Effect of magnesium addition on evolution of inclusions in Mn–Si–Al deoxidised molten steels

Abstract

To reveal the effects of magnesium on the evolution of inclusions in Mn–Si–Al deoxidised steels, both thermodynamic calculations and deoxidised experiments were carried out in the present work. The samples extracted from the melts were polished and analysed by optical microscope and scanning electron microscopy (SEM). The results showed that magnesium can control the size of oxide inclusions in Mn–Si–Al deoxidised melts well. Superfluous MgO raise the melting point of the complex inclusions, and then worsen the steel castability. Therefore, the amount of Mg addition should be under control. The recommend value of [Mg] in present work is 1–3 ppm, based on thermodynamic calculations and experiments. All inclusions observed in the sample were nearly spherical. The evolution mechanisms of inclusions were discussed comprehensively, and proper models for the formation of oxide inclusions were set up. In practice, to achieve the full liquid inclusions in molten steel, the addition amount of magnesium and aluminium should be considered simultaneously.