Hydrogen transport in 17−4 PH stainless steel: Influence of the metallurgical state on hydrogen diffusion and trapping

The recent interest for dihydrogen concerning its ability to decarbonize numerous sectors of our society highlighted the necessity to develop alloys combining high mechanical properties and good resistance to hydrogen embrittlement. With this in mind, the 17–4 PH precipitation hardened stainless steel was studied in order to understand the interactions between hydrogen and the different microstructural elements. Advanced physicochemical characterizations (XRD, SEM, ACOM/TEM) were coupled with electrochemical permeation tests on different metallurgical states of 17–4 PH alloy. The apparent hydrogen diffusivity was around 10−13 m2.s−1 at 23 °C and was found highly dependent on the microstructure. More specifically, when copper precipitates were fine, the copper precipitates/matrix interfaces were found to be the major trapping site. In addition, nature of these interfaces, which can be varied depending on thermal treatments, seemed to influence reversibility of the trapping.