Effect of Cr on Aqueous and Atmospheric Corrosion of Automotive Carbon Steel

oleh: Sang-won Cho, Sang-Jin Ko, Jin-Seok Yoo, Yun-Ha Yoo, Yon-Kyun Song, Jung-Gu Kim

Format: Article
Diterbitkan: MDPI AG 2021-05-01

Deskripsi

This study investigated the effect of Cr alloying element on the corrosion properties of automotive carbon steel (0.1C, 0.5Si, 2.5Mn, Fe Bal., composition given in wt.%) in aqueous and atmospheric conditions using electrochemical measurement and cyclic corrosion tests. Three steels with 0, 0.3, and 0.5 wt.% Cr were studied by electrochemical impedance spectroscopy. Polarization resistance (R<sub>p</sub>) of 0.3 Cr and 0.5 Cr steels was higher than that of 0 Cr steel, and the R<sub>p</sub> also increased as the Cr content increased. Therefore, Cr increases the corrosion resistance of automotive carbon steel immersed in a chloride ion (Cl<sup>−</sup>)-containing aqueous solution. In the cyclic corrosion test results, Cl<sup>−</sup> was concentrated at the metal/rust interface in all of the steels regardless of Cr content. The Cl<sup>−</sup> was uniformly concentrated and distributed on the 0 Cr steel, but locally and non-uniformly concentrated on the Cr-added steels. The inner rust layer consisted of β-FeOOH containing Cl<sup>−</sup> and Cr-goethite, while the outer rust layer was composed of amorphous iron oxyhydroxide mixed with various types of rust. FeCl<sub>2</sub> and CrCl<sub>3</sub> are formed from the Cl<sup>−</sup> nest developed in the early stage, and the pitting at CrCl<sub>3</sub>-formed regions are locally accelerated because Cr is strongly hydrolyzed to a very low pH.