Evaluation of Tribological Behavior of X65, X70, and X80 Pipeline Steels in the Presence of Hydrogen

This study investigated the impact of microstructure on the wear behavior of X65, X70, and X80 pipeline steels in the presence of hydrogen. The ball-on-disk measurement technique was used before and after an electrochemical hydrogen pre-charging process. The microstructure was characterized via an optical microscope and a scanning electron microscope. An electrochemical hydrogen oxidation test was performed to assess the amount of hydrogen charged in steel. Microstructural analysis revealed that X65 steel consists of ferrite (F) and pearlite, while X70 and X80 steels contain F, bainite, and martensite phases. X80 steel exhibited the smallest grain size (2.3 μm), the lowest F volume fraction (75%), and the highest percentage of hard phases (25%). Microhardness testing showed that X80 steel had the highest hardness before and after hydrogen charging, corresponding to the highest amount of diffused hydrogen (7.4 × 10⁻⁶ mol/cm³). Before hydrogen charging, X80 steel displayed the highest wear resistance. However, after charging, the wear rates of X65, X70, and X80 increased by approximately 5%, 35%, and 67%, respectively. These findings suggest that the hardness of uncharged steels could influence their wear rate, while the hydrogen concentration could affect the wear resistance of charged steels.