New Insights on the Corrosion Behavior of a Cr–W–V–Mo-Rich Stainless Steel Containing Cr7C3–Cr23C6 Core–Shell Carbides: A Comparative Study

Abstract

The goal of this study is to provide new insights into the corrosion mechanism of core-shell carbides containing steels. The corrosion behavior of two heat-treated Cr–W–V–Mo-rich stainless steels is evaluated using electrochemical techniques. The studied steels have different carbides microstructure, the first has core–shell carbides (Cr₇C₃–Cr₂₃C₆) in a ferritic matrix, while the second has conventional Cr₂₃C₆ carbides in a duplex matrix. The open-circuit potential results show a nobler behavior of the duplex sample; it is noticed in the potentiodynamic polarization curves where the core–shell carbides containing steel have an oxidation peak at −0.37 V versus saturated calomel electrode with a current density of 0.19 mA cm⁻², contrary to the duplex steel that shows a passive behavior. Electrochemical impedance spectroscopy demonstrates the presence of two degradation mechanisms in the core–shell carbide steel, while the other steel is governed by charge transfer only. These findings are supported by scanning electron microscopy examination that shows the preferential corrosion of the shell while the core and the duplex matrix are kept intact. The passive film stability is evaluated using Mott–Schottky analysis and it shows the presence of a higher defect density on the passive film of the core–shell carbides containing steel.