In this paper, the bainitic transformation during austempering was studied for a 2.11% Al containing ductile iron under different isothermal holding times. The austenitizing time and temperature were selected to be 60 minutes and 920 °C respectively referring to previous studies. The isothermal austempering heat treatments were performed at 350 °C for different durations. Microstructures have been examined by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Microstructural investigations revealed that austempering treatment at 350 °C for durations up to 100 min results in microstructures consisting of carbide-free bainitic ferrite with considerable amounts of retained austenite while the extension of isothermal transformation time leads to precipitation of carbides. Hardness measurements were also carried out the results of which were shown to be consistent with microstructural evolutions.

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