In the present work, the transformation characteristics of ductile iron austempered from inter-critical austenitization temperature ranges were inves_tigated. For this purpose, an unalloyed ductile cast iron containing 3.50 wt% C, 2.63 wt% Si and 0.318 wt% Mn were intercritically austenitized (partially austen_itized) at various temperatures and then rapidly trans_formed to a salt bath held at the 365 °C for austempering for various times to produce dual matrix structure with different ausferrite volume fractions in ferrite matrix. A microstructure map was created to illustrate the transformation of products quantitatively as a function of austempering time for a particular intercritical and austempering heat treatment temper_ature and time. It was demonstrated that the total volume fraction of transformed phases was approxi_mately constant for all austempering times after rapidly transforming samples from a particular inter-critical temperature to austempering temperature. It was found out that the new ferrite (It is also called epitaxial ferrite) introduced into the intercritically austenitized structure during austempering and its content was dependent on the intercritical austenitiz_ing temperature and austempering time.
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