PHASE-TRANSFORMATION AND COMPOSITIONAL PA RTITIONING IN TRIP STEEL

Transformation behavior and compositional partitioning in TRIP (Transf ormation induced plasticity) steel was investigated by means of micros tructural observation and computer modelling. Orthoequilibrium partiti oning of alloying elements of Si and Mn was attained even in short int ercritical annealing time. A model based on transformation mechanism c ontrolled by C diffusion well described the volume fractional change o f ferrite and pearlite during the cooling to austempering temperature. Slower cooling rate significantly increased C concentration to around 0.5% in untransformed gamma and caused pearlite transformation Bainit e volume fraction obtained by austempering increased with austempering temperature. Analysis by computer modelling revealed that transformat ion kinetics above 350 degrees C followed the model based on diffusion mechanism, while it agreed better with the model based on shear mecha nism below 350 degrees C.