Modeling the Behavior Al2O3 Inclusions during the Dendritic Solidification of Steel.

Starting with a distribution of single-particle alumina inclusions, estimates of their collision frequencies and the number concentrations of two- and three-particle clusters in the interdendritic liquid during solidification were made. The alumina clusters possibly serve as pore-nucleation sites, so their number concentrations that form during solidification are of interest. We also show that the smaller alumina inclusions are not entrapped in the dendritic solid during solidification, based on estimates of the interdendritic solidification rates and empirical data on the engulfment of Al2O3 inclusions by solidifying steel. Engulfment by the interdendritic liquid, however, is enhanced by the gradients of the concentrations of oxygen and sulfur in the interdendritic liquid during solidification. These elements are surface active on the liquid-steel/alumina interface and, in turn, introduce very strong capillary forces on the interdendritic alumina inclusions.