Learning about the nucleation pathway of MgO·Al2O3 spinel from an Fe–O–Al–Mg melt using a two-step nucleation mechanism

Abstract

The crystallization process from a melt begins with nucleation, which determines the structure and size of the resulting crystal embryos. Further understanding of multi-pathway crystallizations from a melt through two-step nucleation mechanisms is needed. The formation mechanism of MgO·Al₂O₃, which sheds light on the metastable structures or pathways leading from the molten steel to the solid crystal, was analyzed to improve the understanding of the fundamentals of MgO·Al₂O₃ spinel inclusion. Here a pathway of formation that derives from a variety of metastable structures in earlier crystal nucleation stages was discovered, which drives the formation of MgO·Al₂O₃ more strongly than the traditional mechanism in which it originates from oxide-based inclusions (MgO/α-Al₂O₃). This study uncovers the behavior of the early stages of inclusions crystallization in steels, extends the classical MgO·Al₂O₃ formation theory and highlights the possible pathway to form MgO·Al₂O₃.