Glossary

In steelmaking, a flux is a material added to the molten metal or furnace charge to help remove impurities such as silica (SiO₂), phosphorus (P), sulfur (S), and alumina (Al₂O₃) from the ore, scrap, or additives. Fluxes work by chemically combining with these unwanted substances to form a molten slag, which floats on top of the metal and can be easily removed.

Common flux materials include limestone (CaCO₃), dolomite (CaMg(CO₃)₂), fluorspar (CaF₂), and lime (CaO). These substances melt at high temperatures and react with impurities to form stable, low-density compounds that separate from the molten steel.

Here’s how flux works in the steelmaking process:

- Addition to the furnace: Flux is introduced into the blast furnace, basic oxygen furnace (BOF), or electric arc furnace (EAF) along with iron ore, coke, and other raw materials.

- Chemical reaction: Under high heat, the flux decomposes (e.g., limestone breaks down into calcium oxide (CaO) and carbon dioxide (CO₂)). The CaO then reacts with acidic impurities such as silica to form calcium silicate (slag).

- Slag formation: The molten slag collects at the top of the steel bath, trapping non-metallic impurities and helping to protect the molten metal from oxidation.

- Removal: Once the slag solidifies, it can be removed, leaving behind cleaner, higher-quality steel.

Fluxes also serve secondary purposes: they regulate furnace temperature, protect refractory linings, and improve the fluidity of slag to ensure complete separation of impurities.