The 50% and 75% ferrosilicon (FeSi50 and FeSi75) alloys are produced by carbothermic reduction in a submerged arc furnace. The source of iron is either iron ores or scrap and that for silicon is quartz or quartzite. The principal smelting reaction is the same as that for smelting of metallurgical grade silicon metal.

The smelting reaction between silica and carbon is characterized by the formation of silicon carbide and SiO gas as intermediary products. Silicon carbide reacts with SiO2 at smelting temperature to form Si and SiO. SiO gas transports to a lower temperature region in the furnace and reacts with carbon and silicon carbide.

Unreacted SiO gas escapes to the top of the furnace charge and constitutes a loss of a silicon unit. In smelting 50% and 75% ferrosilicon alloys, iron lowers the activity of silicon, and this reduces the generation of SiO gas. Therefore, the recovery of silicon is higher in 75% and 50% ferrosilicon alloys than in metallurgical grade silicon metal. Ferrosilicon is also used for manufacture of silicon, corrosion?resistant and high-temperature-resistant ferrous silicon alloys, and silicon steel for electromotors and transformer cores