Pitting Features Of 1Cr18Ni9Ti Stainless Steel In The NaCl Solution

The pitting features of 1Cr18Ni9Ti stainless steel in NaCl solution was studied by Electrochemical noise (ECN), Electrochemical Impedance Spectra (EIS) and Electric Speckle Pattern Interferometry (ESPI).The results of research showed that, the noise resistance (Rn) and the value of peak of current noise fluctuation are available parameters which can be used to judge the emergence of pitting. The Rn decrease suddenly, means the transition from metastable to stable pitting. When the pitting develops stably, the change of Rn is not obvious. In the stage of pitting pregnant, the value of peak of current noise fluctuation is small, but the value increases suddenly when the stable pitting emerges. The sudden increase of the value of peak of current noise fluctuation is the symbol of pitting corrosion. It can be used to judge the stage of pitting pregnant and develop. The results are agreement with the analysis of Electrochemical Impedance Spectra (EIS) and the theory of other people.There is such a rule in the analysis of the experiments: when the slope of the spectral noise plots (KRsn) change to more minus with the immersion time prolong, and the amplitude of change is small, there is not turning point in the KRsn-t plot, which indicate no pitting emerge in the surface of 1Cr18Ni9Ti stainless steel. When the amplitude of KRsn change is large, and there are turning point in the KRsn-t plot, which means stable pitting emerge in the surface of the steel.The research of the factors that infuenced the pitting resistance of 1Cr18Ni9Ti stainless steel shows that, the capacity of resist pitting increase with lower the temperature or the concentration of NaCl, but decrease with the value of pH decreasing.Electric Speckle Pattern Interferometry (ESPI) records the interference ray field before and after deformation of object. After subtract and absolute, we obtain the speckle strides, which also reflect the information of the deformation of the object. The monitor equipment with high sensitivity, can be used to measure the microcosmic deformation of the surface. The experiment of ESPI and the anodic polarization indicate that, in the initial stage of pitting emergence, there are white points in the monitor plot, then the white points change to white strides with the developing of the pitting.