Abstract
Chunky graphite is a degenerated graphite form which can be found in the thermal centre of ductile iron heavy section castings. Previous studies made on cubic blocks (300 and 180 mm in side) manufactured using alloys with fully ferritic matrix structures show that low cooling rates, excessive post-inoculation and high silicon and/or cerium contents in the melts are the most important factors that promote this kind of defect. The enhancement of these critical factors led to obtain chunky graphite in sections lower than 50 mm. Different experimental conditions have been used in order to establish the main parameters that affect this graphite malformation. The use of cutting-edge techniques in the analysis of chemical compositions has revealed that no significant differences can be found when comparing chunky areas and well-formed spheroidal graphite areas. On the other hand, it has not been possible to establish any correlation between the oxygen contents and the scale of the defect. However, it is noteworthy that the oxygen content is related to the use of magnesium or cerium as nodulizer agent.
Highlights
Chunky graphite is a degenerated graphite form which can be found in the thermal centre of ductile iron heavy section castings
Previous studies made on cubic blocks (300 and 180 mm in side) manufactured using alloys with fully ferritic matrix structures show that low cooling rates, excessive post-inoculation and high silicon and/or cerium contents in the melts are the most important factors that promote this kind of defect
The use of cutting-edge techniques in the analysis of chemical compositions has revealed that no significant differences can be found when comparing chunky areas and well-formed spheroidal graphite areas
Summary
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]. Es necesario modificar la composición química de la aleación utilizada y/o colar muestras cuya velocidad de enfriamiento sea lo suficientemente lenta como para favorecer la formación y crecimiento del defecto. En la bibliografía existen trabajos en los que se obtiene GCH en piezas de espesor delgado, bien mediante la presencia de elevados contenidos de níquel en el metal[8 y 9] o introduciendo éstas en hornos especiales con el fin de reducir la velocidad de solidificación y aproximarla a las condiciones de enfriamiento en piezas de elevado espesor[15,16,17]. Adicionalmente, se ha intentado relacionar la incidencia del GCH con el contenido de oxígeno en el metal de colada, ya que este elemento juega un papel importante en la morfología grafítica obtenida[18 y 19]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
