Chemistry

Varieties of Iron :
1. Pig iron and cast iron : The iron produced in the blast furnace is pig iron. It contains a comparatively high percentage of carbon due to which it is hard and brittle. It also contains phosphorus, silicon and manganese as impurities. Pig iron is melted, mixed with steel scrap and allowed to cool in moulds to give cast iron. Cast iron is impure iron, and is hard and brittle.
2. Wrought iron : It is almost a pure form of iron. It contains only 0.12% to 0.25% carbon. It melts at a higher temperature (1773 K) than that at which cast iron melts. Wrought iron is obtained by melting cast iron on a hearth lined with ferric oxide (Fe₂O₃) The impurities such as carbon, phosphorus, silicon and manganese are oxidized by Fe₂O₃
Fe₂O₃ + 3C → 2Fe + 3CO
Wrought iron is soft, grey and tough. It is malleable and ductile. Hence, it can be drawn into sheets and stretched into wires. It is used in making chains, wire, anchors and cores of electromagnets.
3. Steel : It is an alloy of iron and carbon. It contains about 0.15 to 1.7% of carbon. There are different types of steel.
(a) Mild steel : It contains less than 0.3% carbon. It is also called soft iron. Mild steel is used for making sheets and wires.
(b) Hard steel : It contains higher percentage (0.7-1.7%) of carbon. It is used in making tools and instruments.
(c) Alloy steels : Alloy steels are prepared by adding small amounts of nickel, cobalt, chromium, tungsten, molybdenum, manganese and silicon to steel. Alloy steels are used extensively in making rock-crushing machinery, helmets, armour plate, cutlery, springs, etc.
(d) Medium steel : It contains 0.3-D.7% carbon. It is hard and is used in making rails, bridges, etc.