Impact of matrix composition and microstructure on nodular cast iron sewage pump corrosion behavior in alkaline solutions

The corrosion resistance of nodular cast iron (NCI) in alkaline sewage environments is critical for ensuring the longevity, efficiency and reliability of sewage pumps.This study systematically investigates the influence of matrix composition, elemental distribution and microstructural features on the corrosion behavior of NCI in alkaline solutions.Using controlled metallurgical processing, samples with varying microstructureferritic, pearlitic, and mixedwere prepared and exposed to simulated alkaline sewage environments (pH=12).Electrochemical techniques, including potentiodynamic polarization, cyclic voltammetry and electrochemical impedance spectroscopy (EIS), were employed to quantify corrosion rates and protective film characteristics.Results reveal that microstructure significantly influences corrosion resistance.Ferritic NCI exhibited the lowest corrosion rate (0.025 mm/year at pH=12), attributed to its homogeneous phase, refined grain structure and lower galvanic coupling effects.In contrast, pearlitic NCI showed higher corrosion rates (0.065 mm/year at pH 12) due to increased cathodic sites from carbide phases accelerating localized corrosion.Mixed microstructures exhibited intermediate corrosion behavior.Surface analysis via scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) confirmed the formation of passive films with varying compositions, with ferritic structures promoting a more stable and protective oxide layer.This study uniquely quantifies the microstructural impact on NCI corrosion in alkaline sewage environments, offering practical insights for optimizing material selection in pump manufacturing.By tailoring matrix composition, corrosion resistance can be significantly improved, enhancing operational lifespan, mechanical integrity and reducing maintenance costs.These findings provide a scientific basis for engineering more durable sewage pump components, addressing a critical challenge in wastewater infrastructure.