Determination of volume fraction of sulfide inclusions in steels

Abstract

This paper examines the effectiveness of a metallographic method suggested by Whiteley [1] for quantitative evaluation of sulfide inclusions in steels using image analyzing computers such as the Quantimet 720. This metallographic method was proposed originally for identification of manganese sulfide inclusions. It involves rubbing a metallographically polished surface with a suitable cloth containing absorbed silver nitrate. The resultant reaction turns the manganese sulfides white in color. In the present work, sulfide inclusions were studied in six steels employing the above metallographic method and the Quantimet 720. In addition, elemental analyses of inclusions before and after silver nitrate treatment were carried out using an ORTEC energy dispersive system attached to a JEOL scanning electron microscope. The conclusions were that not only manganese sulfides, but sulfides of other compositions were also turned white by the above metallographic method, that inclusions other than sulfides were not affected by this surface treatment, and that the whitening of sulfides was due to a silver deposit on them. In addition, it was found that a linear relation exists between the volume fraction of sulfide inclusions and the sulfur content, the constant of proportionality being dependent on the sulfide composition.