Abstract
Orientation changes during fatigue crack initiation process in ferrite steels with different grain size and chemical composition were evaluated by the electron backscattered diffraction(EBSD). EBSD measurement and fatigue test were alternately carried out using small specimen. Crystal rotation was evaluated at the same point before fatigue testing and after fatigue testing by digital image correlation. The crystal rotation is relatively larger at the crack initiation site. The average of rotation angle in the observed area is increased and then constant at crack initiation. The constant value is about 2.0deg regardless of grain size and chemical composition. This result suggests that crystal rotation based on the crystal direction before fatigue testing is quantitative parameter for evaluation of fatigue damage dominating fatigue crack initiation.
