AN APPLICATION OF DIFFERENTIAL THERMAL-ANALYSIS TO DETERMINE THE CHANGE IN THERMAL-PROPERTIES OF MOLD POWDERS USED IN CONTINUOUS-CASTING OFSTEEL SLABS

In continuous casting of steel slabs, all the processing steps have as their objective the attainment of the best superficial quality. The s election of an optimized mold powder is an important goal in attaining the best operating conditions. Therefore, the study of the main therm al properties of this raw material, which regulates the heat transfer between the steel plate and the mold and the lubrication of this inter face during slab casting, needs special attention, as well as the addi tional problems due to the absorption of non-metallic materials from t he fused steel and from the corrosion of the refractory materials of t he equipment. These impurities change the properties of the fluxing ma terial and its performance. If not controlled, they can cause the loss of the quality of the steel produced, and even the interruption of th e process. In this work samples of processed mold powder, taken direct ly from the top of the mold during continuous industrial casting of st eel slabs, were analyzed by differential thermal analysis (DTA), to de termine the changes in thermal properties at different processing time s. There is an increase of 41 degrees C in both, the crystallization a nd melting temperatures after 140 min of processing. From DTA curves i t can be seen that the original mold powder has only one crystallizati on peak and all the contaminated samples present two peaks. In spite o f that, in both samples, pure and contaminated mold powders, cuspidine (Ca4Si2O7F2) and nepheline (NaAlSiO4) were identified by X-ray diffra ction after thermal treatment that induced the crystallization. (C) 19 98 Elsevier Science B.V.