LABORATORY-SCALE REFINING STUDIES ON LOW-CARBON ALUMINUM KILLED STEELS USING SYNTHETIC FLUXES

Laboratory size (4.5-5 kg) low carbon steel melts were deoxidized usin g Al in zirconia crucibles. Some of these heats were treated with diff erent types of synthetic fluxes to evaluate the oxide inclusion remova l and desulfurization characteristics of the respective synthetic flux es. The sulfur, oxygen and aluminum contents in the steel melt were de termined as a function of refining time and temperature. It was observ ed that the reaction between aluminum and oxygen in solution closely f ollows thermodynamic equilibrium. Reoxidation of the steel melt occurr ed through oxygen pick-up from the atmosphere. The extent of this reox idation was found to be a function of both the oxygen content and the exposed surface area of the steel melt. The effectiveness of calcium-a luminate (12CaO.7Al2O3) based fluxes in protecting the steel melt from reoxidation and in increasing the rate of removal of inclusions was e valuated. Synthetic fluxes and refining techniques were developed to o btain total oxygen level of 10 ppm within the first 10 min of refining . Sulfur removal followed first order reaction kinetics. The effective ness of calcia saturated calcium-aluminate (12CaO.7Al2O3) based fluxes in desulfurizing the steel melts was evaluated. The effects of adding barium oxide and fluorspar to the flux, the initial sulfur level of t he steel melt, and addition of tellurium to the steel melt on the kine tics of desulfurization were also studied.