Corrosion Mechanisms Caused on a Submerged Nozzle Applied in Steel Billet Production by Mold Fluxes with and without Fluorine
Journal Title: Scholars Journal of Engineering and Technology - Year 2017, Vol 5, Issue 6
Abstract
Alumina-graphite (Al2O3-C) refractories are used as immersion nozzles for the continuous casting of steel. Carbon containing refractory materials have been widely used due to their excellent mechanical properties, thermal shock resistance and corrosion resistance. The life of these nozzles are limited by the localized corrosion, which occurs at the melt mold flux-metal interface. These refractory pieces are constituted by a body of alumina-graphite (Al2O3-C) with an insert of zirconia-graphite (ZrO2-C). The insert is placed in the bottom of the nozzle to protect the vulnerable zone from chemical attack. For this reason, the deep understanding of the mold fluxes effect on the wear mechanisms of the nozzles is relevant in order to avoid premature damage and contribute to decrease the cost of black refractories in the industry. In this paper, the nozzle selected for the study was characterized considering the chemical composition determination (integrating different instrumental techniques), the thermal behaviour (obtained by thermal analysis DTA/TGA), physical properties (such as density and apparent porosity) and microstructural characteristics (carried out by optical microscopy). The corrosion mechanisms produced by a mold flux with 2.6% of fluorine content on one (Al2O3-C) nozzle is studied by a post mortem study and it is compared with a static corrosion test carried out with the same fluorine flux and besides with another free fluorine mold flux. The microstructural study was performed by light (OM) and scanning electron microscopy (SEM). The information was correlated with results of the thermodynamic corrosion simulation applying the software Fact Sage 7.1. Mould fluxes structural characteristics and physical properties such as surface tension, viscosity, fluidity and the melting behaviour allows to justify the corrosion effects obtained. Keywords: submerged nozzles, alumina-graphite, mold powders, corrosion, continuous casting.
Authors and Affiliations
M. V. Peirani, E. Brandaleze
Keywords
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