Heat treating is a group of industrial, thermal and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are also used in the manufacture of many other materials, such as glass. 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. Although the term heat treatment applies only to processes where the heating and cooling are done for the specific purpose of altering properties intentionally, heating and cooling often occur incidentally during other manufacturing processes such as hot forming or welding.
Heat treating furnace at 1,800 °F (980 °C)
Photomicrographs of steel. Top: In annealed (slowly cooled) steel, the carbon precipitates forming layers of ferrite (iron) and cementite (carbide). Bottom: In quenched (quickly cooled) steel, the carbon remains trapped in the iron, creating great internal stresses in the needle or plate-like grains.
Hypereutectoid steel
Steel castings after undergoing 12-hour 1,200 °C (2,190 °F) heat treatment.
Metallurgy is a domain of materials science and engineering that studies the physical and chemical behavior of metallic elements, their inter-metallic compounds, and their mixtures, which are known as alloys.
Gold smelting workers in Siuna, Nicaragua in the late 20th century
Casting, the process of pouring molten metal into a mold
Artefacts from the Varna Necropolis in present-day Bulgaria
Iron, the most common metal used in metallurgy, is shown in different forms, including cubes, chips, and nuggets