työnkovettumisesta

Työnkovettuminen, known in English as work hardening or strain hardening, is a process in materials science where a ductile metal becomes harder and stronger as it is plastically deformed. This occurs because the deformation process creates and multiplies dislocations within the material's crystal structure. Dislocations are line defects in the crystalline lattice, and their movement allows for plastic deformation. When a metal is plastically deformed, new dislocations are generated, and existing ones interact and tangle with each other. This tangled network of dislocations impedes further dislocation movement, requiring more stress to induce additional deformation. Consequently, the material's yield strength and tensile strength increase, while its ductility decreases.

The phenomenon of work hardening is utilized in many manufacturing processes. For instance, rolling, drawing, and forging are all methods that employ plastic deformation to strengthen metal components. Cold working, which is deformation performed below the material's recrystallization temperature, is particularly effective in inducing work hardening. While work hardening enhances mechanical properties like strength and hardness, it also makes the material more brittle. If a work-hardened material is subjected to excessive stress, it is more likely to fracture rather than deform further. The effects of work hardening can be reversed through annealing, a heat treatment process that allows for recrystallization and the reduction of dislocation density.