Effect of Cerium on the Nucleation and Microstructure of High-Strength Low-Alloy Steel During Solidification

The effect of cerium on the solidification nucleation and microstructure of high-strength low-alloy steel was investigated. The in situ observation, inclusion characterization and microstructure analysis were performed via high temperature confocal laser scanning microscopy, scanning electron microscope, and electron backscatter diffraction. The results showed that Ce significantly increased the nucleation site density. After cerium treatment, the solidification temperature range and time were decreased by 17.6 degrees C and 22.44 s, respectively. Based on the Johnson-Mehl-Avrami-Kologoromov theory, the solidification rate constant increased from 7.59 x 10(-5) to 5.68 x 10(-4) after adding Ce, promoting the phase transformation. The typical inclusions were modified from CaS and CaS+MgAl2O4 to CeAlO3+CaS and Ce2O2S+CaS with an increase in number and a decrease in size when adding Ce. Numerous fine rare earth inclusions could effectively induce the formation of delta-Fe and delta-Fe through heterogeneous nucleation, thereby decreasing the average grain size from 13.76 to 12.38 mu m.