Inclusion Distribution in Ingots - A Guide to Segragation Mechanism

Abstract

The melting point of non-metallic inclusion, and their nature and distribution can be a guide in deciphering the mode of solidification and segregation in an ingot. A commercial ingot was sectioned, and examined micros-copically. Inclusion identification was carried out by optical method as well as by electron probe micro analy-sis. The exten of segregation was obtained by extensive spectro-chemical analysis. It has been found that the shape and position of bottom cone of negative segregation coincide with that of bottom cone of inclusions. A theory of ingot segregation has been suggested that the bottom cone of oxide inclusions is a result of incorporation of these inclusions inthe dendrites of equiaxed grains. The inclusions drop to the bottom end with the shower of relatively pure equiaxed grains. While the interdendritic fluid is enriched in elements like C, Mn, S, P, it is denuded of oxygen. Since the oxygen solubility is low, oxygen enrichment leads to immediate precipitation of oxides.