Cold plastic deformation leaves a metal with a high dislocation density and stored strain energy. Heating can reduce that stored energy through three related microstructural processes.

Recovery rearranges and annihilates some defects without replacing the deformed grain structure. Residual stresses decrease and some physical properties recover, while mechanical strength changes relatively little.

Recrystallization forms new, nearly strain-free grains that grow into the deformed microstructure. Dislocation density drops dramatically, so strength decreases while ductility increases.

After recrystallization is substantially complete, continued heating can cause grain growth: larger grains consume smaller ones because reducing total grain-boundary area lowers interfacial energy.

The temperature at which recrystallization becomes appreciable is not one universal material constant. It depends on time, prior cold work, purity, initial grain size and alloying.

This sequence explains why a heavily worked metal can be softened by annealing and why thermal processing can trade strength against ductility. It also shows that processing changes properties by changing microstructure, even when chemical composition remains fixed.