Carbon and Nitrogen Concentration Profiles of Cassava-Pack Carbonitrided Steel: Model and Experiment

Cassava-leaf-enhanced carbonitriding is a surface hardening procedure that utilizes the high cyanide content that is present in processed cassava leaves to thermochemically diffuse carbon and/or nitrogen into the interstitial sites of steel. This paper presents analytical models for the prediction of carbon and nitrogen concentration profiles, as well as the total case depths associated with the diffusion of carbon and nitrogen during the cassava-leaf-enhanced carbonitriding of low carbon steel. Using Fick's second law of diffusion and approximate initial and boundary conditions, two separate analytical models were presented for intermediate and high temperature cassava-leaf-enhanced carbonitriding processes. The trends in the total case depths are shown to be qualitatively similar to experimental measurements of case depths. The implications of the results are discussed for the surface hardening of steels by carbonitriding processes.