Through microstructure characterisation and industrial experiments, combined with thermodynamic analysis, the formation mechanism composite rare earth steel nozzle nodules were discussed in this paper. The results showed that the nodules could be divided into a reaction layer, a calcium aluminate layer and a rare earth aluminate layer from the inner wall of nozzle towards the centre. The main phases of the reaction layer were refractory compounds such as Al2O3, CaO▪6Al2O3 and CaO▪2Al2O3, the main components of the calcium aluminate layer were CaO▪2Al2O3, CaO▪Al2O3 and (La,Ce)AlO3, the rare earth aluminate layer was dominated by (La,Ce)AlO3 and a small amount of calcium aluminate. Finally, the process optimisation measures were implemented, such as adjusting LF refining slag, feeding pure Ca wire and decreasing the oxygen content in steel. The nozzle clogging situation was improved, and the number of continuous casting furnaces was increased from less than four to five.
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