Acoustic Damping Characterization and Microstructure Evolution during Creep of a Martensitic Stainless Steel
Toshihiro OHTANI
Abstract:Creep-induced microstructural evolution of a martensitic stainless steel, JIS-SUS403, subjected to tensile creep at 873 K, was studied by monitoring the shear-wave attenuation and the velocity using electromagnetic acoustic resonance (EMAR). Taken into account was the observation that the contact-less transduction based on the magnetostrictive effect was the key establishing monitoring of microstructural change in the bulk. The attenuation coefficient shows a peak at around 20% and a minimum value at 50 % of the creep life, being independent of the applied stress. This novel phenomenon is interpreted as resulting from microstructure changes, especially, dislocationsf recovery, which is supported by TEM observations for dislocation structure. The relationship between changes of attenuation and velocity and microstructure evolution can be explained with the string model for dislocation vibration. Thus, it was possible to use this EMAR assessment method to assess the progress of damage in metals and predict their remaining creep life. Key Words:Creep damage, Martensitic stainless steel, Ultrasonic attenuation, Non-contact evaluation, Dislocation damping