The electrochemical behavior of corrosion and passivation for Q235 carbon steel in acidic phosphate buffer solutions without and with NO2−

Purpose The purpose of this paper is to reveal the mechanism of nitrite (NO2−) for the surface passivation of carbon steels in acidic environments through investigating the influences of 0.01 mol/L NaNO2 addition on the corrosion and passivation behaviors of Q235 carbon steel in acidic phosphate buffer (APB) solutions (pH 2 to 6). Design/methodology/approach The electrochemical techniques including open circle potential evolution, potentiodynamic polarization, electrochemical impedance spectroscopy and cyclic voltammetry were applied. Findings In APB solutions without NO2−, the Q235 steel presented the electrochemical behaviors of activation (A), activation-passivation-transpassivation and self-passivation-transpassivation at pH 2 to 4, pH 5 and pH 6, respectively; the corrosion rate decreased with the up of pH value, and the surface passivation occurred in the pH 5 and pH 6 solutions only: the anodic passivation at pH 5 and the spontaneous passivation at pH 6. Originality/value In APB solutions without NO2−, the corrosion rate decreased with the up of pH value, and the surface passivation occurred in the pH 5 and pH 6 solutions only: the anodic passivation at pH 5 and the spontaneous passivation at pH 6. With the addition of 0.01 mol/L NaNO2, into APB solutions, the variation of corrosion rate showed the same rule, but the surface passivation occurred over the whole acidic pH range, including the anodic passivation at pH 2 to 4 and the spontaneous passivation at pH 5 to 6.

Data on the Corrosion Resistance and Polarization Behaviour of Lean Austenitic and Ferritic Stainless Steels in Neutral Chloride Media

Stainless steels are extensively applied in diverse industries due to their exceptional corrosion resistance. The corrosion resistance of alloy stainless steels (316L austenitic and 430Ti ferritic stainless steel) was studied in neutral chloride solutions with chloride concentrations of 1%, 2%, 3%, 4%, 5% and 6%. Their general and localized corrosion resistance were compared and discussed in addition to their passivation characteristics. Corrosion rate results obtained showed 430Ti exhibited slightly greater general resistance to chloride attack compared to 316L. Further investigation showed 316L steel exhibited higher resistance to localized corrosion attack to its resilient passive film. 430Ti exhibited cathodic and anodic passivation compared to 316L which only exhibited anodic passivation. Optical microscopic analysis showed the presence of small, superficial corrosion pits on 316L steel compared to 430Ti, which exhibited deep corrosion pits.