Study of the plasma nitriding effect on high-speed steel drills: performance in dry machining

High-speed steel is one of the most widely used materials in machining tools. However, applications such as dry machining require superior properties to those presented by conventional tools. Surface treatments such as plasma nitriding are alternatives to improve these properties. This work proposes a study of the application of plasma nitriding with lower temperatures and times (300°C, 350°C and 400°C, for 2 hours) on high-speed steel tools to be evaluated in dry drilling process. The samples were characterized by optical microscopy, scanning electron microscopy, X-ray diffraction with application of Rietveld routine, surface microhardness, microhardness profile and average surface roughness (Ra) measurements. Then, the tools were submitted to performance simulation in a CNC machining center and analyzed based on measurements of the flank wear evolution, the required electric current by the machine during cutting times and by the diameter and surface roughness of the machined holes. The results showed an increase in flank wear with the treatment at 400°C due to the higher surface roughness, while the tools treated at lower temperatures showed better performance than the untreated tool, evidenced by the lower wear rate in the steady state, by machining all holes within tolerance limits and by the lower surface roughness of the holes. It was observed, thus, that treatments at lower temperatures produce conditions of greater balance between hardness and surface roughness, contributing to higher wear resistance.