Comparison of Microstructure and Non-metallic Inclusions in Top-Filled and Bottom-Filled Gray Iron Castings

A bottom-filled rigging system was designed to produce gray iron castings, which was compared with a top-filled design in the present study. Filling and solidification of gray iron produced with the bottom-filled mold were compared with that for the top-filled mold. At similar cooling rate and solidification condition, the count of Type A graphite flakes was greater in the bottom-filled casting, while its graphite flakes were also finer in size. In addition, the statistical analysis of non-metallic inclusions using a scanning electron microscope equipped with auto feature analysis software also showed differences in inclusion composition, size, and population density between two castings. The results indicated that the filling turbulence promoted interactions between metal with air, which in turn influenced the formation of non-metallic inclusions. As a result, this impacted the nucleation of flake graphite in the gray iron.