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Hernando, J. C. & Diószegi, A. (2018). On the primary solidification of compacted graphite iron: Microstructure evolution during isothermal coarsening. Materials Science Forum, 925, 90-97
Open this publication in new window or tab >>On the primary solidification of compacted graphite iron: Microstructure evolution during isothermal coarsening
2018 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 925, p. 90-97Article in journal (Refereed) Published
Abstract [en]

It is widely accepted that in most commercial hypoeutectic alloys, both static mechanicalproperties and feeding characteristics during solidification, are extremely linked to the coarseness ofthe primary phase. It is therefore of critical importance to provide tools to control and predict thecoarsening process of the dendritic phase present in hypoeutectic melts. The characterization of theprimary phase, a product of the primary solidification, has traditionally been neglected whencompared to the eutectic solidification characterization in cast iron investigations. This workpresents the morphological evolution of the primary austenite present in a hypoeutectic compactedgraphite cast iron (CGI) under isothermal conditions. To that purpose, a base spheroidal graphitecast iron (SGI) material with high Mg content is re-melted in a controlled atmosphere and reversedinto a CGI melt by controlling the Mg fading. An experimental isothermal profile is applied to thesolidification process of the experimental alloy to promote an isothermal coarsening process of theprimary austenite dendrite network during solid and liquid coexistence. Through interruptedsolidification experiments, the primary austenite is preserved and observed at room temperature. Byapplication of stereological relations, the primary phase and its isothermal coarsening process arecharacterized as a function of the coarsening time applied. The microstructural evolution observedin the primary austenite in CGI and the measured morphological parameters show a similar trend tothat observed for lamellar graphite cast iron (LGI) in previous investigations. The modulus of theprimary austenite, Mγ, and the nearest distance between the centre of gravity of neighbouringaustenite particles, Dγ, followed a linear relation with the cube root of coarsening time.

Place, publisher, year, edition, pages
Trans Tech Publications, 2018
Keywords
Primary austenite, Microstructure evolution, Dendritic coarsening, Compacted Graphite Iron, CGI
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-40548 (URN)10.4028/www.scientific.net/MSF.925.90 (DOI)XYZ ()
Available from: 2018-06-19 Created: 2018-06-19 Last updated: 2018-06-19Bibliographically approved
Domeij, B., Hernando, J. C. & Diószegi, A. (2018). Size distribution of graphite nodules in hypereutectic cast irons of varying nodularity. Metallurgical and materials transactions. B, process metallurgy and materials processing science
Open this publication in new window or tab >>Size distribution of graphite nodules in hypereutectic cast irons of varying nodularity
2018 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916Article in journal (Refereed) Epub ahead of print
Abstract [en]

An SGI was machined into 400 g cylindrical pieces and remelted in an electrical resistance furnace protected by Ar gas to produce materials ranging from SGI to CGI. The graphite morphology was controlled by varying the holding time at 1723 K (1450 °C) between 10 and 60 minutes. The discrete sectional size distribution of nodules by number density was measured on cross sections of the specimens and translated to volumetric distribution by volume fraction. Subpopulations of nodules were distinguished by fitting Gaussian distribution functions to the measured distribution. Primary and eutectic graphite, were found to account for most of the volume of nodular graphite in all cases. For holding times of 40 minutes and greater, corresponding to nodularity roughly below 40 pct, the primary subpopulation was very small and difficult to distinguish, leaving eutectic nodules as the dominant subpopulation. The mode and standard deviation of the two subpopulations were roughly independent of nodularity. Moreover, the nodular and vermicular graphite were segregated in the microstructure. In conclusion, the results suggest that the parallel development of the vermicular eutectic had small influence on the size distribution of eutectic graphite nodules.

Place, publisher, year, edition, pages
Springer, 2018
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-35530 (URN)10.1007/s11663-018-1274-z (DOI)XYZ ()2-s2.0-85048767236 (Scopus ID)
Note

Included in licentiate thesis by Björn Domeij (2017), On the solidification of compacted and spheroidal graphite irons, as manuscript.

