| 1. |
- Diószegi, Attila, 1962-, et al.
(författare)
-
Defect formation mechanisms in lamellar cast iron related to the casting geometry
- 2015
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Ingår i: Advances in the science and engineering of casting solidification. - Hoboken, NJ : John Wiley & Sons. - 9781119082385 - 9781119093367 ; , s. 251-259
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Konferensbidrag (refereegranskat)abstract
- Although lamellar cast iron has been used in advanced applications for about twenty years, our knowledge about the mechanisms affecting microstructure and defect formation is relatively limited. The present paper summarizes some solidification related phenomena from a series of recently published peer reviewed papers and scientific theses and suggests a mechanism of defect formation which is dependent on the shape of the solidifying casting geometry. When shrinkage porosity or metal expansion penetration occurs evidence of material transport in the intergranular zone of primary equiaxed austenite grains in the casting and in the intergranular regions between the sand grains in the mold material is seen. Material transport occurs across the casting-mold interface where the existence of or the permeability of the primary columnar zone determines if material transport can take place.
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| 2. |
- Diószegi, Attila, 1962-, et al.
(författare)
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Modelling and simulation of heat conduction in 1-D polar spherical coordinates using control volume-based finite difference method
- 2016
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Ingår i: International journal of numerical methods for heat & fluid flow. - 0961-5539 .- 1758-6585. ; 26:1, s. 2-17
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Tidskriftsartikel (refereegranskat)abstract
- Purpose - The purpose of this paper is to obtain a finite difference method (FDM) solution using control volume for heat transport by conduction and the heat absorption by the enthalpy model in the sand mixture used in casting manufacturing processes. A mixture of sand and different chemicals (binders) is used as moulding materials in the casting processes. The presence of various compounds in the system improve the complexity of the heat transport due to the heat absorption as the binders are decomposing and transformed into gaseous products due to significant heat shock. Design/methodology/approach - The geometrical domain were defined in a 1D polar coordinate system and adapted for numerical simulation according to the control volume-based FDM. The simulation results were validated by comparison to the temperature measurements under laboratory conditions as the sand mould mixture was heated by interacting with a liquid alloy. Findings - Results of validation and simulation methods were about high correspondence, the numerical method presented in this paper is accurate and has significant potential in the simulation of casting processes. Originality/value - Both numerical solution (definition of geometrical domain in 1D polar coordinate system) and verification method presented in this paper are state-of-the-art in their kinds and present high scientific value especially regarding to the topic of numerical modelling of heat flow and foundry technology.
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| 3. |
- Diószegi, Attila, 1962-, et al.
(författare)
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Shrinkage porosity formation in cast iron components
- 2018
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Ingår i: 73rd World Foundry Congress "Creative Foundry", WFC 2018 - Proceedings. - : Stowarzyszenie Techniczne Odlewnikow Polskich/Polish Foundrymen's Association. - 9788390430638 ; , s. 207-208
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Konferensbidrag (refereegranskat)abstract
- Shrinkage porosity formation mechanisms at production of cast iron components is particularly complex and became more and more difficult to understand since the shape casting complexity have been increased more and more in advanced component applications. The present work intends to summarize the state of the art in understanding the shrinkage porosity formation mechanism of cast iron based on a series of key publications, MSc and PhD theses performed in collaboration between cast iron component users, producers and researchers.
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| 4. |
- Svidró, Peter, et al.
(författare)
-
Characterization of primary dendrite morphology in complex shaped lamellar cast iron castings
- 2014
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Ingår i: 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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Konferensbidrag (refereegranskat)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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| 5. |
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| 6. |
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| 7. |
- 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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| 8. |
- Belov, Ilja, et al.
(författare)
-
A thermal conductivity model for lamellar and compacted graphite irons
- 2024
-
Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193.
-
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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| 9. |
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| 10. |
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| 11. |
- Diaconu, Lucian Vasile, et al.
