Formation and Evolution of Silicate Inclusions in Molten Steel by Magnesium Treatment

The effect of magnesium addition on the formation and evolution of inclusions in Mn–Si killed steel is studied by laboratory experiments and thermodynamic calculation. Samples were taken at different holding time after magnesium addition to study the transient evolution of inclusions. The morphology, composition, number and diameter of inclusions were thoroughly analyzed by SEM-EDS. The results show that four types of inclusions (MgO–SiO2–MnO liquid inclusion, MgO–SiO2–MnO complex inclusion, MgO–SiO2 and MgO solid inclusion) form with different amount of magnesium addition. Liquid inclusion of MnO–SiO2 is promptly modified to MgO–SiO2–MnO liquid inclusion with 0.0005% magnesium addition. As the amount of magnesium is increased to 0.0011%, intermediate product MgO forms immediately and then gradually transforms to MgO–SiO2 solid inclusion with holding time. While MgO solid inclusion keeps stable throughout with 0.0019% magnesium addition.