Quenching process

Quenching also called Hardening, is a heat treatment process in which steel is heated up to austenite temperature (above it's critical temperature), hold for some time and then cooled in water, oil or molten salt (rapid cooling). Due to rapid cooling, it results very hard structure - martensite (hardest form of Steel).

fig.- steel component quench in oil.

Due to hardening process hardness of steel increases and bitterness also increases.(brittleness increases hence hardened Steel nay not directly use). Quenching is always follow by tempering process.

Due to rapid cooling in hardening process metal shape shrink, internal residual stresses are setup. That's the reason why hardening is follow by tempering.