Hydrogen Embrittlement of Steels

Abstract

Consideration of the relation between the cohesive energy and the surface free energy leads to the inference that dissolved hydrogen reduces the maximum cohesive resistive force of which the iron lattice is capable. This forms the basis of a mechanistic model for the velocity of hydrogen‐induced crack propagation in steels. The crack grows when the local tensile elastic stress normal to the plane of the crack equals the local maximum cohesive force per unit area as reduced by the large concentration of hydrogen drawn there by the effect of elastic stress on the chemical potential of hydrogen. The velocity of the growth is given by the solution of the relevant transport equation for the accumulation of hydrogen. Although quantifiable in principle the theory remains implicit because of current ignorance of the needed functional relationships, but some qualitative predictions and insights are possible, as well as the specification of important experiments.

Critical issues in hydrogen assisted cracking of structural alloys

“…High values of Cs, GH and EB promote H enrichment to exacerbate IHAC and HEAC. Emerging results support the notion that very high levels of crack tip H are accumulated, as likely necessary for the decohesion mechanism to be reasonable [38].…”

“…Stress and H Trapping Enrichment The presence of very large stresses in the sub-micron crack tip FPZ is a requisite for hydrogen embrittlement, as recognized qualitatively by Oriani [38]. The reason is the need to raise low lattice and trapped concentrations of H at crack nucleation sites to justify lowering cohesive strength of the lattice or interface.…”

Effect of atomic scale plasticity on hydrogen diffusion in iron: Quantum mechanically informed and on-the-fly kinetic Monte Carlo simulations

“…Among several mechanisms proposed for hydrogen embrittlement (HE) of metals, hydrogen-enhanced decohesion (HEDE) [4][5][6] and hydrogen-enhanced local plasticity (HELP) 2,7,8 have gained acceptance as the two most viable for stable phases. Material degradation via the formation of brittle hydride phases, 9 possibly stabilized by local stresses, 10 is also a viable mechanism but has not been found to be relevant for iron, 1 which is the material of interest in this work.…”

Corrosion in the Oil and Gas Industry: An Increasing Challenge for Materials

“…Due to the previously mentioned facts, an intensive effort has been done to understand the involved mechanisms and hundreds of papers have been published. [8][9][10][11][12][13][14] Despite those efforts, hydrogen embrittlement mechanisms continue to be widely discussed and different theories have been proposed. However, a generally recognized common feature of all the theories that attempt to explain embrittlement in nonhydride former materials is that some critical concentration of hydrogen must be reached at a potential crack site for failure to initiate.…”