Understanding the effect of niobium on hydrogen-induced blistering in pipeline steel: A combined experimental and theoretical study

The effect of Nb on hydrogen-induced blistering in pipeline steel was investigated experimentally and computationally. Nb does not change the nucleation mechanism, but influences the nucleation sites and amount: when the individual precipitate independently contributes to retarding or promoting blister nucleation, the critical size of NbC is (similar to)226 nm, which decreases even to 120 nm when two adjacent precipitates are involved. Nb inhibits the blister growth through optimizing microstructure and NbC-induced strong hydrogen traps, showing no strong correlation with NbC size. Few-nanometer-sized NbC inhibits the blister on blister, while the large NbC facilitates the blister on blister through directly nucleating small blister at NbC/matrix interface and promoting dislocation-stress trap nucleation.