Papers by Keyword: Graphite Morphology

Abstract: Nodular graphite cast iron or known as spheroidal graphite cast iron structurally has a spherical graphite morphology with a matrix consisting of a ferrite-pearlite phase. In general, cast iron has a main alloy consisting of carbon and silicon where both elements have an influence on the potential of graphitization and castability. In this work, the influence of strontium (Sr) added to molten cast iron with a composition of 0, 0.04, 0.06 and 0.08 wt% to graphite morphology were studied. The sample obtained will be carried out a characterization process by observing macro and microstructures using optical microscope equipped with image data processing software that displays graphite fraction, size, form and nodularity. Analysis showed that Sr addition increase in nodularization of graphite from 19.6 % to 31.5% at 0.08 wt% Sr addition.

Abstract: The problem of graphite crystallization and growth in cast iron has recently received increased attention. As most of the published literature describe analysis of room temperature graphite, there is a legitimate concern that the crystallization of graphite is concealed by recrystallization and growth in solid state occurring after solidification. To avoid confusion in the interpretation of room temperature graphite morphology, the authors used Field Emission Gun SEM on deep-etched interrupted solidification (quenched) specimens to reveal the morphology of graphite at the very beginning of solidification, when the graphite is in contact with the liquid. Information from related phenomena, such as crystallization of hexagonal structure snowflakes and metamorphic graphite, as well as of diamond cubic structure silicon crystals in aluminum alloys is incorporated in the analysis. Research discussing graphite produced through gas-solid and solid-solid transformations is also examined. Because the faceted growth of graphite is the result of diffusion-limited crystal growth in the presence of anisotropic surface energy and anisotropic attachment kinetics, a variety of solidification morphologies are found. The basic building blocks of the graphite aggregates are hexagonal faceted graphite platelets generated through the growth of graphene layers. As solidification advances, the platelets thicken through layer growth, and then aggregate through mechanisms that may include foliated/tiled-roof crystals and dendrites, curved-circumferential, cone-helix, helical, and columnar or conical sectors growth.

Abstract: As part of a study devoted to the effect of trace elements on graphite degeneracy, near-eutectic ductile iron melts were prepared to which minute amounts of lead and of both lead and cerium were added. The melts were cast into an insulated Y4 mould, giving a solidification time of about 1 hour and a cooling time to room temperature of about 15 hours. In the thermal centre of the Pb containing sample graphite spheroids as well as intergranular lamellar graphite have been found. At the same location of the casting containing both Pb and Ce, exploded as well as chunky graphite could be observed, while the formation of intergranular lamellar graphite has been suppressed. Deep etching of the samples allowed reaching the following conclusions: i) intergranular graphite in the SG-Pb sample often, if not always, originates on graphite nodules and extends towards the last to freeze areas; ii) in one location of the SG-PbCe sample, chunky graphite strings were observed to originate on an exploded nodule, thus confirming the close relationship between these two forms of graphite. Because of the over-treatment in cerium of the SG-PbCe sample, other unusual degenerate graphite was observed which appears as coarse aggregates of "porous" graphite after deep etching.

Abstract: Experimental researches are developed on grey cast iron surface to clarify the micro-crack formation mechanism and influence law of graphite phase in bond area. The results show that unreasonable morphology of flake graphite phase in bond area is an important cause of micro-crack initiation and propagation. Their cusps almost cross toward the molten layer and through the bond area. Then the micro-crack grows along the grain boundary. Additionally, under condition of certain specific energy input, an appropriate increase in laser power and scanning speed can enhance molten mass convection. It can be also helpful for the distribution rationalization of graphite phase and reduce crack sources.

Abstract: Graphite growth morphology was studied by using InLense detector on FEG-SEM after performing ion etching on the samples. Star like and circumferential growth mechanism of graphite was observed in the graphite nodules. Pure ternary alloy of hypo eutectic and hyper eutectic composition was treated with pure Mg, Ca and Sr, to study the effect of O and S concentration in the melt, on the transition of graphite morphology from nodular to vermicular/compacted and flake graphite. The change in the melt composition between the austenite dendrites due to micro-segregation of S, O and inoculants and their possible effects on the transition of graphite morphologies as well as the nucleation of new oxides/sulfides particles is discussed with the help of thermodynamics.

Abstract: The different shot peening responds of a grey cast iron (GI) with its flake graphite and a compacted cast iron (CGI) with its vermicular graphite was analyzed and compared in this paper. For peening using identical parameters, CGI showed a larger plastic deformation zone with higher subsurface compressive stresses than GI. Electron backscatter diffraction (EBSD) mapping and backscatter electron imaging revealed that plastic deformation of the matrix near graphite inclusions is affected by the size and geometry of the graphite. The different behaviors of graphite are explained by their capability to damp mechanical force but at the same time to cause stress concentration in the matrix. The better shot peening results for CGI may be attributed to a lower damping effect of its graphite inclusions and capability of the matrix for larger plastic deformation.

Abstract: In this paper Cr-Mo-Cu alloy cast irons were prepared by adding nano-additives. The finite element of ANSYS was used to simulate the change of the stress field and strain field of Cr-Mo-Cu alloy cast iron with nano-additives under wear abrasion. The changes of shear stress and strain are also discussed in this paper.

Abstract: The finite element method (FEM) was used to simulate the sliding wear progress. The stress field and strain field of Cr-Mo-Cu alloy cast iron with nano-additives under wear abrasion were analyzed through experiment and numerical investigation in this paper. And then the wear depth was got by calculation for different alloy cast irons by taking graphite morphology into account. The graphite morphology was changed by addition of nano-additives, with the aspect ratio of graphite was transformed from 2 to 10, three kinds of graphite aspect ratio prepared including 2, 5 and 10.

Abstract: Spheroidal graphite was obtained by direct quenching iron melt atfter spheroidization and inoculation procedures. The morphology and the effects of trace elements on the formation of spheroidal graphite were investigated by scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy. Results indicate that all the graphite fixed by quenching, is nearly spheroidal with a diameter of approximately 20μm. In addition, the SEM image of graphite morphology confirms the screwed growth model of spheroidal graphite. The linear distribution of trace elements shows that the nucleus of spheroidal graphite consists of antimony, cerium, magnesium and sulfur element. Meanwhile, trace elements, such as antimony, cerium and magnesium, enrich around graphite nodule, which facilitates the formation of spheroidal graphite.

Abstract: Pure carbon, pure iron and single crystall silicon were firstly loaded into a pure graphite crucible to obtain a hypereutectic Fe-C melt by carburizing at high temperatures in this paper. The powder of oxide La₂O₃ and CeO₂ were added respectively to the melt under the same process conditions and cast iron samples were obtained. The graphite morphology of the samples was observed under optical microscope and SEM. Matrix of the samples were etched by electrolysis way. At last non-ferrous residue on the surface of cast iron samples was gathered, calcined,observed under SEI and BEI and analysed with EDS to find the trace of oxide La₂O₃ or CeO₂. The results showed that oxide La₂O₃ or CeO₂ was really added into the melt but the morphology of graphite did not change. The only effect of the oxides was making the amount of graphiteto increase slightly. All the results of this paper indicat that the oxide La₂O₃ or CeO₂ is possibly the base for graphite flake to precipitate but is not a sufficient condition for graphite to nodularize.