Ferroalloy Production Methods Explained: Blast Furnace, Submerged Arc Furnace, Refining Routes & How to Choose

Ferroalloy Production Methods Explained: Blast Furnace, Submerged Arc Furnace, Refining Routes & How to Choose

Meta-level summary (for the top of the page): Ferroalloys such as ferrosilicon, ferromanganese, silicomanganese and ferrochrome are the backbone of modern steelmaking. This guide compares the main ferroalloy production methods and explains where each fits, from the blast furnace to the electric submerged arc furnace (SAF) and the refining routes. It is written from the point of view of a furnace manufacturer that designs and builds this equipment.

What Is Ferroalloy Production?

Ferroalloys are alloys of iron with one or more elements such as silicon, manganese, chromium, nickel or tungsten. Steel mills use them to deoxidize, desulfurize and alloy molten steel. Producing them means reducing metal oxides from ore and separating the metal from the slag.

No single process suits every product. The right method depends on three things:

• how stable the oxide is, i.e. how hard it is to reduce

• the carbon, silicon and nitrogen specification the customer wants

• local electricity, reductant and raw-material costs

Ferroalloy Production Methods at a Glance

1. Blast Furnace Smelting

The blast furnace follows the same principle as ironmaking. Ore, sinter and coke are charged from the top. Coke burns at the tuyere zone, and the coke and the CO it generates act as the reductant. The combustion heat drives reduction, melts the burden and separates metal from slag.

Where it works: For oxides that are relatively easy to reduce, the blast furnace gives acceptable grades at high productivity, low unit cost and low electricity use. It produces low-silicon ferrosilicon, high-carbon ferromanganese, ferronickel and manganese-rich slag. The slag is low in phosphorus and high in manganese, so it is a good feed for silicomanganese and for medium- and low-carbon ferromanganese.

Limits:

• Heat is limited by coke combustion, so very stable oxides give only low-grade alloys.

• Carburization keeps the carbon content of the alloy high.

• Manganese and silica ores are harder to reduce than iron ore, so coke rate is higher than in pig iron production. Burden load is lighter, the edge gas flow tends to develop, and hearth build-up becomes a risk.

• Primary slag is rich in MnO and very fluid, so it attacks the lining and shortens furnace life.

A ferroalloy blast furnace therefore needs a different profile and structure from an ironmaking furnace. It needs heavier edge charging, together with high blast temperature and high gas volume to keep the center gas flow active.

2. Electric Furnace Methods

2.1 Electric Carbothermic Process: the Submerged Arc Furnace

The submerged arc furnace (SAF), also called a mineral furnace or ferroalloy furnace, is the main route for crude ferroalloys and accounts for the largest share of global output. It is the core product of SR Electric Furnace.

How it works: The electrodes are buried in the burden. The arc and resistance heat is released deep in the charge, where the reduction reactions need it. Hot gas rises through the descending burden and gives up its heat on the way. This lowers the top temperature, cuts volatilization losses of useful elements, and improves both thermal efficiency and element recovery.

Key engineering points:

1. Carbon is both reductant and conductor. The reductant needs good reactivity, high purity and a suitable electrical resistivity. This sets the choice among coke, semi-coke, charcoal and coal.

2. Burden permeability. Every component needs the right size distribution and thermal stability so gas can pass freely.

3. Continuous operation. Melting rate, charging rate and tapping schedule must stay in balance.

4. Slag practice. Depending on the product, the furnace runs with slag (for example silicomanganese, high-carbon ferrochrome and ferronickel) or without slag (for example ferrosilicon and industrial silicon). Slag chemistry and quantity decide productivity, recovery and tapping behavior.

5. Electrodes are the critical component. Carbon, graphite or self-baking (Soderberg) electrodes must match the furnace power and the product. The electrode holding system is equally important: copper contact shoes, pressure rings, bellows or hydraulic clamping, and water-cooled parts.

6. Electrical system. Furnace transformer capacity (MVA), short network design, power factor and electrode regulation all affect energy use and stability.

Limit: Elements that form stable carbides with carbon, such as chromium, manganese and vanadium, end up in a high-carbon alloy. Low-carbon grades need a different route (2.2 to 2.5).

Typical SAF applications: ferrosilicon, silicomanganese, high-carbon ferromanganese, high-carbon ferrochrome, ferronickel, industrial (metallurgical) silicon, pig iron, titanium slag.

2.2 Electric Silicothermic Process (Desiliconization)

Silicides are more stable than carbides, so a silicon-bearing alloy such as ferrosilicon, silicomanganese or silicochrome can reduce oxides without adding carbon. The result is a refined, low-carbon ferroalloy, for example low- and medium-carbon ferrochrome or ferromanganese.

