The application of modified J-integral to creep crack growth in austenitic stainless steel and Cr-Mo-V steel

The creep crack growth behaviour was investigated at 923 K for type 304 stainless steels and at 838 K for a Cr-Mo-V steel, by using series of proportional specimens with various geometries, i.e., 'deep' and 'shallow' center-cracked plate specimens, CT specimens and circumferentially cracked round bar specimens. The validity of modified J-integral (C*-integral) as a correlation parameter of creep crack growth rate was substantiated. Based on previous analytical works on creep crack growth done by the authors, size dependence appeared in correlation curves of creep crack growth rate with net section stress and stress intensity factor for proportional specimens was discussed. Methods of compensating this size dependence were proposed, which were confirmed by the experiments. (author)