The damage process of zirconia sizing nozzle is a complex physical and chemical interaction with steel slag and molten steel at high temperature.
Thermal shock damage
In the actual steel casting process, the zirconia sizing nozzle is heated at a relatively high temperature due to the high temperature of the pouring steel, and the inside of the refractory nozzle is unevenly heated, so that the sizing nozzle is subjected to severe thermal shock. The thermal shock causes large thermal stress inside the sizing nozzle. With the progress of the pouring process, the non-uniform thermal stress causes potential defects or damage to the internal structure of the nozzle, and even micro cracks. The structural damage caused by thermal shock reduces the strength and erosion resistance of the nozzle, and also provides a way for the penetration and erosion of molten steel and steel slag into the nozzle. The particularly severe thermal shock can directly cause macroscopic cracks in the sizing nozzle, even directly at the instant of pouring. Therefore, the thermal shock of the molten steel during the nozzle damage is the most serious damage to the sizing nozzle.
Mechanical erosion damage
The mechanical flushing of the molten steel to the nozzle is very serious. Although molten steel is a high-viscosity liquid, it has a severe heat wash on the nozzle due to the large ratio of molten steel to liquid, high temperature and fast flow rate. The high temperature creates a large temperature gradient across the cross-section of the nozzle wall, greatly reducing the strength of the nozzle wall contacting the molten steel. By estimating, the velocity of the molten steel through the nozzle is 3-5 m/s, and often with a rotating vortex. These factors have increased the erosion of molten steel on the nozzle.