Inclusion reactivity: morphology and composition changes of spinel (MgAl2O4) in steel

Due to an ever increasing demand for cleaner, high quality steels, there is an increasing push for steelmakers to lower the non-metallic inclusion contents of the steel they produce. Understanding inclusion reactivity in steel is key in producing high quality steels at high production rates. Our current knowledge in controlling and predicting inclusion development during liquid steel processing is limited. In this study, spinel (MgAI204) inclusions of close to stoichiometric MgO.AI2O3 and known size distribution where added to the liquid steel bath prior to assessing their reactivity. The pO2 of the gas phase was controlled to 10-13 atm throughout the experiemnt. The inclusions were then tracked for changes in size morphology and composition with time in an aluminium killed steel at 1600 degrees celcius. It was found that the inclusions were evenly distributed through the melt. There was little change in the average size of the spinel inclusioins during the reaction. However, the composition of the inclusions did change. It was found that the Mg: AI mass percentage ratio of the inclusions changed immediately from ~0.5 to 0.08. Other inclusions found in the melt were alumina and complex sulphide inclusions. Of these it was found that the proportion of the alumina inclusioin increased with time.