FERROUS METALS
Introduction:-
There is scarcely a single aspect in our daily lives where in iron does not play an important part. Our food, our means of transport, the buildings, our firesides and its comforts, iron is necessary for them all. The magnitude property of iron alone, by making possible the electrical age in which we live has conferred incalculable benefits on humanity. It is backbone of modern industry and hence indispensable. Iron is fourth common element and second most abundant metal in earth’s crust. The symbol for iron is “Fe”. Its atomic number is 26 and atomic mass is 55.84. It melts at 1539°C. Ferrous is the name, which derived from the Latin word “Ferrum” meaning iron. So all the metals, which contain iron are classified under the name ferrous metals.
THE PRINCIPAL FERROUS MATERIALS USED IN ENGINEERING FIELDS ARE CLASSIFIED AS
1. Pig iron 2. Cast iron 3. Wrought iron 4. Steel
Pig iron: - It is product of a blast furnace and is made by the reduction of iron ore.
Cast iron: -The pig iron is melted and cast into moulds of the desired shape in order to obtain cast iron. It contains so much of the carbon that as cast; it is less malleable at any temperature.
Wrought iron: - It is obtained from pig iron by burning out carbon, silicon, manganese, phosphorous and sulphur impurities. Wrought iron is a pure form of pig iron. In the process of purification a minute quantity of slag is incorporated to give fibrous structure to wrought iron.
Steel: -It is form of iron and carbon with carbon content varying up to 1.5%. It is malleable in some range.
Pig iron: - All iron and steel products are derived originally from pig iron. This is the raw material obtained from the chemical reduction of iron ore in a blast furnace. The reduction of iron to pig iron is known as “Smelting”. The main raw materials required for pig iron are, Iron ore, coking coal and flux.
The coke is used in the blast furnace should be a very high class hard. Cokes obtained from good quality coking coals contain low phosphorus and sulphur. Flux is the mineral substance that is charged into the blast furnace to lower the melting point of the ore and to promote the removal of ash, sulphur and residues of the burnt fuel.
Manufacturing of Pig Iron:-
The blast furnace is a vertical shaft furnace designed for continuous operation. Thus smelting room of the blast furnace consists of a throat, stack, body, bosh and hearth. The raw materials (alternate layers of ore, coke and flux) known as charge is introduced into the throat by means of double bell and hopper arrangement. Hot blast is introduced into the throat by means of double bell and hopper arrangement. Hot blast is forced into a furnace through a number of nozzles called tuyers. The tuyers are cooled by water circulation between the pipe walls. The temperature of the furnace just above the level of the tuyers (melting zone) being 1000°C to 1700°C all substances inside the furnace start melting in the heat. The limestone that serves as a flux combines with the ore to form a molten slag, which floats on top of the molten iron. The slag is tapped off from the furnace through the slag hole. The molten iron is tapped off from 6 to 12 hours intervals, through the tapping hole, blast being turned off mean while.
The chief ores and their approximate yield of metal:
Ores | Appearance | Composition | Percentage of metals |
| Magnetite | Steel-grey or black | Fe3O4 | 72-62 |
| Red hematite | Crystalline or granular, earthy or rock red | Fe2O3 | 70-60 |
| Brown hematite | Brown, dense, earthy | 2Fe3O4 3H2O | 60-42 |
| Siderite or spathic | Shy grey, crystalline | FeCO3 | 48-35 |
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