Abstract

The effect of environmental factors on stress corrosion cracking (SCC) for NiCrFe (Inconel alloy 600) alloy has been studied in deaerated water at 350°C by using the constant extension rate test (CERT) and U-bend test methods. SCC occurred in acidic and alkaline solutions. Especially, NiCrFe alloy suffered severe SCC, intergranular corrosion (IGC), and intergranular attack (IGA) in alkaline solution. On the other hand, SCC did not occur in neutral solution. The results due to Auger electron spectroscopy (AES) analysis showed that the oxide film of the NiCrFe alloy was Cr-enriched and was thin in acidic solution. As the pH of test solution increased, the Ni content of oxide film increased and the Cr content decreased. The oxide film of the NiCrFe alloy was thick and mainly composed of Ni in alkaline solution. The potential-pH diagrams for Ni-H 2O and Cr-H 2O systems and the results of corrosion potential measurement indicated that the oxide film of the NiCrFe alloy was stable in neutral water. On the other hand, the oxide films were unstable in acidic and alkaline solutions, respectively. According to these results, the relationship between the characteristics of oxide film and SCC susceptibility is discussed.

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