Abstract
A systematic analytical electron microscopy (AEM) study was conducted on a series of AISI 304 stainless steels (SSs) to determine the mechanisms by which N affects Cr carbide precipitation and the associated Cr depletion at grain boundaries. Electrochemical potentiokinetic reactivation (EPR) tests conducted on the steels indicate that N additions up to 0.16 wt% retard sensitization, but above 0.16 wt%, they promote it. The microstructural investigation revealed that an increasing N content consistently caused the bulk diffusion coefficient of Cr in austenite to decrease and the grain boundary Cr concentration to increase. The increase in the degree of sensitization (EPR tests) for Cr contents above 0.16 wt% was found to result from Cr carbides precipitating discontinuously, which resulted in grain boundary migration and, hence, wider Cr-depleted zones.
