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Abstract
The quasi-static fracture behaviour (J–R curves) of modified 9Cr–1Mo (P91) steel was studied. The J–R curves were established at 298, 653, 823 and 893 K, and fracture toughness J0·2 at 0·2 mm of crack extension was determined. The value of ∼J0·2 at 653 K was lower compared to that at 298 K followed by increases in J0·2 values at 823 and 893 K. The decrease in J0·2 at 653 K can be attributed to the influence of dynamic strain aging. At 893 K, a significantly higher (more than 200%) J0·2 was observed, since plastic deformation of the net section, rather than crack growth, occurred in this condition.