Influence of gas pressure and substrate temperature on PIII nitrocarburizing process of AISI 304 stainless steel

Plasma immersion ion implantation (PIII) has been used to modify the surface properties of 304 austenitic stainless steel (AISI). The influence of working gas pressure, 0.2 - 1.0 Pa, and substrate temperature, 300 - 500 oC, on the microstructure, treating rate, nitrogen/carbon concentration depth profile, and surface microhardness was investigated. A gas composition of 25 % C2H2, 75 % N2, rf plasma power input of 350 W, and a negatively biased potential of 30 kV were fixed during the experiment. The experimental results show that the substrate temperature and the diffusion process of nitrogen and carbon depend on gas pressure inside the plasma chamber. The thickness of the modified layer has been found to be more than 30 µm after 60 minutes plasma processing time. The results provide recent values of diffusion coefficient and surface microhardness are 3.4 x 10-1 µm2/sec and 1880 kg/mm2 respectively.