| 1. |
- Svidró, Peter, et al.
(author)
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Characterization of primary dendrite morphology in complex shaped lamellar cast iron castings
- 2014
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In: The 10<sup>th</sup> International Symposium on the Science and Processing of Cast Iron, SPCI10, November, 2014, Mar del Plata, Argentina. - : The Institute for Research in Materials Science and Technology (INTEMA). ; , s. 1-7
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Conference paper (peer-reviewed)abstract
- Shrinkage porosity and metal expansion penetration are two fundamental defects appearing during the production of complex shaped lamellar cast iron components. Simplified test models simulating the thermal and geometrical conditions existing in complex shaped castings have been successfully used to provoke shrinkage porosity and metal expansion penetration. A stereological investigation of the primary dendrite morphology indicates a maximum intra-dendritic space in connection with the casting surface where the porosity and the penetration defects appear. Away from the defect formation area the intra-dendritic space decreases. Comparison of the simulated local solidification times and measured intra-dendritic space indicates a strong relation which can be explained by the dynamic ripening process. The slow local solidification time situated at the boundary between the casting surface and its surrounding is explained to be the reason for the formation of an austenite morphology which can promote mass flow between dendrites, thereby provoking shrinkage porosity or metal expansion penetration.
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| 2. |
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| 3. |
- Diaconu, Lucian Vasile, et al.
(author)
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Influence of molybdenum alloying on thermomechanical fatigue life of compacted graphite irons
- 2012
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In: International Journal of Cast Metals Research. - : Maney Publishing. - 1364-0461 .- 1743-1336. ; 25:5, s. 277-286
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Journal article (peer-reviewed)abstract
- In this study four compacted graphite irons (CGIs) and one grey cast iron (FGI) were produced and tested in the laboratory. The molybdenum content of the four CGI grades was varied between 0 and 1·01 wt-%. The purpose of the investigations was to examine the effect of the different molybdenum contents of the CGI on the thermomechanical fatigue (TMF) behaviour. The TMF tests were performed by cycling a constrained specimen between 110 and 600°C. For every material three tests were performed on specimens machined from a Ø20 mm cylinder. Other tests were performed on specimens machined from Ø55 mm and Ø85 mm cylinders respectively. The tests showed that additions of molybdenum improved the fatigue resistance of CGI. It was observed that additions of molybdenum refined the pearlite and that the specimens with a finer metallic matrix had a higher TMF resistance.
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| 4. |
- Diaconu, Lucian Vasile, et al.
(author)
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Stress relaxation of compacted graphite iron alloyed with molybdenum
- 2013
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In: International Journal of Cast Metals Research. - : Taylor & Francis. - 1364-0461 .- 1743-1336. ; 26:1, s. 51-57
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Journal article (peer-reviewed)abstract
- In a previous study, the thermomechanical fatigue resistance of four compacted graphite irons (CGIs) and one grey cast iron was investigated. The molybdenum content of the four CGIs varied between 0 and 1.01 wt-%. It was observed that during thermal cycling, the maximum value of the compressive stress continuously decreased while the value of the maximum tensile stress continuously increased. The continuous decrease in compressive stresses showed that stress relaxation occurs at elevated temperatures during thermal cycling. The goal of the present investigation was to investigate the phenomenon of stress relaxation at elevated temperatures. The tests were performed at 350 and 600uC respectively. The results of the stress relaxation tests performed at 600uC showed the same trend observed at thermomechanical fatigue testing. The tests showed that additions of molybdenum improved the fatigue resistance of CGI by lowering the stress relaxation rate.
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| 5. |
- Diószegi, Attila, 1962-, et al.
(author)
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Austenite Dendrite Morphology in Lamellar Cast Iron
- 2014
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In: The 10<sup>th</sup> International Symposium on the Science and Processing of Cast Iron, SPCI10, November, Mar del Plata, Argentina, 2014. - : The Institute for Research in Materials Science and Technology (INTEMA).
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Conference paper (peer-reviewed)abstract
- Primary austenite has been underestimated in general when the theories of nucleation, solidification, microstructure formation and mechanical properties was established for cast iron and particularly for lamellar cast iron. After extensive use of colour etching during the last two decades it has been found that primary austenite dendrites can be characterized using general morphology parameters like those used for other technical cast alloys with dendritic structure. The present work aims to investigate the primary austenite morphology of as-cast samples of a hypoeutectic lamellar cast iron produced with different cooling rates. Morphological parameters as the area fraction primary austenite, the secondary dendrite arm spacing, the dendrite envelope surface, the coarseness of the primary dendrite expressed as the relation between the volume of the dendrite and its envelope surface and the coarseness of the interdendritic space also known as the hydraulic diameter are measured. Furthermore the role of the size of investigation area is revealed be sequential investigation. A strong relation between all measured morphological parameters and the solidification time have been established excepting the volume fraction of primary austenite which is constant for all cooling conditions.
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| 6. |
- Diószegi, Attila, 1962-, et al.
(author)
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Dynamic Coarsening of Austenite Dendrite in Lamellar Cast Iron Part 1 – Investigation based on interrupted solidification
- 2014
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In: Materials Science Forum. - : Trans Tech Publications. - 0255-5476 .- 1662-9752. ; 790-791, s. 205-210, s. 205-210
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Journal article (peer-reviewed)abstract
- Dynamic coarsening of austenite dendrite in lamellar cast iron has been studied for a hypoeutectic alloy. The common morphological parameter to characterize dynamic coarsening, secondary dendrite arm space has been replaced by the Modulus of primary dendrite (MPD) and the Hydraulic diameter of the interdendritic space (DHydIP) to interpret the dynamic coarsening with respect to the local solidification time. The obtained results demonstrate the coarsening process of both the solid and liquid phase. The interdendritic space is increasing as the contact time between the solid and liquid phase increases. The ratio between the DHydIP/MPD is strongly dependent on the precipitated fraction primary austenite indicating clearly the morphology variation during coarsening. The interrupted solidification method demonstrate that the observed coarsening process is not only a combination of the increasing fraction precipitated solid phase and the rearrangement of the solid - liquid interphase curvature but the volume change due to density variation is also contribute to the coarsening process.
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| 7. |
- Elmquist, Lennart, et al.
(author)
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On the Formation of Shrinkage Porosity in Gray Iron Castings
- 2011
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In: Key Engineering Materials. - : Trans Tech Publications. - 1013-9826 .- 1662-9795. ; 457, s. 416-421
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Journal article (peer-reviewed)abstract
- The formation of shrinkage porosity is a concern in the production of high-quality gray iron castings. In this work, a geometry known to generate this type of defect was used to investigate some of the parameters that influence its formation. The geometry is based on the presence of a migrating hot spot that at the end of the solidification is located close to the interface between the casting and the mold. The occurrence of shrinkage porosity at this position was investigated and the cavities examined using a scanning electron microscope equipped with EDS. It is believed that this type of defect is in contact with the atmosphere during solidification. The risk for shrinkage porosity decreases with increasing carbon content. The effect of high levels of molybdenum and phosphorus was investigated and shown to influence the defect formation. Inoculation is used to control the nucleation and the effect of high levels of inoculants was also examined. The microstructure was investigated by the use of a color etching technique, and the quantification considered eutectic cell size and secondary dendrite arm spacing. The quantification was done on the microstructure in the vicinity of defects as well as in areas without porosity.
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| 8. |
- Fourlakidis, Vasilios, et al.
(author)
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A generic model to predict the ultimate tensile strength in pearlitic lamellar graphite iron
- 2014
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In: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 618, s. 161-167
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Journal article (peer-reviewed)abstract
- Varying the carbon contents, chemical composition and solidification rate greatly influences the microstructural morphology in lamellar graphite iron resulting in large variations in material properties. Traditionally, ultimate tensile strength (UTS) is used as the main property for the characterisation of lamellar graphite iron alloys under static loads. The main models found in the literature for predicting UTS of pearlitic lamellar graphite iron are based on either regression analysis on experimental data or on modified Griffith or Hall-Petch equation.In pearlitic lamellar graphite iron the primary austenite transformed to pearlite reinforces the bulk material while the graphite flakes which are embedded in an iron matrix reduce the strength of the material. Nevertheless a dominant parameter which can be used to define the tensile strength is the characteristic distance between the pearlite grains defined as the maximum continuous defect size in the bulk material, which in this work is expressed by the newly introduced parameter the Diameter of Interdendritic Space. The model presented here covers the whole spectrum of carbon content from eutectic to hypoeutectic composition, solidified at different cooling rates typical for both thin and thick walled complex shaped castings.
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| 9. |
- Fourlakidis, Vasilios, et al.
