The effect of hydrostatic stress on the hydrogen induced mechanical degradation of dual phase steel : a combined experimental and numerical approach

The present study evaluates the influence of the local hydrostatic stress state and resulting local hydrogen concentration on the hydrogen embrittlement of a dual phase steel. Different tensile sample geometries, with and without the presence of a notch, are selected to induce different hydrostatic stress concentration gradients upon mechanical loading. Hydrogen charging was done simultaneously with constant loading to allow coupling with numerical results. These samples were compared to specimens tested after charging without mechanical loading and tests done in air, as a reference. The tensile specimens were sufficiently rapidly fractured to assess the fractography prior to significant hydrogen redistribution. The maximal concentration of hydrostatic stress and related hydrogen concentration occurs at the fracture surface in front of the notch tip. Moreover, the present alumina inclusions in this material are significantly embrittled in the region where hydrostatic stress and hydrogen concentration peak. This is demonstrated by the presence of hydrogen induced fish-eyes in these specific regions