Stepwise adsorption of Mn and S on MgAl 2 O 4 inclusions in steel with magnesium treatment: a first-principles study

Inclusions have a significant impact on the properties of steel. The inclusion modification is performed to control the harmful effect of inclusion on quality of steel. Magnesium and its alloys serve as effective modifiers during the steelmaking process, transforming irregular and clustered Al₂O₃ inclusions into smaller and well-dispersed MgAl₂O₄ particles. During the solidification of steel, MgAl₂O₄ acts as nucleation agent for MnS inclusions, facilitating the formation of MnS–MgAl₂O₄ complex inclusions with a soft exterior MnS layer surrounding a hard MgAl₂O₄ core. In this study, the first-principles computations were performed to obtain the adsorption energies of Mn and S atoms on Al(Mg) termination of the low-index structure of MgAl₂O₄(1 1 1). The adsorption structure was systematically optimised via computational modelling by investigating distinct Mn and S atom adsorption patterns on the MgAl₂O₄ inclusion surface. The most energetically favourable adsorption positions for Mn and S atoms were identified through a comparative analysis of the computed adsorption energies following geometric optimisation. The stable adsorption structure and the optimal adsorption path of Mn and S atoms in the MnS–MgAl₂O₄ complex inclusions were obtained. Furthermore, the density of states (DOS), partial density of states (PDOS) and charge density difference (CDD) provided further insights into the electrical structure of the adsorption structure during the formation of the MnS–MgAl₂O₄ complex inclusions. These findings are important in guiding the modification of complex inclusions, thereby optimising the quality and properties of the steel.