Texture studies of austenitic weld metal using elastic surface waves

Abstract

Austenitic weld metal exhibits an epitaxially developed columnar grain structure which is elastically highly anisotropic. Ultrasonic inspection of such waves has proved difficult because of the directional variability of the velocity and attenuation of elastic waves. Beam skewing, bunching, and spreading take place. If the texture within the weld varies strongly from point to point, it is likely that the reliability of conventional inspection methods will also vary. The purpose of this paper is to outline the use of surface waves in studying the spatial variation of texture within austenitic weld metal. Rotated surface acoustic wave velocities have been measured and compared with X-ray pole figures for several different weld structures and for cast material. Pole figures obtained from an austenitic butt weld reveal that it processes a strong 〈200〉 preferred orientation with the [200] axis parallel to the columnar grain axis, but with isotropic behaviour around this axis. Macroscopically, the weld thus processes a special orthotropic structure. Rotated surface wave velocity measuremen ts about the [200] axis show no directional dependence. On the two other planes, mutually perpendicular to the (200) plane and to each other, the surface wave velocity is directionally dependent in a manner which agrees qualitatively with theoretical calculations from a special orthotropic model. Further correlation was obtained from measurements on a cast austenitic ingot.