(författare)
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Influence of molybdenum alloying on thermomechanical fatigue life of compacted graphite irons
- 2012
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Ingår i: International Journal of Cast Metals Research. - : Maney Publishing. - 1364-0461 .- 1743-1336. ; 25:5, s. 277-286
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Tidskriftsartikel (refereegranskat)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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| 12. |
- Diaconu, Lucian Vasile, et al.
(författare)
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Stress relaxation of compacted graphite iron alloyed with molybdenum
- 2013
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Ingår i: International Journal of Cast Metals Research. - : Taylor & Francis. - 1364-0461 .- 1743-1336. ; 26:1, s. 51-57
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Tidskriftsartikel (refereegranskat)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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| 13. |
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| 14. |
- Diószegi, Attila, 1962-, et al.
(författare)
-
Austenite Dendrite Morphology in Lamellar Cast Iron
- 2014
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Ingår i: 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).
-
Konferensbidrag (refereegranskat)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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| 15. |
- Diószegi, Attila, 1962-, et al.
(författare)
-
Austenite dendrite morphology in lamellar graphite iron
- 2015
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Ingår i: International Journal of Cast Metals Research. - : Maney Publishing. - 1364-0461 .- 1743-1336. ; 28:5, s. 310-317
-
Tidskriftsartikel (refereegranskat)abstract
- Primary austenite has been underestimated in general when the theories of nucleation, solidification, microstructure formation and mechanical properties were established for cast iron and particularly for lamellar cast iron. 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 the investigation area is revealed to be sequential investigation. A strong relation between all measured morphological parameters and the solidification time has been established, except the volume fraction of primary austenite, which is constant for all cooling conditions.
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| 16. |
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| 17. |
- Diószegi, Attila, et al.
(författare)
-
Defect formation mechanisms in lamellar graphite iron related to the casting geometry
- 2016
-
Ingår i: International Journal of Cast Metals Research. - : Taylor & Francis. - 1364-0461 .- 1743-1336. ; 29:5, s. 279-285
-
Tidskriftsartikel (refereegranskat)abstract
- Although lamellar cast iron has been used in advanced applications for about 20 years, our knowledge about the mechanisms affecting microstructure and defect formation is relatively limited. The present paper summarises some solidification-related phenomena from a series of recently published peer-reviewed papers and scientific theses and suggests a mechanism of defect formation which is dependent on the shape of the solidifying casting geometry. When shrinkage porosity or metal expansion penetration occurs, evidence of material transport in the intergranular zone of primary equiaxed austenite grains in the casting and in the intergranular regions between the sand grains in the mould material is seen. Material transport occurs across the casting-mould interface, where the existence of or the permeability of the primary columnar zone determines if material transport can take place.
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| 18. |
- Diószegi, Attila, 1962-, et al.
(författare)
-
Dynamic Coarsening of Austenite Dendrite in Lamellar Cast Iron Part 1 – Investigation based on interrupted solidification
- 2014
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Ingår i: Materials Science Forum. - : Trans Tech Publications. - 0255-5476 .- 1662-9752. ; 790-791, s. 205-210, s. 205-210
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Tidskriftsartikel (refereegranskat)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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| 19. |
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| 20. |
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| 21. |
- Diószegi, Attila, 1962-, et al.
(författare)
-
Method of and device for analysing a phase transformation of a material
- 2018
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Patent (populärvet., debatt m.m.)abstract
- A method of analyzing a phase transformation process of a material comprises providing a spherical sample of the material, measuring and recording a first data series of core temperature at the sample's center of gravity, measuring and recording a respective second data series of temperature at the sample's periphery, measuring and recording a respective third data series of radial displacements at the sample's periphery, and calculating a change in pressure in the sample at a plurality of points in time based on first, second and third said data series.
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| 22. |
- Diószegi, Attila, 1962-, et al.
