Experimental Characterisation of the Bainitic Transformation Kinetics of Residual Austenite in Mn-Si TRIP-Assisted Multiphase Steels

Recent studies on TRIP-assisted multiphase steels have emphasised the drastic importance of the bainitic transformation in the optimisation of properties. Bainitic ageing is necessary for the stabilisation of austenite with respect to the martensitic transformation. This metastable retained austenite can still transform to martensite when plastically deformed (TRIP effect). The present work deals with the bainitic reaction kinetics of the austenite obtained by intercritical annealing in two low carbon Mn-Si steels. Bainitic transformation was followed by dilatometry and SEM observations. X-ray diffraction and Mossbauer spectrometry allowed the measurement of the amount of residual austenite and of the carbon enrichment in austenite. The tempering temperature was found to influence the kinetics of austenite transformation and decomposition.