Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
On Thermal Conductivity and Strength in Compacted Graphite Irons: Influence of Temperature and Microstructure
Jönköping University, School of Engineering, JTH. Research area Materials and Manufacturing - Casting.
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. , 142 p.
Series
Doktorsavhandlingar vid Chalmers tekniska högskola, ISSN 0346-718X ; 3115
Keyword [en]
Compacted Graphite Iron, Thermal Conductivity, Mechanical Properties, Hardness, Microstructure, Plastic Deformation, Hollomon Equation, Elevated Temperature
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:hj:diva-13473ISBN: 978-91-7385-434-4 (print)OAI: oai:DiVA.org:hj-13473DiVA: diva2:355955
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
List of papers
1. Effect of Alloying Elements on Graphite Morphology in CGI
Open this publication in new window or tab >>Effect of Alloying Elements on Graphite Morphology in CGI
2010 (English)In: Materials Science Forum, ISSN 0255-5476, Solidification and Gravity V, Vol. 649, 171-176 p.Article in journal (Refereed) Published
Abstract [en]

Understanding how alloying elements and amounts affect the shape and size of graphite in compacted graphite cast irons could be of great importance. Some important material properties that are affected by the graphite shape are tensile strength and thermal conductivity. Knowing the effect of alloying additions could be of assistance when trying to optimise material for a specific application. In order to determine how graphite changes depending on alloying additions the microstructure of nineteen CGI materials were investigated. All melts were based on one chemical composition and alloying elements were added to obtain melts with variation in magnesium, silicon, copper, tin, chromium and molybdenum. Some of the more important microstructure features that were analysed are the amount and size of different graphite particles. The result from this analysis should give an indication on what features each alloying element affect and how these features varies with alloying amount.

Place, publisher, year, edition, pages
Zurich: Trans Tech Publications, 2010
Keyword
CGI, Alloying Elements, Graphite Morphology, Microstructure
National Category
Materials Engineering
Identifiers
urn:nbn:se:hj:diva-8602 (URN)
Conference
5th International Conference on Solidification and Gravity
Available from: 2009-04-27 Created: 2009-04-24 Last updated: 2017-08-14Bibliographically approved
2. Influence of alloying additions on microstructure and thermal properties in compact graphite irons
Open this publication in new window or tab >>Influence of alloying additions on microstructure and thermal properties in compact graphite irons
2009 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, Vol. 22, no 1-4, 283-285 p.Article in journal (Refereed) Published
Abstract [en]

Nineteen compacted graphite cast irons were investigated in order to determine how alloying additions affect the thermal transport properties and microstructure. All melts were based on one chemical composition and alloying elements were added to obtain melts with variation in magnesium, silicon, carbon, copper, tin, chromium and molybdenum. Increasing amounts of magnesium resulted in a further compaction of the graphite particles, reducing the thermal conductivity. Large amounts of silicon resulted in a fully ferritic metal matrix. Silicon also formed solid solution with iron which had a deteriorating effect on the thermal conductivity, i.e. the larger amount of silicon the lower the thermal conductivity. Copper and tin promoted formation of pearlite that had worse thermal properties compared to ferrite. Increasing amount of ferrite generally had a positive influence of the thermal conductivity. Chromium and molybdenum were carbide forming elements and carbides had a negative influence on the thermal conductivity.

Place, publisher, year, edition, pages
Leeds: Maney Publishing, 2009
Keyword
CGI, Thermal Conductivity, Microstructure, Alloying Addition
National Category
Materials Engineering
Identifiers
urn:nbn:se:hj:diva-8601 (URN)
Available from: 2009-04-27 Created: 2009-04-24 Last updated: 2017-08-14Bibliographically approved
3. Comparison of material properties in as-cast and austempered cast irons with three different graphite morphologies
Open this publication in new window or tab >>Comparison of material properties in as-cast and austempered cast irons with three different graphite morphologies
2008 (English)In: Giessereiforschung (International Foundry Research), ISSN 0046-5933, Vol. 60, no 3, 20-25 p.Article in journal (Refereed) Published
Abstract [en]

