  Austenite grains that underwent the f.c.c. to b.c.c. (or b.c.t.)
transformation are typically composed of 24 Kurdjumov-Sachs variants that can
be categorized by three axes of Bain transformations; thus, a complete
transformation generally displays 3-fold symmetry in (001) pole figures. In the
present work, crystallographic symmetry in 42CrMo4 steel austempered below
martensite start temperature was investigated with the help of the orientation
distribution function (ODF) analysis based on the FEG-SEM/EBSD technique. It is
shown that, upon phase transformations, the specimens contained 6-fold symmetry
in all (001), (011), and (111) pole figures of an ODF. The ODF analysis,
verified by theoretical modeling, showed that under plane-strain conditions
cracks prefer to propagate through areas strongly offset by the high symmetry.
The origin of high symmetry was investigated, and the mechanism of the symmetry
breakdown was explained.
