Laboratory Scale Refining Studies on Low Carbon Aluminum Killed Steels Using Synthetic Fluxes

Abstract

Laboratory size (4.5-5 kg) low carbon steel melts were deoxidized using Al in zirconia crucibles. Some of these heats were treated with different types of synthetic fluxes to evaluate the oxide inclusion removal and desulfurization characteristics of the respective synthetic fluxes. The sulfur, oxygen and aluminum contents in the steel melt were determined as a function of refining time and temperature. It was observed that the reaction between aluminum and oxygen in solution closely follows thermodynamic equilibrium. Reoxidation of the steel melt occurred through oxygen pick-up from the atmosphere. The extent of this reoxidation was found to be a function of both the oxygen content and the exposed surface area of the steel melt. The effectiveness of calcium-aluminate (12CaO·7Al₂O₃) based fluxes in protecting the steel melt from reoxidation and in increasing the rate of removal of inclusions was evaluated. Synthetic fluxes and refining techniques were developed to obtain total oxygen level of 10 ppm within the first 10 min of refining. Sulfur removal followed first order reaction kinetics. The effectiveness 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 the steel melt, and addition of tellurium to the steel melt on the kinetics of desulfurization were also studied.