Improving the technology of late inoculation in the production of thin-walled castings from ductile iron

Abstract

The article presents the results of evaluating the impact of late inoculation on formation the microstructure of thin-wall castings from ductile iron. Existing hypotheses about the mechanism of formation and growth of graphite inclusions in the iron are analyzed. The analysis of the existing theories makes it possible to predict the high efficiency of inoculation treatment as close as possible to melt crystallization. It is noted that idea of late treatment is in introducing of inoculants into the iron melt in the pre-crystallization period, what make it is possible to provide high inoculation impact on the molten metal by creating additional crystallizing nuclei of graphite. Presented type of inoculation treatment makes it possible to obtain the required shape and diameter of nodular graphite, its uniform distribution, increase the area of graphite inclusions, reduce risk of shrinkage defects, and prevent the formation of cementite. In the presented research work the late inoculation was carried out by integrating of solid inserts of the INOCSIL® series produced by NPP Technology Company in the gating feeding system of the mould on the existing foundry factory. It is given the results of metallographical tests of samples from the castings obtained both by the current inoculation treatment of iron and by late inoculation treatment technology. The analysis of results of metallographical research showed the high efficiency of late inoculation compare with the existing technology of ladle treatment on the foundry. The use of late inoculation treatment technology made it possible to improve the microstructure of metal and increase the elongation by more than two times.