These include, but are not limited to, temperature, deoxidation, reoxidation, refractory interactions and sulfide formation. Further complicating this picture is the fact that these factors are frequently interrelated, which adds another layer of confusion. Performing a metallographic analysis of the inclusions in blocked nozzles to determine their main constituents is a good starting point. If earlier steel samples are available, they can also be examined in order to evaluate inclusion morphologies and changes during steelmaking and casting process. Without this type of analysis, formulating a solution is impossible.
Calcium has a very limited solubility in steel and is mainly found in the inclusions present.
If reoxidation occurs, whether from air entrapment, stirring, slag, etc., the calcium content of the inclusions will be effectively lowered because of additional formation of Al 2 O 3 . The grades discussed are particularly susceptible to clogging due because of CaS and Al 2 O 3 formation. Depending on steel temperature and the relative concentrations of C, Ca, Al, S and O, thermodynamics may favor the formation of calcium sulfides as opposed to low melting temperature calcium aluminates. If this is the case, an entirely different approach must be taken. This is an oversimplification, but in general, if clogging is related to alumina buildup, the calcium analysis should be higher.