| 1. |
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| 2. |
- Belov, Ilja, et al.
(författare)
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A thermal conductivity model for grey iron
- 2023
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Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193.
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Tidskriftsartikel (refereegranskat)abstract
- Thermal conductivity is an important property for many iron cast components, and the lack of widely accepted thermal conductivity model for cast iron, especially grey cast iron, motivates the efforts in this research area. The present study contributes to understanding the effects alloy microstructure has on thermal conductivity. A thermal conductivity model for a pearlitic cast iron has been proposed, based on the as-cast alloy composition and microstructural parameters obtained at different solidification rates. According to the model, available parallel heat transfer paths formed by connected graphite flakes across eutectic cells are determined by the space between dendrite arms. The uncertainties both for model inputs and for validation measurements have been estimated. Sensitivity analysis has been conducted to result in better understanding of the model behaviour. The agreement between modelled and measured thermal conductivities has been achieved within 5% on the average for the investigated samples.
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| 3. |
- Belov, Ilja, et al.
(författare)
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A thermal conductivity model for lamellar and compacted graphite irons
- 2024
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Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193.
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Tidskriftsartikel (refereegranskat)abstract
- Thermal conductivity is an important property for cast components produced from different types of cast iron. Development of a general widely-accepted thermal conductivity model for compacted and lamellar graphite irons poses a research challenge. The present study extends the modeling approach introduced earlier for pearlitic lamellar graphite iron toward compacted graphite iron and ferritic lamellar graphite iron. The proposed thermal conductivity model of the bulk material is based on the alloy microstructure and Si segregation between eutectic cells and non-cell regions, at the main assumption that the heat paths in the eutectic cells are formed by connected graphite phases surrounded by ferrite phases. The overall thermal resistance of these heat paths is determined by the hydraulic diameter of the interdendritic region. The uncertainties both for the modeled and for experimentally derived thermal conductivities have been estimated. The importance of considering the Si segregation in the model has been discussed. For the investigated samples, the agreement between modeled and measured thermal conductivities has been achieved within 4% on the average, at the same value of the single fitting parameter found for pearlitic, pearlitic–ferritic lamellar, and compacted graphite iron alloys. The results contribute to the understanding of the material microstructure effects on the cast iron thermal conductivity.
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| 4. |
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| 5. |
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| 6. |
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| 7. |
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| 8. |
- Domeij, Björn, 1988-, et al.
(författare)
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A review of dendritic austenite in cast irons
- 2024
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Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193.
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Forskningsöversikt (refereegranskat)abstract
- Solidification of cast irons usually involves dendritic growth of austenite. This article presents a literature survey about the dendrites in cast irons, their consequences and how they may be manipulated. The literature review is supplemented with relevant micrographs from our research. While austenite usually transforms into ferrite or pearlite, the dendrites limit where liquid flows, where eutectic grows, and where segregated elements go. The amount and shape of dendrites show correlations with tensile strength in pearlitic gray and compacted graphite irons. There are also indications that a coarse dendrite grain structure may be beneficial to tensile strength. The dendrite grain structure depends on melting process parameters and shows sensitivity to melt treatment. The evolution of scale of dendrite arms and their spacing under isothermal condition is by now fairly well-understood; however, work remains to better understand its evolution during cooling and its interaction with the eutectic. The amount and shape of dendrites are less understood in irons of near-eutectic and hypereutectic composition, in particular mixtures of dendrites of distinct scales, associated with regions of distinct graphite morphology. While significant advances have been made in recent years, the role and control of dendrites remain a relatively unexplored area of research with potential to improve production and properties of cast irons.
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| 9. |
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| 10. |
- Domeij, Björn, 1988-, et al.
