A mechanistic theory of hydrogen embrittlement of steels

TLDR

Dissolved hydrogen lowers the maximum cohesive force that the iron lattice can resist, as inferred from the relationship between cohesive energy and surface free energy. The study aims to develop a mechanistic model for the velocity of hydrogen‑induced crack propagation in steels. The model assumes crack growth occurs when local tensile stress equals the hydrogen‑reduced cohesive force per area, with velocity determined by solving the hydrogen transport equation. While the theory cannot yet be quantified due to unknown functional relationships, it yields qualitative predictions and identifies key experiments.

Abstract

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.