Study On The Corrosion Behavior Of 304 Stainless Steel In Simulated Pits Solution

The potentiodynamic polarization curves, electrochemical impedance spectroscopy, chemical immersion, the open circuit potential, pH was monitored continuously polarization process, X ray diffraction and three video microscopy techniques together to explore the 304 stainless steel pitting corrosion in simulated corrosion behavior of solution. The simulated solution of pit was concentrated acidic solution which generated by pitting of 304 stainless steel in 3.5% NaCl solution. The effect and degree of hydrolysis of metal ions in the pores were simulated. The dynamic information of pitting corrosion of 304 stainless steel in simulated solution was determined,and the mechanism was discussed.The main research contents and results are as follows:Electrochemical signal characteristics and chemical characteristics were studied by dynamic potential polarization curve,electrochemical impedance spectroscopy,X-ray diffraction and so on in FeCl₃ solution system.And in order to characterize the variation of pitting corrosion behavior of Fe³⁺ on 304 stainless steel.The results showed that Fe³⁺ hydrolysis was because of Fe³⁺ and OH- in the water complexation.The pH value of the solution decreased linearly with the increase of the concentration.When the concentration of FeCl₃ solution was 3.5 mol/L.the concentration of hydrogen ion was reached to 2.421 mol/L.Self etching current density Jcorr at the concentration of 3.2 mol/L reached the maximum 15.86 mA/cm2,when the concentration of 3.5 mol/L was followed, the self etching current density was no longer changed.The results showed the corrosion products were mainly controlled by the diffusion of corrosion products in the late stage of steady growth.The relationship between pitting corrosion behavior and Fe³⁺ of 304 stainless steel by Fe²⁺ was studied by electrochemical impedance spectroscopy,dynamic potential polarization curves, 3D video microscopy and so on.The results showed that with the increase of the concentration of FeCl2 solution,the self corrosion potential of 304 stainless steel was positive, and the corrosion current density increases,and the protective potential was negative.When the concentration of FeCl2 solution was 3.5 mol/L,the concentration of the hydrogen was 0.132 mol/L, and the self etching current density was 0.285 mA/cm2.In comparison with FeCl₃ solution,both the difference of hydrogen ion concentration and the difference of the self etching current density reached an order of magnitude.The indicated the anodic process was the active dissolution of metal in the process of corrosion of 304 stainless steel,the cathodic process was mainly hydrogen depolarization,and the degress of hydrolysis of Fe³⁺ was stronger than that of Fe²⁺.The mechanism of pitting corrosion of 304 stainless steel was studied by means of dynamic potential polarization curves,chemical immersion, 3D video microscopy and so on.The results showed that the simulated solution concentration of the maximum metal dissolution rate was 2.5 mol/L,and the 2.5 mol/L may be the critical concentration of the 304 stainless steel metastable pitting to the stead state.The open circuit potential of the saturated analog solution was finally stabilized at-0.345 V,and the potential of the bottom of the pit was probably-0.345 V. By measuring the pH value of the three kinds of saturated solution and the measurement of the self etching current density, the result was a positive correlation between the self etching current density and the hydrogen ion concentration. And with the decrease of solution concentration, the metal dissolution rate decreased gradually. The indicated that the pitting growth process, metal ions presented concentration gradient distribution in the corrosion pores, may appeared dilution passivation.