Thin case hardening with radio-frequency energy

Concerns induction heat treating in the 1-20 Mc./s. range. A thin case is one betw. 0.005 and 0.030 in., controllable to within plusmn0.001 in., and capable of duplication in quantity production. Two fundamental energy requirements exist: (1) The frequency should be in the Mc./s. range, (2) power must be applied to the surface of the work at not less than double the rate of heat conduction loss from the surface to the core. Photomicro- and macro- graphs illustrate the metallurgical aspect of the thin case. A mathematical expression is given for the temperature after a time t of a point at x beneath a heated surface.