On the effect of electrodischarge machining parameters on the fatigue life of AISI D6 tool steel

The effects of current setting and pulse-on time on the fatigue lives of AISI D6 tool steel specimens produced using three-dimensional cavity machining are investigated. Optical and scanning electron microscopy, microprobe analysis and microhardness tests have been used to study the characteristics of the machined and fractured specimens. The results have confirmed the deteriorating effect of electrodischarge machining (EDM) on fatigue lives. The discharge energy has been found to affect the fatigue lives as well as the thickness, the uniformity and the solidification cracking of the re-cast layer. Surface imperfections resulting from the EDM process lead to multiple fatigue-crack initiation and subsequent propagation into the substrate material. When sufficient cracks reach a critical length, fast fracture of the remaining cross-section takes place. The chemical compositions of the re-cast layers have been found to have slightly greater carbon content than that of the steel substrate and their hardness values have proven to be greater. (C) 1997 Elsevier Science S.A.