Proceedings of the 5th International Conference on Metals & Hydrogen L02

Proceedings of the 5th International Conference on Metals & Hydrogen L02

Study of hydrogen embrittlement in steels using pressurized disks

D. Lopes Pinto (*) * (1)1(2)2 , Y. Madi (1)1 , L. Lacourt (1)1 , N. Osipov (2)2 , S. Quilici (2)2 , A. El Ouazani Tuhami (2)2 , J. Furtado (3)3 , N. Gallienne (3)3 , J. Besson (*) * (1)1

  • (1) 1

    Centre des Materiaux, MINES Paris, Université PSL, CNRS UMR 7633 France

  • (2) 2

    Transvalor S.A., France

  • (3) 3

    Air Liquide, Innovation Campus Paris, France

  • (*) *

    (corresponding authors)
    daniella.lopes pinto@minesparis.psl.eu, jacques.besson@minesparis.psl.eu

Abstract

The susceptibility to hydrogen embrittlement of steels can be characterized using tests on pressurized disks (bulge test) following the ISO 11114-4 standard. Differently from the standard, this study aims at localising the disk rupture outside the clamping area. For that purpose, new disk geometries are investigated for the bulge test based on a comprehensive Finite Element (FE) study. Two geometries are proposed. The first one consists in a 3 mm thick disk whose centre is thinned so that its minimum thickness is 0.75 mm. The second one consists in a 2 mm thick disk in which an axisymmetric notch is machined. The notch radius is equal to 1.25 mm so that the minimum thickness is also equal to 0.75 mm. The geometries are designed so that the minimum thickness is that of the disk as proposed by the standard, which is 0.75 mm.

The validity of the proposed geometries is first checked by performing tests using helium to pressurize the disc. It is shown that failure occurs where plastic strain is maximum in areas predicted by the FE analysis. The modified setup is then used to study the effect of the hydrogen pressurization rate on the burst pressure. It is shown, as expected, that low rates favour embrittlement. The susceptibility to hydrogen embrittlement is characterized by the ratio of the burst pressure under helium to the burst pressure under H2. It is shown that this ratio depends on the geometry. It is higher in the case of the notched disk.

In order to understand the observed trends, FE simulations with a strong coupling between mechanics and hydrogen diffusion are performed. The finite element formulation is based on mixed displacement—pressure—volume variation elements used to prevent volumetric locking. Using these elements, the hydrostatic stress is a nodal variable so that it becomes straightforward to compute its gradient which strongly influences hydrogen diffusion towards highly stressed regions. The model qualitatively explains the higher susceptibly to hydrogen embrittlement in the case of notched disks.

Keywords

  • Disc test
  • Hydrogen embrittlement
  • Finite Element simulation

Introduction


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