Atomistic Nucleation Mechanism of Titanium Oxides in Steel Based on Homogeneous and Heterogeneous Modes

Inclusions of TixOy and Al2O3-TixOy have often been reported in previous studies and were also observed in our present experiment. To understand the formation mechanism of TixOy inclusions in molten steel at atomic scale by homogeneous and heterogeneous modes, the DFT method was used to calculate the structures and thermodynamic properties of pre-nucleation metastable phases ((TixOy)(n) clusters) of TixOy inclusions and the interface properties between Al2O3 planes and (TixOy)(1) clusters. By comparing the equilibrium curve of (TixOy)(n) clusters with the equilibrium experimental data between dissolved Ti and O in iron melt, it was found that the formation of TixOy inclusions in iron melt is a two-step process and the nanoscale (TixOy)(n) clusters have difficulty growing into the final bulk TixOy at a low supersaturation ratio of [Ti] and [O] in melt. The Ti-deoxidation product in the previous equilibrium experiments should be not only bulk TixOy but also (TixOy)(n) clusters. Comparing the homogeneous and heterogeneous nucleation of TixOy inclusions showed that the critical supersaturation ratio required for forming (TixOy)(n) clusters in heterogeneous mode is smaller than that in homogeneous mode, while the transformation force of (TixOy)(n) clusters into TixOy crystal in heterogeneous mode is the same as that in homogeneous mode. This work is helpful to investigate the nucleation and growth mechanism of TixOy inclusions in steel melt and provide a theoretical basis for the design of steel materials.

Automated summary

This study used the DFT method to investigate the formation mechanism and interface properties of TixOy inclusions in molten steel, revealing a two-step process with difficulty in transforming (TixOy)(n) clusters into bulk TixOy. It was found that the critical supersaturation ratio required for forming (TixOy)(n) clusters in heterogeneous mode is smaller than that in homogeneous mode, while the transformation force of (TixOy)(n) clusters into TixOy crystal is the same in both modes, providing important insights into nucleation and growth mechanisms of TixOy inclusions in steel melt.