Cooling is also an indispensable step in the process of heat treatment. The cooling method varies with different processes, mainly to control the cooling speed. Generally, the cooling speed of annealing is slow, that of normalizing is fast, and that of quenching is faster. But there are also different requirements for different types of steel, such as air hardened steel can be used as the same rate of cooling quenching.

The process of metal heat treatment can be divided into three categories: integral heat treatment, surface heat treatment and chemical heat treatment. According to the different heating medium, heating temperature and cooling method, each category can be divided into a number of different heat treatment process. Different heat treatment process for the same metal can obtain different microstructure and thus have different properties. Iron and steel is a widely used metal in industry, and the microstructure of iron and steel is complex, so there are many kinds of steel heat treatment technology.

Integral heat treatment is a metal heat treatment process in which the workpiece is heated as a whole and then cooled at an appropriate rate to change its overall mechanical properties. The overall heat treatment of steel has four basic processes: annealing, normalizing, quenching and tempering.