Wear Degradation of High-Nitrogen Austenitic Steels for Internal Combustion Engines in Hydrogen-Containing Alternative Fuels

The development of hydrogen and hydrogen-containing fuel infrastructure requires structural materials resistant to the combined effects of hydrogen exposure, cyclic contact stresses, and tribological loading. This study investigates hydrogen-assisted degradation of two cold-worked high-nitrogen Cr–Mn–N austenitic steels, DDT68 and P900, under dry rolling–sliding contact after controlled electrochemical hydrogen charging. Hydrogen uptake, wear intensity, microstructure, subsurface damage, and rolling contact fatigue (RCF) were analyzed comparatively. The mean grain size was approximately 25 μm for DDT68 and 43 μm for P900, while hydrogen concentrations were 15–17 and 12–14 ppm, respectively. Hydrogen increased the wear intensity of both steels, with wear acceleration factors ranging from approximately 2.1 to 10.0 for DDT68 and 1.4 to 4.2 for P900 over 200–600 N. The differences in wear intensity between DDT68 and P900 after hydrogen charging were statistically significant over the investigated load range. The finer-grained DDT68 exhibited greater hydrogen retention and a stronger hydrogen-associated wear response. The observed damage is consistent with HELP-assisted deformation localization, with possible contributions from HEDE and hydrogen–defect interactions, promoting subsurface microcracking, delamination, and spalling. Hertzian analysis located the maximum subsurface shear stresses approximately 0.035–0.062 mm below the contact surface. Finally, an indicator-based framework combining wear response, hydrogen content, and prescribed mass-loss reference levels is proposed for comparative durability assessment under the investigated conditions, rather than as a universally calibrated service-life prediction model.