Effect Of The Deoxidation And Alloying On The Formation, Precipitation Of Inclusions In Silicon-killed Steel

Clogging often happens in ladle nozzle when silicon killed steel is poured. The maincause of clogging nozzle is inclusions, formation of inclusions is related to deoxidation.To reveal the relationship between different deoxidation alloying process andcharacteristic of inclusions and to reveal the mechanism of nozzle clogging havesignificance guidance for solving nozzle clogging of silicon killed steel.In order to generate low melting point and deformable inclusions during hot rolling,element content balanced with low melting point inclusions in three component phasediagram was obtained through thermodynamic calculation and discussion. The effectof alloy composition, slag in steel on morphology, ingredient, number and meltingpoint of inclusions in silicon killed steel have been studied by500g MoSi2electricresistance furnace to simulated the process of silicon steel deoxidation alloying,conclusions are as follows:End total oxygen of the only Si-Mn deoxidation can be reached0.0063%, whileminimum end total oxygen of the addition part of Al to Si-Mn deoxidation can bereached0.0041%, the addition of Al was beneficial to decrease the total oxygencontent; The initial stage of deoxidation inclusions of90%MnO-SiO2-Al2O3weredeoxidation product, and end90%for CaO(MgO)-SiO2-Al2O3were complexinclusions, the CaO (MgO) came from the top slag, morphology of center oxide ininclusions can be determine the melting point of inclusions, low melting point oxideeasy to form the spherical inclusions because it had big interface tension in steel,melting point of inclusions can be estimated from the center oxide; Mn/Si control in2.5~3and Alscontent in0.003~0.0090%in steel, the inclusions were melting state andwould don’t occur and reduce probability of occurrence of nozzle clogging.Deoxidation ability was improved in steel with the increasing of the basicity; oxidemelting point deviated low melting zone in end sample with basicity between0.65and2; the content A12O3in inclusions increased with the A12O3content increasing in slagand first decreased then increased with the increasing of basicity in slag. In order to generate low melting point inclusions to avoid the nozzle clogging, according to theresult of linear fitting, the content of A12O3inclusions was controlled in5~30%,basicity of end slag was controlled in0.77~1.32, w(Fe2O3+MnO) should not beexceeded1.2%; basicity with the1.0~1.5range had good deoxidizationthermodynamic and physical property according to assessment of the refining finalslag.The micro-observation on residue of nozzle clogging to explore the mechanism ofnozzle clogging by inclusions, the results are as follows: through observation andcalculation of the inclusions of coagulation precipitation, the CaO, Al2O3preferentialprecipitation and MgO, and SiO2, MnO in the process of solidification to precipitation,cooling rate, the initial radius of oxide affect on grow in size of inclusions MnSinclusions precipitation in furnace cold sample; the observation on residue in nozzlegot that the high melting point inclusions were embedded in low melting pointinclusions.