More Progress in Steel Production

Iron coming from a blast furnace is called pig-iron, and still contains many impurities which have to be removed before it can be converted into steel. During the Industrial Revolution the demand for steel was so great that better and quicker methods of producing it became necessary. A big step forward was made with the invention of the ‘Bessemer Converter’.

Henry Bessemer (1813 - 1898) was a British civil engineer and inventor. He was elected to the London Royal Society in 1879. During his life-time he patented over a hundred inventions in various fields of technology.

Henry Bessemer’s idea was that the impurities would be burned away if air was blown through molten pig-iron.

An experimental vessel to contain 7 cwts of molten pig-iron was set up in Bessemer’s factory. Air pipes led into the bottom of the vessel, and when the air was turned on, huge flames and showers of sparks shot out of the mouth of the converter, followed by spurts of molten metal and slag. Bessemer and his workers could only retreat and hope for the best. They could not turn off the air because the air-valve had been placed too near to the converter. However, after ten minutes the eruption subsided and it was found that the iron was free of impurities.

The new process was widely adopted, and converters were built which could purify several tons of pig-iron in half-an-hour - an enormous improvement on previous methods. The Bessemer ‘blow’, with flames shooting high into the air, is one of the most dramatic sights in steel manufacture.

Other methods followed, the Siemens ‘open hearth’ furnaces were slower than the Bessemer converter but gave better control. “Electric arc’ furnaces were introduced later.

Two metals, manganese and chromium, discovered in 1774, were to play an important role in steel manufacture. Small quantities of manganese in steel adds greatly to its strength. Chromium is used in the manufacture of stainless steel.