Effect of pre-strain on hydrogen embrittlement of high strength steels

The effect of the pre-strain on hydrogen embrittlement (HE) of high strength steels was investigated by slow strain-rate tensile (SSRT). The specimens were electrochemically hydrogen-charged in 0.5 mol/L H2SO4 with 1 g/L CH4N2S at room temperature for 24 h. It is found that the amount of hydrogen increases linearly with the exponent of pre-strain, i.e., C H = 11.963 + 0.00385 exp ( 1.144 ε P ) . The HE susceptibility of the alloy initially decreases and then increases with increasing pre-strain. The ultimate tensile strength for the hydrogen-charged specimen is highest in the 3% pre-strain, which is interpreted by competition between strain hardening and Hydrogen Enhanced Decohesion (HEDE) mechanism. The fracture mode shows a mixed mode fracture of quasi-cleavage and intergranular fracture for hydrogen-charged specimens while the fracture mode exhibits dimples for hydrogen-free specimens.