9th ECCC European Continuous Casting Conference – ECCC 2017

At voestapine Stahl Linz two different mold powders are used for casting construction steel, where powder A forms significant larger slag rims than powder B. Their chemical compositions are very similar. The CaO/SiO2 ratio for powder A and B is 1.25 and 1.20 respectively. Additionally powder B contains 0.97 wt% MnO. For the clarification of this difference in performance the melting behavior of the original mold powders was investigated by Hot Stage Microscopy, stepwise annealing and Simultaneous Thermal Analysis (STA). A Furnace Crystallization Test (FCT), the STA and a rotational viscometer were used to characterize the solidification of these mold powders. For the testing of the fluidity an Inclined Plane Test was performed, the viscosity was determined by a rotational viscometer. For the investigation of the microstructure polished sections were prepared from annealed samples as well as from FCT samples. For the slag rims itself cross-sections were investigated by microscopical means. From the investigations follows, that the mold powder suppliers use two different raw material concepts. Consequently the powders do not exhibit identical melting behavior. Contrary to this, as the solidification behavior and the viscosity are dependent on the chemical composition, the deviation of these properties for the two mold powders is only small. Analysis of the slag rims shows a lower part built up by solidified slag and an upper part consisting of partly liquified powder only. For slag rims from powder A the upper part is predominant and displays in contrast to powder B by far more trapping of carbon. Accordingly the difference in the formation of the slag rims is mainly affected by the different melting behavior of the two powders.