X-Ray Investigation on Fatigue Fracture of Notched Steel Specimen : Observation of Fatigue Phenomena of Annealed Low-Carbon Steel by X-Ray Microbeam Technique

概要

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It was successful to apply the X-ray microbeam technique for observing fatigue phenomena of annealed low-carbon steel. The following conclusions were obtained : (1) Misorientation and lattice strain increase quickly in the early period of fatigue process, and subsequently they continue to increase till initiation of a crack. Formation of subgrains proceeds relatively slowly in the early period, and it becomes thereafter a main process of fatigue. Formation of subgrains is not observed for fatigue below fatigue limit. (2) Density of excess dislocation of one sign in subboundaries for fatigue is much smaller than those for uniaxial tension and rolling. (3) It is considered that the reason why the half-value breadth increases during fatigue is not the formation of subgrains but is mainly the increase of lattice strain. (4) Schematic diagram of deformation in a grain for fatigue is suggested. The formation of subgrains is closely related to fatigue fracture.
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