In the remaining life assessment of high-temperature components such as boilers after long term service, the practical evaluation of crack growth lifetime using nonlinear fracture mechanics is needed. In this paper, creep-fatigue crack growth behavior under displacement controlled conditions is examined using CT specimen of 21/4Cr-1Mo steel which is the typical high temperature structural steel. The J-integral estimation method and the crack growth prediction method using fully plastic solution are also examined. Creep-fatigue crack growth under displacement hold can be separated into fatigue crack growth in the cyclic portion and creep crack growth in the holding portion. Those mechanisms are competitive to each other, and the crack growth behavior is determined by dominant one of fatigue and creep. The J-integral approach using fully plastic solution is introduced for predicting low cycle fatigue crack growth under the complicated loading condition and creep-fatigue crack growth with the relaxation. The propriety of this solution is verified by comparing the prediction with experiments by the slope-line-control method.
