Evaluation of the Degree of Sensitization of a Stainless Steel 304 Using Local Electrochemical Impedance Spectroscopy

In this work the degree of sensitization of several samples of austenitic stainless steel 304 sensitized at 600 and 700 °C during 1h, was determined by Local Electrochemical Impedance Spectroscopy. The experimental methodology consisted of several steps. Firstly, a chemical analysis of each sample was realized by spark emission spectroscopy, after a metallographic characterization was done and finally tests of double loop- electrochemical potentiodynamic reactivation (DLEPR) were applied in each sample. Additionally, carbides precipitation in the border grain was observed using a Scanning Electron Microscopy (SEM). The spectra of local impedance were realized into austenitic grain, the results obtained showed a capacitive behavior. On the other hand in the grains limits (where chromium carbides are formed), a resistive - capacitive behavior is observed. This difference indicates what zone is most susceptible to intergranular corrosion (CIG), whereas DLEPR is unable to discern any evidence about this.