Effects of plasma nitriding process on the corrosion behavior of GJS700 nodular cast iron

Abstract In this paper, the effect of the plasma nitriding (PN) process on corrosion aspects of GJS700 nodular cast iron has been investigated. The gas ratio of N2:H2 was a variable parameter that changed the electrochemical properties of cast iron. Therefore, to study corrosion properties, Tafel polarization, electrochemical impedance spectroscopy (EIS), and gravimetric experiments were utilized in two corrosive mediums. Moreover, for more details, the evaluation of field emission scanning electron microscopy (FESEM) images plus the energy dispersive spectroscopy analysis was performed. Results showed that plasma nitrided surfaces with the gas ratio of N2:H2 = 9:1 had the highest resistance in 0.6 M NaCl solution. EIS results also demonstrated that the increase in the corrosion resistance of nitrided surfaces was about 56%–86% compared to the cast iron without surface treatment. However, when nitrided surfaces were exposed to 1 M HCl solution, the PN process with both gas ratios was not an effective treatment to reduce the corrosion rate of cast iron. FESEM images showed that corrosion attacks such as pits, cracks, and corrosion products decreased significantly on surfaces with higher corrosion resistance. The weight loss measurements also depicted that specimens exhibited different corrosion behaviors in two utilized corrosive solutions. Consequently, the possible corrosion mechanism was suggested based on the obtained results.