Work hardening

Work hardening is the increase in a metal’s strength and hardness caused by plastic deformation. It arises as deformation creates and multiplies defects that impede further movement within the crystal.

Dislocation: A line defect in a crystal lattice where atomic arrangement departs from the ideal structure. Plastic deformation multiplies dislocations, whose interactions obstruct further dislocation motion.
Cold working: Metal forming performed below the temperature at which substantial recovery or recrystallization occurs. It deliberately uses work hardening to strengthen and shape metal.
Plastic deformation: Permanent change in a material’s shape after applied stress exceeds its elastic limit. It is the deformation that produces work hardening.
Annealing: A heat treatment that changes a material’s microstructure to reduce stored strain and improve ductility. Annealing can soften a work-hardened metal by enabling recovery and recrystallization.
Dislocation multiplication: The generation of additional dislocations during plastic deformation. Multiplication raises dislocation density as work hardening proceeds.
Rolling: A metalworking process that reduces thickness by passing material between rotating rolls. Cold rolling is a common way to impose controlled plastic strain and harden sheet.
Elastic deformation: Reversible deformation that disappears when the applied load is removed. Elastic strain alone does not leave the permanent strengthening associated with work hardening.
Recrystallization: Formation of new, relatively strain-free grains in a deformed material during heating. It replaces work-hardened grains and sharply reduces their dislocation density.
Taylor hardening: A relation connecting a material’s flow stress to the square root of its dislocation density. It quantifies how the growing dislocation population raises strength.
Wire drawing: A process that reduces a wire’s diameter by pulling it through a die. The wire gains strength as drawing imposes successive plastic deformation.

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