The influence of alloying elements on the chill formation in Compacted Graphite Iron (CGI) is investigated. Chill wedges cast in an industrial foundry were used to investigate the chill formation. A total number of 19 chemical compositions were studied, including three trials of varying nodularity treatment level; four trials of varying copper content; four trials of varying silicon content; four trials of varying tin content and four trials of varying carbide promoter content. Three wedges were cast for each alloy composition, of which one was used for measuring the temperature at three different heights in the wedge.

Contrary to some previous reports, the results indicate that low-nodularity CGI is not more prone to chill formation (columnar white) than high-nodularity CGI. Trends regarding the effect of alloying elements on chill formation are shown to generally be in agreement with previous work on spheroidal graphite iron and lamellar graphite iron. Most of the samples also show carbide formation in centre line areas of the wedge (inverse chill), this occurrence is also discussed in the paper.

In the present work the ferrite growth in Compacted Graphite Iron (CGI) has been modeled. The relative amounts of ferrite and pearlite are of vital importance for the mechanical properties of cast iron. Thus, the possibility to predict the matrix microstructure in CGI by means of simulation would be an indispensable tool for foundries and design engineers. The increasing use of CGI, especially for automotive applications, further creates a need for this research.

This study shows that graphite in CGI grows in cells similar to eutectic grey iron cells. In cast irons the ferrite nucleates on the graphite and thereafter grows around the graphite particles until the formation of pearlite interrupts further ferrite formation. The complexity of the graphite particles in CGI imply that the ferrite will grow in different stages. A microstructure study of CGI reveals that ferrite nucleates on compacted graphite particles where low amounts of pearlite stabilizing elements can be found. Growth of ferrite then proceeds until it impinges with ferrite nucleated on adjacent graphite particles. Further ferrite growth takes place radially away from the center of the CGI cell until pearlite nucleation interrupts its growth. At some point during this process ferrite nucleates on graphite nodules in the last to freeze areas of the microstructure giving a contribution to the ferrite content. In the present work growth models of ferrite in nodular cast iron are adapted to CGI.

The influence of alloying elements and cooling conditions on compacted graphite iron is investigated. To investigate the influence of different alloying elements a sampling cup, designed for thermal analysis, and tensile test bars were cast. A total of 19 casting trials were performed and for each of the trials three different cooling conditions were studied for both the sampling cup and the tensile test bars. Mg has a major influence on the graphite morphology and causes a substantial increase in nodularity. Cu, Si and Sn only cause minor changes in the nodularity, but on the other hand affect the mechanical properties primarily by altering the pearlite content of the material. Cr and Mo are investigated mainly with respect to their carbide promoting properties. However, no columnar white structure was found in the microstructure. The relationship between the microstructure and the thermal history caused by differences in alloying content is also studied.

The influence of copper content (0.26 to 1.31 wt-%) on microstructure formation and mechanicalproperties of compacted graphite iron (CGI) has been evaluated through standard metallographicanalysis, colour etching techniques and tensile testing of machined test bars. Theproperties investigated are yield strength, tensile strength and elongation. The castings weremade in an industrial environment from a combination of CGI returns, pig iron, cast iron- and steelscrap. A total of four heats were cast in specially designed sampling cups (3 different coolingrates), chill wedges as well as tensile test bars machined from sand moulded cylinders (20, 45and 85 mm in diameter). The results clearly illustrate the combined effect of copper and coolingrate on nodularity, chilling tendency as well as pearlite content. A discussion concerning the effectof graphite morphology on the ferrite growth is also included.

The literature concerning microstructure formation in Compacted Graphite Iron (CGI) is reviewed. CGI has an intermediate graphite morphology between Lamellar Graphite Iron (LGI) and Spheroidal Graphite Iron (SGI). The formation of compacted graphite morphology is controlled by small changes in alloy composition. Several important factors influencing the formation of the as-solidified microstructure, as well as the microstructure formation during the eutectoid transformation are also reviewed. The focus of this review is to compare mechanisms in which CGI differs from LGI and SGI. The effects of microstructure on some properties that are relevant in commercial applications are included in the study. Additionally the relatively few models for microstructure formation are also summarised.