just as a reminder of terminology:
When a metal is worked such as bending forming welding etc it hardens due to the process which is not desirable. To return the metal to its original state the metal is annealed usually by heating and slow cooling.
Tempering is a process that follows hardening Take a knife formed from a common high carbon steel and then heated to cherry red hot around 900 deg C and quenched in oil or water this makes the knife very hard but brittle
Annealing is softening the metal after work hardening
Tempering is reducing brittleness after quench hardening
Tempering is raising the knife temperature to around 250 deg C and again quenching in oil or water this reduces the brittleness but retains most of the hardness
the exact temperatures/quenching material, etc. depend on the composition of the steel involved.
differential hardening, as used on a khukuri for instance, has the steel heated to hardening temp, and just the edge is quenched, with the spine generally left to air cool and thus become tempered by the residual heat in the item. nepali kami's do that quench with just a teapot & boiling water by the way.
the whole process is better referred to as 'heat treatment' rather than as just 'tempering' which is a part of it rather than a stand-alone process.
|