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Metals 2017, 7(7), 264; doi:10.3390/met7070264

The Role of κ-Carbides as Hydrogen Traps in High-Mn Steels

1
Institute of Inorganic Chemistry, Chair of Solid-State and Quantum Chemistry, RWTH Aachen University, 52056 Aachen, Germany
2
Max-Planck-Institute for Iron Research GmbH, 40237 Düsseldorf, Germany
3
Jülich-Aachen Research Alliance (JARA-HPC), RWTH Aachen University, 52056 Aachen, Germany
*
Author to whom correspondence should be addressed.
Received: 13 June 2017 / Revised: 30 June 2017 / Accepted: 3 July 2017 / Published: 11 July 2017
(This article belongs to the Special Issue First-Principles Approaches to Metals, Alloys, and Metallic Compounds)
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Abstract

Since the addition of Al to high-Mn steels is known to reduce their sensitivity to hydrogen-induced delayed fracture, we investigate possible trapping effects connected to the presence of Al in the grain interior employing density-functional theory (DFT). The role of Al-based precipitates is also investigated to understand the relevance of short-range ordering effects. So-called E21-Fe3AlC κ-carbides are frequently observed in Fe-Mn-Al-C alloys. Since H tends to occupy the same positions as C in these precipitates, the interaction and competition between both interstitials is also investigated via DFT-based simulations. While the individual H–H/C–H chemical interactions are generally repulsive, the tendency of interstitials to increase the lattice parameter can yield a net increase of the trapping capability. An increased Mn content is shown to enhance H trapping due to attractive short-range interactions. Favorable short-range ordering is expected to occur at the interface between an Fe matrix and the E21-Fe3AlC κ-carbides, which is identified as a particularly attractive trapping site for H. At the same time, accumulation of H at sites of this type is observed to yield decohesion of this interface, thereby promoting fracture formation. The interplay of these effects, evident in the trapping energies at various locations and dependent on the H concentration, can be expressed mathematically, resulting in a term that describes the hydrogen embrittlement. View Full-Text
Keywords: steel research; κ-carbides; short-range ordering; hydrogen trapping; hydrogen embrittlement; carbide-austenite interfaces; ab initio calculations; density-functional theory steel research; κ-carbides; short-range ordering; hydrogen trapping; hydrogen embrittlement; carbide-austenite interfaces; ab initio calculations; density-functional theory
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Timmerscheidt, T.A.; Dey, P.; Bogdanovski, D.; von Appen, J.; Hickel, T.; Neugebauer, J.; Dronskowski, R. The Role of κ-Carbides as Hydrogen Traps in High-Mn Steels. Metals 2017, 7, 264.

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