مهدی شبان غازانی

Thanks to their good ductility and corrosion resistance, micro-alloyed steels have been widely used in many industries, such as manufacturing car’s body. Ductility of metallic materials is influenced by their work hardening behavior, which in turn varies with respect to grain refinement. In the present study, the effect of grain refinement using Ex-ECAP on work hardening behavior and electrochemical properties of Ti-Nb microalloyed ferritic steel was evaluated. For this purpose, tensile testing at room temperature and a series of electrochemical analyses (i.e. electrochemical impedance spectroscopy and potentiodynamic polarization test) were used. Two-stage strain hardening behavior was observed for both the coarse-grained and ultrafne-grained samples. It was concluded that uniform elongation of the coarse-grained steel is higher than that of the ultrafne-grained steel. Whereas, the elongation of Ex-ECAPed steel was related to non-uniform deformation occurring after the maximum stress in the engineering stress-strain curves. Results of electrochemical analysis indicated that the passive film formed on surface of iron in contact with acidic solutions is based on iron oxides, such as magnetite (Fe3O4), and hematite (Fe2O3). It was also concluded that the stability of the passive film formed on surface of micro-alloyed steel is increased along with its corrosion resistance through grain refinement achieved by high-temperature Ex-ECAP process.