Rusting Evolution of MnCuP Weathering Steel Submitted to Simulated Industrial Atmospheric Corrosion
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THE enhanced atmospheric corrosion resistance of weathering steel is caused by the formation of a stable, compact, and protective rust layer.[1] The effectiveness of this protective layer depends both on the alloy elements in the steel substrate and on the environmental conditions.[2] For example, Corten A weathering steel shows higher corrosion resistance than Q235 carbon steel in coastal area with chlorides such as Wanning city.[3] However, the two steels show the same corrosion resistance in Qinghai salt lake atmosphere with higher contents of chlorides and higher relative humidity.[4] During the past decades, studies on weathering steels are focused mainly on field exposure tests to quantify the effects of alloy elements on atmospheric corrosion behavior of the steel in specified environmental conditions.[5–9] Less work has been done to investigate the rusting evolution of weathering steels and the electrochemical properties of the rusted steels.[10] In fact, the chemical composition, structure, and electrochemical properties of the rust layer are related not only to the alloy elements and the environmental conditions but also to the corrosion durations. For carbon steel,[11,12] the rust layer formed during the initial corrosion stage is loose, porous, and not adhesive to the steel substrate with almost no ability in resisting the penetration of LONG HAO, PhD Candidate, and JUNHUA DONG and WEI KE, Professors, are with the State Key Laboratory for Corrosion and Protection, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, P.R. China. Contact e-mail: [email protected] SIXUN ZHANG, PhD Candidate, is with the College of Material and Metallurgy, Northeastern University, Shenyang 110016, P.R. China, is also an Engineer, with the Technical Centre of Laiwu Steel Group, Ltd., Laiwu 271104, P.R. China. Manuscript submitted March 28, 2011. Article published online November 2, 2011 1724—VOLUME 43A, MAY 2012
corrosion electrolyte to steel substrate, but the inner rust layer begins to form during the subsequent corrosion stage, which is compact but with cracks and not adhesive to the steel substrate. The rust layer formed during this stage can resist the penetration of corrosion electrolyte to steel substrate, but this barrier effect is not obvious. Therefore, the rust layer formed during different corrosion stages can lead to distinct electrochemical properties. The field exposure test usually takes a long period for one evaluation, and it is usually performed to gain data about the corrosion kinetics.[5–9] Unfortunately, the relationship between corrosion kinetics and the rust layer properties during different corrosion stages has not gained much interest. In practice, weathering steels are often employed with rust layer being covered. Therefore, it is of great importance to investigate the rusting evolution of weathering steel for evaluating a newly developed steel type and for forecasting the lifespan of a steel structure. MnCu steel is a kind of low-cost weathering steel, not alloyed with chrom
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