EFFECTS OF VISCOSITY AND SURFACE TENSION OF FREE FLUORINE FLUXES ON THE WEAR MECHANISMS OF Al2O3-C NOZZLE

E. BENAVIDEZ; M. PEIRANI; M. AVALOS; E. BRANDALEZE

Victoria

Congreso; 13th Biennial Worldwide Congress on Refractories (UNITECR 2013); 2013

Fluoride emissions during continuous casting could cause health problems and equipment corrosion in the steel industry. Nowadays new mold fluxes are developed, using other oxides that substitute the fluoride compounds. Although physical properties of fluxes must be guaranteed to prevent operation problems and to avoid product defects, it is relevant to understand the effect of the new fluxes on nozzle wear mechanisms. Synthetic slags with different contents of B2O3 and Li2O were prepared to determine their effects on the physical properties. In this study, one synthetic slag (A) with 6 wt% B2O3 and 4 wt% Li2O, was selected. Particularly, Li2O was used in order to replace CaF2. A corrosion study on an Al2O3-C (AG) nozzle was carried out in order to identify the B2O3 and Li2O effects on the wear mechanisms. Also a commercial mold flux (PC) with 2.6 wt% F (applied in the continuous casting process of billets), was selected to compare the real corrosion phenomena. The corrosion study includes cup tests developed at 1400ºC and a comparison with a post mortem study carried out in a nozzle after the service in the plant. Physical properties such as viscosity and surface tension of the fluxes were determined at test temperature (1400ºC) and at process temperature (1550ºC), in order to correlate with the microstructural results obtained using light and scanning electron microscopy (SEM), including energy dispersive analysis (EDS) and electron backscatter diffraction (EBSD) analysis. In particular, the EBSD technique contributes to increase the knowledge on wear mechanisms because of the possibility to identify and localize phases together with crystalline condition. Nozzles possess a complex crystal structure coupled with anisotropic materials properties. The phases, the grains orientations and the properties of grain boundaries have a large influence on the useful properties of these materials. Therefore, it is essential to have a characterization technique that can provide information such as grain size, orientation, misorientation angle and phases. In this context, EBSD can provide information on crystallographic and structural analysis on Al2O3-C (AG) nozzle including the insert of ZrO2-C material.