Glossary term
Work Hardening
The increase in strength and hardness that occurs when plastic deformation raises dislocation density in a ductile material.
Definition
processWork hardening is the increase in strength and hardness that occurs when a ductile material is plastically deformed.
Work hardening, also called strain hardening, results from the accumulation and interaction of defects in the material microstructure during plastic deformation. It increases yield strength and hardness while often reducing ductility, formability, and toughness unless followed by recovery or annealing.
When a ductile metal is plastically deformed, its microstructure resists further deformation more strongly. The material may show a rising true stress with increasing plastic strain, often represented in simple form as:
where K is a strength coefficient and n is the strain-hardening exponent over the range where the approximation applies.
Engineering use
Work hardening is central to rolling, drawing, bending, forming, stamping, shot peening, cold forging, and service deformation. It can be beneficial because it raises yield strength and surface hardness. It can also be harmful because it consumes ductility, increases forming loads, creates residual stress, and may promote cracking during subsequent operations.
Annealing can reduce or remove work hardening through recovery, recrystallization, and grain growth, depending on alloy and heat treatment. Some alloys are deliberately supplied in cold-worked tempers to achieve strength without quenching.
Process planning
Manufacturing plans often use work hardening deliberately but must leave enough ductility for later operations. A drawing, bend, swage, or forming sequence may require intermediate annealing, changed tooling radius, lubrication, or altered reduction per pass. In service, local cold work around dents, notches, threads, or machined surfaces can change residual stress and fatigue behaviour even when the bulk material specification is unchanged.
Common mistakes
A common mistake is assuming higher hardness from work hardening always means better performance. Reduced ductility, residual stress, anisotropy, fatigue behavior, and fracture toughness can govern the design. Another is ignoring local work hardening around bends, holes, machined surfaces, or service damage. A strong work-hardening review states alloy, prior processing, plastic strain level, directionality, hardness or tensile data, heat-treatment state, residual stress, and forming or service limits.