Medium Carbon Ferromanganese in Foundry and Steelmaking Use

Definition and Position of Medium Carbon Ferromanganese

Ferromanganese is the master alloy through which manganese enters virtually every ton of steel and a large share of cast iron. The family is divided by carbon content rather than by manganese content, because carbon is the element that decides which melting route the alloy can be used in. High carbon ferromanganese carries roughly 6-8% C, medium carbon ferromanganese is capped near 2% C, and low carbon grades sit below 0.7% C. The medium carbon band, generally 1.0-2.0% C with nominal manganese of 74-80%, is the compromise grade: it is clean enough not to wreck the carbon balance of a low carbon heat, yet it is produced by a cheaper route than the refined low carbon grades.

For a foundry, that compromise matters more than the headline manganese figure. A steel foundry tapping a 0.25% C low alloy casting has almost no carbon budget left after the scrap charge and the deoxidation practice. Adding high carbon ferromanganese at 8 kg per ton of steel would introduce roughly 0.06% C together with the manganese, which is enough to move a grade across a specification limit. Medium carbon ferromanganese delivers the same manganese at a quarter of the carbon load, and that is the single technical reason the grade exists in foundry purchasing schedules.

The alloy is a solid solution of manganese, iron and carbon, with small amounts of silicon, phosphorus and sulphur carried over from the ore and the reduction process. It is sold as lump, as crushed granular material and, less commonly, as briquettes pressed from fines. Its true density is close to that of steel, but the heaped bulk density of a 25-150 mm lump lot is far lower, typically in the region of 2.0-2.5 t/m3, which is the figure that governs silo volume and container loading rather than the density of the individual pieces.

Grade Designations, Chemical Composition and Tolerances

Chinese national standard GB/T 3795 covers ferromanganese and designates grades by the nominal manganese figure followed by the maximum carbon content, so FeMn78C2.0 means nominally 78% Mn with carbon held at 2.00% or below, and FeMn75C2.0 means nominally 75% Mn with the same carbon ceiling. Buyers outside that framework will see the same products described as medium carbon ferromanganese with 1.5% C or 2.0% C, or referenced against a producer's internal grade code. Whatever the label, the negotiation should always fix four numbers in writing: manganese content and its acceptance floor, carbon maximum, phosphorus maximum, and the size fraction.

Phosphorus is the element that separates a good medium carbon lot from a merely compliant one. Manganese ore carries phosphorus, and the electric furnace route does not remove it, so every increment of phosphorus in the alloy lands in the steel at a recovery close to 100%. A medium carbon grade is normally supplied at 0.30% P maximum, with tighter 0.25% P material available at a premium for steel castings that must meet impact requirements at low temperature. Silicon is typically held at 1.5% maximum; silicon above that level is not a defect, but it does mean the alloy will contribute a small silicon addition that must be accounted for in the final analysis.

The table below sets out the ranges that should appear on a mill certificate for the common medium carbon grades. Individual producers work to narrower internal windows, and a buyer is entitled to ask for the actual heat analysis rather than the specification limits.

Parameter	FeMn78C2.0 typical	FeMn75C2.0 typical	How it is judged
Manganese, %	75.0-80.0	72.0-77.0	Lot mean, one heat certificate per lot
Carbon, %	2.00 max	2.00 max	Maximum, no averaging permitted
Silicon, %	1.5 max	1.5 max	Maximum, checked per lot
Phosphorus, %	0.30 max (0.25 on request)	0.30 max	Maximum, decisive for low temperature grades
Sulphur, %	0.03 max	0.03 max	Maximum
Size fraction, mm	10-50, 25-150, or crushed 2-10	10-50, 25-150	Undersize and oversize each 5% max by mass

Physical Properties That Govern Handling and Melting Behaviour

Manganese itself melts at about 1244 C and has a true density near 7.43 g/cm3, but the alloy does not melt at a single temperature. Medium carbon ferromanganese softens and dissolves over a range that begins around 1200 C and is complete only well above 1300 C in a steel bath, which is why the addition is made into the tap stream or into a bath that is already above 1550 C rather than onto a cold furnace bottom. A cold addition that sits on the surface without being entrained will oxidise instead of dissolving, and the manganese that oxidises is exactly the manganese the foundry pays for and does not get.

