Tool Wear in the Machining of Leaded Free-Cutting Steel

Tool wear has been investigated when cutting leaded 0.11%C free-cutting steel with cemented carbide, uncoated high-speed steel and titanium nitride coated high-speed steel tools. The lead addition extended the cutting speed range over which the beneficial effects of the other free-machining additives could be exploited; lead also delayed the maximum height of the built-up-edge to higher cutting speeds, but caused severe grooving wear when cutting at speeds below 120 m/min. with uncoated high-speed steel and cemented carbide tools. With titanium nitride coated tools, however, there was no apparent wear after 20 minutes cutting and no mechanical damage to the coating. The beneficial effects of coating are explained in terms of its interaction with manganese sulphide at the chip tool interface whilst the role of lead in causing wear in uncoated tools is similarly explained.