Effect of Nb Addition on the Machinability of a Pearlitic Gray Cast Iron

Due to its high thermal conductivity, good damping performance and superior machinability, gray cast iron (GCI) has found many applications in the automotive industry. However, this material has given way to other cast irons due to the need for materials with higher mechanical strength and toughness. Actual efforts have been made to reformulate the GCI chemical composition to obtain different microstructures for improving its mechanical properties. In this study, the influence of Nb content on the microstructure and machinability of GCI was investigated when turning under cutting speeds of 240, 360, and 480 m/min, feed rates of 0.25 and 0.50 mm/rev, and using two different chip breaker geometries (Flat Top and GH). The Nb addition decreased the graphite size and refined the pearlitic interlamellar spacing. However, it did not produce significant alteration in the number of eutectic cells and hardness. Regardless of the Nb content, the presence of chip breaker GH and the lower levels of cutting speed and feed rate were associated with superior machinability. The increase in the Nb content in the GCI raised all the components of the machining forces, yet it did not promote significant changes in the chip temperature and decreased the surface roughness after turning.