Measurements by SKPFM and Finite-Element Modeling of Hydrogen Atom Diffusion and Distribution in Ferrite and Bainite Contained in X80 Steel

Herein, the diffusion and distribution of hydrogen (H) atoms in ferrite and bainite contained in an X80 pipeline steel is studied by both scanning Kelvin probe force microscopy and finite-element modeling. The effect of metallurgical microphases on H-atom accumulation in the steel is analyzed. It is showed in the results that H-charging elevates the electrochemical dissolution activity of both ferrite and bainite contained in the steel, as indicated by the increased Volta potential and thus the decreased work function. The H atoms tend to accumulate at ferrite, making the local H-atom concentration much greater than the concentration at bainite. The results imply that, compared with bainite, ferrite is the location to accumulate more H atoms initiating hydrogen-induced cracks once the local H-atom concentration reaches a threshold value.