Abstract: Influences of sulphureous impurity and micro-shrinkage on hydrogen assisted cracking (HAC) and fracture behavior of the super-strength low-alloy steel 40CrMnSzMo VA have been studied in this paper.By way of scanning electron microfractography (SEM)and electron probe microanalyser to investigate the fractography of material constantly strained to failure, it was found that the microscopic segregation of sulphureous impurity and micro-shrinkage not only increased strongly the susceptibility to hydrongen embrittlement (HE), but also made the HAC to initiate preferably in such regions with the assistant of stress induced diffusion of hydrogen. The microscopic observation revealed that the steel has commonly intergranular (IG) and quasi-cleavage (QC)features around the segregation of sulphureous impurity and micro-shrinkage for their strong effects of irreversible traps for hydrogen.

Key words: micro-shrinkage, sulphureous impurity, HAC, HE susceptibility