Embrittlement at 475 degrees C was mapped in ferritic ternary alloys with a wide composition range of Fe-(10-30)Cr-(0-20)Al-(at.%) using a diffusion multiple technique. A large solid solution of Al suppresses the 475 C embrittlement, while a small solid solution of Al promotes embrittlement. Transmission electron microscopy observations on aged samples suggest that suppression of the embrittlement due to Al addition can be attributed to the suppression of phase separation of the ferrite phase into the two phases Fe-rich ferrite and Cr-rich ferrite. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.