Localization of crack initiation sites during fatigue of an austenitic-ferritic duplex steel in the high and very high cycle fatigue (HCF/VHCF) regime

摘要

Austenitic-ferritic duplex steels are characterized by a high corrosion resistance in combination with reasonable strength and good weldability, which makes them very attractive in chemical and petrochemical industry, in off-shore applications and for use in mechanical engineering. In many applications the material is subjected to cyclic loading and hence, the fatigue damage needs to be considered in design considerations. In this study, high-frequency fatigue testing was used to examine the VHCF behavior of a duplex steel. Local plasticity and damage were characterized applying scanning electron microscopy in combination with electron back-scattered diffraction. A simulation model was developed describing the development of crack initiation sites based on a crystal plasticity material model. This approach considers the real two-phase microstructure and its elastic/plastic anisotropy. The simulation results were correlated with SEM observations and a quantitative analysis of slip band geometries. The simulation model is aimed at a physically-base understanding of the microstructural mechanisms leading to crack initiation.