Ferroalloys are various alloys of iron that contain a significant amount of one or more other elements, such as manganese, carbon, or silicon. The term ferro, or ferric, refers to a compound containing or relating to iron. A ferroalloy has iron as the base element — in many cases less than 50% — combined with one or more other reactive elements used during the production of steel. A ferroalloy will physically introduce and carry these elements into molten metal, as steel and cast iron are being produced.
A ferroalloy can use a single reactive element or multiple reactive elements, known as alloy systems, like nickel or cobalt. These alloys were invented experimentally, by identifying different elements to combine with iron and by developing methods to introduce them in a controlled fashion during the production of steel. There are many different types of these alloys available, including ferromanganese, ferrochromium, and ferrosilicon, among others. They are responsible for providing unique qualities in steel and cast iron, and serve a critical function during iron and steel production cycles.
The primary and most common ferroalloys use chromium, manganese, and silicon. Ferrosilicon is used to prevent the loss of carbon from molten steel during production of steel and ferrous alloys. Some ferroalloys have deoxidizing properties, such as silicon. Ferrochromium is used to provide corrosion resistance in stainless steels. Ferromanganese is used to counteract the harmful effects of sulfur during the production of steel and cast iron.
Ferroalloys are primarily associated with the iron and steel industries, which report worldwide annual production in the millions of tons — or megagrams — per year. They are used to produce many of the most advanced materials in use today. These include metal alloys for extremely high temperature service applications, like gas turbines and stainless steels for superior corrosion resistance. Materials used for parts that are exposed to high loads and that transmit mechanical power are also manufactured using them.
Ferroalloys are prepared by combining iron with other elements at very high temperatures in a furnace. They usually have lower melting temperature ranges than pure elements, and can be combined more easily into molten steel — which provides some advantages during production. Different types of furnaces are used to produce ferroalloys, including submerged electric arc furnaces, exothermic or metallothermic reaction furnaces, and electrolytic cells. There are many companies that produce ferroalloys with facilities that can handle and process raw materials; combine the materials in the furnaces; and finish the material for downstream market use.