Author :
Najafi-Zadeh, A.,Golozar, M. A
Abstract :
Several alloys of ductile cast iron containing various amounts of copper and tin were austempered in the temperature range 280 to 375 C. The austempering time were varied between 15 to 150 minutes and the austenitizing temperature was 890 C. The alloying elements of copper and tin have been varied within the range of 0-1.5,and 0-0.4,respectively. The microstructural changes during austempering were evaluated by optical and scanning electron microscopy and the mechanincal properties such as hardness, tensile, and impact also were assessed. The results obtained indicated that, the microstructure and mechanical properties of austempered ductile Cu-Sn iron alloys are significantly influenced by the isothemal transformation time and temperature. The alloying elements of copper and tin had a pronounced effect on the matrix microstructure of as cast and annealed ductile irons. These elements showed no effect on the morphology of bainite in the austempered condition. However, the volume fraction of retained austenite in the austempered ductilw iron alloys incresed duc to addition of these elements. The mechanical properties of austempered ductile iron alloys were also significantly influenced by the alloying elements of copper and tin. At austempering temperature of 375 C and 335 C, the 1,Cu-0.4,Sn ductile iron alloy austempered for 75 minutes showed the most suitable combination of mechanical properties. On the other hand, at austempering temperature of 285 C,the 1,Cu-0.2,Sn ductile iron alloys austempered for 30 minutes represented the most suitable mechanical properties.
