Sensitization phenomena on aged SAF 2205 duplex stainless steel and their control using electrochemical potentiokinetic reactivation test

Duplex stainless steels (DSS) are used widely in chemical plants, oil and gas production and transportation, offshore drilling, and pipeline applications because of their superior performance in comparison to traditional SS.1-3 The alloy content and microstructure determine their good corrosion resistance and mechanical properties. If the percentage of ferrite is increased, the strength is increased. Stress corrosion cracking (SCC) resistance in chloride environments also is increased in comparison to that of conventional austenitic SS, while increases in the austenite amount improves toughness. The balance between ferrite and austenite depends upon composition of the alloy and the thermal history. During heat treatments of DSS, some transformations involving the precipitation of sigma ( ), chi ( ), and R intermetallic phases, body-centered cubic (bcc) ferrite, various carbides, and chromium nitrides can take place.4-10 These transformations induce marked changes in mechanical properties of these alloys, such as embrittlement caused by the presence of and the decrease in toughness caused by the phase. Precipitation of the phase undoubtedly has a great influence on mechanical properties and corrosion susceptibility of the alloys. This influence can be attributed to chromium depletion at grain boundaries.11-12 The kinetics of intermetallic phase precipitation and its influence on corrosion resistance is a function of the effective chemical composition of the alloy. Therefore, each alloy must be studied to establish the effects of aging treatments.