In general, the higher the hardness and strength of grey cast iron, the lower the metal cutting performance and the lower the life expectancy from the blade and tool. The metal cutting performance of most types of cast iron used in metal cutting production is generally good, indicating that the metal cutting performance is related to the structure, and the harder pearlitic cast iron is more difficult to process.
Flake graphite cast iron and malleable cast iron have excellent cutting properties, while ductile iron is quite bad. The main types of wear encountered when machining cast iron are abrasion, bonding and diffusion wear. Abrasion is mainly produced by carbides, sand inclusions and hard cast skin. The ferrite portion of gray cast iron is the easiest to weld to the insert, but this can be overcome by increasing the cutting speed and temperature.
On the other hand, diffusion wear is temperature dependent and occurs at high cutting speeds, especially when high strength cast iron grades are used, which have high resistance to deformation and result in high temperatures. This wear is related to the interaction between the cast iron and the tool, which allows some gray cast irons to be machined at high speeds with ceramic or cubic boron nitride tools for good tool life and surface quality.
Typical tool properties required for machining cast iron are: high heat hardness and chemical stability, but also related to process, workpiece and cutting conditions; the cutting edge is required to have toughness, heat fatigue wear and edge strength. The degree of satisfaction with cutting cast iron depends on how the wear of the cutting edge develops.