Damage Evaluation during Fatigue Crack Initiation Process Using Misorientation Parameter by EBSD

Orientation changes during the fatigue crack initiation process in ferritic steels with different grain size and ferritic-pearlitic steels with different carbon content were evaluated by the electron backscatter diffraction (EBSD). EBSD measurements and fatigue tests were alternately carried out using small specimen. Crystal rotations were evaluated by two misorientation parameters; Grain Reference Orientation Deviation (GROD) and crystal misorientation at the same point before and after fatigue testing (Δθ). Both parameters increased and then remained constant at crack initiation. The variation in GROD was approximately 0.1° and that in Δθ was 1.0 to 2.0° regardless of the grain size and the carbon content. Therefore, Δθ is more sensitive to orientation changes under cyclic loading.