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

• Published in: Steel research international Vol. 95; no. 10
• Main Authors: Maher, Majdouline, Iraola‐Arregui, Itziar, Lasri, Mohammed, Idouhli, Rachid, Ben Youcef, Hicham, Rhouta, Benaissa, Trabadelo, Vera
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01-10-2024
• Subjects: Calomel electrode; Carbides; Charge transfer; Chromium; Comparative studies; core–shell carbides; Corrosion; Corrosion mechanisms; Corrosion tests; Duplex stainless steels; Electrochemical impedance spectroscopy; Electrode polarization; intergranular corrosion; Molybdenum; Oxidation; repassivation; Shell stability; Stability analysis; stainless steel; Steel; sulfuric acid; Tungsten
• ISSN: 1611-3683; 1869-344X
• DOI: 10.1002/srin.202400233

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.
This study provides new insights into the corrosion mechanism of core–shell carbides containing stainless steels. By comparing their electrochemical behavior with that of a conventional stainless steel, this study shows that the presence of core–shell carbides has a deteriorating effect on the corrosion resistance, mainly due to the creation of galvanic cells between the core and the shell of the carbides.