Tetragonality mapping of martensite in a high-carbon steel by EBSD

TL;DR

This study uses high-resolution EBSD to map local tetragonality variations in martensite grains of high-carbon steel, revealing complex interactions between carbon content and lattice distortions.

Contribution

It introduces a novel EBSD-based method for spatially resolving tetragonality variations in martensite at the nanoscale.

Findings

Local tetragonality varies between 1.02 and 1.07

EBSD mapping reveals complex carbon-lattice interactions

EBSD results differ from average X-ray diffraction measurements

Abstract

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 100nm. 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 $\leq$ c/a $\leq$ 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.