Editing Differential heat treatment (section)

===Induction hardening===
{{main|Induction hardening}}
Induction hardening is a surface hardening technique which uses [[induction coil]]s to provide a very rapid means of heating the metal. With [[induction heating]], the steel can be heated very quickly to red-hot at the surface, before the heat can penetrate any distance into the metal. The surface is then quenched, hardening it, and is often used without further tempering. This makes the surface very resistant to wear, but provides tougher metal directly underneath it, leaving the majority of the object unchanged. A common use for induction hardening is for hardening the bearing surfaces, or "journals", on automotive [[crankshaft]]s or the rods of [[hydraulic cylinder]]s.<ref>Prabhudev, pp. 400–407</ref>