Effect of processing parameters on austempering behavior of alloyed/unalloyed ductile iron

Ever since its discovery in 1948, the use of ductile iron is increasing continuously due to the combination of its various excellent mechanical properties. Excessive amount of research is being carried out to develop even better properties. Austempererd ductile iron is the most recent development in the area of ductile iron or SG iron. Two types of spheroidal graphite (SG) cast iron samples with different weight percentage of copper were austempered at four different temperatures. The austempering temperatures were 200°C, 300°C, 350°C, 400°C.The influence of austempering process (i.e time and temperature) on the mechanical properties of spheroidal graphite iron was investigated as a function of austempering time and temperature. The cooling rate and the quenching technique adopted play an important role for the property development of spheroidal graphite iron. XRD analysis has also been carried out to study the formation different phases during isothermal transformation at different austempering conditions. Graphite morphology has been studied by SEM. The samples were taken for XRD analysis from the centre of the castings for this investigation. It was found that both the austenite (111) and ferrite (110) lines are identified nearly in all cases. The maximum intensity of the austenite (111) line is increasing with increasing temperature but ferrite (110) line is increasing with increasing austempering time and decreasing with austempering temperature. Hence austempering calls for very precise control of process variables (austempering time and temperature). It has been found from the result that ADI having the alloying element copper (grade N2) achieved significant mechanical properties as compared to other grade (N1) throughout the different austempering process adopted in this study.