Bessemer Process (1856): Cheap Steel for the Industrial Age

The Bessemer process, announced by the English inventor Henry Bessemer in August 1856, was the first method of making steel cheaply and in bulk. By blowing air through molten pig iron, a converter could produce several tonnes of steel in about twenty minutes, a job that had taken days and large amounts of fuel by older methods. After early setbacks, Bessemer steel transformed railways, shipbuilding and construction in Europe and North America.

Background: iron, steel and their limits

In the early nineteenth century industry ran on two kinds of iron. Cast iron, straight from the blast furnace, was strong in compression but brittle. Wrought iron, made by laboriously stirring molten iron in a puddling furnace, was tough but relatively soft and could only be produced in small batches.

Steel, which lies between them in carbon content, combined strength and toughness. But it was made mainly by the crucible process, in small clay pots in places such as Sheffield, and was expensive. It was used for tools, cutlery and springs, not for rails or bridges.

Engineers wanted a material that was both strong and workable in large pieces. Railways in particular suffered from wrought-iron rails that wore out quickly under heavier locomotives and denser traffic, sometimes needing replacement within a few years on busy lines. Shipbuilders, boilermakers and gunmakers faced similar limits. Whoever could make steel in quantity and at the price of iron stood to reshape industry.

Henry Bessemer’s discovery

Henry Bessemer (1813–1898) was a prolific inventor who had already made a fortune from a method of producing bronze powder for gold paint. During the Crimean War he designed a rotating artillery shell, and discussions with French officers convinced him that guns needed a stronger metal than cast iron.

Experimenting in London, he noticed that air blown over or through molten iron burned out carbon and silicon, and that the reaction itself produced intense heat. The metal grew hotter rather than cooler. He patented the idea in 1855 and 1856 and described it in a paper titled “The Manufacture of Malleable Iron and Steel without Fuel”, read at the British Association for the Advancement of Science in Cheltenham in August 1856. The Times printed it, and ironmasters rushed to buy licences.

How the converter worked

The Bessemer converter was a large egg-shaped steel vessel lined with fireproof brick and mounted on pivots so that it could be tilted. Molten pig iron was poured in, and air was forced through holes in the bottom. For several minutes a roaring flame and shower of sparks poured from the mouth as impurities burned away. When the flame changed, the operator knew the blow was finished and tipped out the steel.

The whole process took around fifteen to twenty minutes and used no fuel beyond the heat already in the molten iron. By comparison, puddling a similar quantity of wrought iron took many hours of skilled, exhausting labour.

Early problems and their solutions

Enthusiasm soon turned to disappointment. Many licensees produced steel that cracked or crumbled. Bessemer’s own successful trials had used pig iron that happened to be low in phosphorus, but most British ores contained phosphorus, which made steel brittle and which the original converter could not remove. Blowing also left too much oxygen dissolved in the metal.

Others supplied key fixes. The metallurgist Robert Forester Mushet showed in 1856 that adding spiegeleisen, an alloy of iron, manganese and carbon, removed oxygen and restored the right amount of carbon. In 1858 the Swedish ironmaster Göran Fredrik Göransson produced good Bessemer steel at Edsken using pure Swedish iron. Bessemer restored confidence by opening his own steelworks in Sheffield in 1858, using low-phosphorus ores, and selling steel at prices rivals struggled to match.

The phosphorus problem was solved only in 1878, when Sidney Gilchrist Thomas and his cousin Percy Gilchrist lined the converter with basic materials such as dolomite, which absorbed phosphorus into the slag. This “basic” Bessemer process opened up the phosphorus-rich ores of Lorraine, Belgium and Germany.

In the United States, the Kentucky ironmaster William Kelly had experimented with air-blown iron independently from the late 1840s and received a US patent in 1857. American Bessemer production began in the mid-1860s, and the engineer Alexander Holley designed many early plants, including Andrew Carnegie’s Edgar Thomson Works near Pittsburgh, opened in 1875.

Consequences: steel everywhere

Cheap steel arrived just as railways spread across continents. Steel rails lasted far longer than wrought-iron ones under heavy traffic, and from the 1860s and 1870s railway companies switched to them on a large scale. The price of steel in Britain is commonly said to have fallen from around £40 to £6–7 a ton within a couple of decades, though figures vary with grade and year.

Steel also changed shipbuilding, boilers, machinery and weapons, and made possible the steel frames of later tall buildings, which together with safe lifts such as the Otis safety elevator reshaped cities. World steel output grew from well under a million tonnes in the 1850s to tens of millions by 1900, with the United States and Germany overtaking Britain.

The process also changed work and towns. A Bessemer plant needed fewer highly skilled puddlers and more machine operators, and it encouraged very large integrated works that combined blast furnaces, converters and rolling mills. Steel towns grew up around them, from Sheffield and Middlesbrough to Pittsburgh and the Ruhr, together with harsh conditions, long shifts and frequent industrial conflict.

Henry Bessemer’s later life

Bessemer became rich from his own works and from royalties paid by licensees in Britain and abroad. He was elected a Fellow of the Royal Society and knighted in 1879. He continued to invent until old age, with mixed results. One project was a passenger steamer with a swinging saloon meant to stay level and prevent seasickness on the English Channel; the ship, launched in the 1870s, handled badly and the scheme was abandoned. He died in London on 15 March 1898 and published an autobiography that appeared after his death, in 1905.

By the numbers

Timeline

• 1855: Bessemer takes out his first patents on air-blown steelmaking.
• 1856, August: Bessemer’s paper on making steel “without fuel” is read at the British Association meeting in Cheltenham.
• 1856: Robert Mushet patents the use of spiegeleisen to improve the steel.
• 1857: William Kelly receives a US patent for his pneumatic process.
• 1858: Göransson makes good Bessemer steel in Sweden; Bessemer opens his own works in Sheffield.
• 1875: Carnegie’s Edgar Thomson Works opens near Pittsburgh.
• 1878: Thomas and Gilchrist solve the phosphorus problem with a basic lining.
• 1879: Henry Bessemer is knighted.

Legacy

The Bessemer process was gradually overtaken by the Siemens–Martin open-hearth furnace, which allowed better control of quality, and after 1950 by the basic oxygen process. Yet the basic oxygen process works on the same principle Bessemer exploited, oxidising impurities with a blast of oxygen. Preserved converters stand at Kelham Island Museum in Sheffield and in Pittsburgh, and towns such as Bessemer, Alabama, carry his name. It joined earlier milestones such as the Iron Bridge at Coalbrookdale in the story of metal remaking the built world.

Why it matters

The Bessemer process turned steel from a costly specialist material into a cheap bulk commodity. That change underpinned the railways, steamships, bridges and skyscrapers of the late nineteenth century and helped shift industrial leadership toward the United States and Germany.