Effect of Mg Addition on the Evolution of Inclusions in Al-Ca Deoxidized Melts

To investigate the effect of magnesium addition on the evolution of inclusions in Al-Ca 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 emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDX). The results showed that the utilization of magnesium significantly influenced the size of oxide inclusions in Al-Ca deoxidized melts. Superfluous MgO raised the melting point of the complex inclusions, and then worsen the steel castability. Therefore, the amount of magnesium addition should be under control. Based on thermodynamic calculations and experimental results, the recommend range of [Mg] is 1-5 ppm. All inclusions observed in the sample were nearly spherical except for solid calcium aluminates inclusions. Oxide inclusions were modified quickly after magnesium addition. Meanwhile, magnesium can also modify solid calcium aluminate inclusions in the melts similarly, but there are 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, to achieve the full liquid inclusions in molten steel, the addition amount of magnesium and calcium should be considered simultaneously.