Effect of Antimony and Cerium on the Formation of Chunky Graphite during Solidification of Heavy-Section Castings of Near-Eutectic Spheroidal Graphite Irons

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

doi:10.1007/s11661-008-9731-y

Cited by 48 publications

(36 citation statements)

References 7 publications

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“…They found that Bi is suppressing or reducing the CHG formation by reducing the undercooling, which is considered the main reason for the CHG formation. In this case, Bi behaves in a similar way like Sb, whose effect was confirmed by P. Larrañaga et al 12 Bismuth also has the function to remove the oxygen absorbed at the interface between graphite and liquid iron, thus reducing the oxygen absorption and preventing the formation of CHG. 5 Although it is known that the correlation between the ratio of RE/subversive elements and the appearance of chunky graphite in thick-walled ductile-iron castings exists, this area is still not fully investigated. More work is needed to provide a correct balancing of the RE/Bi ratio that would prevent the formation of chunky graphite.…”

Section: Introductionsupporting

confidence: 56%

Effect of inoculation on the formation of chunky graphite in ductile-iron castings

Pokupec¹,

Mrvar²,

Bauer³

2017

Mater. tehnol.

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Chunky graphite is one of the most deleterious graphite degenerations in thick-walled ductile-iron castings. This defect normally appears in the thermal center of a casting and dramatically decreases the mechanical properties. Chunky-graphite formation is primarily caused by a reduction in the cooling rate and melt composition. An addition of subversive elements (Bi, Sb, Pb, Sn,...) associated with a small amount of Ce is known to be beneficial to avoid chunky graphite. In this study, the effects of Bi and Ce additions at different cooling rates on the graphite morphology and mechanical properties of ductile-cast iron EN-GJS-400-18-LT were investigated. Y-blocks with wall thicknesses of 25 mm and 75 mm and cylindrical blocks with a diameter of 200 mm and a height of 300 mm were cast. The presence of chunky graphite in the thermal center of the cylindrical blocks and a decrease in the mechanical properties were revealed, regardless of the presence of Bi. Keywords: chunky graphite, cooling rate, graphite morphology, thick-walled ductile-iron castings Grudast grafit je ena od najbolj {kodljivih degeneracij grafita v debelostenskih ulitkih iz gnetljivega`eleza. Ta napaka se obi~ajno pojavi v toplotnem sredi{~u ulitka in mo~no zmanj{a mehanske lastnosti. Nastanek grudastega grafita je posledica zmanj{anja hitrosti ohlajanja in sestave taline. Dodatek {kodljivih elementov v sledovih (Bi, Sb, Pb, Sn,...) v povezavi z majhnim dodatkom Ce je poznan kot ugoden za prepre~itev nastanka grudastega grafita. V tej {tudiji je bil prou~evan vpliv dodatka Bi in Ce pri razli~nih hitrostih ohlajanja na morfologijo grafita in mehanske lastnosti gnetljivega litega`eleza EN-GJS-400-18-LT. Uliti so bili Y-kosi z debelino stene 25 mm in 75 mm ter cilindri~ni kosi s premerom 200 mm in visoki 300 mm. Odkriti sta bili prisotnost grudastega grafita v toplotnem sredi{~u cilindri~nih kosov ter zmanj{anje mehanskih lastnosti, neodvisno od prisotnosti Bi.

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Section: Introductionsupporting

confidence: 56%

Effect of inoculation on the formation of chunky graphite in ductile-iron castings

Pokupec¹,

Mrvar²,

Bauer³

2017

Mater. tehnol.

