Corrosion behaviour of Q235 steel in accelerated simulated acid rain condition

Abstract

This study investigates the corrosion-induced mechanical degradation of Q235 steel under simulated acid rain conditions. An artificial acid rain solution, simulating environmental conditions in Hebei Province, China, was applied through accelerated electrochemical corrosion testing. Following exposure, monotonic tensile tests were conducted to evaluate changes in mechanical properties, including yield strength, ultimate tensile strength, elastic modulus, elongation, and Poisson's ratio. To understand the corrosion mechanisms, microstructural analyses using scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive spectroscopy (EDS) were performed. The results indicate that acid rain corrosion promotes the formation of surface pits and microdefects, which intensify with increasing corrosion ratio and significantly weaken mechanical performance. Yield strength, tensile strength, elastic modulus, and elongation were observed to decrease progressively with corrosion, while Poisson's ratio slightly increased. SEM images show a transition from ductile to brittle fracture patterns, associated with localised stress concentration from pitting. XRD analysis reveals early formation of α-FeOOH and Fe₃O₄, which are gradually replaced by β-FeOOH and γ-FeOOH in later stages. EDS results further identify oxygen and nitrate ions as dominant contributors to corrosion propagation. Based on the experimental data, this study proposes linear empirical models (R² > 0.80) to quantify the degradation of mechanical properties as a function of corrosion ratio. Compared to more complex nonlinear models, the proposed linear formulations offer comparable accuracy with improved simplicity, making them more suitable for engineering applications requiring rapid prediction. These findings provide practical guidance for the design and durability evaluation of steel structures exposed to acid rain environments.