Cold treatment and heat preservation: Although the transformation of a large amount of martensite is completed between the cold to a certain temperature, in order to make the surface and core of a batch of rings reach the cold treatment temperature evenly, the holding time is generally 1-1.5H.
Tempering after cold treatment: the ring is put in the air after cold treatment, and its temperature slowly rises to room temperature, and then it is tempered in time. The temperature rise should not be too fast, otherwise it is easy to crack; tempering should be timely, otherwise the larger residual stress inside the ring will lead to the ring cracking, generally no more than 2 h.
Cryogenic treatment process
With the continuous development of the mechanical industry, the requirements for metal materials are also higher and higher. How to improve the mechanical properties and service life of metal parts as far as possible under the premise of materials and heat treatment technology has become a problem that many frontier people in the heat treatment industry think and explore.