Three cast irons with different graphite morphologies were austempered in order to investigate how some important material properties are affected. The cast irons had similar chemical compositions so valid comparisons could be made between morphologies and between as-cast and austempered samples. The cast irons were austenitized for 2h at 900°C and austempered at 350°C for five different times, resulting in coarse ferrite needles. Microstructure, hardness, scuffing resistance, ultimate tensile strength (UTS) in bending and thermal properties was investigated for both as-cast and austempered samples. The hardness increased by about 25% after 110 min austempering while the thermal conductivity dropped about 30%, for all three morphologies. Scuffing resistance increased significantly when austempering lamellar graphite cast iron but was slightly reduced for both the compacted and nodular graphite morphologies. After 110 min austempering, the ultimate tensile strength was reduced for the lamellar and compacted samples, but was slightly increased for the nodular morphology.

Keyword
Austempering, Ausferrite, Lamellar graphite cast iron, Compacted graphite cast iron, Nodular graphite cast iron, Vickers hardness, Scuffing resistance, UTS, Thermal conductivity
National Category
Materials Engineering
Identifiers
urn:nbn:se:hj:diva-1657 (URN)
Available from: 2009-02-09 Created: 2008-09-30 Last updated: 2017-08-14Bibliographically approved
4. Tensile and Thermal Properties in Compacted Graphite Irons at Elevated Temperatures
Open this publication in new window or tab >>Tensile and Thermal Properties in Compacted Graphite Irons at Elevated Temperatures
2010 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 41, no 12, 3100-3109 p.Article 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.

Keyword
Compacted Graphite Iron, Mechanical Properties, Elevated temperature, Thermal conductivity, Molybdenum
National Category
Materials Engineering
Identifiers
urn:nbn:se:hj:diva-12565 (URN)10.1007/s11661-010-0385-1 (DOI)
Available from: 2010-06-17 Created: 2010-06-17 Last updated: 2010-12-13Bibliographically approved
5. Regression Analysis of Thermal Conductivity Based on Measurements of Compacted Graphite Irons
Open this publication in new window or tab >>Regression Analysis of Thermal Conductivity Based on Measurements of Compacted Graphite Irons
2009 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 40, no 13, 3235-3244 p.Article in journal (Refereed) Published
Abstract [en]

A model describing the thermal conductivity of compacted graphite iron (CGI) was created based on the microstructure analysis and thermal conductivity measurements of 76 compacted graphite samples. The thermal conductivity was measured using a laser flash apparatus for seven temperatures ranging between 35 C and 600 C. The model was created by solving a linear regression model taking into account the influence of carbon and silicon additions, nodularity, and fractions of ferrite and carbide constituents. Observations and the results from the model indicated a positive influence of the fraction of ferrite in the metal matrix on the thermal conductivity. Increasing the amount of carbon addition while keeping the CE value constant, i.e., at the same time reducing the silicon addition, had a positive effect on the thermal conductivity value. Nodularity is known to reduce the thermal conductivity and this was also confirmed. The fraction of carbides was low in the samples, making their influence slight.  A comparison of the thermal conductivity values calculated from the model with measured values showed a good agreement, even on materials not used to solve the linear regression model.

Keyword
Compacted graphite iron, Thermal conductivity, Laser Flash, Modeling, Nodularity, Ferrite, Cementite
Identifiers
urn:nbn:se:hj:diva-8605 (URN)10.1007/s11661-009-0042-8 (DOI)
Available from: 2009-04-27 Created: 2009-04-27 Last updated: 2010-11-23Bibliographically approved
6. Using Regression Analysis to Optimize the Combination of Thermal Conductivity and Hardness in Compacted Graphite Iron
Open this publication in new window or tab >>Using Regression Analysis to Optimize the Combination of Thermal Conductivity and Hardness in Compacted Graphite Iron
2010 (English)In: Key Engineering Materials, ISSN 1013-9826, Vol. 457, 337-342 p.Article in journal (Refereed) Published
Abstract [en]

