On the solidification sequence of ductile iron castings containing chunky graphite

Graphite nodule count and size distribution in thin-walled ductile cast iron

“…(4) nor the more advanced as the FDM will give a reliable 3D nodule count. The problem of degenerated graphite nodules is however normally an issue for castings with low cooling rates and not for castings with high cooling rates as in thin walled castings [22,27]. There are methods for treating spatial size distribution of non-spherical particles but the problem is complex and so are the conversion methods [17].…”

Thermal Analysis of the Formation of Chunky Graphite during Solidification of Heavy-section Spheroidal Graphite Iron Parts

“…[3][4][5]8,15) This limitation of TA is quite unfortunate when dealing with large melts prepared for thick-wall ductile iron castings. In these cases where cooling rate becomes extremely low and where cooling curves are characterised by lengthy eutectic plateaus, [23][24][25][26] the solidification microstructure may be affected by magnesium and inoculation fading, marked intercellular segregation, as well as graphite degeneracy. Among the various forms of degenerate graphite observed, chunky graphite (hereafter denoted CHG) turns out to be the most critical defect due to its negative influence on mechanical properties.…”

“…Among the various forms of degenerate graphite observed, chunky graphite (hereafter denoted CHG) turns out to be the most critical defect due to its negative influence on mechanical properties. 25,27) Graphite degeneracy in large section castings has been extensively studied since the 60's and its formation or avoidance has been often related to the presence of low-level elements. [28][29][30][31][32][33][34][35] Limited amounts of rare earths, lead and antimony added to the melt help avoiding CHG. [31][32][33]36,37) Also, the use of chills has been found efficient to suppress CHG formation, 23,24,38,39) but this is limited to thicknesses up to a few centimetres.…”

Formación de grafito chunky en piezas de pequeño espesor fabricadas utilizando fundición de hierro con grafito esferoidal

“…Estos resultados ponen de manifiesto tanto la ausencia de fenómenos de macrosegregación [21 y 22] como la importancia de todos los factores que promueven la formación del GCH, incluyendo la velocidad de enfriamiento local en cada una de las zonas de la pieza. En relación a la presencia de oxígeno en el metal, a pesar del potente efecto desoxidante del cerio [21] , se observa que aquellas aleaciones tratadas con CeMM presentan contenidos de oxígeno sistemáticamente mayores (25 -50 ppm) que las tratadas con FeSiMg (15 -21 ppm). Este aspecto puede guardar relación con la intensidad de la reacción provocada durante los tratamientos de esferoidización.…”

“…El grafito chunky (GCH) es una degeneración grafítica constituida por una estructura ramificada e interconectada de grafito, habitualmente asociada a los centros térmicos de piezas de fundición grafítica esferoidal con elevado espesor [1][2][3][4][5] . La aparición de este defecto se relaciona con un efecto negativo sobre las propiedades mecánicas del material, por lo que su presencia en piezas con importantes requerimientos constituye un serio problema para la industria eólica y/o de automoción [3 y 6] .…”