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The effect of copper on secondary phase precipitation in duplex stainless steel – a thermodynamic calculations approach

Abstract Thermodynamic calculations with Thermo-Calc software and the steel database TCFE3 was applied to investigate the precipitation behavior of industrial grades of duplex stainless steels with high copper content, 1.6 and 2.3 wt.%, Duplok 27 and DUP 27, respectively. Well-documented super duplex stainless grade SAF 2507 with copper content of 0.20 wt.% was used as the reference steel. The results of the calculations are compared with the experimental results obtained previously for these steels. It is shown that copper decreases the high-temperature limit of precipitation of sigma and chi phases and reduces the equilibrium amount of precipitated chi phase. Copper addition to a duplex stainless steel facilitates precipitation of chromium nitride phase and stabilizes it at elevated temperatures. The ferrite-austenite balance at high temperatures is also affected in these steels by the copper addition.