Initiation and propagation of localized corrosion induced by (Zr, Ti, Al)-O x inclusions in low-alloy steels in marine e
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ORIGINAL PAPER
Initiation and propagation of localized corrosion induced by (Zr, Ti, Al)-Ox inclusions in low-alloy steels in marine environment Wen-zhui Wei1 • Kai-ming Wu1 • Jing Liu1 • Lin Cheng1 • Xian Zhang1 Received: 12 January 2020 / Revised: 19 May 2020 / Accepted: 20 May 2020 China Iron and Steel Research Institute Group 2020
Abstract The effects of inclusions on localized corrosion of Zr–Ti deoxidized low-alloy steels in marine environment were investigated by various analytical techniques including scanning electron microscopy with X-ray microanalysis (SEM/ EDS), confocal Raman microscopy (CRM), and in situ scanning vibrating electrode technique (SVET). It was found that complex (Zr, Ti, Al)-Ox inclusions were responsible for the initiation of localized corrosion. Localized corrosion preferentially occurred at Fe matrix adjacent to these inclusions and formed micro-gaps. In the early stage of corrosion, catalytic-occluded cells and the diffusion of chloride ions played a major role in the propagation of corrosion, further accelerating the dissolution of Fe matrix and (Zr, Ti, Al)-Ox inclusions. Combining SVET and CRM results, it revealed that the maximum anodic current density in local area gradually decreased with prolonged exposure time, indicating that corrosion products covered the steel surface and lowered the propagation rate of corrosion. In the later stage of corrosion, the barrier effect of corrosion products played an important role in inhibiting localized corrosion. Keywords (Zr, Ti, Al)-Ox inclusion Localized corrosion Low-alloy steel Marine environment Scanning vibrating electrode technique
1 Introduction Low-alloy steels, due to their excellent toughness and weldability, are widely used to manufacture construction machinery, ships, bridges, high-rise buildings, and vehicles. However, low-alloy steels are susceptible to localized corrosion during service, especially in chloride ions-containing environments, further inducing steel failure [1–10]. Generally, corrosion occurs in two stages: the initiation stage and the propagation stage [11]. Surface heterogeneities, such as inclusions, defects, and precipitates, are considered as the major sites to induce localized corrosion [8, 12–16]. Many previous studies indicated that inclusions played important roles in the initiation of corrosion
& Xian Zhang [email protected] 1
The State Key Laboratory of Refractories and Metallurgy, Hubei Province Key Laboratory of Systems Science in Metallurgical Process, Collaborative Innovation Center for Advanced Steels, Wuhan University of Science and Technology, Wuhan 430081, Hubei, China
[12, 13, 17–22]. Liu et al. [3] reported that pitting corrosion easily occurred around Al2O3 inclusions in marine environment. Jin and Cheng [23] pointed out that Si-enriched inclusions were related to a high electrochemical activity and preferentially dissolved in the corrosive environment to create a local micro-crevice. In addition, aluminum oxide-rich inclusion
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