Influence of cerium treatment on inclusion modification and as-cast microstructure of high-strength low-alloy steel

The influence of cerium treatment on the inclusion evolution and as-cast microstructure of high-strength low-alloy steel was investigated. Properties including the inclusions characteristics, element distribution, and the in situ solidification were analyzed by scanning electron microscopy, energy-dispersive spectroscopy, and high-temperature confocal laser scanning microscopy, respectively. The results indicated that, after the addition of Ce, the Al2O3 inclusions evolved to form Ce2O2S and CeAlO3 inclusions, which exhibited a decrease in size alongside corresponding increase in their number density. The equiaxed grain ratio exhibited by the as-cast microstructure increased significantly upon the addition of Ce, while a reduction in the segregation and a corresponding increase in the homogeneity of the carbon distribution within the as-cast microstructure were also achieved. The results of the in situ observation of the solidification suggested that the addition of Ce significantly reduced the solidification temperature range, thus reducing the carbon segregation. The nucleation effect imparted by Al2O3, Ce2O2S, and CeAlO3 on the δ-Fe formation was discussed in the context of the disregistry theory, which revealed that the formation of a large number of fine Ce2O2S inclusions promoted δ-Fe formation via heterogeneous nucleation.