Metal heat treatment process can be roughly 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 type can be divided into several different processes. Different microstructures and properties of the same metal can be obtained by different heat treatment processes. 

Iron and steel is the most widely used metal in industry, and its microstructure is also the most complex, so there are many kinds of heat treatment processes for iron and steel.