Browsing by Author "Michler, Thorsten"

Fuel cell vehicles running on hydrogen are seen as the long term solution to enable sustainable mobility. Compressed hydrogen gas storage systems are a promising route for storing hydrogen on board of vehicles, provided that a reliable and cheap material capable of withstanding hydrogen embrittlement is found. In this paper, the physicochemical behaviour of stainless steel in the presence of hydrogen with special focus on a ductility minimum near room temperature is reviewed.

The surface oxide layer on nine different types of solution-annealed austenitic stainless steel (ASS) was evaluated by Secondary Ion Mass Spectrometry (SIMS). Tensile tests were conducted at 25 degrees C and -50 degrees C in hydrogen at 40 MPa and in air at atmospheric pressure. Relative reduction of area (RRA) was calculated accordingly. Additionally the martensite transformation curves were measured in air at -50 degrees C to evaluate the probability of the formation of alpha' martensite nuclei. A linear relationship between RRA and the calculated probability of the nucleation of alpha' martensite nuclei was found on samples represented by the following three oxides types; (a) thick oxide, (b) decaying sub-surface oxide and (c) thin surface oxides. However, type (d) with high constant oxide level down to 60 nm depth does not follow the trend. The observed variation of the oxide layer is linked to the variability of tensile test results. (C) 2013 Elsevier B.V. All rights reserved.

The local surface chemistry of a low-Ni austenitic stainless steel AISI type 304 used for tensile testing in hydrogen atmosphere is characterized by secondary ion mass spectrometry (SIMS). A chemical map on cylindrical austenitic stainless steel samples can be obtained even after a tensile test. In an effort to obtain the proper chemical element distribution on the samples, the influence of contamination and sample orientation is discussed. An iron oxide on top of a chromium oxide layer is present and Si segregation at grain boundaries is detected. Oxides are judged to reduce the initial hydrogen attack but to be of minor importance for crack propagation during the embrittlement process. (C) 2011 Elsevier B.V. All rights reserved.