The cooling rate, density of stacking faults, austenite grain size, and temperature strongly influence the γ fcc → ε hcp → α' bcc martensite transformation in austenitic alloys. During cooling, austenitic Fe-Mn steels can partially transform to ε and α' martensites within a restricted chemical composition. Martensite formation will influence the mechanical behavior of the alloy. The microstructure evolution under three cooling rates of a hot-rolled austenitic steel, Fe-17.0Mn-0.06C (wt%), was analyzed by optical microscopy and scanning electron microscopy/electron backscatter diffraction. The volume fraction of martensite and austenite were measured by X-ray diffraction line profile analysis by directly comparing the as-cast alloy, alloy subjected to different cooling conditions, and this processed with hot rolling.