(author)
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Dynamic Coarsening of Austenite Dendrite in Lamellar Cast Iron Part 2 – The influence of carbon composition
- 2014
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In: Materials Science Forum. - : Trans Tech Publications. - 0255-5476 .- 1662-9752. ; 790-791, s. 211-216, s. 211-216
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Journal article (peer-reviewed)abstract
- Investigation of dynamic coarsening in lamellar cast iron is extended over a wide interval ranging from hypoeutectic to eutectic composition. The dendrite morphology is defined on as-cast samples produced under various cooling rates. The as-cast morphology is considered being close to the one at the end of solidification. The obtained relations describing the coarsening process as a function of local solidification time and fraction austenite are compared to results obtained from interrupted solidification experiments. By using the Modulus of primary dendrite (MPD) and the Hydraulic diameter of the interdendritic space (DHyd IP) become possible to characterize the coarseness of a wide range of lamellar cast irons solidified under various cooling rates.
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| 10. |
- Fourlakidis, Vasilios, et al.
(author)
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Non-metallic inclusions in lamellar graphite iron
- 2014
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In: Proceedings of the 10<sup>th</sup> International Symposium on the Science and Processing of Cast Iron, SPCI10, November, 2014, Mar del Plata, Argentina. - : The Institute for Research in Materials Science and Technology (INTEMA).
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Conference paper (peer-reviewed)abstract
- Cast iron melts with two different carbon contents were used in this experiment. Quenched chill coins were extracted directly from the melting furnace and the size, the number and the composition of the non-metallic inclusions was examined using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and an automate inclusions analysis system (EDAX). Large number of non-metallic inclusions was found in the chilled samples. Most of these inclusions are compounds of MnS with other elements. The number of the detected inclusions was found to increase with decreasing quenching temperature, while the number of large inclusions increases with the increase of the quenching temperature. This work provides supplementary data that helps a better understanding of the dependency between solidification rates, carbon composition, eutectic cells size, and constitutional undercooling in lamellar graphite iron.
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| 11. |
- Lora, Ruben, et al.
(author)
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Solidification Study of Gray Cast Iron in a Resistance Furnace
- 2011
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In: Key Engineering Materials. - : Trans Tech Publications. - 1013-9826. ; 457, s. 108-113
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Journal article (peer-reviewed)abstract
- Solidification of hypoeutectic gray cast iron has been investigated in a resistance furnace. A cylindrical shaped sample with three thermocouples, two inside and one in the surrounding, was solidified and compared to samples quenched at different stages during the solidification interval. An additional sample in the series has been produced to reveal the primary grain structure using Direct Austempering After Solidification (DAAS) treatment. The present paper collect for the first time under the same experimental procedure the solidification of a hypoeutectic gray cast iron where both the growth of the primary and eutectic phase are observed. An increase of the secondary dendrite arm spacing (SDAS) was observed until the end of the solidification interval. A comparison of the measured solidified fractions of the phases with those predicted using Fourier Thermal Analyses evidenced the quenching effectiveness. The eutectic cell size is in agreement with the literature. The method presents good consistency.
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| 12. |
- Svidró, József Tamás, et al.
(author)
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The novel application of Fourier thermal analysis in foundry technologies
- 2014
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In: Journal of thermal analysis and calorimetry (Print). - : Springer Science and Business Media LLC. - 1388-6150 .- 1588-2926. ; 115:1, s. 331-338
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Journal article (peer-reviewed)abstract
- The process of casting in sand moulds is used for a large volume of castings manufactured in the world. Internal channels and complex geometries of these products are formed by the placement of cores within the mould cavity. Resin-bound sand mixtures are essential ingredients in engine component manufacturing. In this study, a state-of-the-art application of Fourier thermal analysis in foundry technologies is presented. Investigation of decomposition phenomena of resin-bound moulding materials during casting production is a brand new area to use the potential of thermal sciences. Temperature measurements in test samples of standard types of moulding mixtures were performed. The registered cooling curves were processed by a numerical iteration algorithm to determine the amount of heat absorbed during degradation of the moulding material. Thermogravimetric analysis (TG) and differential thermal analysis (DTA) of sand mixtures were carried out to compare the results of the Fourier thermal analysis with TG and DTA curves.
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| 13. |
- Svidró, Péter, 1980-, et al.
