Abstract
The comparison of the pitting resistance of alloys with high corrosion resistance can be challenging, as CPT-values (critical pitting temperatures) are often above the boiling point of the test solutions. For high-nickel alloys, the use of potentiostatic electrochemical methods at increasing temperatures can also be questionable, as this alloy type often shows high or continuously increasing current densities with increasing temperature, rather than the desired distinct current peak at pitting. The applied electrochemical potential must also be proven to be below the transpassive potentials of the tested alloys.
A new electrochemical method has been developed in which CPT-values could be determined of alloys UNS N08935, UNS N06625, UNS N06455 and UNS N06985. The electrochemical potential used is shown to be below transpassive potentials. The current density versus temperature curves were analyzed and showed low passive current densities up to temperatures where pitting started.
CPT-values of the tested alloys were around 90°C for UNS N08935, UNS N06625 and UNS N06455 and 55°C for UNS N06985.
