Influence of Hydrogen on the Equilibrium of a Dislocation Submicrocrack in α-Iron

Numerical methods are used to analyze the influence of hydrogen on the fracture of steels with bcc lattice by the mechanism of microcleavage. The behavior of submicrocracks at the head of a dislocation pileup is studied under uniaxial tension. In the case of delivery of hydrogen by merged dislocations of the pileup into the submicrocrack, it loses stability due to the adsorption decrease in the specific surface energy earlier than it becomes possible under the action of the pressure of hydrogen in the crack. We deduce the dependences of the fracture stress on the specific surface energy and the amount of hydrogen delivered by dislocations into the submicrocrack. The influence of hydrogen condensed on dislocations on the formation of submicrocracks is significant. We establish the relationship between the amount of hydrogen condensed on dislocations, the concentration of diffusing hydrogen in the metal, and rapid degradation of mechanical properties of steel even for small concentrations of dissolved hydrogen.