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On modelling of volume related defect formation in cast irons
Division of Component Technology, Jönköping University, Jönköping, Sweden.
Division of Component Technology, Jönköping University, Jönköping, Sweden.
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.

Place, publisher, year, edition, pages
2000. 102-109 p.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-87054ISBN: 3826572300 (print)ISBN: 9783826572302 (print)OAI: oai:DiVA.org:liu-87054DiVA: diva2:584517
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
In thesis
1. On microstructure formation and mechanical properties in grey cast iron
Open this publication in new window or tab >>On microstructure formation and mechanical properties in grey cast iron
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
grey iron, nucleation, primary austenite, eutectic cell, growth rate, inoculation, thermal analysis
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-23153 (URN)2557 (Local ID)91-7373-939-1 (ISBN)2557 (Archive number)2557 (OAI)
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

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