There are four major types of heat treatment processes, which are annealing, normalizing, quenching and tempering. For annealing process, the material is heated to its annealing temperature, hold for at least one hour, then it is cooled in a furnace with a very slow cooling rate like 0.5 degree Celsius per minute. For normalizing and quenching processes, the material will be heated to its austenitic temperature range, also hold at this temperature for at least one hour. However, their cooling rate is different. Normalized materials will be air-cooled. Quenched material will be cooled in a rapidly rate, usually is water quenching. For tempering process, it is the same process as quenching treatment, but the material will be reheated to about 400 degree Celsius after quenching, hold for about 30 minutes, and air-cool at the end.