Heat treatment of steel by high-frequency currents

There has recently been a great increase in the use of highfrequency currents for heat treatment of metals, in such processes as surface hardening, cementation and alloying, welding, hot machining, and zonal tempering. The paper deals chiefly with surface hardening. After giving an account of the advantages of the process and an estimate of the power requirements, the authors deal with the design of the heating coil in relation to the shape of the specimen, and describe a ¿model¿ method whereby the distribution of the electromagnetic field in the system may be investigated. Curves are plotted from the authors´ experimental results to show the distribution of temperature and current density over the specimen, and the variation of the power absorbed, during the heating period. The effect of frequency upon the depth of penetration of eddy currents in steel is examined, and consideration is given to the relation between the depth of penetration and the shape of the surface being treated. The paper concludes with a statement of the results which have been obtained from the application of the high-frequency method to the hardening of tools and gears.