Fei Xue

Abstract:

In this paper, cast austenite duplex stainless steel from main circulating pipe are aged at 400°C for different times, the properties are studied during aging, and the mechanism of material is investigated by microstructure evolution characterization at same aging time. The results show the tensile strength increased nearly 12%, reduction of area decreased nearly 21%, and impact ductility decreased nearly 50%. The reason lies in the ferrite phase becoming weak and harmful to mechanical properties after aging. Transmission electron microscope (TEM) and three dimensional atom probe (3DAP) are used to study the microstructure evolution during aging, effect of aging on duplex stainless steel by spinodal decomposition in ferrite phase, Cr-rich phase formed from Cr-rich segregated region by the concentration of Cr atoms in it after being aged 3000h, and the size of Cr-rich phase between 5-10nm, and then, the difficulty of increased slipping in dislocation and aggregated dislocations, resulting in the local stress concentration around the Cr-rich phase. The phenomenon of spinodal decomposition is that as the aging time and content of Cr in Cr-rich cluster increases, the more stress is required during the deformation, which causes higher level of stress triaxiality ratio; with this focus, dislocations get across the Cr-rich phase, which disperses in ferrite phase and slipping, the plastic deformation is more easily reached, and leads to the decreased of ductility.