Acoustical anisotropy and non-homogeneity of rolled steel plates

Abstract

Rolled steel plates were subjected to ultrasonic inspection in order to examine acoustical anisotropy and non-homogeneity along the thickness direction. Two vertical planes of the plate were observed under a microscope in order to investigate changes in microstructure. Shear wave velocities, which depend on both propagation and polarization directions, were measured for both 40 mm and 26 mm thick steel plates. Changes in the shear wave velocities L are found along the thickness direction. Especially, strong local anisotropy is found due to elongated ferrite grains in the near-surface zone. A high angle beam probe should be used carefully for ultrasonic testing on a plate exhibiting strong anisotropy.