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Home  >  Journal list  >  Journal of the Society of Materials Science, Japan  >  Vol.55  No.4 (2006)  >  pp.416-423

Journal of the Society of Materials Science, Japan
<<Previous article Vol.55  No.4 (2006)   pp.416 - 423 Next article>>

Acoustic Damping Characterization and Microstructure Evolution during Creep of a High Temperature Bolting Steel

Toshihiro OHTANI1), Hirotsugu OGI2) and Masahiko HIRAO2)
1) Materials Lab., Ebara Res. Co., LTD.
2) Grad. Sch. of Eng. Sci., Osaka Univ.


Electromagnetic acoustic resonance (EMAR) is a contactless resonant method with an electromagnetic acoustic transducer (EMAT). This method is free from extra energy losses, resulting in the measurement of intrinsic ultrasonic attenuation in solids. In this study, the EMAR was applied to detect the creep damage of a Cr-Mo-V steel, JIS-SNB16 which is used for high temperature bolt. The material was exposed to the temperature of 923K at various stresses. We measured ultrasonic attenuation for 1-7-MHz frequency range as the creep advanced. The attenuation coefficient exhibits much larger sensitivity to the damage accumulation than the velocity. The attenuation experiences a peak at around 30% 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, dislocations’ recovery. This is supported by TEM observations for dislocation structure. EMAR exhibited a potential for the assessment of damage advance and the prediction of the remaining creep life of metals.


Keyword:
Creep damage, Cr-Mo-V steel, EMAT, Ultrasonic attenuation, Non-contact evaluation, Dislocation

Received: August 26, 2005
Published online: May 17, 2006
Copyright (c) 2006 by The Society of Materials Science, Japan

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