Investigation on the machinability of GGG70 cast iron that mechanical properties have been improved with heat treatment

Austempered ductile cast iron (ADI), produced by applying austenitization and austempering heat treatment to spheroidal graphite cast iron, exhibits superior properties such as high strength to weight ratio, toughness, ductility, wear resistance and fatigue strength. With these features, it takes the place of forged steel, cast iron and carbon steels and it attracts the attention of the automotive industry especially. However, its superior mechanical properties reduce the machinability of ADI. For this reason, despite its superior features, the applications of ADI are expanding in a limited way. For this reason, it is important to carry out the necessary research for the successful machining of ADI. In this study, the machinability of Austempered GGG-70 spheroidal graphite cast iron, which is planned to be used in crank manufacturing in the automotive industry, was investigated. In this context, samples were casted. After casting, its chemical composition was determined. Samples at 930°C for 120 min. austenitized, then 120 min at 350℃. austempered. Machinability tests were carried out in CNC vertical machining center. The effects of cutting conditions on cutting force, surface roughness and cutting tool wear were determined by applying different depths of cut, cutting and feed rates. As a result of the machinability experiments, it was seen that the depth of cut was the parameter that has the most effect on the cutting force and surface roughness. It was found that the surface roughness increased with the increase in cutting speed, while the cutting force decreased. It was determined that the cutting force increased with the increase of the feed rate, but there was no significant change in the surface roughness. With increasing depth of cut, both cutting force and surface roughness increased significantly. In the experiments carried out, the average surface roughness was 1.90 µm at the most and 0.59 µm at the lowest. In the tool wear tests, it was found that crater wear was more dominant than flank wear. It was determined that the tool life was completed when the crater width (KB) value reached 0.36 mm. It has been concluded that when austempered GGG70 material is machined with AlTiN/TiN PVD coated tungsten carbide inserts, 0.5 mm depth of cut and low cutting speeds such as 130 m/min, very smooth surfaces can be obtained, that is, the machinability is high. A reasonable level of tool life, such as 35 minutes, was achieved when the cutting speed was kept at 130 m/min.