Ferro Alloys

Alloys of iron with chromium, manganese, silicon, tungsten, molybdenum or vanadium. Used in steelmaking as a means of introducing these alloying elements into the cast or as deoxidisers.

Ferroalloy refers to various alloys of iron with a high proportion of one or more other element, manganese or silicon for example. It is used in the production of steels and alloys as a raw material.

The main ferroalloys are:

Ferromanganese, a ferroalloy with high content of manganese, is made by heating a mixture of the oxides MnO2 and Fe2O3, with carbon in a furnace. They undergo a thermal decomposition reaction. It is used as a deoxidizer for steel. A North American standard specification is ASTM A99. The ten grades covered under this specification includes; Standard ferromanganese, Medium-carbon ferromanganese & Low-carbon ferromanganese. A similar material is a pig iron with high content of manganese, is called spiegeleisen.

Ferrochrome aka. FeCr is a corrosion-resistant alloy of chrome and iron containing between 50% and 65% chrome. It is a finishing material which contains about 50-70% (depending on ore used a the producer) chromium alloyed with iron. Most of the world's ferrochrome is produced in South Africa, Kazakhstan and India, which have large domestic Cr Ore resources. Increasing amounts coming from Russia and China.

Over 80% of the world's ferrochrome is utilised in the production of stainless steel. Stainless steel depends on chrome for its appearance and its resistance to corrosion. The average chrome content in stainless steel is approximately 18%. It is also used when it is desired to add chromium to carbon steel. FeCr from Southern Africa know as 'charge chrome' produced from a Cr containing ore with a low Cr content is most commonly used in stainless steel production, where as High Carbon FeCr produced from high grade ore found in Kazakhstan is more commonly used in specialist applications such as engineering steels where a high Cr to Fe ratio and minimum levels of other elements such as Sulfur, Phosphorus and Titanium are important and production of finished metals takes place in small electric arc furnaces compared to large scale blast furnaces.

Ferrochrome production is essentially a carbothermic reduction operation taking place at high temperatures. Cr Ore (an oxide of chromium and iron) is reduced by coal and coke to form the iron-chromium alloy. The heat for this reaction can come from several forms, but typically from the electric arc formed between the tips of the electrodes in the bottom of the furnace and the furnace hearth. This arc creates temperatures of about 2800°C. In the process of smelting, huge amounts of electricity are consumed making production in countries with high power charges very costly.

Tapping of the material from the furnace takes place intermittently. When enough smelted ferrochrome has accumulated in the hearth of the furnace, the tap hole is drilled open and a stream of molten metal and slag rushes down a trough into a chill or ladle. The ferrochrome solidifies in large castings, which is crushed for sale or further processed.

Ferrochrome is often classified by the amount of carbon and chrome it contains. The vast majority of FeCr produced is charge chrome from Southern Africa. With high carbon being the second largest segment followed by the smaller sectors of low carbon and intermediate carbon material.

Ferrotitanium is a ferroalloy, an alloy of iron and titanium with between 10-20..45-75 % titanium and sometimes a small amount of carbon. It is used in steelmaking as a cleansing agent for iron and steel; the titanium is highly reactive with sulfur, carbon, oxygen, and nitrogen, forming insoluble compounds and sequestering them in slag, and is therefore used for deoxidizing, and sometimes for desulfurization and denitrification. In steelmaking the addition of titanium yields metal with finer grain structure.

Ferrotitanium powder can be also used as a fuel in some pyrotechnic compositions. Ferrotitanium can be manufactured by mixing titanium sponge and scrap with iron and melting them together in an induction furnace. Manganese alloyed ferrotitanium is investigated as a material for hydrogen storage.

Ferrosilicon, or ferrosilicium, is a ferroalloy an alloy of iron and silicon with between 15 and 90% silicon. It contains a high proportion of iron silicides. Its melting point is about 1200 °C to 1250 °C with a boiling point of 2355 °C. It also contains about 1 to 2% of calcium and aluminium.

