Iron had been the most important material in driving the early stages of the Industrial Revolution. Steel, however, was both stronger and more flexible than iron, and so the question of how to transform iron into steel became a central problem for engineers. In 1856, Henry Bessemer had a major breakthrough, when he discovered that by using a particular kind of clay-lined crucible, it was possible to remove impurities from the molten pig iron - mainly manganese and carbon - after which it was easier to add the necessary alloys to create steel. This piece of equipment, which became known as the Bessmer Converter, enabled the mass-production of cheap steel, which was to revolutionise building techniques in the coming decades.
Editors. "Process for mass-producing steel invented". The Literary Encyclopedia. First published 30 August 2013
[http://www.litencyc.com/php/stopics.php?rec=true&UID=4990, accessed 09 February 2016.]