FeSi 75 vs FeSi 72: which grade fits your heat?
The difference is not just 3% silicon. It changes recovery, slag volume and the cost per tonne of steel — here is how to choose.
Buyers often treat FeSi 75 and FeSi 72 as interchangeable because the price gap looks small. In the ladle, they behave differently: silicon recovery, slag volume and the amount of aluminium and calcium you add alongside the silicon all move together.
KRIS supplies FeSi 75 and FeSi 72 in 10–50 mm, 3–10 mm and 0–3 mm, packed in 25 kg bags or 1 t jumbo bags. Every lot ships with a COA, and mixed containers are available for buyers running several grades. Send the specification and we will quote against it.
Request a quote →What the numbers actually mean
FeSi 75 guarantees a minimum of 75% silicon; FeSi 72 guarantees 72%. The remaining content is iron plus controlled impurities — aluminium, calcium, carbon, sulphur and phosphorus. Because ferro silicon is sold on silicon content, a lower grade means you buy more tonnes for the same silicon units.
| Parameter | FeSi 75 | FeSi 72 |
|---|---|---|
| Si | 75% min | 72% min |
| Al | 2.0% max | 2.5% max |
| Ca | 1.0% max | 1.2% max |
| C | 0.2% max | 0.2% max |
| Typical use | Final deoxidation, low-Al steels | General deoxidation, cost-driven heats |
Where FeSi 75 earns its premium
For low-aluminium and low-calcium steel grades, FeSi 75 gives you more silicon per tonne of addition and less tramp element carry-over. It also reduces the volume of material you handle per heat, which matters when the ladle is tight on space or the cranes are the bottleneck.
In stainless and electrical steel routes, the consistency of the aluminium and calcium specification is often worth more than the headline silicon price.
Where FeSi 72 is the better buy
If your target chemistry tolerates the slightly higher aluminium and calcium, FeSi 72 usually wins on cost per silicon unit. For long-product mills and foundries running stable, high-volume heats, the recovery difference is small and the saving is real.
The calculation is simple: compare price per tonne divided by guaranteed silicon content, then adjust for your measured recovery. A grade that is 2% cheaper but 3% lower in silicon is not cheaper.
How to specify the order
- State the grade and the guaranteed minimum silicon content, not just “FeSi”.
- Give the size range: 10–50 mm for most furnaces, 3–10 mm for ladle additions or injection.
- Ask for the aluminium and calcium limits you actually need — over-specifying adds cost.
- Request a COA per lot and keep a retained sample for the campaign.
FAQ
Is FeSi 75 always better?
No. It is better when the steel grade needs low aluminium and calcium, or when handling space is limited. For general deoxidation, FeSi 72 can be the lower-cost choice.
Can I mix 75 and 72 in one container?
Yes, provided the bags are clearly marked and the COA is issued per lot. Mixed containers are common for buyers running several grades.
What size should I order?
10–50 mm suits most electric and converter furnaces. Choose 3–10 mm for ladle treatment or injection, and 0–3 mm for briquetting or special additions.
This note is general information for buyers. It is not trading, financial or investment advice. Specifications must be confirmed against the COA for each lot.