(författare)
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Evolution of Dendritic Austenite in Parallel With Eutectic in Compacted Graphite Iron Under Three Cooling Conditions
- 2023
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Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science. - : Springer. - 1073-5615 .- 1543-1916. ; 54, s. 2395-2410
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Tidskriftsartikel (refereegranskat)abstract
- Shrinkage defects are common problems in industrially produced metal cast components. Local density changes occur during freezing, which demand material transport between parts of the casting, often involving flow of liquid through partially solid regions. Cast alloys typically freeze with a dendritic morphology, which large interface against the liquid restricts liquid flow. Recent research also indicates that this dendritic structure has an impact on the mechanical properties of the final material. For these reasons it is important to understand and predict the evolution of this structure through the solidification of cast alloys. In this work, the evolution of the dendritic austenite structure is investigated in a near-eutectic compacted graphite iron solidified under three different cooling conditions. The solidification was interrupted by water quenching, enabling characterization of the dendritic austenite structure at different stages of solidification. Higher cooling rate was found to promote a more coherent dendritic austenite structure which constituted a larger volume fraction. In parallel with growth of the eutectic, the amount of dendritic austenite in extra-eutectic regions continued to rise. This rise was associated with both tip growth of new dendrites and with growth by thickening of existing dendrites.
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| 11. |
- Domeij, Björn, 1988-, et al.
(författare)
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Implementation and Validation of Casting Simulation Methodology for Diagnostics of Lamellar Graphite Iron
- 2023
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Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193. ; 17, s. 1507-1517
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes and validates a methodology for implementation of full-scale sand-casting simulation in a general-purpose finite element software, including mold filling, heat transport, solidification kinetics, chemical microsegregation and prediction of microstructure and material properties. The solidification model, customized for gray cast iron, includes novel methods for handling interaction between parallel dendritic and eutectic solidification modes and its impact of their interaction on the final microstructure. The validation involves a previously published gray iron casting experiment and involves comparison of simulated and experimental cooling curves, microstructure parameters and tensile strength. We believe that this is valuable to researchers and engineers seeking to improve the state of the art of casting simulation tools.
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| 12. |
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| 13. |
- Domeij, Björn, 1988-, et al.
(författare)
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Relationships between macrostructure and microstructure in lamellar graphite iron castings
- 2024
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Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193.
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Tidskriftsartikel (refereegranskat)abstract
- Spherical sheet steel molds filled with gray iron melts of varying chemical compositions and metallurgical conditions were air-cooled until solid, followed directly by austempering to preserve the austenite grain structure. The castings were studied using a combination of cooling curves and quantitative metallography, in order to clarify control of the austenite grain structure and its impact on the local microstructure. A novel method utilizing fast Fourier transform provided visual overview of macroscopic trends in the scale of the flake graphite structure. Castings inoculated with Sr-containing ferrosilicon featured finer eutectic cell structure but coarser equiaxed structure of austenite, emphasizing that melt treatments applied to control the graphite structure may have unintended effects on the austenite grain structure. In most non-inoculated castings, the microstructure was banded, with alternating layers of coarse and fine flake graphite with distance from the casting surface. The extent of the columnar zone of austenite grains showed no correlation with the graphite structure nor the volume fraction of dendrites. The volume-to-surface ratio of dendrites was more uniform in the columnar zone, but increased toward the center in the equiaxed zone. The casting with the highest carbon equivalent (4.34), featured zones containing finer dendrites and graphite. These zones appear to be gaps in the early solidification structure which filled later by secondary dendritic growth from surrounding austenite. This highlights that high carbon equivalent may lead to poor dendrite coherency which can make the microstructure less uniform and less predictable.
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| 14. |
- Domeij, Björn, 1988-, et al.
(författare)
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The Distribution of Carbon in Austenite Studied on a Water-Quenched Compacted Graphite Iron Using Electron Probe Microanalysis
- 2020
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Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193. ; 14, s. 782-793
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Tidskriftsartikel (refereegranskat)abstract
- Spheroidal graphite is the defining microstructural feature of ductile iron and also plays an important role in compacted graphite iron. It is widely accepted that graphite spheroids are engulfed by austenite at an early stage of solidification after which their growth is impeded by the slow diffusion of carbon through a layer of austenite. In this work, a compacted graphite iron-containing spheroidal graphite was studied after interruption of its solidification by water quenching. Selected areas of a cross section of the castings were investigated using quantitative electron probe microanalysis, with emphasis on the distribution of carbon in austenite. The measured carbon concentration near graphite was generally below the theoretical carbon concentration in austenite at equilibrium with graphite at 1140 °C. Numerical simulations of diffusion of carbon in austenite around spheroidal graphite suggest that a zone of austenite around graphite was likely depleted of carbon during quenching, possibly explaining the low measured concentrations. The measured carbon concentration near graphite varied by as much as 0.3 wt%, with the lowest concentrations consistently found in the central region of compacted graphite–austenite eutectic cells. Regardless of whether these differences were present prior to quenching or are consequences thereof, they seem to reflect either departures from, or displacements of, the carbon concentration in austenite at equilibrium with graphite. This indicates that there is something about growth of graphite embedded in austenite which is not well understood. Concentrations of Si, Mn and Cu are near equal in the compared regions and do not explain the observed differences in carbon content near graphite.
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| 15. |
- Fourlakidis, Vasilios, et al.
(författare)
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Fatigue limit and microstructure in lamellar graphite iron
- 2021
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Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 802
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Tidskriftsartikel (refereegranskat)abstract
- Demanding environmental legislation and improve performance specifications requires increasing fatigue strength for the engine components that are made of lamellar graphite iron (LGI). Components design, metallurgy and casting conditions define the microstructure formation and mechanical properties. The graphite inclusions embedded in the metallic matrix acting as defects and have a detrimental effect on the fatigue strength of LGI. The cooling conditions determine the coarseness of the microstructure and also have, a great impact on the fatigue resistance. The experimental material was an LGI alloy produced with three different solidification times. A fully reversed fatigue test was performed, and various microstructure features were quantitatively estimated by utilizing the Gumbel's statistics of extremes. The stereological parameter of Hydraulic Diameter of the Inter-dendritic Phase and the graphite Feret size found to be the most suitable microstructure parameters to be correlated with the fatigue limit. The results also indicate the sizeable effect of the solidification time on the fatigue limit. Several other microstructure features that have been reported to influence the tensile strength were also found to be related to the fatigue limit. The obtained endurance ratio ranges from 0.25 to 0.30, a value that is in line with previous investigations.
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| 16. |
- Fourlakidis, Vasilios, et al.
(författare)
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Primary Austenite Morphology and Tensile Strength in CGI for Different C Contents, Cooling Conditions and Nodularity
- 2023
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Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193.
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Tidskriftsartikel (refereegranskat)abstract
- Compacted graphite iron (CGI) is a good option for the blocks and cylinder heads in heavy duty engines due to their well-balanced thermal and mechanical properties. In this work, a remelting technique has been utilized for the production of CGI with different nodularity (10 and 20%), C contents (CE=3.5, 3.8, 4.2) and under different solidification and cooling rates. The employed experimental parameters had a sizeable influence on the morphology and fraction of the inter-dendritic structure and resulted in ultimate tensile strength (UTS) that ranged from 335 to 456 MPa and 371 to 521 MPa for the 10 and 20% nodularity, respectively. The results show that the UTS is linearly related to the solidification time and the microstructural parameter that express the scale length of the inter-dendritic region. Different CE and nodularity provide different relationships between UTS, solidification time and microstructure. Finally, an empirical model has been developed for the prediction of the UTS.
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| 17. |
- Fourlakidis, Vasilios, et al.
(författare)
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Relationship Between Thermal Conductivity and Tensile Strength in Cast Irons
- 2023
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Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193. ; 17, s. 2862-2867
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Tidskriftsartikel (refereegranskat)abstract
- Improved mechanical and thermal properties are important characteristics for enhancing the performance of cast iron components that operate at elevated temperatures. Thermal conductivity defines the temperature distribution within the casting and influences the magnitude of the thermally induced tensile stresses. The microstructural features that increase the thermal conductivity have a negative impact on tensile strength. The results reported in this work show that there is a unique inverse relationship between thermal conductivity and tensile strength, valid for the whole range of cast iron alloys regardless of graphite form, solidification rates, carbon content and matrix constituents. The finding indicates the challenges for the simultaneous improvement of these properties, and it can be utilized as a guideline during the design of cast iron components for high temperature applications.
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| 18. |
- Hellström, Kristina, et al.
