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On the Microstructure and the Thermal Conductivity in Compacted Graphite Iron
Jönköping University, School of Engineering, JTH. Research area Component Technology.
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Compacted graphite iron (CGI) is a cast iron material that has gained much attention due to its attractive material properties which are intermediate between those of grey and ductile cast iron. In the automotive industry compacted graphite iron has become an interesting alternative material to grey cast iron in components like cylinder blocks or cylinder heads. The reason for this interest is the higher strength found in CGI. However, one disadvantage is the lower thermal conductivity of CGI compared to grey cast iron. The aim of the present work is to investigate how chemical composition and cooling rate affects the microstructure in compacted graphite iron and trying to relate the microstructure to the thermal conductivity. The effect of an austempering heat treatment process on some material properties in CGI, grey and ductile cast iron is also investigated.

 

The austempering heat treatment was shown to have a significant influence on many of the material properties investigated. The hardness was increased, while the thermal conductivity was reduced, for all three graphite morphologies observed. Scuffing resistance increased considerably for the austempered grey iron but was slightly reduced for the other two austempered morphologies. The ultimate tensile strength in bending was reduced in the austempered grey iron and CGI samples but slightly increased in the ductile iron sample.

 

It was confirmed that alloying elements like magnesium increased nodularity, while copper and tin promoted formation of pearlite in CGI. Silicon had a ferrite promoting effect as well as an inoculating effect and chromium and molybdenum promoted formation of carbides. The thermal conductivity was highly affected by the fraction of ferrite as well as nodularity and addition of carbon and silicon. Based on these results a mathematical model was developed for calculation of the thermal conductivity at various temperatures. 

Place, publisher, year, edition, pages
Göteborg: Chalmers University of Technology , 2009. , p. 90
Series
Research Series from Chalmers University of Technology, ISSN 1652-8891 ; 46/2009
Keywords [en]
Compacted graphite iron, Microstructure, Thermal conductivity, Ferrite, Cementite, Nodularity, Mathematical modelling, Laser flash technique, Austempering
Identifiers
URN: urn:nbn:se:hj:diva-8606OAI: oai:DiVA.org:hj-8606DiVA, id: diva2:213065
Presentation
2009-03-27, E1405, Gjuterigatan 5, Jönköping, 10:00 (Swedish)
Opponent
Supervisors
Available from: 2009-05-04 Created: 2009-04-27 Last updated: 2009-05-04Bibliographically approved
List of papers
1. 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, p. 20-25Article 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.

Keywords
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
2. 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, E-ISSN 1662-9752, Solidification and Gravity V, Vol. 649, p. 171-176Article 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
Keywords
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: 2017-12-13Bibliographically approved
3. 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, E-ISSN 1743-1336, Vol. 22, no 1-4, p. 283-285Article 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
Keywords
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: 2017-12-13Bibliographically approved
4. Regression Model Describing the Thermal Conductivity of Various Cast Irons
Open this publication in new window or tab >>Regression Model Describing the Thermal Conductivity of Various Cast Irons
2010 (English)In: Solidification and Gravity V, Zurich: Trans Tech Publications , 2010, Vol. 649, p. 499-504Conference paper, Published paper (Refereed)
Abstract [en]

The thermal conductivity of various grades of pearlitic cast iron has been modelled with good results by means of regression analysis. The experimental thermal conductivity data, which the modelling is based on, were obtained by the laser flash method. The microstructure was investigated by digital image analysis combined with a colour etching technique. The model developed takes the carbon content, the silicon content, the nodularity as well as the fraction of cementite into consideration. The graphite morphologies of the samples investigated were lamellar, compacted and spheroidal.

Place, publisher, year, edition, pages
Zurich: Trans Tech Publications, 2010
Keywords
Thermal Conductivity, Modelling, Lamellar graphite Iron, Compacted Graphite Iron, Spheroidal graphite Iron, Microstructure
Identifiers
urn:nbn:se:hj:diva-8604 (URN)
Conference
5th International Conference on Solidification and Gravity
Available from: 2009-04-27 Created: 2009-04-27 Last updated: 2010-09-09Bibliographically 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, p. 3235-3244Article 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.

Keywords
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: 2017-12-13Bibliographically approved

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