1994 年 60 巻 9 号 p. 1314-1318
The drilling tests were performed on austempered ductile cast irons (ADI) with 2-3% silicon and 100-415/mm2 graphite nodules to clarify the factors influencing the machinability of ADI. The machinability of each specimen was evaluated using high speed steel drills of 6mm dia. The ductile cast iron specimens were austenitized at 900°C for 1 hour and then held at 375°C for 2 hours. The increase in graphite nodules raises the machinability of ADI, while the silicon content of matrix has little influence. The larger the number of graphite nodules is, the finer and the less the γ-pools are. The refinement and reduction of γ-pools suppress the fluctuation of thrust and torque loads. Furthermore, the larger number of graphite nodules promote the formation of flow type chips, which also contribute to the longer drill life.