After the workpiece is quenched and cooled to room temperature, it is immediately placed in an environment below room temperature for a certain period of time, and taken out at room temperature. This treatment below room temperature is called cold treatment. The cold treatment of bearing steel is often carried out using a freezer and a dry ice alcohol solution.

1. The role of cold treatment

Precision bearings require high dimensional stability; after ferrule quenching (especially after stage quenching), the internal structure still retains more retained austenite, which is an unstable structure, in storage and use of bearings During the process, it will constantly change, thus changing the accuracy of the bearing. For this purpose, a cold treatment process is used which reduces the retained austenite in the structure and slightly increases the hardness of the part.

2. Cold treatment process

After quenching, it stays at room temperature: after quenching, the inside and outside of the ferrule must be cooled to room temperature and then cooled. Otherwise, it will be easily cracked. Immediately after cooling to room temperature, it will be cold treated (generally no more than 30 min), otherwise it will stop austenite to martensite. The transformation.

Cold treatment temperature: The temperature of the cold treatment is mainly based on the martensite transformation termination temperature Mf of the steel, and the influence of the cold treatment on the mechanical properties and the processability are also considered.

For GCr15 steel, cold treatment is -70 °C; when the ferrule or equipment with less precise requirements is limited, the cold treatment temperature can be -40 ~ -70 °C; ultra-precision bearings can be -70 °C ~ -80 °C Cold treatment is carried out. The too cold temperature affects bearing impact fatigue and contact life.

Cold treatment and heat preservation: Although the transformation of a large amount of martensite is completed between cold and a certain temperature, in order to make the surface of the ferrule and the core evenly reach the cold treatment temperature, a certain holding time is required, generally 1 to 1.5. h.

Tempering after cold treatment: The ferrule is cold-treated and placed in the air, and the temperature is slowly raised to room temperature and then tempered in time. The temperature rise should not be too fast, otherwise it will be easy to crack; the tempering will be timely, otherwise the large residual stress inside the ferrule will cause the ferrule to crack, generally not more than 2h.

Reprinted from the network