Characteristics of inclusions generated during Al-Mg complex deoxidation of molten steel

Abstract

The complex deoxidation of molten steel with magnesium vapor produced in-situ by aluminothermic reduction of magnesium oxide and aluminum wires was carried out. The Mg vapor was directly injected into molten steel with Ar carrier gas from an immersion tube. With injection of magnesium vapor into aluminum killed molten steel, the total oxygen concentration was further decreased due to magnesium deoxidation and removal of inclusions by rising bubbles. The final total oxygen concentration could decrease to 15ppm. SEM observation and EDS analysis show that the periphery around an Al 2O3 inclusion particle was changed into spinel. This is beneficial for prevention of aggregation of inclusions. The inclusion size in the melt was decreased with time, and the inclusions remaining in the ingot contained mainly MgO and spinel. In the case of magnesium deoxidation followed by addition of aluminum wires, the inclusion size In the melt was also decreased with time. Therefore, in the present experiments, the larger inclusions were easily removed from the melt by floating up with the rising bubbles, while the smaller ones tended to remain In the melt. © 2007 ISIJ.