Impact of Mn on the solution enthalpy of hydrogen in austenitic Fe-Mn alloys: A first-principles study

Hydrogen interstitials in austenitic Fe‐Mn alloys were studied using density‐functional theory to gain insights into the mechanisms of hydrogen embrittlement in high‐strength Mn steels. The investigations reveal that H atoms at octahedral interstitial sites prefer a local environment containing Mn atoms rather than Fe atoms. This phenomenon is closely examined combining total energy calculations and crystal orbital Hamilton population analysis. Contributions from various electronic phenomena such as elastic, chemical, and magnetic effects are characterized. The primary reason for the environmental preference is a volumetric effect, which causes a linear dependence on the number of nearest‐neighbour Mn atoms. A secondary electronic/magnetic effect explains the deviations from this linearity. © 2014 Wiley Periodicals, Inc. Adding a substantial amount of manganese to steels yields a material with extraordinary mechanical properties. A tiny amount of hydrogen in high‐Mn steels, however, is already suffcient for the onset of devastating embrittlement effects. Using first‐principles methods, an attraction of both elements is revealed, providing a complete analysis of the elastic, chemical, and magnetic origin of this phenomenon. These insights contribute to strategies to better control the hydrogen distribution in steels.