Case Study on Sensitization of Sensitization-Resistant Stainless Steels in Welded Joints

Stainless steels are made sensitization-resistant by the addition of stabilizing elements to the alloy. These stabilizers provide a carbide-forming alternative that is preferential to the formation of chromium carbides in the base material's welded joint heat-affected zone. In so doing, the corrosion-resistant properties of chromium in the base metal are preserved. The advantage of the stabilizers, however, can be circumvented under certain welding conditions. We will review a case study that involves such a welded-joint failure, identify candidate adverse welding conditions that precipitated the failure, and describe precautions to avoid sensitization of the stainless-steel welded joint. In this case study, it will be shown that two dissimilar thickness materials welded put the thinner material at risk of being overheated, and the omission of a pre- or post-weld heat treatment step in the welding process was, with a reasonable degree of engineering certainty, the root cause of the welded-joint failure.