Significance of crystallographic misorientation at phase boundaries for fatigue crack initiation in a duplex stainless steel during high and very high cycle fatigue loading

The current investigations on the austenitic–ferritic duplex stainless steel X2CrNiMoN22-5-3 documents that the misorientation at a phase boundary determines its strength concerning the transition of plastic deformation from the austenite to the ferrite phase. The misorientation can be described by means of the tilt, twist and slip direction angle between two slip planes of neighboring grains. It has been found that plastic deformation can be transferred from an activated slip system in an austenite grain to a slip system in a neighboring ferrite grain with a moderate Schmid factor, even if not-activated slip systems in this ferrite grain have higher Schmid factors. For this, the tilt and twist angle between the activated austenite slip system and the ferrite slip system with the lower Schmid factor have to be smaller as compared to that of the tilt and twist angle between the activated austenite slip system and the ferrite slip system with the higher Schmid factor. The transition is very localized and mostly followed by microcrack initiation. Beside their significance concerning microcrack initiation, phase boundaries also determine significantly the short fatigue crack propagation.