To cool to room temperature after quenching, immediately placed in an environment below room temperature to stay a certain time, put out at room temperature, this process is called below the room temperature cold treatment. Bearing steel, cold treatment is often used freezer and dry ice alcohol solution.
1 The role of cold treatment
Precision bearings for higher dimensional stability; ring quenching (especially classification quenching), the internal organization retains more residual austenite, the austenite is unstable organization, storage and use in bearing process, will continue to change, thus changing the bearing accuracy. To this end the use of cold treatment process, organizations can reduce the residual austenite, the hardness slightly increased parts.
(2) Cold treatment processes
Stay at room temperature after quenching: Quenching, be sure to make the inside and outside the ring even after cooling to room temperature, cold treatment, or easy to crack, cool to room temperature immediately after cold treatment (usually no more than 30min), otherwise it will abort the austenite to marten site of change.
Cold treatment temperature: the temperature of cold treatment mainly based on steel marten site stop temperature Mf, while also considering the cold treatment on the mechanical properties and processes and other factors.
For GCr15 steel, cold treatment selection -70 ℃; not very high precision ferrule or equipment limitations, the cold treatment temperature can be selected as -40 ~ -70 ℃; super-precision bearings, can be -70 ℃ ~ Cold treatment insulation: Although a large number of martens tic transformation temperature in the cold to a certain moment pour was completed, but the number of rings to make the heart surface and the Ministry of cold treatment are to achieve uniform temperature, requires a certain holding time, usually 1 to 1.5 h.
Tempering after cold treatment: ring on the air after a cold treatment, the temperature slowly rose to room temperature after tempering in a timely manner. Temperature rise can not be too fast, or easy to crack; tempering time, or ring the residual stress within the larger rings will lead to cracking, generally no more than 2h



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