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On microstructure formation and mechanical properties in grey cast iron
Linköping University, Department of Mechanical Engineering. Linköping University, The Institute of Technology.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Jönköping: Jönköping , 2004. , 25 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 871
Keyword [en]
grey iron, nucleation, primary austenite, eutectic cell, growth rate, inoculation, thermal analysis
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-23153Local ID: 2557ISBN: 91-7373-939-1 (print)OAI: oai:DiVA.org:liu-23153DiVA: diva2:243467
Public defence
2004-05-14, Föreläsningssal E 101, Ingenjörshögskolan, Jönköping, 10:00 (Swedish)
Opponent
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2013-01-09
List of papers
1. Measurement and simulation of thermal condition and mechanical properties in a complicated shaped cylinder head cast in gray iron
Open this publication in new window or tab >>Measurement and simulation of thermal condition and mechanical properties in a complicated shaped cylinder head cast in gray iron
2000 (English)In: Proceedings of the Ninth International Conference on Modeling of Casting, Welding and Advanced Solidification Processes / [ed] Peter R. Sahm, Shaker , 2000, 869-876 p.Conference paper, Published paper (Refereed)
Abstract [en]

Development and design of heavy truck engine parts require improved knowledge on solidification kinetics and development of material properties. A suitable tool to handle the complex shape and solidification kinetics is the computer simulation of the casting process.

The quality of calculated results is dependent on the thermo-physical properties used, boundary condition and the quality of kinetic models implemented for calculation of resulting metallographical structure and material properties. A good quality means a good correlation between simulated and measured properties.

The paper will present a casting simulation of a cylinder head in complex shape for a diesel engine cast in grey iron together with results from measured cooling curves and investigated material properties. The values of heat transfer coefficient were calculated for a simple shaped sample, cast in a shell sand mould and used then for simulation of the cylinder head. The calculated and measured cooling curves correlate well, as well as the calculated and measured hardness value do.

Place, publisher, year, edition, pages
Shaker, 2000
Keyword
Cylinder head, cooling curve, casting simulation, heat transfer coefficient
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-87050 (URN)3826572300 (ISBN)9783826572302 (ISBN)
Conference
The 9th International Conference on Modeling of Casting, Welding and Advanced Solidification Processes held in Aachen, Germany, on August 20 to 25, 2000
Available from: 2013-01-09 Created: 2013-01-09 Last updated: 2013-01-09
2. Microstructure evaluation and simulation of mechanical properties of a cylinder head in cast iron
Open this publication in new window or tab >>Microstructure evaluation and simulation of mechanical properties of a cylinder head in cast iron
2001 (English)In: Proceedings of the First International Conference on the Science of Casting and Solidification / [ed] Doru M. Stefanescu, 2001, 269-277 p.Conference paper, Published paper (Refereed)
Abstract [en]

Development. design and manufacturing of heavy truck engine parts require improved knowledge on solidification kinetics and development of material properties. A suitable tool to handle the complex shape and solidification kinetics is the computer simulation of the casting process. The result is dependent on the thermophysical properties used, boundcny condition and the quality of kinetic models implemented for calculation of resulting metallographical structure and material properties.

The paper will present an analysis of the microstructure obtained in the cylinder head casting. The thermal analysis and cooling curves have been obtained through thermocouple measurements in the cylinder head. The microstructure analysis concerns both solidification and solid-state transformation The microstructure is related to the obtained mechanical properties as hardness. The filling, solidification and mechanical properties of the cylinder head have been simulared and compared with the results obtained from measurements. The calculated and measured cooling curves are compared as well.

