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In this paper, a quenching and tempering process was applied to the cold-rolled medium Mn steel with the delta ferrite (Fe-0.18C-6.4Mn-2.8Al). Microstructure characterization was carried out by means of optical microscope, scanning electron microscope (SEM) equipped with electron backscattered diffraction (EBSD) and transmission electron microscope (TEM). Mechanical properties tests were carried out by uniaxial tension tests. The microstructure characterization results revealed that the steel possessed a complex microstructure composed of three phases (austenite, martensite and delta ferrite). The volume fractions of austenite before and after a deformation were determined by X-ray diffraction (XRD). The XRD results indicated that the amount of austenite reached up to 20 vol.% and the TRIP effect occurred quite apparently. The mechanical property results showed that the steel possessed adequate ultimate tensile strength of 800MPa and excellent elongation of 25%. The outstanding combination of strength and ductility with the product of strength and elongation (PSE) reaching up to over 20GPa% indicates that the steel has a bright application prospect.

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