Stabilization of the HCP ϵ phase in an Fe21%Mn alloy subjected to cathodic hydrogen charging

Abstract

Cathodic hydrogen charging induces some phase transformation in the surface layer of FCC iron alloys. Such a hydrogen-induced phase transformation has extensively been studied for austenitic stainless steels, where the FCC [gamma] phase transforms partially into an HCP [var epsilon][sub H] phase. The formation of the [var epsilon][sub H] phase has also been found in FCC Fe-Mn alloys and Fe-Ni-Mn alloys. The [var epsilon][sub H] phase is unstable in the absence of hydrogen and decomposes to an [var epsilon] martensite in the metastable FCC alloys. In order to make clear the nature of the [var epsilon][sub H] phase, it is necessary to reveal the stability of the [var epsilon] phase in FCC iron alloys during cathodic hydrogen charging. In the present study, the authors employed an Fe-21%Mn alloy which consisted of a mixture of the [gamma] and [var epsilon] phases in an as-quenched state. For this two-phase alloy, the [var epsilon] [r arrow] [gamma] transformation has so far been examined by a high-pressure equilibration method in a hydrogen-gas atmosphere. The purpose of this study is to compare the stability of the [gamma] phases in the two-phase alloy subjected to cathodic hydrogen charging in an aqueous solution. The influence of hydrogenmore » on the [var epsilon] phase stability will be discussed, including the transformation in a hydrogen-gas atmosphere.« less