Effect of Composition on Tensile Properties of AISI 316 Variants With Internal Hydrogen

The emerging hydrogen economy has the potential to enhance energy security in locations without abundant natural resources. Hydrogen enables large-scale integration of renewables into power generation, electrification of heavy transport, and advancement of manufacturing with lower emissions, such as in steel making. To enable this transition safely, the materials challenges associated with large-scale, high-pressure hydrogen storage, distribution and usage need to be resolved. Austenitic stainless steels are commonly used in high-pressure hydrogen applications due to their resistance to hydrogen-induced degradation, although many questions remain about the hydrogen-induced damage mechanisms in the class of material. Austenitic stainless steels, particularly grades like AISI 316 that have relatively high content of Ni and Mo, are generally less susceptible to hydrogen embrittlement (HE) than other grades of stainless steels. The underlaying mechanism is related to their high stacking fault energy, but there are still open questions regarding, for example, the role of hydrogen on deformation and subsequent microstructural damage evolution and its role in HE. In this work, different variants of AISI 316 were examined: AISI 316L (EN 1.4404), AISI 316plus (EN 1.4420), and 316LNiMo (EN 1.4435). The microstructure of the materials was characterized, and tensile testing was conducted after pre-charging with hydrogen until saturation (1380 bar H2, 300 °C, 10 days) to explore the effects of main alloying elements on the structural stability and suitability for service under high-hydrogen pressure. Tensile tests were performed under ambient temperature conditions applying a strain-rate of 1×10-3 mm/mm/s. Fracture surface morphologies and cross-sections adjacent to the fracture surfaces were analyzed using optical and electron microscopy techniques, including electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI). The tensile behavior of the studied materials is discussed based on the literature and the obtained results. The deformation and fracture results are interpreted in terms of potential HE mechanisms. Overall, the results from the systematic series of investigations are expected to significantly contribute to the understanding of the hydrogen-induced degradation in these alloys and the role of alloying elements in the management of HE.