Creep-Fatigue Behavior of Alloy 800H at High Temperatures

The objective of this study is to investigate the creep-fatigue behavior of Alloy 800H at three different high temperatures of 700 degrees C, 750 degrees C and 800 degrees C. Creep-fatigue tests were carried out by a series of fully reversed strain-controls with tensile holding time, total strain range of 0.6%, under a constant strain rate of 10(-3)/s. The holding time for creep was 60 seconds in tensile peak strain. The results were compared with the previous low cycle fatigue test results. In all test temperature conditions, the cyclic stress response behavior of Alloy 800H showed the initial cyclic hardening phenomenon at both creep-fatigue and continuous low cycle fatigue. At both creep-fatigue and continuous low cycle fatigue, the degree of hardening decreased linearly as the temperature increased. In all test temperature conditions, the fatigue life of creep-fatigue are shorter than that of low cycle fatigue. Finally, in the creep-fatigue, the crack initiation mode was observed as transgranular, however, the propagation was observed as the mixed mode with trans-and inter-granular, whereas the low cycle fatigue showed the failure mode of typical transgranular.