Effect of rare earths on diffusion coefficient and transfer coefficient of carbon during carburizing

The diffusion coefficient of carbon in surface layer of steel-20 rare earth carburized at 880°C and 900°C for 8 h was calculated by substituting the measured layer depths into the diffusion equation. The mathematical model of the transfer coefficient of carbon was deduced based on the kinetics of weight gain during gas carburizing. The calculated results show that the main reason why the gas carburizing process is accelerated is due to the obvious increase in the diffusion coefficient and transfer coefficient of carbon resulted from the addition of RE.