työkarkaisu

Työkarkaisu is a Finnish term that can be translated to "work hardening" or "strain hardening" in English. It refers to a phenomenon in metallurgy and materials science where a metal becomes stronger and harder when it is plastically deformed. This occurs because the deformation process introduces dislocations within the material's crystal structure. These dislocations are line defects in the crystal lattice that can move when stress is applied. As plastic deformation continues, the density of dislocations increases. These dislocations then interact with each other, impeding their movement. The greater the resistance to dislocation movement, the higher the stress required to cause further deformation, resulting in increased strength and hardness of the material.

This process is commonly used in manufacturing to improve the mechanical properties of metals. For example, bending, rolling, or drawing metal can induce work hardening. The extent of work hardening depends on the amount of plastic deformation. While it increases strength and hardness, it typically reduces the ductility (the ability to deform without fracturing) of the material. Therefore, engineers must carefully consider the balance between increased strength and reduced ductility when designing products that utilize work hardening. In some applications, annealing, a heat treatment process, may be used to soften the material and restore ductility after work hardening if necessary.