Electrolytic pickling of the oxide layer on hot-rolled 304 stainless steel in sodium sulphate

Electrolytic pickling of hot-rolled 304 stainless steel in Na2SO4 electrolyte was investigated with electrochemical, weight loss and SEM–EDX measurements. Pickling took place upon both active and transpassive polarisations. Mechanism and kinetics of pickling during active and transpassive polarisations were unravelled. Metallic phase in oxide layer was dissolved during active polarisation while the oxide layer was significantly undercut. Chromium oxide in the oxide layer was oxidised to soluble anions during transpassive polarisation, while iron oxide and metallic phase could either be remained or removed. Pickling due to undercutting with active polarisation was highly pronounced.