KINETIC MODEL FOR PHASE TRANSFORMATIONS OF LOW CARBON STEELS DURING CONTINUOUS COOLING.

A calculation model for predicting the progress of transformations of low carbon steels during continuous cooling and the microstructure after cooling has been developed. The transformation from austenite to ferrite starts at the equilibrium temperature, Ae//3. The ferrite transformation follows the 'nucleation and growth' model at the early stage and the 'site saturation' model at the later stage. The carbon content of the untransformed austenite increases with the progress of ferrite transformation. The pearlite transformation starts when the carbon content of the austenite reaches the extrapolated Acm line in the equilibrium diagram. The bainite transformation starts when the temperature reaches the bainite start temperature, Bs, which is experimentally determined. Excellent agreement was obtained between the calculated and experimental results for the effect of composition (C, Mn, Si) on the transformation kinetics, continuous cooling transformation diagrams and microstructure after cooling.