Cold treatment on ferrule

2014-04-09 15:00
After the quenching was cooled to room temperature, and immediately placed in an environment below room temperature a residence time taken at room temperature and below room temperature, this process is called cold treatment . Bearing steel cold treatment is often used freezers and dry ice alcohol solution .
The role of a cold treatment
High precision bearings for dimensional stability ; ferrule hardened ( especially quenching ) , the internal organization still retains many of retained austenite , this residual austenite is unstable organization, storage and use bearings process, will continue to change, thus changing the precision of the bearing. Cold treatment process used for this purpose , which can reduce tissue retained austenite , slightly increasing the hardness of parts.
2 cold treatment process
At room temperature after quenching stay : After quenching , must make cold treatment both inside and outside the ring evenly cooled to room temperature , or easy to crack, cool to room temperature immediately after cold treatment ( usually no more than 30min), otherwise it will abort the austenite to martensite changes.
Cold treatment temperature: cold treatment is mainly based on the termination of martensitic steel transition temperature Mf, while also considering the cold treatment on the mechanical properties and the impact of technology and other factors .
For GCr15 steel, cold treatment choice -70 ℃; when accuracy is not very high collar or equipment is limited, optional cold treatment temperature is -40 ~ -70 ℃; super- precision bearings , in -70 ℃ ~ -80 ℃ of between cold treatment . Cold temperatures affect bearing life impact fatigue and exposure .
Cold treatment Insulation : Although a lot of martensite transformation to a certain temperature in a cold room carved pour completed , but to make a number of ferrule surface and core part evenly to achieve cold treatment temperature , requires a certain holding time , usually 1 to 1.5 h.
Tempering after the cold treatment After the ferrule cold treatment on the air , in a timely manner after tempering temperature was slowly raised to room temperature. Temperature can not be too fast, or easy to crack ; tempering timely, otherwise the rings inside a larger residual stress can cause cracking rings , generally no more than 2h

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