Atmospheric Corrosion Kinetics and QPQ Coating Failure of 30CrMnSiA Steel Under a Deposited Salt Film

Atmospheric corrosion in sand dust environments is driven by deposits that bear chloride, which sustain thin electrolyte layers on metal surfaces. We established a laboratory protocol to replicate this by extracting, formulating, and depositing a preliminary layer of mixed salts from natural dust onto samples, with humidity precisely set using the salt’s deliquescence behavior. Degradation was tracked with SEM/EDS, 3D profilometry, XRD, and electrochemical analysis. Bare steel showed progressive yet decelerating attack as rust evolved from discrete islands to a lamellar network; while this densification limited transport, its internal cracks and interfacial gaps trapped chlorides, sustaining activity beneath the rust. In contrast, QPQ-treated steel remained largely protected, with damage localized at coating defects as raised rust nodules, while intact regions maintained low electrochemical activity. By coupling salt chemistries derived from the field with humidity control guided by deliquescence and diagnostics across multiple scales, this study provides a reproducible laboratory pathway to predict atmospheric corrosion.