Effect of the gray cast iron microstructure on milling tool life and cutting force

Gray cast irons are frequently used in machine tool beds due to low cost, high vibration damping capacity, and easiness of manufacturing. The guiding standards for production of these alloys determine their classes based on the range of tensile strength and shape of graphites. This research project aims at investigating the differences in machinability between two gray cast irons belonging to the same class (GG25), i.e., within the same standard tolerance, but with different pearlitic/ferritic concentrations. Machinability was evaluated in terms of tool life and cutting forces in milling operations using carbide and ceramic tools and two different cutting speeds. Two different materials were used as samples, one containing 100 % pearlite and another with 50 % pearlite + 50 % ferrite. The results showed that milling of the 100 % pearlitic alloy led to faster tool wear and higher cutting forces than in the 50 % ferritic alloy. Ceramic tools exhibited longer life than carbide tools. The observed wear mechanisms were diffusion, attrition, and thermal cracks. However, material microstructure was observed to be far more significant for tool life and cutting force than the other input variables (cutting speed and tool material).