Hydrogen embrittlement behaviour of AISI 321 stainless steel: Influence of temperature in tensile testing

Gas turbines powered by hydrogen offer a promising route to cleaner energy production. However, the use of austenitic stainless steel AISI 321, a common material for fuel supply pipes presents challenges due to its susceptibility to hydrogen embrittlement, which is often linked to deformation-induced martensite formation and the presence of δ-ferrite. While deformation-induced martensite is suppressed above the alloy’s Md temperature, the embrittlement role of δ-ferrite at elevated temperatures remains unclear. In this study, slow strain rate tensile tests were conducted in both air and pressurized H2 gas environments at room temperature (RT) and at 150 °C. Hydrogen embrittlement was observed at room temperature, as evidenced by a relative reduction in area of 0.44, whereas specimens tested at 150 °C exhibited no measurable embrittlement. Fractographic and microstructural analysis revealed that cracking of δ-ferrite phase boundaries at room temperature is associated with the formation of deformation induced martensite. These findings demonstrate that hydrogen embrittlement in AISI 321 during tensile testing is primarily governed by the presence of deformation-induced martensite, and that δ-ferrite alone is insufficient to cause embrittlement at elevated temperatures. In addition, the effect of loading mode on HE behaviours is also discussed. The insight provided in this study is crucial for guiding material selection in hydrogen-fuelled gas turbines.