Effects of alloying elements (Cu and Ni) and autempering time on microstructure and mechanical properties in austempered spheroidal graphite cast irons

VIII EFFECTS OF ALLOYING ELEMENTS (Cu and Ni) AND AUTEMPERTNG TIME ON MICROSTRUCTURE AND MECHANICAL PROPERTIES IN AUSTEMPERED SPHEROIDAL GRAPHITE CAST IRONS M. Sc. Thesis Hasan HASIRCI GAZI UNIVERSITY INSTITUTE OF SCIENCE AND TECHNOLOGY February 2000 ABSTRACT In this study specimens with ferritic matrix was produced by the addition of basic alloying elements of 3.5 % C, 2.8 % Si. To investigate the effect of alloying elements of Ni and Cu content on microstructure and mechanical properties 5 different specimens were produced by addition of basic elements mentioned above and Cu content specified levels (0.6, 0.65 and 0.7 % Cu) and varying Ni content at specified levels (0.5, 0.7 and 1 % Ni). These specimens then were austenised at 900 °C for 90 minutes and austempered at 360 °C for different times (60,90,120,150,180 and 200 minutes). It was observed that mechanical properties in austempered specimens having auferrite (a + y high karbon) structure varied depending on austempering temperature, time and alloying element type and their amount. Increment in mechanical properties in austempered specimens were much higher than as cast specimens. However this increment was much higher in alloyed specimens than unalloyed specimens. Generally thoughness properties and elongation decreased and yield and tensile strenght and hardness increased with increasing austempering time due to carbide formation. Science Code : 626. 19. 01 Keywods : Austempered Spheroidal Graphite Cast Irons, Alloying Elements, Autempering Time Page Number :92 Supervisor : Asst. Prof. Dr. Mehmet ERDO?AN