Characterization of creep-fatigue in ferritic 9Cr-1Mo-V-Nb steel using ultrasonic velocity

Abstract

The microstructural evolution of ferritic 9Cr-1 Mo-V-Nb steel, subjected to creep-fatigue at 550 OC, was evaluated nondestructively by measuring the ultrasonic velocity. The ultrasonic velocity was strongly depended on the microstructural changes during creep-fatigue. The variation in the ultrasonic velocity with the fatigue life fraction exhibited three regions. In the first region (within 0.2 Nr), a significant increase in the velocity was observed, followed by a slight increase between the fatigue life fractions of 0.2 Nf and 0.8 Nf and a decrease in the final region. The change of the ultrasonic velocity during creep-fatigue was interpreted in relation to the microstructural properties. This study proposes an ultrasonic nondestructive evaluation method of quantifying the level of damage and microstructural change during the creep-fatigue of ferritic 9Cr-lMo-V-Nb steel. (c) 2008 Elsevier B.V. All rights reserved.