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There are several theories to explain the nucleation and growth mechanism of graphite in cast iron, and certain researchers propose that the magnesium added through the …
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Graphite formation in the solid state is both in ductile cast irons and in steels strongly promoted by high silicon contents above 3 wt.% Si. The matrix microstructure in austempered ductile iron can be further refined by secondary graphite if the austenitization, quench, and isothermal transformation into ausferrite are preceded by an austenitization at a slightly higher …
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A study of the occurrence of graphite flotation as a function of carbon content in a ductile iron of base composition 2.50%Si, 0.16%Mn, …
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It explains that the graphite in CG iron is intermediate in shape between the spheroidal graphite found in ductile iron and the flake graphite in gray iron, giving it distinct advantages in a number of applications. ... Compacted Graphite Irons, Alloying: Understanding the Basics, Edited By J.R. Davis, ASM International, 2001, p 91–99, ...
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The effects of certain elements on the formation of graphite in ductile iron have been investigated using directional solidification. ... Modeling of microstructural evolution during divorced eutectic solidification of spheroidal graphite irons. Acta Mater., 84 (2015), pp. 413-425. View PDF View article View in Scopus Google Scholar [10]
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The quantity and morphology of spheroidal graphite have an important effect on the properties of ductile iron, and the characteristics of spheroidal graphite are determined by the solidification process. The aim of this work is to explore the precipitation and evolution of graphite nodules in hypoeutectic, eutectic, and hypereutectic ductile irons by thermal analysis, liquid …
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Graphite flotation must not be mistaken for kish graphite (q. v.) occurring in flake graphite cast iron. Flotation of graphite influences expansion and contraction of the cast iron during eutectic solidification and thus also interferes with seal …
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piling up of thin graphite plate. The face of plate is the basal plane of graphite crystal structure. Papers [1–93] on CHG formation in heavy section ductile iron castings since 1956 were reviewed, and they were summarized through site theory. The papers have already reviewed by researchers .70,94–107 Such reviews are helpful
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flake graphite (C, Fe-Si alloy, and a trace of iron sulphide) [3]. The cast iron has about 7.20 g/cm3 density, and magnesium has roughly 1.78 g/cm3 density, and these causes melt [13].
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Graphite diffusing from cast iron melts rising to the top of the melt. In metallographic specimen floating graphite is very clearly identifiable even with low degree of magnification.At broken or machined surfaces, the diffused and …
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Structure of graphite precipitates in cast iron
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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 …
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BOTTOM-CHILLED DIRECTIONALL Y SOLIDIFIED DUCTILE IRONS. W.S. Chang a, C.M. Lin a, b, * ... This study has been conducted to better understand the phenomenon of graphite flotation in cast irons. It ...
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Graphite floatation is caused by excessive growth of some nodules, which incorporate carbon directly from the liquid. ... Austempered ductile irons (ADI) have become widely used structural ...
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The Roundness Graphite Shape Factor (RSF), which is considered (by the international standard ISO 945-4-2019) to characterize the representative graphite morphologies in cast irons (Figure 3b), suggests a fall within the slightly irregular spheroidal graphite (Form V ISO 945), in the 4.5%Si ductile cast iron test. For RSF < 0.7, it practically ...
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Graphite nodularity calculated using the graphite Roundness Shape Factor (RSF), according to ISO 16112:2017-CGI (NG 1 ) and ISO 945-4-2019-DI (NG 2 ), and by replacing the RSF with the Graphite ...
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The Carbon Equivalent also indicates the risk for graphite flotation and for exploded graphite in ductile iron. ... Figure 2: In hypereutectic irons, the heat released by primary austenite results in a thermal plateau at Point A. Thereafter, the onset of the eutectic solidification of graphite ...
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Ductile cast irons (DCIs) are of increasing importance in the renewable energy and transportation sectors. The distribution and morphology of the graphite nodules, in particular the formation of degenerate features during solidification, …
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Graphite floating means that there are a large number of graphite balls on the upper surface of the casting, and at this time, the graphite shape, both the original compact ball into …
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High C concentration forms graphite floatation, and low C.E. value results shrinkage porosity and poor nodule count. Moreover, high Si concentration promotes the formation of chunky graphite. ... Chunky graphite formation in ductile cast irons: effect of silicon, carbon and rare earths. Int. J. Mater. Res. 107(11), 1041 (2016) Article Google ...
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Studying how shrinkage porosity changes size when varying the composition of ductile irons is still of interest for manufacturing sound cast parts and defining optimised processing conditions. ... of Cast Iron XI irons are commonly employed with however some limitations in case of heavy-section castings where some graphite flotation should be ...
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Ferritic high-Si ductile cast irons replace an unstable mixed ferrite-pearlite matrix with a unique combination of high elongation, strength and hardness (ideal for automotive drive train components) and resistance to oxidation and corrosion at high temperatures (automotive exhaust and turbocharger systems). The present paper analyses the graphite parameters of …
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-Those related to nodule shape and size, such as compacted graphite structures, exploded and chunky graphite, graphite floatation, spiky graphite and nodule alignment. ... has a marked effect on the shrinkage tendency of ductile irons. Foundries operating at the higher end of the magnesium range, 0.05% or above, will find that the iron is more ...
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In hypereutectic nodular cast irons, primary precipitation of graphite may lead to graphite flotation in thick section castings. Graphite degeneracy such as so-called exploded graphite is then often associated with this flotation phenomenon and it appears as precipitates where the nodular form is replaced by star-like or flower-like shape. It has been reported that …
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This manuscript summarizes recent investigation of the authors into the solidification and shrinkage defect formation of ductile and compacted graphite cast irons. The study makes use of the DAAS (direct austempering after solidification) technique, developed earlier by some of the authors, to reveal the solidification grains. In addition, color metallography is used to reveal …
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It is well-known that graphite flotation occurs in sufficiently hypereutectic compositions of ductile cast iron, accompanied by the formation …
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However, for heavy section ductile iron castings, the mass fraction range of carbon equivalent should be reduced to 4.3-4.4%, otherwise, graphite floating will occur. If the heavy section ductile iron is cooled by metal mold, the carbon equivalent will be increased to 4.6-4.7%, and graphite will not float.
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Graphite is a hexagonal-closepack form of carbon that can grow in both the liquid and solid forms of iron. In theory, in irons above the eutectic composition of carbon, the graphite first nucleates in the liquid, and then continues to grow in the solid. In irons below the eutectic composition, the graphite does not start
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Graphite flotation, which potential causes can be high carbon equivalent, excess of pouring temperature, slow cooling rate in thicker sections or an insufficient inoculation. ... Ductile cast irons are versatile alloys thanks to the possibility to obtain different combinations of mechanical and technological properties by means of the chemical ...
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The aim of the present study is to evaluate the actual status of silicon-alloyed ductile cast irons, as recent knowledge on the structure formation, and to review original data obtained by the authors from recent separate publications with additional unpublished data, specifically concerning the structure peculiarities. New data were added to deeply correlate the most …
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