Aspects on slag/metal equilibrium calculations and metal droplet characteristics in ladle slags

Abstract: In the present work the mixing between the metal and slagphase during the ladle refining process from tapping from theelectric arc furnace to casting in two different Swedish steelplants has been studied.Three slag models and the sulphur-oxygen equilibrium betweenslag and steel was used together with the dilute solution modelfor the liquid steel phase to predict the equilibrium oxygenactivity in steel bulk and metal droplets in top slag inequilibrium with the top slag. The predicted oxygen activitieswere compared with measured oxygen activities from the steelbulk. The results show significant discrepancies between thecalculated and measured oxygen activities and the reasons forthe differences are discussed.Metal droplet distribution in slag samples have also beendetermined using classification according to the Swedishstandard SS111116. It was found that most metal droplets arefound in the slag samples taken before vacuum degassing. Thetotal area between steel droplets and slag has been determinedto be 3 to 14 times larger than the projected flat interfacearea between top slag and steel. The effect of slag viscosityand reactions between steel and slag on the metal dropletformation in slags is also discussed.The chemical composition of the metal droplets in the topslag was determined and possible reactions taking place betweenthe steel droplets and the slag was studied. Differencesbetween steel droplet compositions and the bulk steelcomposition are discussed. The results show significantdifferences between steel droplet and bulk steelcomposition.Key words:oxygen activity, metal droplets, sulphur,slag, ladle, refining, distribution.