Nickel based superalloy Inconel 718 and low alloy steel EN24 are welded by continuous drive friction welding in annealed condition and then post-weld heat treated (PWHT). The welds exhibit low strength and high toughness in the as welded condition. Post-weld heat treatment applicable to either Inconel 718 or EN24, led to reduction in toughness and increase in strength. Toughness degradation after PWHT as per Inconel 718 was predominant. The observed trends in mechanical properties are explained on the basis of observed microstructure, fracture behaviour, electron probe microanalysis and X-ray diffraction. © 2009 Institute of Materials, Minerals and Mining.