työkovettumisen

Työkovettuminen, a Finnish term, translates to "work hardening" or "strain hardening" in English. It is a metallurgical phenomenon where a metal becomes stronger and less ductile through plastic deformation. When a metal is subjected to stress beyond its elastic limit, dislocations within its crystal structure move and multiply. These dislocations interact with each other, hindering their further movement. This increased resistance to dislocation motion is what makes the metal harder and stronger.

The process of work hardening can occur during various manufacturing operations such as rolling, drawing, forging, and stamping. For instance, repeatedly bending a paperclip will eventually cause it to break; this is due to work hardening. While work hardening increases the tensile strength and yield strength of a metal, it simultaneously reduces its ductility and toughness. This means the metal can withstand greater forces before permanently deforming, but it becomes more brittle and more likely to fracture under impact or sharp bending.

The extent of work hardening depends on the amount of plastic deformation the metal undergoes. Excessive work hardening can make a metal too brittle for further processing and may necessitate annealing, a heat treatment process that softens the metal by allowing dislocations to rearrange and reduce their density, thereby restoring ductility. Understanding work hardening is crucial in material science and engineering for selecting appropriate materials and optimizing manufacturing processes to achieve desired mechanical properties.