A New Series of Mo-free 215Cr-35Ni-xW-02N Economical Duplex Stainless Steels

A new series of economical Mo-free duplex stainless steels 21.5Cr-3.5Ni-xW-0.2N(x=1.8-3.0,mass%) have been developed.The effects of W on mechanical properties and corrosion resistance were investigated,and the microstructures were analyzed by optical microscopy,X-ray diffraction,transmission electron microscopy and electron backscatter diffraction.The designed steels have a balanced ferrite-austenite relation and are free of sigma phase after solution treatment at 750-1 300℃for 30min followed by water-quenching,whereas a small number of Cr23 C6 precipitates were found after solution treatment at 750℃.After solution treatment at 1 050℃,the steel with 1.8%(mass percent)W exhibits the highest room temperature tensile strength due to the strongest work hardening effect, while the steel with 3.0%(mass percent)W exhibits the highest fracture elongation owing to the transformation-induced plasticity(TRIP)effect.The ductile-brittle transition(DBT)and martensite transformation are respectively found in the ferrite and austenite,which deteriorates the impact properties of the steels with the increase of W content.The corrosion resistance of the designed steels is improved with the increase of W content.The pitting resistance of austenite is obviously better than that of ferrite for the designed alloys.Among the designed steels,the steel with 1.8%(mass percent)W is found to be an optimum steel with excellent comprehensive properties and lowest production cost.