Ferroalloys are alloys of iron with other elements (Cr, Si, Mn, etc.) mainly used for steel deoxidation and alloying.

Ferrosilicon is a ferroalloy. The main components are ferrum and silicon. Production of ferrosilicon is based on silica reduction. Ferrosilicon is used as deoxidizing and alloying additive for smelting electrical, spring, corrosion- and heat-resistant steels. Increased silicon content in ferrosilicon decreases its density. Silicon increases steel hardness, tear resistance, elastic limit and yield strength, increases oxidation resistance, reduces power losses. Ferrosilicon is made in arc ferroalloy furnaces by coke reduction of silicon from quartzite.

Chemical composition per GOST 1415-93.
GOST 1415-93