Ironmaking and Steelmaking
The exam tests the flow of iron units from burden to liquid steel: what each unit operation does, which reactions it controls, and the slag and temperature rules that make it work.
Ironmaking
- Blast furnace zones from top to bottom: granular zone, cohesive (softening–melting) zone, active coke zone, raceway at the tuyeres, hearth. Hot blast at roughly 1100–1250 °C enters through tuyeres, burning coke to CO and generating the heat and reducing gas.
- Burden: sinter and pellets (agglomerated fines with flux), lump ore and coke. Sinter plant and pellet indurator control size, strength and reducibility.
- Hot metal typically leaves at about 1500 °C with 4.0–4.5% C, 0.3–0.6% Si, plus Mn, P and S. Slag basicity around 1.0–1.2 keeps it fluid while still removing some sulphur.
Steelmaking
- Basic oxygen furnace: high-purity oxygen impinged on hot metal plus scrap. Oxidation of C, Si and Mn supplies the heat, so the process is autogenous - no external fuel. Lime flux builds a basic oxidising slag (basicity 3–4) that strips phosphorus.
- Electric arc furnace: scrap, DRI/HBI or pig iron, arcing electrodes, foamy slag practice.
- Deoxidation with Al or Si, then secondary metallurgy (ladle furnace, vacuum degassing, RH) for sulphur, hydrogen, inclusion and temperature control.
- Continuous casting: tundish, submerged entry nozzle, mould with oscillation and mould flux, secondary cooling, withdrawal straightener.
Worked example
A BOF slag contains 4.2 t SiO2 and 3.0 t CaO. Target basicity 3.5 needs 3.5 × 4.2 = 14.7 t CaO total, so add 11.7 t lime, adjusting for the CaO already in the charge.
Traps that cost marks
Claiming the BOF needs fuel. Confusing phosphorus removal (high basicity, oxidising, lower temperature) with sulphur removal (reducing basic slag, ladle treatment). Ignoring that the EAF is scrap- or DRI-based while the BOF is hot-metal-based.