Heat treatment is a group of industrial, thermal, and metalworking processes used to alter the physical and sometimes chemical properties of a material. Heat treatment involves the use of heating or chilling, normally to extreme temperatures, to achieve the desired result such as hardening or softening of a material. Heat treatment techniques include annealing, case hardening, precipitation strengthening, tempering, carburizing, normalizing, and quenching. The most common application of heat treatment is metallurgical, but it is also used in the manufacture of many other materials, such as glass.

Heat treatment is often used to alter the mechanical properties of a metallic alloy, manipulating properties such as the hardness, strength, toughness, ductility, and elasticity. There are two mechanisms that may change an alloys properties during heat treatment: the formation of martensite causes the crystals to deform intrinsically, and the diffusion mechanism causes changes in the homogeneity of the alloy. Many heat treating methods have been developed to alter the properties of only a portion of an object.

There are different types of heat treatment processes, and the most common ones include annealing, hardening, quenching, and stress relieving. Annealing involves heating the metal to a specific temperature and then cooling it slowly to make it softer and more ductile. Hardening involves heating the metal to a specific temperature and then cooling it quickly to make it harder. Quenching involves cooling the metal rapidly to increase its hardness. Stress relieving involves heating the metal above the point where the internal structure transforms and then air cooling it at a particular rate to reduce internal stress and enhance the strength and hardness of the metal.

Heat treatment is a precision process that requires the proper equipment to closely control all of the factors around heating, cooling, and quenching. The furnace must be the proper size and type to control temperature, including the gas mixture in the heating chamber, and the appropriate quenching media is needed to cool metal correctly.

In summary, heat treatment is a process that uses controlled heating and cooling to modify the crystalline structure of metals and metal alloys to achieve the desired mechanical properties. There are different types of heat treatment processes, and the most common ones include annealing, hardening, quenching, and stress relieving. Heat treatment is a precision process that requires the proper equipment to closely control all of the factors around heating, cooling, and quenching.