The principal ores of iron are oxides and carbonates, and iron ores are widely distributed throughout the world. Until the eighteenth century, oxide ores of iron were reduced to the metal using charcoal as a reducing agent, and steel, which is basically an alloy of iron and carbon, was produced by the cementation process, in which wrought iron bars were packed, together with charcoal, in cast iron boxes and heated to about 1000°C. At the high temperature carbon would slowly diffuse into the iron. The quality of steel produced in this way tended to be erratic, and in the mid-eighteenth century the crucible process was invented. Bars of steel, produced by cementation, were melted in a crucible and the homogeneous melt obtained was cast into bars. The major ferrous constructional materials until the latter part of the nineteenth century were cast iron and wrought iron, and many road and railway bridges built in these materials are still in service. The pattern of working was revolutionised in 1856, when Sir Henry Bessemer introduced his converter process for steel making. The open-hearth process followed a decade later, and these two processes held sway for almost a century.
KeywordsCritical Temperature Carbon Steel Cast Iron Blast Furnace Maraging Steel
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