Methods for estimating the sizes of large inclusions in clean steels

The sizes of large inclusions within a cast of hard steel have a major influence on fatigue characteristics, but are not directly measurable by routine means. Recently, two methods have been proposed for estimation of the size distribution of large inclusions on the basis of measurements made on the sections of inclusions revealed in samples from a polished plane surface of the material. This paper reviews the two methods, showing that they are closely related and that properties found by each may be deduced from those found by the other. The paper also discusses the problem of inferring the distribution of the projected (three-dimensional) size of large inclusions from measurements made by either of the methods on sectional (two-dimensional) sizes. A simple new approximate solution to this stereological problem is proposed and is compared to existing approaches.