Strain hardening, also known as work hardening, is the phenomenon where a material becomes stronger and harder as it undergoes plastic deformation. It occurs after the yield point, in the plastic region of the stress-strain curve, where the material continues to deform under increasing stress.
After yielding, if the material is further loaded, it does not simply deform indefinitely at a constant stress. Instead, additional stress is required to continue deforming the material, resulting in an upward slope in the stress-strain curve. This increase in stress with plastic deformation occurs due to changes at the atomic level—dislocations in the crystal structure become more entangled, making further movement more difficult and increasing the material’s resistance to deformation.

Key Effects of Strain Hardening:
- Increased strength: The material can now withstand higher stresses before failing.
- Reduced ductility: The material becomes less capable of undergoing further deformation without breaking.
- Higher ultimate tensile strength (UTS): The peak of the stress-strain curve occurs due to strain hardening before necking begins.
- Lower toughness: While strength increases, the ability to absorb energy before fracture may decrease.
Engineering Applications:
Strain hardening is used in manufacturing processes such as cold working, where metals are plastically deformed at low temperatures to increase their strength. Examples include drawing, rolling, and forging. However, excessive strain hardening can make a material brittle, requiring processes like annealing to restore ductility.
On the stress-strain curve, strain hardening occurs after the yield point and before the ultimate tensile strength (UTS), marking the transition from uniform plastic deformation to localized deformation (necking) before failure. Understanding strain hardening is crucial in material selection and processing to ensure components achieve the desired balance of strength and ductility.