Calcium treatment is an important way to reduce the clogging of aluminum-killed steel during continuous casting.However,in industrial practice,deposition still occurs after calcium treatment.The morphology,composi-tion and element distribution of the clogging and the large size inclusion at the crack initiation were detected and ana-lyzed by scanning electron microscopy,to study the inclusion clogging behavior of aluminum-killed steel treated with calcium at the the Zr-containing bowl and the inner wall without Zr-containing of the nozzle.Results show that CaO-MgO-Al2O3 were the main components of both the accumulation of the nozzle and the large size inclusions in the cen-ter of the rolled wire,and the mass fraction of 1％-3％ ZrO2 was also detected.It was indicated that there were lots of complex calcium-aluminate inclusions in the steel with the Al2O3 percentage larger than 75％ at high melting temperature,easy to accumulate in the nozzle during casting.At the same time,the reduction reaction between ZrO2,SiO2contained in the bowl of the nozzle and graphite C occured,generating SiO,ZrO and other gases,and diffusing outwards into the accumulated calcium-magnesium-aluminate inclusions,hence,the composite reservoir containing ZrO2 was formed.The attachments of the Zr-containing clogging melted and fell down,part of them ac-cumulated to the inner wall of the nozzle,and part of them entered into the liquid steel and gathered further during the solidification process.The key is to improve the purity of molten steel and appropriately reduce the content of Als and Ca in steel to decrease the inclusions,especially calcium aluminate.It is also necessary to optimize the mate-rial of nozzle to reduce its reactivity.
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