Keyword
Grey iron, austenite, eutectic cell, pearlite lamellar spacing, cylinder head
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-87052 (URN)9739428673 (ISBN)9789739428675 (ISBN)
Conference
First International Conference on the Science of Casting and Solidification: 28-31 May, 2001, Brasov, Romania
Available from: 2013-01-09 Created: 2013-01-09 Last updated: 2013-01-09
3. Inverse thermal analysis method to study solidification in cast iron
Open this publication in new window or tab >>Inverse thermal analysis method to study solidification in cast iron
2004 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, E-ISSN 1743-1336, Vol. 17, no 5, 311-318 p.Article in journal (Refereed) Published
Abstract [en]

Solidification modelling of cast metals is widely used to predict final properties in cast components. Accurate models necessitate good knowledge of the solidification behaviour. The present study includes a re-examination of the Fourier thermal analysis method. This involves an inverse numerical solution of a one-dimensional heat transfer problem connected to solidification of cast alloys. In the analysis, the relation between the thermal state and the fraction solid of the metal is evaluated by a numerical method. This method contains an iteration algorithm controlled by an under relaxation term to achieve a stable convergence. The heat transfer problem is reduced to one-dimension to promote the practical application of the method. Thermo-physical properties such as the volumetric heat capacity tabulated in the calculation are introduced as a function of solidifying phases. Experimental equipment was developed in order to investigate the thermal behaviour of the solidifying metal. Three cylindrically shaped cast samples surrounded by different cooling materials were introduced in the same mould allowing a common metallurgical background for samples solidifying at different cooling rates. The proposed inverse thermal analysis was tested on both experimental and simulated data.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-87053 (URN)10.1179/136404604225020687 (DOI)
Available from: 2013-01-09 Created: 2013-01-09 Last updated: 2017-12-06
4. On modelling of volume related defect formation in cast irons
Open this publication in new window or tab >>On modelling of volume related defect formation in cast irons
2000 (English)In: Proceedings of the Ninth International Conference on Modeling of Casting, Welding and Advanced Solidification Processes / [ed] Peter R. Sahm, 2000, 102-109 p.Conference paper, Published paper (Refereed)
Abstract [en]

Formation of defects, e.g. porosity's and expansion penetration in cast irons, are highly related to volume changes during solidification. Prediction of porosity and expansion penetration requires a detailed modelling of structure formation and of the related volume change during solidification.

The phase transformations in cast iron are highly dependent on the kinetics and therefore also strongly influenced by the cooling rate, nucleation and chemical composition. The transformation of liquid to solid, involves formation of phases with a variety of densities. The resulting volume changes often leads to formation of porosity or excess of material. The excess of material helps to give a sound casting but if the geometry is not favourable the metal penetrates into the sand mould. The balance between shrinkage and expansion is important to understand, since it is a fundamental problem to make iron castings without shrinkage or penetration defects. The volume changes of the phases can not be measured by direct methods, but with a combination of modelling and experiments an improved understanding can be obtained.

The volumes of iron and carbon in liquid and austenite have been modelled by using a sublattice molar volume model. The models of volumes and solidification are implemented in a computer program to simulate the kinetics of phase formation and resulting volume changes of the system. Thermal analysis curves are coupled to the phase and volume changes.

The paper discusses the modelling of solidification using kinetic models and the volume change during the cooling and precipitation of the solid phases. Influence of the compositions, solidification mode and nucleation on the volume change will be calculated.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-87054 (URN)3826572300 (ISBN)9783826572302 (ISBN)
Conference
The 9th International Conference on Modeling of Casting, Welding and Advanced Solidification Processes held in Aachen, Germany, on August 20 to 25, 2000
Available from: 2013-01-09 Created: 2013-01-09 Last updated: 2013-01-09
5. Inverse kinetic analysis method to study eutectic growth
Open this publication in new window or tab >>Inverse kinetic analysis method to study eutectic growth
2005 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, E-ISSN 1743-1336, Vol. 18, no 1, 41-46 p.Article in journal (Refereed) Published
Abstract [en]

