The effect of hydrogen on the deformation mechanisms of 2.25Cr–1Mo low alloy steel revealed by acoustic emission

In this study, acoustic emission (AE) is systematically investigated in as-received and electrolytically hydrogen-charged 2.25Cr–1Mo steel during tensile testing. The role of hydrogen in the deformation mechanisms is discussed and the effects of hydrogen on the stacking fault energy (SFE) are elucidated. It is argued that the increase of AE counts in the elastic stage after hydrogen charging is caused by the promotion of dislocation multiplication. The sharp decrease (more than one order of magnitude) of cumulative energy in the deformation stage after hydrogen charging indicated that hydrogen decreased the SFE, and observations of the microstructure by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) verified the presence of a hydrogen hindered cross-slip. The experimental results are consistent with the hydrogen-enhanced local plasticity mechanism of hydrogen embrittlement. It is concluded that monitoring the AE energy decrease can be an effective technique for the evaluation of hydrogen embrittlement in body-centred cubic (BCC) materials that are easy to cross slip.