(författare)
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Density and thermal expansion coefficients of liquid and austenite phase in lamellar cast iron
- 2020
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Ingår i: China Foundry. - : Springer. - 1672-6421 .- 2365-9459. ; 17:2, s. 127-136
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Tidskriftsartikel (refereegranskat)abstract
- Volume change related defects formation mechanisms are an important detracting phenomenon in production of complex shaped cast components. Among different technical alloys, cast iron behaves in a complex manner due to the combined volume change of the formed phases. The liquid and the austenitic phase are contracting while the graphite phase is expanding during the solidification. The complex volume change in combination with complex casting shapes causes a considerable deviation from isotropy in the solidification domain. The mentioned difficulties are considered the main reason why an extensive research work is condensed in the literature within this topic. The multitude of reported experimental set up and the various efforts to interpret the volume change phenomena in terms of density and thermal expansion coefficients makes the results difficult to compare from different sources. With these difficulties in mind, the present paper presents a broad experimental series and measures unidirectional linear deformation of an industrially spread lamellar cast iron alloy system (Fe-C-2Si) using the push-rod based dilatometer technique. The measurements are divided into two major groups with respect to the liquid iron deformation over the liquidus temperature line, and the austenite deformation below the solidus temperature line. The obtained results are interpreted as thermal expansion coefficients, density variation slopes, and density data at the liquids and solidus temperature. The obtained results are compared with literature data and with calculated values by the Thermo Calc software.
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| 19. |
- Hernando, Juan Carlos, et al.
(författare)
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The role of primary austenite morphology in hypoeutectic compacted graphite iron alloys
- 2020
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Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193. ; 14:3, s. 745-754
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Tidskriftsartikel (refereegranskat)abstract
- This work investigates the role of primary austenite morphology on the eutectic and eutectoid microstructures and the ultimate tensile strength (UTS) in a hypoeutectic compacted graphite iron (CGI) alloy. The morphology of primary austenite is modified by isothermal coarsening experiments in which holding times up to 60 min are applied to the solid–liquid region after coherency. The cooling conditions for the subsequent eutectic and eutectoid reactions are similar. Miniaturized tensile tests are performed to evaluate the UTS. The morphological characteristics related to the surface area of primary austenite, the modulus of primary austenite, Mγ, and the hydraulic diameter of the interdendritic region, DHydID, increase with the cube root of coarsening time. The eutectic and eutectoid microstructures are not significantly affected by the morphology of primary austenite, thus indicating that the morphology of the interdendritic regions does not control the nucleation frequency and growth of eutectic cells or graphite. UTS decreases linearly with the increasing coarseness of primary austenite for similar eutectic and eutectoid microstructures, demonstrating the strong influence of primary austenite morphology on the UTS in hypoeutectic CGI alloys.
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| 20. |
- Matsushita, Taishi, et al.
(författare)
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A model for the effect of microstructure on the ultimate tensile strength of cast irons
- 2024
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Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193.
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the present study is to elucidate the influence of individual microstructural parameters, such as pearlite fraction, nodularity, and eutectic cell size, on the tensile strength (UTS) of cast irons. The UTS model was built by integrating the rule of mixtures for each microstructural component, and the UTS was described as a function of the aforementioned factors. The UTS and the required microstructure parameters for the model calculation were obtained experimentally. In the model, two coefficients were introduced to quantify the influence of the eutectic cell size and the interaction terms for the mixed two components. These coefficients were determined through fitting the experimental data, and the model's accuracy was validated using data not included in the fitting process. The results exhibited reasonable agreement, confirming the model's reliability. The model, thus, offers insights into the influence of each microstructural factor on UTS and serves as a guide for designing alloys to achieve the desired UTS through microstructure modifications.
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| 21. |
- Matsushita, Taishi, et al.
(författare)
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Analysis of the penetration behavior of molten cast iron into the sand mold
- 2023
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Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193.
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Tidskriftsartikel (refereegranskat)abstract
- An evaluation method for the initial penetration of molten cast iron into the sand mold was suggested based on the laboratory-scale penetration experiments for the cast iron. The horizontal penetration depth of the molten cast iron into the sand core was analyzed using the capillary model. The early stage of the penetration was discussed, and it was clarified that the penetration is not stopped by the solidification but is stopped by the decreasing of the equivalent pore radius. It was explained that the equivalent pore radius decreases with increasing the penetration depth, and the penetration is stopped when the critical pressure, i.e., the pressure required for the penetration, becomes higher than the pressure which is acting on the penetration front. Based on the analysis, an evaluation method of the penetration of depth at the early stage of the penetration was suggested. The analysis method was applied for the other type of metals (mercury and steel) as well, and reasonable results were obtained. A simplified finite-element model of liquid iron penetration into a sand core was developed, accounting for heat exchange between the melt and the porous medium, at different pore geometries.
