Modeling of vacuum pulse carburizing of steel

A review on carburization process modeling is presented and a new model for carbon diffusion in steel subjected to heat treatment by vacuum pulse carburizing is proposed. Such a process is carried out by repeating consecutively a carburizing stage (the boost), when the carburizing gas is supplied into a carburizing chamber, and the diffusion stage at vacuum conditions, when the carburizing gas is exhausted and only the diffusion in steel takes place. The model is based on Darken bi-velocity method which comprises two velocities: the diffusion velocity, various for various components, which depends on the diffusion potential gradient and is independent of the choice of the reference frame, and the drift velocity which is equivalent to the lattice velocity, and is common for all components. The model allows predicting the kinetics of carbon transfer at various processing conditions and has been applied in computer simulations. The numerical calculations were performed for varying carburizing and diffusion intervals and the results were compared to the experimental data On the basis of the series of computer experiments some findings, which are important for the carburizing process design, have been formulated.