Effect of Precipitation of Alpha Line and Sigma Phases on the Microstructure and Corrosion Resistance of the Duplex Stainless Steel SAF 2205

The purpose of this work was to evaluate the microstructural alterations associated to the aging thermal treatments performed at 450, 475, 800 and 850°C, for 1, 3 and 12h, besides evaluating the influence of the precipitation of the alpha line phase on corrosion resistance. The samples were characterized by scanning electron microscopy, energy dispersion spectrometry, X-ray diffraction, feritscope, hardness, microhardness, in addition cyclic potentiodynamic polarization and double loop electrochemical potentiokinetic reactivation. In the agings performed at 450°C for 1h and 475°C for 12h, there was precipitation of the alpha line phase inside the ferrite and there was no significant effect on the resistance to pitting corrosion and the phenomenon of sensitization was not promoted. In the aging at 800 and 850°C for 1, 3 and 12h, the sigma phase was formed from the consumption of ferrite, and in the aging at 850°C there was the precipitation of the chi phase, promoting the increase in steel hardness. In agings for 12 h at 800 and 850°C, there was resistance to pitting corrosion decrease and the phenomenon of sensitization was moderated promoted at 800°C, with just the sigma phase precipitation and promoted at 850°C with sigma and chi phases precipitation.

Keywords:
Duplex stainless steel; Aging thermal treatment; Alpha line; Sigma; Corrosion