The Making of Iron
About 5% of the eath's crust is of iron. All iron ore are used in ironworks are combinations of iron and oxygen - the oxygen being removed to obtain usable iron.
At one time, only ore with 40% iron was used, but now with new techniques and shortages, 25% iron is used.
In antiquity, iron was made in order: 1. wrought iron; 2. cast iron, 3. steel.
Wrought Iron. is commercially pure iron of fibrous form, containing slag threads. It is tough. The slag acts as flux as a welding agent, and helps inhibit corrosion. Its tenstile strength is 25 to 35 tons per square inch.
Cast Iron, is an alloy of iron, carbon and other elements up to 2 - 4% It is brittle, and cannot be rolled, forged, but it can be melted and cast. Its tenstile strength is weak at 5 to 8 tons per square inch.
Steel, is made in different forms for different purposes. It is an alloy of iron and carbon ( up tol .5%), with less carbon than cast iron, but more than wrought iron. Mild Steel is much like wrought iron and much used, but does not contain slag threads and so corrosion resistance is not good.
Summing Up. Cast iron has a high carbon content, It can be cast but not forged. Wrought iron has a low carbon content, can be forged but not cast, forged or hardened. Steel has low-to-medium carbon; can be cast, forged and hardened.
Because iron has an affinity for oxygen the ironmaker gets rid of the oxygen to make a useable metal. He does this by using something with an even greater affinity for oxygen, and that is carbon. That carbon source used to be charcoal, but to-day it is coke, which is used for heating.
Reduction of Ore, Simply, a chemical re-action takes place when incandescent carbon comes into contact with iron ore. The re-action is ;- the combination of oxygen from the air, and iron ore with carbon forms gases CO2 and CO (C02 = Carbon Dioxide) leaving behind the iron. Iron ore always contains earthy matter, and limestone etc. is usually charged to act as flux, and unites all the earthy waste and ashes, called slag.
Two Processes of Production
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Direct ( wrought iron) used always until the 15c. (Cast iron made only accidental; a misfortune, iron and effort wasted.)
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Indirect (cast iron and later, steel) Iron treated by further process before being used. later, methods were found to convert cast-iron into wrought iron, then into steel.
Iron Making History. It is convenient to divide into 2 sections: 1. Pre-history to 16c. 2. 16c. to present day.
Using charcoal as fuel, it took several hours to make a few pounds of impure (but useable) iron by ancient methods.