Silicomanganese (SiMn) is a ferroalloy composed chiefly of silicon and manganese; it is smelted by carbon reduction in ore heat-treating furnaces. Silicomanganese with 10–26% Si (the remainder is Mn, Fe, and impurities) is obtained from manganese ore, manganese slag, and quartzite and is used as a deoxidizer and alloying additive in the smelting of steel, as well as in the smelting of ferromanganese with reduced carbon content by the silicothermic process. Silicomanganese with 28-30 percent Si, for which pecially prepared high-manganese low-phosphorous slag serves as raw material, is used in the production of metallic manganese.

The standard grade silicomanganese contains 14 to 16% of silicon, 65 to 68% of manganese and 2% of carbon. The low carbon grade SiMn has carbon levels from 0.05 to 0.10%.