Transições no regime de desgaste por deslizamento do aço inoxidável austenítico AISI 316L processado a plasma

Abstract

This work investigate the influence of different plasma treatments on the wear resistance of AISI 316L austenitic stainless steel. The chosen plasma treatments were: nitriding conducted at 450°C for 5 hour, carburizing at 475°C for 3 hours, and a sequential process composed of nitriding at 450°C for 5 hours followed by carburizing at 475 ° C for 3 hours. In order to correlate wear behavior and microstructure as well as the concentration of nitrogen and carbon at the surface, the plasma treated samples were thoroughly investigated by means of scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), wear tests, profilometry, micro- and nanoindentation. Each plasma treatment led to the formation of a modified surface layer of the AISI 316L steel. The results showed that the surface layers had different thicknesses for each of the three different treatments and two expanded austenitic structures are formed without the presence of precipitates. On the sliding wear tests, sharp transitions were observed, probably due to the plasma modified surface layers. After identifying the sliding distances corresponding to these transitions, the tests were stopped at these points and EDS compositional maps of the wear tracks were taken. The depth of wear tracks and the worn volumes were measured by profilometry. Significant reductions in carbon and/or nitrogen concentrations of each partial wear curve, indicate that the modified layers were almost worn out at these positions. Comparing the worn volumes, the sequentially plasma treated sample showed the best wear resistance. For this system three defined regimes were identified: the first probably correlated with the upper nitrided layer, the second with the carburized layer and finally the third one with the steel AISI 316L no treatment. Micro- and nanohardness measurements demonstrated that the wear behavior can be related to the different mechanical properties of these three different layers. A steady-state wear will be only observed for long sliding distances, when the worn material already corresponds to steel AISI 316L no treatment. This study shows that the wear behavior is strongly related to the particular structure of the modified surface.