Deterministic modelling is a classical method used for solidification simulation. A common procedure uses a kinetic model to describe the growth of solid phases. Formulation of the kinetic models used to be done by direct observation of the solidification process involving thermal analysis and microstructure investigation. Much effort has been invested in studying eutectic alloys and their solidification kinetics. Different growth parameters were observed which are assumed to depend on experimental conditions. The present study uses a direct simulation including a kinetic model for simulation of the eutectic phase. The simulated microstructure and cooling curves were used to carry out inverse thermal and inverse kinetic analyses. The inverse kinetic analysis method introduced indicates a strong equivalence between the direct solidification model and the inverse calculation. The position of the cooling curves used in the inverse analysis has been investigated and the best results are obtained when the cooling curves analysed are from locations closely positioned in space.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-87055 (URN)10.1179/136404605225022829 (DOI)
Available from: 2013-01-09 Created: 2013-01-09 Last updated: 2017-12-06
6. A comparison of Fourier vs. Newtonian thermal analyse and its influence on the inverse kinetic growth calculation
Open this publication in new window or tab >>A comparison of Fourier vs. Newtonian thermal analyse and its influence on the inverse kinetic growth calculation
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Thermal analysis of cooling curves is a metallurgical process control tool. Any phase transformations and their kinetics are reflected in the cooling rate. An interpretation of the cooling rate and temperatures is coupled to critical parameters, which are needed to assure correct quality of the melt and to give recommendations to modify the melt. This paper was inspired by the question, how well does a thermal ana lysis with one or two thermocouples and subsequent numerical analysis reflect the real phase transformations which occur?

Inverse kinetic analysis using Fourier Thermal Analysis and Newtonian Thermal Analysis has been investigated using simulated cooling curves. The present study uses a direct simulation including a kinetic model for simulation of a eutectic phase. In this case, since the solidification sequence is well defined the inverse kinetic analysis should recreate the relation between the growth rate and supercooling of the eutectic phase. The Newtonian Thermal Analysis is based on an interpretation of a single thermal point with respect to solidification and contains a series of assumptions which are not entirely undoubted physically.

Consequently the inverse kinetic analysis results in random quality growth parameters. The Fourier Thermal Analysis is based on interpretation of temperature differences between two thermal points with respect to solidification. The calculations conducted, in combination with the inverse kinetic analysis reveal a stable procedure. The decisive parameter determining the quality of inverse analysis is the distance between the thermal points analysed. Closely situated thermal points assure the best quality. The Fourier Thermal Analysis reflects the solidification most correctly.

Keyword
Inverse model, thermal analyze, fraction solid, kinetic model
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-87057 (URN)
Available from: 2013-01-09 Created: 2013-01-09 Last updated: 2013-01-09
7. Evaluation of eutectic growth in grey cast iron by means of inverse modelling
Open this publication in new window or tab >>Evaluation of eutectic growth in grey cast iron by means of inverse modelling
2003 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, E-ISSN 1743-1336, Vol. 16, no 1-3, 301-306 p.Article in journal (Refereed) Published
Abstract [en]

Computer simulation of casting becomes a valuable tool for developing advanced materials and casting components. Recent investigations and validation work on simulated cast components reveal the necessity of reliable analyses methods to determine solidification behaviour and to extract parameters for kinetic models to use at simulation of complex cast iron materials. The paper will present an inverse modelling method for determination of eutectic growth. The method include an experimental part proper to investigate simultaneously the solidification at three different cooling rates while the cast material has the same metallurgical origin, and a computational part for calculation of grow kinetics. Validation of the inverse method is made together with simulation. The inverse modelling of eutectic growth in grey iron indicates that chemical composition, type and amount of inoculants and cooling condition are strongly influencing the eutectic growth condition and gives different eutectic growth coefficients. By invoking a generalized KJMA* equation, the shape of the growing eutectic interface can be predicted. Deviation from perfectly spherical growth in real solidification cases is the source of variation of eutectic growth coefficients. The results of the inverse model are valuable to simulate differences in solidification behaviour in differently treated grey iron melts. * KJMA is the abbreviation of the name of the famous scientists Kolmogorow, Johnson, Mehl and Avrami who developed and applied the equation.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-87059 (URN)
Available from: 2013-01-09 Created: 2013-01-09 Last updated: 2017-12-06
8. A study of eutectic inoculation in grey iron by addition of Fe-Si-Ca-Al-, Sr, Ba, Zr, Ti, RE and C
Open this publication in new window or tab >>A study of eutectic inoculation in grey iron by addition of Fe-Si-Ca-Al-, Sr, Ba, Zr, Ti, RE and C
2003 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, E-ISSN 1743-1336, Vol. 16, no 1-3, 29-34 p.Article in journal (Refereed) Published
Abstract [en]