Ferrosilicon is used in steelmaking and foundries as a source of silicon in production of carbon steels, stainless steels, and other ferrous alloys for its deoxidizing properties, to prevent loss of carbon from the molten steel (so called blocking the heat); ferromanganese, spiegeleisen, silicides of calcium, and many other materials are used for the same purpose. It can be used to make other ferroalloys. 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. In manufacture of cast iron, ferrosilicon is used for inoculation of the iron to accelerate graphitization. In arc welding, ferrosilicon can be found in some electrode coatings.

Ferrosilicon is a basis for manufacture of prealloys like magnesium ferrosilicon (FeSiMg), used for modification of melted malleable iron; FeSiMg contains between 3-42% of magnesium and small amounts of rare earth metals. Ferrosilicon is also important as an additive to cast irons for controlling the initial content of silicon.

Ferrosilicon is also used in the Pidgeon process to make magnesium from dolomite. In contact with water, ferrosilicon may slowly produce hydrogen. Ferrosilicon is produced by reduction of silica or sand with coke in presence of scrap iron, millscale, or other source of iron. Ferrosilicons with silicon content up to about 15% are made in blast furnaces lined with acid fire bricks. Ferrosilicons with higher silicon content are made in electric arc furnaces. An overabundance of silica is used to prevent formation of silicon carbide. Microsilica is a useful byproduct.

The usual formulations on the market are ferrosilicons with 15, 45, 75, and 90% of silicon. The remainder is iron, with about 2% of other elements like aluminium and calcium. Its CAS number is [8049-17-0]. A mineral perryite is similar to ferrosilicon, with its composition Fe5Si2. Ferrosilicon is used by the military to quickly produce hydrogen for balloons by the ferrosilicon method. The chemical reaction uses sodium hydroxide, ferrosilicon, and water. The generator is small enough to fit a truck and requires only a small amount of electric power, the materials are stable and not combustible, and they do not generate hydrogen until mixed. The melting point and density of ferrosilicon is dependent on its silicon content.

NameSi content[%]Melting point[°C]Density [g/cm³]
FeSi451215 - 13005.1
FeSi751210 - 13152.8
FeSi901210 - 13802.4

Ferrocerium is the "flint" in lighters, and its ability to give a large number of sparks when scraped against a rough surface (pyrophoricity) is used in many other applications, such as clockwork toys and strikers for welding torches. Also known as Auermetall after its inventor Baron Carl Auer von Welsbach, it is sold under such trade names as Blastmatch, Fire Steel, and Metal-Match.

While ferrocerium-and-steel function in a similar way to flint-and-steel in fire starting, ferrocerium actually takes on the role that steel played in traditional methods. When small shavings of it are removed quickly enough, the heat generated by friction is enough to ignite those shavings. The sparks generated are in fact tiny pieces of burning metal.

Lighter "flint" is composed mostly of an alloy of rare earth metals called mischmetal, mischmetal containing approximately 50% cerium and 45% lanthanum, with small amounts of neodymium and praseodymium. The origin of its easy sparking is cerium's low temperature pyrophoricity, its ignition temperature occurring between 150 and 180 degrees celsius. Since smaller scrapings become better sparks, the mechanical properties of rare earth metals must be adjusted to give a usable material; to that end, at least two strategies have been developed to make such alloys more brittle:

Oxide - most contemporary flints are hardened with 20% iron oxide and 2% magnesium oxide. Intermetallic - in the Baron von Welsbach's original alloy, 30% iron (ferrum) was added to purified cerium, hence the name "ferro-cerium". Iron reacts with rare earth metals to form hard intermetallic compounds similar to those in neodymium magnets; such magnets are also known to generate sparks quite easily when broken.

Silicomanganese (SiMn), a ferroalloy with high contents of manganese and silicon, is made by heating a mixture of the oxides manganese oxide (MnO2), silicon dioxide (SiO2), and iron oxide (Fe2O3), with carbon in a furnace. They undergo a thermal decomposition reaction. It is used as a deoxidizer and an alloying element in steel. 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%.