Induction hardening of complex geometry and geared parts

Mechanical gear parts for automotive or aeronautical industry are highly stressed toothed workpieces, which need to be heat treated in order to improve their mechanical properties. Up to now the most common heat treatment technology is carburizing. This method permits to achieve strength and wear resistance but cannot be integrated in a production line. Moreover, the carburizing process takes several hours and the workpiece must be completed heated up to the austenization temperature, resulting in extensive deformation. The induction contour hardening process is an alternative to carburizing. The purpose of this paper is to present the induction contour hardening process with particular reference to geared parts. In the paper are first recalled the basic laws of induction heating and is given an historical overview of the induction hardening process of gears. Induction hardening involves electromagnetic and metallurgical phenomena, which are described in the third and fourth paragraph. Some practical industrial applications of the induction hardening are presented in the fifth paragraph.