The shape of early persistent slip markings in fatigued 316L steel

Polycrystalline austenitic 316L steel specimens were polished and cyclically deformed with constant strain amplitude into the early stage of fatigue life (N/Nf=0.006). Surface relief consisting of persistent slip markings (PSMs) has been studied using high resolution SEM and FIB cuts. Mostly extrusions were produced in this early stage of fatigue damage. Only in a few well developed PSMs the intrusions were detected lying parallel to an extrusion. The findings were discussed in relation to fatigue crack initiation models and it was concluded that fatigue cracks start at the tip of crack-like intrusions in the central part of the PSMs where corresponding persistent slip band (PSB) depth is most pronounced.