Available from: 2017-05-16 Created: 2017-05-16 Last updated: 2018-07-03
Domeij, B. & Diószegi, A. (2018). Solidification Chronology of the Metal Matrix and a Study of Conditions for Micropore Formation in Cast Irons Using EPMA and FTA. Materials Science Forum, 925, 436-443
Open this publication in new window or tab >>Solidification Chronology of the Metal Matrix and a Study of Conditions for Micropore Formation in Cast Irons Using EPMA and FTA
2018 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 925, p. 436-443Article in journal (Refereed) Published
Abstract [en]

Microsegregation is intimately coupled with solidification, the development of microstructure, and involved in the formation of various casting defects. This paper demonstrates how the local composition of the metal matrix of graphitic cast irons, measured using quantitative electron microprobe analysis, can be used to determine its solidification chronology. The method is applied in combination with Fourier thermal analysis to investigate the formation of micropores in cast irons with varying proportions of compacted and spheroidal graphite produced by remelting. The results indicate that micropores formed at mass fractions of solid between 0.77 and 0.91, which corresponded to a stage of solidification when the temperature decline of the castings was large and increasing. In 4 out of the 5 castings, pores appear to have formed soon after the rate of solidification and heat dissipation had reached their maximum and were decreasing. While the freezing point depression due to build-up of microsegregation and the transition from compacted to spheroidal type growth of the eutectic both influencing solidification kinetics and the temperature evolution of the casting, the results did not indicate a clear relation to the observed late deceleration of solidification.

Place, publisher, year, edition, pages
Trans Tech Publications, 2018
Keywords
Solidification, Microsegregation, EPMA, Microporosity, Cast Iron
National Category
Materials Engineering
Identifiers
urn:nbn:se:hj:diva-40787 (URN)10.4028/www.scientific.net/MSF.925.436 (DOI)
Available from: 2018-06-25 Created: 2018-06-25 Last updated: 2018-06-25Bibliographically approved
Hellström, K., Diószegi, A. & Diaconu, L. (2017). A broad literature review of density measurements of liquid cast iron. Metals, 7(5), Article ID 165.
Open this publication in new window or tab >>A broad literature review of density measurements of liquid cast iron
2017 (English)In: Metals, ISSN 2075-4701, Vol. 7, no 5, article id 165Article, review/survey (Refereed) Published
Abstract [en]

The literature on density measurements, with a particular interest in methods suitable for liquid cast iron, is reviewed. Different measurement methods based on a number of physical properties are highlighted and compared. Methods for the calculation of density are also reviewed, and the influence of alloying elements on density is, to some extent, discussed. The topic is of essence for the understanding of the material behaviour at solidification, which is pivotal in software applications for casting simulation. Since a deeper understanding of the relationship between the density of liquid cast iron and volume expansion is necessary, the conclusion that further research within the field is needed lies close at hand.

Place, publisher, year, edition, pages
MDPI, 2017
Keywords
Calculation, Density, Experimental methods
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-36608 (URN)10.3390/met7050165 (DOI)000404052600014 ()2-s2.0-85019918559 (Scopus ID)
Funder
VINNOVAKnowledge Foundation
Available from: 2017-07-04 Created: 2017-07-04 Last updated: 2017-11-13Bibliographically approved
Domeij, B. & Diószegi, A. (2017). Inferring the development of microsegregation and microstructure in Spheroidal and Compacted Graphite Iron using EPMA‐WDS. In: Zhongyun Fan (Ed.), Solidification Processing 2017: Proceedings of the 6th Decennial International Conference on Solidification Processing. Paper presented at 6th Decennial International Conference on Solidification Processing, 25th-28th July 2017, Beaumont Estate, Old Windsor, UK (pp. 455-458). Uxbridge: Brunel University (1)
Open this publication in new window or tab >>Inferring the development of microsegregation and microstructure in Spheroidal and Compacted Graphite Iron using EPMA‐WDS
2017 (English)In: Solidification Processing 2017: Proceedings of the 6th Decennial International Conference on Solidification Processing / [ed] Zhongyun Fan, Uxbridge: Brunel University , 2017, no 1, p. 455-458Conference paper, Published paper (Refereed)
Abstract [en]

