In-situ observation of engulfment and pushing of nonmetallic in steel melt by advancing melt/solid interface

Engulfment or pushing of inclusion particle by advancing melt/solid interface of steel has been investigated in-situ with a confocal scanning laser microscope. When the velocity of advancing interface exceeds a critical value V_c for a particle with radius R, solid alumina cluster particle or liquid silicate/aluminate globular particle in steel melt is found engulfed by the interface which extends in a convex way to form a bump toward the particle. At lower velocities or for smaller radii, the particles in both classes are pushed by the interface which does not form the bump. For solid alumina clusters, V_c (μm/s) = 60/R (μm), whereas V'_c = 23/R for the liquid globular particles, although V_c is not much different from V'_c at same R. The shape of the bump is reasonably reproduced by a two-dimensional FEM analysis of heat transfer from the melt across the particle to the interface. Reduced heat transfer caused by the intervening particle is considered responsible for the bump formation and resulting engulfment at V_c usually encountered in conventional casting process of steel.