Abstract

Plasma carbonitriding has been used to improve the tribological and mechanical properties of materials, specially iron-based alloys. The Pulsed Glow Discharge (PGD) technique was used for carbonitriding steel in order to investígate the effect of the cooling conditions on the properties of the formed layers. This method is more económical than others because it provides for faster nitrogen and carbon diffusion, which in turn allows for lower processing temperatures and/or shorter treatment limes with satisfactory results. Two sample sets were carbonitrided in a gas mixture of 2 vol % CH4, 20 vol % N2  78 vol % H2 under a pressure of 400 Pa, discharge frequency of 9 kHz, the temperature of 580 °C, for 90 minutes. The first sample set was cooled under vacuum and the second set was quíckly removed from the furnace and then quenched in oil. The two sets were characterized by optical microscopy (OM). X-ray diffraction (XRD), and microhardness. Our results showed that it is possible to change the microstructural profile of carbonitrided steel by using different cooling modes. For the sample slowly cooled inside the chamber, the compound layer consists of Epsilon-Fe2-3N, Gamma-Fe4N, Fe3C. Gamma-FeN0.0095 and CrN phases. The Epsilon-Fe2-3N and Gamma-Fe4N phases of the nitrided layer are not detected for the sample cooled in oil. Also, the Alfa-Fe and FeFe2O4 phases were detected at the surface of the sample quenched in oil.