High Temperature Precipitation Behavior of High-Nitrogen Duplex Stainless Steel

摘要

Precipitation behavior of high-nitrogen duplex Fe-24Cr-7Mn-4Ni-4Mo-0.43N stainless steel aged at 850°C was investigated using scanning transmission electron microscopy. Based on the analyses of selected area diffraction patterns, four kinds of precipitates (intermetallic sigma (a) and chi (x), Cr_2N and secondary austenite) were identified. At the ferrite/austenite phase boundary, the σ phase and secondary austenite were formed via α - > γ + a eutectoid reaction. The precipitation of Cr_2N occurred at the austenite grain boundary as well as the interior of the ferrite. The intermetallic % phase also formed within the ferrite and showed a cube-cube orientation relationship with the ferrite. Further aging produced a lamellar structure composed of Cr_2N and austenite along the ferrite/austenite boundary and enhanced the precipitation of the % phase. The crystallographic features of the precipitates were also examined in terms of the orientation relationship with the austenite or ferrite matrix.