Thermodynamic studies of slags containing FeO and their impact on ladle refining process

Abstract

In the ladle refining process, the FeO content of the ladle slag is of great importance in the chemistry as well as the energetics of the process. Optimisation of the process requires an accurate knowledge of the thermodynamic activities of FeO in the ladle slags. Due to the discrepancies in existing data, renewed attempts are being made at the Royal Institute of Technology to generate reliable data for binary, ternary and multicomponent slags containing FeO at steelmaking temperatures. In order to measure the activities of FeO in the slags, a gas equilibration technique was employed in the present work. The slags, kept in Pt crucibles were equilibrated with a CO–CO2–Ar gas mixture and quenched after equilibration. The chemical composition of the slag was analysed. From knowledge of the thermodynamics of the Fe–Pt system, the 'FeO' activities in the slag were evaluated. The results of the present studies, together with other literature values, were optimised in the slag software THERMOSLAG developed at the Royal Institute of Technology, Sweden. The results of the optimisation are presented. Model calculations were performed with the KTH slag software THERMOSLAG using plant data from Ovako Steel, Hofors, Sweden. It was found that oxygen estimations in the metal from the FeO analyses of slags, obtained by a conventional sampling and analysis method were less reliable. Estimation of the oxygen levels utilising the sulphur partition between the slag and the metal were carried out using the THERMOSLAG software. Reasonable estimations of the oxygen content in the metal confirmed that this could be a very useful tool for the plant operator.