Duplex stainless steel (DSS), characterized by a dual phase ferrite-austenite microstructure, offers an excellent combination of higher mechanical properties and corrosion resistance, and has been increasingly used in chemical, petrochemical, marine and pollution control industries. Due to the soaring nickel prices, “lean” diplex stainless steels, in which part of the expensive nickel is substituted by nitrogen or manganese, is the most significant development of the duplex stainless steel market in recent years. DSS 2204 developed by Bao steel Co., Ltd. is a newly introduced lean duplex stainless steel with a typical composition of 22Cr-1.5Mn-4Ni-0.2N-1.2Mo. This grade DSS has better welding properties, higher corrosion resistance in the heat affected zone and higher strength compared with the conventional DSS 2304, which make it well suited for various applications
The intrinsic resistance to pitting corrosion of DSS can be estimated by the pitting resistance equivalent number, which is determined by the element content (1 mass %Cr + 3.3 mass %Mo + 16 mass %N). Due to the two-phase structure of DSS, the three key alloying elements (Cr, Mo and N) are partitioned between of the ferrite and austenite phase (Cr and Mo are enriched in ferrite phase and N is concentrated in austenite), leading to the different corrosion resistance of different phase.