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- Selin, Martin, 1979-, et al.
(författare)
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Effect of Alloying Elements on Graphite Morphology in CGI
- 2010
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Ingår i: Materials Science Forum. - Zurich : Trans Tech Publications. - 0255-5476 .- 1662-9752. ; 649, s. 171-176
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Selin, Martin, 1979-
(författare)
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On Thermal Conductivity and Strength in Compacted Graphite Irons : Influence of Temperature and Microstructure
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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