The use of mould powder is essential for the continuous casting process. It forms liquid slag which prevents reactions between the steel melt and air oxygen, regulates the heat flux from the mould and acts as a lubricant between the mould and the solidifying steel shell. During the casting process a slag rim consisting of semi-molten powder and slag solidifies on the mould wall. This crust is located near the steel meniscus. If the slag rim reaches a critical thickness, it might influence the slag infiltration and causes surface defects in the slab. This thesis describes the growth behavior of the slag rim. For this reason, the dependence of the crust size on several casting parameters was investigated. Furthermore, it was important to determine the chemical and mineralogical compositions of the slag rim samples for a better understanding of the crust formation. The used analysis methods were scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and X-ray fluorescence analysis (RFA). On the basis of these measurement results the creation of overview pictures which describe the phase distribution over the cross sections of different crust types was possible. In addition to this, the effects of the slag rim on slag infiltration and subsequently on the slab quality were investigated. The results of the investigations show that by the use of powder “164” a very pronounced vertical slag rim growth will be observed during the process. This results from the contact of the crust with the steel shell in the course of the mould oscillation. This affects the slab surface quality in a negative way.