Electrochemical study on the corrosion resistance of surface modified Cr-Mo-V steel by elevated temperature plasma nitriding

This study presents the effect of plasma nitriding on corrosion resistance of low alloy 90CrMoV8 steel. At a selected temperature of 500 degrees C, nitriding was performed by varying the exposure time. X-ray diffraction of nitrided steel revealed the presence of Fe, gamma'(Fe, Cr)(4) N and epsilon-(Fe, Cr)(2-3)N) phases. The cross section of the nitrided steel was analyzed by scanning electron microscope. To understand the effect on corrosion resistance, potentiodynamic polarization along with the electrochemical impedance spectroscopy (EIS) was performed in 3.5% NaCl. The corrosion resistance of the nitrided steel was found to be much higher than the as-received steel. It was also found that the steel nitrided for shorter duration of 6 h has better corrosion resistance than that for 8 h. This enhancement of corrosion resistance may be attributed to the presence of nitrogen in solid solution, gamma'-(Fe, Cr)(4)N and epsilon-(Fe, Cr)(2-3)N phases.