In cast iron there is a contradictory relationship between thermal conductivity and strength. In many applications it is desirable to optimize the material properties to obtain both sufficiently high thermal conductivity and sufficiently high strength. The aim of this paper is to investigate how various microstructure parameters and alloying elements affect thermal conductivity and hardness in compacted graphite irons. It was found that the fraction of ferrite, the fraction of cementite, nodularity and content of carbon and silicon are parameters that influence the thermal conductivity and hardness the most. Based on these five key parameters linear regression equations were created for calculation of thermal conductivity and hardness. Ferrite and carbon have a positive influence on the thermal conductivity, while silicon, cementite and nodularity have a deleterious effect. All parameters except ferrite have a positive influence on the hardness. This is because the thermal conductivity is dependent on the movement of free electrons, and therefore unfavourable growth directions and grain boundaries which impede the electron movement will reduce the thermal conductivity. Ferrite has quite high thermal conductivity, while cementite has poor thermal conductivity, due to an unfavourable crystal structure. Nodular shaped graphite has a lower thermal conductivity than compacted graphite which explains the deleterious influence of nodularity. The soft ferrite phase will reduce the hardness value, while increasing the fraction of harder graphite nodules and harder cementite phase will increase the hardness. To investigate how these five parameters affect the combination of hardness and thermal conductivity, values for hardness and thermal conductivity were calculated for all combinations of key parameters in given intervals, using two linear regression equations. From these it is possible to predict the combination of parameters which gives a particular combination of hardness and thermal conductivity in compacted graphite iron.

Keyword
Compacted Graphite Iron (CGI), Regression Analysis, Thermal Conductivity (TC), Vickers Hardness
National Category
Engineering and Technology
Identifiers
urn:nbn:se:hj:diva-13472 (URN)10.4028/www.scientific.net/KEM.457.337 (DOI)
Available from: 2010-10-08 Created: 2010-10-08 Last updated: 2011-12-14Bibliographically approved
7. Comparing Three Equations Used for Modeling the Tensile Flow Behavior of Compacted Graphite Cast Irons at Elevated Temperatures
Open this publication in new window or tab >>Comparing Three Equations Used for Modeling the Tensile Flow Behavior of Compacted Graphite Cast Irons at Elevated Temperatures
2010 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 41, no 11, 2805-2815 p.Article in journal (Refereed) Published
Abstract [en]

A comparison between three constituent relationships used to approximate the plastic part of a tensile test curve, was performed on compacted graphite cast iron (CGI) samples at temperatures between room temperature and 600{degree sign}C. The investigated relationships were Hollomon, Ludwigson and Voce equations, where Ludwigson equation adjusts Hollomon equation by adding a correction term. The investigated CGI materials were alloyed with four different amounts of molybdenum and each chemical composition was cast with three different solidification rates. The coefficients in the equations generally were quite temperature independent between room temperature and 300{degree sign}C, but changed much in value as the temperature was further increased. Compared to Hollomon and Ludwigson equation, the coefficients in Voce equation directly showed correlation between proof stress at 0.1 % strain and ultimate tensile strength. Another difference between Voce equation and the other two equations is that Voce is not intended to give an accurate description of the stress values at small plastic strain values. The overall best approximation of the stress values was made by Ludwigson equation, followed by Hollomon and last Voce equation. The downside with Ludwigson equation was that its correction term could either be positive or negative, depending on the total plastic strain and the value of coefficients in Hollomon equation. This makes it harder to use as a general equation to approximate stress values compared to Hollomon and Voce equations.

Keyword
Hollomon, Ludwigson, Voce, Compacted Graphite Iron, Elevated Temperature, Plastic Deformation
National Category
Materials Engineering
Identifiers
urn:nbn:se:hj:diva-12566 (URN)10.1007/s11661-010-0354-8 (DOI)
Available from: 2010-06-17 Created: 2010-06-17 Last updated: 2010-11-23Bibliographically approved

Open Access in DiVA

No full text

Search in DiVA

By author/editor
Selin, Martin
By organisation
JTH. Research area Materials and Manufacturing - Casting
Materials Engineering

Search outside of DiVA

GoogleGoogle Scholar

Total: 409 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf