Effect of annealing temperature on pitting behavior and microstructure evolution of hyper-duplex stainless steel 2707

Hyper-duplex stainless steel (HDSS) 2707 is a competitive material for application in extremely caustic environments. In this study, different annealing temperatures ranging from 1020 degrees C to 1200 degrees C were examined by electrochemical tests and microstructure analysis. The microstructure characterization indicated that precipitations were detected when the annealing temperature was below 1050 degrees C and a relatively balanced austenite-ferrite phase structure was obtained at 1100 degrees C. Through electrochemical measurements in NaBr solution, it was revealed that with the increase of temperature the pitting resistance of HDSS 2707 first rose then declined, peaking at 1100 degrees C. The highest critical pitting temperature was about 67 degrees C. In addition, the pitting position shifted from austenite phase to austenite-ferrite boundary and finally to ferrite interior with the annealing temperature increasing, which was in agreement with the pitting resistance equivalent values (PREN) of the two phases.