We studied the evolution of microstructure in a Cr-Mo-V steel (JIS-SNB16) during creep by monitoring internal friction. After obtaining a series of creep samples with various strains under a tensile stress of 25 and 35 MPa at 923K, we removed small samples from the creep samples and measured free vibration resonance frequencies and internal friction with electromagnetic acoustic resonance (EMAR). EMAR is a combination of the resonant acoustic technique with a non-contact electromagnetic acoustic transducer (EMAT). The measurement of internal friction is inherently free from any energy loss, resulting in pure attenuation in a metal sample. Furthermore, we observed the evolution of microstructure with electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The result from the small samples shows the same trend as our previous result from larger sample. We propose a non-destructive method using EMAR to evaluate creep damage in small specimens sampled from structural metals in-service.
