Tempering metal parts is carried out in cases when it is necessary either to increase the strength, hardness, wear resistance, elasticity of the part or tool, or, conversely, to make a metal softer, lighter amenable to mechanical processing.
To achieve the various metal structures using various techniques of carrying out heat treatment. The main types of heat treatment  are:

• Hardening — heat treatment (heat-treated) steel, alloys based on recrystallization of steel (alloys) when heated to above the critical temperature; after a sufficient soaking at the critical temperature to complete the heat treatment follows the rapid cooling. Hardened steel (alloy) has a non-equilibrium structure, therefore, we apply another kind of heat treatment — leave;
• Grouting — specialized chemical-heat treatment in which the surface of steel is saturated with carbon. There are two types of saturation: solid and gaseous carbon. Carburizing steel, generally carried out at temperatures above 930–950°C, when the austenite stable, solvent carbon in large quantities. The main goal of this process — significantly increase the hardness of the metal, its resistance to wear and also to increase the torsion resistance;
• Annealing — heat treatment (heat treatment) of metal is heated the metal and then slowly cooling. This heat treatment (annealing) can be of different types (a kind of annealing depends on the heating temperature, the cooling rate of the metal);
• Vacation — heat treatment (heat-treated) steel, alloy, carried out after quenching to reduce or relieve residual stresses in the steel and alloys, which increases the viscosity, reduces the hardness and brittleness of the metal;
• Normalization — heat treatment (heat treatment), similar to the annealing. The differences of these heat treatments (normalizing and annealing) is that when you normalize the steel is cooled in air (annealing — in a furnace).