Experimental Evidence for Metallurgical Modification Associated to Chunky Graphite in Heavy-Section Ductile Iron Castings

Effects of high silicon contents on graphite morphology and room temperature mechanical properties of as-cast ferritic ductile cast irons. Part I – Microstructure

“…OTA records for solidification showed features characteristic for solidification in the stable system, and in particular with no arrest that could relate to precipitation of FeSiC phase. Observation of the mi crostructure of these remelted alloys gave results much in line with a previous work [15] where the presence of chunky graphite in the ori ginal samples was correlated to the highest magnesium contents in the alloy. These results will be detailed and discussed elsewhere.…”

Some paradoxical observations about spheroidal graphite degeneracy

“…After remelting and resolidifi cation during the DTA run, the graphite is lamellar in the two samples that contained antimony; it is compacted in those samples free of antimony. In the previous DTA study [6] , similar changes in graphite shape were observed which were assumed to be related to the remaining magnesium content. From Table 1, a similar trend was found in the present work, namely, that the two alloys with lamellar graphite are those having the lowest amounts of magnesium and cerium, and that higher contents in magnesium and cerium are related to compacted graphite.…”

“…As part of a study devoted to high-silicon spheroidal graphite cast irons [5] , it appeared of interest to perform differential thermal analysis (DTA) on samples machined out of materials showing various amounts of chunky graphite. Indeed, such an analysis had been performed previously on a common SGI which showed DTA samples consisted of either spheroidal/compacted graphite or lamellar graphite after remelting and resolidifi cation [6] . In the present work, as-cast and DTA microstructures of selected highsilicon spheroidal graphite cast irons are described, and results are then discussed to pave the way for a better understanding of graphite growth transition from spheroidal to chunky or compacted shapes.…”

Chunky Graphite in Ferritic Spheroidal Graphite Cast Iron: Formation, Prevention, Characterization, Impact on Properties: An Overview

“…Nevertheless, graphite degenerations-among which chunky graphite (CHG) is seen to be the most common and detrimental one-may occur in the castings under certain circumstances. The formation probability of such degenerations significantly increases with heavy sections above wall thicknesses of approximately 100-200 mm and solidification times longer than approximately 1 h. [6][7][8] However, chunky graphite has occasionally been observed even in 10-mm-thick castings. 9 CHG has been reported to be a major problem with nickelcontaining austenitic ductile iron materials 10 as well, but this is outside the scope of this article.…”

“…6 Although a considerable amount of research on chunky graphite has been done over the last decades, the understanding of this graphite degeneration and its impact is still limited and a unanimous view on formation mechanism and technical avoidance of chunky graphite has not yet been acquired. While the specialists almost unanimously claim that avoidance of chunky graphite in heavy sections cannot yet be rated a hundred percent process safe, 2,6,7,[13][14][15][16][17][18][19][20] a single study has been identified testifying chunky graphite could be prevented by using state-of-the-art foundry procedures and appropriate charge materials. 1 Nevertheless, due to the economic impact as well as high safety and quality requirements, the manufacturers must be aware of the origins of chunky graphite and how to avoid it.…”