Crack growth characteristic and damage evaluation under Creep-fatigue interactive condition for W-Added High-Cr Steel

Crack growth characteristic under the conditions of high temperature creep and fatigue interaction is dominated by cyclic dependent mechanism due to fatigue and time dependent mechanism due to the time of load application (creep). For many cases, this characteristic changes from the cyclic dependent to the time dependent mechanisms through an unstable transition region induced by creep and fatigue competitive mechanisms. To understand the physical mechanism of the interactive effects of creep and fatigue, it is important to clarify the damage mechanics around the crack. In the present study, the experiments of creepfatigue crack growth tests and the quantitative analysis of damage by measuring Vickers hardness were conducted to understand the interactive effects of creep and fatigue on the crack growth characteristic. Additionally, by observing the material microstructure using EBSD, damage mechanisms were clarified. As a result, creep effect contributed to the expansion of damage region and fatigue effect increased the degree of damage. Interaction of these effects resulted in the occurrence of unstable transition region on the characteristic of creep-fatigue life.