Process Overview
The Electric Arc Furnace melts metallic charge by passing high-current electricity (50–150 kA) through graphite electrodes to strike arcs between the electrode tips and the charge material, generating temperatures in excess of 3,000 °C at the arc. Modern EAFs range from 60 to 400 t capacity. The process is highly flexible: it can melt 100% scrap, 100% DRI/HBI (hot briquetted iron), or any combination. This flexibility makes the EAF the dominant process for electric steelmaking and the primary vehicle for decarbonising the steel industry, since it can operate on renewable electricity.
Charge Composition: Scrap vs DRI
Scrap-based EAFs dominate in the Americas and Europe, where ferrous scrap is abundant. The scrap mix — typically comprising 60–80% heavy melting scrap (HMS), 10–20% shredded scrap, and 5–10% prime grades — determines the residual tramp element content (Cu, Sn, Ni, Cr), which limits the achievable steel grades. DRI/HBI-based charges are used where scrap quality is insufficient (e.g., flat-rolled automotive grades) or where natural gas is cheap (Middle East, India). DRI typically contains 90–94% total iron, 1.5–3.5% carbon, and 2–5% gangue (SiO₂, Al₂O₃), which increases lime and electrode consumption relative to a clean scrap charge.
Electrode Operation and Power-On Time
Three graphite electrodes (diameter 550–750 mm for large furnaces) are lowered into the charge and the arc is struck. During the initial bore-down phase, the electrodes penetrate into the scrap and the arc is shielded from the furnace shell by the surrounding charge. As a liquid pool forms, the furnace transitions to flat bath operation and power input is increased to maximum. Power-on time for a 150 t heat is typically 35–55 minutes; total tap-to-tap time is 45–70 minutes including charging, tapping, and furnace preparation. Specific energy consumption is 300–450 kWh/t for high-quality scrap charges, rising to 500–650 kWh/t for DRI-heavy charges.
Foamy Slag Practice
Maintaining a deep, foamy slag — typically 300–600 mm deep — throughout the flat bath period is essential for energy efficiency and electrode protection. Foaming is achieved by injecting oxygen and carbon (coal or graphite fines) through submerged tuyeres or wall-mounted injectors. The injected oxygen reacts with bath carbon to produce CO bubbles; these bubbles are stabilised by the iron oxide content of the slag (FeO typically 15–25%) and the slag viscosity. A well-maintained foamy slag reduces electrical energy consumption by 10–20% by shielding the arc and reducing radiation losses to the furnace shell.
Tap-to-Tap Cycle and Productivity
EAF productivity is measured primarily by tap-to-tap time and power-on time. Modern ultra-high-power (UHP) furnaces with 900–1,200 kVA/t transformer ratings achieve tap-to-tap times of 45–60 minutes. Continuous charging technology (Consteel, finger-shaft, twin-shell) improves yield and reduces energy consumption by continuously feeding preheated scrap. Eccentric bottom tapping (EBT) replaces the traditional spout, enabling slag-free tapping and reducing reoxidation of the steel during ladle transfer.
End-Point Chemistry
At tap, EAF steel typically contains 0.05–0.15% C, with temperature 1,600–1,650 °C. Phosphorus removal is less efficient in the EAF than in the BOF because the process operates with a smaller slag volume and higher FeO activity; DRI charges with gangue-derived slag can remove P more effectively. Like BOF steelmaking, all EAF heats require secondary metallurgy (LF, VD, RH) for final composition and cleanliness targets.