Recently, a group of scientists (K. Jalava et. al.) from Aalto University and Wärtsilä Finland Oy have investigated the thermal conductivity of cast iron as function of alloying and austemperering in two recent publications:
- Effect on Silicon and Microstructure on Spheroidal Graphite Cast Iron Thermal Conductivity at Elevated Temperatures, International Journal of Metalcasting, 2017
- Elevated Temperature Thermal Conductivity of some As-Cast and Austempered Cast Irons, Material Science and Technology, 2017
The link between microstructure and thermal conductivity in cast irons is investigated and made obvious in these studies. As a matter of fact, it is clearly shown that higher levels of alloying elements will reduce thermal conductivity. The same is true for more complex microstructures. Consequently, improving mechanical properties typically results in reduced thermal conductivity. Examined was also the thermal conductivity as a function of temperature. The temperature range from ambient to 400 °C was in focus, showing a thermal conductivity peak in the 200 °C to 300 °C area for most materials. Lamellar graphite cast iron is the exception, which instead show a decreasing thermal conductivity in the entire temperature range.
Hot Disk benefits
The key to the successful thermal conductivity testing in this project was the Hot Disk TPS 2500 S instrument and the versatility of the samples possible to test. Samples can have almost any shape or finish when working with the Hot Disk method. As a result, sample preparation is comparably easy. With no need to spend precious time to prepare identical samples, a greater number of samples could be processed. Furthermore, larger sample size made synthesis easier in this case. Another benefit of testing samples with more volume is that the results become more representative and stable.
We would like to thank Kalle Jalava and his co-authors for this interesting research and clever use of the Hot Disk technique. To read the full publications, please use the links at the beginning of the article.