Plasma nitriding behavior of AISI 316L stainless steel

IV ABSTRACT In this investigation, the surface hardening of AISI 316L stainless steel, an important engineering material, by using plasma nitriding technique has been aimed with various temperatures (400...600°C), times (1... lOh) and the volumetric ratio of N2 in the plasma atmosphere of N2+H2 gaseous mixture as process parameters. Mcrohardness measurements and optical microscopy techniques have been used to investigate the nitriding response of the steel. The work has focused on the surface hardening behavior of the steel, the morphology of the nitrided layers and study of wear properties of plasma nitrided specimens. Pin-on ring type of wear tests were carried out under dry sliding conditions. Besides its reduced processing times, causing no environmental pollution, considerably smooth surfaces, low electricity and gaseous consumptions and compatibility for automation, the plasma nitriding process with controllable diffusion thickness and hard but less ductile metallic surfaces, has allowed for remarkable increase in the hardness of AISI 316L stainless steel. By microhardness measurements and optical microscope investigations, the maximum surface hardness and the deepest diffusion layer has been obtained in the plasma nitrided sample over a period of 7h 550°C in a nitriding atmosphere containing %40N2+%60H2 gaseous mixture. The case depth were found to increase with increasing process temperature and time. Nitrogen content of the plasma nitriding atmosphere while increasing slightly decreased the case depth and surface hardness. Wear rates were observed to increase with increasing compound layer thickness and decreasing surface hardness.