  The spatial variation in martensite tetragonality (c/a ratio) in Fe-0.77C
(wt.%) alloy was investigated by means of pattern matching of electron
backscatter diffraction patterns combined with high angular resolution electron
backscatter diffraction analysis. It was found that the c/a ratio varies within
a martensite block and between blocks. The c/a variation within a block is
particularly evident in the vicinity of grain boundaries and shear strains are
also present in addition to tetragonal distortion. The c/a variation between
blocks is more apparent than that within a block. The lattice parameter
frequency profile predicted by our approach well matches with the X-ray
diffraction profile from the same material by assuming reasonable residual
strain acting on a- and b-axes. The heterogeneities of the crystal distortion
are brought by a decrease and scatter in solid solution carbon and in carbon
ordering as a result of the martensite transformation sequence as well as
heterogeneous residual strain.