Microsegregation is closely related to the solidification characteristics and microstructure development of a material. In this paper, the microsegregation of Si, Cu, Mn, and P was investigated on a spheroidal and a compacted graphite iron using a modified EPMA equipped with WDS spectrometers. On the basis of the approximated local equilibrium eutectic temperature, the solidification sequence of the matrix was estimated. The inferred microstructure development appeared to correspond well to published interrupted solidification experimental results. Solute profiles and effective partition coefficients were constructed using the solidification sequence. While the spatial microsegregation patterns clearly differed between the two materials, solute profiles and effective partition coefficients were very similar. For Si, Cu and Mn, the solute profiles corresponded reasonably with simulation results produced using the Scheil-Gulliver module of the Thermo-Calc software with the TCFE7 databank, indicating back-diffusion of these elements is negligible for SGI and CGI with solidification times up to 10 min. The effective partition coefficients for Si, Cu and Mn were fairly constant until about 90% of the matrix had solidified, after which they appeared to approach unity.

Place, publisher, year, edition, pages
Uxbridge: Brunel University, 2017
Keywords
Cast Iron, Microsegregation, Electron microprobe analysis
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-35531 (URN)978-1-908549-29-7 (ISBN)
Conference
6th Decennial International Conference on Solidification Processing, 25th-28th July 2017, Beaumont Estate, Old Windsor, UK
Note

Included in thesis in manuscript form.

Available from: 2017-05-16 Created: 2017-05-16 Last updated: 2018-06-25Bibliographically approved
Svidró, P., Diószegi, A., Pour, M. S. & Jönsson, P. (2017). Investigation of dendrite coarsening in complex shaped lamellar graphite iron castings. Metals, 7(7), Article ID 244.
Open this publication in new window or tab >>Investigation of dendrite coarsening in complex shaped lamellar graphite iron castings
2017 (English)In: Metals, ISSN 2075-4701, Vol. 7, no 7, article id 244Article in journal (Refereed) Published
Abstract [en]

Shrinkage porosity and metal expansion penetration are two casting defects that appear frequently during the production of complex-shaped lamellar graphite iron components. These casting defects are formed during the solidification and usually form in the part of the casting which solidifies last. The position of the area that solidifies last is dependent on the thermal conditions. Test castings with thermal conditions like those existing in a complex-shaped casting were successfully applied to provoke a shrinkage porosity defect and a metal expansion penetration defect. The investigation of the primary dendrite morphology in the defected positions indicates a maximum intradendritic space, where the shrinkage porosity and metal expansion penetration defects appear. Moving away from the defect formation area, the intradendritic space decreases. A comparison of the intradendritic space with the simulated local solidification times indicates a strong relationship, which can be explained by the dynamic coarsening process. More specifically, long local solidification times facilitates the formation of a locally coarsened austenite morphology. This, in turn, enables the formation of a shrinkage porosity or a metal expansion penetration.

Place, publisher, year, edition, pages
MDPI, 2017
Keywords
Coarsening, Dendrite morphology, Lamellar cast iron, Metal expansion penetration (MEP), Primary austenite, Shrinkage porosity (SP)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-37108 (URN)10.3390/met7070244 (DOI)000407365900015 ()2-s2.0-85022339105 (Scopus ID)
Funder
Knowledge Foundation
Available from: 2017-08-31 Created: 2017-08-31 Last updated: 2017-08-31Bibliographically approved
Svidró, J. T., Diószegi, A., Svidró, J. & Ferenczi, T. (2017). The effect of different binder levels on the heat absorption capacity of moulding mixtures made by the phenolic urethane cold-box process. Journal of thermal analysis and calorimetry (Print), 130(3), 1769-1777
Open this publication in new window or tab >>The effect of different binder levels on the heat absorption capacity of moulding mixtures made by the phenolic urethane cold-box process
2017 (English)In: Journal of thermal analysis and calorimetry (Print), ISSN 1388-6150, E-ISSN 1588-2926, Vol. 130, no 3, p. 1769-1777Article in journal (Refereed) Published
Abstract [en]

