View source for Indirect reduction of steel

'''Indirect reduction''' is the production of [[steel]] from [[iron ore]] in two steps: first adding carbon, then removing carbon.

Note: Numerous details have been left out for the sake of clarity. The information below is not sufficient for the production of high-quality metal.

==Process overview==
'''Pig iron''' (which is high-carbon iron similar to [[cast iron]], but not intended as a final product) is produced in a blast furnace and then has excess carbon removed in an oxygen furnace.

[[Oxygen]] is blown into the molten pig iron at supersonic speeds, where it burns with [[carbon]] (a stronger reducing agent than iron) to produce [[carbon dioxide]] gas (which escapes) and heat. The reaction is highly energetic and serves to agitate the molten metal (mixing it) and also heats it (molten pig iron comes out of the blast furnace at less then the melting point of steel). The '''Bessemer converter''', the original 19th century oxygen furnace, had a lining of acidic materials. The modern furnace is known as the '''basic oxygen furnace''', due to its basic lining. This process lowers the carbon content of the metal to the desired value.

After the composition is further fine-tuned, the steel can be cast into various shapes.

==Alternative process==
Steel can also be produced from [[wrought iron]] or other low-carbon iron. If the iron is alternately heated in a furnace burning [[charcoal]] or [[coke]] (or [[graphite]], [[diamond]] or other high-purity forms of [[carbon]], though this does not make economic sense) and the slag expelled by hammering, the iron will eventually absorb enough carbon to become steel. This is the pre-industrial method and is known as '''steeling'''.<ref name=Sims>L. Sims - ''The backyard blacksmith: Traditional techniques for the modern smith'' 2006. ISBN 978-0-7858-2567-8 p. 46</ref>

The wrought iron for this process would itself have been converted from pig iron (see [[wrought iron]] for details), making it a three-step process of adding carbon, removing carbon and then adding carbon again.

==Comparison with direct reduction==
*Advantages
**Simpler, provided that large quantities of carbon and oxygen are available.
**Requires less instantaneous [[electric power]] (when compared to melting [[direct reduction of steel | directly reduced iron]] with an [[electric arc furnace]]).
**There is a reduced risk of [[hydrogen fracturing]] when compared to direct reduction by [[hydrogen]] gas.
*Disadvantages
**Uses more energy overall.
**Using hydrogen gas as the main reducing agent inherently implies direct reduction.

==References==
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[[Category:Mining and Refining]]