Ferro chrome is sold in three broad carbon classes, and they are not interchangeable. Order high carbon material for a low carbon stainless heat and you will spend the rest of the shift trying to decarburise your way out of it. This is what separates the grades, and how to decide which one belongs in your charge.
The three carbon classes
Chromium is the reason you are buying the alloy, but carbon is the reason there are different grades of it. Ferro chrome is produced by carbothermic reduction of chromite ore in a submerged arc furnace, and that process leaves carbon in the product. Getting it back out costs money, which is why the grades are priced the way they are.
| Grade | Chromium | Carbon | Silicon | Typical use |
|---|---|---|---|---|
| High carbon (HC) | 60–70% | 6–8% | up to 3% | Standard 400-series stainless, tool and alloy steels where carbon is wanted |
| Medium carbon (MC) | 60–70% | 1–4% | up to 1.5% | Intermediate grades; trimming additions where HC would overshoot carbon |
| Low carbon (LC) | 60–72% | 0.03–0.15% | up to 1.5% | 304L, 316L and other low carbon stainless grades |
You will also see charge chrome quoted separately. It is a high carbon material with lower chromium, typically in the 50–60% Cr range with 6–8% carbon, produced from lower-grade ores. For bulk stainless production where the chromium units are what matter and the carbon is going to be removed in the converter anyway, charge chrome is usually the cheaper way to buy chromium.
Why low carbon costs more
The price gap between HC and LC ferro chrome is not a chromium story — the chromium content is broadly similar. You are paying for the decarburisation.
Low carbon ferro chrome is generally made by a silicothermic route: silicon, usually supplied as ferro chrome silicon, reduces chromium oxide in place of carbon. That adds a second processing stage, consumes an expensive reductant, and gives up some yield. The result is a product with carbon an order of magnitude lower, at a price that reflects the extra work rather than the extra chromium.
This is worth internalising because it points at the real decision: if your process can remove carbon downstream more cheaply than the supplier can remove it upstream, buy the high carbon grade.
Choosing a grade
Start with the carbon ceiling of the finished steel
An "L" grade stainless such as 304L or 316L caps carbon at 0.03%. Work backwards from that. If you are adding, say, 18% chromium as high carbon ferro chrome at 7% carbon, you are also adding roughly 1.8% carbon to the heat. Unless you have an AOD or VOD converter to strip it back out, that heat is finished before it started.
With a converter, the calculation changes completely. Argon oxygen decarburisation is very good at removing carbon while retaining chromium, and mills running AOD routinely charge high carbon ferro chrome or charge chrome precisely because it is the cheapest source of chromium units. Without one, low carbon material is not a preference — it is a requirement.
Then check silicon and sulphur
Silicon rides along with the chromium, and in some grades it matters as much as the carbon. High carbon ferro chrome can carry up to 3% silicon; if your steel has a tight silicon specification, that addition has to be counted.
Sulphur is usually the limit that catches people out on high carbon material. Specify a maximum rather than assuming one. For most structural and stainless work 0.03% maximum is a reasonable ask; tighter is available but costs more.
Finally, size it for where it goes
Sizing is not a detail. A 10–50 mm fraction charged into a furnace behaves completely differently to the same chemistry supplied as 0–10 mm fines. Fines blow out with the off-gas and depress your recovery; oversized lumps do not fully dissolve before you tap. State the fraction and a maximum fines percentage on the purchase order, not just the chemistry.
A worked example
Suppose you need to add 18% chromium to a 100 tonne heat of 430 stainless, using high carbon ferro chrome at 65% Cr with an assumed 95% recovery.
- Chromium required: 18 tonnes
- Allowing for 95% recovery: 18 ÷ 0.95 = 18.95 tonnes of chromium to charge
- At 65% Cr: 18.95 ÷ 0.65 = 29.2 tonnes of ferro chrome
- Carbon carried in at 7%: 29.2 × 0.07 = 2.04 tonnes, or about 2% of the heat
That last line is the whole argument. Two percent carbon is fine for a 430 heat that is going to be decarburised anyway, and impossible for a 304L heat that is not. The recovery figure matters too: assume 95% and actually get 88% and you are 1.7 tonnes of chromium short, which you will discover at the analysis stage when correcting it is most expensive.
Common mistakes
- Specifying chromium only. "65% ferro chrome" describes maybe a third of what you are buying. Carbon, silicon, sulphur, phosphorus and size all need ranges.
- Ignoring the size distribution on delivery. Material that met specification at the load port can arrive with 15% fines after two transhipments. Agree where sampling happens.
- Assuming a recovery figure from another plant. Recovery is a function of your slag chemistry, your addition practice and your tapping time. Measure your own.
- Buying low carbon out of caution. If you have decarburisation capacity, you may be paying a substantial premium for carbon removal you were going to do anyway.
In short
The grade decision follows from two questions: what is the carbon ceiling of the steel you are making, and can you remove carbon downstream? If the ceiling is tight and you have no converter, you need low carbon material. If you have an AOD, the high carbon grades are almost always the more economical source of chromium units. Everything else — silicon, sulphur, sizing — is about making sure the alloy behaves predictably once you have chosen the class.
We supply ferro chrome in all three carbon classes to customer specification. Send us your requirement with tonnage and destination for a quotation.
Frequently asked questions
What is the difference between HC and LC ferro chrome?
The carbon content. High carbon ferro chrome carries roughly 6–8% carbon and is the cheapest source of chromium units. Low carbon ferro chrome is refined down to 0.03–0.15% carbon and is used where the finished steel has a tight carbon ceiling, such as 304L and 316L stainless grades.
Why is low carbon ferro chrome more expensive?
Removing carbon takes additional refining — typically a silicothermic or decarburisation step — which consumes energy and reduces yield. You are paying for that processing, not for extra chromium.
What chromium content should I specify?
Most commercial ferro chrome sits between 60% and 72% Cr. Specify the chromium range, the carbon ceiling, the silicon and sulphur limits, and the size fraction. Chromium alone does not define the product.