Ab initio study of the solubility and kinetics of hydrogen in austenitic high Mn steels

Chemical trends for the solubility and diffusivity of hydrogen in austenitic high Mn steels have been studied employing density-functional theory. Considering the dilute limit of hydrogen, we observe strong volumetric effects of substitutional Mn and interstitial carbon on the energetics of a hydrogen atom within the lattice. This volume dependence yields a significant increase both in the solubility and the mobility of the H impurity when comparing Fe(1-x)Mn(x)C(y) with pure Fe. By means of kinetic Monte Carlo calculations, we also show that H impurities can use Mn percolation chains as efficient diffusion channels. These trends may explain why Mn-rich steels are often observed to be more prone to hydrogen embrittlement than conventional austenitic steels.