The effect of holding time on the mechanical properties of Austempered Ductile Iron

Project describes experiments done to study the effects of some variants in the austempering process on mechanical properties, especially fatigue of ADI. The calculation of the stress intensity factor is also looked into.. Some factories in Indonesia plan to produce Austempered Ductile Iron (ADI), because this material offers some advantages over other cast irons, such as having excellent fatigue properties and also being cheaper than steel. This thesis describes some experiments done to study the effect of some variants in the austempering process on mechanical properties, especially fatigue of ADI. In particular the effect of holding time on fatigue properties of ADI were studied, and an attempt was made to answer the question "Can the stress concentration factor theory proposed by Kubicki be applied to ductile cast iron and ADI?" This stress concentration model enables quantification of the influence of both matrix yield strength and size ofinclusions on the endurance limit of inhomogeneous material. Initially some laboratory experiments were done such as tensile tests, hardness tests and fatigue tests. The tensile and hardness data are plotted on a histogram diagram while the fatigue results are plotted on an S-N curve. The results of the calculations were compared withthe fatigue test results. The conclusions are: Increasing holding time can decrease the mechanical properties of ADI; Comparing Kubicki's theoretical result with the fatigue test result shows quite strong agreement.