Graphite degeneration is the most prominent microstructural defect in the casting skin of ductile iron. Induced by either sulfur or oxygen contained in the molding material, its occurrence can be observed in a large range of iron castings, having substantial negative influences on the mechanical properties, especially fatigue resistance. Previous investigations …
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This paper discusses the various forms of graphite structures found in cast irons, particularly focusing on the differences between ductile iron and grey cast iron. Key classifications include exploded graphite, chunky graphite, and spiky graphite, which arise due to variations in purity, section thickness, and tramp elements.
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On the Morphology Variation of Graphite in Ductile Cast … 2.1 Melting and Sample Preparation. In this research, experimental ductile iron with a specific chemical composition (as shown in Table 1) was produced using an induction furnace, following the guidelines of ASTM E351 [].The melt was prepared based on ASTM A536 [] for SG40 cast iron, and FeSiMg alloy was introduced …
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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. …
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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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2.1 Melting and Sample Preparation. In this research, experimental ductile iron with a specific chemical composition (as shown in Table 1) was produced using an induction furnace, following the guidelines of ASTM E351 [].The melt was prepared based on ASTM A536 [] for SG40 cast iron, and FeSiMg alloy was introduced into the molten metal at a temperature of …
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The nucleation and growth behaviour of chunky graphite in heavy section ductile cast irons was studied. The microstructure in the quenched samples during solidification was observed using optical ...
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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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It was early suggested that the spheroidal graphite of ductile irons grows predominantly outside of the coupled zone. 3 It has later been proposed that ductile irons do not have a coupled zone; 51 however, this is disputed by observations of chunky graphite in slowly cooled ductile irons, featuring finer graphite morphologies growing coupled ...
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Carbon flotation in ductile iron is caused when the foundry allows the Carbon Equilivant to exceed the ability of the magnesium to suppress graphite formation in the liquid. …
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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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The three presented microstructural highlights on solid-state transformation of graphite, namely secondary graphite formation in ductile cast irons, graphite formation in high …
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The evolution of ductile iron with martensitic matrix during annealing at 700 °C was studied in the present study. The results showed that the ultrafine graphite nodules with a count of 8500 nod/mm2 and an average diameter of about 1 µm were obtained in ductile iron through annealing treatment. The martensite in ductile iron was first decomposed into granular …
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Indeed, the ductile iron foundry, which truthfully claims not to have shrinkage concerns is the exception to the rule. Other common defects may be divided into two basic categories: -Those related to nodule shape and size, such as compacted graphite structures, exploded and chunky graphite, graphite floatation, spiky graphite and nodule alignment.
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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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Sertucha, Jon Chunky graphite formation in ductile cast irons: effect of silicon, carbon and rare earths . (2016) International Journal of Materials Research, vol. 107 (n° 11). pp. 1041-1050. ISSN 1862-5282 Any correspondence concerning this service should be sent to the repository
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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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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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But frequenttly the range of equivalent carbon is 4,2 to 4,4% because the graphite flotation and to the casting soundness this relation is a good information ... I too was relating it to grey iron casting. Infact GG series is now grey iron and GGG is related to ductile irons. I have reproduced an extract in German giving mechanical properties ...
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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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The present work brings new insights by transmission electron microscopy allowing disregarding or supporting some of the models proposed for spheroidal growth of graphite in cast irons. Nodules consist of sectors made of graphite plates elongated along a 〈a〉 direction and stack on each other with their c axis aligned with the radial direction. These …
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Carbon flotation in ductile iron is caused when the foundry allows the Carbon Equilivant to exceed the ability of the magnesium to suppress graphite formation in the liquid. My experience suggests that limit is about 4.55 - 4.60 with moderate levels of …
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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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Ultraseed® inoculant is designed for pure Mg produced ductile iron, irons of low oxygen and sulphur levels and dead iron which has been held for extended periods of time. This inoculant will give high nodule counts in ductile iron which is normally difficult to inoculate and will help to prevent micro-shrinkage. Chunky Graphite Potential Causes:
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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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58 / Cast Irons Table 1 Comparison of properties of cerium-treated CG iron with FG iron of the same chemical composition, high-strength pearlitic FG iron, and ferrilic SG iron in the as-cast condition
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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 exploded graphite …
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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 quenching and ...
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Chunky graphite appears easily in heavy-section spheroidal graphite cast irons and is known to affect their mechanical properties. A dedicated experiment has been developed to study the effect of ...
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Because the density of graphite is lower than that of molten iron, the graphite floats to the upper part of the casting under the drive of magnesium vapor. The higher the carbon equivalent, the more serious the graphite floating …
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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 3 b), suggests a fall within the slightly irregular spheroidal graphite (Form V ISO 945), in the 4.5%Si ductile cast iron test.
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2013 Keith Millis Symposium on Ductile Cast Iron Review of Microstructural Features of Chunky Graphite. in Ductile Cast Irons. J. Lacaze CIRIMAT, Université de Toulouse, Toulouse, France
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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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As a matter of fact, hypereutectic cast irons are commonly employed with however some limitations in case of heavy-section castings where some graphite flotation should be avoided. The results obtained in the present work show an optimal composition for minimising shrinkage that corresponds to slightly hypereutectic alloys.
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