Phase Transformation and Internal Friction in Fe-Cr-Mn Alloys Subjected to Cathodic Hydrogen Charging

Hydrogen-induced phase transformation was studied on Fe-Cr-Mn alloys composed of the single (γ) phase, the dual (γ+ε) phase and the ternary (γ+ε+α) phase. In all the alloys, a new HCP structure was observed after cathodic hydrogen charging, which corresponds to the εH phase in austenitic stainless steel. The εH phase of the single-phase alloys seems to be transformed from the γ matrix, whereas the εH phase of the dual-phase and ternary-phase alloys is considered to be separated from the pre-existing ε phase.In manganese-rich alloys composed of single phase (γ), a hydrogen peak of internal friction was detected after cathodic hydrogen charging. This hydrogen peak seems to be attributed to a Snoek-type relaxation caused by hydrogen diffusion in the γ matrix, as has been proposed for austenitic stainless steel and Fe-Ni alloy. Its relaxation strength decreased considerably with the content of manganese in these alloys at almost the same hydrogen concentration.