Effect of temperature on hydrogen assisted fatigue crack growth rate of a gaseous hydrogen precharged austenitic stainless steel

The fatigue crack growth rate (FCGR) of austenitic stainless steel 1.4404 was measured as a function of temperature in both, uncharged and in gaseous hydrogen precharged conditions. At room temperature, the FCGR of precharged 1.4404 specimens is by a factor of about 5 higher compared to uncharged specimens. The related FCGR at ΔK = 22–25 MPa m0.5 as a function of temperature revealed a maximum at temperatures between 250 and 270 K. This is about 50 K higher than the temperature of minimum tensile relative reduction of area (RRA), which is about 220 K. An interpretation based on the respective governing embrittlement mechanism, HEDE and/or HELP, is proposed. For the interpretation of the experimental findings, a phenomenological model is developed, based on the mechanics of metals and on the thermodynamic defactant concept, which incorporates the two prominent mechanisms for hydrogen embrittlement, HEDE and HELP. From the comparison of our theoretical and experimental results we conclude that the experimentally observed temperature dependence of hydrogen effects on the mechanical properties of the studied steel can be explained quite well by HELP but not by HEDE.