Fracture criterion for hydrogen embrittlement of high strength steel

The notch tensile strength of a boron bearing steel at 1305 MPa has been investigated by means of slow strain rate tests after electrochemical hydrogen charging. Results show that the notch tensile strength of the steel decreased with increasing diffusible hydrogen content and the decrease in the notch tensile strength was more pronounced for specimens at a higher stress concentration factor. Finite element analysis results show that the dependence of the notch tensile strength on stress concentration factor cannot be accounted for by the local peak stress and local peak hydrogen concentration; however, the equivalent plastic strain at the notch root at an applied stress equal to the notch tensile strength was independent of stress concentration factor. The equivalent plastic strain at the notch root can be used as a fracture criterion for hydrogen embrittlement of the steel.