Characteristics of Nozzle Clogging and Evolution of Oxide Inclusion for Al-Killed Ti-Stabilized 18Cr Stainless Steel

Abstract

Characteristics of nozzle clogging and evolution of oxide inclusion were studied by sampling the deposits of submerged entry nozzle (SEN) and the molten steel in tundish during Al-killed Ti-stabilized 18Cr stainless steelmaking process. The deposits found in the clogging of SEN were mainly composed of frozen steel and inclusions. The inclusions in the deposits and tundish were both mainly (MgO-Al2O3)rich-CaO-TiOx. The compositions of most inclusions were Liquid+Spinel or Liquid+TiSp phase. The (MgO-Al2O3)rich-CaO inclusions that were not effectively modified by calcium treatment could be a source of clogging. By combining both the experimental results and thermodynamic calculation, (MgO-Al2O3)rich-TiOx inclusions (TiSp inclusions) would be formed with the decreasing temperature in steel during continuous casting, which could be transported and accumulated on the inner wall of the SEN. Increasing the calcium content in the molten steel could decrease the formation of TiSp inclusions. During continuous casting, these inclusions accumulated on the inner wall of the SEN and gradually formed porous network of clog. Molten steel would gradually solidify in the porous space of the clog due to the increased residence time of the molten steel when flowing through it. The clogging gradually increased and caused the shutdown of continuous casting.