Multi-objective optimisation of gas carburising process in batch furnaces with endothermic carburising atmosphere

Abstract

A methodology for multi-objective optimisation of gas carburising heat treatment has been developed in terms of cost, cycle time and quality of carburised parts. The optimisation strategy is based on: modelling the effect of process parameters (carbon potential, temperature and time) on the mass transfer coefficient and carbon diffusivity in austenite, correlating the observed variations in the process parameters on the carburising kinetics, and developing a robust multiobjective optimisation technique to achieve the desired case depth with minimum cost and minimum case depth variation. The tradeoff between these two objective functions corresponded to carburising at 938?5uC and carbon potential of 1?14 wt-%C. This combination produced the target case depth of 0?6 mm with corresponding ¡0?05 mm case depth variation and minimum total cycle cost. Overall, application of this multi-objective optimisation will result in significant energy reduction by shortening cycle time and thereby enhancing furnace capacity.

Surface Characteristics Analysis of Gas Carburized New Hot Working Tool Steel

“…Case depths are a function of carburizing temperature-time and the available carbon potential at the surface while case hardness is primarily a function of the carbon content. The time necessary for making deeper case depths can be reduced by high temperatures related to the process [15]. When prolonged carburizing times are used for deep case depths, a high carbon potential produces a high surfacecarbon content, which may thus result in excessive formation of carbide networks and retained austenite.…”