The Bessemer Process and the Age of Steel

Steel is stronger and more flexible than wrought iron, but before the 1850s it was expensive and made only in small quantities. In 1856 Henry Bessemer announced a process that blew air through molten pig iron in a large vessel, called a converter, burning off carbon and impurities in minutes; American William Kelly had experimented with a similar idea. Early Bessemer steel was sometimes brittle until additives such as manganese improved it.

In the 1860s the Siemens-Martin open-hearth process offered greater control, and in 1878 Sidney Gilchrist Thomas and Percy Gilchrist found a way to use phosphorus-rich iron ores, opening vast deposits in Lorraine and elsewhere. Cheap steel transformed railways, ships, bridges, machinery and buildings, and historians see it as a foundation of the Second Industrial Revolution of roughly 1870 to 1914, when Germany and the United States began to overtake Britain.