työkarkaistuminen

Työkarkaistuminen, a Finnish term, translates to "work hardening" or "strain hardening" in English. It is a phenomenon observed in ductile materials, such as metals, where their strength and hardness increase when they are plastically deformed. This occurs at temperatures well below the material's melting point, distinguishing it from other heat-treating processes.

The underlying mechanism of work hardening involves the movement and interaction of dislocations within the material's crystal structure. Dislocations are line defects in the crystal lattice. When a material is deformed, these dislocations move, multiply, and interact with each other, forming tangles and barriers. These tangles impede further dislocation movement, requiring more stress to cause additional deformation. Consequently, the material becomes stronger and harder, but also less ductile.

Work hardening is a widely utilized process in manufacturing. For example, bending, rolling, or drawing metals can all induce work hardening, enhancing the strength of the final product. This is beneficial in applications where components need to withstand significant stress. However, excessive work hardening can make a material brittle, limiting its formability. Annealing, a heat treatment process, can be used to reverse work hardening by allowing dislocations to annihilate or rearrange, restoring ductility.