The chemical composition of cast iron used for casting ball bearing machining disks was varied to optimize the properties such as castability, hardenability, and durability in ball machining. The cast iron characteristics were most strongly dependent on the Ni content and the carbon saturation degree, Sc. This paper describes the types of test specimens, the working conditions, and the experimental results. The in- crease of the degree of carbon saturation reduces the tendency to form shrinkholes in the castings. The de- crease in the Ni content negatively affects the final hardening treatment. A way to control solidification de- fects in cast iron, by reducing the Ni content, has been verified on cast disks. The chemical composition of cast iron used for casting ball bearing machining disks was varied to optimize the properties such as castability, hardenability, and durability in ball machining. The cast iron characteristics were most strongly dependent on the Ni content and the carbon saturation degree, Sc The paper describes the types of test specimens, the working conditions, and the experimental results. The in- crease of the degree of carbon saturation reduces the tendency to form shrinkholes in the castings. The de- crease in the Ni content negatively affects the the final hardening treatment. A way to control solidification de- fects in cast iron, by reducing the Ni content, has been verified on cast disks.