Efficiency of grain and phase boundaries as microstructural barriers during hcf and vhcf loading of austenitic-ferritic duplex steel

U KRUPP; A GIERTLER; MC MARINELLI; H KNOBBE; HJ CHRIST; P KOSTER; CP FRITZEN; S HEREÑU; I ALVAREZ

Berlin

Conferencia; 5th International Conference on Very High Cycle Fatigue; 2011

DVM

HCF and VHCF studies on austenitic ferritic duplex steel specimens in two different heattreatment conditions have revealed that even beyond 108 cycles local plasticity causessurface modifications in form of pronounced slip bands that are extending with an increasingnumber of cycles. By means of scanning electron microscopy (SEM) in combination withelectron back-scatter diffraction (EBSD) being applied after certain intervals during fatigueloading of the specimens, the appearance of the slip bands was correlated with thecrystallographic misorientation distribution and the phase arrangement within the duplexmicrostructure. In general, plastic deformation of the austenite is present for all stressamplitudes of technical relevance, manifesting itself by the generation of heat. Therefore, theexistence of a fatigue limit in duplex steel is believed to depend quantitatively on (i) theefficiency of the austenite-ferrite phase boundaries, and (ii) the free slip length withinaustenite phase patches. The experimental observations have been served as input for thedevelopment of short crack modelling concepts using both a finite-element and a boundaryelementapproach, which are outlined and discussed in the present paper.