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

Abstract

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 γfcc→ ∊hcptransformation 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 ∊-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 ∊-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.