All the heat treatment processes specify a soaking time of 1 to 2 minutes per mm of section (or 30-60 minutes per inch). This is done to have unifiorm heating across section and also to allow diffusions (in certain cases of heat treatment) to take place. Of course the exact time taken is governed by Fick's Law. But the time above is a thumb rule.
And this is except hardening. In hardening operation you are crossing the upper critical temperature to fully austenite the metal. You stay less and the insides do not transform. Stay too long, and the austenitic grain growth starts. Both has a severe effect on the property of the final product especially in the core, where you need the toughness.
Difefrent materials have different soaking time requirements. Also consider the Induction hardening process - the soaking time is next to zero?
Heat Treatment
Re: Heat Treatment
