The basic requirements of submerged nozzle material are: good resistance to molten steel corrosion, strong slag erosion resistance and good thermal shock resistance. The commonly used materials are fused quartz and Al2O3-C.

Fused quartz submerged nozzle

With molten quartz as raw material, it is cast by slurry and sintered at high temperature. The nozzle has the advantages of low thermal conductivity (2W/m · K at 1000 ℃), good thermal stability, low thermal expansion rate (e.g., the expansion rate of quartz containing 99% SiO2 is 0.05%~0.06% at 1000 ℃) and is not easy to form nodules. It can be used without preheating. Therefore, it is widely used. The disadvantage of this material is that it is not suitable to cast steel with manganese content more than 0.5%. Because Mn reacts with SiO2 in the nozzle to produce MnO · SiO2 glass with a melting point of only 1300 ℃, which greatly reduces the viscosity of the glass layer on the surface of the long nozzle and accelerates the melting loss of the nozzle.

Al2O3-C submerged nozzle

It is made of corundum and graphite as basic raw materials, added with metal silicon, silicon carbide, etc., formed in an isostatic press, and then sintered under protection. The nozzle has uniform structure, low wettability with molten steel and strong erosion resistance. Therefore, it is suitable for pouring most steel grades. Al2O3-C water nozzle must be preheated before use, otherwise, the water nozzle will have the risk of cracking and immersion. During preheating, graphite burning (decarburization) will occur, which will increase the porosity of the nozzle surface layer and reduce its corrosion resistance. When casting aluminum-killed steel, deoxidization products α— Al2O3 is easy to deposit on the inner wall of the nozzle, resulting in nozzle blockage, which affects the normal operation of continuous casting. The manufacturer of tundish upper nozzle believes that the other disadvantage of the nozzle is poor slag resistance and good thermal conductivity, so the slag line part is seriously corroded and the inner wall of the nozzle is easy to solidify steel, so effective measures should be taken to protect it: for example, the nozzle is provided with a refractory fiber protective sleeve, the surface is coated with an anti-oxidation layer, the slag line part is provided with a composite ZrO2-C material to improve slag corrosion resistance, and argon is injected into the porous refractory layer of the inner wall of the nozzle.