Microstructure and fracture of alloyed austempered ductile iron

An investigation has been conducted on two austempered ductile irons alloyed with Cu and Cu + Ni, austenitized at 900 °C and austempered at 350 °C. The microstructure and fracture mode developed through these treatments have been identified by means of light and scanning electron microscopy and X-ray diffraction analysis. Impact energy measurements were performed on un-notched Charpy specimens. The maximum value of retained austenite volume fraction observed in the material alloyed with Cu + Ni was higher than in that alloyed with Cu austenitized and austempered under the same conditions. This led to the material alloyed with Cu + Ni having higher impact energy and substantial plastic deformation.