OS0203 EBSD法を用いたフェライト鋼の疲労き裂発生過程における結晶方位変化に及ぼす粒径・強化機構の影響評価(放射光およびEBSD法による材料評価,OS-2 回折法による材料評価)

Abstract

The crystallographic orientation changes during fatigue crack initiation process in ferrite steels with different grain sizes and chemical compositions were evaluated by the electron backscattered diffraction (EBSD). EBSD measurement and fatigue test were alternately carried out using small specimen. Misorientation parameter named Grain Reference Orientation Deviation (GROD), which is defined as orientation difference between each measuring point and datum orientation, was calculated. GROD_<ave>, which is average of GROD within observed area, increased until crack initiation, and then remained constant. However, the value of constant (the threshold of crack initiation) is different with grain sizes and chemical compositions. In order to consider the influence of grain size, a new parameter ΔGROD_<ave>/d_<ave>^2 (d_<ave>; the average of grain size) was proposed. The threshold of this parameter is approximately the same for the similar chemical component with the different grain size. Moreover, the threshold increased along with fatigue strength improvement for the different chemical compositions with the same grain size. This result suggests that the proposed parameter is effective for fatigue damage evaluation in crack initiation process.