Nucleation Mechanism of TiS in Al/Ti Simultaneously Deoxidized Steel based on Homogeneous and Heterogeneous Modes

Simultaneous deoxidation of Al/Ti in steel was performed to analyze the TiS-containing inclusions, TiS single inclusions and Al₂O₃(or Ti_xO_y)-TiS two-layered inclusions were observed in the steel smaple. Density functional theory calculations were performed to study the structures and properties of the intermediate products of TiS before critical nucleation, and the nucleation mechanism of TiS in Al/Ti simultaneously deoxidized steel was discussed based on homogeneous and heterogeneous nucleation modes. The results show that the TiS nucleation is controlled by the formation of (TiS)_n clusters; the homogeneous nucleation of TiS inclusions in the steel can only occur using (TiS)_n clusters with n ≥ 4, whereas the heterogeneous nucleation of (TiS)_n clusters on the surfaces of Al₂O₃ and Ti₂O₃ can occur using all the (TiS)_n clusters. As a result, the inclusions of Al₂O₃ and Ti₂O₃ can act as effective sites to induce the heterogeneous nucleation of TiS inclusions in steel. The Gibbs free energy change values for the (TiS)_n clusters formed on the Ti₂O₃ surface were lower than those on the Al₂O₃ surface, and the mismatch values of Ti₂O₃(001)-TiS(001) interface were smaller than those of Al₂O₃(001)-TiS(001) interface. Thus, TiS inclusions formed more easily on the surface of Ti₂O₃ than on Al₂O₃.