Wear performance of surface treated drills in high speed drilling of AISI 304 stainless steel

In the present work, the effect of three surface-treated drills and one AlCrN (Alcrona) coated drill have been investigated at different levels of the cutting speed for drilling holes in AISI 304 SS. Three different high-speed steel (HSS) grades, including M2, M42, and M35, were utilized for the said purpose. Two types of drills, including M2 and M42 grades, were steam tempered (ST), which was performed at a temperature of 850 F to deposit a stable and corrosive resistance magnetite (Fe3O4) layer on the tool surface. One type of drill made from M35 HSS grade was ground (GR), while the other one was coated with similar to 4 mu m thick AlCrN PVD coating. With respect to tool life, M2-ST drill outperformed all other evaluated counterparts with a maximum tool life of 48 holes at 11 m/min cutting speed, while at this cutting speed, the M42-ST tool drilled just 15 holes. The lesser volume fraction of primary carbides present in the microstructure of M2-ST drills was thought to be the reason for its better performance in terms of reduced tool wear/higher tool life. Catastrophic fracture was encountered in the majority of the tests conducted with M35-GR and M35-AlCrN drills. The inferior performance of the former tools was attributed to strain hardening/brittleness induced as a result of grinding, while non-uniformity of the coating along the cutting edge was thought to be the possible cause of the poor performance of the latter drills. Regarding hole quality, M2-ST drills outclassed all other equivalent tools with diametric error ranging from 7 mu m to 25 mu m and surface roughness variations within 1 pm to 2.60 mu m.