Annealing is a heat treatment process which alters the microstructure of a material to change its mechanical or electrical properties. Typically, in steels, annealing is used to reduce hardness, increase ductility and help eliminate internal stresses.
Annealing will restore ductility following cold working and hence allow additional processing without cracking. Annealing may also be used to release mechanical stresses induced by grinding, machining etc. hence preventing distortion during subsequent higher temperature heat treatment operations. In some cases, annealing is used to improve electrical properties.
Application & materials
One of the main applications of annealing is reversing the effects of work hardening. During cold forming, drawing, bending etc. the material can become hardened to the point where further working can be impossible or result in cracking. An annealing operation at this stage will make the material more ductile, permitting further forming. In a similar manner, annealing is utilized to remove the internal stresses which occur when welds solidify.
Besides steels, other metals may also benefit from annealing such as copper, aluminium, and brass.