workhardens

Work hardening, also known as strain hardening, is a metallurgical phenomenon in which a metal becomes harder and stronger as a result of plastic deformation performed at temperatures below its recrystallization temperature. The primary mechanism is the accumulation and interaction of dislocations within the crystal lattice, which creates barriers that impede further dislocation motion. As deformation continues, the material exhibits higher yield strength and tensile strength, while ductility generally decreases.

The extent of work hardening depends on the material and its microstructure, the amount and rate of deformation, and the temperature during deformation. Metals with different stacking fault energies respond differently: cold working typically produces a more pronounced strengthening effect than warm or hot working. Recovery and recrystallization at higher temperatures can reduce or erase the effects of work hardening.

In practice, work hardening is exploited in metal forming processes such as drawing, rolling, and bending to increase strength, hardness, and wear resistance. It also affects subsequent processing, because a pre-hardened portion may require higher forming forces or exhibit reduced ductility. The degree of hardening is commonly assessed by hardness tests or tensile tests, which show increases in yield and tensile strength with reductions in elongation.

Reversing work hardening is possible through annealing, which promotes recovery, recrystallization, and grain growth, restoring ductility and softening the material. Work hardening is a fundamental concept in materials science and engineering, influencing the design of components and the selection of processing routes.