quench hardening

Quench hardening is a heat treatment process in which metal is strengthened and hardened. It is done by heating the material to the annealing temperature and keeping it there just long enough for the grain structure to change (so the metal becomes an austenite structure), but not so long that the grains grow large. The hot metal is then submerged in water or oil and swirled in a figure-eight pattern, hardening it all the way through.

In this way, quench hardening differs from case hardening, a process in which only the surface of the metal is hardened.

Immediately after quench hardening, the metal is brittle. Tempering is often performed next in order to reduce brittleness.