Effect of Phosphorus Grain Boundaries Segregation and Precipitations on Mechanical Properties for Ti-IF Steel after Recrystallization Annealing

The cold-rolled (75% reduction ratio) Ti-IF (interstitial-free) steels of 1 mm thickness were recrystallized by annealing at 810°C for different times. The microstructure, mechanical properties and phosphorus segregation at grain boundary were investigated by means of optical microscopy (OM), tensile testing and field emission transmission electron microscopy (FE-TEM). It was observed that recrystallization was completed after annealing at 810°C for 180 s. The yield strength and tensile strength decreased as annealing time increased. The FE-TEM observation showed that after the annealing treatment, the grain boundary was broadened and the dislocations with higher density of phosphorus atoms and phosphide at grain boundaries became evident. The amount of phosphorus segregated at grain boundaries increased with annealing time.