Evaluation of quasistatic fracture toughness of a modified 9Cr-1Mo (P91) steel

For a modified 9Cr-1Mo (P91) grade steel in the normalised and tempered (NT) condition and also after accelerated thermal ageing (2900 h at 923 K), the elastic–plastic fracture toughness parameter J for 0.2 mm crack extension, J0.2, has been determined at 653 and 803 K, and compared with J0.2 of the NT material at 300 K. It is concluded that this thermal ageing does not significantly influence the toughness at 653 and 803 K. Also testing temperature has a marginal effect on J0.2 at 300 and 653 K. At 803 K, however, creep effects become so prominent that a basic premise for J-controlled crack growth, namely rate-independent plasticity, is seriously violated, giving rise to anomalously high values of J0.2.