Plasma Assisted Ion Nitriding of High Carbon Steel

Abstract

Nitriding is a thermochemical surface engineering process to improve surface mechanical, tribological and corrosion properties of various materials including steels. It is a more favorable technique owing to its low cost and better effectiveness. Unlike the gas and salt bath nitriding techniques, plasma nitriding is environment friendly and its demand is growing rapidly in several areas including the aerospace and automobile industries. The Cathodic Cage Plasma Nitriding (CCPN) is a comparatively new technique and is more valuable because of the complete removal of edge effect, arcing and overheating, which were associated with conventional plasma nitriding. This dissertation focuses on the optimization of the CCPN reactor. The results from the surface analysis, are found to be important precursors in surface hardening of high carbon steels. The specimens are at fixed substrate temperature, pressure, and different treatment times of 1 hour, 1.5 hours, 2 hours, 2.5 hours and 4 hours. The high carbon steel, which is generally supposed to be unfavorable for nitriding due to its in-depth nitrogen diffusion, is successfully nitrided,. This is achieved by using austenite stainless steel CC, which contains enough amount of chromium and can trap nitrogen and forms stable nitrides on the surface of nitrided layer. Samples are characterized by X-ray Diffraction, Vickers micro hardness tester and scanning electron microscopy. These results show that the modified surface specimens of nitrided high carbon steel mainly comprises of iron nitrides and carbon nitrides. The best results are obtained for 1.5 hours treatments showing much improved hardness value of 922 HV with thick nitrided layer and this is also supported by SEM micrographs but the other of the conditions did not show much improvement.