محمدعلی مهتدی بناب

Three grades of high strength pipeline steel (API X60, X60SS, and X70) are subjected to cathodic hydrogen charging to determine the susceptibility of each steel grade to hydrogen-induced cracking (HIC). The specimens are subjected to tensile stress until failure to generate stress-strain, ductility, and toughness data. The fractured specimens are analyzed using a scanning electron microscope equipped with an EDS detector to determine crack initiation sites for the investigated grades of steel. The expectation that the X60SS steel grade will perform better than other grades is not met, instead it is found that under the cathodic hydrogen charging condition, the X60SS is more susceptible than the other two steel grades with respect to loss of toughness, ductility, and ultimate tensile strength. The presence of Ca-Albased inclusions is the most common along the fracture surfaces. Therefore, these inclusions also act as fairly strong trapping sites that under plastically strained conditions, they can result in fisheye features which severely impact the mechanical properties of the steel specimens.