Reoxidation on the surface of molten low-carbon aluminum-killed steel

The unwanted formation of oxide on the surface of molten steel is a process that plagues virtually all grades of steel and often results in unacceptable defect distributions in the finished product. The kinetic rates of the reaction remain largely unknown due to the difficulties in experimental measurements at high temperature involving reactive molten melts. This paper presents recent experimental work and analysis of oxide evolution on the surface of Al-killed steel melts at oxygen partial pressures of Po₂= 1-5×10 ^-5atm, by using a Confocal Scanning Laser Microscope (CSLM) equipped with a gold image furnace. The effects of gas flow rate (170-300 cm ³/min) and temperature (1580-1630°C) were investigated. The oxide phase formed on the melt surface was in all cases Al₂O₃ but not the thermodynamically stable FeAl₂O₄. It was found, under the range of experimental conditions in this study, that the rate controlling mechanism for oxide nucleation and growth was gas phase mass transfer of oxygen to the melt surface. The morphology of the oxide changed gradually from distinctly dendritic at low gas flow rates to aggregates as the flow rate was increased.