  This study details the development and validation of a new algorithm that
determines the dominant habit plane of a transformed child phase from
orientation maps of a single planar cross-section. The method describes the
habit plane in terms of its five-parameter grain boundary character and couples
it to the specific orientation relationship of the identified orientation
variant. The symmetry operations associated with the specific orientation
relationship of the variants are applied to transform habit plane traces as
determined in the specimen-fixed reference frame into the parent or child
reference frame, allowing for the fitting of the habit plane. Our algorithm
stands out by its robustness, computational efficiency, automation and ability
to operate on fully transformed microstructures. Four automated methods for
habit plane trace determination are proposed and compared. Detailed sensitivity
analysis reveals that the proposed algorithm is exceptionally robust against
poor accuracy in the measured traces and distortions in the orientation map,
but more sensitive to inaccuracies propagated from parent grain reconstruction.
Validation on a synthetic microstructure with a known habit plane and returned
consistent results when applied to high and low carbon steels with different
prior austenite grain sizes and orientation map resolutions. The habit planes
were not significantly affected by the austenite grain sizes. The habit plane
of the steel with 0.35 wt.% C was close to (111){\gamma} whereas the habit
plane of steel with 0.71 wt.% C was closer to (575){\gamma}, in close agreement
with previous work using two-surface stereological analysis and transmission
electron microscopy-based trace analysis.
