A STEM Examination of the Localized Corrosion Behavior of a Duplex Stainless Steel

Abstract

Abstract The most susceptible site for pit initiation was found by optical metallography and transmission electron microscopy to be the retained delta ferrite/austenite interface. Microanalysis results, which were obtained with scanning transmisssion electron microscopy, virtually disprove the chromium depletion theory for pit initiation at these interfaces. The most likely explanation is a segregation of impurities such as sulfur or phosphorus to the interface during the nonequilibrium solidification process associated with weldments. The passive film over the delta ferrite/austenite interface as well as the repassivation kinetics of this interface are degraded by the presence of the impurities and are therefore the most susceptible sites for pit initiation and growth.