Structural and Mechanical Characterization of Austempered Cu - Sn Ductile Iron Alloys

The effect of heat treatment and alloying elements of copper and tin on the microstructure and mechanical properties of austempered ductile cast iron alloys is investigated. The austenitizing temperature of 890°C, the isothermal transformation (austempering) temperatures of 285, 335 and 375°C, and austempering times of 15, 30, 75 and 150 minutes are studied. The alloying elements of copper and tin are varied within the range of 0 -1.5% and 0 - 0.4%, respectively. The results obtained indicate that the microstructure and mechanical properties of austempered ductile Cu-Sn iron alloys are significantly influenced by the isothermal transformation time and temperature. The alloying elements of copper and tin have a pronounced effect on the matrix microstructure of as-cast and annealed ductile irons. These elements show no effect on the morphology of bainite in the austempered condition. However, the volume fraction of retained austenite in the austempered ductile iron alloys increase due to the addition of these elements. The mechanical properties of austempered ductile iron alloys are also significantly influenced by alloying elements. At austempering temperatures of 375 and 335°C, the 1% Cu - 0.4%Sn ductile iron alloy austempered for 75 minutes shows the optimum combination of mechanical properties. Conversely, at austempering temperature of 285°C, the 1% Cu - 0.2% Sn ducitile iron alloys austempered for 30 minutes represent the optimum combination of mechanical properties.