Mechanism of Hydrogen Embrittlement in Iron and Low Strength Steels

The Griffith-Irwin fracture mechanism in relation to hydrogen embrittlement in iron and low strength steels is explained. Lattice embrittlement theory and modified Elliott crack propagation are covered. Theory of H-enhanced localized plasticity and plastic instability and their analogies to liquid metal embrittlement and stress corrosion cracking are addressed. Internal stress theory exaggerating the role of molecular H release at defects in the metal is criticized. Fractography data and experiments dealing with H effects on dislocation form are surveyed. Atomic theory approach is covered that was applied to alpha Fe and nickel and employed molecular dynamics, first principles techniques, embedded atom method, etc. In its current state, it relies on two-dimensional models, which impairs its validity. A convergence between the atomic approach and the theories of lattice embrittlement and H enhancing is noted.