The content of silicon dioxide in light burnt magnesia spheres should be controlled at a certain percentage. If the content of silicon exceeds the standard, the plasticity and toughness of steel will be significantly reduced. For magnesia manufacturers, silicon can reduce the density, thermal conductivity and electrical conductivity of steel. It can promote ferrite grain coarsening and reduce coercivity. Silicon can promote columnar crystal growth and reduce plasticity in cast steel. Silicon can reduce the weldability of steel. Because the bonding ability of silicon with oxygen is stronger than that of iron, it is easy to produce low melting point silicate during welding, which increases the fluidity of molten slag and molten metal, causes splashing phenomenon and affects the welding quality. Therefore, the content of silicon must be strictly controlled in light-burned magnesia spheres to avoid being brought in as raw materials in steelmaking.