Correlation of metallurgical analysis & higher harmonic ultrasound response for long term isothermally aged and crept FM steel for USC TPP turbine rotors

This study investigated the higher harmonic ultrasound response of 9-12Cr ferritic-martensitic (FM) steel, long-term isothermally aged and crept up to 20,000 h near the operating temperature of ultra-super critical (USC) thermal power plants (TPP). Metallurgical analysis, including quantitative measurements of dislocation density and second-phase distribution showed that the lath conversion to sub-grain, Laves phase development, and coarsening of pre-existing second phase MX and M23C6 by aging could be correlated with β parameter variation. The possibility of the higher harmonic ultrasound technique to monitor creep damage is quite obvious since a dramatic increase of the β parameter of 300% on long-term crept material was observed in this study.