Mathematical Model of Bainitic Transformation in Austempered Ductile Iron

Abstract

A mathematical model of austenite -bainite transformation in austempered ductile cast iron has been presented. The model is based on a model developed by Bhadeshia [1,2] for modelling the bainitic transformation in high-silicon steels with inhibited carbide precipitation. A computer program has been developed that calculates the incubation time, the transformation time at a preset temperature, the TTT diagram and carbon content in unreacted austenite as a function of temperature. Additionally, the program has been provided with a module calculating the free energy of austenite and ferrite as well as the maximum driving force of transformation. Model validation was based on the experimental research and literature data. Experimental studies included the determination of austenite grain size, plotting the TTT diagram and analysis of the effect of heat treatment parameters on the microstructure of ductile iron. The obtained results show a relatively good compatibility between the theoretical calculations and experimental studies. Using the developed program it was possible to examine the effect of austenite grain size on the rate of transformation..

Bainite transformation time model optimization for Austempered Ductile Iron with the use of heuristic algorithms

“…As research has shown (Nofal, 2013;Kuziak et al, 2010), the wide range of the mechanical properties of ADI can be obtained by appropriately selecting isothermal strength parameters leading to the formation of the final microstructure. As part of the research, to calculate the bainite transformation time in ductile cast iron, the mathematical Bhadeshia model (Equation (1)) was used, which was originally used for high-silicon steels (Chester & Bhadeshia, 1997;Olejarczyk-Wożeńska et al, 2017):…”