A layered workpiece consisting of a surface layer (sleeve) of the high-carbon steel S45C and an inner layer (core) of the low-carbon steel S15C was used to study the conditions for gear extrusion. The specifications of the gear examined are as follows: module m=1.25 - 3.0 mm, number of teeth Z=18 - 11, and whole depth h=2.25 module. The conditions for obtaining a layered gear with a carbon content that allows the hardening of only the surface layer by high-frequency hardening were investigated in terms of sleeve thickness, reduction in area, and other factors. The result showed that such a layered gear could be produced, and that the punch pressure required was far below the strength of the punch material. Because high-frequency hardening allows processing within a short time period, it appears possible to produce such gears in a production line including heat treatment. However, because the sleeve and core were not jointed, the extrusion of the core and a low deformation resistance in ahead of the sleeve were observed.