The phenolic urethane cold-box (PUCB) process was first introduced to the foundry industry in the late 1960s. Since then, it has become one of the most popular methods to make foundry purpose sand moulds and cores, utilized in the manufacturing of aluminium and cast iron cast components. The factors to be considered, affecting the general performance of a PUCB moulding mixture, are the temperature of sand, the moisture content, the mixing conditions, etc. Moreover, there are variable production parameters such as binder level, to improve certain properties of the mould and/or the core based on their specific area of application. These are mainly mechanical properties such as tensile or splitting strength. They have significant influences on the behaviour of the moulding material and are usually tested at room temperature. Although the production phases of the PUCB system are refined to a high extent today, the effect of binder content on the quality of the mould/core and the final casting should be supported by new approaches also in thermal sciences, interpreted in high-temperature environment. In this work, different PUCB mixtures were produced to evaluate the effect of various binder levels on the thermophysical properties of sand cores. Thermogravimetry, differential thermal analysis and a novel application of Fourier thermal analysis were used to study the decomposition processes of the PUCB mixture and to reveal the impact of binder level on the heat absorption (cooling) capacity of sand cores at temperatures relevant in the manufacturing of cast iron parts (1300 ± 10 °C).

Place, publisher, year, edition, pages
Springer, 2017
Keywords
Casting process; TG–DTA; Fourier thermal analysis; Heat absorption; Phenolic urethane resin
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-37099 (URN)10.1007/s10973-017-6611-y (DOI)000415619800056 ()2-s2.0-85028008121 (Scopus ID)JTHMaterialIS (Local ID)JTHMaterialIS (Archive number)JTHMaterialIS (OAI)
Available from: 2017-08-30 Created: 2017-08-30 Last updated: 2017-12-11Bibliographically approved
Svidró, J., Diószegi, A., Tóth, L. & Svidró, J. T. (2017). The influence of thermal expansion of unbonded foundry sands on the deformation of resin bonded cores. Archives of Metallurgy and Materials, 62(2), 795-798
Open this publication in new window or tab >>The influence of thermal expansion of unbonded foundry sands on the deformation of resin bonded cores
2017 (English)In: Archives of Metallurgy and Materials, ISSN 1733-3490, E-ISSN 2300-1909, Vol. 62, no 2, p. 795-798Article in journal (Refereed) Published
Abstract [en]

Depending on the preparation and the applied materials, moulds and cores can be of high rigidity or can be flexible. Although, chemically bonded moulding materials have relatively good flexibility, their high temperature behaviour determines the dimensional accuracy, the stresses in the castings and can induce several casting defects, such as rattail, veining, etc. The phenomenon is based on two major effects: the thermal expansion of the unbonded foundry sands and the deformation of the sand mixtures. The main objective of the present work was to study the relationship between these two effects, and to improve the knowledge related to the thermo-mechanical interactions between the casting and the mould. Dilatometric analysis of unbonded sand samples were performed and compared to the results of hot distortion tests of moulding mixture specimens. The results showed, that the thermal expansion of foundry sand largely influences the hot distortion behaviour, but depending on the type of binder used.

Place, publisher, year, edition, pages
De Gruyter Open, 2017
Keywords
foundry sand, hot distortion, moulding material, phenolic resin, thermal expansion
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-36936 (URN)10.1515/amm-2017-0118 (DOI)000406180900049 ()2-s2.0-85026783797 (Scopus ID)JTHMaterialIS (Local ID)JTHMaterialIS (Archive number)JTHMaterialIS (OAI)
Available from: 2017-08-21 Created: 2017-08-21 Last updated: 2017-08-21Bibliographically approved
Hernando, J. C., Ghassemali, E. & Diószegi, A. (2017). The morphological evolution of primary austenite during isothermal coarsening. Materials Characterization, 131, 492-499
Open this publication in new window or tab >>The morphological evolution of primary austenite during isothermal coarsening
2017 (English)In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 131, p. 492-499Article in journal (Refereed) Published
Abstract [en]