Manganese has a strong affinity for oxygen at steelmaking temperatures, stronger than iron and weaker than silicon and aluminium. That ranking explains the usual practice of pairing a manganese addition with a silicon or aluminium deoxidation step: the manganese is added when the oxygen potential has already been pulled down, so that the manganese reports to the steel instead of to the slag. The manganese oxide that does form is a liquid at steelmaking temperature and is readily absorbed by a lime-based slag, which is why manganese losses in a well-controlled ladle are modest while losses in an oxidising furnace atmosphere are not.

Lump size controls dissolution more than any other physical variable. Large pieces survive the slag layer and reach the bottom of the ladle, where they may not fully dissolve before casting; fines dissolve almost instantly but are prone to being carried into the slag or into the dust extraction system. A 10-50 mm fraction is the standard choice for ladle and tapping stream additions, 25-150 mm is used where a deep bath and a long holding time allow it, and crushed 2-10 mm material is reserved for continuous or semi-continuous feeding and for small induction furnaces where a large lump would never fully dissolve.

The Two Functions in the Foundry: Deoxidation and Alloying

In a foundry, medium carbon ferromanganese works twice. The first function is alloying: manganese is added to grey and malleable irons and to carbon and low alloy steel castings to reach a specified manganese range, commonly 0.5-1.0% in structural steel castings and 0.6-1.2% in wear-resistant grades. Manganese raises hardenability, so it is one of the cheapest ways to make a thick section through-harden, and it also raises strength and wear resistance in the as-cast or normalised condition.

The second function is metallurgical rather than analytical. Manganese combines with sulphur to form manganese sulphide, and the ratio of manganese to sulphur in the finished steel governs whether sulphur exists as scattered sulphide inclusions or as iron sulphide films on grain boundaries. Iron sulphide films cause hot tearing and hot shortness during solidification and rolling. A manganese to sulphur ratio of at least 20:1 in the finished analysis is the usual working rule in casting and steelmaking practice, and in low sulphur steels this is achieved with a manganese level that may be well below the grade minimum for the alloy itself.

Manganese also acts as a mild deoxidiser and, in combination with silicon, forms manganese silicate inclusions that rise into the slag. This is the reason a foundry addition is often specified as ferromanganese plus ferrosilicon rather than either alone. Adding silicon first and manganese second gives a cleaner result than the reverse: the strong deoxidation step produces a slag that the manganese addition is not competing with.

Recovery, Addition Practice and Slag Control

Recovery is the number that determines the purchase quantity, and it varies by practice far more than by alloy specification. A properly entrained addition into a tapped stream or an induction furnace bath at 1560-1620 C typically recovers 85-92% of the manganese; an addition dropped onto a cold bath, made under an oxidising slag, or held for a long time before casting can fall below 80%. The difference between 85% and 92% on a 500 kg addition is 35 kg of alloy, which is usually more than the price difference between two suppliers.

Practical rules that hold across furnace types: calculate the addition against the actual bath weight rather than the nominal charge weight, account for manganese already present in the scrap, add after the slag has been reduced, and keep the addition time short. In induction furnaces, placing the alloy at the bottom of the crucible before charging, or plunging it with a bell during the final minutes, gives more consistent recovery than surface charging. In arc furnaces and ladles, the tap stream addition is standard because the turbulence provides the entrainment that surface charging lacks.

Slag control determines how much of the dissolved manganese stays dissolved. A basic slag with a lime to silica ratio in the range 2.5-4 and a ferrous oxide content kept low will hold manganese in the metal. An oxidising slag with high ferrous oxide will reoxidise manganese out of the bath even after a successful addition, which is why a heat that analyses correctly in the furnace can miss on the final casting analysis.

Sampling, Certificate Review and Lot Acceptance

Ferroalloy acceptance is covered by GB/T 3650 for delivery, packing, marking and certification and by GB/T 4010 for taking and preparing samples for chemical analysis, with ISO 3713 providing the equivalent international framework for sampling and sample preparation. In practice, the buyer's protection lies in three documents: the heat analysis from the producer, the size analysis of the delivered fraction, and a third-party check on a composite sample drawn from the delivered lot.

Sampling a lump lot is not a matter of taking a few pieces from the top of the bag. Manganese and carbon segregate within an ingot and between pieces of different thickness, so a composite sample should be built from a number of increments taken across the lot, crushed to a defined particle size and reduced by quartering before analysis. A single piece analysis can be several tenths of a percent away from the lot mean on manganese and is not a valid basis for rejecting a delivery. Where a dispute is likely, retain a sealed duplicate of the composite sample so that both parties can test the same material.

