Scientific and experimental justification for the industrial application of accelerated electrochemical methods for testing resistance to intergranular corrosion

The purpose of this work is to provide a scientific and experimental justification for the widespread industrial application of accelerated electrochemical methods for testing the resistance of austenitic stainless steel products to intergranular corrosion as an alternative to prolonged (up to 240 hours) boiling tests in acid solutions. A large-scale comparative study was conducted using standardized methods for assessing the intergranular corrosion resistance: (a) in weakly oxidizing environments – an accelerated electrochemical method of potentiostatic etching in 1 N HClO4+0.25 N NaCl, compared with a prolonged test involving the boiling of samples in 35% H2SO4 with the addition of CuSO4 and metallic copper (Practice E, ASTM A-262); and (b) in highly oxidizing environments – an accelerated electrochemical method of anodic etching of metallographic sections in 10% H2C2O42H2O, compared with a prolonged test involving the boiling of samples in 65% HNO3 (Practices A and C, ASTM A-262, respectively). The study was conducted on experimental 304L-type stainless steel samples with a carbon content of 0.018–0.05%, sensitized under different conditions, as well as on industrially manufactured Cr–Ni and Cr–Ni–Mo stainless steel products. A strong correlation was found between the results obtained using the proposed accelerated methods and the traditional prolonged tests. Additionally, quantitative criteria for satisfactory intergranular corrosion resistance were established when testing by the potentiostatic etching and Practice A methods. The study demonstrated the high corrosion resistance of special 3 twin grain boundaries when using method A, as described in the coincident site lattice theory. The obtained results support the recommendation of using the accelerated potentiostatic etching and Practice A methods as viable alternatives to prolonged testing procedures in industrial production of austenitic stainless steel products.