Surface Hardening of Ferritic Spheroidal Graphite Cast Iron by Friction Stir Processing

Abstract

A ferrite-based spheroidal graphite cast iron (FCD450) is difficult to harden using a conventional surface hardening method, because the carbon content in the matrix is very low. In order to solve this problem, the friction stir processing (FSP) was used in this study as a new hardening method for cast irons. The authors have clarified in a previous study that the pearlite-based cast iron, such as FC300 and FCD700, can be hardened using the friction stir processing and that there are several advantages, such as a higher hardness and no required post surface machining. In this study, it was clarified that a Vickers hardness of about 700HV is obtained due to the formation of fine martensite even in the ferrite-based spheroidal graphite cast irons, although the optimal process range is much narrower than that of the pearlite-based cast iron due to the requirement of both the heat input for diffusion of the carbon into the matrix and the high cooling rate for the martensitic transformation.