Abstract
We studied the evolution of microstructure in a Martensitic Stainless Steel (JIS-SUS403) during creep by monitoring ultrasonic attenuation. After a series of creep samples with various strains under a tensile stress of 120MPa at 873K was obtained, small samples were removed from the creep samples and free vibration resonance frequencies and attenuation coefficients were measured with electromagnetic acoustic resonance (EMAR). EMAR is a combination of the resonant acoustic technique with a non-contact electromagnetic acoustic transducer (EMAT). We measured changes in ultrasonic attenuation of the small creep sample by free vibration resonance with EMAR through a magnetostrictive mechanism. The attenuation measurement is inherently free from any energy loss, resulting in pure attenuation in a metal sample. Furthermore, the evolution of microstructure was observed with electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The result from the small samples showed 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.
