The Experts below are selected from a list of 1836 Experts worldwide ranked by ideXlab platform
Edward Tyrala - One of the best experts on this subject based on the ideXlab platform.
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effect of cooling rate on microstructure and mechanical properties of thin walled ductile iron castings
Journal of Materials Engineering and Performance, 2013Co-Authors: M Gorny, Edward TyralaAbstract:This article addresses the effect of cooling rate on microstructure and mechanical properties as determined by changing molding media and section size. The research was conducted for thin-walled iron castings with 2-5-mm wall thickness and for the reference casting with 13-mm wall thickness, using different molding materials (silica sand and insulating sand “LDASC”) to achieve various cooling rates. Thermal analysis was performed to determine the real cooling rate at the beginning of the Graphite eutectic solidification. In general, it was found that the predictions based on theoretical analysis of the solidification process of ductile iron are in good agreement with the experimental outcomes. Finally, the present study provides insights into the effect of cooling rate on the Graphite Nodule count, the ferrite fraction and mechanical properties of thin-walled ductile iron castings. The study shows that the cooling rate of thin-walled castings varies in a wide range (80-15 °C/s) when changing the wall thickness from 2 to 5 mm, accompanied by significantly changing the mechanical properties of ductile iron. The cooling rate can be effectively reduced by applying an insulating sand to obtain the desired properties of thin-walled castings practically in the whole range of ductile iron grades in accordance with the ASTM Standard.
Niels Skat Tiedje - One of the best experts on this subject based on the ideXlab platform.
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Analysis of Local Conditions on Graphite Growth and Shape During Solidification of Ductile Cast Iron
Transactions of the Indian Institute of Metals, 2018Co-Authors: Niels Skat Tiedje, M.a. Azeem, Mathias Karsten Bjerre, Jesper H. HattelAbstract:3D X-ray tomography recordings have been used to study Graphite growth during solidification of ductile cast iron. Using data from such recordings, it is shown how local growth conditions influence growth rate and morphology of Nodules during solidification. Experiments show that it is common for Nodules to gradually change shape during solidification so that sphericity decreases. It is also found that different shaped Nodules can evolve in direct contact with liquid iron and also after they are encapsulated in austenite. It is observed that a significant proportion of originally complete spherical Nodules become less spherical via formation of protrusions on the surface; these new surfaces are observed to grow relatively faster. It is shown that encapsulation of the Graphite Nodule by austenite may be incomplete and that at the end of solidification, partial encapsulation and the effect of the number of nearest Graphite Nodules play a crucial role in determining the final Graphite morphology.
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Synchrotron quantification of Graphite Nodule evolution during the solidification of cast iron
Acta Materialia, 2018Co-Authors: M.a. Azeem, Mathias Karsten Bjerre, Robert C. Atwood, Niels Skat Tiedje, Peter D. LeeAbstract:Abstract In cast iron, Graphite develops in conjunction with the metallic matrix during solidification. The morphology and distribution of the embedded Graphite is pivotal for mechanical properties from yield strength to fatigue. A novel high temperature environmental cell was developed and combined with in situ synchrotron tomography to investigate and quantify microstructural evolution, including Graphite Nodule nucleation and growth rates in ductile cast iron. The mechanisms of degenerate Graphite Nodule formation were also revealed. The formation of a coherent primary gamma phase dendritic network before the Graphite nucleation is demonstrated. The Graphite Nodule nucleation rate, mobility and growth rates are compared to classical models, highlighting the limitations in these models. The results provide unique insights to tune the temperature pathways during cast iron solidification to achieve desired uniform rounded Graphite morphologies and size distributions.
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Modeling of damage in ductile cast iron - The effect of including plasticity in the Graphite Nodules
IOP Conference Series: Materials Science and Engineering, 2015Co-Authors: Tito Andriollo, Niels Skat Tiedje, Jesper Thorborg, Jesper H. HattelAbstract:In the present paper a micro-mechanical model for investigating the stress-strain relation of ductile cast iron subjected to simple loading conditions is presented. The model is based on a unit cell containing a single spherical Graphite Nodule embedded in a uniform ferritic matrix, under the assumption of infinitesimal strains and plane-stress conditions. Despite the latter being a limitation with respect to full 3D models, it allows a direct comparison with experimental investigations of damage evolution on the surface of ductile cast iron components, where the stress state is biaxial in nature. In contrast to previous works on the subject, the material behaviour in both matrix and Nodule is assumed to be elasto-plastic, described by the classical J2-flow theory of plasticity, and damage evolution in the matrix is taken into account via Lemaitre's isotropic model. The effects of residual stresses due to the cooling process during manufacturing are also considered. Numerical solutions are obtained using an in-house developed finite element code; proper comparison with literature in the field is given.
