Plasma carburizing was applied to AISI 316L stainless steel to increase surface hardness. To achieve desired surface hardness, case depth and carburizing uniformity, the plasma carburizing conditions such as applied voltage, gas pressure, $CH_4$ to $H_2$ ratio, carburizing temperature and treatment time were varied. Plasma carburized specimens were analyzed with optical microscopy, microhardness test, and AES.
The surface was hardened at the high applied voltage of 600V, but not at the low applied voltage of 360 and 420 V. Addition of $H_2$ to $CH_4$ and increase of gas pressure enhanced carburizing uniformity. Decrease of the surface hardness which was observed in liquid carburizing of AISI 316L presumably due to nitrogen diffusion, was not found in plasma carburizing. AES depth analysis indicates that the cause of non-uniformity of carburizing in the plain specimens is surface oxidation during the carburizing process at high temperature. This surface oxide seems to cause sooting on the surface of stainless steel.
