White Layer Control on AISI 316L Using Temperature and Gas Nitriding Diffusion Stage Process

Abstract

The aim of the study was to compare the hardness properties resulting after the nitriding fluidized bed thermochemical treatments in different media and the diffuse temperature process, to evaluate the efficiency of the white layer formation on stainless steel substrats. The White layer is a layer with a high nitrogen atom concentration between the surface and the layer underneath. This concentration causes the layer to be hard and brittle. The use of diffusion stage after the boost stage (550°C) in a fluidized bed reactor aims at reducing the formation of the white layer. The results show that a reduction in white layer is followed by the increase of brittleness in the form of crack formation in the layer underneath. The imbalance reaction due to the exothermic reaction is the primary reason. An increase in the atmosphere temperature without nitrogen gas during the diffusion stage increases the supersaturated reaction. The optimal process is fixed diffusion at boost temperature of 550°C in the gas diffusion media without nitrogen. The use of atmosphere without nitrogen gas during diffusion increases the depth of diffusion of the nitrogen atom and reduces the white layer, thereby reducing brittleness. In addition, micro-cracks have been formed under white layers at the higher diffusion temperature of 650°C.