Vsevolod I. Razumovskiy

In this work laser oxidation of the tempered martensitic steel was performed and the effect of the formed oxide layer on hydrogen embrittlement (HE) susceptibility was investigated. Influence of the laser process temperature on the morphology and the protectiveness of the oxide layer was scrutinized in the range 450-800 °C utilizing Slow Strain Rate Tensile (SSRT) tests combined with electrochemical hydrogen charging. In addition, pre-treatment of the steel with organic additive was employed to enhance the functional performance of the oxide layer through modification of oxidation kinetics. The optimal oxidation conditions were obtained at 600 °C resulting in the duplex oxide layer structure consisting of an inner Fe3O4 and outer Fe2O3 phase with thickness in range of 100 nm. Oxide layers formed on the steel surface exhibited effective hydrogen barrier properties, reducing hydrogen uptake by approximately 30% under electrochemical charging conditions and by up to 95% in a gaseous hydrogen atmosphere as quantified by Thermal Desorption Spectroscopy (TDS). Hydrogen diffusion inhibition was further confirmed by electrochemical permeation measurements, showing a reduced effective diffusion coefficient. HE susceptibility index derived from the tensile tests indicated 25% higher resistance to hydrogen-induced damage.

Comprehensive studies of hydrogen embrittlement in high-strength austenitic alloys under cryogenic conditions are scarce, leaving the combined effect of hydrogen charging and extreme temperatures largely unexplored. Given the demands of cryogenic applications such as hydrogen storage and transport, understanding material behavior under these conditions is crucial. Here, we present the first systematic study of hydrogen’s effect at liquid helium temperature (4.2 K) on the mechanical properties of precipitation hardened austenitic alloys, specifically the nickel-based Alloy 718 and austenitic stainless steel A286. Both materials were subjected to pressurized hydrogen charging at 473 K followed by slow strain rate tensile testing at room temperature and at 4.2 K. Hydrogen charging caused significant ductility loss at room temperature in both alloys. In contrast, testing at 4.2 K resulted in increased strength and no evidence of hydrogen embrittlement. Notably, materials pre-charged with hydrogen and tested at 4.2 K exhibited higher stress drop amplitudes and increased strain accumulation during serration events, suggesting persistent hydrogen–dislocation interactions and possible enhanced dislocation pinning by obstacles such as Lomer–Cottrell locks. These results indicate that while hydrogen influences plasticity mechanisms at cryogenic temperatures, embrittlement is suppressed, providing new insight into the safe development of austenitic alloys in cryogenic hydrogen environments.

The analysis of thermal desorption spectra (TDS) and the calculation of hydrogen detrapping activation energies rely on Gaussian peak deconvolution and Choo-Lee plot regression since 1982. However, this method imposes important assumptions about the number and shape of the TDS peaks used for fitting.In this study, we propose the fingerprint method, an alternative approach that eliminates these long-standing constraints. By applying the fingerprint analysis to eight TDS spectra from three different Fe-C model alloys, we demonstrate its exceptional sensitivity and ability to resolve activation energy distributions -- the material fingerprint -- unattainable with traditional methods. We further showcase by manual and automated analysis how the such obtained fingerprints can be used to uniquely distinguish the TDS spectra of each alloy independent of the heating rate. Thus the fingerprint method also increases experimental efficiency by reducing the amount of necessary heating rates for TDS down to one.

Copper (Cu) in steel production can be a residual element, causing challenges during steel processing, as well as an alloying element, improving corrosion resistance and providing hardenability by nanosized precipitates. For the transition toward a green economy, increased recycling rates in steel production and alternative energy carriers, such as hydrogen, are of vital importance. As hydrogen is known for its embrittling effect on high-strength steels, this work sought to explore possible mitigation strategies for hydrogen embrittlement (HE) with the help of Cu precipitates. Hydrogen trapping at Cu/Fe interfaces following the complex phase transformations in the Cu precipitation sequence from body-centered cubic (bcc) to the so-called 9R structure to face-centered cubic (fcc) was addressed by a series of systematic density functional theory calculations. In combination with thermodynamic calculations, the pressing question regarding which of the precipitate structures was most desirable for the tackling of HE was alluded to. We found that hydrogen trapping at the Cu/Fe interfaces increased from −0.05 to −0.18 eV following the precipitation sequence. Despite this relatively weak hydrogen trapping, which was in the range of dislocations, we showed through thermodynamic calculations that fcc Cu precipitates could still contribute to lowering the risk of triggering the hydrogen-enhanced localized plasticity (HELP) mechanism of HE.