EIS Behavior of Experimental High-Strength Steel in Near-Neutral pH and Load Conditions
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STRESS corrosion cracking (SCC) can be defined as the failure that results from the interaction among mechanical load, corrosion, and a susceptible material. This synergic interaction leads to a slow crack propagation in a metallic material.[1] SCC has been registered in different materials such as steel,[2–4] magnesium,[5] and aluminum alloys,[6] among others. The SCC in buried steel pipelines, where water is trapped inside a coating disbondment, has been classified in two ways—near-neutral pH (NNpH) and high pH (HpH)—based on the pH inside the disbondment.[7] The former has been associated with diluted bicarbonate electrolytes at a pH value between 6 and 7.5, while the latter has been related to carbonate–bicarbonate solutions at pH between 9 and 11.[7] The NNpH SCC has been linked specifically to an environment with JESUS ISRAEL BARRAZA-FIERRO and HOMERO CASTANEDA are with the Materials Science and Engineering Department, Texas A&M University, College Station, TX 77843. Contact e-mail: [email protected] SERGIO ALONSO SERNABARQUERA is with the Centro de Investigacio´n en Ingenierı´ a y Ciencias Aplicadas, Universidad Auto´noma del Estado de Morelos, 62209 Cuernavaca, Morelos, Mexico. BERNARDO FABIAN CAMPILLO-ILLANES is with the Facultad de Quı´ mica-Instituto de Ciencias Fı´ sicas, Universidad Nacional Auto´noma de Me´xico, 04510, Ciudad de Me´xico, Mexico. Manuscript submitted August 9, 2016. Article published online February 6, 2017 1944—VOLUME 48A, APRIL 2017
anaerobic conditions at a pH from 6 to 7.5.[8] This pH results from CO2 dissolution. The preponderance of cases in steel has been in HpH environments, and the typical mechanical failure mode has been intergranular cracking.[2,4] However, cases of SCC have been registered in near-neutral pH electrolytes with transgranular failure mode.[3] The SCC at HpH has been well understood, and failure mechanisms have been proposed and validated.[2–4] In contrast, the SCC at near-neutral pH (NNpH SCC) has not been completely studied.[9] Cheng and coworkers have established research that could disclose important features of NNpH SCC such as the strain effect on the cathodic reaction,[10] effect of dynamic and static load,[11] and products effect on cathodic and anodic reactions.[12] In these studies,[13,14] a deposit on the metal surface was found, and it was porous and non-compact in nature. However, the chemical composition was not acquired. The understating of SCC in NNpH could be improved resulting from a testing that considers the mechanical and corrosion factors for a complete characterization. The mechanical factor could be accomplished by the correct application of the stress (or strain), and the corrosion factor could be acquired by recording the interfacial behavior using electrochemical techniques. However, the corrosion behavior has not been recorded by electrochemical techniques when the SCC susceptibility has been studied. The susceptibility is assigned only with mechanical indicators and fracture examination.[15] METALLURGICAL AND MATERIALS TRANSACTIONS
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