Role of cold rolled followed by annealing on improvement of hydrogen induced cracking resistance in pipeline steel

In this study, we investigated the effect of cold rolled followed by annealing on hydrogen induced cracking susceptibility in an API X60 pipeline steel. To this, we carried out cold rolling on X60 steel up to 20%, 50% and 90% in thickness reduction to change the microstructure and texture of steel. Then, we annealed all specimens at 850 degrees C for 90 s. We studied all tested specimens by electron backscatter and X-ray diffraction techniques. EBSD results showed that the grain refinement process was properly done via cold rolling and annealing treatments in tested specimens. However, the dislocation density was high for all tested steels. Moreover, electrochemical hydrogen charging experiment on tested steels proved that all specimens were still highly susceptible to hydrogen induced cracking. Therefore, we increased the annealing temperature and its duration of the 90% cold rolled specimen (the specimen with finest grains) up to 950 degrees C for 5 min. Interestingly, there was no HIC crack on this steel after hydrogen charging experiment. EBSD measurements on this steel showed strong textures of {100}//ND and {111}//ND. As a result, such strong textures, low Kernel Average Misorientation data, a high proportion of recovered grains and coincidence site lattice boundaries were recognized as the most important reasons for the highest HIC resistance in the mentioned steel.