Size acceptance deserves the same attention. Undersize and oversize content are normally limited to 5% each by mass, and the check should be done on a sample of at least 100 kg sieved on the specified screens. Fines in a 10-50 mm lot are not merely an accounting loss: they change the dissolution behaviour and can block feeding equipment, so a lot that passes the chemical certificate but carries 12% undersize is still a lot that will run badly.

Where Medium Carbon Ferromanganese Is the Wrong Choice

The grade is not universal, and three situations call for something else. The first is ductile iron: manganese above roughly 0.3% in ductile iron segregates to the cell boundaries, promotes pearlite and carbides, and degrades elongation and impact toughness, so ductile iron practice uses low manganese charge materials and avoids ferromanganese additions wherever the charge can be controlled. A foundry that reaches for medium carbon ferromanganese to trim manganese in ductile iron is solving the analysis and damaging the structure.

The second is any heat with a carbon ceiling tight enough that 2% carbon in the alloy still matters, such as low carbon stainless or interstitial-free grades, where a low carbon or refined grade with 0.5% C or less is the correct addition. The third is any application where phosphorus is critical: a 0.30% P alloy adds roughly 0.003% P per 1% Mn added at a 2% addition rate, which is acceptable in structural steel and unacceptable in steels specified at 0.015% P maximum unless the base charge is exceptionally clean.

A fourth consideration is cost per unit of recovered manganese rather than cost per ton. The relevant comparison is the delivered price divided by manganese content divided by recovery. A cheaper alloy with 3% lower manganese and a dirtier surface can be more expensive per point of manganese in the casting, and that calculation should be done before the purchase order rather than after the first heat.

Storage, Transport and Handling

Medium carbon ferromanganese is delivered in 1 t big bags, 25 kg bags or in bulk, and it should be stored under cover on a dry floor. The alloy itself does not deteriorate in clean dry conditions, but damp fines generate hydrogen when they meet water, and a sealed container holding wet fines can develop a flammable atmosphere. Storage areas should be ventilated, kept free of standing water, and separated from acids and oxidisers.

Dust from crushing and handling contains manganese, and inhalation of manganese fume and dust is a recognised occupational hazard with effects on the central nervous system. Crushing and screening areas need extraction, and furnace additions should be made without standing in the plume. National occupational exposure limits for manganese apply and should be checked against local regulation rather than assumed. The alloy is not classified as a dangerous good for transport in solid lump form, but the shipper's declaration should still be verified for the specific packing.

FAQ

Q: What is the carbon content of medium carbon ferromanganese?
Medium carbon ferromanganese is supplied at 2.00% C maximum, commonly 1.0-2.0% C, which places it between high carbon grades at 6-8% C and low carbon grades below 0.7% C.

Q: What does the designation FeMn78C2.0 mean?
The 78 is the nominal manganese content in percent and C2.0 is the maximum carbon content in percent. A conforming lot is typically 75-80% Mn with carbon not exceeding 2.00%, silicon at 1.5% max and phosphorus at 0.30% max.

Q: Why is manganese added to steel rather than used as pure metal?
Manganese has a strong affinity for oxygen and a high vapour pressure as a pure metal, so it is added as ferromanganese, which has a lower melting point than pure manganese, a higher density for easier immersion, and a manganese content high enough to keep addition weights manageable.

Q: What manganese to sulphur ratio prevents hot shortness?
A ratio of at least 20:1 in the finished analysis is the usual working rule. Below that, sulphur can exist as iron sulphide films at grain boundaries rather than as dispersed manganese sulphide inclusions, and hot tearing risk rises.

Q: What lump size should be ordered for a 500 kg induction furnace?
A 10-50 mm fraction is the practical choice for small and medium induction furnaces, since large 25-150 mm lumps may not fully dissolve in a short melt. Crushed 2-10 mm material suits continuous feeding but is more prone to loss into the slag.

Q: How is the delivered lot checked against the certificate?
Draw a composite sample across the lot per GB/T 4010 or ISO 3713, crush and quarter it, and test manganese, carbon, phosphorus and silicon. Sieve at least 100 kg for size, with undersize and oversize each limited to about 5% by mass.