In hydrogen-based direct reduction, iron ore is reduced in solid state — eventually using green hydrogen instead of natural gas — and the resulting DRI is then melted into steel in the EAF. It sounds like an elegant solution. But for refractory technology, this is where new problem areas begin. The decisive difference from conventional scrap-based EAF routes comes down to a single word: carbon — which is simply absent in H-DRI.
In classic EAF operation with carbon-containing DRI (C-DRI), carbon combustion produces CO bubbles in the steel bath. The CO foams the slag, buries the electrodes, and thereby improves heat transfer to over 93% thermal efficiency — while at the same time lowering the FeO content in the slag, which extends the service life of the refractory lining.
With H-DRI, this mechanism is absent entirely. Without carbon, not only is the chemical energy missing as a heat source, but so is the CO-generated foamy slag effect — and with it, one of the most important protective functions for the lining. The arcs radiate more directly onto the vessel wall, increasing thermal load and local wear rates.
Because carbon is missing, remaining iron oxides in the melt bath can no longer be reduced further — FeO increasingly passes into the slag, which raises iron losses and intensifies the attack on the refractory.
Corrosion is the most important wear mechanism for EAF refractory materials. MgO from the lining is soluble in the liquid slag, with saturation levels between 6% and 14% depending on FeO content and bath temperature. A higher FeO share in the slag shifts this saturation unfavorably and significantly accelerates the erosion of MgO-C bricks.
More Slag, Longer Melting Times, Harsher Conditions
The oxidic gangue of DRI not only raises the risk of insufficient slag basicity, but also significantly increases the quantity and volume of process slag compared to scrap-based operation — with a direct effect on lining service life.
Added to this is the phenomenon of so-called “ferrobergs”: at high DRI input rates, unmelted solid clusters can form in the bath, delaying the melting process, extending operating time, and increasing energy consumption. Longer melting times mean longer thermal exposure for the lining — a direct and effective lifespan killer.
The Shaft Furnace: Refractories Under a Reducing H₂ Atmosphere
It’s not just the EAF — the direct reduction shaft furnace itself also raises new questions for refractories. Shaft furnace linings show altered wear patterns under hydrogen operation; the higher gas volumes compared to natural-gas-based processes increase erosion rates in gas heaters and heat exchangers. High-alumina and silicon-carbide-based linings, proven in natural-gas DRI plants, must be re-evaluated for their long-term stability under a pure H₂ atmosphere.
The refractory industry’s responses follow several tracks:
- MgO saturation of the slag through targeted addition of burnt dolomite or magnesite, to slow the corrosive attack on the lining.
- Development of carbon-optimized MgO-C bricks with adapted antioxidants (Al, Si) that slow carbon oxidation under the altered atmospheric conditions.
- Adapted hearth geometries for the DRI-EAF: DRI-based EAFs operate with an increased liquid steel fraction (hot heel) of up to 30% of total melt volume, placing new demands on the bottom lining.
- Digital condition monitoring of the lining through temperature measurements and wear models — a growing field.
Conclusion: Refractories Must Be Rethought
Refractory attack will increase — through carbon dissolution, longer melting times, and FeO erosion — unless refractory systems are fundamentally redesigned. That’s not bad news, but a clear mandate: the transformation to green steel is at the same time one of the most exciting development periods for refractory technology in decades.
