Affect of cementite precipitation on the extend of bainite reaction in ADI

Presented paper demonstrates how the precipitation of cementite from ferrite or/and austenite in ADI may influence the extend of bainite reaction. Analytical calculations and experimental measurements of volume fraction of bainitic ferrite and volume of the untransformed austenite indicate that there is a necessity of carbides precipitation. A consequence of the precipitation of cementite from austenite during austempering is that the growth of bainitic ferrite can continue to larger extent and that the resulting microstructure is not an ausferrite but it is a mixture of bainitic ferrite, retained austenite and carbides. In case of this microstructure, the product of austempering reaction in ductile iron is rather bainite than “ausferrite”. The results are discussed in the context of displacive mechanism of bainite transformation.