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| 22. |
- Matsushita, Taishi, et al.
(författare)
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Kinetic model for the decomposition rate of the binder in a foundry sand application
- 2024
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Ingår i: Archives of Foundry Engineering. - : Polish Academy of Sciences. - 1897-3310 .- 2299-2944.
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Tidskriftsartikel (refereegranskat)abstract
- Accurate kinetic parameters are vital for quantifying the effect of binder decomposition on the complex phenomena occurring during the casting process. Commercial casting simulation tools often use simplified kinetic parameters that do not comprise the complex multiple reactions and their effect on gas generation in the sand core. The present work uses experimental thermal analysis techniques such as Thermogravimetry (TG) and Differential thermal analysis (DTA) to determine the kinetic parameters via approximating the entire reaction during the decomposition by multiple first-order apparent reactions. The TG and DTA results reveal a multi-stage and exothermic decomposition process in the binder degradation. The pressure build-up in cores/molds when using the obtained multi-reaction kinetic model is compared with the earlier approach of using an average model. The results indicate that pressure in the mold/core with the multi-reaction approach is estimated to be significantly higher. These results underscore the importance of precise kinetic parameters for simulating binder decomposition in casting processes.
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| 23. |
- Matsushita, Taishi, et al.
(författare)
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Thermodynamic discussion on the influence of the magnesium addition and temperature on the oxygen potential in the cast irons
- 2024
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Ingår i: Steel Research International. - : John Wiley & Sons. - 1611-3683 .- 1869-344X.
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Tidskriftsartikel (refereegranskat)abstract
- The primary objective of this study is to explore the impact of temperature and magnesium addition on the partial oxygen potential in lamellar, compacted, and spheroidal cast irons during the cooling process. The oxygen potential is assessed in large-scale plant trials with a 1000 kg scale. Thermodynamic calculations are conducted, and the results are compared with the experimental values. There is a reasonable agreement between the experimental and calculated values, facilitating the prediction of oxygen potential in temperature ranges where measurements are challenging. According to the thermodynamic calculations, it is observed that varying amounts of added magnesium result in the formation of different types of inclusions during cooling. This, in turn, influences the temperature dependency of the oxygen potential in the molten metal.
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| 24. |
- Queirós, Ricardo, et al.
(författare)
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Unraveling compacted and nodular cast iron porosity : Case studies approach
- 2024
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Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193. ; 18, s. 1811-1830
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Tidskriftsartikel (refereegranskat)abstract
- Porosity is the culprit for a large fraction of scrap in cast iron foundries, resulting in significant environmental and productivity losses. The present work focuses on characterizing and explaining porosity defects in industrial compacted and nodular graphite cast iron components, utilizing current literature for reference. The goal is to identify existing knowledge gaps in the field, fostering further research work. Complex-shaped castings were sampled from three foundries, weighing between 100 and 300 kg. These were carefully selected to capture recurring defects during stable production. The mechanisms behind these defects were discussed, and the findings were compared to the literature. Scanning electron microscopy (SEM) was used to investigate the inner surfaces of the pores with secondary electron imaging. The surrounding microstructure was captured with optical microscopy in combination with image analysis, where panoramic images and nodularity maps were built. Ultimately, etching based on Si segregation was employed. The results suggest that the understanding of pore surface film formation remains limited, particularly regarding graphite film formation. Notably, the observations reveal a multitude of previously unreported graphite structures within the pores, some with particles in their centers containing Ce, Ca, La and S. These novel structures can provide additional insights regarding pore formation chronology.
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| 25. |
- Ramos, A. K., et al.