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Graphite Nodule count and size distribution in thin walled ductile cast iron
Materials Characterization, 2008Co-Authors: Karl Pedersen, Niels Skat TiedjeAbstract:Abstract Graphite Nodule count and size distribution have been analysed in thin-walled ductile cast iron. The 2-D Nodule counts have been converted into 3-D Nodule counts by using a finite difference method (FDM). Particles having a diameter smaller than 5 μm should be neglected in the Nodule count as these are inclusions and microporosities that do not influence the solidification morphology. If there are many small Graphite Nodules, as in thin-walled castings, only 3-D Nodule counts calculated by FDM will give reliable results. 2-D Nodule counts and 3-D Nodule counts calculated by simple equations will give low results. The 3-D size distribution showed the presence of primary Graphite Nodules in hypereutectic castings. In thin plates the Nodule count is similar in both eutectic and hypereutectic plates. In thicker plates the hypereutectic casting has the higher Nodule count.
M Gorny - One of the best experts on this subject based on the ideXlab platform.
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effect of cooling rate on microstructure and mechanical properties of thin walled ductile iron castings
Journal of Materials Engineering and Performance, 2013Co-Authors: M Gorny, Edward TyralaAbstract:This article addresses the effect of cooling rate on microstructure and mechanical properties as determined by changing molding media and section size. The research was conducted for thin-walled iron castings with 2-5-mm wall thickness and for the reference casting with 13-mm wall thickness, using different molding materials (silica sand and insulating sand “LDASC”) to achieve various cooling rates. Thermal analysis was performed to determine the real cooling rate at the beginning of the Graphite eutectic solidification. In general, it was found that the predictions based on theoretical analysis of the solidification process of ductile iron are in good agreement with the experimental outcomes. Finally, the present study provides insights into the effect of cooling rate on the Graphite Nodule count, the ferrite fraction and mechanical properties of thin-walled ductile iron castings. The study shows that the cooling rate of thin-walled castings varies in a wide range (80-15 °C/s) when changing the wall thickness from 2 to 5 mm, accompanied by significantly changing the mechanical properties of ductile iron. The cooling rate can be effectively reduced by applying an insulating sand to obtain the desired properties of thin-walled castings practically in the whole range of ductile iron grades in accordance with the ASTM Standard.
Pradeep K. Rohatgi - One of the best experts on this subject based on the ideXlab platform.
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Effect of rare earth element on microstructure formation and mechanical properties of thin wall ductile iron castings
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2004Co-Authors: J.o. Choi, C.o. Choi, Pradeep K. RohatgiAbstract:Abstract Ductile iron castings with 2, 3, 4, 6, 8, and 25 mm thickness and various amount of rare earth elements (RE) (from 0 to 0.04%), were cast in sand molds to identify the effects of sample thickness and the content of RE% on microstructural formation and selected mechanical properties. The effects of RE content and sample thickness on microstructural formation, including on Graphite Nodule count, Graphite Nodule shape, spherodization, and ferrite amount, were observed. The yield strength of the samples with RE within the range investigated were lower than those of the specimens without RE. The elongation was improved with the addition of RE up to 0.03% in ductile iron castings. The additions of 0.02% RE caused a smaller Graphite Nodule size and a higher number of Graphite Nodules than those in the specimen without RE at all levels of RE addition; the Nodule count decreased with increase in section size. The chill zones were observed in the 2 mm thick samples, but were absent in the samples from castings which were thicker than 2 mm, irrespective of the addition of RE. The nodularity of Graphite Nodules improved due to the addition of 0.02–0.04% RE. The specimens with RE content up to 0.03% had a lower tensile strength and hardness, higher elongation than that of the specimens without RE. The ferrite content in all castings increased with additions of 0.02% RE. The tensile strengths of the 2 and 3 mm thick samples were also estimated using the relationship between strength and hardness, obtained from the data on the tensile strength and hardness of the 25 mm thick samples.
Simon N. Lekakh - One of the best experts on this subject based on the ideXlab platform.
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Formation of complex nuclei in Graphite Nodules of cast iron
Carbon, 2021Co-Authors: Jingjing Qing, Simon N. Lekakh, Daniel M. FieldAbstract:Abstract The complex nature of nodular Graphite nuclei was studied in a partially solidified and quenched spheroidal Graphite iron (SGI) that contained small Graphite Nodules. The reduced Graphite to nuclei diameter ratio obtained by the accelerated solidification process increased the probability of nuclei exposure during metallographic cross sectioning. Ten thousand Graphite Nodules were analyzed to identify nucleation sites using an automated scanning electron microscopy-energy dispersive X-ray (SEM-EDX) system and the resultant ternary plot presents a chemistry of oxides, sulfides and nitrides located inside the Graphite Nodules. Focused ion beam milling was used to extract thin foil specimens and extensive high-resolution transmission electron microscopy (TEM) analysis of several representative nuclei was conducted. The nucleus of a Graphite Nodule was composed of a Mg–O core with Mg–Ca–S and Mg–Al–Si–N compounds attached on its sides. The crystallographic orientation relationships between different nucleating compounds and between Graphite and nucleating compounds were analyzed using selected area diffraction patterns. For the first time, the direct observation of the nuclei interfaces revealed the presence of nano-structured boundary layers. The formation of a complex nodular Graphite nucleus was thermodynamically simulated and the nucleation behavior of the complex compound was linked to the novel experimental results.
