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

The effect of cerium on the solidificationSolidification nucleation and microstructureMicrostructure of high-strength low-alloy steelSteel was investigated. The in situ observationIn situ observation, inclusionInclusions characterizationCharacterization and microstructureMicrostructure analysis were performed via high temperatureHigh 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 treatmentCerium treatment, the solidificationSolidification temperatureTemperature range and time were decreased by 17.6 °C and 22.44 s, respectively. Based on the Johnson-Mehl-Avrami-Kologoromov theory, the solidificationSolidification rate constant increased from 7.59 × 10–5 to 5.68 × 10–4 after adding Ce, promoting the phase transformationPhase transformations. The typical inclusionsInclusions were modifiedModified 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 inclusionsRare earth inclusions could effectively induce the formation of δ-Fe and γ-Fe through heterogeneous nucleation, thereby decreasing the average grain size from 13.76 to 12.38 µm.