Kinetics of nucleation and growth in a eutectoid plain carbon steel

An accurate prediction of the continuous cooling transformation (CCT) history of steels, obtained using isothermal transformation data has been of considerable academic and industrial importance for many years. The Additivity Principle, which is required to permit this calculation, has been defined but in general not completely satisfied. In this thesis the kinetics of nucleation and growth of the austenite-to-pearlite transformation in eutectoid, plain-carbon steels have been measured with the aim of clarifying the limits of applicability of this additivity principle. As a result, a new satisfactory condition, termed "effective site saturation", is proposed. The pearlite nucleation and growth rates were obtained for a range of austenite grain sizes and transformation temperatures. This data has also been used to develop a grain size parameter which could be included in the empirical transformation equation. The significance of the measured grain size exponent, 'm', in terms of the operational pearlite nucleation sites has been examined. The relationship between the thermal history of the austenite phase and the resulting austenite grain size has also been examined. The applicability of an available empirical expression for predicting the austenite grain size as a function of peak temperature and time at temperature has been confirmed.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat