Steelmaking process: Electric arc furnace steelmaking
An electric arc furnace (EAF) is a cylindrical refractory-lined vessel equipped with graphite electrodes that uses the high temperatures generated by an electric arc to melt scrap steel, direct reduced iron, or pig iron. Due to its efficiency, flexibility, and relatively low environmental impact, this process is widely used and increasingly adopted in modern steelmaking.
Electric Arc Furnace Steelmaking Process
Charging phase
The process begins with charging the furnace with scrap steel, alloys, and flux. The composition and stratification of the scrap steel are carefully planned to ensure efficient melting and the desired chemical properties of the final steel product.
Melting stage
After charging, the powerful current generates extremely high heat (the arc zone reaches up to 3,000°C). During the initial drilling, 15% of the scrap steel is melted. After a few minutes, the electrodes penetrate the scrap deep enough to allow for higher voltages without damaging the furnace structure.
Refining stage
The refining stage is crucial for adjusting the chemical composition of molten steel and removing impurities.
1. Oxidation period: Oxygen is injected to form oxides, which escape in gaseous form or form part of the slag, thereby oxidizing impurities.
Fe + 1/2O₂ → FeO（Slag）
Si + O₂ → SiO₂（Slag）
Mn + 1/2O₂ → MnO（Slag）
2 Cr + 3/2 O₂ → Cr₂O₃（Slag）
4P + 5O₂ → P₂O₅（Slag）
S + O₂ → SO₂（gas）
2Al + 3/2 O₂ → Al₂O₃（Slag）
2. Decarburization: reducing the total carbon content of steel.
C + O₂ → CO₂
C + 1/2O₂ → carbon monoxide
3. Reduction period: After oxidation, a reduction environment is established in a specific amount (by adding reducing agents such as carbon and silicon) to recover metal elements and improve the quality of steel.
Slag formation
Slag plays a crucial role in capturing impurities and protecting molten steel from atmospheric gases. It consists of a combination of oxidized impurities and added flux.
2 Cr₂O₃ + 3 Si → 4 Cr + 3 SiO₂
SiO₂ + CaO → CaSiO₃
P₂O₅ + 3CaO → Ca₃（PO₄）₂
Electric arc furnaces (EAFs) are less effective than blast furnaces at removing impurities because they rely primarily on waste materials, which may contain persistent residual elements such as copper, nickel, and tin. While blast furnaces (BFs) operate under optimized reducing conditions to remove impurities like sulfur and phosphorus through slag chemistry, the oxidizing atmosphere and limited slag capacity of electric arc furnaces (EAFs) result in lower efficiency in impurity removal. Furthermore, the BF-BOF process offers comprehensive refining, while EAFs place greater emphasis on recycling and sustainability.
Steel tapping:
Once the required chemical composition and temperature are reached, the molten steel is drawn from the furnace into a ladle for further processing or casting.
