What is Strain Hardening?

• Phenomenon where ductile metals become stronger and harder when they  are deformed plastically is called strain hardening or work hardening. 
• Increasing temperature lowers the rate of strain hardening. Hence materials are strain hardened at low temperatures, thus also called cold working. 
• During plastic deformation, dislocation density increases. And thus their interaction with each other resulting in increase in yield stress. 
• Strain hardening (work hardening) is the reason for the elastic recovery. 
• The reason for strain hardening is that the dislocation density increases with plastic deformation (cold work) due to multiplication. 
• The average distance between dislocations then decreases and dislocations start blocking the motion of each one