(författare)
-
Microstructures and Characterization of Gray Irons
- 2017
-
Ingår i: ASM Handbook, Volume 1A. - Materials Park, Ohio : ASM International. - 9781627081337 - 162708133X - 9781627081344 ; , s. 583-589
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Bokkapitel (refereegranskat)
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| 23. |
- Diószegi, Attila, 1962-
(författare)
-
On microstructure formation and mechanical properties in grey cast iron
- 2004
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A major user of cast components is the automotive industry, where the functionality of the components is related to environmental demands. Internal combustion engines are constantly being improved to emit less pollution. A vital part in this development is to increase the material properties of engine components during their life cycle. In particular, cylinder heads, cylinder blocks and piston rings for diesel engine are produced in grey cast iron. Cast iron is expected to be in use far into the foreseeable future, due to favourable properties and low production costs. This work has been devoted to study microstructure formation, the tensile properties of cast iron and to some extent defect formation.The microstructure develops during solidification and solid state transformations. An inverse thermal analysis method was developed to study the kinetics of the microstructure formation. The inverse thermal analysis used, the Fourier method, analyses the cooling curves of two thermocouples to study the solidification or transformation. To decrease experimental errors, simulations have been done and the cooling curves were analysed. The best results were obtained when the thermocouples were placed close to each other.With the help of the thermal analysis a time dependent and fading nucleation law of the eutectic cells was found to fit the experimental results best. The experiments were made by multiple thermal analyses, and six different types of inoculants were investigated. The eutectic growth behaviour during solidification was evaluated with inverse thermal analysis, and it was found that commercial inoculants not only affect the eutectic nucleation but they also control the eutectic growth rate.Models of densities and volume changes are an integral part of a microstructure simulation of cast irons. These models are important for the inverse thermal analysis and an understanding of the porosity and expansion penetration in cast iron.The tensile strength of grey cast iron has been discussed by examining the fracture mechanism of the material at failure. The ultimate tensile strength is a result of the intimate collaboration between the graphite flake and the primary phases. Several parameters, including the graphite morphology, carbon content, inoculation and cooling conditions influence the ultimate tensile strength by offseting the equilibrium between the major constituents, the graphite flakes embedded in the primary metallic matrix. A model to predict the ultimate tensile strength is developed based on the interpretation of the stress intensity behaviour in a eutectic cell.The models developed for nucleation, eutectic growth and prediction of tensile strength were introduced into a casting simulation program. Mould filling, solidificauon, microstructure development and tensile strength of a complex. shaped cylinder head were simulated.
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| 24. |
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| 25. |
- Diószegi, Attila, 1962-, et al.
(författare)
-
Prediction of volume fraction of primary austenite at solidification of lamellar graphite cast iron using thermal analyses
- 2016
-
Ingår i: Journal of thermal analysis and calorimetry (Print). - : Springer Netherlands. - 1388-6150 .- 1588-2926. ; 124:1, s. 215-225
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Tidskriftsartikel (refereegranskat)abstract
- Lamellar graphite cast iron was investigated with carbon equivalents varied between CE = 3.4 and 4.26, cast at various cooling rates between 0.195 and 3.5 °C s-1 covering the limits used for technical applications in the production of complex-shaped lamellar graphite cast iron. Registered cooling curves displaced in two positions in the casting were used to predict the solidification and microstructure formation mechanisms. The predicted volume fraction of primary austenite was compared with the fraction of primary austenite measured on colour micrographs with the help of image analyses. A good correlation has been obtained for medium and slow cooling conditions, while a less good correlation at fast cooling condition was attributed to the used protective environment to preserve thermocouples. The observed fraction and the predicted fraction of primary austenite were in good correlation and followed a consequent variation dependent on the carbon equivalent. Furthermore, the quality of the prediction was dependent on the used numerical algorithm involving cooling information from either one or two thermocouples.
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| 26. |
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| 27. |
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| 28. |
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| 29. |
- Domeij, Björn, 1988-, et al.
(författare)
-
A review of dendritic austenite in cast irons
- 2024
-
Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193.
