The Heat Capacity and Coefficient of Linear Expansion of Non-alloyed Spheroidal Graphite Cast Iron
Introduction
Spheroidal graphite (SG) cast iron has an excellent combination of properties that are suitable for various applications. It is a preferred material for components subjected to high stresses and rigors. In order to select the material the following properties have to be taken into consideration that include the heat capacity and coefficient of linear expansion. An understanding of these properties and how they vary for different SG cast iron compositions is important for the selection and design of components.
Heat Capacity
Heat capacity is the specific heat amount at constant pressure (cp) or constant volume (cv) and is measured in joules per gram Kelvin (J/gK). Heat capacity is an important property of materials as it affects the amount of heat required to increase the temperature of the material.
The heat capacity of SG cast iron is higher than that of other types of cast iron due to its greater crystallite size and larger volume fraction of graphite. The heat capacity of SG cast iron increases with increasing graphite content and is inversely proportional to the temperature, decreasing with increasing temperature. This decrease in heat capacity is attributed to the reduction in bonding energy at increasing temperatures resulting in a decrease in available heat capacity.
Coefficient of Linear Expansion
The coefficient of linear expansion (α) is the percentage increase in length per degree of temperature change, measured in units of m/mK. The coefficient of linear expansion is an important property of materials as it affects the rate at which components expand or contract as temperature changes.
The coefficient of linear expansion of SG cast iron is higher than that of other types of cast iron due to its greater graphite content and smaller grain size. The coefficient of linear expansion increases with increasing graphite content and is proportional to the temperature, increasing with increasing temperature. This increase in coefficient of linear expansion is attributed to the increase in mobility of atoms in materials as the temperature rises resulting in an increase in available expansion.
Conclusion
The heat capacity and coefficient of linear expansion of SG cast iron are important properties that affect the selection and design of components. The heat capacity of SG cast iron is higher than that of other types of cast irons due to its greater crystallite size and larger volume fraction of graphite. The coefficient of linear expansion of SG cast iron is higher than that of other types of cast iron due to its greater graphite content and smaller grain size. Both properties increase with increasing graphite content and are proportional to the temperature, increasing with increasing temperature. These properties should be taken into consideration when selecting or designing components subjected to high stresses and rigors.
