Quenching and Tempering Heat Treatment is a process that combines quenching and high-temperature tempering to form a uniform and fine strengthening phase within metal materials, enhancing their strength and toughness. The main principle involves controlling the heating and cooling processes of the material to adjust the metal structure and phase transformations, resulting in a structure with good mechanical properties and stability.
The quenching and tempering heat treatment includes the following steps:

1. Heating: The metal material is heated to a certain temperature, bringing it into the solid solution region. In this region, the alloying elements in the material dissolve in the matrix, forming a single solid solution structure.
2. Soaking: The material is held at high temperature for a period to allow the alloying elements to fully dissolve, creating a uniform solid solution structure.
3. Rapid Cooling: The material is rapidly cooled, preventing the alloying elements from returning to a uniformly distributed state. This can result in some non-equilibrium structures, such as bainite and martensite.
4. Tempering: The material is reheated to a higher temperature, causing the non-equilibrium structure to undergo phase transformations, forming fine and uniformly distributed strengthening phases. These phases can enhance the strength and toughness of the material while maintaining good machinability.