Effect of Al2O3 Addition on Mineralogical Modification and Crystallization Kinetics of a High Basicity BOF Steel Slag

Basic oxygen furnace (BOF) steel slag is a main byproduct that is produced during the converter steelmaking process. The volume instability and fast crystallization of BOF slag limits its added-value application. This article aims to understand the effect of Al2O3 on the mineralogical modification and crystallization kinetics of a high basicity BOF steel slag. Continuous cooling transformation and time–temperature–transformation curves were constructed to determine the crystallization characteristics of BOF slag. The critical cooling rate to vitrify the slag was experimentally obtained. The crystallization sequence was clarified by integrating in situ and post-mortem observations with thermodynamic calculations. The results suggest that the addition of Al2O3 can effectively remove free lime, decrease the melting point, and improve the glass formation ability of the high basicity BOF slag. Undercooling the slag is enhanced by increasing the cooling rate and/or adding Al2O3. By steering the addition of Al2O3 and the cooling rate, BOF slag can be modified to obtain a more amorphous phase, presenting an enhanced potential to be a binder for added-value applications.