添加Al2O3--ZrO2复合粉改性氧化锆质定径水口及其损毁机理

通过添加溶胶-凝胶法制备的Al2O3-ZrO2复合粉,对陶瓷型和颗粒型氧化锆质定径水口进行改性.对比研究了陶瓷型和颗粒型定径水口改性前后物理性能,矿物相组成和显微结构的变化,并通过现场连铸实验对四种定径水口损毁机理进行了探讨.结果表明:相较于颗粒型定径水口,陶瓷型定径水口的显气孔率较低,体积密度和耐压强度较高,热震稳定性较差,抗侵蚀和冲刷性能较好.通过添加Al2O3-ZrO2复合粉改性后的定径水口显气孔率降低,体积密度增加,耐压强度提高,颗粒型定径水口的热震稳定性有了较大的提升,热震次数约为改性前的1.5倍以上.通过对连铸现场实际使用35 h后的残样分析发现,陶瓷型水口损毁主要是由于热震稳定性差导致使用时发生炸裂,炸裂产生的裂纹引起一定程度的剥落和扩径.未改性颗粒型定径水口由于强度低和显气孔率高,剥落和扩径更为严重,添加Al2O3-ZrO2复合粉改性后生成的镁铝尖晶石增强相大幅度提高了颗粒水口的热震稳定性和抗冲刷侵蚀性能,连铸现场使用后几乎未扩径.

Damage mechanism of zirconia metering nozzles modified by Al2O3--ZrO2 composite powder

The modified metering nozzles were fabricated by using sol-gel Al2O3-ZrO2 composite powder as additives in particle and ceramic type zirconia metering nozzles. The physical properties, mineral phase and microstructure of metering nozzles of particle and ceramic types before and after modification were studied and the damage mechanism of nozzles in continuous casting field test was analyzed. The results show that the ceramic type metering nozzle has lower apparent porosity, higher bulk density, higher compression strength and poorer thermal shock stability compared with the particle type metering nozzle. By adding Al2O3-ZrO2 composite powder, the apparent porosity of modified nozzles decreases, the bulk density and compression strength get higher, the thermal shock resistance of the particle type metering nozzle improves markedly, and the count of thermal shocks is about 1. 5 times of that before modification. After the analysis of residual samples in continuous casting field test for 35 h, the damage of the ceramic type nozzle is mainly caused by the fracture in the service process for the poor thermal shock stability, cracks generating in the fracture process cause a certain de-gree of flaking and hole enlargement. Due to low strength and high apparent porosity, flaking and hole enlargement of the unmodified type particle metering nozzle is more serious. The thermal shock, scouring and erosion resistance of the particle type nozzle after being modified by Al2O3-ZrO2 composite powder improve remarkably because of the formation of MgAl2O4 spinel enhanced phase, but little hole enlargement occurs after casting test.