Charge: Fe2O3 + coke + CaCO3 (limestone flux). Hot air blast from bottom. Zones: (1) Combustion zone (2000 K): C + O2 → CO2 (exothermic, provides heat). (2) Reduction zone (1200 K): CO2 + C → 2CO (Boudouard reaction); then CO is the actual reductant: Fe2O3 + 3CO → 2Fe + 3CO2. (3) Slag zone (1500 K): CaCO3 → CaO + CO2; CaO + SiO2 → CaSiO3 (liquid slag, floats on molten iron). (4) Charge/feed zone (500-800 K): stepwise reduction Fe2O3 → Fe3O4 → FeO → Fe. Products: Pig iron (4% C, Si, Mn — brittle, high m.p.); cast iron (3% C, shaped by pouring into moulds); wrought iron (<0.2% C, puddled, malleable, used for gates/fences); steel (0.2-2% C).