The Influence of Ni Alloying on Corrosion Behaviour of Low Alloy Steels Under Wet/Dry Cyclic Conditions

Abstract

The atmospheric corrosion of Ni-bearing low alloy steels was investigated by wet/dry cyclic corrosion tests (CCT) in a 0.3%NaCl solution at 30 °C and 60% relative humidity (RH). The prepared samples were studied using gravimetry, electrochemical corrosion tests (polarization curves (PC), electrochemical impedance spectroscopy (EIS)) and analytical techniques (SEM and XRD). The Ni-bearing steels showed higher corrosion resistance than that of mild steel in the test. The results of electrochemical tests demonstrated that the addition of Ni to mild steel restrained anodic dissolution of iron, shifted the corrosion potential (E_corr) in a noble direction and increased the corrosion resistance of rust layer by improving the adhesion and compactness of the rust layer and ameliorating the physicochemical property of the substrate/rust interfaces. The rust analysis demonstrated that Ni alloying ameliorated rust composition by facilitating the formation of fine NiFe₂O₄, α-FeOOH and decreasing the β-FeOOH, γ-FeOOH and Fe₃O₄. In addition, Ni alloying could retard the crystallization of α-FeOOH, Fe₃O₄ and γ-FeOOH to a certain extent.

The atmospheric corrosion of Ni-bearing low alloy steels was investigated by wet/dry cyclic corrosion tests (CCT) in a 0.3%NaCl solution at 30 °C and 60% relative humidity (RH). The prepared samples were studied using gravimetry, electrochemical corrosion tests (polarization curves (PC), electrochemical impedance spectroscopy (EIS)) and analytical techniques (SEM and XRD). The Ni-bearing steels showed higher corrosion resistance than that of mild steel in the test. The results of electrochemical tests demonstrated that the addition of Ni to mild steel restrained anodic dissolution of iron, shifted the corrosion potential (E_corr) in a noble direction and increased the corrosion resistance of rust layer by improving the adhesion and compactness of the rust layer and ameliorating the physicochemical property of the substrate/rust interfaces. The rust analysis demonstrated that Ni alloying ameliorated rust composition by facilitating the formation of fine NiFe₂O₄, α-FeOOH and decreasing the β-FeOOH, γ-FeOOH and Fe₃O₄. In addition, Ni alloying could retard the crystallization of α-FeOOH, Fe₃O₄ and γ-FeOOH to a certain extent.

On a étudié la corrosion atmosphérique d'alliages faiblement alliés porteurs de Ni au moyen d'essais cycliques humides/secs de corrosion (CCT) dans une solution à 0.3% NaCl, à 30 °C et 60% d'humidité relative (RH). Les échantillons préparés ont été étudiés au moyen de la gravimétrie, d'essais électrochimiques de corrosion (courbes de polarisation (PC)), de la spectroscopie électrochimique à impédance (EIS) et de techniques analytiques (SEM et XRD). Les aciers porteurs de Ni ont montré une résistance plus élevée à la corrosion que celle des aciers doux lors de l'essai. Les résultats des essais électrochimiques ont démontré que l'addition de Ni à l'acier doux empêchait la dissolution anodique du fer, déplaçait le potentiel de corrosion (E_corr) dans la direction noble et augmentait la résistance à la corrosion de la couche de rouille en améliorant son adhésion et sa compacité et en améliorant les propriétés physicochimiques des interfaces substrat/rouille. L'analyse de la rouille a démontré que l'alliage au Ni améliorait la composition de la rouille en facilitant la formation de NiFe₂O₄ fin, de α-FeOOH et en diminuant le β-FeOOH, le γ-FeOOH et le Fe₃O₄. De plus, l'alliage au Ni pourrait retarder la cristallisation de α-FeOOH, de Fe₃O₄ et de γ-FeOOH, jusqu'à un certain point.