Ferrochrome: properties, grades and applications / Articles

Ferrochrome (FeCr) is a ferroalloy whose main elements are iron and chromium. 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 stainless, structural and special steels. Due to the high affinity of chromium for carbon and its ability to dissolve in iron, ferrochrome occupies a central place in the processes of alloying, deoxidation and modification of metals.

Chemical Nature and Physicochemical Properties

Ferrochrome is an alloy of chromium with iron, in which the chromium content can vary from 45% to 95% by mass depending on the grade. The rest is iron and unavoidable impurities: carbon (up to ~5–8%), silicon (up to 8%), sulfur (up to 0.05%), phosphorus (up to 0.05%). The properties of the alloy directly depend on the chromium and carbon content. High-carbon ferrochrome contains 6–8% carbon, medium-carbon — 0.5–4%, and low-carbon — up to 0.1–0.5%. The melting point of ferrochrome is about 1900 °C. The density of high-carbon ferrochrome must be at least 6.8 g/cm³, and of low- and medium-carbon — at least 7.10 g/cm³.

Classification, Grades and Standards

In Russia and CIS countries, requirements for ferrochrome are regulated by GOST 4757-91 (harmonised with ISO 5448-81). According to the standard, ferrochrome is divided into several categories depending on the carbon and phosphorus content:

High-carbon ferrochrome (HC FeCr): carbon content 6–8%. Used for smelting structural and tool steels, cast iron, as well as for producing other ferroalloys.
Medium-carbon ferrochrome (MC FeCr): carbon content 0.5–4%. Used for alloying steels for various purposes.
Low-carbon ferrochrome (LC FeCr): carbon content up to 0.1–0.5%. Used in the production of stainless and heat-resistant alloys where an increase in carbon content in the metal is unacceptable.

Nitrided ferrochrome (FeCrN) is also produced, containing nitrogen (up to 10%), which improves corrosion resistance and increases the yield strength of steel. The marking includes the chromium and carbon content, for example, FeCr70C1 means ferrochrome with ~70% Cr and ~1% C. Ferrochrome 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, 20–50 mm, 50–200 mm, etc.).

Production Technology

Ferrochrome production is based on the reduction of chromite ore (or concentrate) by a carbonaceous reducing agent (usually coke) in powerful submerged arc electric furnaces. The charge, consisting of chromite ore, coke and fluxes (lime, quartzite), is loaded into the furnace. When electric current is passed, a temperature of about 2000 °C develops, at which chromium and iron are reduced from their oxides. Molten high-carbon ferrochrome accumulates at the bottom of the bath and is periodically tapped through a taphole. The bulk of the world's ferrochrome is produced in South Africa, Kazakhstan and India.

To obtain low-carbon ferrochrome (LC FeCr), a more complex scheme is used: first, high-carbon ferrochrome is smelted, then ferrosilicochrome is produced (by reducing silicon from quartzite in the presence of ferrochrome melt), and finally, chromium and iron oxides from the ore are reduced by silicon of liquid ferrosilicochrome (usually in the presence of lime as a flux). The aluminothermic method is also used, allowing particularly pure grades with low carbon and nitrogen content to be obtained.

Applications

Stainless steel production. More than 80% of all ferrochrome in the world is used for the production of stainless steel, the chromium content of which is from 12 to 20%. Ferrochrome gives steel corrosion resistance, hardness and strength, and also promotes the formation of a homogeneous microstructure.

Alloying of structural and tool steels. High-carbon ferrochrome is used in smelting structural and tool steels, as well as cast iron, increasing their wear resistance and hardness.

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

Deoxidation and modification. Ferrochrome is used for deoxidising alloys and modifying cast iron.

Safety and Storage

Ferrochrome 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 metallic ferrochrome in the working area air is 2 mg/m³. The condensation aerosol of ferrochrome contains Cr (VI) compounds, which belong to hazard class 1 (extremely hazardous substances), with a MAC of 0.1 mg/m³ (calculated as CrO₃). When working with ferrochrome dust, personal protective equipment must be used: respirators, safety goggles, gloves and protective clothing. Ferrochrome is non-flammable. Ferrochrome 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 ferrochrome market is closely linked to stainless steel production. The largest producers are South Africa, Kazakhstan, India and China. Key industry trends include the transition to ferrochrome production with a minimal carbon footprint, the development of technologies for processing low-grade chromite ores, and growing attention to the recycling of chromium-containing materials. The Asia-Pacific region remains the largest consumer of ferrochrome, while countries with rich resource bases are the main exporters.

Conclusion

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