The significant effect of tantalum on the hydrogen-induced cracking of pipeline steel: Morphology, hydrogen permeation, and theoretical studies

Abstract

This study reported the significant influence of Ta on hydrogen-induced cracking of pipeline steels. It was found that with decreasing TaC size, the hydrogen diffusivity of steels was decreased, as the hydrogen trapping of TaC is surface-dominant. Ta inhibited crack initiation through deep H-traps provided by small semi-coherent/incoherent TaC (<35 nm), whilst trigger cracks directly at incoherent TaC/α-Fe interfaces when TaC > ~223 nm. Moreover, Ta suppressed crack propagation as it increased effective H-trap densities, optimized crystallographic characteristics (changing the proportions of Σ3, Σ11, Σ17 and high-angle grain boundaries), and inhibited H-dislocation interaction, which was more pronounced when TaC was smaller.