非金属介在物の最大寸法推定上の問題点について

抄録

The fatigue strength of hard steels is frequently influenced by the existence of nonmetallic inclusions. The statistics of extreme values is useful for the estimation of the maximum or the minimum value in a statistical lot. This method can be also used to estimate the maximum size of nonmetallic inclusions in metals or to estimate the maximum size of grain size in a microstructure. However, since the observation plane does not necessarily coincide with the one which cuts the section of the maximum diameter of the maximum inclusion or grain, the estimation of the maximum values by the statistics of extreme values includes some error. In this study, this error was investigated by measuring the distribution of the size of graphites in a nodular cast iron and also measuring the grain size of a few kinds of steels. Based on the estimated errors, the applicability of the statistics of extreme values is discussed.