Inclusions in Ultra-low Carbon Ferromanganese Obtained via Aluminothermic Reduction of Different Pre-reduced Mn Ores

The inclusions present in manganese ferroalloys produced by aluminothermic reduction of pre-reduced manganese ores were studied by scanning electron microscopy coupled with energy dispersive spectroscopy. Two major categories of alloys were classified and evaluated, one with Si < 1 wt pct mostly containing MnS and complex compounds of manganese oxide, aluminum oxide, silicon oxide, and manganese sulfide. The second type contained Si > 1 wt pct. The second type can be sub-classified based on Fe content as and Fe < 10 wt pct and was found to contain MnO–Al2O3–SiO2–CaO–MgO–MnS similar type of inclusion as the first type except that these inclusions had higher amount of Al2O3 and lower amount of MnO and some amount of CaO and MgO in them. And the other with Fe > 10 wt pct which contained larger-sized (100 μm) MnO–FeO–SiO2 inclusions. This is a new inclusion type not reported elsewhere in ferromanganese alloys. The mechanism of inclusions formation was studied and based on the thermochemistry of the system and morphology of inclusions it was proposed that they are formed upon cooling and solidification via the significant decrease of sulfur and oxygen solubilities in liquid metal. Unlike carbothermic production, aluminothermic reduction generates Al2O3-rich complex inclusions with lower stability and improved removability, offering a cleaner and more efficient pathway for ultra-low carbon ferromanganese synthesis.