Machinability of Gray Cast Iron: A Drilling Study

摘要

C-bars of gray cast iron from nine different cupola-based heats were cast into nobake sand molds and then shaken out at a variety of temperatures and times. Alloy variations included carbon equivalence and the selection of various amounts of alloying elements. Shakeout temperatures were made consistently for each heat by the inclusion of thermocouples in the centers of each C-bar. Cooling curves were obtained for the entire temperature interval between solidification and including the pearlite reaction for each alloy and shakeout condition. A drilling study was carried out on the cross section of each C-bar in which a new titanium nitride coated drill bit was used for each specimen. Holes were drilled for a constant time at a constant drill speed with a constant load on the drill press spindle. The weight loss during drilling was taken as a measure of the machinability. It was shown that the machinability increased with decreasing shakeout temperature, decreased marginally with certain alloy additions and decreased significantly in heavily alloyed irons or in lower carbon equivalent irons, and increased significantly as the graphite fineness increased. X-ray diffraction analysis was used to estimate the amount of iron carbide present in the pearlite. Scanning electron microscopy and optical met-allography were used to evaluate the fineness of the pearlite.