Evaluation of hydrogen induced damage of steels by different test methods

The deleterious effect of hydrogen on mechanical properties of microalloyed pipeline (X70) and structural (S355) hot rolled steel strips was evaluated by static tensile testing of smooth and notched specimens (flat specimens with a central hole) and Charpy V impact testing. Hydrogen induced changes of the fatigue crack growth behavior were also examined. Most of the tests were performed on specimens exposed to the ageing for 4-years as well as on specimens who were after four years of ageing electrolytically charged with hydrogen. The comparison of mechanical properties of both studied steels before and after hydrogen charging showed that the degradation effect of hydrogen may or may not be detected, depending on the conditions of testing. The effect of hydrogen on the development of local plastic strain during deformation and fracture process as well as plastic zone size around the holes, notches and cracks observed on surface specimens was studied by differential interference contrast in optical microscope. The most important result of this work was the finding that the plastic zone size at the tip of the growing fatigue crack observed on the surface of hydrogenated specimens was significantly larger than for nonhydrogenated specimens.