抄録
An ultrasonic techique for the evaluation of creep cavities in steel for high temperature use is proposed. By using samples taken from crept or ruptured specimens, longitudinal wave velocities in the parallel and normal propagation directions to the stress axis (VLP and VLN) were measured. Then the shear wave velocities both in the parallel propagation direction to the stress axis (VSP) and in the normal propagation direction for parallel and normal polarizations to the stress axis (VSNP and VSNN, respectively) were measured. These results showed that all of the ultrasonic wave velocities decrease linearly with increasing amount of creep cavities. Wave velocities were also sensitive to the directions of the propagation and the polarization. This sensitivity suggests the usefulness of VLP/VSP, VLN/VSNN and VSNP/VSNN as new parameters. The values of these three parameters were found to decrease linearly with an increase of the amount of creep cavities, and the comparison among these parameters showed that the ratio VLP/VSP was most sensitive to the amount of creep cavities. The evaluation method of the amount of creep cavities using the parameters of ultrasonic wave velocity may be useful for practical purposes because it does not require the propagation path length.
