Combined effect of refractory and refining slag on inclusions in tire cord steel

Abstract

To understand the combined effect of refractory and refining slag on the inclusions in tire cord steels, steel grade LX72A was reacted with different MgO crucibles (impurity CaO <0.05 %; Al₂O₃ 1.45 %–4.98 %) and different slags [basicity R = w(CaO)/w(SiO₂), 0.6–1.0] in laboratory at 1550 °C, and the variation of the inclusion in steel was investigated. It was found that without slag, the MgO matrix and the impurities of Al₂O₃ and CaO in the crucibles would result in the increases of MgO, Al₂O₃ and CaO contents in inclusions. When the slags were employed, the increasing trend of MgO, Al₂O₃ and CaO contents in inclusions would be constrained by the slags, and lower slag basicity presented a stronger effect of containment. Besides, more Al₂O₃ impurities in crucibles cause a higher Al₂O₃ content in the inclusions. Two heats with different crucibles and slags may obtain close Al₂O₃ contents in the inclusions, e.g. (crucible Al₂O₃ 4.98 % and slag R = 0.8) vs. (crucible Al₂O₃ 2.77 % and slag R = 1.0). In this case, the combined effects of refractory and refining slag on the inclusions need to be considered. When the refractory contains relatively higher impurities, slag with lower basicity should be chosen. In contrast, relatively higher basicity can be considered in case of high refractory purity.