Hydrogen-Induced Delayed Fracture in a 1.5 GPa Dual-Phase Steel via Coalescence of Surface and Sub-surface Cracks

Hydrogen embrittlement susceptibility of a 1.5 GPa class ferrite/martensite dual-phase steel was evaluated using the U-bend test. Hydrogen-induced delayed fracture occurs via the coalescence of surface and sub-surface cracks. While surface cracking is caused by the growth of pre-existing cracks formed during the U-bending, sub-surface cracks are formed by tensile stress that evolved during reloading. Despite the non-monotonic stress gradient across the U-bent cross-section, the crack propagation mechanism for surface and sub-surface cracks is identical. Graphical Abstract