Study on clogging of submerged entry nozzle of 321 stainless steel

The 06Cr18Ni11Ti (321) stainless steel has good corrosion resistance and mechanical properties.However, the addition of Ti leads to the formation of Ti N inclusions, which deteriorates the condition of continuous casting and causes the clogging.The formation of clogging in the submerged entry nozzle (SEN) of 321 stainless steel was studied by scanning electron microscopy (SEM) , energy disperse spectroscope (EDS) and thermodynamic calculation.According to the change of components, three layers in sample were defined:the refractory materials layer, the reaction layer and metal layer from the outer layer to the inner layer of SEN.The results show that the molten steel corrodes the refractory materials of SEN and the high-melting-point slag phase forms.Then Ti N inclusions attach to the inner layer and form curved chain or reticular structure with slag phase, which causes the clogging of SEN.Resultsof thermodynamic calculation indicate that the equilibrium solubility of titanium and nitrogen increases with temperature.There is high Ca/Al proportion in Ca O-Al₂O₃-Ti O₂-5%MgO phase.So controlling the compositions of slag is needed to prevent clogging.