Influência da temperatura de nitretação aplicada a brocas de aço rápido (HSS)

Abstract

The high-speed steel HSS M2 is one of the most used steels for the production of drills for the drilling process. As the drilling process is a machining operation which involves long operating time and high thermal power generation, the tool life is compromised. This tool life can be improved with the use of a thermochemical treatment. The main objective of this work is to investigate the influence of plasma nitriding temperature in the properties of the high-speed steel – HSS M2 applied to extracted samples from drill bits. In nitriding, the gas composition of the mixture, the treatment pressure and time were fixed for all samples, and the temperarure was changed. The gas composition of the mixture used was 25% N2 and 75% H2 in volume at a pressure of 2,5 mBar, with a four-hour treatment.The used temperarures were 400, 450 e 500 °C. The mechanical properties of the nitreted layers were characterized by surface microhardness, optical microscopy for the meansurement of the nitriding layer and X-ray diffraction for phase identification. As a result, we can check an increase in surface microhardness in all the treatment temperatures in relation to the non-nitrided substrate, but thje higher microhardness values were observed in the sample of lower nitriding temperature. The optical microscopy in the nitrited samples showed the formation of a layer of nitrides in the three treatments, with the thickness of the layer being proportional to the treatment temperature. The x- ray diffraction test revealed, for all treatment temperatures, the formation of iron nitrides ε-Fe3N e γ’-Fe4N