Preparation of an overall intergranular fracture surface caused by hydrogen and identification of lattice defects present in the local area just below the surface of tempered martensitic steel

An overall intergranular (IG) fracture surface was prepared in a load reduction test and analyzed by low-temperature thermal desorption spectroscopy (L-TDS). The purpose was to clarify on the atomic scale lattice defects present in the local area just below the surface of a hydrogen-induced IG fracture in tempered martensitic steel. The tracer hydrogen peak corresponding to vacancies and vacancy clusters was present just below the IG fracture surface. Local plasticity and nano-voids were observed on and near the prior austenite grain boundaries by the combined use of electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI). These findings clearly indicate that local plastic deformation and associated vacancy formation play an essential role in hydrogen-induced IG fracture in tempered martensitic steel.