Crystallographic texture before and after post weld heat treatment of high-frequency electric resistance welded API X65 linepipe

The microstructure and crystallographic textures of API X65 grade linepipe steel were studied in the base metal, the weld interface after high-frequency electric resistance welding (HF-ERW), and the weld interface following post-weld heat treatment (PWHT). Optical microscopy, scanning electron microscopy (SEM), and electron-backscattered diffraction (EBSD) were used to study the microstructure and texture evolution and correlated with Charpy V-notch impact toughness. The Charpy values were 172.9 ± 5.2 J for the base metal, 7.5 ± 1.6 J for the as-welded weld interface, and 69 ± 24 J after PWHT, with the latter still significantly lower than the base metal. Base metal showed a low fraction of low-indexed cleavage planes at about 9% and major texture components were (113)[110], (112)[110], and (332)[113]. In the as-welded condition, major intensities of rotated Cube (001)[110] and Goss (110)[001] texture components were observed near the weld interface. Although PWHT reduced the texture intensities, rotated Cube and Goss components were still observed. The fraction of cleavage planes was about 44% for the as-welded and about 30% for the PWHT-ed weld interface. Clearly, PWHT has reduced but not eliminated the detrimental rotated Cube and Goss textures at the weld interface. These detrimental textures likely have contributed to the low Charpy toughness after welding and continuing after PWHT.