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 is 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.

Effect of a surface treatment consisting of electron beam remelting and gas nitriding on the corrosion resistance of cast iron

“…[9] However, the formation of the nitrided layer leads to a significant improvement in corrosion behavior compared to untreated cast iron. [10][11][12][13][14][15] Electrochemical corrosion studies of nitrided unalloyed and low-alloy steels show that the resistance against the pitting corrosion caused by chloride ions is better for compound layers consisting mainly of ε-Fe nitrides than those consisting primarily of γ'-Fe nitrides. [16,17] A combined surface treatment of electron beam remelting (EBR) and subsequent nitriding can be used to generate a dense, hard compound layer, which is supported by the hardness gradient within the diffusion layer and, in particular, by the hard, white-solidified, ledeburitic remelted layer.…”

“…[ 9 ] However, the formation of the nitrided layer leads to a significant improvement in corrosion behavior compared to untreated cast iron. [ 10–15 ] Electrochemical corrosion studies of nitrided unalloyed and low‐alloy steels show that the resistance against the pitting corrosion caused by chloride ions is better for compound layers consisting mainly of ε ‐Fe nitrides than those consisting primarily of γ '‐Fe nitrides. [ 16,17 ]…”