Evaluating the Effect of Chemical Composition on the Performance of a Mold Powder in Continuous Casting of Steel Mold powders are fluxing agents used as raw materials in the steel industry, composed mainly of oxides of 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 B 2 O 3 , Na 2 CO 3 , TiO 2 and Li 2 CO 3 on the viscosity and crystallization properties, as alternative substitutes for CaF 2 , 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 CaF 2 , 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, TiO 2 was added in about 2, 5 and 8wt% to increase the crystallization by increasing the formation of perovskite (CaTiO 3 ) and schorlomite