Low-Temperature Plasma Nitriding of Sintered PIM 316L Austenitic Stainless Steel

This work reports experimental results on sintered PIM 316L stainless steel low-temperature plasma nitriding. The effect of treatment temperature and time on process kinetics, microstructure and surface characteristics of the nitrided samples were investigated. Nitriding was carried out at temperatures of 350, 380, 410 and 440 degrees C, and times of 4, 8 and 16 h, using a gas mixture composed by 60% N-2 + 20% H-2 + 20% Ar, at a gas flow rate of 5.00 x 10(-6) Nm(3)s(-1), and a pressure of 800 Pa. The treated samples were characterized by scanning electron microscopy, X-ray diffractometry and microhardness measurements. Results indicate that low-temperature plasma nitriding is a diffusion controlled process. The calculated activation energy for nitrided layer growth was 111.4 kJmol(-1). Apparently precipitation-free layers were produced in this study. It was also observed that the higher the treatment temperature and time the higher is the obtained surface hardness. Hardness up to 1343 HV0.025 was verified for samples nitrided at 440 degrees C. Finally, the characterization of the treated surface indicates the formation of cracks, which were observed in regions adjacent to the original pores after the treatment.