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

Abstract

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 beta parameter variation. The possibility of the higher harmonic ultrasound technique to monitor creep damage is quite obvious since a dramatic increase of the beta parameter of 300% on long-term crept material was observed in this study. (C) 2012 Elsevier Ltd. All rights reserved.