Ferromanganese: One Alloy Family, Two Very Different Grades
Ferromanganese is the master alloy through which the great majority of manganese enters steel. Manganese combines with sulphur, helps deoxidise the melt, and gives steel the hardenability and toughness that plain carbon steel cannot reach on its own. Because manganese ore is reduced with carbon, the alloy inevitably carries carbon, and the amount of that carbon is what separates high-carbon ferromanganese (HC FeMn) from low-carbon ferromanganese (LC FeMn). The distinction is not cosmetic. Carbon content dictates the production route, the manganese and silicon levels that accompany it, the way the alloy dissolves in the ladle, the carbon pick-up the steelmaker has to allow for, and ultimately the range of steels for which the grade can be used at all.
How Ferromanganese Grades Are Named
GB/T 3795 writes the designation of ferromanganese as a single code that combines the guaranteed manganese content with the maximum carbon content. FeMn78C8.0 is a grade with at least 78% manganese and no more than 8.0% carbon; FeMn80C0.7 is a grade with at least 80% manganese and no more than 0.7% carbon. Reading the two numbers side by side is enough to place any grade on the spectrum.
High-carbon ferromanganese: grades such as FeMn78C8.0, with carbon in the 6.0-8.0% band and manganese typically 75-82%.
Medium-carbon ferromanganese: grades such as FeMn78C1.5 and FeMn75C2.0, with carbon around 1.0-2.0%.
Low-carbon ferromanganese: grades such as FeMn80C0.7, FeMn80C0.4 and FeMn80C0.2, with carbon from about 0.7% down to 0.2% and manganese typically 78-88%.
The two-tier wording often used in trade, high carbon above 1% and low carbon from 0.1% to 1.0%, is a simplification. A three-tier classification of high, medium and low carbon matches the way steel mills actually order, because the carbon figure has to be pinned to a tenth of a percent before a heat is released.
Side-by-Side Comparison
| Characteristic | High-carbon ferromanganese | Low-carbon ferromanganese |
|---|---|---|
| Typical carbon content | 6.0-8.0% | 0.2-0.7% |
| Typical manganese content | 75-82% | 78-88% |
| Silicon | Generally below 2% | Commonly 0.5-2% |
| Production route | Carbothermic reduction of ore with coke | Silicothermic refining with silicomanganese and lime |
| Deoxidation and desulphurisation | Strong | Moderate, with part of the duty passed to silicon |
| Carbon pick-up in the melt | Significant and must be allowed for | Minimal |
| Cost per unit of manganese | Lower | Higher |
| Typical products | Carbon and low-alloy steels, heavy sections | Low-carbon, alloy and stainless steels, welding consumables |
Production Routes
High-carbon ferromanganese is produced by carbothermic reduction. Manganese ore, coke and flux are smelted together in a submerged-arc electric furnace, or historically in a blast furnace, and the carbon that drives the reduction stays in the metal. That is why high-carbon ferromanganese cannot be made with a low carbon content, no matter how the furnace is run.
Low-carbon ferromanganese is made by taking that carbon out again. In the silicothermic route, molten high-carbon ferromanganese or manganese ore is refined with silicomanganese and lime. Silicon reduces the manganese oxide, the carbon content falls to a fraction of a percent, and lime keeps the slag fluid and basic enough to hold the silica that is generated. The route consumes an extra master alloy and more electrical energy per tonne of manganese, which is precisely why low-carbon ferromanganese carries a price premium.
Behaviour in the Steel Melt
High-carbon ferromanganese dissolves readily and reacts strongly with oxygen and sulphur, so it is normally added early, during tapping or in the ladle, where its carbon can be absorbed or trimmed later in the process. Its carbon content makes it unsuitable for grades that must finish below about 0.10% carbon unless a decarburisation step follows.
Low-carbon ferromanganese is added when the carbon specification leaves no room for pick-up: low-carbon steels, alloy steels, stainless grades and welding consumables. Recovery is generally high because the alloy dissolves without a violent reaction, and the silicon it contains contributes to deoxidation, so the addition practice has to be balanced against the silicon specification of the steel rather than treated as an isolated manganese addition.
Selection Guidance
Carbon steels and heavy sections: high-carbon ferromanganese gives the lowest cost per unit of manganese and its carbon is easily accommodated.
Low-carbon and interstitial-free steels: low-carbon ferromanganese, or silicomanganese where silicon is also freely specified.
Stainless and heat-resisting steels: low-carbon ferromanganese, so that the carbon balance of the chromium-bearing melt is not disturbed.
Welding consumables: low-carbon ferromanganese, because electrode and wire chemistries are specified to tight carbon and silicon windows.
Non-steel duties: high-carbon ferromanganese also serves as a friction modifier in brake pad formulations and as a heavy medium in dense-media separation plants.
Frequently Asked Questions
Q: What is the main difference between high-carbon and low-carbon ferromanganese?
High-carbon ferromanganese contains roughly 6.0-8.0% carbon and is used mainly for deoxidation, desulphurisation and alloying of carbon steels, while low-carbon ferromanganese contains about 0.2-0.7% carbon and is used where the melt cannot accept carbon pick-up.
Q: Which grade contains more manganese?
Low-carbon ferromanganese usually carries the higher manganese figure, typically 78-88% against 75-82% for the high-carbon grades, because the silicothermic refining step also removes part of the iron and other impurities.
Q: Can high-carbon ferromanganese be used in stainless steel?
Only for grades with a generous carbon allowance. For standard austenitic stainless steels the carbon limit is far too tight, so low-carbon ferromanganese or another low-carbon manganese carrier is required.
Q: Why is low-carbon ferromanganese more expensive?
It needs a second, energy-intensive refining step with silicomanganese and lime, consumes more electrical energy per tonne of contained manganese, and recovers less manganese into the metal than the carbothermic route.
Q: How is carbon content reported on a certificate?
Carbon, manganese, silicon, phosphorus and sulphur are reported for each lot, and the carbon figure is quoted to one decimal place or better so that the buyer can compare it directly with the FeMn designation.
Q: Does ferromanganese have uses outside steelmaking?
Yes. High-carbon ferromanganese is used in friction materials such as brake pads and in dense-media separation, while the low-carbon grades appear in specialised alloy and welding applications.
