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

Microstructure evolution during cyclic deformation of a coarse-grained (similar to 25 mu m) high-Mn steel under high-cycle bending fatigue at room temperature is reported. Vickers microhardness initially increased until 10,000 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 similar to 10(14) m(-2).