Sustainable Direct Mn Alloying Practice to Produce Medium Mn Steel

Abstract

Manganese alloying via. direct reduction of MnO in ladle refining slag is a promising alternative to energy and cost intensive conventional ferroalloy production methods. This study explores the aluminothermic reduction of MnO in CaO–SiO2–Al2O3–MgO slag under varying CaO/SiO2 ratios, Al2O3 content, and stoichiometric addition of aluminum for 4 and 8 mass% Mn concentrations in molten iron. The results showed that the slag containing 30 mass% Al2O3 suppressed Mn volatilization, whereas Al2O3-free slags exhibited a faster MnO reduction but a larger vaporization loss. On the other hand, the slag with CaO/SiO2 ratio of 2 without second-phase precipitation, facilitating enhanced slag–metal separation and reduced metal droplet suspension, showed significant improvement in Mn recovery of 68%. Furthermore, excessive Al addition leads to higher Mn loss. An empirical equation for Mn loss was developed to correlate Mn loss with factors such as slag basicity, Al2O3 content, Mn distribution ratio between slag and metal, and the amount of aluminum added.