Effect of titanium on machinability of ductile iron

摘要

There is an increasing amount of titanium-containing steel entering the scrap cycle, but iron foundries are uncertain whether or not this can be used for producing iron castings. As part of a large project to assess the effects of Ti in cast iron, this paper describes the use of drilling tests to characterize the machinability of ferritic, pearlitic and ausferritic (austempered) ductile irons with varying Ti contents. The wear rate was very low when drilling ferritic ductile irons containing 0.006% Ti that had been cast in molds containing a ceramic foam filter in the running system. The addition of Ti increased drill wear, particularly when the Ti content was increased from 0.065 to 0.10%. The removal of the filter was also found to decrease the drill life significantly. The deliberate addition of nitrogen to a high-Ti iron melt (by injecting calcium cyanamide) was also found to have a beneficial effect on machinability. The drilling tests on the pearlitic ductile irons were not completed due to the unpredictable premature failure of the drills, but the available results suggest that the effect of Ti was much less marked. No satisfactory explanation for the premature failures was found. Cemented carbide drills gave a satisfactory performance for drilling austempered ductile iron (ADI) once conditions were optimized. Drill wear with the ADI plates did not seem to be a function of either the Ti content or the plate hardness, and seemed to reach a stable geometry after comparatively few holes.