What is heat treatment? (2)

The heating temperature is one of the important process parameters of the heat treatment process. The selection and control of the heating temperature is the main issue to ensure the quality of the heat treatment. The heating temperature varies with the metal material being processed and the purpose of the heat treatment, but it is generally heated above the phase transition temperature to obtain a high-temperature structure. In addition, the transformation requires a certain time. Therefore, when the surface of the metal workpiece reaches the required heating temperature, it must be maintained at this temperature for a certain period of time to make the internal and external temperatures consistent and complete the microstructure transformation. This period of time is called the holding time.

When high-energy density heating and surface heat treatment are used, the heating speed is extremely fast, and there is generally no holding time, while the holding time of chemical heat treatment is often longer. Cooling is also an indispensable step in the heat treatment process. The cooling method varies from process to process, and the main thing is to control the cooling rate.