Abstract
Two fundamental aspects of austenite stabilisation are investigated. Firstly, we examine the ‘transformation stasis’ or ‘incomplete transformation’ of bainite which determines the absolute maximum carbon content of residual austenite. A new criterion is proposed stating that the growth of bainite will stop when the instantaneous driving force for bainite growth vanishes because of the plastic resistance of the matrix. Secondly, we investigate the evolution of carbon enrichment and volume fraction of residual austenite during the growth of bainite and its relation to carbide precipitation. Based on these observations, a kinetic model is proposed for simultaneous transformation into bainite and cementite which contains only two fitting parameters. Considering the low level of complexity of the model, calibration with literature data gives satisfactory results.Nous examinons plusieurs aspects fondamentaux de la stabilisation de l’austénite : 1) arrêt de la transformation bainitique qui détermine le maximum absolu de la teneur en carbone de l’austénite résiduelle. Nous proposons un nouveau critère selon lequel la croissance de la bainite s’arrête lorsque le travail plastique dans l’austénite dissipe toute la force motrice chimique pour faire avancer la transformation ; 2) évolution de la teneur en carbone et de la fraction volumique d’austenite résiduelle en lien avec la transformation bainitique et la précipitation des carbures. Sur la base de ces observations, nous proposons un modèle cinétique rendant compte de la formation simultanée de la bainite et de la cémentite qui contient seulement deux paramètres ajustables. Compte-tenu de sa simplicité, le modèle reproduit les données expérimentales de façon satisfaisante.
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