Magnetic Field Effect on Anodic Dissolution of Axle Steel in Bicarbonate Solution with Chlorides

Abstract

The vehicle axle in the railway locomotive is a very important component. Localized corrosion is a cause of its degradation. Localized corrosion is usually caused by corrosive environments especially in media containing chloride ions. Harmonic currents in the power supply loops (contact nets and guide rails) of the train during train travel can produce stray current that produces stray magnetic fields. Some studies have shown that magnetic fields can accelerate or inhibit localized corrosion of metals. In this study, optical microscopy (OM) and electrochemical measurements were used to study the effects of magnetic field on the electrochemical behavior and corrosion morphology of axle steel in sodium bicarbonate solutions with and without chloride ions. Different scan rates were used in the measurements of anodic polarization curves. Potentiostatic polarization measurements were performed with applying or removing a 0.4 T magnetic field. The surface morphologies of the electrodes were observed after potentiostatic polarization. Figure 1 show that, for axle steel in 0.05 mol/L NaHCO3 with or without 0.001 mol/L NaCl, the magnetic field increased the peak current, positively shifted the potential for the onset of passivation, and narrowed the passivation range. Chlorides increased the anodic current in the transpassivation region. The synergistic effect of magnetic field and chlorides on breakdown of passivation was more significant at high potential scan rate for the anodic polarization curve measurements. Obvious corrosion pits could be found after polarization, according to the morphology of the axle steel after polarization at a scan rate of 50 mV/min. It is found that the magnetic field significantly accelerated the corrosion. For axle steel in 0.05 mol/L NaHCO3 system, the potentiostatic polarization was carried out at -0.3 V(SCE). The current density decreased with increasing the polarization time. The current decreasing rate was mitigated by applying a 0.4T magnetic field, i.e., the anodic current density tended to be more stable under applied magnetic field, showing a significant magnetic field effect on anodic dissolution and pitting behavior of axle steel in this environments. Figure 1