It is well known that clogging constitutes one of the main issues encountered during casting in the steel industry. To clarify how clogging deposits are formed and to minimize their impact in the process, their microstructure and relationship between the different constituents need to be studied. In the tundish well the studied deposits consist predominantly of Al2O3 inclusion fans but are found interspersed with islands of pearlite along the margins. These islands of coarse pearlite, i.e. thick cementite/ferrite plates surrounded by large ferrite grains are formed even in Ti-rich ultra low carbon steels and the orientation relationships are used to track the initial composition of the deposit when it was formed. The crystallographic orientation relationship (ORS) between ferrite and cementite in pearlite can follow Isaichev (I), Bagaryatskii (B) or Pitsch-Petch (PP). Results showed that the pearlite islands are formed with ORS relatively close to PP and are intersected by alumina particles which show a specific relation with the islands and with the ferrite matrix. It was concluded that an external carbon source and temperatures just above the eutectoid are needed to form those islands.