Electrochemical Characterisation and Galvanic Coupling Behaviour of Carbon Steel and Shape Memory Steel

 

Abstract

One important technical application of shape memory steel (SMS) is the manufacture of fishplates for joining rail segments. This study investigates the electrochemical behaviour of a hypoeutectoid carbon steel rail and a Fe-Mn-Si-Cr-Ni SMS fishplate, specifically addressing their interaction under galvanic coupling conditions.

Morphological characterisation revealed pronounced microstructural heterogeneity, including multiphase structures and a variety of inclusions, which strongly influence the electrochemical behaviour of both elements. Open-circuit potential monitoring revealed a polarity reversal over time as the SMS developed a more stable protective film, particularly after thermal activation. Potentiodynamic polarization results confirmed the anodic role of the rail and the superior corrosion resistance of SMS, in agreement with impedance measurements. Galvanic coupling experiments showed that, despite relatively small potential differences, the rail’s anodic dissolution rate increased by up to 150%.

Electrochemical impedance spectroscopy analysis of the coupled system showed that the overall response was governed by the lower-impedance component (steel rail), consistent with the parallel electrochemical behaviour of the two elements. Although increasing the cathode-to-anode area ratio increased the galvanic current, corrosion acceleration was more strongly governed by microstructural heterogeneity than by geometric factors. In some cases, galvanic interactions were established between microstructurally dissimilar regions within the SMS itself. This aspect highlighted the importance of metallurgical control in the manufacturing of these structural components.

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