Study on the formation mechanism of clogging layer of rare earth microalloyed Q355 steel's submerged entry nozzle and process optimization

The formation mechanism of the clogging layer of the alumina-carbon submerged entry nozzle in the smelting process of rare earth Q355 steel was investigated in this paper. First, the inclusions in the molten steel were discovered to be primarily composed of CaAl2O4, MgO, CaS, and CeAlO3. The mass fraction of solid inclusions increases as the rare earth content increases, and the proportion of inclusions, primarily CaAl2O4, changes. Calcium titanate and cerium aluminate formation can be inhibited by high [Ca] content. XRD and scanning electron microscopy were then used to examine the phase composition and morphology of the inner and outer arcs of the clogging nodules. The clogging was found to be divided into three layers: the nozzle matrix, the reaction layer, and the steel layer. Finally, it is concluded that the dissolution of C element in refractory material is the cause of nozzle blockage, and the core cause of nozzle blockage is the deposition of Al2O3, CaAl2O4, and rare earth compounds. Meanwhile, solutions to nozzle blockage are provided from the perspectives of top slag optimization, the deoxidization process, the calcium treatment process, and protective pouring.