Abstract
ABSTRACT The nanoindentation creep behaviour of crept HR3C austenitic steels was investigated to study the microstructural evolution of the steel after long-term creep at 650 °C. The corresponding microstructure evolution was characterised by optical microscopy, scanning electron microscopy, electron back-scattered diffraction and transmission electron microscopy. Results show that the nanoindentation hardness and creep displacement decreased with increasing creep time. The dominated nanoindentation creep mechanism was most likely changed from dislocation slip to grain boundary (GB) sliding induced by the decrease of dislocations density inside the grain and coarsening of carbides at the GB. The coarsening and growth of the precipitates distributed along the GB weakened the pinning effect of the precipitates and accelerated the migration of the grain and twin boundaries. With prolonged the creep time, large numbers of cavities were formed at the grain boundaries, which might lead to terrible intergranular corrosion and brittle cracking under the action of stress and high temperature.
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