Abstract
In this study, we investigated the relationship between microstructural change and the evolutions of two nonlinear acoustic characterizations, resonant frequency shift and other three-wave mixing, with electromagnetic acoustic resonance (EMAR) throughout the creep life in welded joint for high Cr terrific heat resisting steel, ASME Grade 122. EMAR was a combination of the resonant acoustic technique with a non-contact electromagnetic acoustic transducer (EMAT). We used bulk shear-wave EMAT. Creep tests of thick welded joints specimens were interrupted at several time steps at 873 K, and100 MPa. Two nonlinear acoustic parameters and ultrasonic attenuation decreased from the start to 40% of creep life. After that, they gradually increased to rupture. Creep void initiated from 40% of life, and slightly increased to 90 % creep life. After that it rapidly increased to the rupture. The changes of two nonlinear acoustic parameters, attenuation caused by the microstructural change related to creep void initiation and growth. This noncontact resonance-EMAT measurement can monitor the evolution of nonlinear acoustics throughout the creep life and has a potential to assess the Type IV creep damage advance and to predict the creep life of high Cr ferritic heat resisting steels.
