Compacted graphite iron (CGI) is an intermediate material between conventional grey cast iron and the stronger, more wear resistant ductile iron, making it a suitable material choice for different automotive applications. The improved material properties of CGI as to conventional grey cast iron makes it more difficult to machine, and finding a suitable tool material with low wear rates is a challenge and remains largely unexplored in research. This study examines the performance of multilayer PVD (Ti,Si)N-(Ti,Al)N coated cemented carbide round inserts at varying cutting data parameters in the down face dry milling of pearlitic CGI grade EN-GJV-450. Eight different cutting conditions, with a cutting speed range vc = 154–461 m/min and feed per tooth range fz = 0.277–0.554 mm/rev were evaluated. As-worn tools are studied and later cross-sectioned to be further analysed under a scanning electron microscope (SEM). The primary wear mechanisms identified included adhesion, abrasive wear, thermal crack formation, particularly comb cracks, and diffusional dissolution of WC and Co. Cobalt diffusion from the binder into the CGI material, along with a potential tungsten oxidation within cracks, led to significant tool degradation, forming Co carbides and Fe-doped WO3, respectively. The interaction between CGI material and the PVD coating also resulted in the formation of a Mg-Si-O rich layer atop (Ti,Si)N-(Ti,Al)N coating, which could potentially act as a protective barrier. Additionally, in some conditions due to outward diffusion from WC grains together with Fe form a strong carbide Tool Protection Layer (TPL) which is developed as flank built-up edge atop the exposed cemented carbide, potentially extending tool life by reducing further wear.