非線形超音波法による高クロム・フェライト系耐熱鋼溶接継手材のクリープ損傷評価

抄録

We investigated creep-induced evolutions of two nonlinear acoustic characterizations; resonant frequency shift and harmonic components, in welded joints the of high Cr ferritic steel, ASME Gr. 92 steel with electromagnetic acoustic transducer (EMAT). We used axial-shear-wave EMAT, which transmits and receives shear wave propagating in the circumferential direction along a cylindrical surface of a circular specimen. The EMAT was consisted by a solenoidal coil and meander-line coil surrounding the cylindrical sample. Creep specimens cut from tests of thick-walled welded joints were performed at 873 K and 90 MPa and interrupted at several creep life ratio. After two nonlinear acoustics and attenuation showed peaks at 20% of creep life, increased from 40% of the life. These phenomena related to evolution of dislocation structure and initiation and growth of creep voids.