Effect of Hydrogen on the Impact Behaviour of an Austenitic Fe-Mn-Al Alloy.

Impact studies on hydrogen precharged and uncharged charpy specimens of Fe-0.45C-17Mn-2.8Al steel were conducted in the temperature range 77 to 300 K. For the uncharged specimens, it was observed that values of total absorbed energy and crack propagation energy decreased with lowering of temperature. The crack initiation energy followed the same trend in the temperature range 77-230 K but decreased with increase of temperature above 230 K. Hydrogen precharging resulted in decrease of these energy values and also the value of dynamic yield stress at all temperatures. Maximum decrease was noted in the temperature range 220-300 K. Analysis of fracture surfaces, using the X-ray diffraction technique (XRD) and scanning electron microscopy (SEM) studies, suggested that the stable austenitic Fe-Mn-Al steel is prone to hydrogen degradation even at low temperatures and high strain rates. These observations are rationalised on the basis of an atomistic model for hydrogen embrittlement which does not essentially require redistribution of hydrogen concentration or martensitic transformation during the test.