Investigation of intergranular corrosion by electrochemical methods

As mentioned before, austenitic stainless steels are susceptible to IGC due to sensitization caused by exposure to high temperatures (450-850 C). The IGC of austenitic stainless steel can also be characterized by normalized classical tests ASTM G28, ASTM A262-86, SEP 1877, AFNOR A05-159 and AFNOR A05-160, currently known as the Strauss, Huey and Streicher tests [54-57]. These methods however are destructive, difficult to perform on site and require sampling that can be harmful to the integrity of materials during service. For this reason, the electrochemical, non-destructive tests commonly known as EPR (electrochemical potentiokinetic reactivation) and DL-EPR (double loop electrochemical potentiokinetic reactivation) were developed to measure the sensitivity of austenitic stainless steels to IGC [58-66]. However, EPR and DL-EPR are based on measurements of characteristic potentials and currents of passive/active zones on potentiody-namic curves in an aqueous solution (linear voltammetry curve from oxygen to hydrogen evolution in the 

In the present work OCP measurements, linear voltammetry (LV) and electrochemical impedance spectroscopy (EIS) were tested as possible methods for studying IGC in molten chlorides. 

In a separate series of experiments, impedance spectra were recorded before and after the sensitization process has taken place. Typical dependencies of imaginary and real parts of the electric resistance (Nyquist 

Time of exposure (h) Type of steel Gravimetric method Linear voltammetry 

Under applied anodic potential the corrosion of stainless steels in molten chlorides is electrochemical in nature. At the initial period the exchange reaction between steel components and alkali metal cations takes place in parallel with the electrochemical process. It was found that titanium in steels forms stable carbonitride species that do not dissolve during anodic oxidation. Preliminary thermal treatment of austenite steels has an effect on anodic dissolution processes. 

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