spheroidizers are predominantly used to treat iron in the ladle when producing castings having pearlite and pearlite-ferrite structures by means of the sandwich process. These castings are in high demand by the machine-building industry where they are used in critical assemblies
The choice of spheroidizers and their consumption depends on the quality of molten metal, viz: the content in it of such detrimental impurities as sulfur and phosphorus as well as carbide-forming and deglobularizing impurities such as chromium, vanadium, titanium, etc., the saturation of the molten metal with dissolved gases such as oxygen, nitrogen and hydrogen. The more impurities the molten metal contains, the more active components the spheroidizer in question should contain. In fact, the numerical grade designations of spheroidizers indicate the average percentage contents of magnesium, calcium and REM.
When selecting the grade, it is also necessary to consider the temperature of the molten metal when it is poured from the furnace into a treatment ladle. The higher the temperature, the higher percentage content of calcium should be. Calcium significantly reduces losses of magnesium as it combines with the latter to form an intermetalide whose dissociation temperature is higher than that of magnesium silicide. Calcium contained in spheroidizers not only reduces magnesium losses caused by flare but also reacts with some of the oxygen and sulfur contained in the molten metal, and as a result they exit the melt as slag.
All spheroidizer grades contain REM whose content does not exceed 1%.They slow down the growth rate of globules, which makes the microstructure of the melt more refined. They also promote binding of non-metallic inclusions thus forming additional graphite crystallization centers, and the strength properties of resultant castings significantly improve.