Structure and microstructure evolution during martensitic transformation in wrought Fe–26Mn–0.14C austenitic steel: an effect of cooling rate

Structure and microstructure evolution under various cooling rates of a wrought austenitic steel, Fe–26Mn–0.14C (composition in mass %), were studied by the Rietveld method of X-ray diffraction pattern fitting, grain boundary characterization by electron back-scattered diffraction (EBSD) and optical microscopy. Cooling rate, density of stacking faults, and austenite grain size and grain boundaries influence the observed γ_fcc → [epsilon]_hcp transformation and lead to significant anisotropic X-ray line broadening. Depending on the cooling conditions, the grain boundaries are misoriented at both lower and higher angles. In the [epsilon]-martensites, the dominant planar fault is twins (∼10⁻³). The austenite grains were found to contain low to moderate density of stacking faults (∼10⁻⁴–10⁻³), which act as efficient nucleation sites of the [epsilon]-martensites. Both X-ray and EBSD analyses estimated negligible twins in the austenite. Approximate average dislocation densities have been estimated and correlated with the grain structure.