Modelling of kinetics of austenite formation in steels with different initial microstructures

The main aim of this work is to study the mechanisms that control the auste nitisation process in steels with different initial microstructures. The co mpiled knowledge in literature regarding the isothermal formation of austen ite from different initial microstructures (pure and mixed microstructures) , has been used in this work to develop a model for non-isothermal austenit e formation in steels with initial microstructure consisting of ferrite and /or pearlite. The microstructural parameters that affect the nucleation and growth kinetics of austenite, and the influence of the heating rate have b een considered in the modelling. Moreover, since dilatometric analysis is a technique very often employed to study phase transformations in steels, a second model to describe the dilatometric behaviour of the steel and calcul ate the relative change in length which occurs during the austenite formati on has been developed. Both kinetics and dilatometric models have been vali dated. Experimental kinetic transformation, critical temperatures as well a s the magnitude of the overall contraction due to austenite formation are i n good agreement with calculations.