Machinability of calcium-treated steels using TiN-coated high-speed steel tools

AbstractTurning tests were carried out with TiN-coated and uncoated high-speed steel (HSS) inserts. The workpiece materials consisted of steels corresponding approximately to AISI 4140 and AISI 8620. In addition to the standard grades, calcium-treated variants of each steel were studied. The calcium-treated grades produced from 15 to 80% longer lifetimes than the standard grades when cut with uncoated HSS tools. When the tools were TiN-coated, the lifetimes with calcium-treated grades increased from 40 to 500%. Energy dispersive X-ray spectrometry revealed increased amounts of elements including manganese, calcium, silicon, and sulphur on the surface of the TiN-coated tools, indicating the formation of a non-metallic protective layer on the tool surface, which is suggested as an explanation for the observed increase in the wear resistance.MST/565