Surface hardening of metals using electric currents

摘要

Method and apparatus for modifying the surface properties of a metal part made of a metal which changes its properties with heating to a transformation temperature and subsequent cooling in which method electric current having a frequency of at least 3000 Hz is supplied to a pair of contacts respectively at the opposite ends of the surface area to be modified through a proximity conductor or conductors which are spaced from the surface area by not more than two times the width of the conductor. The duration, frequency and magnitude of the current and the width of the proximity conductor or conductors are chosen so that the metal of such area heats at least to the transformation temperature before the adjacent metal reaches a temperature which would prevent self-quenching of the area metal, by means of conduction of heat from the area metal to the adjacent metal, when the current is discontinued. Apparatus for producing lines of hardening on valve seats is disclosed.