How did coal replace charcoal in iron and steel production?

The transition from charcoal to coal in iron production was driven by a critical scarcity of wood for charcoal as iron output increased during the 16th century. This environmental pressure necessitated the adoption of coal in the form of [coke]—a solid, carbon-rich residue produced by heating bituminous coal to remove volatile constituents.12

While Dud Dudley experimented with "pit-coal" in the early 17th century, the successful, widespread smelting of iron ore with coke is most notably credited to Abraham Darby in 1709. The shift to coke offered significant industrial advantages:134
* Structural Strength: Unlike charcoal, which was too weak to support a heavy charge, coke’s higher strength allowed for the construction of much larger furnaces.13
* Increased Efficiency: Larger furnaces enabled significantly higher production volumes, with weekly outputs of pig iron increasing to 5–10 tons.1
* Economic Viability: The industry was freed from its reliance on forests and encouraged to relocate near major coalfields, facilitating the mass production of iron that fueled the Industrial Revolution.5

Following this, the development of the steam engine and Henry Cort’s 1784 puddling furnace further integrated coal-fired technology into the conversion of pig iron into malleable wrought iron.1