Impact of heat treatment on the mechanical properties of AISI 304L austenitic stainless steel in high-pressure hydrogen gas

Hydrogen environment embrittlement of metastable austenitic stainless steels is a well-known phenomenon partially related to the formation of strain-induced martensite. In the literature, hydrogen environment embrittlement is often discussed on the basis of nominal chemical compositions only and neglects effects of metallurgical production and processing. The aim of this study is to investigate the influence of the δ-ferrite volume fraction and grain size on the mechanical properties of a standard grade 1.4307 (AISI 304L) tested in high-pressure hydrogen gas. A negligible influence was found for δ-ferrite volume fractions between 2 and 10 %. This result is explained by the dominating influence of machining-induced α-martensite on the surface of the tensile samples. In contrast, the grain size was found to have a significant effect on hydrogen environment embrittlement. In particular, grain sizes smaller than 50 μm were found to have a higher ductility. The results are discussed with respect to stacking fault energy, formation of strain-induced α-martensite, trapping of hydrogen and microsegregations. The results are of particular interest for the materials selection and development of materials for hydrogen applications.