-
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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| 30. |
- Domeij, Björn, 1988-
(författare)
-
Compacted graphite iron : On solidification phenomena related to shrinkage defects
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An improved understanding of solidification of compacted graphite iron (CGI) is necessary to predict shrinkage related casting defects. Spheroidal graphite is not only found in ductile iron (SGI) but usually also in CGI, but its characteristics and role in this material is less understood. Uncertainties also remain regarding the segregation of alloying elements in cast irons. This is important because of its important role in the solidification process. The dendritic austenite structure has received little attention in cast iron research. A good understanding of the development of this structure is important to understand feeding of melt through the solidifying material.Nodularity is a measure of the amount of spheroidal versus compacted graphite in the microstructure. At a lower nodularity, the compacted graphite tips were found to grow in contact with the melt for a longer time before being encapsulated in the austenite. Moreover, as the nodularity was reduced, the subpopulation of larger spheroidal graphite gradually disappeared, reducing the bimodal size distribution to unimodal.Segregation of Si, Mn and Cu in SGI and CGI with a solidification time of near 10 min was found to be rather predictable under assumptions of no diffusion in austenite and complete mixing in the melt. Gradients of these elements contribute to a decrease in the driving force for diffusion of carbon into the austenite from the liquid, which is important for the growth of graphite which is separated from the liquid by austenite.During solidification of a near-eutectic CGI, the carbon concentration of austenite was found to deviate considerably from local equilibrium with graphite during solidification. This is important to consider in growth models for graphite by diffusion of carbon through a barrier of austenite.Micropores were shown to have displaced liquid from the solid structure at a late stage of solidification when solidification was slowing down and the temperature of the casting was falling at an increasing rate.The development of dendritic austenite in a near eutectic CGI was investigated. The contact area between liquid and the dendritic structure exceeded the contact area between liquid and eutectic cells through the dominant part of solidification. This highlights the importance of good understanding of the development of this structure in order to predict feeding of melt through the solidifying material. The coarsening of the structure was found to proceed at a higher rate compared to studies under isothermal condition. The dendritic structure continued to grow in parallel with the eutectic by a combination of thickening and dendritic growth.
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| 31. |
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| 32. |
- 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
-
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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| 33. |
- Domeij, Björn, 1988-, et al.
(författare)
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Implementation and Validation of Casting Simulation Methodology for Diagnostics of Lamellar Graphite Iron
- 2023
-
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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| 34. |
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| 35. |
- Domeij, Björn, 1988-
(författare)
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On the solidification of compacted and spheroidal graphite irons
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A good understanding of the solidification process of a cast material is essential to understand how the combination of alloy composition and the casting process variables combines into the solid cast component and its performance. The wrong combination may result in poor performance or casting defects. Spheroidal graphite has been well researched in ductile irons (SGI) where it is predominant. Spheroidal graphite is also present in smaller amounts in compacted graphite irons (CGI), but its nature and role in this material is less understood. Recent associations of spheroidal graphite in CGI with shrinkage porosity problems highlights the need for better understanding in this area. The importance of the dendritic austenite structure to the properties and solidification behaviour of cast irons has been highlighted in recent research. However, progress is to a degree limited by lack of practical means to characterize the structure.In the present work, the transition of a cast iron from SGI to CGI though remelting was studied. As the fraction of SG dropped, the tips of the compacted graphite tended to lose contact with the melt at a later stage. After this occurred, solidification appeared to be dominated by spheroidal graphite. Compacted and spheroidal graphite was found to solidify mostly segregated, and the increased recallescence induced by a higher fraction of compacted graphite displayed small influence on the size distribution of spheroidal graphite apart from the total number and fraction. The partitioning of Si, Mn and Cu in SGI and CGI was found to agree well with each other, as well as with theoretical predictions under the assumptions of zero diffusion of the elements in the solid. This shows that the proportions of spheroidal and compacted graphite has small or no influence on the evolution of these elements in the melt during solidification. A method for characterization of the dendritic austenite in quenched cast irons was introduced and evaluated. The method includes a technique for producing a visual contrast between the ledeburite matrix and the dendritic austenite, and a scheme for producing binary images from the resulting micrographs which are suitable for automatic image analysis. Measurements of the volume fraction and surface area per unit volume of the dendritic austenite structure using the introduced method was found to agree reasonably with traditional point counting and line intercept techniques. The difficulty in finding the exact boundary was proposed to be the major source of systematic disagreement.
