Relationship between mechanical response and microscopic crack propagation behavior of hydrogen-related intergranular fracture in as-quenched martensitic steel

The present study investigated the relationship between the mechanical response and microscopic crack propagation behavior of hydrogen-related intergranular fractures in high-strength martensitic steel. In contrast to cracks in the uncharged specimen, the cracks in the hydrogen-charged specimen propagated under a small crack opening displacement. Crack tip bluntings were frequently observed in the uncharged specimen, whereas no obvious blunting of the tip was observed in the hydrogen-related intergranular cracks. In addition, a high strain was localized around the hydrogen-related intergranular crack tip. The results indicate that strain localization can induce the formation of new quasi-cleavage cracks inside prior austenite grains ahead of the existing crack tip. The hydrogen-enhanced decohesion at prior austenite grain boundaries and the quasi-cleavage crack formation/propagation ahead of the arrested intergranular crack result in hydrogen-related crack propagation with a small crack opening displacement.