Ferromanganese: properties, grades and applications

Ferromanganese (FeMn) is a ferroalloy whose main elements are iron and manganese. It is one of the most massive and strategically important materials in metallurgy, without which it is impossible to imagine the production of high-quality steels and cast irons. Due to the high affinity of manganese for sulfur and oxygen, as well as its ability to dissolve in iron and stabilise the austenitic structure, ferromanganese occupies a central place in the processes of deoxidation, alloying and modification of metals.

Chemical Nature and Physicochemical Properties

Ferromanganese is an alloy of manganese with iron, in which the manganese content can vary from 65% to 95% by mass depending on the grade. The rest is iron and unavoidable impurities: carbon, silicon, phosphorus and sulfur. The properties of the alloy directly depend on the manganese and carbon content. High-carbon ferromanganese contains 6.5–8.0% carbon, medium-carbon — 0.5–2.0%, and low-carbon — up to 0.1–0.5%. The melting point of high-carbon ferromanganese is about 1250 °C, and its density is about 7000 kg/m³.

Manganese increases the hardness of steel, its hardenability, wear resistance and strength. The most important property of manganese is its ability to bind sulfur into manganese sulfide, which floats into the slag, eliminating the harmful effect of sulfur on steel properties (the phenomenon of "red brittleness"). In addition, manganese stabilises the austenitic phase: steels with a manganese content of 12–14% are fully austenitic and possess exceptional wear resistance.

Classification, Grades and Standards

In Russia and CIS countries, requirements for ferromanganese are regulated by GOST 4755-91 (harmonised with ISO 5446-80). According to the standard, ferromanganese is divided into several categories depending on the carbon and phosphorus content:

• High-carbon ferromanganese (HC FeMn): carbon content up to 7.0–8.0%. The most massive type, used for deoxidation and alloying of structural steels, as well as for cast iron production. Typical grades — FeMn78, FeMn70.

• Medium-carbon ferromanganese (MC FeMn): carbon content 0.5–2.0%. Used for alloying steels where a reduced carbon content is required. Typical grades — FeMn88, FeMn80C20, FeMn90C15.

• Low-carbon ferromanganese (LC FeMn): carbon content up to 0.1–0.5%. Used in the production of stainless, heat-resistant and special alloys where an increase in carbon content is unacceptable. Typical grades — FeMn80C05, FeMn90C01.

Nitrided ferromanganese is also produced, containing nitrogen (up to 6–8%), which improves corrosion resistance and increases the yield strength of steel. The marking includes the manganese and carbon content, for example, FeMn78 means ferromanganese with ~78% Mn, and FeMn90C20 — with ~90% Mn and ~2% C. Ferromanganese is supplied in pieces weighing no more than 20 kg or in the form of crushed and screened particles with various size classes (5–20 mm, 10–50 mm, 10–100 mm, etc.). The mass fraction of the fraction less than 10 mm usually does not exceed 10%.

Production Technology

The main industrial method for producing high-carbon ferromanganese is the carbothermic reduction of manganese ores (oxides MnO₂ and Mn₂O₃) by carbon (coke or coal) in powerful submerged arc electric furnaces. The charge, consisting of manganese ore or concentrate, coke and fluxes (lime, dolomite), is loaded into the furnace. When electric current is passed, a temperature of about 1600–1800 °C develops, at which manganese and iron are reduced from their oxides. Molten ferromanganese accumulates at the bottom of the bath and is periodically tapped through a taphole. The resulting slag, rich in manganese oxide (MnO), can be processed into silicomanganese.

To obtain medium- and low-carbon (refined) ferromanganese, the silicothermic method is used: manganese ore, silicomanganese and low-phosphorus manganese slag are remelted in submerged arc furnaces, where the silicon of silicomanganese reduces manganese from the ore. This method allows alloys with a manganese content of 86–89% and low carbon content to be obtained. The aluminothermic method is also used for particularly pure grades.

Applications

Steel deoxidation. The bulk of ferromanganese is consumed in ferrous metallurgy for steel deoxidation, i.e., to remove dissolved oxygen from the metal. Manganese, having a high affinity for oxygen, binds it into oxides that pass into the slag, improving the quality and homogeneity of the steel.

Alloying and modification. Ferromanganese is used for alloying steels, especially structural, rail, high-manganese (Hadfield steel), as well as for modifying cast iron. Manganese increases the hardness, wear resistance and hardenability of steel, and also stabilises the austenitic structure.

Production of special alloys. Ferromanganese is used to create alloys with unique properties required in the aerospace industry, energy and mechanical engineering.

Sulfur binding. Manganese binds sulfur into manganese sulfide, which floats into the slag, eliminating the harmful effect of sulfur on steel properties.

Other applications. Ferromanganese is used in the production of welding materials, as well as a source of manganese in the chemical industry.

Safety and Storage

Ferromanganese dust is low-toxic, has a moderate fibrogenic effect and belongs to hazard class 3 according to GOST 12.1.007. The maximum allowable concentration (MAC) of ferromanganese in the working area air is 2 mg/m³. The condensation aerosol may contain manganese compounds, which, with prolonged exposure, can cause damage to the nervous system (manganese encephalopathy). When working with ferromanganese dust, personal protective equipment must be used: respirators, safety goggles, gloves and protective clothing. Ferromanganese is non-flammable. Ferromanganese should be stored in dry, closed warehouses or on areas with hard surfacing, protected from moisture and contamination. It is supplied in big bags with polyethylene liners weighing up to 1000 kg or in steel drums.

Market and Trends

The global ferromanganese market is closely linked to steel production. The largest producers are China, India, South Africa, Kazakhstan and Ukraine. Key industry trends include the transition to ferromanganese production with a minimal carbon footprint, the development of technologies for processing low-grade manganese ores, and growing attention to the recycling of manganese-containing materials. The Asia-Pacific region remains the largest consumer of ferromanganese, while countries with rich resource bases are the main exporters.

Conclusion

Ferromanganese remains a fundamental material of modern metallurgy, providing the production of structural, high-manganese and special steels. The variety of grades by carbon and manganese content allows the optimal composition to be selected for each specific task. Understanding the classification, production technologies and applications of ferromanganese is the basis for competent material selection and the organisation of efficient supplies.