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| 36. |
- Domeij, Björn, 1988-, et al.
(författare)
-
Relationships between macrostructure and microstructure in lamellar graphite iron castings
- 2024
-
Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193.
-
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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| 37. |
- Domeij, Björn, 1988-, et al.
(författare)
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Solidification Chronology of the Metal Matrix and a Study of Conditions for Micropore Formation in Cast Irons Using EPMA and FTA
- 2018
-
Ingår i: Materials Science Forum. - : Trans Tech Publications. - 0255-5476 .- 1662-9752. ; 925, s. 436-443
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 38. |
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| 39. |
- 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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| 40. |
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| 41. |
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| 42. |
- Dugic, Izudin, 1962-, et al.
(författare)
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Metal Expansion Penetration on Concave Casting Surfaces of Grey Cast Iron Cylinder Heads
- 2006
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Cylinder heads have an extremely complex shape with large areas of concave casting surfaces. The concave casting surfaces are often associated with metal expansion penetration problems or other surface defects, e. g. surface shrinkage. The defects cause high production costs due to component rejection and increased fettling time. This report presents an investigation of the microstructure in grey cast iron close to the sand-metal interface affected by metal penetration in a complex shaped casting. The dominant penetration defect observed in the cylinder heads was expansion penetration. Even pre-solidification penetration and sand crack defects were observed. The microstructure found in the non penetrated areas is typical for solidification of grey iron cast in sand moulds.
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| 43. |
- Dugic, Izudin, 1962-, et al.
(författare)
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The Influence of Inoculation on the Metal Expansion Penetration With Respect to the Primary and Eutectic Solidification
- 2005
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The mechanism of metal expansion penetration of grey cast iron components is dependent on both solidification anomalies at the metal – mould interface and the inclination of the sand mould to permit the metal liquid to penetrate between the sand grains. The present work utilizes the latest development of primary austenite inoculation in combination with classic eutectic inoculation to limit the metallurgical contribution to metal expansion penetration. A solid shell containing the primary austenite dendrite network constitutes the barrier between the liquid metal and mould interface. Inoculants of both the primaryand eutectic phase control the permeability of the dendrite network.
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| 44. |
- Ekengård, Johan, 1976-, et al.
(författare)
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A STUDY OF OXYGEN ACTIVITIES BEFORE THE START OF SOLIDIFICATION OF CAST IRONS
- 2016
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Ingår i: International Journal of metalcasting. - : Springer Science and Business Media LLC. - 1939-5981 .- 2163-3193. ; 10:4
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Tidskriftsartikel (refereegranskat)abstract
- Focus in this work was to study dissolved oxygen content and oxygen activities in different cast irons. Plant trials were performed at three occasions for lamellar, compacted and nodular iron melts. The results show that at temperatures close to the liquidus temperature the oxygen activities ranged from 0.03-0.1 ppm for LGI, around 0.02 ppm for CGI and 0.001ppm for SGI. In addition, it was found that as oxygen activities increase with time after an Mg treatment, the ability to form compacted graphite or nodular graphite in Mg-treated iron melts was lowered. Also, oxygen activity differences up to 0.07 ppm were found for different hypoeutectic iron compositions for lamellar graphite iron at the liquidus temperature. Overall, the observed differences in the dissolved oxygen levels are believed to influence how graphite particles are incorporated into the austenite matrix and how the graphite morphology will be in the cast product.
