A Modified Electrochemical Technique (Electrochemical Potentiokinetic Reactivation) for Evaluating the Susceptibility of Inconel 600 to Intergranular Corrosion

The electrochemical potentiokinetic reactivation (EPR) method has recently become a popular test for evaluating the intergranular attack (IGA) of high-nickel alloys and different types of stainless steels (SSs). The EPR method was used in a study on the IGA and intergranular stress corrosion cracking (IGSCC) of a high-nickel alloy (Inconel 600). A number of experimental test conditions were optimized to (1) cause selective grain boundary attack and (2) suppress other types of corrosion. It was found that the EPR curve is composed of different peaks. Microstructural analysis showed that the peak at –30 mV/SCE corresponds with the IGA of the sample, and the peak at –150 mV/SCE corresponds with a pitting-like attack. The IGA of Inconel 600 was tested with the modified EPR technique and compared with the results from chemical (Huey and Streicher) tests. Good agreement was found for sensitized samples. Mill-annealed samples showed moderate sensitization in the chemical tests. The modified EPR technique, on the contrary, revealed some pitting attack, but no IGA.