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Defect Formation during Solidification in Grey Iron Castings
Jönköping University, School of Engineering, JTH. Research area Materials and Manufacturing - Casting.
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The presence of defects is of major concern in the production of grey iron castings. Some defects are merely an aesthetic problem while others can be detrimental for the performance of the component. Among the several possible defects, shrinkage porosity is one of the more challenging to understand and avoid. This type of defect can penetrate through the casting as a three-dimensional network. The purpose of this work has been to develop knowledge and understanding about the foundry process in order to increase product quality by eliminating or at least minimising the presence of shrinkage porosity in the production of vital engine components. This was done by developing fundamental knowledge concerning factors known to influence the presence of shrinkage porosity.

Initially, an investigation was carried out in order to characterize shrinkage porosity commonly occurring in cylinder heads. Factors found to be important and contributing to the formation of shrinkage porosity were identified. It was found that this type of defect is formed at hot spots that have migrated during solidification. Knowledge of the migrating hot spot was used as a design criterion in the development of a geometry with the purpose of deliberately generating porosity. Based on this geometry a mechanism for the formation of this type of shrinkage porosity was proposed.

The formation of shrinkage porosity depends on gases dissolved in the melt. In this work, their levels and variations in the melting process were investigated. It was shown how the solubility of oxygen depends on the temperature but not on the method used to produce the iron. On the other hand, the total amount of oxygen depends on the process but not on temperature. The discussion about gases also included hydrogen and nitrogen.

The solidification of grey cast iron is complex. It is during the solidification that not only the final properties of the component but also the conditions for defect formation are established. Shrinkage porosity is formed due to volumetric changes followed by an inability to supply material to the contracting areas. The solidification of grey iron starts with nucleation and growth of the primary austenite followed by nucleation of eutectic cells. It was found that the microstructural constituents are interconnected. The importance of the macrostructure was also discussed and it was shown that shrinkage porosity can be found not only between eutectic cells but also between equiaxed crystals.

Place, publisher, year, edition, pages
Göteborg: Chalmers University of Technology , 2009.
Series
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie, ISSN 0346-718X; nr 2935, ISSN 0346-718X ; 2935
Keywords [en]
Shrinkage Porosity, Grey Iron, Solidification, Nucleation, Primary Austenite, DAAS, Eutectic Cells, Microstructure, Macrostructure, Hot Spot, Oxygen, Hydrogen
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:hj:diva-11606ISBN: 978-91-7385-254-8 (print)OAI: oai:DiVA.org:hj-11606DiVA, id: diva2:293039
Public defence
2009-05-12, E1405, JTH, Gjuterigatan 5, Jönköping, 10:00 (English)
Opponent
Supervisors
Note
Thesis from the Department of Materials and Manufacturing Technology, Chalmers University of Technology AND the Department of Mechanical Engineering, Materials and Manufacturing – Castings, School of Engineering, Jönköping University Available from: 2010-02-10 Created: 2010-02-10 Last updated: 2010-02-10Bibliographically approved
List of papers
1. Shrinkage Porosity and its Relation to Solidification Structure of Grey Cast Iron Parts
Open this publication in new window or tab >>Shrinkage Porosity and its Relation to Solidification Structure of Grey Cast Iron Parts
2010 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, E-ISSN 1743-1336, Vol. 23, no 1, p. 44-50Article in journal (Refereed) Published
Identifiers
urn:nbn:se:hj:diva-10768 (URN)10.1179/174313309X436664 (DOI)
Available from: 2009-11-02 Created: 2009-11-02 Last updated: 2017-12-12Bibliographically approved
2. On the Problems of a Migrating Hot Spot
Open this publication in new window or tab >>On the Problems of a Migrating Hot Spot
2010 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 649, p. 443-448Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Roósz: Trans Tech Publication, 2010
Identifiers
urn:nbn:se:hj:diva-10804 (URN)10.4028/www.scientific.net/MSF.649.443 (DOI)
Available from: 2009-11-03 Created: 2009-11-03 Last updated: 2017-12-12Bibliographically approved
3. Characerizing Shrinkage Porosity in Gray Cast Iron using Microstructure Investigation
Open this publication in new window or tab >>Characerizing Shrinkage Porosity in Gray Cast Iron using Microstructure Investigation
2008 (English)In: Transactions of the American Foundry Society: volume 116 ; One Hundred Twelfth Annual Metalcasting Congress, May 17-20, 2008, Schaumburg, Ill.: American Foundry Society , 2008, Vol. 116, p. 691-703Conference paper, Published paper (Other academic)
Place, publisher, year, edition, pages
Schaumburg, Ill.: American Foundry Society, 2008
Identifiers
urn:nbn:se:hj:diva-8034 (URN)9780874333183 (ISBN)
Available from: 2009-03-01 Created: 2009-03-01 Last updated: 2010-02-10Bibliographically approved
4. Influence of Melting Process on Oxygen Content in Gray Iron
Open this publication in new window or tab >>Influence of Melting Process on Oxygen Content in Gray Iron
2007 (English)In: Transactions of the American Foundry Society: One Hundred Eleventh Annual Metalcasting Congress May 15 - 18, 2007, Schaumburg, Ill.: American Foundry Society , 2007, Vol. 115, p. 625-636Conference paper, Published paper (Refereed)
Abstract [en]

