Role of Grain Boundaries in Intergranular Corrosion in Austenitic Stainless Steels

Grain boundaries play a very important role in intergranular corrosion. They determine whether the material is prone to intergranular corrosion or not. A study has been carried out to determine the influence of grain boundaries on the degree sensitization of Type 304 stainless steel (SS) and Type 316L stainless steel. The alloys were different thermomechanical treatment to obtain a variation in grain boundaries. They were then annealed and sensitized. The degree of sensitization was evaluated by using the Double Loop Electrochemical Potentiokinetic Reactivation (DL-EPR) technique and intergranular corrosion was evaluated by ferric sulfate-sulfuric acid test. In these tests, the degree of sensitization was measured by determining the ratio of the maximum current generated by a reactivation scan to that of the anodic scan, i.e. Ir: Ia, and intergranular corrosion was measured from weight loss of specimens. The grain boundary character distribution was measured with the help of Orientation Imaging Microscope (OIM). The degree of sensitization was then related to the grain boundary measurements. It was found that the degree of sensitization and intergranular corrosion is low at high angle grain boundaries in both types of stainless steel.