The hydrogen induced damage of generic Fe-C-Ti and Fe-C-V ferritic alloys was investigated to assess the influence of precipitates on the hydrogen sensitivity of a material. The precipitates, formed during heat treatment, were evaluated by scanning transmission electron microscopy (STEM). The hydrogen/material interaction was evaluated by: 1) melt and hot extraction to determine the total and diffusible hydrogen content, respectively, 2) permeation experiments to calculate the diffusion coefficient, 3) thermal desorption spectroscopy to determine the hydrogen trapping characteristics of the materials. Furthermore, two different types of hydrogen induced damage were evaluated, i.e. hydrogen assisted cracking and blistering, resulting from electrochemical hydrogen charging with and without the application of an external load, respectively. Evaluation of the hydrogen induced damage and the role of the precipitates was performed by combining optical microscopy, scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). An important though divertive role of diffusible hydrogen is observed in both damage mechanisms for the investigated microstructures. On the one hand, a large amount of diffusible hydrogen compared to strongly trapped hydrogen promotes hydrogen assisted cracking of materials, while on the other hand, the blistering phenomenon is delayed under such conditions.

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Hydrogen induced cracks were introduced in an ultra-low carbon (ULC) steel by subjecting it to electrochemical hydrogen charging. The damage characteristics were investigated for three material conditions, i.e. cold deformed, recovered, and recrystallized state. The aim of the work was to understand the effect of deformation induced defects on the hydrogen induced cracking of this material. Additionally, the effect of the charging conditions, i.e. charging time and current density, on the cracking characteristics were verified. The blister surfaces and related hydrogen induced cracks were studied by optical microscopy, scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Deformed samples were considerably more sensitive to hydrogen induced cracking, which demonstrates the important role of dislocations in hydrogen induced damage mechanisms. Permeation tests were performed in order to elucidate the role of hydrogen diffusion in the process. Charging conditions had a clear influence on the hydrogen induced cracking behavior of the material. This should be taken into account when designing experimental parameters in order to obtain results valid under real life conditions.@en