Influence of Nb on Microstructure and Property of Low-Carbon Mn-Series Air-Cooled Bainitic Steel

The effect of Nb on the microstructure evolution of low-carbon Mn-series air cooled bainitic steels has been studied by using thermomechanical simulation machine, SEM, and TEM observation. The results show that the amount of ferrites is relatively higher in the steel without Nb than that of Nb-bearing steel under same deformation conditions, and the ferrites in Nb-bearing steel are more finer. The mechanical properties of the Nb-bearing steel are higher than those of the steel without Nb at the same finishing rolling temperature (FRT), and the toughness of the Nb-bearing steel is about 100 J higher than that of the steel without Nb at the finishing rolling temperature 750 °C. The toughness of Nb microalloyed steel will be improved more effectively than that of the steel without Nb with the decrease of FRT.