巨大共晶炭化物を含む超高炭素綱の疲労き裂進展抑制機構

概要

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Superior resistance to the stage 11 fatigue crack growth was obtained on an ultra high carbon steel containing massive eutectic carbide extended in the direction perpendicular to the original crack growth direction by forging. The fatigue crack growth rate obtained in this study was about 1/4 times as low as that of general mild steel without eutectic carbides. Microscopic observations revealed that the fatigue crack path was bent or branched when it encountered the massive carbide. Taking the actual crack configurations affected by the carbide into consideration, the "Effective stress intensity factor (SIF_<eff>)" for fatigue crack growth was estimated, in which significant reduction of the SIF_<eff> was obtained. An analytical study showed that the SIF_<eff>of the bent crack would decrease significantly with increasing the angle θ between the carbide extention direction and the loading direction. The relation between the growth rate and SIF_<eff>was examined on various specimens that have different carbide orientation on the basis of the above analysis. It was found that the growth rate drastically changed in accordance with θ and also found that the dependense of the growth rate on θ was in good agreement with the SIF_<eff>-θ relation. It was made clear that crack growth retardation was due to the reduction of SIF_<eff> resulting from the complicated crack morphology affected by massive carbide.
社団法人日本材料学会の論文
1987-06-15