Analysis On The Mineral Composition Of The Zirconia Metering Nozzle In Service Temperatures

The Zirconia metering nozzle with the enlarged diameter, burst, loss, or even clogging during used affect the normal production. The life of the metering nozzle is directly related to the life of the tundish, so a new metering nozzle with slowly expanding, long service life is imminent. In this study, in order to obtain the mineral composition of the zirconia metering nozzle in continuous steel casting, the paper makes a study of simulated experiment to different formulations（Mg-PSZ metering nozzle; Mg,Y-PSZ metering nozzle; adding Al₂O₃-ZrO₂ composite powder of sol-gel preparation to modificate zirconia nozzle） nozzle. The chemical composition, mineral phase and micro-morphology of the samples were investigated by X-ray fluorescence instrument, X-ray diffractometer and scanning electron microscope.The results are as follows:（1） The metering nozzle based on Mg-PSZ（A） has lager apparent prosity, smaller density, lower tensile strength and the thermal shock resistance is poor; the metering nozzle based on Mg,Y-PSZ（B） has a better basic physical properties than A sample; The performance of the nozzle（G） is obviously improved afer added a certain amount of Al₂O₃-ZrO₂ composite powder of sol-gel prepared, the porosity reduces 11.21%,the volume density increases 3.41%,compressive strength increases 25.37%,and the thermal shock resistance has been significantly improved 41 times. This is due to the addition of Al₂O₃-ZrO₂ composite powder, fills the intergranular pores and reduces the porosity of materials; at the same time composite powder amount of contraction produced a certain amount of shrinkage pores and magnesia alumina spinel phase, to improve the material strength and thermal shock resistance.（2） The content of c-ZrO₂ in three different metering nozzle after quenching with water is increased, but the content of m-ZrO₂ is decreased. The content of c-ZrO₂ in Mg-PSZ nozzle increased from 26% to 32%; The content of c-ZrO₂ in Mg,Y-PSZ nozzle increased from 41% to 57%; The content of c-ZrO₂ in nozzle with adding Al₂O₃-ZrO₂ composite powder increased from 26% to 32%.The results showed that a sufficiently rapid cooling rate can suppress the occurrence of phase transition. The temperature zone with c-ZrO₂ to m-ZrO₂ is reduced in quenching with water, the transition of c-Zr O₂ is suppressed, resulting the cubic zirconia is retained to room temperature. Slowly cooling rate may lead to the phase transition between c-ZrO₂ and m-Zr O₂ in the natural cooling after tilting tundish. Therefore, the research results of samples with natural cooling after tilting tundish cannot represents the actural situation of the zirconia metering nozzle at working environment. The content of the monoclinic phase and the cubic phase have changed at different temperatures. Different thermal expansion coefficients lead to the different thermal stresses. At the same time, the transition between c-ZrO₂ and m-ZrO₂ produce a certain volume expansion, shear deformation, etc. Thus phenomena affect the thermal shock resistance of the nozzle in actual use, and accelerate the damage process of the metering nozzle.（3） MgO and molten steel and slag inclusions react exsolution in unmodified metering nozzle. The stabilizers exsolution lead the transition between c-ZrO₂ and m-Zr O₂ and produce a certain volume expansion, shear deformation, etc. The metering nozzle by adding composite powder modified to produce the formation of magnesia alumina spinel phase to improve the interface betweenparticles and matrix bonding strength and thermal shock resistance, thermal shock crack meet interface cannot continue to expand, while generating magnesia alumina spinel tightly pinned between the ZrO₂ particles, improves the nozzle of the resistance to molten steel erosion resistance and erosion ability.