Microstructure and Precipitates of High-pure Ferritic Stainless Steels Stabilized by Niobium and Titanium

As stabilization elements added into ferritic stainless steels, various kinds of precipitates of niobium and titanium will form and have great effect on their microstructure, which has great effect on the mechanical and corrosion properties of the final products. Combined with thermodynamic calculation by FactSage software, microstructure and precipitates of ferritic stainless steels containing different niobium and titanium were investigated by optical microscope, scanning electron microscope, transmission electron microscope and energy dispersive spectrometer. The results show that titanium mainly exists in form of TiN but niobium exists mainly in form of NbC. Moreover, a certain amount of NbN particles precipitate when there is not enough titanium to react with nitrogen. TiN particles with size of 2 mu m similar to 8 mu m promote the recrystallization but Nb-rich precipitates with size of less than 500nm suppress the recrystallization in the process of annealing.