Estudo da cristalização de pós fluxantes vítreos à base de (CaO-SiO2-CaF2) e à base de (CaO-SiO2-TiO2) utlizando as técnicas DSC e de DRX

Abstract

Mold fluxes are used at continuous casting, a stage of steel making, for the propose of controlling the cooling of steel, which is initially liquid, controlling the heat transfer between the steel and the mold, avoiding the formation of cracks, which generate a fragile steel and is caused by a fast cooling. Injected between the mold and the newly formed metallic surface, is also responsible for the lubrification of steel, avoiding the problem of sticking and resulting on a product with better quality. The behavior of crystallization of the powder is a fundamental factor for heat transfer control. Conventional mold fluxes used in the industry has fluorine (F) in the composition, a fluorine free mold flux is desirable to avoid the environmental problems caused by it, but removing fluorine also remove cuspidine, a key crystal formed during the process. In this work was studied a mold flux with the system CaO-SiO2-CaF2 and other CaO-SiO2-TiO2, using differential scanning calorimeter (DSC) to observe the behavior of crystallization and with the key temperatures, apply x-ray diffraction to identify the formed crystals. The transformation phase of both powders was similar on the devitrification stage, while the cooling from liquidus state has remarkable differences, with the mold flux with titania forming crystals with 150 ºC below the mold flux with fluorine. Previously published research concluded the time of incubation of the crystals from the system CaO-SiO2-TiO2 is much higher than the cuspidina at high temperatures. This results a thinner crystal layer during the continuous casting, needing adjustments or the development of news mold fluxes with different components or concentration, aiming one with the behavior more alike the system of CaO-SiO2-CaF2.