Dependency of machinability in gray cast iron on nitride-induced age strengthening

Work of previous researchers has suggested that room temperature age strengthening in gray cast irons improves machinability. Verification and quantification of the machinability improvement is important to industry. Improved machinability will reduce overall manufacturing costs and reduce raw material consumption by decreasing the rate at which tools are replaced.;Experimental work was performed to determine a connection between improved machinability in gray cast iron and changes in machining mechanics. An industrial tool wear study verified that age strengthening improved machinability by reducing tool wear to less than one-quarter of the unaged value. Laboratory tests on iron castings from the same foundry determined that tool forces decreased with age strengthening. Additional tool force experiments were performed on castings produced in the Missouri S&T laboratory of varying carbon equivalent and microstructure. Results showed that casting microstructure played a key role in determining how age strengthening affects machinability and that the equilibrium precipitate content did not solely dictate magnitudes of hardness increases or tool force decreases after age strengthening.;Machining work with industrial castings resulted in cases in which gray iron decreased in machinability after age strengthening, a situation that was previously only anecdotally reported. The determination was made that irons containing greater than one percent free ferrite increase in machinability after age strengthening.;Research concluded that gray iron age strengthening improved machinability by lowering fracture toughness which decreases tool-chip contact time thereby reducing tool temperature and tool wear.