Runner-up Simulation of Gas Carburising: Development of Computer Program with Systematic Analyses of Process Variables Involved

Abstract

Numerous process parameters involved in different stages of gas carburising make the process difficult to control, which in turn makes predictions of properties difficult. In the present work, a computer program was developed to simulate the entire gas carburising process, focusing on the thermodynamics of the gas phase and thermochemical reaction kinetics at the gas/solid interface in endothermic atmospheres. By combining gas phase kinetics and carbon activities in gas and steel with the alloy dependent diffusivity of carbon in austenite, the program can predict accurate carbon diffusion profiles for both batch and continuous furnaces. The program has been designed to account for all the major process variables that affect resultant carbon diffusion such as steel alloy composition, part geometry, gas composition and basic treatment parameters with their possible variations during the process. It is also able to predict other important properties such as transformation temperatures and the as quenched and tempered hardness of carburised parts. Comparison with the results of the experiments performed in industrial carburising furnaces provided validation of the model predictions.

Carbon Diffusion in Steels: A Numerical Analysis Based on Direct Integration of the Flux

“…The input diffusivity values for carbon profiles simulation were calculated from the equations for carbon diffusion in austenite that have been reported in the literature. [10][11][12][24][25][26][27][28][29][30][31][32][33] These equations were subdivided into two categories: the equations that depend on temperature only; and those that consider carbon content in the steel as well. To account for the variation of diffusivity with concentration, the values were recalculated for instantaneous carbon concentration levels along every space and time increment.…”

Measurements of Carbon Diffusivity and Surface Transfer Coefficient by Electrical Conductivity Relaxation during Carburization: Experimental Design by Theoretical Analysis

“…Among the carburization technologies, gas carburization is a versatile and widely used technology with well-controlled gas composition and temperature. It is recognized that the carburizing process can be divided into three steps: (1) the reactions in gas phase for the build-up of carbon potential; (2) the reactions on steel/gas interface for the transfer of carbon; and (3) the diffusion of carbon into the bulk of steel [1]. A rational design of the carburizing process depends on both the equilibrium thermodynamic parameters (e.g., carbon potential and temperature), and the kinetic parameters (e.g., durations of heating, holding, and cooling, and the flow rates of gases).…”