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History of Iron
Iron occurs in the native metal state as meteoric iron which was
exploited by the North American Indians to make weapons. Since iron has a
high melting point of around 1550oC it was commonly produced in the Old
World by reducing the ore to metal in the solid state to produce bloomery
iron which was then wrought to give low carbon wrought iron (0.1-0.2 % C).
The Hittite kingdom of the mid second millennium BC was one of the major
early iron producing centers and was thought to have a monopoly of iron
production, and iron production became widespread in Greece and the
Mediterranean by the beginning of the 1st millennium BC. Iron seems to have
been used in India from about the late second millennium BC and iron
smelting and the use of iron was especially well established in the south
Indian megalithic cultures of this period.
The forging of wrought iron seems to have reached its zenith in India in
the first millennium AD. The earliest large forging is the famous iron
pillar at New Delhi dated by inscription to the Gupta period of the 3rd c.
AD at a height of over 7 m and weight of about 6 tons. The pillar is
believed to have been made by forging together a series of disc-shaped iron
blooms. Apart from the dimensions another remarkable aspect of the iron
pillar is the absence of corrosion which has been linked to the composition,
the high purity of the wrought iron and the phosphorus content and the
distribution of slag.
In fact the use of high-carbon iron alloys was developed in parts of Asia
before they came into vogue in Europe. We may mention high-carbon steel from
India and cast iron from China, both of which required higher furnace
temperatures and more reducing conditions than the bloomery iron process.
Cast iron was produced in China prior to other parts of the world in small
blast furnaces which were precursors to the modern blast furnaces. Cast iron
with a high carbon content of between 2-4% C is a brittle and fairly
unworkable alloy with poor strength, but it has the lowest melting point in
the iron-carbon system being a eutectic at around 1100oC. By the early
Christian era in China cast iron was used on a very large scale for
producing tools, weapons, vessels and utensils.
In Europe the use of cast iron was not appreciated until after about the
14th c. AD when it was used for making cannons. By the end of the 18th
century cast iron began to be used extensively in England in building and
construction. The famous Mysore Palace in Mysore near Bangalore built by the
Wodeyars at the turn of the century was the first royal palace in India to
make use of cast iron in architectural construction.
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Iron
Element (Fe), Atomic No. 26, density 7.87 kg/litre, M.Pt 1537°C
First isolated in prehistoric times, for many years iron was not used as
currency as it was heavy, brittle in the most commonly available cast form,
and liable to rust.
(Before someone tells me that copper and gold are denser, I mean heavy in
terms of its weight per unit value.)
Cast iron contains between 3% and 4.2% C, melting at between 1150°C and
1250°C, depending on the carbon content. Iron alloys containing small levels
of carbon are normally called steel.
Source:
http://www.tclayton.demon.co.uk/metal.html
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