Investigation of hydrogen sulfide stress corrosion cracking of PH 13-8 Mo stainless steel

Slow displacement rate tensile tests were carried out in a saturated H2S solution to investigate the effect of hydrogen embrittlement on notched tensile strength (NTS) and fracture characteristics of aged PH 13-8 Mo stainless steel. Hydrogen diffusivity, permeation flux and apparent hydrogen solubility were determined by an electrochemical permeation method, and correlated with the inherent microstructure of the specimens. All aged specimens were susceptible to sulfide stress corrosion cracking (SSCC) to various degrees. Similar permeation properties were observed for specimens aged in the temperature range of 427 °C (800 °F) to 538 °C (1000 °F). In contrast, much lower diffusivity and hydrogen flux together with a higher solubility of hydrogen were found for the specimen aged at 593 °C (1100 °F), i.e. the H1100 specimen. For specimens aged below 538 °C, the resembling permeation behavior led to the same level of susceptibility to hydrogen embrittlement as revealed by their NTS losses. Whereas, the H1100 specimen with low diffusivity and hydrogen flux implied that less hydrogen could be transferred to the strained region, resulting in a low NTS loss. The trapping of hydrogen in the matrix enhanced the quasi-cleavage fracture for specimens aged below 538 °C in the notched tensile test. On the other hand, hydrogen tended to trap at grain boundary austenite of the H1100 specimen, resulting in an intergranular separation under the test.