Effect of vanadium content on hydrogen diffusion behaviors and hydrogen induced ductility loss of X80 pipeline steel

Abstract

In this study, the number and size distribution characteristics of fine nanoscale precipitates and their effects on hydrogen diffusion and hydrogen induced ductility loss were investigated in X80 pipeline steel. The results showed that with the increase of vanadium content, more vanadium carbides precipitated in the tested steels and the proportion of precipitates with size less than 10 nm distinctly increased, which fixed a large amount of diffusible hydrogen atoms as effective traps. The hydrogen diffusion coefficient decreased from 5.12 × 10−6 cm2 s−1 in the vanadium-free V1 steel to 9.94 × 10−7 cm2 s−1 in the V4 steel with 0.13% V. In addition, for the tested steels containing vanadium, the hydrogen embrittlement gradually decreased with increasing nanoscale vanadium precipitates, which pinned the movable dislocations and weakened the hydrogen-enhanced localized plasticity. The V4 steel with 0.13% V had the best performance to resist to hydrogen induced ductility loss.