The crystallographic structures of the [0 1 1]/54.7° lath boundary and the intralath and interlath cementite precipitates in a 0.2C steel tempered at 400 °C have been observed by high resolution transmission electron microscopy and discussed in terms of the O-lattice model. The [0 1 1]/54.7° lath boundary which is composed of one Kurdjumov-Sachs variant (α1) and one Nishiyama-Wasserman variant (α2) is likely to facet on the (0 12 7)α1//(5 19 14)α2 irrational plane. The O-lattice analysis indicated that the facet coincides with a plane with a high density of O-points. Intralath cementite obeys the Isaichev orientation relationship (OR) with ferrite and has a habit plane of (1 0 1) θ//(1 2 1)α. Interlath cementite precipitating on the [0 1 1]/54.7° boundary maintains a strict Bagaryatskii OR with the ferrite on one side of the boundary and has a (1 0 0)θ habit plane.
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