真空浸炭におけるエッジ部過剰浸炭の疲労強度に対する影響

概要

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The objective of this reseach is to study the effect of over-carburizing on the strength at edges of vacuum-carburized (VC) samples. The relationship between the edge angles and fatigue strength was investigated using developed bending tests in which stress maximized at the top of edges. It was found that the strength of atmosphere carburized (AC) samples rarely depends on edge angles. The fatigue strength of VC samples with edge angle near 180° is higher than that of AC ones. The fatigue strength of VC samples decreases sharply with decreasing edge angle and becomes lower than that of AC samples for the edge angles smaller than 90°, because of the over-carburizing at the edge caused by the overlapping of the carbon diffusion field. In order to improve fatigue strength of VC samples with sharp edges it is suggested that VC conditions are changed so that carbon content on planar surface and edges is lower thus lowering the degree of over-carburization.