Two steps are needed to make iron and steel – the key materials of the industrial era - from iron ore. First, the ore has to be smelted in the blast furnace to produce pig iron, which is then refined in the fire to produce wrought iron or steel. Both steps are dependent on the type of fuel used. Hard ... more
Two steps are needed to make iron and steel – the key materials of the industrial era - from iron ore. First, the ore has to be smelted in the blast furnace to produce pig iron, which is then refined in the fire to produce wrought iron or steel. Both steps are dependent on the type of fuel used. Hard coal is not suitable for producing iron because its trace elements, above all sulphur, can damage the metal. For this reason charcoal was used in furnaces and forges until the start of the 18th century when a shortage of firewood made it very expensive. Thereupon Abraham Darby, the owner of an ironworks in the Midlands county of Shropshire which was rich in coal, resorted to a fuel that was used in malt houses and coked the coal hermetically. In this way he was able to remove the harmful trace elements. From 1709 onwards Darby was able to use coke to produce iron in his blast furnace at Coalbrookdale.
This was a decisive step. Nonetheless many decades were to pass before the new fuel could establish itself: since a huge amount of coke was necessary to make iron and steel, it was only economically viable in mass production in large furnaces. But the technical preconditions were still not in place; more than anything else powerful blowing engines were needed.
Hard coal was soon to revolutionise refining processes. The second step in producing wrought iron is necessary because, when the pig iron emerges from the blast furnace it still contains a very high proportion of carbon. True, you can cast it: but it is too brittle either to forge or roll. The carbon is therefore burnt off at high temperatures and the resulting iron can be processed in many different ways. During this process it is vital to prevent the pig iron from coming into direct contact with the coke, which still contains many destructive elements. In 1740 a Sheffield man named Benjamin Huntsman came up with a solution. He filled the pig iron into closed crucibles which were then heated up in a coke oven. The result was steel – but later regulations prescribed that steel should not contain more than 1.6% of carbon. For many decades hard crucible steel was in great demand as a valuable basic material, and the region around Sheffield became a centre for the iron industry.
In 1784 Henry Cort came up with an alternative: he refined pig iron in a half-open furnace, on which the iron was separated from the burning coal only by a low wall. The hot air from the furnace was conducted over the pig iron to heat it. At the same time it was stirred by a worker with a long rod to release the carbon into the air. The result of this "puddling" process was a highly resilient iron which could be used equally for making swords and ploughshares. Cort also invented the heavy rolling process, whereby the iron could be shaped into sheet iron, pipes and railway lines. Now iron began to replace timber as the universal working material and chimneys and blast furnaces began to spring up at ironworks in the coalfields of Shropshire and Staffordshire, in the south of Scotland and in Wales. By the end of the 19th century Great Britain had become the world's largest producer of iron.
The government in France now began to commit all its efforts to producing iron, not least because it was afraid it would fall behind in the manufacture of arms. It lured over British experts to France and in the 1780s set up the Royal Foundries at Le Creusot in Burgundy. Like the glassworks, also at Le Creusot, and the older salt works at Arc et Senans, the symmetrically designed plant reflected the centralised industrial policies of the French state.
Other European regions only reached the level of British industry in the 19th century. The Belgian iron region around the rivers Sambre and Maas received a boost in 1827 when the first coke furnace went into action in Charleroi. The German iron industry originated in Upper Silesia and the Saar region: other isolated works arose in the countryside, like those in Wetter in the Ruhrgebiet and Rasselstein, near Neuwied. But the German economy only really began to get moving in 1834 with the establishment of the Customs Union. Within the space of a few decades a close-knit industrial topography sprang up in the Ruhrgebiet, dominated by pithead towers, blast furnaces and working-class housing settlements.
In 1828 a Scotsman by the name of James Beaumont Neilson came up with the last vital improvement to blast furnaces. He discovered that, by blowing in hot air, it was possible to drastically reduce the amount of coke needed. Production exploded in the subsequent years. In 1850 Great Britain was producing at least 10 times as much pig iron as it was at the start of the century; by 1900 more than 30 times as much.
Give the boom in iron, it was not long before the next technical advance occurred. In 1856 Henry Bessemer, yet another Englishman, invented a refractory-lined pear-shaped vessel for refining iron. When it was filled with pig iron and blasted with air, a spectacular reaction occurred within the Bessemer converter. The silicon burnt off and heated the glowing iron to such an extent that almost all the carbon was removed, without having to insert any fuel from outside. The result was high-quality Bessemer steel which could be used to manufacture cannons, railway lines and knives.
Almost at the same time competitors – this time on the Continent - were developing yet another alternative to the open refining furnace. Wilhelm Siemens used to the warmth from waste gases in his "regenerative furnace" to additionally heat up the combustion air needed to process the pig iron. In this way iron could be smelted at higher temperatures than had previously been possible, and at the same time fuel could be saved. A French ironworks owner by the name of Pierre Martin brought the process to maturity in 1864. The Siemens-Martin furnace was able to produce top quality steel like that needed for shipbuilding plates, and for many decades it was regarded as the very best method of producing steel.
But the more problems in processing poor quality iron ore containing phosphorus. In 1879 a chemist by the name of Sidney Gilchrist Thomas came up with a solution. He had a Bessemer converter lined with a basic material which eliminated phosphorus. Now it was possible to use iron ore areas like Lorraine, for example; but the region which profited the most was the Ruhrgebiet. Here the steelworks were able to produce huge amounts of wire, pipes, and construction steel - not to mention railway lines - from low quality steel.
Again in 1879, Wilhelm Siemens succeeded in making a further improvement. His electric arc furnace was able to produce very high temperatures with ease. That said, electric power was more expensive than coke. For this reason the process was initially restricted to the manufacture of highly stable steel which was alloyed with chromium, nickel or tungsten. The resulting material could be used to make large corrugated sheets, marine propellers, armour plating and engineering tools. It was only after the First World War that electric steel was mass manufactured. By that time steel production in Great Britain, the cradle of industrialisation, had been overtaken by the USA and Germany.