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Bessemer steel process
1856 (Bessemer; William Kelly in parallel)· Invention or discovery· Tools, energy & materials
Mostly agreedGood evidence; some details, dates or numbers uncertain.
A method of blowing air through molten iron to make steel quickly and cheaply in large batches.
See it on the Technology & Medicine map →How it works
Steel was costly and made in small batches. Henry Bessemer announced in 1856 that blowing air through molten pig iron in a 'converter' burns off carbon and impurities, and that the reaction's own heat keeps the metal liquid without extra fuel. Several tons became steel in about 20 minutes. Fixes followed: Robert Mushet's manganese additive, and in 1878 Thomas and Gilchrist's lining for phosphorus-rich ores. American William Kelly had worked on a similar process.
Why it mattered
Cheap steel made possible long-lasting rails, big bridges, steel ships and skyscraper frames, and built fortunes such as Andrew Carnegie's.
How we know
Bessemer's 1856 paper and patents, Kelly's 1857 US patent, production statistics, and surviving converters, such as the one at Kelham Island Museum, Sheffield.
Still unknown or debated
Credit is disputed between Bessemer and Kelly; a claim that Kelly learned from Chinese ironworkers is unproven.
Connections (4)
▸Iron smelting (the Iron Age) was transformed by the Bessemer steel processWell documented
The connection
For about 3,000 years smiths made iron by smelting ore with charcoal, then hammering it. Steel, iron with just the right amount of carbon, was costly and made in small batches. Bessemer blew air through molten pig iron, burning off carbon and impurities in about 20 minutes, turning steel into a bulk material.
When and how
Ironmaking from Anatolia about 1400 BC; Bessemer in London, 1856, with his own steelworks in Sheffield from 1858.
How we know
Production figures: world steel output rose from under one million tons around 1870 to roughly 28 million by 1900, by estimates.
Debates and open questions
Chinese ironworkers had removed carbon from cast iron by blowing or stirring for centuries; whether any of that knowledge reached Bessemer or Kelly is unproven.
▸Gunpowder weapons and cannon drove the search that produced the Bessemer steel processWell documented
The connection
During the Crimean War, Bessemer designed a spinning artillery shell. Military men told him existing cast-iron cannon could not safely fire it. Seeking a stronger metal for guns, he experimented with blowing air through molten iron and found that it purified the metal into steel.
When and how
London and France, 1854–56; Bessemer tested his shell at Vincennes with encouragement from Napoleon III.
How we know
Bessemer's patents and his autobiography (1905) describe the chain from shell to gun metal to converter; the account is his own, written decades later.
Debates and open questions
How much of the story is Bessemer's later polishing, and whether his other ironmaking work would have reached the process anyway, is uncertain.
▸Railways created demand for the Bessemer steel processWell documented
The connection
Wrought-iron rails wore out fast under heavy trains, sometimes within months on busy lines. Steel rails lasted many times longer. Railways were the biggest early buyers of Bessemer steel, and their orders financed new steelworks such as Andrew Carnegie's Edgar Thomson Works near Pittsburgh.
When and how
First steel rail laid at Derby station, England, 1857, using Robert Mushet's steel; US from the 1860s; Edgar Thomson Works, 1875.
How we know
Production data show rails took most American Bessemer steel into the 1880s; the Derby rail lasted about 16 years where iron had lasted months.
Debates and open questions
Whether railways created the steel industry or cheap steel created modern railways is partly circular; historians debate railways' overall pull on industry.
▸Bessemer steel process supplied the steel frames of Skyscrapers (steel frames and safety elevators)Well documented
The connection
Bessemer's converter blew air through molten iron to make steel by the ton, making it cheap. Steel beams are stronger and less brittle than cast iron, so frames could rise higher. The Home Insurance Building used Bessemer steel beams in its upper floors in 1885, and steel frames soon became standard.
When and how
Chicago, 1884–85, with beams from Carnegie, Phipps and Company mills in Pittsburgh. Open-hearth steel later replaced Bessemer steel for most structural work.
How we know
Construction records and the 1931 examination of the Home Insurance Building's frame found Bessemer steel beams above the sixth floor.
Debates and open questions
How much of the early frame was iron versus steel, and how much it still relied on masonry walls, is debated, which fuels the 'first skyscraper' argument.