On the Fatigue ProPerties and Effect of GraPhite Nodules of Spheroidal GraPhite Cast Iron

本 硏究는 球狀黑鉛鑄鐵의 硬度를 넓은 範圍로 變化시켜 被勞强度를 測定하고 最大被勞限度를 推定함과 同時에 球狀黑鉛의 notch 效果를 밝히고자 했다. 被勞限度는 球狀黑鉛鑄鐵의 硬度가 增加함에 따라서 增加하지만 H_B 385 以上에서는 오히려 減少하고 있었다. 球狀黑鉛鑄鐵의 被勞限度는 基地組織의 差異에는 別 影響이 없고 基地組織의 硬度에만 對應한다는 것을 알 수 있었다. 鑄鐵에 內在하는 球狀黑沿의 notch 效果는 球狀黑沿의 notch 係數(βg)에 依해서 評價하였다. βg는 球狀黑沿端에서의 應力集中因子와는 거의 無關하다고 생각되었다.The significance of this investigation is in that fatigue strength data have been obtained for DCI wide range of variation in hardness. The upper limit of the curve showing the maximum fatigue limit was determined and notch effect of graphite nodules was clarified. The fatigue limit iincreases with increasing hardness of DCI. but when the hardness of DCI exceeds H_B 385, no further increment in fatigue limit is achieved. It was recognized that the fatigue strength of DCI was not essentially influenced by the difference of the matrix structure and that the fatigue strength corresponds almost only to the hardnesss of the matrix. The notch effect of graphite nodules contained in this cast iron was evaluated with a notch coefficient(or factor)βg, the ratio of the maximum fatigue limit of steel to that of DCI.ope