Abstract
A critical examination was made on the applicability of fracture mechanics parameters to creep crack propagation rate of 21/4 Cr-1 Mo steel at 565 deg C by using specimens of different dimensions at a high stress level. The crack length, crack propagation rate and fracture mechanics parameters were evaluated through electron fractographs, since it was difficult to measure them optically on a specimen surface due to the small crack opening displacement in such a low ductility material as the one used here. It was found that the modified J-integral J evaluated experimentally was a better parameter that the elastic stress intensity factor K or the net section stress σnet to correlate the creep crack propagation rate for this low ductility material. The necessity of a similar examination with larger specimens at lower stress levels was suggested. Fractographic features concerning with the mechanism of creep crack propagation were briefly described.
