Modified Electrochemical Potentiokinetic Reactivation Method for Detecting Sensitization in 12 wt% Cr Ferritic Stainless Steels

An investigation has been carried out to demonstrate the possibility of using the electrochemical potentiokinetic reactivation (EPR) method for determining the degree of sensitization of 12% Cr ferritic stainless steels. EPR tests were conducted on as-received and thermal-treated samples of a commercial heat of steel AISI 405. The EPR testing conditions were optimized to reduce the test aggressiveness to levels compatible with the relatively low Cr content of AISI 405 and to enhance the selectivity of the test minimizing the undesirable attack of the martensite phase, which was present along the ferrite grain boundaries in the thermal-treated samples. In the latter case, the EPR reactivation curve was generally composed of a sharp peak corresponding to intergranular attack and a broad shoulder related with the selective dissolution of the more anodic martensitic phase. Results of the EPR test were compared with those of properly modified versions of Huey and Strauss tests. Although some discrepancies in the test responses were unavoidable because of the different nature of the tests, they generally agreed, showing that sensitization induced by austenitizing treatment at 1,050°C could be removed after aging treatments are performed at temperatures higher than 650°C.