440 Analysis of Ultrasonic Reflection by Wavelet Transform for Thermally Degraded Cr-Mo Steel

Abstract

Ultrasonic nondestructive tests with a high frequency contact transducer were carried out to thermally degraded Cr-Mo steel. Frequency dependent ultrasonic characteristics were obtained by means of Morlet wavelet transform. It is shown that, with the increase of grain size, the ultrasonic attenuation and its change with frequency gradually increased within a significant frequency band. Velocity was found hardly to change with thermal degradation. The effectiveness of time-frequency analysis for the quantitative evaluation of thermal damage is clarified.