Effect of Pre Oxidation on Microstructure and Hardness of Low Carbon Steel during Nitrocarburising

This paper deals with the effect of pre-oxidation on Nitrocarburizing heat treatment of Low carbon steel (with a carbon range of 0.31wt% to 0.60wt% and a manganese content ranging from (0.60wt% to 1.65wt %). The nitrocarburized steel is used in the applications where corrosion resistance, wear resistance, and lower local stresses properties play a vital role. The purpose of Pre-oxidation in nitrocraburizing process is to develop multi-layer thickness uniformly and to enhance heat treatment (nitriding) kinetics. During Pre-oxidation iron oxide layer forms on the surface, this layer supports the nucleation of an iron nitride layer to develop faster owing to greater nitrogen content in the part of the multifaceted layer adjoining to the surface. The pre-oxidation is performed on the standard specimens by blowing gases such as atmospheric air (O2), carbondioxide (CO2), and humidified N2. The pre-oxidized samples are then preceded to the ?Nitrocarburizing? by blowing gases (N2, NH3, and LPG) at constant temperature and flow rates with different exposure time in ?Fluidized Bed Furnace?. From microstructural studies and hardness test results, higher deposition layer thickness and higher hardness is achieved for samples which have undergone peroxidation with humidified nitrogen, due to more amount of nitrogen deposition onto thick oxide layer.