The Bessemer process was the first inexpensive industrial process for the mass-production of steelfrom molten pig iron. Its inventor, Sir Henry Bessemer, revolutionized steel manufacture bydecreasing its cost, increasing the scale and speed of production of this vital material, anddecreasing the labor requirements for steel-making. The key principle was the removal of excesscarbon and other impurities from the iron by oxidation with air being blown through the molteniron. The oxidation also raises the temperature of the iron mass and keeps it molten.Sidney Gilchrist Thomas developed a more sophisticated process to eliminate the phosphorusfrom iron. Collaborating with his cousin, Percy Gilchrist, a chemist, he patented his process in1878. His process was especially valuable on the continent of Europe, where the proportion ofphosphoric iron was much larger than in England, and both in Belgium and in Germany the nameof the inventor became more widely known than in his own country. In America, although nonphosphoriciron largely predominated, an immense interest was taken in the invention.The next great advance in steel making was the Siemens-Martin process. Sir Charles WilliamSiemens developed his regenerative furnace in the 1850s, claiming in 1857 to be recovering2The Second Industrial Revolutionenough heat to save 70-80% of the fuel. The furnaceoperated at a high temperature by using regenerativepreheating of fuel and air for combustion. Throughthis method, an open-hearth furnace can reachtemperatures high enough to melt steel, but Siemensdid not initially use it for that. French engineer Pierre-Émile Martin was the first to take out a license for theSiemens furnace and apply it to the production of steelin 1865. The Siemens-Martin process complementedrather than replaced the Bessemer process. Its mainadvantages were that it did not expose the steel to excessive nitrogen (which would cause thesteel to become brittle), it was easier to control, and that it permitted the melting and refining oflarge amounts of scrap steel, lowering steel production costs and recycling an otherwisetroublesome waste material. It became the leading steel making process by the early 20th century.The availability of cheap steel allowed building large bridges, railroads, skyscrapers, and largeships. Other important steel products - also made using the open hearth process - were steelcable, steel rod and sheet steel. With large amounts of steel it became possible to build muchmore powerful guns and carriages, tanks, armored fighting vehicles and naval ships.
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