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 0.5mol/L H₂SO₄ with 1g/L CH₄N₂S at room temperature for 24h. It is found that the amount of hydrogen increases linearly with the exponent of pre-strain, i.e., _{C H} = 11.963 + 0.00385exp(1.144_εP). 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.