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Searching for Graphite Nodule Nuclei Using Automated SEM/EDX Analysis
International Journal of Metalcasting, 2020Co-Authors: Simon N. LekakhAbstract:Nonmetallic inclusions play a vital role for Graphite Nodule nucleation in cast iron with spheroidal Graphite (SGI). Therefore, knowledge about composition of heterogeneous nuclei is practically important and can be used to control solidification in SGI castings. Thermodynamic simulations were performed to predict types of nonmetallic precipitates formed in the entire SGI processing, including melt nodularization and inoculation as well as followed melt cooling and casting solidification. To verify simulation results, the experimental SGI heats were performed with variations in nodularization and inoculation practices. Two types of specimens were collected. The first one was direct-quenched from the inoculated melt, and the second one was taken from the castings. An automated SEM/EDX inclusion analysis was used for evaluation of families of nonmetallic inclusions located in the matrix and inside Graphite Nodules. Nucleation activity of different precipitates was determined from the partitioning of active elements (Mg, Al, Si, Ca, Ce, La, Ti, Zr) between the Graphite nuclei and the matrix. Simulation and experimental data were used to discuss a nucleation mechanism of Graphite Nodules in inoculated SGI. Engineering of nonmetallic inclusions can be used to control SGI solidification.
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searching for Graphite Nodule nuclei using automated sem edx analysis
International Journal of Metalcasting, 2020Co-Authors: Simon N. LekakhAbstract:Nonmetallic inclusions play a vital role for Graphite Nodule nucleation in cast iron with spheroidal Graphite (SGI). Therefore, knowledge about composition of heterogeneous nuclei is practically important and can be used to control solidification in SGI castings. Thermodynamic simulations were performed to predict types of nonmetallic precipitates formed in the entire SGI processing, including melt nodularization and inoculation as well as followed melt cooling and casting solidification. To verify simulation results, the experimental SGI heats were performed with variations in nodularization and inoculation practices. Two types of specimens were collected. The first one was direct-quenched from the inoculated melt, and the second one was taken from the castings. An automated SEM/EDX inclusion analysis was used for evaluation of families of nonmetallic inclusions located in the matrix and inside Graphite Nodules. Nucleation activity of different precipitates was determined from the partitioning of active elements (Mg, Al, Si, Ca, Ce, La, Ti, Zr) between the Graphite nuclei and the matrix. Simulation and experimental data were used to discuss a nucleation mechanism of Graphite Nodules in inoculated SGI. Engineering of nonmetallic inclusions can be used to control SGI solidification.
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Effect of Nonmetallic Inclusions on Solidification of Inoculated Spheroidal Graphite Iron
International Journal of Metalcasting, 2019Co-Authors: Simon N. LekakhAbstract:Inoculation treatment of spheroidal Graphite cast iron (SGI) controls Graphite Nodule heterogeneous nucleation and is used for elimination of solidification microporosity and improvement in casting performance. In this study, thermodynamic simulations were performed to predict precipitates formed in the inoculated melt above a liquidus temperature (primary precipitates) and during solidification (secondary precipitates). The experimental inoculation treatments were designed targeting formation of primary precipitates (Ti and Zr additions) and secondary precipitates (S and N additions to inoculant). An automated SEM/EDX analysis was applied to analyze the Graphite Nodule distribution statistics and a family of nonmetallic inclusions in the experimental castings. In inoculated SGI, the observed bimodal distributions of Graphite Nodules were related to continuous nucleation with the second nucleation wave that occurred toward the solidification end. The measured microporosity in the castings was linked to Graphite nucleation. The origin of the continuous Graphite Nodule nucleation and the possibility of engineering nonmetallic inclusions to control casting soundness are discussed.
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Solidification Kinetics of Graphite Nodules in Cast Iron and Shrinkage Porosity
International Journal of Metalcasting, 2016Co-Authors: Simon N. Lekakh, Brenton HrebecAbstract:The shrinkage porosity of castings made from cast iron with spherical Graphite (SGI) depends on a combination of intrinsic (density and volume of phases, solidification kinetics) and extrinsic conditions related to casting-mold thermo-mechanical interactions. Precipitation of Graphite Nodules increases the specific SGI volume, and control of the nucleation rate in solidified castings can be used for improving casting soundness. In this article, the method of structural reconstruction of solidification kinetics was used to link the nucleation rate of Graphite Nodules to experimentally observed shrinkage porosity in a specially designed test casting. An automated SEM/EDX system was used to determine the “true” two-dimensional Graphite Nodule distributions in the casting sections. These two-dimensional distributions were converted into the volume particle distribution functions ( PDF ), and the solidification kinetics were reconstructed by applying inverse simulations. The experiments were performed with variations in inoculation and pouring temperature. The shrinkage porosity was compared to the restored sequence of Graphite Nodule nucleation in the specific casting volumes. It is shown that the second nucleation wave in low-temperature poured and inoculated SGI eliminated interdendritic microporosity. The suggested method could be used in industry to improve the soundness of SGI castings.
