The Microstructural Causes of Intergranular Corrosion of Alloys 82 and 182

This paper reports a study of the microstructural causes of intergranular corrosion (IGC) in the nickel base weld metals designated as Alloy 182 and Alloy 82. Both unwelded electrode material and welds made from various production heats of the electrodes were examined. In all cases, it was found that Alloy 182 corroded significantly more than Alloy 82 after various thermal aging treatments. This difference could be attributed to the fact that the precipitation of chromium-rich carbides along the grain boundaries caused more chromium depletion in Alloy 182 than in Alloy 82. The greater amount of chromium depletion in Alloy 182 resulted from the fact that it contains more carbon and iron and less chromium in its matrix than Alloy 82. Welds of Alloy 82 could be made susceptible to IGC if they picked up carbon during the welding process.