Diffusion modeling of the carburization process

Abstract

Mathematical models have been developed for simulating the carburization process. One model simulates carburization in low alloy steels where temperature, time, surface carbon content, and diffusion coefficient vary during the process. Two step and vacuum carburization are among the treatments considered. The other model simulates the ef-fect of major ternary alloying additions such as Mn, Cr, Ni and Si during carburization. The importance of the off diagonal or cross diffusion coefficientD ³₁₂ on carbon diffusion is calculated. The Crank-Nicolson finite difference equations are used to provide numeri-cal stability and flexability. Calculated carbon profiles for low alloy steels were com-pared with experimental data available in the literature. Agreement between calculated and measured data was very good. Chromium and silicon have large cross coefficient ef-fects and it is predicted that they have a large influence on the amount of carburization which will occur. Experimental data for carburization treatments of Fe-C-Cr alloys are in excellent agreement with model predictions of major increases in effective surface carbon content and the formation of carbides in austenite at the carburization tempera-ture. These computer models are relatively easy to apply and can be used to design car-burization treatments for specific alloy steels.