The interest to improve the mechanical properties and decrease shrinkage or expansion defects in grey cast irons, the inoculation is an important issue for component manufactures. The inoculation, growth of graphite and eutectic structure, are related to those demands. The paper will show a study of the effect of some inoculants on the graphite nucleation and eutectic microstructure in grey cast iron. The procedure to achieve this was to study the influence of inoculants and cooling rate on the eutectic microstructure. Six inoculants were chosen with a base of Fe-Si-Ca-Al with additions of Sr, Ba, Zr, Ti, RE and C at different proportions. Two of the inoculants were investigated at three different levels of additions. The inoculants gave eutectics with great variety of microstructure. The experimental equipment was designed to produce cast samples under controlled thermal conditions and equipped with thermocouples. To study the influence of cooling rate on the eutectic nucleation, the mould was equipped with three different cooling conditions. In order to measure the eutectic cell size the samples were colour etched. The measurements were made near the thermocouples to relate the eutectic cell size and cells/area with the cooling curves. The microstructure, cell-size and cooling curves were used to model the nucleation behaviour of the investigated compositions and solidification behaviour. The investigation showed that the type and amount of inoculation influenced the number of potent nuclei of graphite eutectic and the fading followed Lifshitz-Slyosov-Wagner (LSW) theory of ripening.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-87060 (URN)
Available from: 2013-01-09 Created: 2013-01-09 Last updated: 2017-12-06
9. Microstructure and tensile properties of grey cast iron
Open this publication in new window or tab >>Microstructure and tensile properties of grey cast iron
2004 (English)Report (Other academic)
Abstract [en]

Gray cast iron is a widely used construction material with a unique combination of properties such as very good thermal conductivity, vibration damping ability, and good machinability. The production method of casting is convenient to achieve a near final shape of complex geometries. A significant use of this beneficial construction materials can be found in diesel engine components, including cylinder heads, cylinder blocks and piston rings. Environmental and economic factors necessitate the development and optimization of engine components. The present paper summarizes a study of major process and material parameters to maximize and optimize the mechanical properties under static load of grey cast iron.

The tensile strength of grey cast iron has been discussed by revealing the fracture mechanism of the material at failure. The ultimate tensile strength is clearly the result of the intimate collaboration between the graphite flake and the primary phases. Several parameters, including the graphi te morphology, carbon content, inoculation, and cooling conditions during solidification influence the ultimate tensile strength by affecting the equilibrium between the major constituents and cracks in the 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.

Place, publisher, year, edition, pages
Jönköping: Ingenjörshögskolan, 2004. 35 p.
Series
Research Report. School of Engineering., ISSN 1404-0018 ; 1
Keyword
Grey iron, Eutectic cell, Graphite morphology, Carbon content, Inoculation, Cooling rate, Mechanical properties, Tensile strength, Maximum stress intensity factor, Primary austenite
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-87061 (URN)
Available from: 2013-01-09 Created: 2013-01-09 Last updated: 2013-01-09
10. Microstructure and tensile property simulation of grey cast iron components
Open this publication in new window or tab >>Microstructure and tensile property simulation of grey cast iron components
2004 (English)Report (Other academic)
Abstract [en]

Designers and manufacturers of grey cast iron components have for a long time been interested in predicting microstructures and tensile properties. Accurate predictions are desirable to develop and optimize cast components as well as to reduce manufacturing expenses.

Recent developments in the field of eutectic nucleation, eutectic growth and prediction of tensile strength in grey cast iron have been implemented into commercial, finite difference method based, simulation software. Cylindrical samples with varied cooling conditions and a complex shaped cylinder head have been simulated. The simulation procedure includes kinetic models for microstructure prediction. A new fading law is introduced to calculate the nucleated eutectic and inoculants adapted eutectic growth. The tensile strength is calculated using a model based on the stress intensity in the metallic matrix caused by the presence of graphite flakes.

Cooling curves, microstructure and tensile properties obtained by simulation are compared to measured values.

Place, publisher, year, edition, pages
Jönköping: Ingenjörshögskolan, 2004. 16 p.
Series
Research Report. School of Engineering., ISSN 1404-0018 ; 2
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-87062 (URN)
Available from: 2013-01-09 Created: 2013-01-09 Last updated: 2013-01-09

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