Cluster properties of sensitized grain boundaries in Type 304 stainless steel

Abstract

Electron Backscatter Diffraction (EBSD) and Image Analysis (IA) techniques have been coupled with Double Loop-Electrochemical Potentiokinetic Reactivation (DL-EPR) testing to characterize the development of sensitized grain boundary clusters in Type 304 stainless steel. DL-EPR testing revealed differences in the sensitization response of thermo-mechanically processed microstructures, despite similar grain size and grain boundary character distributions (GBCD). The same sensitization treatment produced different distributions of sensitized grain boundary clusters, and susceptible boundary clusters percolated through all microstructures after sensitization treatments of 4 hrs at 650°C. Assessment of the connectivity of ∑3 n (1≤n≤3) grain boundaries in EBSD maps showed a trend to longer clusters with increasing ∑3 n (1≤n≤3) fractions. A comparison to DL-EPR data showed the attacked grain boundary networks were generally in excess of 80% of the potentially susceptible grain boundary fraction. © 2009 by NACE International