An analysis of retained austenite in austempered ductile iron

Data from the literature have been analyzed to understand aspects of the retained austenite in austempered ductile irons, especially its relationship with the transformation mechanism of bainite. The final and initial carbon concentrations in austenite, (C) over bar gamma and C-gamma(0), respectively, are important in determining the maximum extent of reaction, and hence, the amount of austenite and bainitic ferrite (C) over bar (gamma) and C-gamma(0) data have been expressed in terms of chemical compositions and reaction temperature, with reasonable agreement between experimental and predicted results. It is demonstrated that, in connection with the lever rule, the calculated (C) over bar (gamma) and C-gamma(0) values can be employed to predict the microstructural constituents of austempered ductile irons.