① Preheating before quenching heating: The main purpose is to shorten the quenching heating time, reduce deformation and cracking, and also reduce the tendency of overheating and decarburization. This process adopts preheating in a salt bath furnace at a temperature of about 600℃. 8-10 minutes, if the box-type electric furnace is used for preheating, the temperature will be longer at about 530-550℃.
② Determination of heating time: The determination of heating time is not completely the same in different factories. Generally, the heating time after preheating is 10-15s/mm, and the box-type electric furnace is 35-50s/mm. The salt furnace without preheating is 30-35s/mm, and the box-type electric furnace is 90-100s/mm. In this example, the GCr15 bearing balls are preheated and then quenched in the salt furnace. The heating time is considered to be 8 minutes.
③ Quenching and cooling: Because the GCr15 bearing ball contains more alloying elements, it hinders the homogenization of the composition. In order to prevent the deformation of GCr15 bearing steel and also have certain toughness and fatigue strength, oil cooling is used