Role of crystallographic texture in hydrogen-induced cracking of low carbon steels for sour service piping

This work presents the results of ongoing investigations aimed at determining the influence of crystallographic texture on hydrogen-induced cracking (HIC) in low carbon steels for sour service piping. Electron backscatter diffraction (EBSD) and X-ray texture measurements have been performed on HIC samples of API 5L X46 and ASTM A106 steels. The results obtained in this study show that the resistance to HIC of low carbon steels for sour service piping could be improved through crystallographic texture control and grain boundary engineering. Controlled rolling schedules can be proposed in order to induce a crystallographic texture dominated by the {112}//ND, {111}//ND, and {011}//ND fibers, where ND is the sample normal direction. Such a texture is expected to decrease significantly the steel susceptibility to HIC by (1) reducing the number of available transgranular and intergranular low resistance cleavage paths provided by the {001}//ND oriented grains, (2) reducing the probability of crack coalescence and stepwise HIC propagation through large HIC-induced plastic strain, and (3) increasing the number of high resistance intergranular crack paths provided by coincidence site lattice (CSL) boundaries and low-angle boundaries between grains with orientation within the {111}//ND texture fiber.