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Metal heat treatment processes are generally divided into three categories: overall heat treatment, surface heat treatment, and chemical heat treatment. Overall heat treatment is a metal heat treatment process in which the entire workpiece is heated and then cooled at an appropriate rate to change its overall mechanical properties. The overall heat treatment of steel mainly includes annealing, normalizing, quenching, and tempering. Annealing: (Involves heating to a certain temperature followed by cooling in the furnace to achieve complete annealing; the purpose is to reduce the hardness of the steel and eliminate any uneven structures or internal stresses within it.) The workpiece is heated to an appropriate temperature, with the holding time varying depending on the material and size of the workpiece, after which it is cooled slowly. The purpose is to bring the internal structure of the metal to an equilibrium state, or to relieve the internal stresses generated in previous processing steps, thereby achieving good processability and performance, or to prepare the structure for further quenching. Normalizing, also known as normalization treatment: A metal heat treatment process in which the workpiece is heated to an appropriate temperature and then cooled in air, with the aim of obtaining a finer microstructure; it is often used to improve the machinability of materials. The effect of normalizing is similar to that of annealing. Quenching: (Heating to a certain temperature and then cooling in a medium, with the aim of obtaining a martensitic or bainitic structure) is a metal heat treatment process in which the workpiece is heated to an appropriate temperature and then rapidly cooled in quenching media such as water, oil, other inorganic salt solutions, or organic aqueous solutions. The steel becomes harder, but also more brittle, with poor plasticity and toughness. Tempering: To reduce the brittleness of steel parts, the quenched steel parts are held at an appropriate temperature above room temperature but below 650 degrees Celsius for a prolonged period of time before being cooled. Quenching + high-temperature tempering during quenching and tempering treatment.