| 304 austenitic stainless steel has good corrosion resistance,and it is easy to passivate in Fe3+solution to form a protective passive film to prevent corrosion and damage of the substrate.However,the Cl-in the solution has a good destruction effect to passive film,which can penetrate and destroy the passive film,causing local corrosion of the substrate.Therefore,in the FeCl3 solution,304 austenitic stainless steel will undergo complete passive film formation,destruction,and pitting corrosion of the substrate,which is significant for research.Therefore,a variety of electrochemical test methods are used to obtain the electrochemical parameters of the corrosion process,and the corrosion behavior of 304 stainless steel in FeCl3 system is described and analyzed in combination with surface morphology.Four electrochemical methods,such as open circuit potential,electrochemical impedance spectroscopy,cyclic polarization curve and EFM,are used in this paper.The surface morphology is observed by SEM.The effects of Cl-concentration and immersion time on the electrochemical behavior of 304 stainless steel in different Cl-concentration systems are studied.The effects of Fe3+concentration and immersion time on corrosion electrochemical behavior of 304 stainless steel in different Fe3+concentration systems were also analyzed.The related electrochemical parameters of the corrosion process are obtained from different electrochemical monitoring methods.Comparing and analyzing the consistency of the results,the corrosion process of stainless steel is studied and analyzed.At the same time,the above measurement results are used to verify the measuring precision and accuracy of the EFM technology used in this study.In the FeCl3 solution,as the concentration of Cl-increases,the passive film is formed and becomes dense with the potential range narrowing.The Rctt value decreases gradually and the CPE-P value decreases.The capacity of ion diffusion is improved.The stability of surface passive film of 304 stainless steel is reduced and the corrosion rate is increased.The Ecorrorr is decreased and the breakdown potential?Eb?is negatively shifted.The pitting resistance is decreased.CF2 and CF3 are deviated from the theoretical value.The current fluctuation amplitude is increased and pitting corrosion is highly prone to occur.In the solution of Fe3+0.001mol·L-1+Cl-0.2mol·L-1,the Rctt value reaches the maximum at 6h and then the Rctt value decreases.The protective effect of the passive film is best when immersed for 6h.In the FeCl3 solution,with the increasing of Fe3+concentration,the passive film of304 stainless steel is formed and the dense potential interval is widened.The Rctt value is increased and the passive film stability is improved.The self-corrosion potential(Ecorr)is positively shifted and corroded and the corrosion rate is reduced.The corrosion resistance is enhanced and the current fluctuation amplitude is reduced.The surface is less prone to become pitting corrosion.In Cl-0.001mol·L-1+Fe3+0.2mol·L-11 solution,with the prolongation of immersion time,the Rctt value is increased and the surface passive film is stable.The Ecorrorr value is increased and the fluctuation range of CF2 and CF3smooth.The range of current disturbance values is rapidly decreased and pitting resistance is improved.Comparison of cyclic polarization curve and EFM method which has tested corrosion rate showed that the corrosion rate values obtained by two electrochemical measurements in the same state were similar.EFM judgment of pitting corrosion trend is in good agreement with the corrosion behavior described by EIS and cyclic polarization curve of 304 stainless steel.Therefore,the EFM test data are accurate and reliable,which can be used as a conventional electrochemical monitoring method to analyze instantaneous corrosion rate. |
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