Evolution of microstructure and acoustic damping during creep of a Cr–Mo–V ferritic steel

The microstructural evolution of the Cr–Mo–V ferritic steel ASTM A193-B16, subjected to a tensile creep test at 923 K, was studied by monitoring the shear wave attenuation and velocity using electromagnetic acoustic resonance (EMAR). This study revealed an attenuation peak independent of the applied stress at around 30% of the creep life and a minimum value at 50%. This novel phenomenon is interpreted as resulting from microstructural changes, including strain hardening and dislocation recovery. This interpretation is supported by transmission electron microscopy observations of the dislocation structure. The relationship between attenuation change and microstructure evolution can be explained with the string model for dislocation vibration. EMAR is shown to have the potential to assess the progress of creep damage and predict the remaining creep life of various metals.