Experience Producing Compacted Graphite Cast Irons by Sulfur Addition After Magnesium Treatment

摘要

Sulfur additions were employed after magnesium-treatment to produce Compacted Graphite Iron without using antinodularizing elements (Ti, Al). The amount of sulfur additive needed to obtain a certain NG/CG ratio in Mg-treated iron depends on the residual magnesium content after treatment, holding time prior to pouring, wall thickness of the casting and the type of mold Results show that it is possible to use magnesium treated ductile iron, at lower Mg levels (0.03-0.04 percent) with added sulfur (less than 0.02 percent S) to "denodulize" it from the same furnace melt, in order to have a transition from ductile iron to compacted graphite iron in continuous production. Critical parameters include levels of final magnesium (0.010-0.025 percent) and Mg/S ratio (0 5-2.0). Software in a thermal analysis system was adapted to monitor CG vs. NG formation conditions. Degree of undercooling (DU) was found to be a critical factor for compacted graphite formation (DU=-40 to -60), coral graphite (DU=<-60) and nodular graphite (DU=> 0).