A Novel Method for Microstructural Characterization of Gray Cast Iron

The difficulty in the metallography of gray cast iron lies in the differentiation of ferrite and iron phosphide eutectic (steadite) microconstituents using normal etchants like nital and picral, and both phases appear bright (white color, unaffected) under normal light microscopy. Hence, it is difficult to find out the relative amounts of phases either photomicrographically or using sophisticated image analysis software. On the whole, the samples are etched with 2-3% nital for quantification of ferrite, steadite, pearlite, and carbides under optical (light) microscopy. This method of inspection requires high skill to differentiate the ferrite and steadite microconstituents, and also, sometimes it leads to misinterpretation which results in uncertainty in results. This led to the development of a novel etching method using "selenic reagent" which unveiled different microconstituents in the microstructure with higher confidence level.