Corrosion behaviour of microstructurally modified elastic rail clip steel under crevice and aggressive salt fog exposure

Abstract

Abstract In the present work, existing Indian elastic rail clip steel (tempered martensite) is microstructurally modified to bainite using austempering route. Crevice corrosion of elastic rail clip (ERC) is of major concern as metal dissolution can cause the loosening of the rail clip assembly (such as rail clip‒insert and rail clip‒liner) and lack of performance. Furthermore, the surface of rail clip exposed to the atmosphere could also be affected by the corrosive environment. The present work concentrates on the findings of crevice corrosion and wet‒dry salt fog exposure of the austempered ERC steels in 3.5 wt.% NaCl solution for 30 days and compared with the as‒received (existing) ERC steel which consists of tempered martensitic structure. The severity of corrosion has been investigated by studying the surface dissolution and the rust formed on the exposed surfaces of the ERC steels after the crevice and salt fog tests. Scanning electron microscopy (SEM) and optical profilometry have been used for the analysis of surface dissolution behaviour. Moreover, the rust formed on the exposed surfaces characterized using SEM shows the presence of various rust phases, such as α‒FeOOH, β‒FeOOH, γ‒FeOOH, α‒Fe2O3, etc. Furthermore, Raman spectroscopy has been used for the confirmation and quantification of these rust phases. The higher protective ability index (PAI) calculated from the quantitative assessment of different rust measured from Raman spectroscopy shows the better corrosion resistance of the austempered ERC steels.