In this study, effect of severe cold rolling of API 5L X70 pipeline steel on the microstructure and texture evolution and hydrogen permeability is deeply investigated. Optic microscopy, X-ray diffraction technique, and Devanathan-Stachurski hydrogen permeation test are conducted on two different cross sections of the sample: the normal surface and 45 deg twice-tilted surface. Results indicate that the microstructures of the initial and cold-rolled steel include granular ferrite and conventional upper bainite. However, the equi-axed grains of the as-received steel is changed to elongated ones with low-angle grain boundaries due to cold rolling. The X-ray diffraction macro-texture analysis revealed a rotation in crystallographic texture from the predominant {110}||ND to the {110}||ND on the normal surface and in the 45 deg tilted cross section indicate that the predominant {110}||ND texture is replaced by an intense texture of {100}||ND due to cold rolling. Investigation of hydrogen permeability in cold-rolled samples with a textured microstructure shows a higher diffusion coefficient into {100} planes compared to {110}. Also, it was observed that the increase in the defects due to applying cold work results in a decrement of the hydrogen diffusivity into the same planes and an increase in its solubility.

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