Principles and Classification of Heat Treatment

　　1. Heat treatment:

　　Heat treatment is a process in which solid metals or alloys are heated, held at a specific temperature, and then cooled in a controlled manner to achieve the desired microstructure and properties.

　　2. Purpose of heat treatment:

　　①. Enhance the service performance of parts;

　　② Fully harness the potential of steel;

　　③. Extend the service life of parts;

　　④ Improve the process performance of workpieces, enhance machining quality, and reduce tool wear.

　　3. The heat treatment methods include: annealing, normalizing, quenching, tempering, and surface heat treatment.

　　However, each of these processes consists of three stages: heating, holding, and cooling.

　　4. The reason why heat treatment causes changes in the properties of steel:

　　Due to the allotropic transformation of iron, steel undergoes changes in its microstructure and structure during heating and cooling processes.