Study Of Zirconia Nozzle On The Mechansim Of Damage

The ideal state of tundish refractories is synchronous damaged and replacement,so that the life of each material is matching as soon as possible,however,the non-swirl nozzle has been the bottleneck of the whole life of the tundish.Therefore,it is important for steel mills reducing costs and improving the profit of per-ton steel to improve the service life of the nozzle so as to prolong the service life of tundish.Based on fine particles and ceramic type nozzle produced by a factory,this experiment is adding Al2O3-ZrO2 composite powder of sol-gel preparation to modificate zirconia nozzle and preparation of the new nozzle as the research object,with XRD and SEM analysis,to study the differences in performance and damage mechanism.The results are as follows:(1)Compared the nozzle(A,B) of the ceramic type to particle nozzle(C,D),ceramic type nozzle have lower apparent porosity and lagre volume density,high tensile strength,but the thermal stability is poor;The performance of the nozzle is obviously improved after added a certain amount of Al2O3-ZrO2 composite powder of sol-gel prepared,the modified ceramic nozzle type B compares to ordinary ceramic nozzle A,the porosity decreases 27.9%,volume density increases 0.7%,compressive strength increases by 26.1%;the modified particle type nozzle D compares to ordinary particle type nozzle C,the porosity is reduced by 11.1%,the volume density is increased1.7%,compressive strength is increased by 44.6%,especially the thermal shock resistance of particle nozzle addded Al2O3-ZrO2 composite powder is more than 50 times,and the thermal shock frequency of particle nozzle without addded Al2O3-ZrO2 composite powder is only 41.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 and columnar zirconium oxide is enhanced in the presence of a phase, to improve the material strength and thermal shock resistance.(2)In the process of the continuous casting test:①The fine particle type nozzle C’s strength is low, thermal shock stability is poor,ater used 35 h offline,spalling and expanding diameter is most serious,steel column diameter is up to 28 mm and fill with steel tumor;②Due to type ceramic nozzle A and B’s thermal shock stability is poor,does not reflect the characteristics of high strength,after used offline35 h,expanding is very serious;③After the particle nozzle D added Al2O3-ZrO2 composite powder used 35 h, basically no expanding, the use of in the continuous casting test is best.(3)The damage of ceramic nozzle is mainly due to low porosity,less porosity and cracks can not absorb thermal shock generated by cyclic stress,resulting in nozzle to produce thermal shock damage,and appear big crack.The ceramic nozzle after modified,addded composite powder particle size is small,activity is more large,promoting the nozzle sintering densification,resulting in porosity dropped to3.1%,it is not conducive to the absorption cycle thermal shock and thermal expansion,thus after adding composite powder the damage is more serious.(4)The damage of particle type nozzle is mainly due to the particles and fine powder with low strength and more porosity for the beginning of molten steel and slag intrusion provides a favorable channel,the reaction of MgO and molten steel and slag inclusion result in exsolution,stabilizer exsolution lead to unstable zirconia steady by the cubic phase transition to the monoclinic phase,resulting in volume expansion and shear deformation can cause cracking and peeling of the nozzle to accelerate damage.Desolution stabilizer is large,high content of monoclinic phase;stabilizer is small,high content of cubic phase.At the same time,the use of fine particle nozzle in each layer of zirconia crystal mainly according to the mechanism of coordination polyhedron growth,resulting in cubic phase content increases,using a nozzle brick layer,transition layer,metamorphic layer among three layers structure and mineralcomposition is different,the differences of nozzle on structure and mineral composition is generated in the interior of the structure stress and acceleration rupture damage.The particle type nozzle by adding composite powder modified to produce the formation of magnesia alumina spinel phase and columnar zirconium oxide phase to improve the interface between particles 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,in the use of effective resistance to the thermal shock and prevent the steel slag and molten steel enters the nozzle through the pores and cracks, so as to avoid further damage.