New technology reinforces the industrial manufacturing of Compact Graphite Iron (CGI) components

Based on thermal analysis, the new development from AZTERLAN Metallurgy Research Center correlates the various factors involved in the formation of compact graphite (CGI) and provides a significant boost to the industrial production of compact graphite iron cast components.

Compact graphite iron (CGI), also known as vermicular graphite iron, displays outstanding mechanical properties such as high thermal conductivity and vibration damping, comprised between those of lamellar and spheroidal cast iron.

These qualities make this material notably attractive for applications that require high thermal conductivity, which are currently manufactured in grey cast iron. Due to its higher mechanical properties, the use of CGI allows to implement design optimization and weight reduction strategies, which are a key factor for diverse applications, like in the automotive sector.

Nevertheless, despite of the great features and performance of this material, the complicated and not quite stable production process impedes CGI to jump into industrial manufacturing.

As explained by the AZTERLAN researcher Mr. Urko de la Torre, “the characteristics offered by this material rely on the compact shape of the graphite, an intermediate state between the isolated graphite nodules from ductile iron and the interconnected lamellae graphite characteristic from the grey iron. This intermediate morphology increases the thermal conductivity and the capacity to damp vibrations compared to ductile iron; at the same time, not being an interconnected structure, presents optimised mechanical properties compared to grey iron. Therefore CGI is considered a promising material to be implemented in high performance applications”.

To achieve the characteristic graphitic morphology from CGI the conventional methodology applied by foundries entails the addition to the molten metal of a smaller portion of nodulizing alloy, than the one used for ductile iron. Nevertheless, this step is not enough to ensure a correct graphitic development. Other process factors such as the cooling rate (defined by the geometry of the part and the thermal modules from its different zones), the sulphur and oxygen content from the base metal and its chemical composition (for instance, the titanium content, that promotes the formation of compact graphite), are also key to achieve the correct graphite formation in the CGI.

With the aim of overcoming these limitations and building a robust process, researchers from AZTERLAN Metallurgy Research Centre have developed a methodology that, based on thermal analysis, allows to predict in real time the index of nodularity and the proper formation of compact graphite. “This new method makes it possible to ensure, in less than 3 minutes, that the graphite formed owns the desired shape. To achieve that, we rely on the Thermolan® thermal analysis system taking into account the metallurgical properties from liquid metal by the control of its solidification curve and the geometric characteristics of the part, to extrapolate the results according to the specific reference being manufactured at the moment”.

This new development provides a significative boost to the industrial production of compact graphite iron castings. “We have overcome the great instability and variability that were present so far during the CGI production process. With this new and affordable control system we can assure systematically a stable manufacturing process assuring the required characteristics for a proper solidification scheme. If not, the foundry has the capacity to react at the right time during the manufacturing process. Thanks to this important development doors are now wide open for this promising material to reach new applications and developments”.

Real time control of the formation of CGI by means of Thermolan® system

Thermolan®, thermal analysis to ensure iron castings quality

Thermolan® is the metallurgical quality prediction system for spheroidal, lamellar and compact graphite iron developed by AZTERLAN Metallurgy Research Centre and VEIGALAN (developer of technological solutions for metallic transformation processes).

By correlating cooling curves and their decisive temperatures, as well as the shape they acquire from the beginning to the end of the solidification process, Thermolan® determines the effect of raw materials, chemical composition and inoculation on the base metal, among many other aspects, as well as how these parameters affect to graphite generation and shape. Apart from predicting the metallurgical quality of each casting process, it proposes corrective actions to improve it in real time.