Computer-aided three-dimensional visualization of twisted cementite lamellae in eutectoid steel

The three-dimensional morphology and crystallography of cementite lamellae in a 0.8 mass% C–Fe alloy were examined by a combination of scanning electron microscopy using a double-beam field emission gun, electron back-scattered diffraction, and transmission electron microscopy. The cementite lamellae were twisted in three-dimensions from changes in both the ferrite/cementite habit plane and ferrite orientation, but they maintained their orientation relationship. The cementite lamellae were straight while they grew along the colony/austenite boundary. As the colony/austenite boundary migrated sideways, isolating the cementite from the austenite, the cementite lamellae curved. A possible mechanism for the cementite twisting is proposed.