Wrought Iron

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MME 214 Metallography sessional
Exp. 2 Microstructure of Wrought Iron

Wrought Iron
• Wrought iron was once the most important metallic engineering material but it has now been almost totally replaced by the different grades of steel. • A little wrought iron is still made and will probably continue to be made since it possesses certain extremely valuable properties. • Wrought iron is a soft but ductile metal made from pig iron by a low temperature oxidation process called ‘Puddling’. • It is not fully molten when withdrawn from the furnace and therefore, always contains some slag.

Production of Wrought Iron
• Wrought iron is made by removing silicon, sulphur, manganese, phosphorus and carbon from pig iron by oxidation conducted at a temperature of about 1300oC. • Oxygen required for oxidation is supplied partly by the atmospheric air passing through the furnace and partly by the additions of iron oxide. • Silicon, manganese and phosphorus in molten pig iron form SiO2, MnO and P2O5. These oxides combine with iron oxide to form a low melting point liquid slag. • As the iron loses its silicon, manganese, phosphorus and carbon, the melting point of the iron is raised and at the end of the refining the iron is in a pasty condition. • At this stage the iron is gathered in the form of balls, worked as free of slag as possible and dragged out of the hearth. These balls are then placed under a hammer where as much of the slag as possible is squeezed out.

The puddling process of smelting iron ore to make wrought iron from pig iron, Tiangong Kaiwu encyclopedia published in 1637, written by Song Yingxing (1587– 1666).

Production of Wrought Iron
• The squeezed balls are then rolled into “muck bars” (3/4 to 1 in. thick and 2.5 to 8 in. wide). The muck bars are then piled, reheated, and rolled into billets, plates, or other suitable shapes • This rolling serves to elongate the slag. The slag, therefore, occurs in the direction of rolling and visible in the...
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