Nucleation, Growth, and Aggregation of Alumina Inclusions in Steel

Whether a nonmetallic inclusion is detrimental to steel properties or not depends on its size. The final size of an inclusion in steel is influenced by several factors, including nucleation, growth, and aggregation. In the current work, the thermodynamics for homogeneous nucleation of alumina was calculated, and the three-dimensional alumina morphologies after Al deoxidation were observed in laboratory. It is indicated by the calculation that, when the interfacial tension between steel melt and alumina is higher or the nucleus radius is larger, it is harder for alumina to nucleation. One minute after the deoxidation, many single-alumina particles with different shapes, including spherical, dendritic, flower, plate-like, and irregular, were observed. The formation of various shapes is due to different growth mechanisms. During the holding process after deoxidation, several types of aggregation morphologies were observed, such as disorderly type and regular type. Owing to the effects of sintering and Ostwald ripening, the aggregated inclusions changed from angular shape to smooth coral shape.