Electrochemical behavior of hot-rolled 304 stainless steel during chemical pickling in HCl-based electrolytes

The mechanism and kinetics of chemical pickling of hot-rolled 304 stainless steel oxidized at high temperatures was investigated in HCl-based electrolytes with weight loss, corrosion potential, and electrochemical impedance spectroscopy (EIS) measurements. Corrosion products were characterized with scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX) and X-ray photoelectron spectroscopy (XPS). The mechanism of chemical pickling in HCl-based electrolytes is associated with anodic brightening. A highly ionically conductive corrosion product layer covering the brightened surface ensures a high corrosion rate of the underlying stainless steel. The addition of ferric ions to HCl-based electrolytes significantly enhances the corrosion rate. On the contrary, the influence of HCl becomes less important because it is highly concentrated, resulting in a brightening of the stainless steel surface. The effect of ferrous ions on the corrosion rate is negligible. The charge-transfer resistance of hot-rolled stainless steel decreases with pickling time due to the progressive removal of oxide layers. (c) 2006 The Electrochemical Society.