Heat transfer,inclusion characteristics and fluid flow phenomena during up-hill teeming

Sammanfattning: Clean steel production requires good control of the sizedistribution and the composition of the inclusions at allstages of the steel making process. So far, there exists verylittle information on the behavior of the inclusion populationduring ingot casting of steel. The overall goal of this projectis therefore, to study the factors involved in formation ofinclusions, especially macro inclusions due to reactionsbetween the steel and the mold flux or entrainment of mold fluxduring up-hill teeming of steel. This work has mainly, beendevoted to three different areas in connection to the formationof exogenous inclusions during mold filling, namely (i) thermaldiffusivity measurements of synthetic slags, (ii)characterization of the inclusion population during the ladletreatment and up-hill teeming of ingots and (iii) the fluidflow in an ingot mould during filling. In an attempt tosystematize the knowledge on the heat conduction of liquidsilicates, the thermal diffusivities of some synthetic slags inthe CaO-Al2O3-SiO2 and CaO-Al2O3-SiO2-MgO-Na2O system have beenmeasured, using the three-layer laser flash method on adifferential scheme in the temperature range 1625 to 1825 K.The thermal diffusivity needed both for subsequent modeling ofthe process of up-hill teeming and for an understanding of thethermal conductivities of silicate melts from a more generalmetallurgical viewpoint was measured onseveral slagcompositions chosen in such a way that the changes in thethermal diffusivities would reflect the changes in thestructure of the slags. The present status of the inclusioncharacteristics during the ladle treatment process and duringthe filing of an ingot mold, have also been established basedon plant trials. The non-metallic inclusion have beencharacterized using light optical microscopy and classifiedaccording to the Swedish standard SS111116 (JK chart II) andscanning electron microscope equipped with EDX The fluid flowis also known to affect the inclusion population in the ingotduring mold filling in several ways, such as reaction kinetics,growth and removal of inclusions and entrainment of mold fluxinto the steel. The velocity fields in a 1:3 scale water modelof a 4.2 tone ingot mold during filling have therefore beendetermined using a Laser Doppler Anemometry (LDA)technique.