Abstract
A delayed fracture test using a thin sheet specimen of a single-crystalline Fe-3wt%Si alloy under constant load in a hydrogen environment was performed. After the test, the fracture surface was investigated by scanning electron microscopy (SEM). Subsequently, dislocation structure and plastic strain beneath the fracture surface were investigated by electron channeling contrast imaging (ECCI) and electron backscattering diffraction (EBSD) correspondingly. The crack propagation was discontinuously and left the appearance of the striations on the fracture surface. Extensive plastic deformation was observed to accompany crack propagation. The crack tip plastic deformation associated with hydrogen effect during the crack propagation leaves three adjacent regions beneath the fracture surface: (Region C) the region immediately beneath the fracture surface has an extremely high plastic strain, (Region B) the region adjacent to Region C has high dislocation density and high plastic strain, and its width is constant despite the crack length increases, (Region A) the region away from the fracture surface has low dislocation density and low plastic strain, and its width linearly increases with the crack length. These findings reveal the effects of plastic deformation and hydrogen-dislocations interaction around the crack tip on the rate-limiting process of hydrogen-induced delayed crack propagation in thin specimens.