The amount of dissolved oxygen, as well as oxygen available as oxides, is considered to affect the nucleation and growth of porosity defects in gray iron castings. Therefore, the influence of melting process on oxygen content was investigated in the production at two foundries. The importance of temperature on the equilibrium between the melt and its surrounding was especially examined. It was found that the amount of dissolved oxygen decreased with decreasing temperature, but the total amount of oxygen remained unchanged, meaning that the amount of oxygen found as oxides increased as the temperature decreased.

Place, publisher, year, edition, pages
Schaumburg, Ill.: American Foundry Society, 2007
Series
American Foundry Society. Transactions, ISSN 0065-8375 ; 115
Keywords
Oxygen content, Gray Iron, Porosity, Castings, Defects, Melting
Identifiers
urn:nbn:se:hj:diva-4779 (URN)9780874333381 (ISBN)
Available from: 2008-05-20 Created: 2008-05-20 Last updated: 2010-02-10Bibliographically approved
5. Inoculation and its effect on primary solidification structure of hypoeutectic grey cast iron
Open this publication in new window or tab >>Inoculation and its effect on primary solidification structure of hypoeutectic grey cast iron
2010 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, E-ISSN 1743-1336, Vol. 23, no 2, p. 124-129Article in journal (Refereed) Published
Abstract [en]

The solidification of grey cast iron is controlled by the addition of inoculants. This is done in order to provide nucleation sites and hence facilitate the formation of eutectic cells and decrease the degree of undercooling. The number of eutectic cells and the graphite morphology affect the final properties of the casting. Preceding the nucleation of graphite and the eutectic cells is the nucleation of the primary austenite. It was found that the addition of inoculants also influences the primarysolidification. The largest effect on the primary dendrites is obtained by inoculation using pure ironpowder. It was also shown how the columnar to equiaxed transition (CET) depends on the number ofequiaxed dendrites per unit volume. In addition, the primary structure was found to influence the eutectic solidification. The relationship between the secondary dendrite arm spacing and the eutectic cell size was found to correlate well with the work of others.

Place, publisher, year, edition, pages
Taylor & Francis, 2010
Keywords
Grey cast iron, Equiaxed dendrites, CET, Primary austenite, Inoculation, Eutectic cells
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:hj:diva-10769 (URN)10.1179/136404609X12490478029317 (DOI)000275308000007 ()2-s2.0-77952867716 (Scopus ID)
Available from: 2009-11-02 Created: 2009-11-02 Last updated: 2018-08-30Bibliographically approved
6. Influence of Melting Process on Hydrogen and Nitrogen Content in Gray Iron
Open this publication in new window or tab >>Influence of Melting Process on Hydrogen and Nitrogen Content in Gray Iron
2007 (English)In: Transactions of the American Foundry Society: One Hundred Eleventh Annual Metalcasting Congress May 15 - 18, 2007, Schaumburg, Ill.: American Foundry Society , 2007, Vol. 115, p. 617-623Conference paper, Published paper (Refereed)
Abstract [en]

High concentrations of hydrogen and nitrogen in molten gray iron increase the risk of porosity in castings. Therefore, equilibrium variations of these gases at different stages in the process chain from melting to casting have been mapped. Both hydrogen and nitrogen content are affected by the melting method. The amount of hydrogen is also sensitive to the dwell-time in ladles and holding furnaces. The total amount of nitrogen, i.e. bonded and dissolved nitrogen, is not significantly affected by the temperature, while the hydrogen content is indirectly affected because of the relationship between dwell-time and temperature.

Place, publisher, year, edition, pages
Schaumburg, Ill.: American Foundry Society, 2007
Series
American Foundry Society. Transactions, ISSN 0065-8375 ; 115
Keywords
Gray iron, Porosity, Castings, Gas content
Identifiers
urn:nbn:se:hj:diva-4778 (URN)9780874333381 (ISBN)
Available from: 2007-12-07 Created: 2007-12-07 Last updated: 2010-02-10Bibliographically approved

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