Research on Pitting Corrosion Behavior of Cast Duplex Stainless steel

Pitting corrosion behaviors of 5 kinds of cast duplex stainless steels in 6% FeCl₃ solution were investigated by using chemical immersion corrosion test and microstructure and chemical composition analyses, and then were compared with that of 316 L austenite stainless steel. The results indicated that all the 5 kinds of cast duplex stainless steels exhibited better pitting corrosion resistance than 316 L austenite stainless steel. Compared with that of 316 L austenite stainless steel, both corrosion rates and pitting corrosion depth of cast duplex stainless steels were lower. Main pitting corrosion resistant alloying elements were non-homogeneously distributed in austenite phase and ferrite phase, with Cr and Mo more likely in ferrite phase and Ni and N in austenite phase, and the pitting resistance equivalent (PRE=Cr% + 3. 3Mo% + 16N%) of ferrite phase was higher than that of austenite phase. The pitting resistant properties of duplex stainless steels depended on their chemical compositions and increased with the increasing of PRE value. However, copper-rich phase precipitated from ferrite phase would lead pitting corrosion to preferentially occur and develop in ferrite phase, deteriorating the pitting corrosion resistance of the duplex stainless steel.