Influence of temperature field on the microstructure of low carbon microalloyed ferrite–bainite dual-phase steel during heat treatment

To investigate the quantitative relation between the temperature and the microstructure of low carbon steel, the low carbon microalloyed ferrite–bainite dual-phase (FBDP) steel was prepared by heat treatment. On a series of positions chosen in the sample which was cut from the treated FBDP steel, the volume fractions of bainite in the microstructures were measured and the corresponding temperatures were also obtained through the finite element method. The results show that not only the volume fraction of bainite increases linearly, but also the size of bainite increases with the increase of the outset water-cooling temperature. In addition, by comprehensively evaluating the microstructure and the temperature, it can be estimated that the lowest bainite formation temperature for this steel is about 550 °C, which had been proved by the experiment.