(author)
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Determination of the columnar to equiaxed transition in hypoeutectic lamellar cast iron
- 2014
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In: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 54:2, s. 460-465
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Journal article (peer-reviewed)abstract
- Shrinkage porosity as a volume change related casting defect in lamellar cast iron was reported in theliterature to form during solidification in connection to the dendrite coherency. The present work includesan experimental study on dendrite coherency – also called columnar-to-equiaxed transition in lamellar castiron using thermal analysis and expansion force measurements. Investigation was carried out in order tostudy the mechanism of dendrite coherency formation. Cylindrical test bars were cast from the same alloywith different pouring temperature, amount of inoculant and time between the addition of inoculant andstart of pouring the samples. Cooling rate and expansion force was recorded as a function of time. Anumerical algorithm based on temperature differences measured under solidification was used to inter-pret the solidification process. Three different methods have been compared to determine the columnarto equiaxed transition. The compared methods were based on registered temperature differences, basedon registered expansion forces during the volume change of the solidifying samples and based on the cal-culated released latent heat of crystallization. The obtained results indicate a considerable influence on theformation and progress of coherency due to variation of casting parameters. It has been shown that thecoherency is not a single event at a defined time moment rather a process progressing during a timeinterval.
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| 14. |
- Svidró, Péter, 1980-, et al.
(author)
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Investigation of cooling rate dependent dendrite morphology in hypoeutectic lamellar cast iron
- 2013
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Reports (other academic/artistic)abstract
- Shrinkage porosity and metal expansion penetration are two fundamental defects appearing at production ofcomplex shaped lamellar cast iron components. In previous work it has been shown that both shrinkageporosity and metal expansion penetration are related to the primary austenite dendrite network and itsformation mechanisms. The purpose of the present work is to study the morphology of primary austenite intest casting with a high tendency to form shrinkage porosity and metal expansion penetration. Simplified testmodels simulating the thermal and geometrical conditions similar to the conditions existing in complex shapedcasting have been successfully used to provoke shrinkage porosity and metal expansion penetration.Stereological investigation of the primary dendrite morphology indicates a maximum interdendritic space inconnection to the casting surface where the porosity and the penetration defect appear. Away from the defectformation area the interdendritic space decreases. Furthermore the local solidification times of the investigatedsamples were calculated in a 3D simulation software. Comparison of the simulated local solidification timesand measured interdendritic space indicates a strong relation of the same shape as it is known from theliterature when dynamic coarsening mechanism is characterized. The main outcome of the present paper is theobserved gradient of increasing interdendritic space from sections with high local solidification to sectionswith low solidification time. The mechanism of increasing the interdendritic phase can be explained by thedynamic ripening process. The unfortunate thermal conditions with the slowest local solidification timesituated in the border between the casting surface and its surrounding are considered the reason to form anaustenite morphology which can promote the mass flow between dendrite provoking shrinkage porosity ormetal expansion penetration.
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| 15. |
- Svidró, Peter, et al.
(author)
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On problems of volume change measurements in lamellar cast iron
- 2014
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In: International Journal of Cast Metals Research. - 1364-0461 .- 1743-1336. ; 27:1, s. 26-37
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Journal article (peer-reviewed)abstract
- Solidification of lamellar cast iron is a complex mechanism due to the contracting austenite phase and the expanding graphite phase precipitation. The combined effect of contraction–expansion has an influence on the volume change related defects (shrinkage porosity and penetration). Critical moments in measuring volume change are the methods used for measurement together with the interpretation of the solidification based on the macrostructure. Reliable results are obtained using displacement measurement in both axial and radial direction of a cylindrical sample in combination with using two thermocouples and a force measurement unit. Common drawback of the used method together with other methods presented in the literature is the early expansion observed before the coherence of the solidifying grains. The introduced force measurement gives a novel interpretation of the columnar to equiaxed transition, and the displacement measurement in different directions within a cast sample reveal the anisotropic character of the volume change.
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| 16. |
- Vazehrad, Sadaf, et al.
(author)
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On factors influencing macro shrinkage porosity formation in compacted graphite iron
- 2014
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In: Solidification and Gravity VI. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. - 9783038350934 ; , s. 429-434
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Conference paper (peer-reviewed)abstract
- The purpose of this work is to investigate the relation between macro shrinkage porosity level and the level of graphite nodularity, gaseous elements and the size of eutectic colonies in compacted graphite iron. Also, the internal shrinkage-pore surfaces were analyzed by SEM and EDS techniques. It was found that samples with higher shrinkage porosity level, contained higher level of graphite nodularity and number of eutectic colonies. Also, samples with higher level of gaseous elements (Hydrogen and Nitrogen) showed higher tendency to shrinkage porosity formation. Austenite dendrites with different morphologies were observed inside the pores, indicating that were formed at different times during solidification, and the surface of the pores were covered with a layer of carbon film indicating that the pores were internal, with no contact to the atmosphere at elevated temperatures.
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