(författare)
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Microstructure of compacted graphite iron near critical shrinkage areas in cylinder blocks
- 2020
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Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193. ; 14:3, s. 736-744
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Tidskriftsartikel (refereegranskat)abstract
- To study the microstructure of CGI near areas prone to shrinkage, a special sample was developed that resembles critical areas in cylinder blocks. Foundry trials were conducted with different magnesium contents and inoculation amounts. Using color etching techniques to follow the solidification sequence, four areas were observed with different macrostructure: (i) direct chill and columnar region near the surface; (ii) small eutectic cells and small intercellular space; (iii) large eutectic cells and large intercellular space; and (iv) eutectic cells with carbides in the last to freeze area. By increasing the amount of inoculation, the size of the eutectic cells in the zone with large eutectic cells (iii) is reduced, and the eutectic cells are now smaller and more evenly distributed through the section. Increasing the magnesium content brings a similar effect. In zone (iv), the samples with less inverse chill formation show smaller shrinkage porosities, which are located in the same regions where the inverse chill are, between the eutectic cells, in the last to freeze areas; they also have higher amounts of spheroidal graphite in the last-to-freeze areas. The amount of inverse chill carbides observed in zone (iv) did not present any clear relation with inoculation levels or magnesium content variations used in the experiments.
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| 26. |
- Sundaram, Dinesh, et al.
(författare)
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A Novel Approach to Quantifying the Effect of the Density of Sand Cores on Their Gas Permeability
- 2022
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Ingår i: Journal of Casting & Materials Engineering. - : AGH University of Science and Technology. - 2543-9901. ; 6:2, s. 33-38
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Tidskriftsartikel (refereegranskat)abstract
- The density of moulding mixtures used in the foundry industry plays a significant role since it influences the strength, porosity, and permeability of moulds and cores. The latter is routinely tested in foundries using different solutions to control the properties of the moulding materials that are used to make moulds and cores. In this paper, the gas permeability of sand samples was measured using a custom-made setup to obtain the gas permeability in standard units instead of the usual permeability numbers (PN) with calibrated units. The aim of the work was to explore the effect of density variations in moulding materials on their gas permeabilities. Permeability in this work is quantified in SI units, square metres [m<sup>2</sup>]. The setup works based on Darcy’s law and the numbers obtained from the measurements can be used to deduce the gas permeability, <em>k</em>, of a sample. Two furan resin bonded mixtures with the same grain size distribution were hand-rammed with varying compaction forces to obtain a variation in density. Cylindrical samples (50 × 50 mm) were prepared using a silica sand aggregate sourced from a Swedish lake. The results of the measurement provided the difference in gas permeability between the samples that have varying densities. The results of permeability were then extrapolated by modifying the viscosity value of the air passed through the sample. In order to find the effect of apparent density variation on the pore characteristics of the samples, mercury intrusion porosimetry (MIP) was also performed. The results were in line with the gas permeability measurements.
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| 27. |
- Sundaram, Dinesh, et al.
(författare)
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Evaluation of permeability models for foundry molds and cores in sand casting processes
- 2024
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Ingår i: Archives of Foundry Engineering. - : The Katowice Branch of the Polish Academy of Sciences. - 1897-3310 .- 2299-2944. ; 24:1, s. 94-106
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Tidskriftsartikel (refereegranskat)abstract
- Predicting the permeability of different regions of foundry cores and molds with complex geometries will help control the regional outgassing, enabling better defect prediction in castings. In this work, foundry cores prepared with different bulk properties were characterized using X-ray microtomography, and the obtained images were analyzed to study all relevant grain and pore parameters, including but not limited to the specific surface area, specific internal volume, and tortuosity. The obtained microstructural parameters were incorporated into prevalent models used to predict the fluid flow through porous media, and their accuracy is compared with respect to experimentally measured permeability. The original Kozeny model was identified as the most suitable model to predict the permeability of sand molds. Although the model predicts permeability well, the input parameters are laborious to measure. Hence, a methodology for replacing the pore diameter and tortuosity with simple process parameters is proposed. This modified version of the original Kozeny model helps predict permeability of foundry molds and cores at different regions resulting in better defect prediction and eventual scrap reduction.
