SOME NEW RESULTS IN THERMOMECHANICAL PROCESSING OF MICROALLOYED STEELS

In recent times, efforts have been directed towards a better understan ding of the mechanisms associated with deformation and restoration of austenite during continuous multipass hot rolling of microalloyed stee ls. The correspondence between the condition of austenite before trans formation and the resultant microstructure upon cooling holds the key to the attainment of interesting properties. In the present paper, som e results obtained on the deformation of austenite in a microalloyed s teel, using a hot compression machine, are presented. Here, the idea w as to simulate actual plate rolling or hot strip rolling conditions an d study the evolution of microstructure at different stages of the hot deformation process i.e. after precise reductions at given strain rat e and temperature of deformation. The paper further discusses recent r esults obtained by us on the influence of hot deformation parameters ( strain, finish rolling temperature, temperature of deformation) and co oling rates (air cooling, spray water cooling) on the microstructure o f microalloyed steel. The precise conditions leading to the evolution of acicular ferrite and bainitic microstructures have been identified. New information on the influence of short tempering treatments (15 mi n at 550, 600 and 650 degrees C) on the microstructure and properties of a microalloyed steel are also outlined.