Cools work piece quenching after the room temperature, lays aside immediately in is lower than the room temperature under the environment to pause certain time, takes out puts in the room temperature, this kind is lower than the room temperature processing to be called the cold treatment.The bearing steel cold treatment often uses the freezer and the dry ice spirit of ethyl-nitrite.

 
1. cold treatment functions
The precision bearing is high to the size stability request; After ferrule quenching (in particular step quench), the underlying tissues still retained many residual austenites, this kind of residual austenite was the unstable organization, in the storage and in the use bearing process, could change unceasingly, thus changed the bearing the precision.Uses the cold treatment craft for this, it can reduce in the organization the residual austenite, enhances the components slightly degree of hardness.

2. cold treatment crafts
After quenching in room temperature pause: After quenching, must certainly cause inside and outside the ferrule even coldly to carry on the cold treatment after the room temperature, otherwise easy to crack, coldly immediately the cold treatment (generally does not surpass 30min) after the room temperature, otherwise can stop the austenite to the martensite transformation.

Cold treatment temperature: The cold treatment temperature mainly acts according to the steel martensite transformation termination temperature Mf, moreover also must consider the cold treatment to factors and so on mechanical property influence and technology capability.
Regarding the GCr15 steel, the cold treatment selects - 70℃; When the precision request not very high ferrule or the equipment have the limit, the cold treatment temperature may elect for - 40~-70℃; The ultra precision bearing, may in - 70℃~-80℃ between carry on the cold treatment.Excessively cold temperature influence bearing impact fatigue and contact life.

Cold treatment heat preservation: Although the massive martensite transformation is in suddently completes as coldly as certain temperature, but for causes one batch of ferrule surface and the heart department all evenly achieved the cold treatment temperature, needs certain soaking time, is generally 1~1.5h.

After cold treatment tempering: After the ferrule cold treatment places in the air, its temperature rises after the room temperature to carry on the tempering promptly slowly.The temperature rise cannot too be quick, otherwise easy to crack; The tempering is prompt, otherwise the ferrule interior big residual stress can cause the ferrule dehiscence, does not surpass 2h generally.




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