Surface hardening of AISI 316L stainless steel using plasma carburizing

Abstract

AISI 316L, stainless steel was carburized using CH4/H-2 plasma to increase surface hardness. Plasma carburizing conditions such as applied voltage, carburizing temperature, gas pressure, CH4/(CH4 + H-2) ratio and process time were varied to achieve the desired surface hardness, effective hardening depth and carburizing uniformity. Plasma carburized specimens were analyzed with optical microscopy, microhardness tester, scanning electron microscopy and Auger electron spectroscopy. Effective removal of surface oxide which grows during plasma carburizing is essential for successful carburizing and good uniformity in AISI 316L stainless steel. Adding H-2 to CH4 as well as increasing process pressure enhances carburizing uniformity. Hardness obtained after plasma carburizing has a linear relation with carbon concentration. By carrying out plasma carburizing over 90 min at 800 degrees C, 600 V, 2 Torr and 25% CH4/(CH4 + H-2) ratio, the back-female type AISI 316L stainless steer specimen was uniformly carburized with a surface hardness above 735 HV50g and an effective hardening depth above 40 mu m. (C) 1997 Elsevier Science S.A.