The workpiece quenched and cooled to room temperature, immediately placed in the environment below the room temperature for a certain period of time, taken out at room temperature, this treatment called cold treatment. Bearing steel cold treatment often use freezer and dry ice alcohol solution.
 

The role of cold treatment:

Precision bearing requires higher dimensional stabilityon the dimensional stability, after ring quenching, the internal organization still retains more retained austenite, this residual austenite is unstable and the process will continue to change in the storage and use of bearings, thus changing the accuracy of the bearing. For this purpose, we use cold treatment, which can reduce the organization of retained austenite, slightly improve the hardness of parts.
 

Cold treatment process:

After quenching, be sure the cold treatment be made after the ring inside and outside uniform cooling to room temperature, otherwide, it’s easy to crack, cold to room temperature immediately after cold treatment (usually not more than 30min), otherwise it will stop the change froom austenite to martensite.
 

Cold treatment temperature:

cold treatment temperature mainly according to the martensitic transformation of steel martensitic termination temperature Mf, in addition to consider the cold treatment on the mechanical properties of the impact of process and other factors. For GCr15 steel, cold treatment select -70 ℃; If the precision requirements of bearings are not very high or equipments are limited, the cold treatment temperature can be selected from -40 ~ -70 ℃; ultra-precision bearings, in -70 ℃ ~ -80 ℃ cold treatment. Subcooled temperature affects bearing impact fatigue and contact life.
 

Cold treatment insulation:

Although a large number of martensite transformation to a certain temperature is completed in the moment, but in order to make a number of rings and the heart of the ring to achieve uniform cooling temperature, it needs for a certain holding time, generally 1 ~ 1.5 H

The tempering after cold treatment, ring placed at the air after cold treatment after, do the tempering in time after the temperature slowly rose to room temperature. Temperature rise can not be too fast or easy to crack, tempering in time, otherwise the larger internal residual stress will lead to ring cracking, generally not more than 2h.