Austempering transformation kinetics of austempered ductile iron obtained by Mössbauer Spectroscopy

The composition of metallic matrix in ductile iron as-cast and after austempering at temperatures of 280, 330 and 380C (ADI) was examined. The study presents the results of these examinations obtained by Mossbauer spectroscopy. The specimens were taken from cast rods of 60mm diameter. Using calculated values of the parameters of hyperfine interactions (isomeric shift IS, quadrupole splitting QS and hyperfine effective magnetic field H), isolated by deconvolution of the experimental spectrum, the constituents of the metallic matrix were identified in terms of both quantity and quality. The measured values as well as the data compiled in literature indicate that component Z1 (the, so called, Zeeman spectrum sextet) is related with Fe atoms present in the structure of ferrite α1 (I stage of o→α1 + st transformation), component Z2 is typical of ferrite α2 (II stage of st→α2 + carbides transformation), while component Z3 has its origin in Fe atoms seated in the structure of carbides (Fe3C, Fe2C or Fe2,4C). On the other hand, by analysis of the parameters of hyperfine interactions describing the non-magnetic components (L and Q) it has been proved that they are typical of austenite.