Intergranular crack paths during fatigue in interstitial-free steels

Interstitial-free (IF) steels are known to exhibit intergranular (IG) faceting during fatigue under certain conditions. The presence of IG facets is often ascribed to either environmental effects or to grain boundary embrittlement. In many cases this attribution to environment or embrittlement is erroneous with the IG faceting actually arising from the intrinsic slip characteristics of body-centred cubic (bcc) alloys. This paper summarises the background to slip-induced intergranular fatigue and explores two issues of importance to users of IF steels; alloy conditions in which IG fatigue occurs and whether the fatigue performance in the presence of an IG crack path is lower than similar IF steels which exhibit a transgranular crack path. To explore this latter issue fatigue performance is presented as a function of yield strength.