Evolution of deformation microstructure in a coarse-grained Fe-Mn-Al-C steel under bending fatigue

• Pre-saturation stage was fully austenitic under cyclic loading. • γ → ∊ martensitic transformation was detected. • Extended dislocations and channel-vein structures were observed. • Dislocation densities were relatively low. Microstructure evolution during cyclic deformation of a coarse-grained (∼ 25 μm) high-Mn steel under high-cycle bending fatigue at room temperature is reported. Vickers microhardness initially increased until 10000 cycles indicating cyclic hardening but almost saturated at prolonged cycling. The cyclic deformation of austenite leads to formation of perfect dislocations and stacking faults, as well as shear bands in the pre-saturation stage, while the formation of minor amount of ∊ -martensite was observed at intersections of shear bands at the saturation stage. Dislocation densities estimated by X-ray diffraction were relatively low ∼ 10 14 m -2 .