The Characterization Of Electrochemistry Behaviors Of Ferritic Stainless Steel In Hydrochloric Acid-Based Solution

With the wide application of stainless steel, the requirements for its surface integrity is more stringent. The oxide layer and the chromium-depleted layer formed during thermal treatment may reduce the surface quality of stainless steel and its corrosion resistance. Consequently, the pickling process which aim at the removal of oxide layer holds significance for stainless steel production.Pickling in mixed HNO3-HF is widely applied, but nowadays the application of such HNO3-containd mixed acids is restricted for environmental concerns. Meanwhile, this pickling process is weak in the removal of the chromium-depleted layer. Therefore, study on pickling process corresponded to oxidized stainless steel heat treatment is beneficial to improve the competition of products.In this paper,430 ferritic stainless steel was the object of study. With utilizing electrochemical approaches, electrochemical behavior of ferritic stainless steel in the pickling process of hydrochloric acid was studied and the reactions were learned, which could be theoretical guidance of hydrochloric acid pickling for stainless steel. In this experimental condition, conclusions were discussed as follows:(1) In the single Hydrochloric acid solution, the reactions of hydrogen evolution and the reactions of anode metal dissolution determined the corrosion potential. The impedance spectra solely consisted of a capacitive loop at high frequencies. Radius of capacitive loop and charge transfer resistance decreased with the increase of hydrochloric acid concentration and temperature. The controlling step of electrochemical reaction was the anodic reaction.(2) In the solution containing ferric ions, the anodic reactions of metal dissolution and catholic reactions of hydrogen evolution and ferric ions reduction determined the corrosion potential. The impedance spectra illustrated as a capacitive loop at high frequencies and an inductive loop at low frequencies. The presence of the inductive loop indicated that the surface area was partly or wholly active. With ferric ions increasing, the charge transfer resistance decreased and corrosion rate increased. The corrosion rate controlled by the anodic reaction.(3) In the solution containing an addictive A, the anodic reaction of metal dissolution and catholic reactions of the reduction of addictive A and ferric ions reduction and hydrogen evolution determined the corrosion potential. The impedance spectra included a capacitive loop and an inductive loop at low frequencies. With increasing concentration of additive A, inductive loop in the low frequency gradually expanded which means the expansion of the active area of anodic.(4) Corrosion rate accelerated with the increasing concentration of addictive A. When the concentration of additive A is 2%, because of the change in the electrode reaction, multiple peaks emerge in the polarization curves.(5) In the solution containing an addictive A, The corrosion potential decreased with the increasing concentration of hydrochloric acid. In the solution containing 2% hydrochloric acid the impedance spectra included Warburg impedance at low frequency, which means corrosion process is mainly controlled by the diffusion process.