Step 1 — Ironmaking
In the integrated route, the first step is converting iron ore into liquid iron. This happens in a blast furnace — a tower up to 100 metres tall that is continuously charged with iron ore, coke (a carbon-rich fuel made from coal), and limestone.
Hot air is blown into the bottom of the furnace, igniting the coke and creating temperatures above 2,000°C. The carbon in the coke reacts with oxygen in the ore, stripping it away and leaving liquid iron — called hot metal or pig iron. The hot metal taps out of the furnace at around 1,450°C and is transported to the steelmaking shop.
An alternative to the blast furnace is Direct Reduction (DRI), which uses natural gas or hydrogen instead of coke to reduce iron ore. DRI is used primarily in regions with cheap gas or as a feedstock for electric arc furnaces.
Step 2 — Steelmaking
Hot metal from the blast furnace contains too much carbon (around 4–5%) and a range of other impurities to be useful as steel. The steelmaking step burns these off.
In a Basic Oxygen Furnace (BOF), a lance blows pure oxygen at supersonic speed into the liquid iron. The oxygen reacts with carbon, silicon, and phosphorus, oxidising them into gases and slag that float off the top. The whole process takes about 20 minutes and produces a heat of liquid steel ready for the next step. The cross-section below shows the vessel internals during a blow — the thick refractory lining, the descending lance, the slag layer sitting above the steel bath.
In an Electric Arc Furnace (EAF), powerful graphite electrodes create an electric arc that generates intense heat — up to 3,500°C — melting a charge of scrap steel. The EAF process takes around 40–60 minutes per heat.
Step 3 — Secondary metallurgy (refining)
After the furnace, the liquid steel is still not quite right — its temperature may be too low, its chemistry slightly off, or it may contain dissolved gases that would cause defects. Secondary metallurgy fixes this.
The steel is tapped into a large ladle (a heat-resistant vessel that holds 100–300 tonnes of steel) and moved to a Ladle Furnace (LF). The ladle furnace heats the steel with electrodes and allows fine adjustments to the chemical composition by adding alloys. For ultra-clean steel grades, the ladle may then go to a Vacuum Degasser (RH or VD), where dissolved hydrogen and nitrogen are pulled out under vacuum. This step is critical for automotive and electrical steel grades.
The EAF route — from scrap to steel
In the EAF mini-mill, an electric arc furnace melts a charge of scrap steel (or DRI) using three large graphite electrodes powered by a 3-phase AC transformer rated at 80–250 MVA. The arc temperature reaches 3,500 °C, melting 100–250 t of scrap in 30–40 minutes. Tap-to-tap cycle time is 40–60 minutes total — charge, melt, refine with oxygen injection, and tap.
The EAF route requires no iron ore, no coke ovens, and no blast furnace — just scrap, electricity, and lime. CO₂ emissions per tonne of steel are typically 0.4–0.8 t CO₂/t when using grid electricity (vs 1.8–2.0 t CO₂/t for BF-BOF) — and approach near-zero when powered by renewable electricity.
After the EAF, steelmaking is identical to the integrated route: the ladle proceeds to the ladle furnace for temperature and chemistry adjustment, then to the continuous caster. The EAF does not eliminate secondary metallurgy — it just eliminates the ironmaking step.