Influence of sigma phase on corrosion and mechanical properties of 2707 hyper-duplex stainless steel aged for short periods

2707 hyper-duplex stainless steels (HDSSs) contain high contents of alloying elements (Cr, Ni, Mo and N), which may shorten the incubation period and promote both nucleation and growth of sigma (σ) phase. 2707 HDSS was first aged at different temperatures and periods of time for drawing the time-temperature-transformation profiles. The results identified the main precipitates as σ phase, with nose temperature of about 950℃. Also, 2707 specimen was aged at 950℃ for a short time, and the morphology, distribution and amount of σ phase were examined through the scanning electron microscope and X-ray diffraction,σ phase was initially formed at the boundaries of ferrite and austenite and then transformed through the eutectoid reaction (α→σ+γ2). Finally, the precipitation and growth of σ phase in 2707 steels aged at nose temperature for a short period reduced the corrosion resistance and deteriorated the mechanical properties, and the corresponding reason was further analyzed.