Effect of Hydrogen on Fracture of Austenitic Fe-Mn-Al Steel

Abstract

In this investigation a stable high manganese austenitic steel, 0.45C-17Mn-2.8Al, has been studied for hydrogen embrittlement using cathodically precharged specimens. Tensile testing of axisymmetric and plane strain specimens precharged with hydrogen show an appreciable loss of 8-10% reduction in area (RA) whereas the loss in % elongation is lesser. The true fracture strain decreased from 0.88 to 0.73 for axisymmetric and from 0.79 to 0.60 for plane strain specimens. Hydrogen precharging is observed to result in decrease of CTOD at crack initiation by about 0.07 mm and a decrease in crack tip fracture strain for crack initiation from 0.53 to 0.34. The greater effect of hydrogen precharging thus observed is attributed to existence of higher stress triaxiality in CTOD and plane strain tensile testing in comparison to axisymmetric one.
On SEM examination of fracture surfaces the uncharged tensile specimens showed only dimpled fracture, the precharged specimens showed transition from dimpled to quasicleavage and intergranular fracture near the surface. Regions close to the pre-fatigue tip in CTOD specimens depict intergranular fracture. The fractographic changes are attributed to the combined role of stress intensity and hydrogen concentration variation arising out of hydrogen transport inside the specimen.