Investigation of hydrogen assisted cracking of a high strength steel using circumferentially notched tensile test

The novel circumferentially notched tensile (CNT) test technique is used for the first time for an investigation of hydrogen assisted stress corrosion cracking. Effect of hydrogen on the fracture strength of high strength steel AS-4340 is examined in neutral 3.5% NaCl solution at room temperature and under hydrogen supply from within the material and/or external environment. A progressive drop in the stress intensity factor at the fracture was observed as a result of: (a) increasing span of hydrogen pre-charging (hence increasing internal hydrogen) and (b) decreasing rate of loading (hence increasing external supply of hydrogen). The measured critical stress intensity factors corresponding to varying degrees of supply of internal hydrogen are consistent with the computed hydrogen concentrations ahead of the crack tip. The experimentally determined threshold for hydrogen embrittlement in the regime of slower loading rates are consistent with the published data. The results presented here establish the usefulness of the CNT test technique for the investigation of HASCC in high strength steel over a wider range of loading rate.