Streaking effects arising from hydrogen-induced ϵ martensite phase in stainless steel

Electron diffraction studies of cathodically hydrogen-charged type 316L stainless steel were carried out by means of transmission electron microscopy. The extra spots and intensity spikes which appear in the electron diffraction patterns were interpreted as arising from [111]_ψ streaks running through reciprocal lattice points of the ε{lunate} martensite phase. In order to assess the validity of such an interpretation, a special method for determining the exact position of the plane of the diffraction pattern was developed. To apply this method, prior knowledge about the orientation relationships between the ε{lunate} phase and the ψ matrix and a reasonable suggestion about the direction of the reciprocal lattice streaks are necessary. The existence of the reciprocal lattice streaks indicates that the ε{lunate} phase plates formed in cathodically hydrogen-charged type 316L stainless steel are very thin. The thickness of the ε{lunate} phase plates was estimated to be less than 2 nm.