2.25%Cr-1%Mo鋼のクリープ損傷に伴う超音波減衰と材料微視組織の変化

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We studied microstructure evolution caused by creep in 2.25%Cr-1%Mo steel using ultrasonic attenuation. The material was exposed to the temperature of 923K at various stresses. We used electromagnetic acoustic resonance (EMAR) to measure attenuation. EMAR is a contactless acoustic-resonance method and free from energy losses associated with contact transducer, resulting in the intrinsic attenuation in solids. We used axial-shear-wave EMAT, which transmits and receives SH wave propagating in the circumferential direction of a cylindrical specimen. The attenuation coefficient was obtained from the ringdown curve at the resonance by interrupting the creeping. The attenuation exhibits much larger sensitivity to the damage accumulation than the velocity. Approaching the rapture, the attenuation coefficient becomes five times as large as the initial state. We correlate this attenuation evolution with the microstructure change, especially, the changes in dislocation structure that most contributes to the attenuation change. This is supported by TEM observations. The technique has a potential to assess the damage advance and predict the creep life of metals.
2002-02-15