Texture, local misorientation, grain boundary and recrystallization fraction in pipeline steels related to hydrogen induced cracking

In the present study, API X60 and X6OSS pipeline steels were cathodically charged by hydrogen for 8 h using 0.2 M sulfuric acid and 3 g/I ammonium thiocyanate. After charging, SEM observations showed that the hydrogen induced cracking CHIC) appeared at the center of cross section in the X60 specimen. However, HIC did not appear in the X6OSS steel. Therefore, electron backscatter diffraction (EBSD) technique was used to analyze the center of cross section of as-received X6OSS, X60 and HIC tested X60 specimens. The results showed that the HIC crack not only can propagate through (100>vertical bar vertical bar ND oriented grains but also its growth may happen in various orientations. In HIC tested X60 specimen, an accumulation of low angle grain boundaries around the crack path documented that full recrystallization was not achieved during hot rolling. Kernel Average Misorientaion (KAM) histogram illustrated that the deformation is more concentrated in as-received and HIC tested X60 specimens rather than in as received X6OSS specimen. Moreover, the concentration of coincidence site lattice (CSL) boundary in HIC tested X60 specimen was very low compared with other samples. The recrystallization area fraction in X6OSS steel was very high. This high amount of recrystallization fraction with no stored energy is one of the main reasons for high HIC resistance of this steel to HIC. The orientation distribution function (ODF) of the recrystallized, substructured and deformed fractions in as-received X6OSS and X60 steel showed relative close orientations in both as-received specimens. (C) 2014 Elsevier B.V. All rights reserved.