Mathematical modeling of a carburizing process of a SAE 8620H steel

Pack carburizing experiments have been conducted employing samples of an SA E 8620M steel. Three different carburizing mixtures have been used, each wi th a different content of carbonate. added to a metallurgical coke as catal yst. The change in carbon concentration along the case depth has been deter mined quantitatively by means of chemical analysis conducted at every 0.1 m m from the outer surface of the workpiece. It has been shown that the carbo n concentration profile can be satisfactorily modeled employing the classic al solution derived from Fick's second law. For this purpose, a two-step op timization procedure has been developed in order to compute, as a first ste p, the optimum values of the activation parameters (activation energy for d iffusion and the diffusivity coefficient) of carbon in austenite, as well a s the carbon potential that is established at the surface of the carburizin g specimen under different processing conditions. The second step of the al gorithm involves the re-computation of the carbon potential at the surface, once the activation parameters are assumed to be constant. In general, it has been observed that the addition of carbonates (BaCO3 and NaCO3) to the metallurgical coke gives rise to an increase in the carburization rate and case depth which allows the achievement of the required carbon concentratio n profiles more efficiently. nigh carburization temperatures are observed t o give rise to undesired acicular structures in the workpiece at low temper atures, due to the austenite grain growth during the carburizing processing . (C) 1999 Published by Elsevier Science S.A. All rights reserved.