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Iron and Steel

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Rural Technology

The Stone Age, Bronze age and Iron age are the three main era of human history. In the beginning man was making weapons like axe and sword, using stones. A sharpened stone was fitted in a wooden base and used. Then man invented bronze, from minerals having mixture of copper and zinc. Though, Copper was available, it was not useful for making weapons because of its soft & flexiblenature. Bronze is hard. Therefore, it was used in most of the instruments. Use of iron started 2500 to 3000 years ago. In the beginning iron was obtained only from meteorites falling from the sky. Since Iron was scare, it was considered to be the most valuable metal. The process of producing iron from minerals was difficult and the iron received was hard and brittle. The technique of melting iron was known in our country from 1500-2000 years ago. Iron pillar Kutubminar in Delhi was built at the time of Chandragupta is a proof of it. Use of iron became common only after industrial revolution in England. Today, Worldwide production of iron is in thousand of crores tonnes.

Production

Iron is available in nature in the form of minerals. These minerals are combination of iron, oxygen and sulpher. Iron is obtained from these minerals by following process. Minerals (iron + oxygen) + (Carbon) = iron + (Carbon + oxygen) Minerals are heated in the oven over 1500oC. In the oven, Carbon and oxygen combines together to form carbon-di-oxide (CO2). This gas evaporates and iron remains in the oven. This liquid iron is solidified in moulds. Because of the shape of solid iron, it is called pig iron’. This iron is again melted and poured into different moulds to make different articles of cast iron. Cast Iron is hard but brittle in nature. It contains 3%–4% Carbon.

Types of iron and steel

Steel-Iron gets combined with carbon to form steel. Properties of Steel are different from that of iron. Following are types of iron steel: 1) High Carbon Steel: Steel containing 0.6%–2% carbon is called high carbon steel. It is used to make tools. 2) Cast Iron: Cast iron contains 3%–4% carbon. The cast Iron is hard in nature. You might be aware diamond is allotrope of carbon and it is very hard and used to cut glass. 3) Mild Steel: It contains 0%–0.3% carbon. It is used in the production of iron shades, angles, rods, pipes etc. 4) Stainless Steel: It is made of iron, chromium and nickel. Stainless steel does not stain, corrode, or rust as easily as ordinary steel. The price of stainless steel is more than the original metal. Stainless steel are commonly used in cutlery, utensil’s etc.

Heat Treatment

As the percentage of carbon in steel increases, it becomes harder. Hardness of iron also changes with heat given to it. If steel is made red hot and then cooled rapidly then it becomes hard. If it cooled slowly then it become less hard. This is called heat treatment.

Intext Questions

Fill in the blanks: i) Hardness of iron depends on content in it. ii) Tool used in lathe machine is made of . iii) Kitchen appliances are made of steel because it does not get corroded.

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