Achieving superior strength and ductility combination in Fe–28Mn–8Al–1C low density steel by orthogonal rolling

Fe-Mn-Al-C austenitic steels have promising prospects for lightweight applications, due to their low density, excellent strength, and ductility. But the specific strength ratio of these alloys are still low as compared to other alloys. Herein, an orthogonal rolling (OR) process was used to improve the mechanical strength of a Fe-28Mn-8Al-1C low-density steel. The effect of this deformation method on the microstructural evolution and mechanical properties was studied by means of microscopy techniques, e.g. optic, scanning and transmission electron microscope, electron backscattered diffraction, X-ray diffraction, micro hardness and tensile test measurements. Microstructural characterization results show that OR significantly promotes the activation of multiple slip systems within grains in the material. The development of more uniform deformation microstructure, compared with that that after unidirectional cold rolling to the same strain was mainly due the improvement of the uniformity of strain distribution by rolling deformation in multiple directions. It resulted in an average 84.5 nm sized ultrafine grain structures after 8-pass OR. The tensile and yield strengths were significantly increased to 1813 MPa and 1798 MPa, respectively. Despite of the still-exiting strength-ductility trade-off, a much higher elongation at tensile failure of 9.6% was achieved, compared to only 5.2% of unidirectional cold rolled material. This superior strength and ductility combination was likely promoted by the increased dislocation density and deformation substructures in forms of dislocation cells, and deformation twins induced by OR.