Effect of Hyperbaric Chamber Gas on Transformation Texture of the API-X70 Pipeline Weld Metal

The development of the texture components in the X70 weld metal under several shielding
environments was investigated using the electron-backscattered diffraction (EBSD) and orientation
imaging microscopy (OIM) techniques. A new method for assigning the reference
direction (RD), transverse direction (TD), and normal direction (ND) was introduced based on
the morphological orientation of the grains. The analyses showed that different shielding gases
affect the weld metal texture and microstructure. The shielding environment with pure argon
shows the highest orientational pole density values and dominant acicular ferrite microstructure.
It was observed that the distribution of misorientation angle and special coincidence site
lattice (CSL) grain boundaries play significant roles in determining the tensile characteristics of
the weld samples. Moreover, the bainite lattice orientation was found dependent on the directional
heat flow unlike the other detected constituents.