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Study of solidification and volume change in lamellar cast iron with respect to defect formation mechanisms
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Lamellar cast iron is a very important technical alloy and the most used material in the casting production, and especially in the automotive industry which is the major consumer. Beside the many great properties, it is inclined to form casting defects of which some can be prevented, and some may be repaired subsequently. Shrinkage porosity is a randomly returning problem, which is difficult to understand and to avoid. This defect is a volumetric deficiency which appear as cavities inside the casting in connection to the casting surface. Another frequent defect is the metal expansion penetration. This defect is a material surplus squeezed to the casting surface containing sand inclusion from the mold material. Shrinkage porosity is usually mentioned together with metal expansion penetration as the formation mechanism of both defects have common roots. It is also generally agreed, that these type of defects are related to the volumetric changes occurring during solidification. Additionally, the formation of these defects are in connection with the coherency of the primary austenite dendrites.

The purpose of this work was to develop knowledge on factors affecting a volume-change related casting defect formation in order to minimize the presence of these defects in engine component production. This was done by extending the existing solidification investigation methods with novel solutions. Introduction of expansion force measurement in the determination of dendrite coherency combined with multi axial volume change measurement refine the interpretation of the solidification. Comparison of registered axial and radial linear deformation in cylindrical samples indicated an anisotropic volume change. Different methods for dendrite coherency determination have been compared. It was shown that the coherency develops over an interval. Dependent on the added inoculant the coherency is reached at different levels of fractions of a solidified primary phase. It is also shown, that inoculation has an effect on the nucleation and growth of the primary phase. Quantitative image analysis has been performed on the primary phase in special designed samples designed to provoke shrinkage porosity and metal expansion penetration. It was found, that the inter-dendritic space varies within a casting. This was explained by the coarsening of the primary dendrites which originates from differences in the local time of solidification.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , x, 29 p.
Keyword [en]
lamellar cast iron, shrinkage porosity, solidification, volumetric change, dendrite coherency, inter-dendritic space
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-136985ISBN: 978-91-7501-938-3 (print)OAI: oai:DiVA.org:kth-136985DiVA: diva2:677655
Presentation
2013-12-05, Sal M131 Sefström, Brinellvägen 23, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20131210

Available from: 2013-12-10 Created: 2013-12-10 Last updated: 2013-12-10Bibliographically approved
List of papers
1. On the problems of measuring volume change in Lamellar cast iron
Open this publication in new window or tab >>On the problems of measuring volume change in Lamellar cast iron
(English)Manuscript (preprint) (Other academic)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-136981 (URN)
Note

QS 2013

Available from: 2013-12-10 Created: 2013-12-10 Last updated: 2013-12-10Bibliographically approved
2. Determination of the columnar to equiaxed transition in hypoeutectic lamellar cast iron
Open this publication in new window or tab >>Determination of the columnar to equiaxed transition in hypoeutectic lamellar cast iron
(English)Manuscript (preprint) (Other academic)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-136982 (URN)
Note

QS 2013

Available from: 2013-12-10 Created: 2013-12-10 Last updated: 2013-12-10Bibliographically approved
3. Investigation of cooling rate dependent dendrite morphology in hypoeutectic lamellar cast iron
Open this publication in new window or tab >>Investigation of cooling rate dependent dendrite morphology in hypoeutectic lamellar cast iron
2013 (English)Report (Other academic)
Abstract [en]

Shrinkage porosity and metal expansion penetration are two fundamental defects appearing at production ofcomplex shaped lamellar cast iron components. In previous work it has been shown that both shrinkageporosity and metal expansion penetration are related to the primary austenite dendrite network and itsformation mechanisms. The purpose of the present work is to study the morphology of primary austenite intest casting with a high tendency to form shrinkage porosity and metal expansion penetration. Simplified testmodels simulating the thermal and geometrical conditions similar to the conditions existing in complex shapedcasting have been successfully used to provoke shrinkage porosity and metal expansion penetration.Stereological investigation of the primary dendrite morphology indicates a maximum interdendritic space inconnection to the casting surface where the porosity and the penetration defect appear. Away from the defectformation area the interdendritic space decreases. Furthermore the local solidification times of the investigatedsamples were calculated in a 3D simulation software. Comparison of the simulated local solidification timesand measured interdendritic space indicates a strong relation of the same shape as it is known from theliterature when dynamic coarsening mechanism is characterized. The main outcome of the present paper is theobserved gradient of increasing interdendritic space from sections with high local solidification to sectionswith low solidification time. The mechanism of increasing the interdendritic phase can be explained by thedynamic ripening process. The unfortunate thermal conditions with the slowest local solidification timesituated in the border between the casting surface and its surrounding are considered the reason to form anaustenite morphology which can promote the mass flow between dendrite provoking shrinkage porosity ormetal expansion penetration.

Place, publisher, year, edition, pages
Jönköping: School of Engineering, 2013. 7 p.
Series
JTH research report, ISSN 1404-0018 ; 2013:04
Keyword
lamellar cast iron; primary austenite; dendrite morphology; coarsening
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-136980 (URN)
Note

QC 20131210

Available from: 2013-12-10 Created: 2013-12-10 Last updated: 2015-03-03Bibliographically approved

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