Equipment and practice:

• An electric arc furnace, either fixed or tilting. Early operation is submerged-arc style, and after the charge melts the arc is open.

• Graphite electrodes, to avoid carbon pickup. The electrodes must not dip into the bath.

• Higher secondary voltage, and usually a magnesia (MgO) lining.

• Batch production. Part of the metal is left in the furnace after tapping to protect the lining.

• The reduction releases a lot of heat, and the open arc radiates strongly onto the lining. The lining must therefore have high refractoriness and slag resistance.

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2.3 Out-of-Furnace (Metallothermic) Process

This route needs no external electric heat. Silicon, ferrosilicon or aluminum reduces the oxide, and the reaction heat is enough to melt metal and slag.

• Raw materials must be dry, crushed and well mixed.

• Fluxes are added to control reaction speed and to separate metal from slag. An igniter is used to start the reaction.

• Production is batch-wise and cost per ton is higher, because reductants are expensive.

It is the usual route for alloys with very high melting points or low carbon requirements, such as metallic chromium, ferrovanadium and ferrotitanium.

2.4 Vacuum Solid-State Resistance Furnace

A horizontal, sealed steel furnace is lined with refractory brick and heated by graphite rods. The furnace is first evacuated, then heated, and pumping continues during the run. The temperature stays below the melting point of the charge, so the reaction is a gas–solid reaction.

• Vacuum drives forward reactions that release gas, mainly CO.

• Reactants must be mixed very evenly.

• Production is batch-wise.

It is used for micro-carbon ferrochrome.

2.5 Oxygen Converter Refining

Similar to converter steelmaking, this is a refining route that selectively oxidizes unwanted elements. For medium-carbon ferromanganese or ferrochrome, oxygen volume and blowing temperature are controlled to lower carbon while keeping manganese or chromium in the alloy. It has high productivity and no extra heat source, and it is a batch process.

2.6 Induction Furnace Remelting

Micro-carbon ferrochrome is crushed and melted in an atmospheric induction furnace. Nitrogen is blown onto the bath through a lance in the furnace cover, and the alloy absorbs nitrogen to become nitrided ferrochrome. Operation is batch-wise.

Hot Charging and Secondary Refining

For refined alloys, plants can charge liquid metal hot or transfer it hot between furnaces, and can add ladle refining. This saves power and cost. These practices are combinations of the methods above, not separate processes.

How to Choose the Right Ferroalloy Furnace

Sizing a SAF depends on power rating (MVA), electrode diameter, furnace shell diameter, hearth power density, and whether the furnace is open, semi-closed or closed. Closed furnaces let you recover CO gas and cut emissions. They are the better choice where energy costs and environmental limits are strict.

FAQ

1. What is the difference between a submerged arc furnace and an electric arc furnace?

A submerged arc furnace buries its electrodes in the charge and works mainly by resistance and arc heating inside the burden. It is used to reduce ores into ferroalloys. An electric arc furnace (EAF) melts scrap with an open arc, for steelmaking. Some refining operations, such as silicothermic ferroalloy production, use an EAF-type furnace.

2. Why does carbothermic ferroalloy contain high carbon?

Carbon is the reductant, and elements such as chromium and manganese form stable carbides. Producing low-carbon alloy needs silicothermic, metallothermic, vacuum or oxygen-refining routes.

3. Which ferroalloys are made in a submerged arc furnace?

Ferrosilicon, silicomanganese, high-carbon ferromanganese, high-carbon ferrochrome, ferronickel and industrial silicon are the most common.

4. How much power does a ferroalloy furnace use?

It varies by product. As a rough guide, ferrosilicon (75%) needs far more power per ton than high-carbon ferromanganese or high-carbon ferrochrome. Actual figures depend on raw materials, furnace design and operation.

Work With SR Electric Furnace

SR Electric Furnace (Xi’an Sanrui Electric Furnace Co., Ltd.) designs, manufactures, installs and commissions metallurgical furnaces. The company was founded in 2009 by a retired chief technical engineer of a state-owned metallurgical electric furnace plant. Our range covers submerged arc furnaces, electric arc furnaces, LF and VD/VOD refining furnaces, induction furnaces, dust removal and water treatment systems, and key parts such as forged copper tiles, pressure rings, short networks and water-cooled roofs. Equipment is exported to Germany, Spain, Iran, Ethiopia, Uzbekistan, Kazakhstan, Thailand, Vietnam, Indonesia, India and Myanmar.

Send us your raw materials, target product and capacity, and our engineers will propose a furnace solution from A to Z.

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