First-principles study on atomic formation and manganese diffusion in MnS/Mg-Ti-oxide complex inclusions in steel

Abstract

Mg-Ti oxide/MnS complex inclusions effectively serve as nucleation sites for intragranular ferrite. This study employs first-principles calculation methods to investigate the inducing properties of complex inclusions, including the growth of MnS on Ti oxide, the absorption of Mn atoms by Ti oxide, and the diffusion behavior of Mn atoms within Ti oxide, both untreated and Mg-treated. Ti2O3 indicates the untreated group, while MgTiO3 indicates the Mg-treated group. Computational analysis indicated that MnS is more likely to adsorb and grow on MgTiO3 than on Ti2O3. MnS vertically grows on the O-Mg-Mg surface of MgTiO3. By calculating the dissociation energy, it can be determined that the Mn in the oxide of the MnS/oxide complex inclusions originates from the steel matrix rather than from MnS. By analyzing the diffusion behavior of vacancies and Mn atoms through energy barrier calculations, it is evident that the addition of Mg alters the diffusion pathways of Mn atoms in Ti oxide and confirms that the bonding between Mn and O is the limiting step for Mn atom diffusion within the oxides. The diffusion path of Mn atoms in MgTiO3 is Path I → Path II → Path I. Path I: Mn atoms diffuse within the cationic layer. Path II: Mn atoms diffuse by traversing across two layers of O atoms.