Formation of oxide-inclusions by ladle glaze and a preliminary examination on the possibility of inclusion seperation by bubble floatation

Abstract: The present work was to study the role of ladle glaze as apotential supplier of inclusions to the steel melt during theladle refining process. In this study, the total number ofinclusions at the beginning and at the end of the ladletreatment process was found to be increasing with ladle age,which is the number of heats, the ladle being used. Asubstantial increase in inclusion population was noticed aftera certain ladle age.Totally four types of inclusions named as; type-1 (MgO),type-2 (spinel), type-3 (an oxide solution) and type-4 (spinelin the center surrounded by the oxide solution of type-3) wereobserved in the beginning of the ladle refining process.Thermodynamic calculation revealed that the type-3 and type-4inclusions were generated by the reactions between EAF slag andladle glaze. Even a part of inclusions of type-2 (spinel phase)could be formed by these reactions. Three types of inclusionswere found before casting, viz. type-5 (oxide solution with lowcontents of MgO and SiO2), type-6 (small MgO islands embeddedin an oxide solution) and type-7 (spinel in the centersurrounded by the oxide solution of type-5). Inclusions of bothtype-5 and type-7 were the products of the reaction betweeninclusions of type-2 and the liquid metal. On the other hand,the occurrence of pieces of MgO having sharp edges in the oxidesolution suggested that the type-6 inclusions were generated bythe ladle glaze.A preliminary examination on the possibility of inclusionseparation by bubble floatation, experiments using cold modelswere also carried out. De-ionised water and silicon oil wereused as the bulk phase. Charcoal particles of different sizeranges were employed as the dispersed phase. The examination ofcharcoal-water-gas system indicated that the positivefloatation coefficient is not a sufficient condition for theinclusion separation. The experimental results were found to bein contradiction with the prediction of a typical model thatconsiders interfacial energies. The omitting of the drag forcewas believed to be the reason causing the failure of the modelprediction in the charcoal-water-gas system. The failure of themodel prediction suggested a need of a new model taking intoaccount interfacial energies, drag force, buoyancy force andgravity force.Key words:oxide inclusions, ladle metallurgy, ladleglaze, inclusion population, ladle age, interfacial tension,inclusion separation