hardening

Hardening is a process that increases the firmness or solidity of a material, or makes it more able to withstand strain and hardship. In metallurgy, work hardening involves physically deforming metals like hammering or rolling to increase their hardness. This happens because repeated stress causes crystal structures within the metal to slip, and these slips eventually create obstacles that impede further movement, thus strengthening the metal.1

Surface hardening is a technique used to make the outer layer of steel harder while keeping the core relatively soft. This combination is valuable in engineering for parts like gears and bearings, as it allows them to withstand high stress and fatigue while remaining flexible. Methods include carburizing, where carbon diffuses into the steel's surface, nitriding, which uses nitrogen, and flame or induction hardening, which use rapid heating and quenching.2