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| 45. |
- Elmquist, Lennart, et al.
(författare)
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Characterizing shrinkage porosity in gray cast iron using microstructure investigation
- 2008
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Ingår i: Transactions of the American Foundry Society. - Schaumburg, Ill : The American Foundry Society. - 9780874333183 ; , s. 691-703-
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Konferensbidrag (refereegranskat)abstract
- The presence of shrinkage porosity in gray cast iron cylinder heads is a common reason for rejected castings. Therefore, an investigation was carried out to characterize the microstructure around these defects in order to achieve a better understanding of their origin. Cylinder heads from two different foundries, producing cylinder heads with different design, were examined. Despite the differences, shrinkage porosity was found to appear at similar positions. Color etsching technique was used to reveal the microstructure and the characteristic features of the porosity. Besides, also solidification simulation was used to compare thermal distribution at the positions of interest. The investigation shows that there are similarities, as well as differences, and these will be discussed in detail together with the characteristic features found. In both cases, the simulations shows a thermal center crossing the interface between mould and casting. This leads to a discussion of how the solidification is progressing and the importance of the solidification skin, or columnar zone, as well as the equiaxed zone on shrinkage porosity formation.
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| 46. |
- Elmquist, Lennart, et al.
(författare)
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On the Formation of Shrinkage Porosity in Gray Iron Castings
- 2011
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Ingår i: Key Engineering Materials. - : Trans Tech Publications. - 1013-9826 .- 1662-9795. ; 457, s. 416-421
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Tidskriftsartikel (refereegranskat)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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| 47. |
- Fourlakidis, Vasilios, et al.
(författare)
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A generic model to predict the ultimate tensile strength in pearlitic lamellar graphite iron
- 2014
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 618, s. 161-167
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Tidskriftsartikel (refereegranskat)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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| 48. |
- Fourlakidis, Vasilios
(författare)
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Dendritic morphology and ultimate tensile strength of pearlitic lamellar graphite iron
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The continued development, of cylinder blocks and cylinder heads for heavy truck engines that are made of lamellar graphite iron (LGI) is focused on achieving high ultimate tensile strength (UTS) whilst conforming to environmental regulations. The purpose of this work is to further improve the tensile strength as well as the predictive engineering tools for optimization of LGI aimed to enhance the efforts for producing lighter and sustainable components without sacrificing performance.Varying the carbon content and solidification rate greatly influences the amount and the coarseness of the microstructure phases resulting in large variations of material properties. The experimental data set provided in this work covers a comprehensive range of microstructure and the UTS values aimed to be used in a holistic model for UTS prediction.In pearlitic LGI the primary austenite dendritic network reinforces the material while the distance between the pearlite grains defines the maximum continuous defect size. The novel parameter of Hydraulic Diameter of the Inter-dendritic Phase (DIPHyd) has been introduced in this work to express the amount and the coarseness of the space between the pearlite grains that have been solidified as primary austenite dendrites. The DIPHyd has proven to be the generic parameter that defines the maximum continuous defect size in the material, and hence it has been applied in modified Griffith and Hall-Petch models for prediction of UTS.Microstructure models have been developed for prediction of the key microstructure parameters that define the strength of LGI. These models have been combined with the modified Griffith and Hall-Petch equations and incorporated into casting simulation software to enable the strength prediction for pearlitic LGI alloys with various carbon contents. The results show that the developed models can be successfully applied, along with the simulation tools across a wide range of carbon content from eutectic to hypoeutectic composition, for the alloys solidified at various cooling rates typical for both thin and thick walled complex shaped iron castings.
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| 49. |
- Fourlakidis, Vasilios, et al.
(författare)
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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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Ingår i: Materials Science Forum. - : Trans Tech Publications. - 0255-5476 .- 1662-9752. ; 790-791, s. 211-216, s. 211-216
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Tidskriftsartikel (refereegranskat)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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| 50. |
- 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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