| Sizing nozzle,as one of the important continuous casting functional refractory,is used to control the stabilization of the flux of molten steel,its quality directly affects the continuous casting time.Zirconia has excellent performance,such as high melting point,high resistance to chemical corrosion,resistance to wear,etc.Especially the partially stabilized zirconia after stabilizing treatment,which is the main raw material for the production of sizing nozzle,which has high melting point,high toughness,high refractoriness,good chemical stability,high strength,excellent properties.However,it is commonly to be expended diameter,crackled and jammed for zirconia sizing nozzle caused by the continuous washing of high temperature molten steel, which affects the efficiency of continuous casting production.Thus,improving the texture of zirconia sizing nozzle,and optimizing the material preparation process and microstructure,which is an effective way to improve the efficiency of the production of the continuous casting.At present,the particle part of the raw materials widely used for the preparation of sizing nozzle is mainly partially stabilized zirconia(PSZ),and the matrix part usually use the monoclinic zirconia added stabilizer and then formed partially stabilized zirconia by sintering.The former is commercial PSZ and the content of stabilizer is hard to adjust according to the needs of sizing nozzle.Basing on above consideration,this subject research ZrO2 sizing nozzle matrix by adding different types and content of stabilizer which were 2.8%MgO,2.1%MgO and 2.2%MgO+1%Y2O3respectively which noting A,B and C respectively in the desilication zirconium powder.The effects of stabilizer on the physical properties,composition of phase and the microstructure of ZrO2 sizing nozzle matrix before and after sintering and of the sizing nozzle treated at its working temperature 1540℃ holding 4,8,12 h,respectivelywere studied by XRD,SEM and EDS,which provide important basis for investigating the composition of sizing nozzle matrix.This study can be concluded from the following six aspects.Firstly,the cubic phase(c-Zr O2)content increased largely and the content of monoclinic phase(m-ZrO2)decreased significantly for all samples added stabilizer after sintering at 1710℃,and it is found that the specise and feed ratio of stabilizer in raw materials made cubic and monoclinic phase variation of each sample were not the same after sintering.Secondly,after sintering at 1710℃,the solid solution was formed by MgO and ZrO2, with the location of MgO particle closer,the substitution degree of Mg2+and Zr4+was more obvious,but the diffusion and solid solution of the stabilizer were far from uniform state.For the sinteried sample combining MgO+Y2O3 stabilizer, cubic phase gained the most, and solid solution generated largest, the degree of stabilization was the highest and the combination between Zr O2 particles which have uniform size and angular shape is much close without abnormal growing.Thirdly,in the process of forming solid solution,there is small amount of MgO aggregating to the impurities silicon in the desilication zirconium powder and formed magnesium olivine(Mg2SiO4),which can be used to reduce thermal shock stability. Fourthly,in all samples sintered at 1710,the thermal shock resistance of A sample was the best, above 36times;the volume density and compressive strength at room temperatureof sample C was the best. Fifthly, after sintering at 1710 ℃,there is a small amount of residual stabilizer and the stabilizer would migrate and further form the substitutional solid solution with zirconium oxide particles at working temperature for long time. Sixthly,after keeping the working temperature for 4,8,12 h, respectively, zirconium oxide phase composition of sample A and B was mainly cubic and monoclinic phase which increase with the time heat preservation,and the content of cubic phase of zirconia(c-Zr O2) and monoclinic zirconia(m-ZrO2) appear increase and decrease of a ladder type with the time increased; the content of cubic phase of zirconia(c-ZrO2) and monoclinic zirconia(m-ZrO2) of sample C changed a little. |
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