Strain Amplitude and Temperature Effects on the Low Cycle Fatigue Behavior of Alloy 617M

In the present investigation, comparative evaluation of the low cycle fatigue (LCF) of tube and forged Alloy 617M have been studied. Total axial strain controlled tests were performed on sub-sized specimens between 300 and 1023 K employing strain amplitudes ranging from +/- 0.25 to +/- 1 % at a nominal strain rate of 3 x 10(-3) s(-1). The alloy underwent cyclic hardening at all temperatures and strain amplitudes and the rate of hardening was sensitive to both temperature and strain amplitude. There were distinct differences in the LCF behavior of forged and tube products. The forged alloy exhibited better fatigue life than that of tube material and significant difference in the rate of hardening was observed between the material conditions at 1023 K. The variation in the LCF behavior of the two products was found to be associated with the difference in the initial microstructure. The grains of the tube product were equiaxed having 214 mu m average size whereas a distribution of both large grains (average 65 mu m) and clusters of small grains (average 15 mu m) were found in the forged product. Microstructural investigations revealed mixed mode of failure for both the product forms.