Modification of inclusions in linepipe steels by Ca-containing ferrosilicon during ladle refining

In the current study, the cleanliness of ferrosilicon used for linepipe steels was analysed. The Alt and T·Ca in ferrosilicon are respectively 1.36 and 0.76%, which was neglected in the previous works. The Al and Ca in ferrosilicon mainly concentrate at the interphase between the Si and Fe phases. Two plant trial heats for the ladle refining without and with ferrosilicon addition were compared. In the molten steel without the addition of ferrosilicon, the inclusions evolve from Al2O3 to MgO·Al2O3 to half liquid CaO–MgO–Al2O3. However, the addition of ferrosilicon in the ladle refining process introduces several ppm Ca in the molten steel, significantly modify Al2O3 and MgO·Al2O3 to liquid CaO–Al2O3 at the steelmaking temperature. The addition of Ca-containing ferrosilicon scarcely affects the formation of more and larger inclusions in the molten steel.