Unveiling microzone corrosion resistance of U75V rail flash-butt-welded joints of high-speed rails: a comparative study of microstructure and electrochemical behaviour in salt and acidic solutions

Corrosion poses a substantial threat to the structural integrity of railway tracks. The microzones formed in welded joints of rails exhibit different microstructures and stress distributions, which affect the corrosion performance. The corrosion behaviours of the weld microzones have a significant impact on the overall rail performance. To protect the rail joints from corrosion and enhance the service life of high-speed rails, we evaluated the corrosion properties of different microzones of U75V welded joints in 3.5 wt.% NaCl and acidic solutions using potentiodynamic polarisation curves, electrochemical impedance measurements, and immersion tests. The corrosion rate of the base metal was the lowest and that of the incomplete recrystallisation zone was the highest in both corrosive media. The corrosion rates of the recrystallisation zone were comparable to those of the weld zone. Furthermore, the corrosion rates of all the microzones in the acidic solution were significantly higher than those in NaCl solution. All the polarisation curves in NaCl solution showed passivation behaviours of varying degrees, and the anodic polarisation curves in the acidic solution showed pseudo-passivation caused by pitting.