Abstract
Orientation changes during fatigue crack initiation process in Si-added ferrite steels were evaluated by the electron backscatter diffraction (EBSD). To discuss the mechanism of the orientation changes, height measurement by leaser scanning microscope and transmission electron microscope (TEM) observation are conducted. The area of large orientation rotations and that of large slope had good correlation with fatigue damaged area. Moreover, the upper 2.3% value of orientation rotation was almost equal to that of large slope. TEM observation showed that steel with lower Si content tends to form clear sub-grain. However, there was little difference in dislocation structure between large and small orientation region in each steels, regardless of Si content. These results suggest that orientation change is mainly brought about by the transformation of surface slope.
