Addition of Titanium Oxide Inclusions into Liquid Steel to Control Nonmetallic Inclusions

Titanium oxide inclusions in steel are well known to inhibit grain growth and act as nucleation sites for acicular ferrite because of absorbing manganese from the surrounding steel resulting in a manganese depleted zone around the inclusion. In this article, the inclusions resulting from TiO₂ additions to low-alloyed C-Mn-Cr steel were studied. Different types of TiO₂ containing materials were added to liquid steel before or during casting to get small titanium-oxide–rich inclusions in steel. The main goals were to find out what happens to TiO₂ in liquid steel after addition and during cooling and to study further what type of inclusions are formed in the steel as a result of the TiO₂ addition. Based on the thermodynamic calculations and the results of scanning electron microscope (SEM)-energy dispersive spectroscope (EDS) and SEM-electron backscatter diffraction (EBSD) analysis, TiO₂ is first reduced to Ti₃O₅ in liquid steel at high temperatures and then to Ti₂O₃ during cooling at around 1573 K (1300 °C). Both reactions liberate oxygen, which reacts with Ti, Mn, and Al forming complex Ti₂O₃-rich inclusions. The results also show that TiO₂ additions result in more TiO_x + MnO inclusions compared with experiments with Ti addition and that the absolute amount of manganese present in the inclusions is much higher in experiments with TiO₂ addition than in experiments with Ti additions.