Berlin 2012 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 30: Functional Materials III

MM 30.1: Vortrag

Mittwoch, 28. März 2012, 10:15–10:30, H 0106

Impact of alloying elements on H solubility in steels — •Roman Nazarov, Tilmann Hickel, and Jörg Neugebauer — Max Planck Institute für Eisenforschung, Duesseldorf, Germany

Hydrogen embrittlement is a major failure mechanism in modern high-strength steels. Recent experimental studies indicate that alloying steels with selected elements largely improves their resistivity with respect to this failure mechanism. The origin of this mechanism, however, is unknown. We have therefore studied how various alloying elements affect H trapping in different steel phases. The solution enthalpies for a large set of common alloying elements in these phases have been calculated. Our results show that substitutional elements (Al, Cr, Mo, Nb, Si, Ti) energetically prefer the ferrite phase, while interstitial elements (B, C, and N) prefer austenite. Computing the interaction of these alloying elements with H we find that in the ferrite phase most of them repel an H atom from their neighborhood. In an austenitic matrix Nb and Ti bind H atoms in the first shell. Furthermore, these elements expand the Fe matrix, resulting in an increased interstitial volume and subsequent increased H solubility. In contrast, in an austenitic matrix P, Si and S repel H from their neighborhood. Based on this insight we derive a thermodynamic model which allows us to determine the solubility of H in real steels at any given temperature and H chemical potential.