ELECTRODISSOLUTION OF AISI-304 STAINLESS-STEEL IN CONCENTRATED ACIDS LEADING TO ELECTROPOLISHING

The electrochemical polarization behaviour of austenitic stainless ste el 304 has been studied with a special reference to electropolishing i n concentrated phosphoric and sulphuric acid and in various compositio ns of their mixtures containing acetic acid at 30 +/- 1 degrees C in d eaerated condition. The specimen of SS 304 invariably showed active, p assive and transpassive behaviour id different solution mixtures. The conditions which cause electropolishing of the specimen have been work ed out. Highly reflecting and smooth electropolished surface of the SS 304 was obtained only in a few compositions of the electrolytes. The electropolishing was observed in the transpassive potential region at or beyond a limiting current plateau. Phosphoric acid based solutions with acetic acid appeared to be more suitable for electropolishing of SS 304 in comparison to phosphoric acid-sulphuric acid-sulphuric acid mixtures and the presence of acetic acid in overall reaction mixture a ppeared to be beneficial.