Theoretical study of temperature dependencies in HELP- and HEDE-based damage models on the fatigue behavior of ferritic steel by hydrogen

In this theoretical study, the influence of temperature dependencies in hydrogen embrittlement (HE) models on the fatigue damage of ferritic steel is investigated by using a coupled hydrogen-diffusion and crystal-plasticity finite-element simulation framework. We focus on the characteristic ‘bell-shaped’ dependence of HE on temperature and examine its effects by means of HE models based on hydrogen enhanced local plasticity and hydrogen enhanced decohesion mechanisms. Hydrogen-induced fatigue damage is monitored by a fatigue indicator parameter: maximized damage occurs within a narrow temperature range consistent with experimental results reported in literature. Our results arise from an interplay of plastic strain localization and hydrogen trapping, combined with a sufficiently efficient supply of hydrogen. The findings of this study highlight how the interplay of hydrogen diffusivity, trap filling kinetics, and available diffusible hydrogen plays a critical role for the temperature dependence of HE. In addition, the influence of varying trap binding energies is explored, which has a substantial effect on both temperature behavior and induced fatigue damage.