Transformation characteristics of ductile iron austempered from intercritical austenitizing temperature ranges

In the present work, the transformation characteristics of ductile iron austempered from intercritical austenitization temperature ranges were investigated. 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 austenitized) at various temperatures and then rapidly transformed 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 temperature and time. It was demonstrated that the total volume fraction of transformed phases was approximately constant for all austempering times after rapidly transforming samples from a particular intercritical 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 austenitizing temperature and austempering time. © 2006 Springer Science+Business Media, LLC.Devlet Planlama Örgütü 07/2003–41 2001 K120590Acknowledgements The authors wish to acknowledge the financial supports of Gazi University Scientific Research Fund (Project no 07/2003–41) and DPT (The State Planning Organization of Turkey, Project no. 2001 K120590). The author is also indebted to ALFA Casting Company for Castings (Ankara, Turkey) and to Ankara Nuclear Research and Education Center (TAEK-ANAEM) for providing X-ray facilities