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 ˜ 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.