The overall heat treatment is a metal heat treatment process that heats the workpiece as a whole and then cools it at an appropriate rate to change its overall mechanical properties. The overall heat treatment of steel generally has four basic processes: annealing, normalizing, quenching and tempering.

Annealing is to heat the workpiece to an appropriate temperature, adopt different holding times according to the material and the size of the workpiece, and then slowly cool it, the purpose is to make the internal structure of the metal reach or close to the equilibrium state, or to release the internal stress generated by the previous process. Obtain good process performance and performance, or prepare for further quenching.

Normalizing or normalizing is to heat the workpiece to a suitable temperature and then cool it in the air. The effect of normalizing is similar to that of annealing, but the obtained structure is finer. It is often used to improve the cutting performance of materials, and is sometimes used for some requirements. Parts that are not tall as final heat treatment.

Quenching is to quickly cool the workpiece in a quenching medium such as water, oil or other inorganic salt solutions, organic aqueous solutions, etc. after heating and maintaining the workpiece. After quenching, the steel becomes hard, but at the same time becomes brittle.

In order to reduce the brittleness of steel parts, the quenched steel parts are kept at an appropriate temperature higher than room temperature but lower than 650 ° C for a long time, and then cooled. This process is called tempering. Annealing, normalizing, quenching, and tempering are the "four fires" in the overall heat treatment. Among them, quenching and tempering are closely related and are often used together, and neither is indispensable.