Austenitic structure formation in an Fe-32% Ni alloy during slow heating in the critical temperature range

Electron diffraction is used to show (for the first time) that the reverse α → γ transformation in an Fe-32% Ni during slow heating develops via the formation of an intermediate paramagnetic 9R phase. Coarse extended lamellae form according to a shear mechanism in the central part of the temperature range of the reverse transformation, which is called the critical range (here, the physical properties of the alloy change anomalously). The extended lamellae consist of 9R-phase lamellae with γ-phase interlayers. A high density of periodic stacking faults in the structure of the 9R phase and a high density of chaotic stacking faults in the complex 9R + γ phase determine the nature of phase transformation-induced hardening.