Corrosion Behaviors of Random and Special Grain Boundaries in a Sensitized 304 Stainless Steel

The corrosion behaviors of random and special grain boundaries were compared in a sensitized type 304 stainless steel sheet previously treated by particular grain boundary engineering process. In order to evaluate the corrosion susceptibility of various grain boundaries, the samples were corroded (etched) in a particular solution and then the characters of grain boundaries were determined by electron backscatter diffraction (EBSD), associating with the microstructure acquired by optical microscopy. The results show that random boundaries are susceptible to corrosion whereas most of CSL grain boundaries (mainly Σ3 and Σ9) exhibit better resistance to corrosion. The incoherent Σ3 boundaries, located in the random grain boundary network, play a more significant role in arresting the development of corrosion along the random grain boundary path than coherent ones. The symmetrical incoherent Σ3 boundaries are more resistant to corrosion than asymmetrical ones. In addition, the more the boundary plane deviates from the exact CSL position, the more susceptible to corrosion it is.