workharden

Workhardening, also known as strain hardening or cold working, is the process by which a metal becomes stronger and harder as it is plastically deformed. This phenomenon occurs because the deformation introduces dislocations, which are line defects in the crystal structure of the metal. As more dislocations are formed and move through the crystal, they interact with each other, impeding their further movement. This increased resistance to dislocation motion is what leads to the observed increase in strength and hardness.

The degree of workhardening depends on the amount of plastic deformation. More deformation generally leads to a greater increase in strength, but also a decrease in ductility. Ductility refers to a material's ability to deform plastically before fracturing. Therefore, while workhardened metals are stronger, they become more brittle.

Workhardening is a significant factor in many manufacturing processes. For example, bending, rolling, and drawing operations all induce plastic deformation and thus workharden the metal. This can be desirable if increased strength is needed, but it can also be a limitation. If a metal is deformed too much, it may become too brittle to undergo further processing without fracturing. In such cases, annealing, a heat treatment process, can be used to relieve the internal stresses and reduce the dislocation density, thereby restoring ductility. The process of workhardening is a fundamental concept in materials science and engineering, influencing the properties and applications of metallic materials.