A Calphad assessment of Al-C-Fe system with the κ carbide modelled as an ordered form of the fcc phase

As part of an extensive Study devoted to the development of new high-Al steels, a CALPHAD-type assessment of the Al-Fe-C system has been carried out. In place of the Usual cementite, these steels show precipitation of the so-called K carbide that is an ordered form of austenite. Inconsistencies between the scarce experimental information in the Al-Fe-C system and extrapolations from the available Al-Fe and Al-C descriptions made it necessary to revise them. This has been done in part by using new ob initio calculations as well as phase diagram data. The K carbide has been described as all ordered form of the fcc phase, with its Gibbs energy calculated as the SUM of a disordered and all ordered contribution. The additional parameters needed to express the ordered part were evaluated using phase equilibria information and new ab initio data related to the K carbide. With this approach, addition of new alloying elements, like Mn or Ni, for extrapolation to higher-order systems should be straightforward. (C) 2008 Elsevier Ltd. All rights reserved.