Mechanical properties and microstructure evolution of cold-deformed high-nitrogen nickelfree austenitic stainless steel during annealing

The mechanical properties and microstructure evolution of cold-deformed CrMnN austenitic stainless steel annealed in a temperature ranging from 50 °C to 650 °C for 90 min and at 550 °C for different time were investigated by tensile test, micro hardness test, and Transmission Electron Microscope (TEM). The steel was strengthened when it got annealed at temperatures ranging from 100 °C to 550 °C, while it was softened when it got annealed at temperatures ranging from 550 °C to 650 °C. Annealing temperature had stronger effect on mechanical properties than annealing time. TEM observations showed that nano-sized precipitates formed when the steel was annealed at 150 °C for 90 min, but the size and density of precipitates had no noticeable change with annealing temperature and time. Recrystallization occurred when the steel was annealed at temperatures above 550 °C for 90 min, and its scale increased with annealing temperature. Nanosized annealing twins were observed. The mechanisms that controlled the mechanical behaviors of the steel were discussed.