Abstract

The present work has as an objective to explain why a simple PREN calculation cannot be used to select Duplex Stainless Steels (DSS) for field applications. Most commercially available DSS have to be heat treated (annealed followed by oil or water quenched). A second heat treatment to release the stresses originating from machining or welding may be used in some alloys. Therefore, the size of the ferrite and the size of the austenite grains (microstructure), ferrite-to-austenite ratio, and inclusions will have an impact on the physical and chemical properties of the alloy. Results from a commercially available 25Cr DSS UNS S32550 heat treated to four different temperatures revealed that the temperature used during the heat treatment influenced the grain size of the alloys, the ferrite to austenite ratio and their corrosion resistance in different environments (particularly in Cl-containing solutions). Electrochemical tests done on the alloy also showed that pitting corrosion resistance was also dependent on the heat treatment temperature.

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