EFFECTS OF SIMULATED ON LINE ACCELERATED COOLING PROCESSING ON TRANSFORMATION TEMPERATURES AND MICROSTRUCTURE IN MICROALLOYED STEELS .2. PLATE PROCESSING

The effects of three on line accelerated cooling parameters (accelerat ed cooling start temperature T-A, cooling rate T and cooling interrupt temperature T-I) on transformation temperatures and microstructure in a low carbon microalloyed plate steel were studied by laboratory simu lations in a quench deformation dilatometer. Varying the on line accel erated cooling parameters changes the austenite condition and transfor mation path. In general, the transformation path shifts from polygonal ferrite towards bainite with increasing T-A, increasing T and decreas ing T-I. There is also a corresponding refinement in the microstructur e and increase in hardness. In comparison with the laboratory thermome chanical processing treatments, the multipass industrial rolling sched ule produces a much more heavily deformed austenite structure than lab oratory thermomechanical processing treatments, which would favour hig h transformation temperatures, fine polygonal ferrite microstructure, and lower hardness.