Creep-fatigue crack growth behavior of G115 steel at 650 °C

The micro-mechanism of creep-fatigue interaction of novel 9% chromium tempered martensitic steel, G115, was investigated after creep-fatigue crack growth experiment using compact tension (CT) specimens. It indicated that the mode of crack growth changed from transgranular to intergranular when the crack growth stage changed from the initial to the accelerated region. At the initial crack growth region, fatigue striations and fatigue bands were observed. Then, creep voids were nucleated and the number increased. In addition, many secondary cracks were generated at the second stage and the number of cracks were increased steeply when the crack growth rate was accelerated at the tertiary crack growth stage. Furthermore, the variation of the creep, fatigue and the interaction damage during the crack growth process was analyzed using numerical simulation. The results agreed with experiment which illustrated that creep damage increased and fatigue damage reduced from the initial to the third crack growth stage and the increased interaction damage aggravated the crack propagation.