Abstract: This investigation indicates that the primary dendritic particles lower significantly the property of low cycle fatigue in K136 ECD (Est-Cast-to-Shape Disc). The possible reason for this phenomenon is as following:
(1) Arousing the main crack to early form;
(2) Acting as internal source of fatigue cracks.
These both effects depend on the fatigue stress and fatigue crack growth rate. Under the condition of high fatigue stress or higher crack growth rate this detrimental effect can be reduced. However, if the fatigue stress is lower, the primary dendritic larger particles decrease the fracture life significantly. Increasing solid solution temperature can decrease the number of primary particles resulting in the improvement of fatigue porperty.