Study on the σ-phase precipitation of SAF2906 duplex stainless steel

Samples of SAF2906 duplex stainless steel were aged at 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C and 950 °C for 1 h, after high temperature solution heat treatment. The morphology of 𝜎-phase in aged SAF2906 duplex stainless steel was then studied by means of scanning electron microscopy, X-ray diffraction and transmission electron microscopy, and the chemical composition of the 𝜎-phase was determined using X-ray energy dispersive spectrometry. The results indicated that the 𝜎 precipitation in SAF2906 duplex stainless steel formed both inside δ-ferrite with high Cr and Mo concentrations, and along δ-ferrite/γ-austenite interfaces; however, relative to the SAF2205 and SAF2507 duplex stainless steels, the content of Cr in 𝜎-phase increased significantly up to 70 %, which was much higher than Fe in the same phase and became the major element of 𝜎-phase.