Effect of austenite morphology on the electrochemical properties of super Duplex stainless UNS S 32750

Abstract

Volume fraction, Pitting resistance equivalent (PRE) as well as morphology of austenite on Duplex stainless steel can be changed through heat treatment by controlling annealing temperature and cooling rate. All specimens were evaluated for corrosion resistance according to shape of austenite phase after optimizing corrosion resistance as 5:5 volume fraction. The corrosion behavior was measured by the potentiodynamic polarization test and the pitting resistance was measured by Critical pitting temperature CPT. Austenite morphology increase corrosion current density on uniform corrosion without corrosion potential changing. The CPT of the specimen with the smallest grain boundary length of 2.3 μm/ μm2 has the highest CPT as 76.3°C. Scanning Electron Microscopy showed that the pitting occurred in the grain boundary and propagated. It is confirmed that the reduction of the grain boundary length due to the control of the austenite morphology improve the pitting corrosion resistance of the UNS S 32750.