Evolution of corrosion behavior in gray cast iron and implications for iron cultural relics

The changes of surface morphology and corrosion process of iron cultural relics are challenging to study due to long time spans and complex environments. In this study, gray cast iron was employed as a representative material, and its corrosion behavior and mechanism of gray cast iron under acid salt spray conditions simulating atmospheric corrosion was systematically investigated. The effect of corrosion time on the morphology and properties of rust layers formed on the surface of gray cast iron was examined using laser confocal microscopy (LSCM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), corrosion weightlessness method and electrochemical impedance spectroscopy (EIS). LSCM results revealed that increased corrosion time led to more pronounced surface protrusions, resulting in higher surface roughness. SEM analysis showed that there were many pores and cracks on the rusted gray cast iron, owing to the pitting corrosion and the formation of cracks in the rust layers. EDS and XRD analyses identified that the corrosion products were α-FeOOH, γ-FeOOH, Fe ₃ O ₄ , and a small amount of β-FeOOH. Electrochemical and corrosion weight loss results indicated that the formation of stable rust layers after 144 hours significantly reduced corrosion rates to 1.04 mg/(cm²·h) and increased the corrosion current density (9.4×10 ^− 4 A/cm ² ). These findings can provide valuable insights into the long-term corrosion behavior and mechanism of archaeological cast iron relics.