Hydrogen Trapping Models in Steel

This article describes the role of hydrogen trapping in steel. Trapping increases the solubility of hydrogen and decreases the diffusivity. Traps are characterized by their nature, i.e., reversible or irreversible, saturable or unsaturable. A dislocation core is a saturable, reversible trap, while voids and crack are unsaturable, reversible traps. A trap model based on saturable, reversible traps is developed, which is slightly different from the trap model of McNabb and Foster. In equilibrium, the trap model corresponds to Orianiʹs trap model. Kumnick and Johnson found experimentally that the trap density increases as the plastic strain increases. Using their trap data, it is shown that equilibrium between hydrogen in lattice sites and trap sites can be assumed when strain rates are used as in standard tensile tests.