Nitretação de aço inoxidável martensítico (aisi 4120) por descarga luminosa

In the present work was investigated nanoscale tribo-mechanical properties of martensitic stainless steel (AISI 420) subjected to nitriding by glow discharge (DL). Martensitic steels have been previously heat-treated in 1025 °C with subsequent rapid cooling in oil. The samples have been nitrided using the following parameters of temperature (°C) – time (h): 350/6, 400/6 e 450/6. The treatments were held in atmospheres of N2/H2 in the proportions of 20%-80% (in volume). For the characterization of the samples were employed the techniques of x-ray diffraction (DRX), scanning electron microscopy (SEM), optical microscopy (OM), atomic force microscopy (AFM) and Energy Dispersive X-ray Spectrometry (EDS). The nano scratch resistance and the mechanical properties were evaluated by instrumented indentation (II). To the samples treated by DL the temperature influences the formation of different stages (γN or αN, γ'-Fe4N, ε-Fe2 + xN, CrN). In the treatments carried out at low temperature (350 °C) the predominant phases formed was γ' and ε, due to difference in solubility and diffusivity of nitrogen in the martensite phases. Nitriding treatments cause the effect of chromium depletion in the temperature of 450 °C. The scratch resistance of modified surfaces increases to any conditions of treatment. Samples treated by the DL technique proved to be adequate to improve the properties of the studied steels.