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چكيده انگليسي :

Evaluating the Effect of Chemical Composition on the Performance of a Mold Powder in Continuous Casting of Steel Satia Soltan Attar s soltanattar@ma iut ac ir 14th March 2011 Department of Materials Engineering Isfahan University of Technology 84156 83111 Isfahan Iran Degree M Sc Language Farsi Dr Ahmad Monshi Prof Supervisor E mail a monshi@cc iut ac ir Dr Mahmoud Meratian Assoc Prof Supervisor E mail meratian@cc iut ac ir Dr Hasan Hadadzadeh Assoc Prof Advisor E mail hadad@cc iut ac ir Mold powders are fluxing agents used as raw materials in the steel industry composed mainly of oxides of Abstract silicon aluminum alkaline and alkali earth metals with minor contents of fluorides and carbon They are used in continuous casting of steel slabs to protect the steel meniscus from oxidation provide thermal insulation to prevent the steel from freezing provide lubrication of the steel shell absorb inclusions floating up from the steel and provide the optimum level of horizontal heat transfer between shell and mould Mold powders play a very important role on the processing stability and on the final surface quality of the product Especially the surface quality depends on viscosity and heat transfer of the infiltrated mold flux between the mold wall and the solidified steel shell Among all of the constituents of these powders fluorine mainly controls the viscosity solidification temperature and crystallization behavior of mold flux films However the volatilization and acidification of fluoride is a significant health hazard and causes environmental pollution In this work three industrial mold powders that are used in Mobarakeh steel complex were characterized Start powder PF2 was used as the reference powder for determining the effect of different chemical compounds on the viscosity and crystallization properties of similar powders in order to lower the fluorine content in commercial start flux The substitution possibility was examined by measuring the viscosity and crystallization behavior when compared with the properties of the industrial powder In present study 33 samples were made based on two base materials of blast furnace slag and Portland cement clinker and the effect of other components such as B2O3 Na2CO3 TiO2 and Li2CO3 on the viscosity and crystallization properties as alternative substitutes for CaF2 were investigated The high temperature viscosity of liquid mold flux was measured by using a groove viscometer on a 45 slope and also calculated by mathematical models Devitrification has been investigated by means of DTA XRD and SEM Using of blast furnace slag were limited because of its high sulfur content It has been shown that cryolite is much more effective on lowering the viscosity than CaF2 but it decreases the crystallization tendency and this causes a decrease of the heat flux between the steel shell and the mold wall In this case TiO2 was added in about 2 5 and 8wt to increase the crystallization by increasing the formation of perovskite CaTiO3 and schorlomite Ca3 Fe Ti 2 Si Ti O4 3 crystalline phases Results show that the fluorine free sample with 8wt TiO2 and 1wt Li2O has the same viscosity and crystallization fraction compared to the reference powder and it can be used as a substitution for the commercial powder In addition a new mathematical model was introduced in this study This model is evaluated by some experimental data in the literature for calculation of the constants and then the obtained equation is used for the prediction in other produced samples It has been shown that this model is much more accurate than the Riboud and Urbain models in prediction of the viscosities and it can be used for a wide range of the chemical compositions Keywords Mold powder Viscosity Crystallization Fluorine Titanium dioxide Blast furnace slag Portland cement clinker Mathematical model

سلطان عطار، ستيا

بررسي اثر تغيير تركيب شيميايي بر عملكرد يك نوع پودر قالب ريخته گري مداوم فولاد

ويسكوزيته , كريستاليزاسيون , فلورين , سرباره , كلينكر سيمان پرتلند , اكسيد تيتانيوم , مدل رياضي