työkovetta

A työkovetta is a Finnish term that translates to "work harden" or "work hardening" in English. It refers to a phenomenon in metallurgy where a metal becomes stronger and harder when it is plastically deformed. This occurs because the deformation process introduces and multiplies dislocations within the crystal structure of the metal.

Dislocations are linear defects in the crystal lattice of a metal. When a metal is stressed beyond its elastic limit, it undergoes plastic deformation. This involves the movement of these dislocations. As dislocations move, they can interact with each other and with other defects, such as grain boundaries. These interactions impede further dislocation movement.

The increased resistance to dislocation movement makes the metal harder to deform further, thus increasing its strength and hardness. This is a common and often desirable characteristic of many metals, as it allows them to be shaped and strengthened through processes like rolling, drawing, and forging. However, excessive work hardening can make a metal brittle, meaning it is more prone to fracture.

To counteract or reverse work hardening, a process called annealing can be used. Annealing involves heating the metal to a specific temperature and then cooling it slowly. This process allows dislocations to rearrange themselves, reducing their density and facilitating further deformation if needed. Therefore, work hardening is a fundamental concept in materials science and metalworking.