Effects of plasma nitriding in the corrosion behavior of an AISI 4140 steel using a seawater medium solution

•Plasma Nitriding has been studied in low temperature seawater solution.•The nitriding treatment at low temperature increase corrosion resistance of AISI 4140 steel.•A compact layer of ε-F2-3N and γ'-Fe4N contributes to the charge transfer resistance. In this work, a comprehensive analysis was performed to characterize the corrosion response of untreated and nitrided AISI 4140 steel. Samples were plasma nitrided at low temperature (∼400 °C) with two different gas composition. Electrochemical impedance spectroscopy, potentiodynamic polarization in artificial seawater solution at room temperature test were performed. Nitrided samples increases hardness on surface compared to the untreated sample. Nitrided samples composed by a mixture of ε-Fe2-3N and γ′-Fe4N nitrides phases offered significant influence on anodic and cathodic polarization. Nyquist curves indicated a higher corrosion resistance of nitrided samples compared to untreated sample.