Post –by Gautam Shah
1 Iron or Steel is one of the most complex of all metals used by man. In spite of its very large volume of use, it still remains a very enigmatic material.
2 Iron changes the properties during manufacture, post processing, aging and usage. Many of the changes are known to man for years, but ignored. Some of these effects became apparent very late in the life span of the structure, or functional entities. Such realizations, though late have not affected us very severely, because superior technologies of later dates provided better guaranteed and efficient solutions.
3 Many of the Industrial revolution period steel structures, such as large span buildings, bridges and ships were formed of very inferior materials and fastening techniques (hind sight realizations). But ‘change solutions’ that became available 30 / 50 years later were better enough to have no regrets for replacement. In few cases there have been losses of life, such as Titanic or Liberty series of ships. The only regrets were that often such structures collapsed suddenly.
4 The technological deficiencies that affected the structures and entities were due to ignorance and lack of inadequate knowledge, but similar problems have continued even today due to insincere applications.
5 However, birth of steel fabrication was with cast shapes like parts of columns, capitals, brackets and sections of arches. These were components of compression. Tensile capacity was untested. Hollowed out brackets and arch forming sections had few subsections that were tensile stressed. Tensile behaviour of steel was not completely unknown quality. As the integrity of castings improved, through constitution and methods of cooling, the tensile reliability increased.
6 One of the most widely used form of ferrous metal has been the sheets. Sheets are re-rolled, cut into strips and folded or formed into various sections.
7 Compared to cast steels, drawn steels had better grain alignment and tensile strength was known. Mild steels produced through use of Bessemer process provided the much needed ductility and tensile stress capacity.
8 Steels were re-rolled into sheets, but in the manufacturing number of annealing, tempering, hardening processes were perfected.
9 Annealing and Hardening, are nominally considered two extreme processes, former a softening and the later its opposite method. But Tempering that is readjusting the quality of steel is now considered even more important. It is chiefly used in forming various sections, automobile bodies and cages for white-goods. Companies producing furniture, automobiles and white-goods have a selfish interest in replacement markets, and so design their product for 10 years life cycle. After that no one is bothered about the product.