Transmission electron microscopic study was carried out on a δ-eutectoid structure formed by carburization of a ferritic Fe–Cr alloy. The structure has a lamellar configuration of martensite and M₂₃C₆ carbide at room temperature. The orientation relationship between these phases was verified to be
(011)_α′⁄⁄(111)_M23C6, [1\bar11]_α′⁄⁄[01\bar1]_M23C6.
From this result, it may certainly be inferred that the austenite phase had an orientation relationship of
{111}_γ⁄⁄{111}_M23C6, ⟨011⟩_γ⁄⁄⟨011⟩_M23C6,
with respect to the carbide at the transformation temperature. The habit plane of these phases were found to be {111}_γ and {111}_M23C6 planes, respectively. High resolution observations by electron microscopy were carried out on the M₂₃C₆ carbide in the δ-eutectoid structure, and the lattice images of {111}, {200}, and {220} planes of the carbide were resolved. It was found that the habit plane of the carbide can definitely be determined by the observation of lattice images.