Cast irons are characterized by their wide range of achievable mechanical and physical properties, in addition to their competitive prices compared to other materials in most industries. Cast irons, in general, consist of an iron matrix (pearlite, ferrite, austenite, etc.) and graphite, as well as smaller percentages of other additives. The morphology of graphite whether it is flaky, compact, or nodular, has a significant impact on the mechanical (and physical) properties of cast iron.

The graphite structure in compacted graphite iron (CGI) is more coral-like and interconnected only within each eutectic cell. The irregular surface of the graphite-matrix interface has blunt edges which results in the intimate adhesion of the graphite particles to the metal matrix producing more resistance to crack initiation and more vermicular paths arrest crack propagation. Furthermore, the coral-like graphite particles, which are characterized with round edges, also do not promote crack propagation and serve as crack arrestors once cracks are initiated. This unique morphology of graphite in CGI, thereafter, pays off in a higher tensile strength and modulus of elasticity while possessing reasonable thermal conductivity. This useful combination of double the ultimate strength, reasonable thermal conductivity, high modulus of elasticity, and superior crack initiation/propagation resistance in CGI as compared to gray cast iron (GCI), as well as the greater resistance to distortion and better thermal conductivity as compared to ductile (nodular) cast iron (SGI), all result in a valuable overall performance.

However, the same mechanical properties of compacted graphite iron (CGI) that contribute to higher performance than gray iron and aluminum alloys that are currently used in automotive and locomotive industries, make it relatively difficult to machine. Current approaches to deal with the relatively poor machinability of CGI have led to significant compromises. Despite the many efforts to improve the machinability of CGI at a practical level, it is evident that much work needs to be invested to reach current production and cost targets based on operations using gray cast iron.

This work is divided into two phases. The first phase establishes a foundation of a microstructure modeling technique which will be then applied to model CGI in machining. Modeling is being done to shift the approach away from trial and error as is currently being done to a more physics based approach. As machining is conceptually a controlled fracture process, this stage comprehensively studies and models the initiation and propagation of fracture in compacted graphite iron.

Very little research to date has been directed to the study of CGI’s mechanics under different loading scenarios. The absence of a comprehensive foundation to assist with the understanding of CGI’s mechanics under different loading scenarios motivates the initiation of this phase. One effective methodology to establish this comprehensive foundation is by utilizing the finite element method approach that is validated by metallurgical investigations. Most crack initiation and propagation investigations are performed as after-the-event procedures, thus the application of finite element method makes it possible to better understand the effect of graphite morphology on crack initiation and propagation. In addition, the finite element modeling of CGI crack initiation and propagation can exclude most of the complex interacting variables to make it possible to understand the inherently complex fracture phenomena which take place during machining.

The second phase serves as an application of the previously built model to capture the more complex scenario involving machining of CGI at different cutting speeds and feeds. The finite element modeling of CGI in machining provides an as of yet unavailable procedure on which future optimization techniques can be performed. The study of chip formation, cutting insert wear, and force measurements are performed in parallel with the modeling process and are employed as means to validate the FE model. Validation of both work phases has been completed to support the model developed in this thesis that captures the critical aspects of machining CGI under different operating scenarios.