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Model of phase transformations in steels subject to heating-cooling thermal cycles in continuous annealing line

ABSTRACT The need for fast mean field models describing phase transformations in varying temperatures was the motivation for the research. The aim was to propose an austenite-ferrite transformation model which can be successfully substituted for the JMAK model and eliminate its weak points. The model consists of a second order differential equation which describes the kinetics of both the austenite-ferrite and the reverse transformations. The main advantage of such an approach is the ability to perform calculations for varying temperature without using the additivity rule. The coefficients in the equations were determined by performing the inverse analysis for the dilatometric data. The inverse approach was transformed into an optimisation task, which was solved using the Particle Swarm Optimization (PSO) algorithm. The first part of the work is devoted to the description of the model and is completed with the calculation of the coefficients obtained for two DP steels. The second part consists of numerical tests and the validation of the model, which was performed by simulations of two industrial thermal cycles. The final part of the work is devoted to the optimisation of the thermal cycle for continuous annealing, in order to obtain the required phase composition by changing parameters of the thermal cycle. This part also contains the results of sensitivity analysis of final phase distribution.