Study on the Corrosion Behavior and Mechanism of ER8 Wheel Steel in Neutral NaCl Solution

This paper analyzed the corrosion behavior and corrosion performance of ER8 wheel steel through a full immersion test. The average corrosion rate of the ER8 wheel specimen in 2.0% NaCl solution shows a gradual increase over the whole corrosion cycle. Although the corrosion rate showed fluctuations at 3.5% and 5.0% concentration before 576 h, the corrosion rate also showed a steady increase after 576 h. The corrosion rates of specimens at different concentrations after 2160 h were over 0.12 mm/year. With increasing immersion times or concentrations of NaCl solution, the coverage area of the corrosion products dominated by iron oxides gradually increased, and the corrosion products on the surface became denser. The corrosion products were primarily γ-FeOOH, α-FeOOH and Fe3O4. As the density of the surface corrosion products increased, cracks and holes appeared on the surface of the rust layers, which made the rust layer unable to protect the substrate from further corrosion. After removing the corrosion products, pitting corrosion appeared on the surface of the substrate. The radius of the capacitive reactance arc gradually decreased with the increasing immersion time. The impedance modulus in the low-frequency region decreases and then increases with increasing NaCl solution concentration, which is the highest in 3.5% NaCl solution. Icorr increased with an increasing Cl− concentration, which was similar to the mechanism of catalytic electrolysis due to Cl−. The specimens with rust layers have worse corrosion resistance when the immersion time is extended. The corrosion product did not protect the substrate but accelerated the corrosion process.