Study of microsegregation buildup during solidification of spheroidal graphite cast iron

Selig, Christophe; Lacaze, A.

doi:10.1007/s11663-000-0119-7

Cited by 20 publications

(9 citation statements)

References 16 publications

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“…From the thermodynamic assessment of the Fe-Ce system carried out by Su and Tedenac [42], the Ce partition coefficient between austenite and liquid, k c=l Ce , and the slope of the austenite liquidus, m l=c Ce , were evaluated at 0.002 and -15.2 8C/mass% respectively. Data for carbon and silicon were taken from a previous work on microsegregation in cast irons [43]:…”

Section: Appendixmentioning

confidence: 99%

Chunky graphite formation in ductile cast irons: effect of silicon, carbon and rare earths

Torre

Lacaze

Sertucha

2016

International Journal of Materials Research

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Use of rare earths, high silicon and carbon contents, and low cooling rates are reported as possible reasons for formation of chunky graphite in ductile iron castings. The understanding of this graphite degeneration is however limited, and the above conclusions are still controversial. To get further insight into this topic, ductile cast iron melts have been prepared with various carbon and silicon contents and using nodularizing alloys with various rare earth levels. These melts have been cast in blocks with different sizes to include also the effect of cooling rate on graphite degeneration. Metallographic investigation revealed that the chunky-affected areas enlarge when decreasing the cooling rate, when increasing the silicon content and without low-level addition of rare earth. In the discussion, a schematic based on change of liquid/graphite interfacial energy with alloying elements is proposed which describes the conditions for the formation of chunky graphite instead of nodular graphite.

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Section: Appendixmentioning

confidence: 99%

Chunky graphite formation in ductile cast irons: effect of silicon, carbon and rare earths

Torre

Lacaze

Sertucha

2016

International Journal of Materials Research

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“…Historically, the direction of partitioning has been decided by either: (1) comparison of the compositions of several specific dendritic and interdendritic areas, [6,38] (2) a microprobe line scan that traverses primary dendrite cores into the interdendritic regions, [39] (3) elemental X-ray maps, [40] or (4) reference to partition coefficient values reported in the literature. [41] The former three methods are preferred since partition directions may vary from one alloy to another.…”

Section: A Step 1: Determination Of Partitioning Directionsmentioning

confidence: 99%

A technique for characterizing microsegregation in multicomponent alloys and its application to single-crystal superalloy castings

Ganesan

Dye

Lee

2005

Metall Mater Trans A

144

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Instrumental errors in microsegregation measurements in multicomponent alloys complicate the treatment of randomly sampled data. In this article, two new alloy-independent data treatment algorithms are presented that are capable of separating the effects of scatter in the data from the underlying segregation trends, assigning each measurement location a unique fraction solid. These new methods are physically reasonable and result in improved estimates of segregation parameters, particularly the solute partitioning at the dendrite tip. This is demonstrated by determining the microsegregation in four successive generations of single-crystal (SX) nickel-based superalloys. Artificial, noise-induced, tails commonly seen in the microsegregation profiles are also minimized. A methodology for evaluating sorting schemes is introduced that does not depend upon a priori knowledge of the partitioning direction. Comparison is made to both other sorting methods and CALPHAD predicted partition coefficients. Implications for alloy design are reported, illustrating the interaction between solute species such as Ru, Re, Co, and W.

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“…[17][18][19][20] It was proved that microsegregation of various elements had a significant effect on stable to metastable transition as well as the solid-state transformation or heat treatment. The microsegregation behavior is quite different among various elements, for example, silicon segregates negatively during stable while positively in metastable solidification; manganese segregates positively in both reactions, 17) which makes the content of manganese in liquid increase during solidification.…”

Section: Microsegregationmentioning

confidence: 99%

“…20) The comparison of nodule counts and sizes between simulation and quantitative experiment is shown in Fig. 4.…”

Section: Comparison Of Simulation and Experimentsmentioning

confidence: 99%

Modeling of Stable and Metastable Eutectic Transformation of Spheroidal Graphite Iron Casting.

Zhao

Liu

2001

ISIJ International

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In this work, a mathematical model for stable and metastable transformation of SG cast iron, coupling with microsegregation of some elements and latent heat resulted from different phase formation, was presented. The quantitative experimental results of specimens obtained from a step-shape sample casting were compared with the simulation, and two results of nodular counts and sizes agreed quite well. For white eutectic growth in mottled SG iron, the frequent impingement of white eutectic with austenitegraphite bulks might suppress its growth remarkably and result in quite lower growth rate than that from the melt exclusively. Meanwhile, the relationship of morphology of carbides and solidification was discussed, and it was indicated that the growth of white eutectic and carbide morphology could also be predicted by solidification simulation. It was found that neglecting silicon microsegregation, if metastable transformation was advantageous to stable, the simulated carbide fraction was higher, and vice versa.KEY WORDS: spheroidal graphite cast iron; stable and metastable microstructure; eutectic transformation; modeling and simulation.ously, and may grow first freely and then surrounded by austenite shells. Considering the carbon diffusion and limited convection of liquid in front of liquid and graphite interface of Fig. 1, the growth rate of graphite spheres without austenite shell can be computed as follows:.... (5) where R t G is radii of graphite spheres (m) (superscript t and tϪdt are the calculation time) r l , and r G are densities of liquid and graphite (kg/m 3 ), D l C is diffusion coefficient of carbon in liquid (m 2 /s), C ළ l and C G are carbon content of initial liquid and graphite (%), C l * is carbon content of liquid in equilibrium with graphite and equals to C l/G approximately (Fig. 1), and d is thickness of carbon diffusion boundary layer in front of liquid-graphite interface (m).After the nodule was encapsulated by the austenite shell, its growth is dominated by the diffusion. 9) On the basis of carbon diffusion through the shell, the growth rates of bulks and graphite spheres were given as follows 10) :........... (6) ....... (7) where R g is radii of austenite shell of eutectic bulk, D C g is diffusion coefficient of carbon in austenite, r g is density of austenite, C g/l and C l/ g are carbon concentration of austenite and liquid in liquid-austenite interface respectively, and C g/G is carbon concentration of austenite in equilibrium with graphite.The growth of graphite spheres during eutectoid transformation could be determined by calculating the growth of ferrite shells with the model in the former research. 11)The growth of lamellar eutectic structure, such as ledeburite eutectic, was characterized by the well-known relationship 12,13) : where KЈ and KЉ are constants related materials properties, V is solidification rate (m/s). Because of crystal defects, the white eutectic grain often grows bending, and eventually becomes spherical. Therefore, the white eutectic was usually simplified ...

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Study of microsegregation buildup during solidification of spheroidal graphite cast iron

Cited by 20 publications

References 16 publications

Chunky graphite formation in ductile cast irons: effect of silicon, carbon and rare earths

Chunky graphite formation in ductile cast irons: effect of silicon, carbon and rare earths

A technique for characterizing microsegregation in multicomponent alloys and its application to single-crystal superalloy castings

Modeling of Stable and Metastable Eutectic Transformation of Spheroidal Graphite Iron Casting.

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