Efeito da variação do fluxo de metano e nitrogênio na cementação a plasma a baixa temperatura de ferro puro sinterizado

Abstract

Low temperature plasma carburizing is a surface thermochemical treatment commonly performed on stainless steels as it prevents the sensitization phenomenon when compared to carburizing at high temperatures. Other advantages of performing such a low temperature treatment is, for example, the greater geometric and dimensional control, the lower energy consumption. However, the effects of pulsating the gases during carburizing and carburizing - nitriding have not yet been evaluated in the carburizing of steels, [1, 2]. In this work, carburizing and carburizing - nitriding were carried out at 500 ° C of sintered pure iron, and the influence of the gas pulse was studied. Surface cleaning of the samples improved when the gases were pulsed during the treatments in which there was no gas pulse. The layer thickness had a slight increase for the samples with a longer carburizing pulse time. For samples cemented with pulse of gases a with higher methane pulse time presented the best regularity and uniformity of layer. As for the cemented and nitrided samples with pulse of the gases, the sample with the intermediate time of nitrogen pulse was the one that presented better regularity and uniformity of layer. In the diffractographic analysis, all the samples had cementite (Fe3C) and the ferrite phase (α - Fe). In the cemented and nitrided samples with pulse of gases, there was also the presence of a diffusion zone and nitrites, except for the sample with the shortest pulse time of the nitrogen. In general, the gas pulse during the treatments was efficient in avoiding the formation of graphite on the surface of the samples as well as improving the uniformity and average thickness of the formed layer.