Heat Treatment Process of Precision Bearing

The heat treatment process of precision bearings generally includes the following steps:

1. Preliminary heat treatment:

   （1.）1. Normalizing: normalizing is to heat the workpiece to 30-50 ℃ above Ac3 (Ac is the final temperature at which free ferrite is completely transformed into austenite during heating, generally from 727 ℃ to 912 ℃) or Acm (Acm is the critical temperature line for complete austenitization of hypereutectoid steel during actual heating). After keeping the temperature for a period of time, the metal heat treatment process cooled in the air or by water spraying, spraying or blowing is taken out from the furnace. The purpose is to refine the grain size and homogenize the carbide distribution. Parameters: different components of the normalizing temperature slightly different.

   (2.) Spheroidizing annealing: Its main purpose is to reduce hardness, improve machinability, and prepare for later quenching. This process is conducive to plastic processing and cutting processing, but also can improve the mechanical toughness.

 2.final heat treatment: 

  (1.) quench: that quenching is to heat the raw material to the austenitizing temperature and keep the temperature for a period of time as required. And then rapidly cool to obtain a tissue with higher hardness and strength than that original one, so as to enhance the mechanical property of the material and increase the durability of the material. For example, 45 steel, the original structure is ferrite + pearlite, martensite is obtained after quenching, and the strength and hardness are doubled.

(2.) Cold treatment: The residual austenite which is not fully transformed in the quenching process continues to transform to martensite, which can not only improve the dimensional stability of the parts, but also slightly improve the hardness and anti-rust performance of the parts. But it will reduce the toughness of bearing steel. Sometimes, the principle of martensite larger than the volume can be used to save the products scrapped due to size reduction by cold treatment.

(3.) Tempering: The parts must be tempered after quenching (or cold treatment). Tempering can reduce and stabilize residual stress, stabilize microstructure, avoid crack and deformation, properly reduce hardness and greatly improve toughness, so that parts can finally obtain the best combination of mechanical properties and dimensional stability of strengthening and toughening.

(4.) Additional tempering (stabilization treatment): The function of additional tempering is to eliminate the grinding stress and further stabilize the structure so as to improve the dimensional stability of the parts.