The grain boundary microstructure characteristics of interstitial free(IF) steel was changed by changing the annealing time. Phosphorus-bearing IF steel grain boundary characteristics and segregation of P at grain boundaries were analyzed by using electron backscatter diffraction(EBSD) and Auger electron spectroscopy(AES). The ductile-to-brittle transition temperature(DBTT) obtained by impact test was compared.The results show that the main influencing factors of IF steel DBTT are the grain boundary segrega...