Estudo da camada nitretada em superfícies externas e internas de tubulações metálicas

Abstract

Plasma nitriding allows obtaining physical modification on the metal surface, such as hardness, wear resistance and corrosion. In metal pipes lines, the great challenge is their action in reducing the pressure on liquids and their contaminants. In this sense, the present work proposes to produce thin films of iron nitride in pipe lines of low-carbon steel aiming at the improvement of mechanical properties that can infer improvement in resistance to corrosion. For this purpose, Cathodic Cage Plasma Nitriding (CCPN) was used. The proportion of gases (80% N 2 + 20% H2 + Ar or 20 N2 + 80% Ar + H2) and temperature (400 ° C, 450 ° C, 500 ° C) was changed, the sample was positioned outside the cage, at cathodic potential, and the other parameters were fixed. The thin films produced were evaluated using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and microhardness analysis. The presence of thin films in all the treated samples was identified and the increase in the thickness of these films was proportional to the increase of the temperature when the same proportion of gas was kept constant. However, due to the high pressure, the samples treated with predominantly inert atmosphere had a lower film thickness. Fe4N needles were found and proved by XRD analysis, also observing the presence of other phases of iron nitride (FeN, Fe2N, Fe3N). The determination of these phases evidenced the ability of corrosive protection of the films formed through previous studies. Regarding the hardness of the samples, the higher hardness was obtained in the treated samples with lower temperature (400ºC), but this increase was not propagated inside the models. The samples with higher diffusion zone and more uniform microhardness were found with a higher treatment temperature.