Effects of Annealing Temperature on Microstructure and Mechanical Properties of High Nb-IF Steel With Strength Level of 440 MPa

Compared with traditional high strength IF steel,the recrystallization behavior during annealing process of a high C-Nb high strength IF steel was studied by using a Gleeble-1500 simulator. The effects of annealing temperature on microstructure and mechanical properties of the steel was also investigated using salt annealing method. Results show that the recrystallization finishing temperature of high C-Nb IF steel is 20 ℃ higher than that of traditional high strength IF steel. After completely recrystallized,the ferrite grains of the steel have a small growing tendency,and the average grain sizes are much finer than that of traditional IF steel. For the high C-Nb IF steel,the mixture of ferrite and bainite is obtained when salt bath annealing temperature is above 870 ℃. In order to obtain good comprehensive mechanical properties,the optimum annealing temperature of high C-Nb IF steel should be controled between 810 ℃ and 830 ℃.