Failure analysis of nozzle clogging during Super304H stainless steel continuous casting production

This study elucidates the clogging mechanisms of the submerged entry nozzle (SEN) during the continuous casting of Super304H stainless steel through an integrated approach combining systematic analysis and thermodynamic calculations. The dissection of a clogged SEN revealed a stratified morphology comprising: (i) an initial solidified steel layer (Layer A) containing entrapped steel and eroded refractory; (ii) a slag-type inclusion layer (Layer B) predominantly composed of Al-Ca-Si-Mg-F-O inclusions with elevated Al₂O₃ content and diminished liquid phase fraction, attributed to interfacial oxidation and thermal gradients; and (iii) a dense clogging layer (Layer C) consisting of both slag-derived and endogenous inclusions, embedded within solidified steel. It was demonstrated that during the tundish stage, the formation of high-Al₂O₃ inclusions and their aggregation into a porous network critically impede melt flow, thereby initiating clogging. To suppress the formation of Layer B, the Al₂O₃ content in inclusions should be constrained below 56 %. Furthermore, maintaining the total oxygen (T.O) content within the range of 0.0049–0.0075 wt% ensures a liquid phase ratio of inclusions exceeding 50 %, thereby mitigating the risk of flow blockage. The outcomes of this study provide a scientific basis and process control strategy for the mitigation of SEN clogging and the enhancement of continuous casting product quality in advanced stainless steel manufacturing.