Grey iron (G3000) is a class of iron that is used to manufacture a wide variety of components throughout the world. More than 32 million tons were poured in 1996 (1). The machinability of cast iron at various times is difficult and often cannot readily be linked to the manufacturing or casting processes. This recurring machinability problem coupled with an inability to positively identify its cause has been very costly. A closer look at the microstructural differences in castings revealed that there is a qualitative difference in the coarseness of the pearlite between parts that machine well and those that were difficult to machine in a production setting.