LCF Mechanisms of the 25 Cr 7 Ni 0.25 N Duplex Stainless Steel Investigated by Atomic Force Microscopy*

Abstract Surface relief evolution during the fatigue life has been studied by Atomic Force Microscopy in a duplex stainless steel fatigued at a total strain range Δε t = 1.6%. In austenite, hill-like extrusions, observed since the beginning of the fatigue life, were the basic morphology. For ferritic grains, the modification took place later and the disposition of the persistent slip markings was irregular in a given grain. Highly rugged areas were the more developed surface morphology in ferrite after 60 percent of the fatigue life. These areas seemed to be connected with the austenitic neighbour grain in terms of surface activity and disorientation, and are proposed as the possible crack nucleation sites in the ferrite, near the ferrite austenite interfaces. It is shown that the origin of crack nucleation in ferrite is strongly dependent on the relative crystallographic orientation of the austenite and its plastic activity.