Effect of Mg on Behavior and Particle Size of Inclusions in Al-Ti Deoxidized Molten Steels

To investigate the effect of magnesium addition on the evolution of inclusions in Al-Ti deoxidized melts, both thermodynamic calculations and deoxidized experiments were carried out in the present work. The samples took from the melts were polished and analyzed by field scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDX). The results showed that the addition of magnesium significantly influenced the size of oxide inclusions in Al-Ti deoxidized melts. Superfluous MgO raised the melting point of these complex inclusions, and then degraded the steel castability. Therefore, the amount of magnesium addition should be carefully controlled. Based on thermodynamic calculations and experimental results, the recommended range of [Mg] is 1~5 ppm. All inclusions observed in the sample were nearly spherical except for solid titanium aluminate inclusions. Oxide inclusions were modified quickly after magnesium addition. Meanwhile, magnesium could also modify solid titanium aluminate inclusions in the melts similarly, but there were unreacted cores in the inclusions at the initial stage. The evolution mechanisms of inclusions were comprehensively discussed, and models for the formation of oxide inclusions were set up. As for the production practice, the addition amount of magnesium and titanium should be considered simultaneously to liquefy inclusions in molten steel.