Role of Metallographic Studies in Characterization of Ductile Cast Iron

Abstract

Metallography is the study of micro – structural features of metals and alloys with the help of optical microscope. Various features can be revealed through this type of study. The present work precisely deals with the metallographic study of ductile cast iron [also known as modular or spheroidal graphite (S.G.) iron]. The microstructure of ductile or S.G Iron contains nodules of graphite embedded in different types of matrix. The matrix may be ferritic, pearlitic, ferito – perlitcs (ferrite + pealite), austenitic, martensitic etc. The nature of the matrix as well as the size, volume fraction and distribution of graphite nodules embedded in the matrix influence the mechanical properties. Ductile iron is now being extensively used for its high strength combined with considerable ductility along with various other properties. Recently extensive research work is being conducted to develop various properties to make the material suitable for making casks to carry nuclear fuel. In the present work differently heat treated ductile iron specimens were examined to find the best possible one (with respect to this specific purpose). For this purpose the most important mechanical property is the impact toughness. It has been found that the best possible combination of strength and ductility is obtained for a particular type of matrix as well as favorable distribution of graphite nodules within it. To determine the shape, size and distribution of graphitic nodules, metallographic study with the help of optical microscope is the only way.