Mechanism of MnS Precipitation on Al₂O₃–SiO₂ Inclusions in Non-oriented Silicon Steel

This study investigates the mechanism of MnS precipitation on Al₂O₃–SiO₂ inclusions during the solidification of non-oriented silicon steel, especially the influence of the phase structures and sizes of the oxides on the MnS precipitation, by scanning electron microscopy and transmission electron microscopy coupled with energy dispersive spectrometry. The investigation results show that MnS tends to nucleate on submicron-sized Al₂O₃–SiO₂ inclusions formed by interdendritic segregation and that it covers the oxides completely. In addition, MnS can precipitate on micron-sized oxides and its precipitation behavior is governed by the phase structure of the oxides. The MnS embryo formed in a MnO-containing oxide can act as a substrate for MnS precipitation, thus permitting further growth via diffusion of solute atoms from the matrix. MnS also precipitates in a MnO-free oxide by the heterogeneous nucleation mechanism. Furthermore, MnS is less prone to precipitation in the Al₂O₃-rich regions of the Al₂O₃–SiO₂ inclusions; this can be explained by the high lattice disregistry between MnS and Al₂O₃.