Annealing is a heat treating process that consists of heating steel or other metals to below, in between, or above a critical temperature where the constituent grains recrystallize and carbide is redistributed throughout the material. This is followed by controlled cooling to reduce hardness and increase the toughness, ductility and machinability of a metal.
Full anneal – Full anneals involve heating the material to a temperature where it becomes fully austenitized. This type of anneal is conducted on some stainless steels and superalloys, among others.
Inter-critical anneal – This level of anneal works between the lower critical temperature (where austenite starts to form) and the upper critical temperature (where austenite is fully formed) of a material. It is typically conducted on materials including carbon steels, alloy steels and engineering alloys.
Sub-critical anneal – The temperature with this type of annealing process fully remains below the critical temperature where a material begins to form austenite. It can also be conducted on carbon steels, alloy steel and engineering alloys, but is typically conducted as an intermediate step between fabrication sequences.