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| 28. |
- Sundaram, Dinesh
(författare)
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Gas evolution and transport in foundry sands
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sand-casting is one of the most widely used cost-effective manufacturing techniques to produce metal components for various industries. Constantly evolving environmental regulations have increased the necessity for circular and sustainable manufacturing practices. During the casting process, the mold and core undergo a thermal shock when they come in contact with the molten metal. This triggers a severe reaction due to the evaporation of volatiles and the decomposition of chemical binders. This phenomenon can cause defects such as blow-holes and pinholes, leading to increased scrap. The heat removed from the solidifying melt due to these generated gases also affects the cast component by influencing the mechanical properties. From an ecological perspective, some of the gases generated from the decomposing binders have been identified as environmentally hazardous. Studying the gas generation and transport phenomena during the sand-casting process becomes essential in this context.In this work, the phenomena that affect heat and mass transport due to the generated gases are studied with the help of newly developed experimental techniques in combination with porous material characterization tools. Combining the experimental data with thermal analysis techniques, a computational model for the heat and mass transport in the foundry core is also developed.The permeability of the molds and cores plays a significant role in determining how efficiently these gases are transported. The permeability and gas volume affect the pressure build-up and defect formation mechanisms of the mold and core. Traditional measurement methods used for determining permeability are not scientifically comparable, nor can they be used for computing the flow characteristics of the molds and cores. In this work, a custom-made measurement setup to measure the permeability of molds and cores is presented. Using the setup, the effect of variation in the grain size distribution and the density on the permeability is quantified. The results show that density affects the permeability more than the grain size distribution. The samples investigated were also characterized using mercury intrusion porosimetry and X-ray microtomography to study the pore characteristics and pore network of the samples. The existing models to predict permeability were evaluated using experimentally measured values and the obtained pore characteristics. The most suitable model to predict the permeability of foundry cores was identified. The identified model was modified to be able to predict permeability using process parameters.The gas generation rate and volume vary depending on the production parameters of the molds and cores. Commercially available simulation tools often use simplified models for binder decomposition and gas generation, resulting in reduced accuracy in predicting phenomena pertaining to the sand-casting processes. In this work, a novel method to quantify the gases generated from foundry sand mixtures where the core/mold is subjected to conditions similar to the actual casting process is presented. Along with accurate gas volume data, simultaneous temperature measurements in the central and lateral parts of the sample enabled accurate estimation of the heat absorption characteristics associated with the binder decomposition and the gas generation.Additionally, thermogravimetry analysis was performed for the Furan binder with several heating rates to study the decomposition characteristics and kinetics. Several possible reactions were identified, and the kinetic parameters for each identified reaction during binder decomposition were computed using the integral method. Using the obtained gas transport properties and the kinetic parameters of the binder decomposition and assuming a local thermal non-equilibrium model for heat transport in the porous material, a computational model was developed for the gas generation and transport process in foundry sand cores/molds. The developed model has been validated to a certain extent based on the experimentally obtained gas volume data. The results of the simulation show that the developed model accurately predicts the rate and volume of gases generated and the pressure build-up in the cores.
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| 29. |
- Sundaram, Dinesh, et al.
(författare)
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Measurement of Darcian Permeability of foundry sand mixtures
- 2021
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Ingår i: International Journal of Cast Metals Research. - : Taylor & Francis. - 1364-0461 .- 1743-1336. ; 34:2, s. 97-103
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Tidskriftsartikel (refereegranskat)abstract
- Gas permeability of moulds and cores is an important factor to consider in the casting process. In foundries, gas permeability is measured by using instruments which give dimensionless numbers. This approach enables the comparison of values between samples and is often not quantified in units. In this study, a custom-made measurement system is introduced that applies Darcy?s law, where pressure gradients for different flow rates are studied. The Darcian permeability in standard cylindrical samples was determined using a method that is familiar with those in earth sciences. Two types, steady-state and unsteady-state approaches were used for the calculations, and the difference in permeability values generated by these two methods is discussed. The results of a silica sand sample with furan resin and a 3D-printed sample that consists of artificial granulous material with phenolic resin were compared.
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| 30. |
- Sundaram, Dinesh, et al.
