Annealing is a heat treatment process that changes the physical and chemical properties of a material to increase ductility and reduce hardness.
Critical Temperatures, Controlled Cooling.
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.
Stage 1 – Recovery
Recovery is a process that acts to restore the physical properties of the metals.
Stage 3 – Grain Growth
When annealing is allowed to continue after recrystallization, the microstructure of the metal becomes coarse and loses strength, which can typically be regained through a hardening process.
Stage 2 – Recrystallization
Workpieces must be heated to a temperature that’s above its recrystallization temperature to replace deformed grains of the crystal structure with new, stress-free grains developed during recovery.
Get the Right Process for Your Job.
The specific type of annealing procedure used for steel varies depending on the type of material being treated. The main differences between these procedures are the maximum temperature and rate of cooling used in each. In many cases, the annealing process is conducted as a part of the overall manufacturing process.
Types of Annealing:
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.
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