Ingot of Bessemer steel, c 1865.

UNITED KINGDOM - FEBRUARY 19: Sir Henry Bessemer (1813-1898) cast this ingot at a works in Greenwich, London. Bessemer learned metallurgy working in his father�s foundry. In 1856, in response to demand for stronger cannon able to fire a new type of artillery shell in the Crimean War, he invented the Bessemer process, enabling molten pig-iron to be turned into steel by a blowing air through it in a tilting converter. This was the first process for producing large amounts of good quality steel cheaply. Previously, steel was available in small quantities produced by either the cementation or crucible processes. Hence engineers were restricted to using wrought iron, which is relatively strong in tension, or cast iron, which is brittle and weak in tension. (Photo by SSPL/Getty Images)