Abstract
The long term creep rupture properties of 2.25Cr-1Mo ferritic steel have been studied at eight temperatures between 723 and 923 K and the rupture lives varied in the range of 100 to 113 000 h. Three fracture mechanisms have been identified on the basis of microstructural investigations, namely transcrystalline, cavitation, and recrystallisation. A transcrystalline fracture mode was observed at most of the test temperatures and often up to medium term rupture lives. A transition from transcrystalline fracture mode to cavitation mode was observed at very long rupture lives, whereas a transition to recrystallisation fracture mode was observed at the highest test temperatures. The variation of reduction in cross-sectional area of the sample at fracture, with the Larson-Miller parameter, has been found to reflect the transitions in fracture behaviour. Changes in the density of the material due to creep deformation were measured and found to exhibit a close correlation with reduction in cross-sectional area.
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