Influence of Microstructure on Pitting Corrosion Resistance of Alloy 904L Superaustenitic Stainless Steel

Alloy 904L (UNS N08904) is a superaustenitc stainless steel with high Cr and Mo additions. The steel also contains high nickel content, which is important to maintain the austenitic structure. Because of its high corrosion resistance, Type 904L alloy is being used in much equipment in chemical and petrochemical plants. Some of this equipment may experience high temperatures in service or during fabrication. The microstructural changes associated with exposures in the range of 650°C to 850°C or as a consequence of melting were analyzed in this paper. The microstructure/corrosion resistance relationships were studied by means of electrochemical pitting corrosion tests and microstructural analysis. Critical pitting temperatures (CPT) of annealed and cast specimens were determined and compared. The results show that the corrosion resistance can vary significantly with fabrication processes and/or service at high temperatures.