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Tensile and Thermal Properties in Compacted Graphite Irons at Elevated Temperatures
Jönköping University, School of Engineering, JTH. Research area Materials and Manufacturing - Casting. Jönköping University, School of Engineering, JTH, Mechanical Engineering.
2010 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 41, no 12, p. 3100-3109Article in journal (Refereed) Published
Abstract [en]

Tensile and thermal properties of compacted graphite irons, or CGI, prepared with various molybdenum additions and solidification rates have been investigated for temperatures between room temperature and 873 K (600{degree sign}C). A slower solidification rate resulted in larger and fewer graphite particles as well as in an increase of intercellular cementite, or carbides. Molybdenum is a carbide stabilizing element, i.e. increasing additions of molybdenum increased the amount of carbides. Young's modulus decreased with increasing temperature and a lower solidification rate increased this parameter slightly. Both increasing content of carbide and increasing nodularity increased the Young's modulus. Strength parameters like yield strength and ultimate tensile strength was affected in similar ways by temperature and solidification rate. The strength values were generally quite temperature independent for temperatures below 573 K (300{degree sign}C) but decreased rapidly for higher temperatures. Increasing nodularity increased the strength while increasing content of carbide had little influence on the values. The thermal conductivity decreased with increasing content of carbide and increasing nodularity. The thermal conductivity generally showed a maximum value at 573 K (300{degree sign}C). A contradictory linear relationship was found between yield strength and thermal conductivity.

Place, publisher, year, edition, pages
2010. Vol. 41, no 12, p. 3100-3109
Keywords [en]
Compacted Graphite Iron, Mechanical Properties, Elevated temperature, Thermal conductivity, Molybdenum
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:hj:diva-12565DOI: 10.1007/s11661-010-0385-1OAI: oai:DiVA.org:hj-12565DiVA, id: diva2:325037
Available from: 2010-06-17 Created: 2010-06-17 Last updated: 2017-12-12Bibliographically approved
In thesis
1. On Thermal Conductivity and Strength in Compacted Graphite Irons: Influence of Temperature and Microstructure
Open this publication in new window or tab >>On Thermal Conductivity and Strength in Compacted Graphite Irons: Influence of Temperature and Microstructure
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Thermal conductivity, hardness and strength are all highly important material properties, affecting the performance and life expectancy of components operating at elevated temperatures. The main purpose of this work has been to increase the knowledge and understanding concerning how mechanical and physical properties are affected by temperature and microstructure in compacted graphite irons. This was accomplished by investigating the whole chain from how a certain microstructure can be achieved, how that microstructure affects mechanical and physical properties, how those properties were related and how they can be estimated.

 

By investigating how specific alloying elements affected the microstructure it was possible to confirm the pearlite promoting effects of copper and tin, the carbide stabilizing effects of chromium and molybdenum and magnesium’s ability to alter the compactness of the graphite particles. An ausferritic metal matrix could be attained by performing an austempering heat treatment or by increased solidification rate on samples highly alloyed with molybdenum. Increasing the content of ferrite improved the thermal conductivity, while increased content of free carbide, ausferrite or nodularity reduced the thermal conductivity. Ferrite containing high amount of dissolved silicon had a negative influence on thermal conductivity values but also a strengthening effect. Thermal conductivity values in CGI generally showed a maximum at about 300 °C but a large content of ferrite resulted in quite temperature stable values below 300 °C. Tensile strength parameters such as ultimate tensile strength and yield strength were temperature stable for temperatures up to 300 °C before the values rapidly decreased at higher temperatures. The values of Young’s modulus continuously decreased with increasing temperature and seemed to increase slightly with increasing content of free carbide and nodularity. Increasing nodularity also increased the values of the strength parameters. Contradictory linear relationships between strength or hardness and thermal conductivity were found highlighting the problem in optimizing both these properties. Linear regression models based on five key parameters were created to describe thermal conductivity values and hardness values, where the model describing thermal conductivity included temperature. Stress values for plastic deformations were possible to approximate with good accuracy by using constituent equations such as the Hollomon and Ludwigson equations.

Place, publisher, year, edition, pages
Göteborg: Chalmers Reproservice, 2010. p. 142
Series
Doktorsavhandlingar vid Chalmers tekniska högskola, ISSN 0346-718X ; 3115
Keywords
Compacted Graphite Iron, Thermal Conductivity, Mechanical Properties, Hardness, Microstructure, Plastic Deformation, Hollomon Equation, Elevated Temperature
National Category
Materials Engineering
Identifiers
urn:nbn:se:hj:diva-13473 (URN)978-91-7385-434-4 (ISBN)
Public defence
2010-10-29, Gjuterisalen E1405, Gjuterigatan 5, Jönköping, 10:00 (English)
Opponent
Supervisors
Available from: 2010-11-23 Created: 2010-10-08 Last updated: 2010-11-23Bibliographically approved

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Selin, Martin

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