Pitting Corrosion Behaviour in 9Cr18 Bearing Steel Under Salt Spray Environment

Abstract

Pitting corrosion poses a significant challenge to 9Cr18 high-carbon chromium bearing steel in chloride-rich environments, severely compromising its structural integrity. The study systematically investigates the pitting behaviour of 9Cr18 bearing steel under salt spray conditions, focusing on the progressive evolution of surface morphology and cross-sectional characteristics of pits on finished bearings. Scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction were employed to examine the surface morphology, elemental composition and phase structure of corrosion products over varying salt spray exposure durations. The results show that 9Cr18 steel exhibits localized pitting with “volcanic crater”-like pits in the early stage of salt spray corrosion. After 48 h, pitting develops into a “multi-point” pattern, marking the initial transition toward uniform corrosion. Until 240 h, corrosion products completely cover the surface, indicating the complete transformation from localized pitting to uniform corrosion. The high carbon and chromium content in 9Cr18 steel promotes carbide precipitation and uneven distribution in the matrix. Cr-depleted regions near the carbide/matrix interface serve as preferential sites for pitting initiation. The low effective utilization of chromium reduces the overall corrosion resistance of 9Cr18.