Tetragonality mapping of martensite in a high‑carbon steel by EBSD.

The locally varying tetragonality in martensite grains of a high‑carbon steel (1.2 mass percent C) was resolved by electron backscatter diffraction (EBSD) with a spatial resolution in the order of 100 nm. Compared to spatially integrating X-ray diffraction, which yielded an average tetragonality of c / a = 1.05, the EBSD measurements in the scanning electron microscope allowed to image a local variation of the lattice parameter ratio c / a in the range of 1.02 ≤ c / a ≤ 1.07. The local variation of tetragonality is confirmed by two different EBSD data analysis approaches based on the fitting of simulated to experimental EBSD patterns. The resulting EBSD-based tetragonality maps are pointing to a complex interaction of carbon concentration and local lattice distortions during the formation process of martensitic structures. • Fe-1.2%C martensite tetragonality (c/a ratio) was resolved using EBSD pattern matching. • EBSD pattern matching results are compared to XRD. • EBSD pattern matching provides spatial information about c/a. • c/a of Fe-1.2%C martensite varies significantly in the measured sample area, with an average value close to one acquired with XRD. [ABSTRACT FROM AUTHOR]