Non-Destructive Evaluation of the AISI 304 Stainless Steel Susceptibility to Intergranular Corrosion by Electrical Conductivity Measurements

This paper examined the degree of sensitization (DOS) to intergranular corrosion (IGC) and the level of electrical conductivity of the welded and non-welded AISI 304 stainless steel to obtain a suitable correlation. The DOS was determined by the double loop electrochemical potentiokinetic reactivation method (DL EPR), while the level of electrical conductivity was measured using a commercial device (non-destructive method). After electrochemical etching in oxalic acid, the microstructure of the specimen surface was analyzed by scanning electron microscopy (SEM). At DOS greater than ~ 0.5%, a clear linear dependence between the electrical conductivity and the value of the DOS was obtained, while there was a higher deviation from linearity for lower DOS values. The mentioned correlations were discussed in the sense of the precipitation kinetics of the Cr-carbide and the formation of Cr-depleted areas of different levels near the grain boundaries. Cr-depleted areas during anodic polarization measurements show lower resistance to pit formation. The presence of Cr-depleted areas in the vicinity of grain boundaries and the reduction of carbon content in the austenite crystal lattice increases the electrical conductivity of the stainless steel