The morphological evolution of primary austenite in an industrial hypoeutectic lamellar cast iron was studied under isothermal conditions for coarsening times varying from 0 min to 96 h. The dendritic austenite structure formed during the primary solidification suffered major morphological changes during the isothermal coarsening process. After a sufficient coarsening time, dendrite fragmentation, globularization, and coalescence of austenite were studied using electron backscatter diffraction (EBSD) technique. This study confirmed that the secondary dendrite arm spacing (SDAS) is an inappropriate length scale to describe the primary austenite coarsening process for longer times. The application of shape independent quantitative parameters confirmed the reduction of the total interfacial area during microstructural coarsening. The modulus of the primary austenite, Mγ, which represents the volume-surface ratio for the austenite phase, and the spatial distribution of the austenite particles, measured as the nearest distance between the center of gravity of neighboring particles, Dγ, followed a linear relation with the cube root of coarsening time during the whole coarsening process. The mean curvature of the austenite interface, characterized through stereological relations, showed a linear relation to Mγ and Dγ, allowing the quantitative characterization and modeling of the complete coarsening process of primary austenite.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Dendrite fragmentation, Dendritic coarsening, EBSD, Microstructure evolution, Primary austenite, Austenite, Cast iron, Isotherms, Microstructure, Dendrite fragmentations, Electron backscatter diffraction technique, Micro-structure evolutions, Microstructural coarsening, Quantitative characterization, Secondary dendrite arm spacing, Coarsening
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-36890 (URN)10.1016/j.matchar.2017.07.030 (DOI)000411535600054 ()2-s2.0-85026387205 (Scopus ID)
Note

Included in licentiate thesis in submitted form.

Available from: 2017-08-16 Created: 2017-08-16 Last updated: 2017-10-19Bibliographically approved
Svidró, J. T., Diószegi, A., Svidró, J. & Ferenczi, T. (2017). Thermophysical aspects of reclaimed moulding sand addition to the epoxy-SO2 coremaking system studied by Fourier thermal analysis. Journal of thermal analysis and calorimetry (Print), 130(3), 1779-1789
Open this publication in new window or tab >>Thermophysical aspects of reclaimed moulding sand addition to the epoxy-SO2 coremaking system studied by Fourier thermal analysis
2017 (English)In: Journal of thermal analysis and calorimetry (Print), ISSN 1388-6150, E-ISSN 1588-2926, Vol. 130, no 3, p. 1779-1789Article in journal (Refereed) Published
Abstract [en]

The most important advantage of foundry purpose moulding sand is that it can be reclaimed and reused through the casting manufacturing process. Supplying the foundry with a new source of material, sand reclamation brings along both environmental and economic advantages. Utilization of used sand can be considered as a common technological routine in the production of most types of chemically bound moulding materials. The epoxy-SO2 process is prevalent in the processing of cast iron engine components worldwide. Based on its excellent properties, it is mainly suitable for producing internal sand cores with complex geometry. Even though reclaimed sand addition is an active and well-functioning feature in ferrous foundries, the scientific and thermophysical background of its effects on the casting process is yet to be explored. In this work, the thermal aspects of different reclaimed sand levels in the epoxy-SO2 moulding system were examined. Thermogravimetry and differential thermal analysis of the epoxy-SO2 and reclaimed sand in focus were carried out to obtain basic understandings about their high-temperature behaviour. A state-of-the-art Fourier thermal analysis method presented in a recent paper was used at temperatures corresponding to actual cast iron production (1300 ± 10 °C), contrary to the previous tests at the typical temperature range of aluminium melt processing (660 ± 10 °C). By the right of the method, the effects of reclaimed sand addition on the heat absorption (cooling) capacity of the epoxy-SO2 moulding mixtures were investigated.

Place, publisher, year, edition, pages
Springer, 2017
Keywords
Cast iron; TG–DTA; Fourier thermal analysis; Epoxy resin; Heat absorption; Reclaimed foundry sand
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-37098 (URN)10.1007/s10973-017-6612-x (DOI)000415619800057 ()2-s2.0-85027969356 (Scopus ID)JTHMaterialIS (Local ID)JTHMaterialIS (Archive number)JTHMaterialIS (OAI)
Available from: 2017-08-30 Created: 2017-08-30 Last updated: 2017-12-11
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