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The effects of Cu addition on the microstructure and localized corrosion of hyper duplex stainless steels aged at 748 K were investigated using TEM analysis and electrochemical test. The addition of Cu to the base alloy facilitated the precipitation of a Cr-enriched ¡A-phase due to an increase in the Cr activity, thereby reducing the localized corrosion resistance. The localized corrosion was initiated at the Cr-depleted regions around the Cr-enriched ¡A-phase.

Influence of annealing temperature on the microstructure and resistance to pitting corrosion of the hyper duplex stainless steel was investigated in acid and neutral chloride environments. The pitting corrosion resistance is strongly dependent on the microstructure, especially the presence of chromium nitrides (Cr 2 N), elemental partitioning behavior and volume fraction of ferrite phase and austenite phase. Precipitation of deleterious chromium nitrides reduces the resistance to pitting corrosion due to the formation of Cr-depleted zone. The difference of PREN (Pitting Resistance Equivalent Number) values between the ferrite and austenite phases was the smallest when solution heat-treated at 1060 o C. Based on the results of electrochemical tests and critical crevice temperature tests, the optimal annealing temperature is determined as 1060 o C.

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