The overall heat treatment technology of steel generally includes four basic processes: annealing, normalizing, quenching, and tempering.
1. Annealing is the process of heating a workpiece to an appropriate temperature, using different holding times based on the material and workpiece size, and then slowly cooling it to achieve or approach an equilibrium state of the internal structure of the metal, achieve good process and service performance, or prepare for further quenching.
2. Normalizing is the process of heating a workpiece to a suitable temperature and then cooling it in air. The effect of normalizing is similar to annealing, except that the resulting microstructure is finer and is commonly used to improve the cutting performance of materials. It is also sometimes used for final heat treatment of parts with low requirements.
3. Quenching is the rapid cooling of a workpiece in a quenching medium such as water, oil, or other inorganic salts, organic water solutions, etc. after heating and insulation. After quenching, the steel parts become hard, but at the same time they become brittle.
4. In order to reduce the brittleness of steel parts, the quenched steel parts are held for a long time at an appropriate temperature above room temperature but below 710 ℃, and then cooled. This process is called tempering.
