Will quench cooling to room temperature, immediately placed in below room temperature under the environment of the stay time, take out at room temperature, the lower than the processing of room temperature called cold treatment. Bearing steel cold treatment often USES freezer and dry ice alcohol solution.
1. The cold treatment effect
Precision bearing the dimension stability of demand is higher; Contractor quenching (especially hierarchical quenching), internal organization still retain more austenite, this kind of austenite is not stable organization, in the storage and use bearing process, will continue to change and change the precision of the bearing. Therefore the cold treatment process, it can reduce the tissue of the austenite, slightly improve the hardness of parts.
2. Cold treatment technology
After quenching in room temperature stay: after quenching, must make internal and external uniform collar cold to room temperature after the cold treatment, or easy craze, cold to room temperature cold treatment immediately after the (usually not more than 30 min), otherwise, it will suspend austenitic to martensite transformation.
Cold treatment temperature: the temperature of cold treatment according to the main steel martensite transformation temperature Mf termination, and to consider cold treatment of mechanical properties of the influence and the technology, and other factors.
For GCr15 steel, cold treatment choose-70 ℃; Accuracy is not very high rings or equipment limited, cold treatment temperature can be elected-40 ~-70 ℃; The ultra precision bearings, can be in-70 ℃ ~ 80 ℃-between cold treatment. Too cold temperature on the impact and fatigue life of contact bearings.
Cold treatment thermal insulation: although the martensite transformation is large in the cold to a definite temperature between the finish out of the moment, but for a batch of rings surface and heart department are evenly to cold treatment temperature, need certain of holding time, generally for 1 ~ 1.5 h.
Cold treatment after the tempering: front-runners in the air after the cold treatment on, its temperature slow to room temperature in time after that follows. Temperature can not be too fast, otherwise easy to crack; Tempering in time, otherwise the residual stress of larger rings inside can lead to collar craze, usually less than 2 h.
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