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“…Es decir, la superficie afectada por el GCH (C C ) aumenta con su intensidad (A A ). Esta relación es contraria a la encontrada en trabajos previos [4,[11][12][13][14] , realizados sobre bloques cúbicos de fundición esferoidal con elevado módulo de enfriamiento y tratados exclusivamente con FeSiMg. En estas pie- zas de gran tamaño, cuando aumenta el volumen afectado por el GCH disminuye considerablemente la intensidad del mismo.…”

Section: Resultados Y Discusiónunclassified

“…En este caso, la presencia de magnesio en el metal utilizado para fabricar la cuña nº 3 parece ser un factor determinante a la hora de compensar el efecto del cerio y reducir la cantidad de defecto obtenida. Este comportamiento coincide con los resultados obtenidos en trabajos publicados ante- riormente [14] . En otro caso descrito en la bibliografía [4] , se observa reiteradamente la obtención de mayores cantidades de GCH en metales inoculados y con valores de ∆T más bajos en relación a los correspondientes metales no inoculados.…”

Section: Resultados Y Discusiónunclassified

“…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

REVMETAL

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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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“…7,8) Also, the interplay between the many impurities and low-level elements has been scarcely looked for. 9) Further, because of the duration of cooling heavy-section castings, it seems reasonable that quite many complex chemical reactions take place during solidification of heavy-section cast-iron as suggested by Javaid and Loper.…”

Section: Introductionmentioning

confidence: 99%

Improved Analytical Method for Chemical Analysis of Cast Irons Application to Castings with Chunky Graphite

et al. 2011

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Chunky graphite is a particular form of graphite degeneracy that appears in the centre of large iron castings, with a well-defined transition from the outer unaffected area and the inner affected one. All previous works that looked for macrosegration to explain the phenomenon concluded that there are no significant composition differences between the inner and outer parts of such castings. This was challenged again because the analytical methods generally used for chemical analysis are not efficient for low-level elements. Accordingly, an ICP-MS procedure has been developed and validated to replace the usual ICP-OES method. Together with the usual methods for analysis of C, S and Si, this ICP-MS procedure has been applied to characterize chemical heterogeneities in a large block with chunky graphite in its centre, and to a standard part for comparison. It could be concluded that no macrosegregation has built up during the solidification process of the block investigated, i.e. that chunky graphite appearance is not related to any composition changes at the scale of the cast parts, in particular of elements known to affect graphite shape such as Ce, Mg, Sb, S, · · · .KEY WORDS: nodular cast-iron; chunky graphite; chemical analysis; segregation; heavy section. measuring trace elements in small samples being about 0.1 g in weight is thus presented. Measurements of silicon, carbon and sulfur contents were performed with 0.5 g samples following the standard procedures that will be also shortly described for consistency. In the present work, these procedures have been applied to materials coming from the outer part (without CHG) and inner part (with CHG) of a heavy-section block. For purpose of comparison, measurements were also performed on material taken out from a light-section part that was cast with a melt of similar composition. This light-section part showed no CHG and presented a much larger nodule count. Experimental DetailsThe chemical analyses have been performed with three methods: -gravimetric method for silicon; -combustion with a LECO CS-200 facility for carbon and sulfur; -induction coupled plasma-mass spectroscopy (ICP-MS) with an Agilent 7500 CE apparatus for all other elements considered in this study. The first and third methods apply to solutions obtained by dissolving the material in acids having ACS analytical grade, i.e. containing less than 5 ppm metal atoms. These three methods are successively detailed below with more detail for ICP-MS; they all give results per weight percents that are recalculated, either automatically or manually, from the initial masses of material involved for analysis which were weighed on calibrated balances with the following requirements: -silicon analysis: 0.5Ϯ0.005 g; -carbon and sulfur analysis: 0.5Ϯ0.005 g; -trace elements: 0.1Ϯ0.0005 g. Measurement of SiliconSilicon is analysed along a procedure based on the E350 ASTM standard. The method consists in first dissolving the sample in a mixture of HNO 3 (68 mass%) and HCl (38 mass%). Silicic acid H 4 SiO 4 forms i...

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Effect of Antimony and Cerium on the Formation of Chunky Graphite during Solidification of Heavy-Section Castings of Near-Eutectic Spheroidal Graphite Irons

Cited by 48 publications

References 7 publications

Effect of inoculation on the formation of chunky graphite in ductile-iron castings

Effect of inoculation on the formation of chunky graphite in ductile-iron castings

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

Improved Analytical Method for Chemical Analysis of Cast Irons Application to Castings with Chunky Graphite

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