ABSTRACT
Nitriding is among the most effective surface treatments. The main benefits of nitriding on steels are the increasing in hardness, wear resistance, fatigue resistance and corrosion resistance. Therefore, this study aims to evaluate the response of AISI 4140 to different nitriding conditions, regarding chemical, microstructure, hardness and tribological properties. To accomplish this, metallographic analyzes, optical emission spectroscopy glow discharge (GDOES), x-ray diffraction, hardness and pin-on-disc test were performed. Gaseous nitriding were performed in two different conditions, with nitriding potential of 0.6 and 2.0. The process time was two, four and six hours. Additionally, a nitrocarburizing treatment was carried out with the addition of carbon via CO2 gas injection with carburizing potential of 1.0. The results showed the formation of white layer followed by a diffusion layer with gradient properties as hardness and chemical composition. A significant increase in hardness about 400 HV is observed in the diffusion. The different treatments showed that the nitriding potential have more influence on the thickness than the treatment time. The nitrocarburized sample formed a nitrided layer 21% less thick than the nitrided sample with same nitriding potential, while the pore layer was similar. In performed tribological tests, there was a 61% decrease in wear due to the presence of the nitrided and the wear mode changed from abrasive / adhesive to abrasive mode.
Keywords:
Gas nitriding; AISI 4140 steel grade; pin-on-disc; x-ray diffraction; GDOS
