Effect of copper on the austempering behaviour of spheroidal graphite iron

Abstract

Two types of spheroidal graphite cast iron samples, one with Cu and other without Cu were austempered at four different temperatures. The austempering temperatures were 250 ˚C, 300 ˚C, 350˚C, 400˚C. The main objective of the project was to develop the physical properties and morphology of the microstructures by austempering process. The tensile strength, yield strength, ductility, hardness and morphology of microstructure were studied after austempering. The effects of Cu on graphite nodule count, nodularity and pearlite percentage were observed. Samples with Cu showed higher values of tensile strength, yield strength, hardness but lower values of ductility as compared to samples without Cu. The effect of Cu on the formation of nodular graphite is not completely understood and much further work remains to be done. Both the types of irons have good nodular structure. Iron without Cu had a matrix of 95% ferrite and 5% pearlite. Iron with Cu % (0.42%) had about 50% ferrite and 50% pearlite as determined by using image analyzer. Thus offering all the production advantages of a conventional ductile iron casting, subsequently it is subjected to the austempering process to produce mechanical properties that are superior to conventional ductile iron.