The fatigue properties of ductile irons with dual matrix structure austempered from intercritical annealing tempatures

THE FATIGUE PROPERTIES OF DUCTILE IRONS WITH DUAL MATRIXSTRUCTURE AUSTEMPERED FROM INTERCRITICAL ANNEALINGTEMPATURES(M.Sc. Thesis)smail OVALIGAZ UNIVERSITYINSTITUTE OF SCIENCE AND TECHNOLOGYSeptember 2006ABSTRACTIn this study, effect of austempering from intercritical annealing temperatureson microstructure and fatigue properties of unalloyed ductile cast iron wasinvestigated. For this aim, ductile cast iron were annealed at intercriticalannealing temperatures of 810 ºC, 820ºC and 830 ºC for 20 min and thenaustempered at 315 ºC and 375 ºC for 120 minutes. Some specimens were alsoconventionally austempered at the same austempering conditions from 900ºCfor comparison. Fatigue strength of specimens was determined by Rotatingbending fatigue method. Results showed that all heat treated specimensaustempered had better fatigue strength than that as cast ductile iron. In thespecimens austempered from critical temperatures (Ae1-Upper criticaltemperature) fatigue strength and hardness increased with increasing ausferritevolume fractions. The coarse ausferrite structure formed at high austemperingtemperature decreased fatigue strength of samples. Conventionallyaustempered samples exhibited much greater fatigue strength than allspecimens austempered from intercritical annealing temperature ranges.Science Code : 710.1.092Key Words : Austempered Ductile Iron (ADI), Dual Matrix Structure,Austempering Time, Ausferrite Volume Fraction, FatiguePage Number : 90Adviser : Prof.Dr.Mehmet ERDOĞAN