Investigations were conducted for the development of multiple microalloyed air-hardenable forging grade steels. A number of multiple microalloying combinations were tried for optimisation of the alloy design. In the initial laboratory investigations, the hot forged steels were austenitised at 1100 deg C and then forced air-draft cooled. A range of mechanical properties (Y.S: 350 to 1100 N/mm~2, ITS: 500-1150 N/mm~2, El.: 25-40 percent) would be developed primarily by varying the microalloying combinations and the carbon equivalent. Further industrial trial was conducted on forged steels. Connecting rods hot-forged in successive stages after initial soaking at 1175 deg C were forced air draft cooled and tempered at 500 deg C. There was good correlation between the mechanical properties of the connecting rods and those of laboratory test specimens. An attempt has been made to characterise the microstructures of these steels by transmission electron microscopy.
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