Investigation on influence of alloying on phase transitions of duplex stainless steel based on thermochemical calculation

This paper investigated on influence of different alloying elements added into duplex stainless steel (DSS) on phase transitions using thermochemical methods in comparison with experiment. The results showed that the most possible species in the ferrite phase, austenite phase, σ phase, Hcp phase, χ phase, and carbide were Cr:Va-type, Fe:Va-type, Ni:Cr:Mo-type, Cr₂N-type, Fe₂₄Mo₁₀Cr₂₄-type, and Cr:Mo:C-type, respectively. Furthermore, the Ni, N, Cr, and Mo alloying had significant influences on the transition of each DSS phase. The Ni and N additions obviously raised the temperature at ferrite-1/austenite-1 balance while the Cr and Mo decreased the dual-phase balance temperature. In addition, the Ni addition can promote the precipitating of σ phase at relatively high temperature while the precipitating of Hcp phase at relatively low temperature. The Hcp phase and χ phase can be obviously increased by the N addition. The introduction of Cr and Mo notably enhances the precipitation of σ phase. However, the promotion of χ phase precipitation is facilitated by the presence of Mo, while the Cr element acts as an inhibitor for χ phase precipitation. Furthermore, the ferrite/austenite ratio tested by experiment was higher than that calculated by thermochemical methods, thus pre-designed solution temperature should be lower about 30−100 ℃ than that calculated by thermochemical methods.