Effect of mould inoculation on formation of chunky graphite in heavy section spheroidal graphite cast iron parts

Asenjo, Iker; Larrañaga, P.; Sertucha, Jon; Súarez, Ramón; Gómez, Javier Martínez; Ferrer, Inaki; Lacaze, Jacques

doi:10.1179/136404608x286138

Cited by 41 publications

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“…Influence of Si and Ni on CHG formation is in accordance with literature [6]. The irregular distribution of CHG on the cross-section of the casting is consistent with [12]. In [12], CHG appeared in the casting center only when there was a little amount.…”

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confidence: 77%

Effect of Si and Ni Addition on Graphite Morphology in Heavy-Section Spheroidal Graphite Iron Parts

Bauer

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Petrič

et al. 2018

MSF

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Abstract. Metallographic analysis is applied to the study of the chunky graphite morphology in heavy-section castings of spheroidal graphite cast irons. Three castings with different Si and Ni contents were prepared. Three positions in casting from the edge to the centre, with different cooling rates, were chosen for microstructure observation. The effect of the Si and Ni content on the graphite morphology and mechanical properties of heavy-section spheroidal graphite cast iron parts was investigated. Cerium containing commercial inoculant was used for in-stream inoculation. Chunky graphite area was estimated in micro-and macrostructure. Mechanical properties were determined on tensile test bars taken from the centre of the casting. Macro-and microstructure examination showed that the castings with high Si-content and Ni addition had chunky graphite present, while the castings produced by use of low Si and Ni containing charge had no chunky graphite. High Si-content is strong chunky graphite promoter, especially in castings with slow cooling rate. Ni addition also promotes chunky graphite formation, but only in thermal centre of the casting (where the cooling rate is the lowest). The elongation is severely lowered when chunky graphite appears in the microstructure.

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supporting

confidence: 77%

Effect of Si and Ni Addition on Graphite Morphology in Heavy-Section Spheroidal Graphite Iron Parts

Bauer

Pokopec

Petrič

et al. 2018

MSF

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“…En todos los casos, el estudio metalográfico posterior permitió definir correctamente la superficie afectada por la degeneración grafítica (C C ). Por otra parte, la intensidad de GCH en el interior de las superficies afectadas por el defecto se define con ayuda del paráme-tro A A [4] . De este modo, es posible definir el porcentaje de área total afectada por el GCH (S S ) a través de la siguiente ecuación:…”

Section: Methodsunclassified

“…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] .…”

Section: Introductionunclassified

“…Es necesario destacar que, salvo en fundiciones especiales con elevados contenidos de silicio (3,5 -4,5 %) y/o níquel (18 -38 %) [8][9][10] , tratadas con FeSiMg, el GCH prácticamente no constituye un problema en la fabricación de piezas con módu-los de enfriamiento inferiores a 2,5 cm [4] . En el caso de las piezas de mayor tamaño, existen remedios experimentales los cuales se usan de forma convencional para evitar la aparición de este defecto (utilización de enfriadores, adición de pequeñas cantidades de antimonio, etc.).…”

Section: Introductionunclassified

“…Cuando se emplean cargas con bajos contenidos de elementos de aleación, únicamente se detecta GCH cuando la velocidad de solidificación es lenta. En estas condiciones, se ha comprobado que la utilización de altos contenidos de silicio y/o un exceso de inoculación en el molde incrementa considerablemente la formación de esta malformación grafítica [4] . Por otra parte, se ha observado que la presencia de ciertos contenidos de cerio (< 0,015 %), adicionados deliberadamente o procedentes de la aleación nodulizante y/o el inoculante, también tiene una influencia relevante en la formación del GCH [12][13][14] .…”

Section: Introductionunclassified

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

Asenjo¹,

Larrañaga²,

Sertucha³

2011

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El grafito chunky es una malformación detectada habitualmente en las zonas de última solidificación pertenecientes a piezas de fundición grafítica esferoidal con enfriamientos muy lentos. Estudios previos realizados sobre bloques cúbicos de 300 y 180 mm de lado y fabricados con aleaciones de matriz ferrítica, indican que los factores que promueven la formación de este defecto son: bajas velocidades de enfriamiento, excesiva post-inoculación del metal de colada y la presencia de elevados contenidos de silicio y/o cerio. La intensificación de estos factores en la fabricación de piezas con espesores más reducidos ha permitido obtener grafito chunky en secciones inferiores a 50 mm. Se han utilizado diferentes condiciones experimentales y se han determinado los factores de mayor influencia en la formación del defecto. La utilización de técnicas analíticas de gran precisión ha mostrado una gran similitud en las composiciones químicas entre las zonas afectadas por la malformación grafítica y aquellas en las que el grafito aparece únicamente bajo formas perfectamente esferoidales. Por otra parte, los contenidos de oxígeno medidos en los materiales estudiados en este trabajo no muestran relación con la cantidad de grafito chunky formado, sin embargo sí dependen del tipo de elemento químico utilizado para realizar el tratamiento de esferoidización del metal fundido. Palabras claveGrafito chunky; Fundición esferoidal; Pequeño espesor; Cerio; Magnesio; Curvas de solidificación. Chunky graphite formation in small section ductile iron castings AbstractChunky 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.

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Modeling the Porosity Formation in Austenitic SGI Castings by Using a Physics‐Based Material Model

et al. 2010

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On solidification, microsegregations build up in solid phases due to changes in solid concentrations with temperature. Diffusion, which is a kinetic process, usually reduces the occurrence of microsegregations. This work is aimed at modeling such kinetic effects on the solidification of austenitic cast iron, using a holistic approach. For this purpose, a microsegregation model is developed and validated. Moreover, this model is directly coupled to a commercial process‐simulation tool and thermodynamic software. A series of GJSA‐XNiCr 20‐2 clamp‐rings is cast by varying the inoculation state and the number of feeders. The composition of this cast alloy is analyzed and the microstructure characterized to provide input data for the microsegregation model. In order to validate the software, cooling curves are recorded; differential thermal analysis, electron dispersive X‐ray analysis and electron probe micro analysis are carried out. Furthermore, the porosity within the casting is analyzed by X‐ray. By performing coupled simulations, the different cooling characteristics within the casting lead to pronounced differences in phase fractions and solidification temperatures which are due to dendrite arm coarsening. The hot spot effect below the feeders is assisted by a shift towards lower solidification temperatures over the solidification time. This shift is a result of the local cooling characteristics, which can only be predicted when process simulation is directly coupled with material simulation. The porosity predictions and the porosity analysis exhibit good agreement. A comparison between experimental and virtual cooling curves closes, implying that the novel coupling concept and its implementation are valid.

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Effect of mould inoculation on formation of chunky graphite in heavy section spheroidal graphite cast iron parts

Cited by 41 publications

References 0 publications

Effect of Si and Ni Addition on Graphite Morphology in Heavy-Section Spheroidal Graphite Iron Parts

Effect of Si and Ni Addition on Graphite Morphology in Heavy-Section Spheroidal Graphite Iron Parts

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

Modeling the Porosity Formation in Austenitic SGI Castings by Using a Physics‐Based Material Model

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