Correlation of the Solidification Path with As-Cast Microstructure and Precipitation of Ti,Nb(C,N) on a High-Temperature Processed Steel

The solidification path of a high-temperature processed (HTP) X65 sour service steel with 0.039 wt pct C, 0.09 wt pct Nb, and 0.54 wt pct Mn and its effect on the segregation, microstructure, and precipitation distribution of Ti,Nb(C,N) was studied using optical and confocal microscopy, scanning electron microscopy (SEM), and computational simulation (Thermo-Calc and DICTRA). The results were compared with those obtained for another commercial microalloyed steel, containing 0.09 wt pct C, 0.04 wt pct Nb, and 0.97 wt pct Mn. The results indicate that the main parameter that influences microsegregation is the C content, which has a large influence on the solidification path. The difference in segregation between different positions in industrial continuous cast slabs of the steels was also observed, as expected. The larger solidification interval (T_L-T_S) of the commercial microalloyed steel indicates the formation of a solidification front that has higher solute concentration than the X65 HTP sour service steel, which concurs with the higher macro- and microsegregation observed.