Research And Application Of Characterization Method Based On Stainless Steel Pitting Corrosion

The effects of chloride ion concentration,pH value and corrosion inhibitor on pitting corrosion of stainless steel were characterized by macroscopic and microscopic electrochemical methods.Firstly,the corrosion resistance of stainless steel materials was tested by traditional electrochemical methods,such as AC impedance spectroscopy and polarization curves,and the advantages and disadvantages of traditional methods were analyzed.Then,the current density distribution in the micro-area of stainless steel under natural corrosion conditions was measured by scanning electrode vibrating technology（SVET）,and the corrosion inhibition effect of different corrosion inhibitors was verified.The flow rate and current density of specific ions involved in the metal corrosion process were measured,which provided a new characterization method for studying the corrosion mechanism.The measured ion flow rate was quantitatively compared with the SVET current density to further clarify the recognition of the anode and cathode regions on the metal surface,the magnitude of the anode and cathode current,the concentration of cations and anions,the flow rate and the influence of the corrosion inhibitor on each parameter.Through the above research,the following conclusions are obtained:（1）The pitting corrosion of stainless steel was characterized by macroscopic electrochemical test.Although the degree of corrosion,the influence of various corrosive media and corrosion inhibitors on the pitting corrosion of stainless steel can be generally judged,the information obtained is about the average value of the whole sample surface,and the corrosion parameters of the local area are difficult to obtain.At the same time,when measuring the polarization curve,due to the application of polarization voltage,the surface of the stainless steel sample was seriously damaged after the test,and many large pitting pits and rusts appeared obviously.The measured results were not the electrochemical parameters of the stainless steel sample in the natural corrosion state.（2）SVET was used to scan the current density distribution map of 304 stainless steel under the condition of corrosion inhibitor without external polarization voltage.By observing the current density distribution interval and peak value,the corrosion inhibition effect was obtained,which was consistent with the macroscopic electrochemical measurement results.The characterization method can obtain the corrosion current without destroying the stainless steel surface,and can obtain the corrosion of the entire surface,and know where the corrosion is most severe.（3）By proposing a new method to characterize the corrosion mechanism,the flow rate and current density of specific ions involved in a certain point corrosion process of the sample were measured,and a H⁺and Zn²⁺selective microelectrode with superior performance was established to monitor the real-time flow rate and current density of H⁺and Zn²⁺ions in the micro-area of the metal surface.This ion flow detection technology based on non-destructive micro-measurement provides a valuable research method for in-depth understanding of the dynamic transmission process and mechanism of metal sample surface and solution micro-interface under natural corrosion（no external polarization）conditions.