The evolution of nonmetallic inclusions was examined for 4320 steel at an industrial steel foundry. The steel was followed from electric arc furnace melting through ladle refining to final casting. Timed sampling was performed at all stages of the process. Samples were analyzed using an automated SEM/EDS system. The overall evolution of oxide inclusions in terms of nucleation, growth, and flotation during liquid processing was studied using area fraction and average diameter. Chemical composition evolution was observed using a joint ternary plotting tool developed under this program. It was found that the use of zirconium as an addition for nitrogen/oxygen removal leads to a large number of ZrO2 inclusions, which is related to insufficient flotation due to the higher density of zirconia and in turn less effective calcium treatment. In addition, no ZrN formation was observed, likely due to the high FeO acid slag practice used. Argon stirring was found to reduce the flotation problems associated with the zirconium addition somewhat and significantly contribute to the removal of large size ( > 5µm) inclusions.