Umformhärtung

Umformhärtung, also known as work hardening or strain hardening, is a metallurgical process where a metal becomes stronger and harder as it is plastically deformed. This phenomenon occurs when dislocations, which are line defects in the crystal lattice of a metal, move and interact during plastic deformation. As more dislocations are generated and tangled, they impede each other's movement, requiring more stress to continue deformation.

The process involves applying mechanical force to a metal, causing it to permanently change its shape. This deformation can be achieved through various methods like rolling, drawing, forging, or extrusion. During these operations, the grains within the metal are elongated and distorted, and the density of dislocations increases significantly. This increase in dislocation density is the primary reason for the observed increase in strength and hardness.

Umformhärtung is a desirable property in many applications where increased mechanical strength is needed without altering the material's composition. However, it also leads to a decrease in ductility, making the material more brittle. This trade-off must be considered in material design and manufacturing. For instance, metals that are heavily work hardened may require annealing, a heat treatment process, to restore some of their ductility before further processing or use. The extent of umformhärtung depends on the amount of plastic deformation, the type of metal, and the processing temperature.