Detection of sensitisation on aged lean duplex stainless steel with different electrochemical methods

Ageing at 600 degrees C (from 0.1 h up to 20 h) leads to the formation of precipitations at the ferrite-ferrite (alpha/alpha) and ferrite-austenite (alpha/gamma) grain boundaries of the lean duplex stainless steel (LDSS) X2CrNiN22-2. This leads to sensitisation due to chromium depletion and decreased pitting corrosion resistance proven by the results of various electrochemical methods (DL-EPR and determination of CPT, E-pit). These results were compared with the KorroPad method, which uses an agar-based gel-electrolyte for the detection of stainless steel surfaces prone to pitting corrosion. However, the standard configuration of the KorroPad showed no differentiation for the various ageing conditions. Therefore, modified versions of the KorroPad with two, five and ten times higher NaCl and potassium ferrocyanide III (K-3[Fe(CN)(6)]) concentrations were successfully used to visualise the behaviour detected by DL-EPR, E-pit and CPT. Therefore, the KorroPad method can also detect a microstructure related reduction of pitting corrosion resistance, which can drastically reduce the experimental effort to generate sensitisation diagrams for stainless steels. (C) 2019 Elsevier Ltd. All rights reserved.