In metallurgy , an increase in hardness of a metal induced, deliberately or accidentally, by hammering, rolling , drawing (see wire drawing ), or other physical processes.
The first few deformations imposed by such treatment weaken the metal, but because of the crystalline structure of metal its strength increases with continued deformations. Crystals slip against each other; but, because of the complexity of the crystal structure, the more such slips are multiplied, the more they tend to place obstacles in the way of further slippage, as the various dislocation lines crisscross each other. See also carburizing , tempering .