What is strain hardening?
Strain Hardening is when a metal is strained beyond the yield point. An increasing stress is required to produce additional plastic deformation and the metal apparently becomes stronger and more difficult to deform.
Strain hardening is closely related to fatigue. Example, bending the thin steel rod becomes more difficult the farther the rod is bent. This is the result of work or strain hardening. Strain hardening reduces ductility, which increases the chances of brittle failure.
Strain hardening is generally defined as heating at a relatively low temperature after cold-working. During strain hardening the strenth of the metal is increased and ductility decreased.
To go a step further in explaining, if a low-carbon steel is cold-worked, or strained passed the yield point, then aged for several days at room temperature, it will have a higher yield stress after the aging. This happens because during the aging carbon or nitrogen atoms diffuse to dislocations, reanchoring them.
Also, not everything can be strain aged, or recovered at low temperatures. The low carbon steel is just an example. Different materials will show different behaviors during recovery.
