High-carbon ferromanganese, generally with 70–80% Mn and 6–7% C, is by far the largest tonnage ferro alloy used. It is a deoxidizing agent in steelmaking and an important  alloying element. It has also the property of controlling the harmful effect of sulfur. Manganese combines with sulfur and forms manganese sulfide, which tends to float out of the liquid steel. Manganese has the effect of stabilizing the austenite phase; steels with 12–14% Mn are fully austenitic, which are used on a large scale for their wear and abrasion-resisting characteristics.

Manganese ferroalloys are also manufactured by carbothermic reduction of manganese ores containing both iron and manganese oxides in submerged arc electric furnaces. The slags produced during the process contain significant amounts of manganese oxide; MnO and these slags can be reprocessed to ferrosilicomanganese (also called silicomanganese) and then to refined or low carbon (LC) ferromanganese or even to manganese metal.