EBSD法による結晶方位差パラメータを用いたフェライト鋼の疲労き裂発生過程における損傷評価

概要

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Orientation changes during fatigue crack initiation process in ferrite steels with different grain size were evaluated by the electron backscatter diffraction (EBSD). EBSD measurement and fatigue test were alternately carried out using small specimen. Crystal rotation was evaluated by two misorientation parameters; Grain Reference Orientation Deviation (GROD), which is misorientation between measuring points and the average orientation in each grain, and crystal misorientation at the same point before and after fatigue testing (Δθ). Both parameters are increased and then constant at crack initiation. The variation of GROD is about 0.1° and that of Δθ is about 2.0° regardless of grain size. Therefore, Δθ is more sensitive to orientation change under cyclic loading. In addition, the large Δθ area shows better agreement with fatigue damaged area (crack and slip band) than large GROD area. These results suggest that Δθ is quantitative parameter for evaluation of fatigue damage dominating fatigue crack initiation.
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