General method of phase transformation modeling in advanced high strength steels

Abstract

In the present paper, a new modeling approach is proposed for the austenite to ferrite and bainite transformation kinetics in transformation induced plasticity (TRIP) and complex phase (CP) steels. Based on experimental data obtained by dilatometry during continuous cooling, Rios' method has been successfully applied assuming additivity to calculate the parameters for the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model, i.e. exponent n and the rate parameter k. Limitations of the Rios' method have been identified when k is a function of both temperature land fraction transformed X. For these cases that are in particular relevant for the bainite transformation, a new modeling method has been developed to investigate the exact relationship of k with T and X. The new method has been used to describe the transformation kinetics in a TRIP and a CP steel. Good agreement has been obtained between the calculated and measured transformation data. The proposed new modeling method provides a general modeling approach that promises to be useful in predicting the complex phase transformation kinetics during industrial processing of advanced high strength steels (AHSS). © 2010 ISIJ.