(författare)
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On the relation between the gas-permeability and the pore characteristics of furan sand
- 2021
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Ingår i: Materials. - : MDPI. - 1996-1944. ; 14:14
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Tidskriftsartikel (refereegranskat)abstract
- Furan sand is one of the most commonly used chemically bonded molding materials in foundries across the world. It consists of a furfuryl alcohol-based resin and an acid-based liquid catalyst. When the molding material comes in contact with the molten metal, it undergoes a thermal shock accompanied by a certain release of volatile gases. In order to evacuate these gases, molds and cores should have optimal gas permeability values and proper venting by design. If the volatile compounds are not appropriately evacuated, they are prone to enter the melt before the first layer of solidified metal is formed which can lead to the formation of gas-related casting defects. Standard gas permeability measurements are commercially available tools used in the industry to compare and to quality control different sands, however, they only provide reference numbers without actual units. Permeability in a standard unit, m2, provides uniformity and helps the comparison of results from difference sources. In this paper, a new method using Darcy’s law (prevalent in earth sciences), was adapted to measure the gas-permeability of furan samples made of silica sand with various grain size distributions. The effect of grain size distribution on the gas-permeability of furan sand samples was studied. Gas-permeability values in m2 were then correlated with mercury-porosity measurement results to bring new light on the relation between pore size, pore volume and the permeability of molding materials.
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| 31. |
- Sundaram, Dinesh, et al.
(författare)
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Thermal analysis and gas generation measurement of foundry sand mixtures
- 2024
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Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193.
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Tidskriftsartikel (refereegranskat)abstract
- Gas generation from molding materials creates a complex atmosphere in the mold–metal interface and is one of the primary causes of defects in cast components. Moisture, crystalline water, and decomposing binders are significant gas sources. The presence of volatiles and decomposing binder in the mold also affects the rate of heat absorption from the solidifying metal during the casting process. This work presents a measurement methodology to evaluate the rate and volume of gases generated from sand mixtures in combination with the temperature distribution and applied thermal analysis. The presented results show high reproducibility of the method. The thermal analysis results provide the start and end temperature of the binder decomposition reactions and the corresponding heat absorbed in this interval. The results obtained from the presented methodology can be used to validate the models/simulation tools developed to predict the gas evolution and related transport phenomena in the sand casting process.
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| 32. |
- Svidró, Judit, et al.
(författare)
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The origin of thermal expansion differences in various size fractions of silica sand
- 2020
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Ingår i: International Journal of Cast Metals Research. - : Taylor & Francis. - 1364-0461 .- 1743-1336. ; 33:6, s. 242-249
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Tidskriftsartikel (refereegranskat)abstract
- In this study, thermophysical properties of a commonly used silica sand were investigated and their relation to its granulometric and chemical composition was studied. Thermal expansion and differential scanning calorimetry tests were performed on individual fractions of the silica sand together with X-ray fluorescence measurements to determine their constituents. It was found that the various size fractions of silica sand exhibit different levels of thermal expansion based on the differences in SiO2 content. The expansion behaviour of two additional silica samples and a recycled olivine sand was also investigated in relation to its grain size to justify the findings.
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| 33. |
- Svidró, Judit, et al.
(författare)
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The role of purity level in foundry silica sand on its thermal properties
- 2020
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Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP).
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Konferensbidrag (refereegranskat)abstract
- Silica sand is the most commonly used mineral for molding and core making applications in foundry technology due to its availability, thermal and chemical attributes. However, there are many additional requirements foundry sands need to meet regarding their sizing, chemical purity, physical durability and thermal properties. This research studies the thermophysical properties of a foundry silica sand comprehensively. After separating one sand batch into numerous grain size ranges, the chemical composition and thermophysical properties of the fractions were investigated, respectively. By means of this approach, the chemical properties and thermal behavior can be directly linked. The silicon dioxide content shows a strong correlation with the thermal expansion properties of the various fractions. The results give a better understanding of the high temperature behavior of foundry silica sands and clarify the role of factors affecting their thermophysical properties.
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| 34. |
- Tan, He, et al.
(författare)
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Data-driven modeling of mechanical properties of cast iron using fuzzy logic
- 2020
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Ingår i: Fuzzy Systems and Data Mining VI. - Amsterdam : IOS Press. - 9781643681344 - 9781643681351 ; , s. 656-662
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Konferensbidrag (refereegranskat)abstract
- For many industries, an understanding of the fatigue behavior of cast iron is important but this topic is still under extensive research in materials science. This paper offers fuzzy logic as a data-driven approach to address the challenge of predicting casting performance. However, data scarcity is an issue when applying a data-driven approach in this field; the presented study tackled this problem. Four fuzzy logic systems were constructed and compared in the study, two based solely upon experimental data and the others combining the same experimental data with data drawn from relevant literature. The study showed that the latter demonstrated a higher accuracy for the prediction of the ultimate tensile strength for cast iron.
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