A New Series of Mo-free 21.5Cr-3.5Ni- x W-0.2N Economical Duplex Stainless Steels

A new series of economical Mo-free duplex stainless steels 21.5Cr-3.5Ni- x W-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 – 1300 °C for 30 min followed by water-quenching, whereas a small number of Cr 23 C 6 precipitates were found after solution treatment at 750 °C. After solution treatment at 1050 °C, 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.