Effect of grain boundary structure on sensitization and corrosion of stainless steel

Abstract

This paper reports on the influence of misorientation angle and structure of a grain boundary on the sensitization and grain boundary corrosion of austenitic and ferritic stainless steels. To establish grain boundary atomic structure, orientation information of the adjacent grains, obtained with the electron backscattering (EBS) technique, was combined with the SEM image of the surface to obtain the orientation of the grain boundary. Modeling of the grain boundary structure was based on ideal crystallography and the coincident site lattice concept. The results support the concepts (1) of a threshold misorientation angle whose value is a function of the aging time and temperature, below which boundaries are of sufficiently low energy that sensitization does not occur, and (2) of a major role of grain boundary structure in explaining the wide variation in sensitization that occurs in grain boundaries of misorientation angle greater than the threshold value. It was also found that the grain boundary corrosion mechanism is not simply the dissolution of chromium depleted alloy since the observed groove widths were 10 to 100 times larger than the Cr-profile widths.