Papers by Keyword: Graphite Morphology

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Authors: Peng Yi, Chang Feng Fan, Peng Yun Xu, Chuan Xiu Li
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.
Authors: Babette Tonn, Jacques Lacaze, Stephanie Duwe
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.
Authors: Martin Selin, Daniel Holmgren, Ingvar L. Svensson
Abstract: Understanding how alloying elements and amounts affect the shape and size of graphite in compacted graphite cast irons could be of great importance. Some important material properties that are affected by the graphite shape are tensile strength and thermal conductivity. Knowing the effect of alloying additions could be of assistance when trying to optimise material for a specific application. In order to determine how graphite changes depending on alloying additions the microstructure of nineteen CGI materials were investigated. All melts were based on one chemical composition and alloying elements were added to obtain melts with variation in magnesium, silicon, copper, tin, chromium and molybdenum. Some of the more important microstructure features that were analysed are the amount and size of different graphite particles. The result from this analysis should give an indication on what features each alloying element affect and how these features varies with alloying amount.
Authors: Suo Mei Zhang, Zi Dong Wang
Abstract: In this paper 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. The powder Ce2S3 was added to the melt with different proportion under the same process conditions and cast iron samples were obtained. The graphite morphology of the samples was observed under optical microscope. Then matrix of the samples was etched by electrolysis way. At last the non-ferrous residue gathered from the surface of cast iron sample after electrolysis process was calcined and analysed with BEI and EDS to find the trace of Ce2S3. The results showed that the powder Ce2S3 was really added into the melt but did not make any change in graphite morphology.The only effect of Ce2S3 was to make the amount of graphite increase slightly.All results of this paper indicat that the additive Ce2S3 is only the base for graphite flake to precipitate but is not a sufficient condition for graphite to nodularize.
Authors: Xin Zhao, Xiao Ling Yang
Abstract: Gray iron was hot-compressed on a Gleeble 3500 machine. The effect of hot compression on mechanical properties of gray iron was studied. The result shows that gray iron with the sandwich structure of graphite and ferrite matrix is prepared after more than 45% reduction of hot compression. The mechanical properties of 80% hot-compressed gray iron are significantly enhanced: tensile strength from 117MPa to 249MPa, and total elongation from 0 to 5.2%. The tensile fracture surface presents ductility characters after more than 45% reduction of hot deformation. The increase of the strength and ductility of the hot-compressed gray iron is caused by delamination toughening.
Authors: Suo Mei Zhang, Zi Dong Wang
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.
Authors: Zhen Hua Li, Yan Xiang Li
Abstract: In order to clarify the effect of antimony on graphite morphology and mechanical properties in heavy section ductile iron, experiments were carried out using a newly developed thermal simulation system. Results show that with 0.011% addition of antimony, tensile strength of heavy section ductile iron are obviously improved by elimination of graphite degeneration in it, and the effect of antimony is increased when the addition is increased to 0.02%. In the range of 0.01~0.04%, antimony is beneficial to graphite morphology and tensile strength although the advantageous effect on them become not so obvious when addition is exceed 0.02%.
Authors: Qin Xin Ren, Ming You, Yun Bang Yao, Guang Min Wen, Qi Zhou Cai
Abstract: Ductile iron specimens with dimensions of 400mm×400mm ×450mm were prepared by treating the melt with an yttrium-containing nodulizer. The effect of yttrium on microstructure and mechanical properties was investigated, and the formation of degenerate graphite was discussed as well. The results show that the yttrium-containing nodulizer has good nodulization fading resistance for heavy section ductile iron, since the high melting point hexagonal oxide Y2O3 particles were formed from the nodulizer in the melt and those could act as heterogeneous nuclei for graphite nodule for a long time. Segregation of Ti and MgO at grain boundaries broke the austenite shell, resulting in graphite degeneration. When heavy section ductile iron castings with pearlite matrix were cast, graphite nodule size became finer and the nodularity of graphite nodules improved due to the addition of 0.01wt% Sb to the melt, and pearlite content in specimens increased due to alloying with Cu, Cr, Mo. The heavy section ductile iron tool bed was fabricated by treating the melt with the yttrium-containing nodulizer and Ni. The nodularity of the attached block was 85%~90%, tensile strength, elongation and impact toughness were 440MPa, 23.3% and 5.0J/cm2 respectively.
Authors: Xiao Gang Diao, Zhi Liang Ning, Fu Yang Cao, Shan Zhi Ren, Jian Fei Sun
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.
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