STEEL
The characteristic feature of metals is that their physical and chemical properties can be altered as per the requirement. Metals can be grouped into the following two categories.
(1) Ferrous metals
Ferrous metals contain iron (ferrous) as their main constituent. The most common forms of ferrous metals are (a) cast iron (b) wrought iron (c) steel
(2) Non-ferrous metals
- Commonly used non-ferrous metals are aluminium, copper etc.
- These metals are obtained by processing the iron ores mined from the earth. Important varieties of iron ores are :
- (1) Haematite Fe2O3 (65-70 per cent of iron)
- (2) Limonite 2Fe2O3.3H20 (60% of iron)
- (3) Magnetite Fe3O4 (70-73% iron)
- (4) Pyrite FeS2 (45% of iron)
- (5) Siderite FeCO3, (40% of iron)
- The crude iron extracted from iron ores is called Pig iron, which forms the basic material for manufacturing cast iron, wrought iron and steel.
The manufacturing process of Pig iron
- The first step is referred to as dressing.
- In this process, The iron ore obtained is crushed and washed of impurities.
- The next step is the calcination of the ore, which is the heating of the ore in presence of oxygen so that it is oxidised.
- This remoes the water and carbon dioxide from the ore.
- The next step is of roasting the ore to make it very hot and dry.
- Heating the ore helps in removing the volatile content of the ore especially sulphur.
- Roasting is not necessary if the ore is sulphur free.
- The next step is of smelting of iron which is to separate metal from the ore, which carried out in blast furnace.
Working of Blast Furnace
- The raw material fed to the furnace is the fluxing material and fuel. The fluxing material is a substance that easily combines with the impurities and forms a fusible slag. The most common fluxing material is limestone.