Kylmämuovauskovettuminen

Kylmämuovauskovettuminen, also known as work hardening or strain hardening, is a process by which a ductile metal becomes harder and stronger as it is plastically deformed. This occurs at temperatures below the metal's recrystallization temperature, meaning that the deformation does not trigger the formation of new, strain-free grains. Instead, the process involves the movement and interaction of dislocations, which are line defects within the crystal structure of the metal.

During plastic deformation, these dislocations move through the crystal lattice. As the deformation increases, the density of dislocations also increases. These dislocations can interact with each other, becoming tangled and impeding further movement. This increased resistance to dislocation motion is the underlying cause of the increased strength and hardness observed in the metal. The metal also becomes less ductile, meaning it can withstand less plastic deformation before fracturing.

Kylmämuovauskovettuminen is a common phenomenon in many manufacturing processes, such as rolling, drawing, and forging, when performed at room temperature or below. It can be a desirable effect, as it allows for the strengthening of metal parts without the need for heat treatment. However, it can also be a limitation, as excessive work hardening can make subsequent processing more difficult or even impossible without annealing, a heat treatment process that softens the metal by allowing recrystallization. The degree of kylmämuovauskovettuminen depends on the metal's composition, the amount of deformation, and the temperature at which the deformation occurs.